1 00:00:01,040 --> 00:00:03,380 The following content is provided under a Creative 2 00:00:03,380 --> 00:00:04,770 Commons license. 3 00:00:04,770 --> 00:00:06,980 Your support will help MIT OpenCourseWare 4 00:00:06,980 --> 00:00:11,070 continue to offer high-quality educational resources for free. 5 00:00:11,070 --> 00:00:13,640 To make a donation or to view additional materials 6 00:00:13,640 --> 00:00:17,600 from hundreds of MIT courses, visit MIT OpenCourseWare 7 00:00:17,600 --> 00:00:18,480 at ocw.mit.edu. 8 00:00:22,560 --> 00:00:26,430 MICHAEL SHORT: Today I want to pick up where we left off-- 9 00:00:26,430 --> 00:00:29,770 well, to remind you where we left off last time, 10 00:00:29,770 --> 00:00:32,520 we were watching videos of crushing things 11 00:00:32,520 --> 00:00:35,610 with the explicit purpose of understanding material 12 00:00:35,610 --> 00:00:38,422 properties, so that we can talk a little bit about radiation 13 00:00:38,422 --> 00:00:39,630 damage and nuclear materials. 14 00:00:39,630 --> 00:00:41,980 Since I got more than a few requests to say, 15 00:00:41,980 --> 00:00:44,040 what's all this nuclear materials? 16 00:00:44,040 --> 00:00:46,440 It's like the biggest research field in the department, 17 00:00:46,440 --> 00:00:48,450 and yet, it's not talked about in 22.01. 18 00:00:48,450 --> 00:00:49,830 Well, now it is. 19 00:00:49,830 --> 00:00:52,800 So we talked before about all the different stages 20 00:00:52,800 --> 00:00:56,370 in radiation damage from creation of single defects 21 00:00:56,370 --> 00:01:00,360 to their clustering into things like voids or loops 22 00:01:00,360 --> 00:01:02,550 and super structures that have end up 23 00:01:02,550 --> 00:01:05,010 having macroscopic effects on material properties, 24 00:01:05,010 --> 00:01:07,920 and all of them is due to the production of crystal 25 00:01:07,920 --> 00:01:10,610 and defects due to radiation. 26 00:01:10,610 --> 00:01:13,290 And to refresh your memory quickly, 27 00:01:13,290 --> 00:01:16,350 I'm going to jump ahead to the stress strain curve 28 00:01:16,350 --> 00:01:19,440 that we were looking at before we started watching videos 29 00:01:19,440 --> 00:01:21,925 of crushing things, to remind you 30 00:01:21,925 --> 00:01:23,550 about the different material properties 31 00:01:23,550 --> 00:01:24,717 and what they actually mean. 32 00:01:24,717 --> 00:01:28,470 So anyone remember what we mean by toughness in relation 33 00:01:28,470 --> 00:01:30,470 to this curve? 34 00:01:30,470 --> 00:01:31,720 AUDIENCE: The area [INAUDIBLE] 35 00:01:31,720 --> 00:01:32,410 MICHAEL SHORT: That's right. 36 00:01:32,410 --> 00:01:34,810 The amount of energy it would take to actually cause 37 00:01:34,810 --> 00:01:36,650 this material to fail. 38 00:01:36,650 --> 00:01:38,518 That's a measure of toughness. 39 00:01:38,518 --> 00:01:39,310 How about strength? 40 00:01:48,420 --> 00:01:52,730 Remember this curve is stress, which is a force per unit area, 41 00:01:52,730 --> 00:01:55,623 versus strain, which is an amount of elongation. 42 00:01:55,623 --> 00:01:57,290 The strength of the material is how much 43 00:01:57,290 --> 00:01:59,480 stress you can put in until it starts 44 00:01:59,480 --> 00:02:01,490 to either plastically deform or it 45 00:02:01,490 --> 00:02:05,420 hits its UTS, ultimate tensile strength, where it will just 46 00:02:05,420 --> 00:02:06,770 fail. 47 00:02:06,770 --> 00:02:09,090 How about ductility? 48 00:02:09,090 --> 00:02:12,030 What do we mean by that? 49 00:02:12,030 --> 00:02:14,010 Either intuitively or on the curve, yeah? 50 00:02:14,010 --> 00:02:15,930 AUDIENCE: How much you can stretch it? 51 00:02:15,930 --> 00:02:16,530 MICHAEL SHORT: Exactly. 52 00:02:16,530 --> 00:02:18,363 How much you can stretch it before it fails, 53 00:02:18,363 --> 00:02:20,490 indicated by this point right here. 54 00:02:20,490 --> 00:02:23,680 The strain to failure would be a good measure of activity. 55 00:02:23,680 --> 00:02:24,750 And finally, stiffness. 56 00:02:24,750 --> 00:02:25,500 What do you think? 57 00:02:29,360 --> 00:02:31,380 Stiffness is more of a response function, 58 00:02:31,380 --> 00:02:35,240 so it's how much does it deform in relation to how much stress 59 00:02:35,240 --> 00:02:35,930 you put into it. 60 00:02:35,930 --> 00:02:38,090 So it's the slope of this part right 61 00:02:38,090 --> 00:02:40,280 here, so that's why I want you guys to know 62 00:02:40,280 --> 00:02:42,290 that we mean actually different physical things 63 00:02:42,290 --> 00:02:46,190 by these properties, which will be important to note 64 00:02:46,190 --> 00:02:49,250 when we start to discuss what radiation damage actually does. 65 00:02:52,080 --> 00:02:54,130 So the basic mechanism of radiation damage 66 00:02:54,130 --> 00:02:55,420 is like you might imagine. 67 00:02:55,420 --> 00:02:58,810 Let's say this green particle is a neutron or a heavy ion 68 00:02:58,810 --> 00:03:02,440 or a proton or an electron or anything. 69 00:03:02,440 --> 00:03:06,680 Anything that's energetic enough to cause atomic displacement. 70 00:03:06,680 --> 00:03:09,100 So as that neutron or whatever enters, 71 00:03:09,100 --> 00:03:13,060 it will strike some of the atoms in this perfect crystal, 72 00:03:13,060 --> 00:03:16,390 creating what's called a primary knock on atom, or PKA, 73 00:03:16,390 --> 00:03:17,680 for short. 74 00:03:17,680 --> 00:03:20,620 And then that neutron and the released PKA 75 00:03:20,620 --> 00:03:23,680 will go on to hit more and more atoms, 76 00:03:23,680 --> 00:03:26,410 resulting in what we call a damage cascade, 77 00:03:26,410 --> 00:03:29,653 leaving behind a lot of different types of defects. 78 00:03:29,653 --> 00:03:31,570 We talked about these last time, but I'll just 79 00:03:31,570 --> 00:03:33,160 refresh your memory. 80 00:03:33,160 --> 00:03:36,190 A vacancy is a type of defect that, well, it's not really 81 00:03:36,190 --> 00:03:36,970 a thing, right? 82 00:03:36,970 --> 00:03:39,950 It's just the absence of where an atom would have been, 83 00:03:39,950 --> 00:03:42,850 but we refer to them as defects of their own 84 00:03:42,850 --> 00:03:45,310 that can diffuse and move because let's say 85 00:03:45,310 --> 00:03:49,360 another atom moved into the position of this vacancy. 86 00:03:49,360 --> 00:03:53,800 Then we can say the vacancy moved to that atomic position. 87 00:03:53,800 --> 00:03:55,510 There's also interstitials, or atoms 88 00:03:55,510 --> 00:03:58,730 where they shouldn't quite be. 89 00:03:58,730 --> 00:04:01,820 And this leaves behind a whole bunch of damage 90 00:04:01,820 --> 00:04:04,220 that we quantify using a measure called DPA, 91 00:04:04,220 --> 00:04:06,380 or displacements per atom. 92 00:04:06,380 --> 00:04:10,370 It's a simple measure of how many times has every atom left. 93 00:04:10,370 --> 00:04:13,150 It's a lot of sight. 94 00:04:13,150 --> 00:04:14,590 That's it, though. 95 00:04:14,590 --> 00:04:16,240 It's not actually a unit of damage, 96 00:04:16,240 --> 00:04:17,810 and I'll be giving a talk at MRS, 97 00:04:17,810 --> 00:04:21,660 the materials research conference tomorrow, railing 98 00:04:21,660 --> 00:04:23,415 against this DPA unit because I'm 99 00:04:23,415 --> 00:04:25,290 going to explain this a little bit right now. 100 00:04:25,290 --> 00:04:27,630 What is a DPA? 101 00:04:27,630 --> 00:04:30,210 A DPA measures the number of times 102 00:04:30,210 --> 00:04:33,360 that each atom has moved out of its original site, 103 00:04:33,360 --> 00:04:36,810 but it has nothing to do with how many times it stays out 104 00:04:36,810 --> 00:04:39,870 of its original site because a lot of those atoms 105 00:04:39,870 --> 00:04:43,470 will get knocked away and then just move right back, 106 00:04:43,470 --> 00:04:45,360 but the DPA part only measure is what 107 00:04:45,360 --> 00:04:48,510 we call the ballistic stage of radiation damage. 108 00:04:51,770 --> 00:04:52,840 Let's see if this works. 109 00:04:52,840 --> 00:04:55,090 I've just realized I can jump back to a slide 110 00:04:55,090 --> 00:04:58,080 without inducing epilepsy. 111 00:04:58,080 --> 00:04:59,290 Yeah. 112 00:04:59,290 --> 00:05:01,930 So what DPA actually measures is how many times does 113 00:05:01,930 --> 00:05:03,610 this process happen? 114 00:05:03,610 --> 00:05:07,120 How many times do the atoms get knocked around? 115 00:05:07,120 --> 00:05:10,100 But it says nothing about where they end up, 116 00:05:10,100 --> 00:05:12,050 and that's the really interesting part 117 00:05:12,050 --> 00:05:16,010 about specifically radiation material science. 118 00:05:16,010 --> 00:05:19,070 Because let's say one of these interstitials 119 00:05:19,070 --> 00:05:21,200 were then to combine with one of these vacancies. 120 00:05:21,200 --> 00:05:22,700 It's like they were never there. 121 00:05:22,700 --> 00:05:24,740 Even though they were displaced, and would 122 00:05:24,740 --> 00:05:28,250 be counted as part of the DPA, or the radiation damage dose, 123 00:05:28,250 --> 00:05:32,570 the net effect on the crystal material is nothing. 124 00:05:32,570 --> 00:05:34,380 So let's say what really the DPA is. 125 00:05:34,380 --> 00:05:38,290 It's a simple formula that I think you guys may recognize. 126 00:05:38,290 --> 00:05:40,230 This look familiar from all of neutronics 127 00:05:40,230 --> 00:05:41,620 that we've been doing? 128 00:05:41,620 --> 00:05:43,710 It's yet another reaction rate. 129 00:05:43,710 --> 00:05:47,130 It's an energy dependent flux times another type 130 00:05:47,130 --> 00:05:49,580 of cross-section that we call the damage displacement 131 00:05:49,580 --> 00:05:52,140 cross-section, or sigma D, and it's 132 00:05:52,140 --> 00:05:54,120 integrated over your entire energy range, 133 00:05:54,120 --> 00:05:55,600 and that's all there is to it. 134 00:05:55,600 --> 00:05:58,890 So with what you know 22.01, you can understand the basic unit 135 00:05:58,890 --> 00:06:00,480 of radiation damage. 136 00:06:00,480 --> 00:06:03,503 As you might imagine, we've had four lectures on neutronics, 137 00:06:03,503 --> 00:06:04,920 so if you can understand all there 138 00:06:04,920 --> 00:06:07,630 is to know about DPA after four sophomore lectures, 139 00:06:07,630 --> 00:06:10,080 it's probably a pretty simple unit. 140 00:06:10,080 --> 00:06:11,940 You're right, it is. 141 00:06:11,940 --> 00:06:14,550 What goes into this damaged displacement cross-section 142 00:06:14,550 --> 00:06:17,370 is also something that might look a little familiar 143 00:06:17,370 --> 00:06:19,680 is a cross section that says, what's 144 00:06:19,680 --> 00:06:23,790 the probability of some particle coming in with energy E 145 00:06:23,790 --> 00:06:28,590 and imparting kinetic energy T to another struck atom? 146 00:06:28,590 --> 00:06:30,510 That comes right from-- 147 00:06:30,510 --> 00:06:32,260 remember our treatment-- 148 00:06:32,260 --> 00:06:35,450 I think I've drawn this probably 50 times now. 149 00:06:35,450 --> 00:06:39,840 Our hollow cylinder treatment of a charged particle 150 00:06:39,840 --> 00:06:43,710 with charge little ze interacting with a particle 151 00:06:43,710 --> 00:06:49,310 a big ZE at some impact parameter B. 152 00:06:49,310 --> 00:06:51,810 We wanted to know well, for all possible approach 153 00:06:51,810 --> 00:06:57,270 paths, the area of this hollow circle, 154 00:06:57,270 --> 00:06:59,790 or the probability that this particular approach 155 00:06:59,790 --> 00:07:06,870 path is taken, is just the area here 2pi b db. 156 00:07:06,870 --> 00:07:09,040 With some constants in front of it, 157 00:07:09,040 --> 00:07:10,890 which actually is that cross section 158 00:07:10,890 --> 00:07:14,820 what's the probability that our particle goes in with energy E 159 00:07:14,820 --> 00:07:16,590 and imparts kinetic energy T? 160 00:07:16,590 --> 00:07:20,240 It's directly related to that impact parameter B. 161 00:07:20,240 --> 00:07:22,980 And this is the same thing that you're seeing right here. 162 00:07:22,980 --> 00:07:25,080 You then multiply by this little function 163 00:07:25,080 --> 00:07:30,310 nu of T, which represents the amount of damage, 164 00:07:30,310 --> 00:07:32,320 or the number of displacements done, 165 00:07:32,320 --> 00:07:35,230 for each one of these reactions. 166 00:07:35,230 --> 00:07:38,560 And there are simple models, there are mostly linear models 167 00:07:38,560 --> 00:07:39,490 for-- 168 00:07:39,490 --> 00:07:43,180 if a particle comes in with energy E, leaves with energy T, 169 00:07:43,180 --> 00:07:45,010 how many displacements happen? 170 00:07:45,010 --> 00:07:47,940 It's a pretty simple linear piece-wise model, 171 00:07:47,940 --> 00:07:49,690 and that fairly well approximates 172 00:07:49,690 --> 00:07:52,320 the number of displacements that happen, 173 00:07:52,320 --> 00:07:55,810 but I want to get the idea of DPA versus damage. 174 00:07:55,810 --> 00:07:57,270 They're two very different things, 175 00:07:57,270 --> 00:07:58,950 and they're often equated. 176 00:07:58,950 --> 00:08:00,980 Much like the material properties of strength, 177 00:08:00,980 --> 00:08:03,150 ductility, hardness, and toughness 178 00:08:03,150 --> 00:08:04,740 are equated in colloquial speech, 179 00:08:04,740 --> 00:08:06,780 but that's absolutely wrong. 180 00:08:06,780 --> 00:08:11,070 So is the idea of DPA and radiation damage. 181 00:08:11,070 --> 00:08:12,480 Because DPA, again, just measures 182 00:08:12,480 --> 00:08:15,060 the number of times that an atom is displaced. 183 00:08:15,060 --> 00:08:18,150 Damage is some measure of the number of messed up atoms 184 00:08:18,150 --> 00:08:20,650 at the end of the game, and they operate 185 00:08:20,650 --> 00:08:22,450 in very different timescales. 186 00:08:22,450 --> 00:08:25,240 It takes femtoseconds to picoseconds 187 00:08:25,240 --> 00:08:26,810 for a damage cascade to happen. 188 00:08:26,810 --> 00:08:30,580 So the DPA is all over in less than a picosecond, 189 00:08:30,580 --> 00:08:33,820 but it can take years for all these different defects 190 00:08:33,820 --> 00:08:37,960 to diffuse, to cluster up, and to form these super structures, 191 00:08:37,960 --> 00:08:39,970 and actually end up causing the damage that 192 00:08:39,970 --> 00:08:43,710 can lead to material property degradation. 193 00:08:43,710 --> 00:08:46,310 So what sort of factors would affect 194 00:08:46,310 --> 00:08:48,920 the speed at which these different defects end up 195 00:08:48,920 --> 00:08:51,080 finding each other? 196 00:08:51,080 --> 00:08:54,770 What could you vary about a material or its environment 197 00:08:54,770 --> 00:08:57,753 to change the speed of these atomic diffusion jumps? 198 00:08:57,753 --> 00:08:58,670 AUDIENCE: Temperature. 199 00:08:58,670 --> 00:08:59,587 MICHAEL SHORT: Indeed. 200 00:08:59,587 --> 00:09:00,482 Temperature. 201 00:09:00,482 --> 00:09:02,690 Reading off my list-- well, the whole list jumped up. 202 00:09:02,690 --> 00:09:03,563 OK. 203 00:09:03,563 --> 00:09:04,480 You got the first one. 204 00:09:04,480 --> 00:09:05,522 What were you going to say? 205 00:09:05,522 --> 00:09:07,000 AUDIENCE: I was going to say temperature also. 206 00:09:07,000 --> 00:09:07,640 MICHAEL SHORT: OK. 207 00:09:07,640 --> 00:09:08,348 Yeah, absolutely. 208 00:09:08,348 --> 00:09:11,030 Temperature determines diffusivities. 209 00:09:11,030 --> 00:09:16,010 It also can change phases or crystal arrangements, 210 00:09:16,010 --> 00:09:18,730 like for the case of anything iron-based. 211 00:09:18,730 --> 00:09:22,040 The dose rate, the rate at which those neutrons come in 212 00:09:22,040 --> 00:09:25,430 can change the rate at which the defects cluster up. 213 00:09:25,430 --> 00:09:28,880 Chemistry, if you have solute atoms, which I've drawn here. 214 00:09:28,880 --> 00:09:31,640 You may have let's say chromium atoms and iron, 215 00:09:31,640 --> 00:09:33,710 and the chromium atoms are a little bit bigger. 216 00:09:33,710 --> 00:09:36,680 Defects may be attracted to or repelled 217 00:09:36,680 --> 00:09:40,130 to those extra solute atoms, changing the way that they 218 00:09:40,130 --> 00:09:41,750 interact with each other. 219 00:09:41,750 --> 00:09:43,070 And then micro structure. 220 00:09:43,070 --> 00:09:45,460 Things that are bigger than on the order of atoms. 221 00:09:45,460 --> 00:09:49,100 Grain boundaries, dislocations, all of those defects 222 00:09:49,100 --> 00:09:51,470 that we talked about last time, just to refresh 223 00:09:51,470 --> 00:09:54,250 your memory of what those are. 224 00:09:54,250 --> 00:09:58,370 We have been talking about zero dimensional defects 225 00:09:58,370 --> 00:10:00,080 like vacancies. 226 00:10:00,080 --> 00:10:03,350 We spent a while on dislocations, these one 227 00:10:03,350 --> 00:10:08,130 dimensional defects that other defects can be attracted to. 228 00:10:08,130 --> 00:10:11,400 We saw an example of a two dimensional defect, 229 00:10:11,400 --> 00:10:14,590 known as a grain boundary, where you 230 00:10:14,590 --> 00:10:18,340 can see this line between different arrangements 231 00:10:18,340 --> 00:10:19,930 of atoms. 232 00:10:19,930 --> 00:10:23,450 And there can be three dimensional defects. 233 00:10:23,450 --> 00:10:27,190 Like inclusions of some separate face sitting in the material. 234 00:10:27,190 --> 00:10:30,250 Like the manganese sulfide we found in the Alcator fusion 235 00:10:30,250 --> 00:10:33,460 reactors power rotor. 236 00:10:33,460 --> 00:10:35,500 And all of the presence and density 237 00:10:35,500 --> 00:10:37,750 of all those different defects can 238 00:10:37,750 --> 00:10:40,480 be quite strongly influenced. 239 00:10:40,480 --> 00:10:42,168 Let me start that sentence over. 240 00:10:42,168 --> 00:10:43,960 The movement in clustering of those defects 241 00:10:43,960 --> 00:10:46,270 can be quite strongly influenced by the presence 242 00:10:46,270 --> 00:10:49,820 of all those other defects. 243 00:10:49,820 --> 00:10:52,550 So again, the DPA actually tells us 244 00:10:52,550 --> 00:10:54,830 this part of radiation damage, and that's 245 00:10:54,830 --> 00:10:58,400 what we tend to simulate with these ballistic binary 246 00:10:58,400 --> 00:11:00,140 collision approximation simulations, 247 00:11:00,140 --> 00:11:02,120 where we just say like billiard balls, 248 00:11:02,120 --> 00:11:04,010 how many atoms knock into each other? 249 00:11:04,010 --> 00:11:06,770 What it doesn't tell us is everything else, 250 00:11:06,770 --> 00:11:09,710 and it's the stuff that happens here that can tell us 251 00:11:09,710 --> 00:11:12,980 will our materials fail in nuclear reactors? 252 00:11:12,980 --> 00:11:14,230 And there's evidence for this. 253 00:11:14,230 --> 00:11:17,820 I'm not just ranting against it, no I am, 254 00:11:17,820 --> 00:11:20,430 but I'm doing so with evidence, so it's justified. 255 00:11:20,430 --> 00:11:22,180 So here's a nice experiment I like to show 256 00:11:22,180 --> 00:11:24,730 in every talk for this case. 257 00:11:24,730 --> 00:11:29,350 These folks took pure nickel and put it in the same reactor, 258 00:11:29,350 --> 00:11:34,350 at the same temperature, and got the same amount of swelling. 259 00:11:34,350 --> 00:11:35,725 All the conditions were the same. 260 00:11:35,725 --> 00:11:38,680 Same temperature, same materials, same microstructure, 261 00:11:38,680 --> 00:11:40,990 same reactor, same neutron energies. 262 00:11:40,990 --> 00:11:42,820 Just a different dose rate. 263 00:11:42,820 --> 00:11:45,220 A 30% difference in the rate at which 264 00:11:45,220 --> 00:11:47,500 neutrons arrived at the nickel, and they 265 00:11:47,500 --> 00:11:49,600 get the same result in void swelling, one 266 00:11:49,600 --> 00:11:51,730 of those bad things that happens, 267 00:11:51,730 --> 00:11:55,070 at two and a half times the DPA, which tells us 268 00:11:55,070 --> 00:11:58,310 that there's a very strong dose rate effect 269 00:11:58,310 --> 00:12:00,257 for material damage. 270 00:12:00,257 --> 00:12:02,090 So if you want to answer the question, well, 271 00:12:02,090 --> 00:12:06,050 how much dose does it take to reach 3% swelling in nickel? 272 00:12:06,050 --> 00:12:09,050 Can't answer that question, you don't have enough information. 273 00:12:09,050 --> 00:12:10,730 Even if you say, how much dose does it 274 00:12:10,730 --> 00:12:15,230 take with one of the neutrons at 600 Celsius in this one 275 00:12:15,230 --> 00:12:15,860 reactor? 276 00:12:15,860 --> 00:12:17,720 You can't answer that question. 277 00:12:17,720 --> 00:12:18,750 Kind of tricky. 278 00:12:18,750 --> 00:12:21,470 And a lot of the rest of nuclear materials data 279 00:12:21,470 --> 00:12:22,620 looks something like this. 280 00:12:22,620 --> 00:12:25,520 Now, I don't want you to worry about what the axes say. 281 00:12:25,520 --> 00:12:27,860 They're not readable because they're not important. 282 00:12:27,860 --> 00:12:29,815 What I do want you to know is what's the quality of this data 283 00:12:29,815 --> 00:12:30,440 set you see? 284 00:12:34,850 --> 00:12:38,030 Would you be bold enough to draw a trend line 285 00:12:38,030 --> 00:12:40,670 through a single data point? 286 00:12:40,670 --> 00:12:42,550 No. 287 00:12:42,550 --> 00:12:45,610 What about three where it doesn't actually 288 00:12:45,610 --> 00:12:46,960 match up with one of them? 289 00:12:46,960 --> 00:12:48,910 Or is there any reason why you think 290 00:12:48,910 --> 00:12:51,847 they made this parabolic instead of a linear line? 291 00:12:51,847 --> 00:12:53,930 I can draw a line that would fit between the error 292 00:12:53,930 --> 00:12:57,090 bars of these two right here. 293 00:12:57,090 --> 00:12:59,720 So the trick is doing these experiments is extremely 294 00:12:59,720 --> 00:13:01,730 difficult and expensive. 295 00:13:01,730 --> 00:13:05,450 So just throwing something near the MIT reactor for a month, 296 00:13:05,450 --> 00:13:08,630 because we did this, we took a few hundred milligrams 297 00:13:08,630 --> 00:13:11,000 of copper, aluminum, and nickel, threw it 298 00:13:11,000 --> 00:13:15,620 in near core position of the MIT reactor, and that cost $40,000, 299 00:13:15,620 --> 00:13:19,810 and that did about 0.002 DPA, or about the dose 300 00:13:19,810 --> 00:13:22,870 that you'd receive in a normal power reactor in one day. 301 00:13:22,870 --> 00:13:24,850 If you want to actually say how long will it 302 00:13:24,850 --> 00:13:28,520 take to get materials to the end of their useful life, 303 00:13:28,520 --> 00:13:31,750 this tends to be anywhere from 10 DPA in light water reactors, 304 00:13:31,750 --> 00:13:35,290 to hundreds of DPA in proposed fast reactors 305 00:13:35,290 --> 00:13:39,410 to 500 DPA for TerraPower's traveling wave reactor. 306 00:13:39,410 --> 00:13:41,490 Now, I don't particularly have-- 307 00:13:41,490 --> 00:13:43,840 let's see what's 500 divided by 0.00-- 308 00:13:43,840 --> 00:13:47,260 I don't have 10,000 years to wait for the final answer. 309 00:13:47,260 --> 00:13:49,660 The best we can do right now is to stick them 310 00:13:49,660 --> 00:13:51,548 in a reactor called BOR-60 in Russia. 311 00:13:51,548 --> 00:13:52,590 I've actually been there. 312 00:13:52,590 --> 00:13:54,873 It's in the very Western edge of Siberia-- 313 00:13:54,873 --> 00:13:56,540 I don't know if you could call it that-- 314 00:13:56,540 --> 00:13:58,600 in a city called Dimitrovgrad. 315 00:13:58,600 --> 00:14:01,173 They have a sodium cooled fast reactor. 316 00:14:01,173 --> 00:14:02,590 For those of you who are wondering 317 00:14:02,590 --> 00:14:04,548 when our advanced reactor is going to be built, 318 00:14:04,548 --> 00:14:08,470 they are built. Just not in this country, not very much. 319 00:14:08,470 --> 00:14:10,030 But Russia's got a fleet of sodium 320 00:14:10,030 --> 00:14:14,180 cooled fast reactors that can get you 25 DPA per year. 321 00:14:14,180 --> 00:14:17,080 And if your reactor is going to go to 500 DPA, 322 00:14:17,080 --> 00:14:19,720 you have to know whether or not your materials will survive, 323 00:14:19,720 --> 00:14:21,920 you have to wait 20 years for the answer. 324 00:14:21,920 --> 00:14:23,920 So what investor is going to be like, all right, 325 00:14:23,920 --> 00:14:26,110 here's $10 billion, but I can wait 20 years 326 00:14:26,110 --> 00:14:27,730 for a return on investment. 327 00:14:27,730 --> 00:14:28,360 No. 328 00:14:28,360 --> 00:14:30,040 I can wait 20 years to start building 329 00:14:30,040 --> 00:14:31,480 the reactor, which means 40 years 330 00:14:31,480 --> 00:14:33,250 for a return on investment. 331 00:14:33,250 --> 00:14:35,380 Chances are, if someone's got $10 billion to give, 332 00:14:35,380 --> 00:14:37,760 they're going to be dead by the time they get a return. 333 00:14:37,760 --> 00:14:40,565 So this is a no win proposition. 334 00:14:40,565 --> 00:14:41,940 So what we really need to know is 335 00:14:41,940 --> 00:14:45,900 what is the full population of every single type of defect 336 00:14:45,900 --> 00:14:47,640 in an irradiated material? 337 00:14:47,640 --> 00:14:50,150 That's what I mean by damage. 338 00:14:50,150 --> 00:14:51,660 Did I show you guys this movie yet? 339 00:14:51,660 --> 00:14:54,510 The orange one? 340 00:14:54,510 --> 00:14:57,190 We've talked about vacancies in an abstract sense, 341 00:14:57,190 --> 00:14:59,340 but this is a movie of one of them actually 342 00:14:59,340 --> 00:15:01,720 moving about on the surface of germanium. 343 00:15:01,720 --> 00:15:07,410 So this is a scanning tunneling microscope image-- 344 00:15:07,410 --> 00:15:08,970 I think that's what it stands for-- 345 00:15:08,970 --> 00:15:12,870 and these are atoms on the surface of germanium. 346 00:15:12,870 --> 00:15:15,360 And that right there, that darker orange thing 347 00:15:15,360 --> 00:15:17,130 moving about is vacancy diffusion. 348 00:15:17,130 --> 00:15:18,130 It's actually happening. 349 00:15:18,130 --> 00:15:20,315 You can see it in real time. 350 00:15:20,315 --> 00:15:21,690 AUDIENCE: Is this real time then? 351 00:15:21,690 --> 00:15:23,223 MICHAEL SHORT: Pretty much, yeah. 352 00:15:23,223 --> 00:15:24,390 So I think this was-- yeah-- 353 00:15:24,390 --> 00:15:26,820 30 frames a second, or so. 354 00:15:26,820 --> 00:15:29,183 Anyway, I don't remember exactly, 355 00:15:29,183 --> 00:15:31,350 but I'd say that's why I always reference everything 356 00:15:31,350 --> 00:15:32,225 in the presentations. 357 00:15:32,225 --> 00:15:33,695 I encourage you guys to look it up. 358 00:15:33,695 --> 00:15:35,820 And then the only reason these slides aren't up yet 359 00:15:35,820 --> 00:15:37,195 is because they're 300 megabytes, 360 00:15:37,195 --> 00:15:40,050 and I didn't have the bandwidth to upload that from my house. 361 00:15:40,050 --> 00:15:42,510 Now that I'm on campus, I can get a 300 meg presentation 362 00:15:42,510 --> 00:15:45,930 up there because it's full of movies. 363 00:15:45,930 --> 00:15:50,050 What sort of things could happen to these defects? 364 00:15:50,050 --> 00:15:52,330 So radiation produces all these crazy defects, 365 00:15:52,330 --> 00:15:54,560 then the DPA description is over. 366 00:15:54,560 --> 00:15:55,820 What could happen next? 367 00:16:00,104 --> 00:16:02,000 [INTERPOSING VOICES] 368 00:16:02,000 --> 00:16:03,970 MICHAEL SHORT: Sorry, Jared, and then-- yeah. 369 00:16:03,970 --> 00:16:05,270 AUDIENCE: Material could crack. 370 00:16:05,270 --> 00:16:06,770 MICHAEL SHORT: Material could crack. 371 00:16:06,770 --> 00:16:08,548 That would be the worst case scenario, 372 00:16:08,548 --> 00:16:10,340 but that is indeed what happens in the end, 373 00:16:10,340 --> 00:16:12,590 and I'll show you some pictures of that actually happened. 374 00:16:12,590 --> 00:16:13,010 Yeah? 375 00:16:13,010 --> 00:16:14,843 AUDIENCE: You mentioned that displaced atoms 376 00:16:14,843 --> 00:16:16,190 can find their way back? 377 00:16:16,190 --> 00:16:17,360 MICHAEL SHORT: Yep. 378 00:16:17,360 --> 00:16:20,300 So they could recombine with different types of defects 379 00:16:20,300 --> 00:16:21,950 and annihilate each other. 380 00:16:21,950 --> 00:16:24,683 If you have a vacancy and an interstitial nearby, 381 00:16:24,683 --> 00:16:26,100 the interstitial can plug the hole 382 00:16:26,100 --> 00:16:28,800 of the vacancy and your left with another perfect crystal. 383 00:16:28,800 --> 00:16:32,820 But now what happens if two vacancies find each other? 384 00:16:32,820 --> 00:16:35,040 Then you've got the makings of a void, 385 00:16:35,040 --> 00:16:36,900 or we then call it a small vacancy 386 00:16:36,900 --> 00:16:39,540 cluster of two vacancies, but it's actually 387 00:16:39,540 --> 00:16:42,360 more stable for these vacancies or interstitials 388 00:16:42,360 --> 00:16:45,270 to find each other and make these larger 389 00:16:45,270 --> 00:16:47,550 defects than it is for them to sit alone 390 00:16:47,550 --> 00:16:48,970 in the crystal structure. 391 00:16:48,970 --> 00:16:51,660 So there is a thermodynamic driving force bringing them 392 00:16:51,660 --> 00:16:55,200 together, and then as those defects build up, 393 00:16:55,200 --> 00:16:57,240 then what Jared said could happen. 394 00:16:57,240 --> 00:17:00,000 You could crack the material because it could get weaker, 395 00:17:00,000 --> 00:17:03,050 less ductile, less tough. 396 00:17:03,050 --> 00:17:04,970 Weaker is the opposite of strong, 397 00:17:04,970 --> 00:17:07,520 and what's the other one? 398 00:17:07,520 --> 00:17:10,920 Toughness-- oh, and harder, actually. 399 00:17:10,920 --> 00:17:12,569 So the origins avoid swelling I'll 400 00:17:12,569 --> 00:17:15,375 start with the humble vacancy. 401 00:17:15,375 --> 00:17:17,730 A void is nothing but a bunch of vacancies 402 00:17:17,730 --> 00:17:20,470 or a pocket of vacuum or gas in a material, 403 00:17:20,470 --> 00:17:24,359 and it all has to start with these single vacancies. 404 00:17:24,359 --> 00:17:28,200 As they cluster together, they reached this threshold 405 00:17:28,200 --> 00:17:30,960 in terms of free energy where putting a few of them 406 00:17:30,960 --> 00:17:33,720 together is not quite energetically favorable, 407 00:17:33,720 --> 00:17:36,720 but it's not so unfavorable that it never happens. 408 00:17:36,720 --> 00:17:39,930 So once in a while, you'll get a few vacancies to come together, 409 00:17:39,930 --> 00:17:43,110 and that cluster will survive for a little while. 410 00:17:43,110 --> 00:17:46,170 All the while, you're making more and more vacancies nearby, 411 00:17:46,170 --> 00:17:47,610 and if it gets to a certain size, 412 00:17:47,610 --> 00:17:49,915 that free energy goes negative. 413 00:17:49,915 --> 00:17:51,540 And when the free energy goes negative, 414 00:17:51,540 --> 00:17:54,960 it becomes stable on its own, and then that void 415 00:17:54,960 --> 00:17:58,360 will simply continue to grow, and grow, and grow. 416 00:17:58,360 --> 00:18:02,130 And so there's this process of absorption and emission 417 00:18:02,130 --> 00:18:04,260 of defects by larger or smaller void, 418 00:18:04,260 --> 00:18:06,790 so if you have a whole bunch of voids near each other, 419 00:18:06,790 --> 00:18:08,610 some of them can be emitting vacancies, 420 00:18:08,610 --> 00:18:10,422 which can be captured by the other ones, 421 00:18:10,422 --> 00:18:12,630 and this is part of why they don't all just disappear 422 00:18:12,630 --> 00:18:13,530 at once. 423 00:18:13,530 --> 00:18:15,540 They have finite lifetimes, long enough 424 00:18:15,540 --> 00:18:17,670 that you can build them up to the size 425 00:18:17,670 --> 00:18:19,110 where they become stable. 426 00:18:19,110 --> 00:18:23,250 Then this free energy eventually curves down, becomes negative, 427 00:18:23,250 --> 00:18:26,840 and then they just stick around, and we've actually 428 00:18:26,840 --> 00:18:29,760 seen these clusters or voids diffusing, 429 00:18:29,760 --> 00:18:33,380 so it's not like vacancies alone are the only thing that moves. 430 00:18:33,380 --> 00:18:37,850 We've actually seen clusters of defects diffusing, mostly 431 00:18:37,850 --> 00:18:40,130 in one dimension, but what you're seeing here 432 00:18:40,130 --> 00:18:43,400 is a TEM, or transmission electron microscope image, 433 00:18:43,400 --> 00:18:46,580 of one dimensional diffusion of a vacancy cluster. 434 00:18:46,580 --> 00:18:48,650 That little black blob right there 435 00:18:48,650 --> 00:18:52,080 is a pocket of vacuum that's moving back and forth. 436 00:18:52,080 --> 00:18:54,320 And if it happens to find another pocket of vacuum, 437 00:18:54,320 --> 00:18:57,110 it could then combine to a bigger pocket, 438 00:18:57,110 --> 00:19:01,000 becoming a bigger and bigger void. 439 00:19:01,000 --> 00:19:03,520 The other problem too is that most materials 440 00:19:03,520 --> 00:19:07,420 generate helium when you irradiate them with neutrons. 441 00:19:07,420 --> 00:19:12,780 Did we go over the what's called the N alpha cross-section? 442 00:19:12,780 --> 00:19:14,777 Does that sound familiar to anyone? 443 00:19:14,777 --> 00:19:16,360 All right, I'm going to pull up Janice 444 00:19:16,360 --> 00:19:20,080 like I do pretty much every class. 445 00:19:20,080 --> 00:19:23,360 Let me show you what's going on. 446 00:19:23,360 --> 00:19:26,570 But this is an important one to note. 447 00:19:26,570 --> 00:19:29,780 Because a pocket a vacuum is not that stable, 448 00:19:29,780 --> 00:19:31,220 but if you get a little bit of gas 449 00:19:31,220 --> 00:19:33,262 to stabilize that pocket of vacuum, 450 00:19:33,262 --> 00:19:34,970 then that pressure differential goes down 451 00:19:34,970 --> 00:19:38,710 and that void becomes a bubble, and that bubble is more stable. 452 00:19:38,710 --> 00:19:39,210 Good. 453 00:19:39,210 --> 00:19:40,490 Because on the last isotope, where 454 00:19:40,490 --> 00:19:42,115 I was showing someone [INAUDIBLE] alpha 455 00:19:42,115 --> 00:19:43,190 cross-section. 456 00:19:43,190 --> 00:19:45,280 How convenient. 457 00:19:45,280 --> 00:19:47,460 So among the millions of cross sections 458 00:19:47,460 --> 00:19:49,620 that we've gone through, there is this one right 459 00:19:49,620 --> 00:19:52,420 here called Z alpha. 460 00:19:52,420 --> 00:19:53,720 So what-- Yeah? 461 00:19:53,720 --> 00:19:57,087 AUDIENCE: [INAUDIBLE] 462 00:19:57,087 --> 00:19:58,750 MICHAEL SHORT: Got to clone the screen. 463 00:19:58,750 --> 00:19:59,292 That's right. 464 00:19:59,292 --> 00:20:01,620 Thanks. 465 00:20:01,620 --> 00:20:02,700 There we go. 466 00:20:02,700 --> 00:20:05,100 So there's this one here called Z alpha, which 467 00:20:05,100 --> 00:20:08,670 means neutron comes in, alpha particle goes out, 468 00:20:08,670 --> 00:20:10,830 alpha particle is just an ionized helium 469 00:20:10,830 --> 00:20:13,950 ion, which very quickly pulls in two electrons 470 00:20:13,950 --> 00:20:17,430 from anywhere else in the metal and becomes helium gas. 471 00:20:17,430 --> 00:20:20,780 And this cross-section is not zero, 472 00:20:20,780 --> 00:20:24,830 especially at higher energy starting around 2 MeV, 473 00:20:24,830 --> 00:20:27,470 there is a small, but non-negligible chance 474 00:20:27,470 --> 00:20:30,902 that a neutron will go in, and a helium atom comes out. 475 00:20:30,902 --> 00:20:32,360 And those helium atoms have nowhere 476 00:20:32,360 --> 00:20:35,270 to go, they find the easiest place to sit, 477 00:20:35,270 --> 00:20:37,820 that happens to be pockets of vacuum. 478 00:20:37,820 --> 00:20:39,170 Voids. 479 00:20:39,170 --> 00:20:42,710 And what that actually does is stabilizes those voids so 480 00:20:42,710 --> 00:20:45,170 the curve I showed you back here. 481 00:20:45,170 --> 00:20:50,650 This is the case of free energy for a vacuum pocket of void, 482 00:20:50,650 --> 00:20:53,000 and that free energy gets lower and lower as you start 483 00:20:53,000 --> 00:20:55,640 to fill that void with gas. 484 00:20:55,640 --> 00:20:58,430 So as the voids fill with gas, they 485 00:20:58,430 --> 00:21:00,950 become more and more stable, and a lot of materials 486 00:21:00,950 --> 00:21:02,910 generate their own gas. 487 00:21:02,910 --> 00:21:08,232 So that's that, and they end up forming these bubbles. 488 00:21:08,232 --> 00:21:10,690 You guys remember, last time I showed you a bunch of voids. 489 00:21:10,690 --> 00:21:13,358 They look like diamonds all aligned in the same direction. 490 00:21:13,358 --> 00:21:14,650 What do you see different here? 491 00:21:18,760 --> 00:21:21,600 They're not quite circles, right? 492 00:21:21,600 --> 00:21:25,110 But they're kind of round edge squares. 493 00:21:25,110 --> 00:21:28,300 They are also all pointing in the same direction. 494 00:21:28,300 --> 00:21:30,630 If you look carefully at this one, 495 00:21:30,630 --> 00:21:32,175 this one, the one above it. 496 00:21:32,175 --> 00:21:33,300 And the big one over there. 497 00:21:33,300 --> 00:21:34,900 It's harder to see for the small ones, 498 00:21:34,900 --> 00:21:36,960 but for these three big ones, you 499 00:21:36,960 --> 00:21:39,420 can see that they're all rotated in the same direction, 500 00:21:39,420 --> 00:21:42,090 giving away the crystal orientation of the material. 501 00:21:42,090 --> 00:21:43,590 But the reason that they're starting 502 00:21:43,590 --> 00:21:47,840 to swell up from diamonds into bubbles, is they're full of gas 503 00:21:47,840 --> 00:21:50,670 and they stabilize the voids. 504 00:21:50,670 --> 00:21:53,310 You can also get dislocation buildup. 505 00:21:53,310 --> 00:21:56,010 Normally, you would have to deform a material 506 00:21:56,010 --> 00:21:59,910 to create and move dislocations, but when you apply radiation, 507 00:21:59,910 --> 00:22:03,727 you can just create dislocations. 508 00:22:03,727 --> 00:22:04,560 I mean look at that. 509 00:22:04,560 --> 00:22:05,820 This is kind of cool. 510 00:22:05,820 --> 00:22:08,460 You've got a dislocation source right here. 511 00:22:08,460 --> 00:22:10,560 Every one of those lines you see is a dislocation, 512 00:22:10,560 --> 00:22:13,530 and you can see it's spiraling out and ejecting dislocations 513 00:22:13,530 --> 00:22:15,360 from this one little spot. 514 00:22:15,360 --> 00:22:18,210 Any combination of small clusters 515 00:22:18,210 --> 00:22:21,810 can collapse into dislocations or the stress induced 516 00:22:21,810 --> 00:22:24,330 from irradiating things can cause more stress that 517 00:22:24,330 --> 00:22:26,088 can move more dislocations. 518 00:22:26,088 --> 00:22:27,630 You create what's called this network 519 00:22:27,630 --> 00:22:30,030 forest of dislocations that makes 520 00:22:30,030 --> 00:22:31,890 things a lot harder to deform. 521 00:22:34,860 --> 00:22:37,710 So let's see, I want to show a couple more videos of this 522 00:22:37,710 --> 00:22:40,200 because it's very clear in some of these. 523 00:22:40,200 --> 00:22:43,860 You can actually see along these lines right here 524 00:22:43,860 --> 00:22:46,830 a few different orientations of dislocations, 525 00:22:46,830 --> 00:22:50,380 and if you watch up here, you can 526 00:22:50,380 --> 00:22:52,420 see some dislocations moving, and then 527 00:22:52,420 --> 00:22:54,650 there's a source that emits more right there, 528 00:22:54,650 --> 00:22:57,517 and so all the time, you're creating dislocations 529 00:22:57,517 --> 00:22:59,350 that are being emitted from different places 530 00:22:59,350 --> 00:23:01,433 and colliding with each other. 531 00:23:01,433 --> 00:23:03,100 The trick that we didn't talk about yet, 532 00:23:03,100 --> 00:23:05,290 is when dislocations from different directions 533 00:23:05,290 --> 00:23:07,720 collide, they get stuck. 534 00:23:07,720 --> 00:23:09,930 And when they get stuck, they can't move. 535 00:23:09,930 --> 00:23:14,350 And when they can't move, you shift the balance from slip 536 00:23:14,350 --> 00:23:16,210 to fracture, which means, like Jared said, 537 00:23:16,210 --> 00:23:19,840 it's easier to just break something, rather than 538 00:23:19,840 --> 00:23:23,150 plastically deform it. 539 00:23:23,150 --> 00:23:26,360 And the effects of this are things like stiffening. 540 00:23:26,360 --> 00:23:28,730 An increase in the Young's Modulus. 541 00:23:28,730 --> 00:23:31,130 Because if you remove some of the compliance 542 00:23:31,130 --> 00:23:33,613 from the material or make it stiffer by injecting 543 00:23:33,613 --> 00:23:35,030 all sorts of different defects, it 544 00:23:35,030 --> 00:23:38,872 takes more stress to impart the same strain. 545 00:23:38,872 --> 00:23:40,580 That might not be a bad thing on its own. 546 00:23:40,580 --> 00:23:43,038 Your materials get stronger, that sounds like a good thing, 547 00:23:43,038 --> 00:23:44,470 right? 548 00:23:44,470 --> 00:23:49,498 Not always because it doesn't just come as stiffening. 549 00:23:49,498 --> 00:23:51,040 But now from an atomic point of view, 550 00:23:51,040 --> 00:23:53,140 why does this stiffening happen? 551 00:23:53,140 --> 00:23:54,070 Anybody have an idea? 552 00:24:01,050 --> 00:24:04,450 I'm going to jump back to the stress strain curve. 553 00:24:04,450 --> 00:24:06,580 So the stress, or the yield stress of a material, 554 00:24:06,580 --> 00:24:09,160 is usually defined as this point right here. 555 00:24:09,160 --> 00:24:12,370 When you go from elastic reversible deformation 556 00:24:12,370 --> 00:24:14,980 to irreversible plastic deformation. 557 00:24:14,980 --> 00:24:16,480 If something gets stronger, it means 558 00:24:16,480 --> 00:24:19,300 that this yield stress goes up. 559 00:24:19,300 --> 00:24:22,450 And if something gets stiffer, it means the slope goes up. 560 00:24:22,450 --> 00:24:25,230 These two tend to happen at the same time. 561 00:24:25,230 --> 00:24:28,070 So if something is stiffer and stronger, then 562 00:24:28,070 --> 00:24:31,520 the stress strain curve would be drawn more like that. 563 00:24:31,520 --> 00:24:35,120 And what actually physically happens at this point? 564 00:24:35,120 --> 00:24:38,020 This is when dislocations start to move. 565 00:24:38,020 --> 00:24:40,160 Dislocation movement is irreversible. 566 00:24:40,160 --> 00:24:43,660 You can't just snap it back when you relieve the stress. 567 00:24:43,660 --> 00:24:46,270 And by making something stronger and stiffer, 568 00:24:46,270 --> 00:24:48,370 you make it more difficult for those dislocations 569 00:24:48,370 --> 00:24:50,050 to start moving. 570 00:24:50,050 --> 00:24:53,080 And you can do that by throwing any defect in their way. 571 00:24:53,080 --> 00:24:55,630 And since radiation creates pretty much any and all 572 00:24:55,630 --> 00:24:58,568 defects, it's a great way to stiffen and strengthen 573 00:24:58,568 --> 00:24:59,110 the material. 574 00:25:04,800 --> 00:25:07,460 So one of the reasons things get stiffer and stronger 575 00:25:07,460 --> 00:25:10,340 is, remember before we showed you that video of dislocation 576 00:25:10,340 --> 00:25:13,805 sliding through material? 577 00:25:13,805 --> 00:25:14,680 Folks don't remember. 578 00:25:14,680 --> 00:25:17,290 I'll bring it up right now. 579 00:25:17,290 --> 00:25:18,790 I didn't see a lot of shaking heads. 580 00:25:24,010 --> 00:25:25,240 This one, right? 581 00:25:25,240 --> 00:25:26,820 This one right here. 582 00:25:26,820 --> 00:25:28,240 So remember, before, we showed you 583 00:25:28,240 --> 00:25:29,840 the way that dislocations move. 584 00:25:29,840 --> 00:25:32,950 So the ways that materials can deform without breaking. 585 00:25:32,950 --> 00:25:36,040 If you throw anything in its way, 586 00:25:36,040 --> 00:25:39,100 you're going to make this process a lot more difficult. 587 00:25:39,100 --> 00:25:41,880 And all radiation damage does is throw things in the way. 588 00:25:45,570 --> 00:25:47,280 So if you throw absolutely anything 589 00:25:47,280 --> 00:25:52,888 in the way from solute atoms to interstitials to vacancies, 590 00:25:52,888 --> 00:25:54,930 all of a sudden, it's harder for that dislocation 591 00:25:54,930 --> 00:25:57,180 to move because some of those bonds are stretched out, 592 00:25:57,180 --> 00:25:59,550 or there's a few extra atoms in the way. 593 00:25:59,550 --> 00:26:02,280 And you can then start to create what's 594 00:26:02,280 --> 00:26:06,300 called little pin sections called jogs. 595 00:26:06,300 --> 00:26:09,390 Let's say a little vacancy moves over to this dislocation, 596 00:26:09,390 --> 00:26:12,210 meaning that it goes up by one atomic position. 597 00:26:12,210 --> 00:26:14,340 Then you've got pieces of this dislocation that 598 00:26:14,340 --> 00:26:19,417 are not in this preferential slip plane, and they get stuck. 599 00:26:19,417 --> 00:26:21,625 So all of a sudden you go from a completely gliding-- 600 00:26:21,625 --> 00:26:23,700 or what we call glissile dislocation-- 601 00:26:23,700 --> 00:26:25,950 to one that's stuck, or sessine, those 602 00:26:25,950 --> 00:26:28,630 are the actual material science words that we use. 603 00:26:28,630 --> 00:26:32,280 And what it ends up leading to is a strong loss in ductility. 604 00:26:32,280 --> 00:26:36,090 At the same time as things get stronger and stiffer, 605 00:26:36,090 --> 00:26:38,070 they tend to get much less ductile. 606 00:26:38,070 --> 00:26:41,970 So what you're looking at here are fuel shrouds. 607 00:26:41,970 --> 00:26:45,810 These are fuel boxes that surround the fuel pins 608 00:26:45,810 --> 00:26:48,725 in a Russian sodium fast reactor, and usually 609 00:26:48,725 --> 00:26:50,850 what you do is you would grab onto this piece right 610 00:26:50,850 --> 00:26:53,940 here and lift up to remove this fuel from the reactor 611 00:26:53,940 --> 00:26:55,320 during refueling. 612 00:26:55,320 --> 00:26:59,040 What happened here is they grab that, they started to pull, 613 00:26:59,040 --> 00:27:02,610 and they heard a little clink, and up came half the fuel box, 614 00:27:02,610 --> 00:27:05,040 and the fuel stayed down in the reactor with no way 615 00:27:05,040 --> 00:27:06,660 to pull it out. 616 00:27:06,660 --> 00:27:09,270 So this is the reason why radiation damage is such 617 00:27:09,270 --> 00:27:11,550 an important field of study is you might not 618 00:27:11,550 --> 00:27:14,730 know anything has happened until you shut the reactor down 619 00:27:14,730 --> 00:27:16,460 and go to take out the fuel and realize 620 00:27:16,460 --> 00:27:18,180 that you can't because everything 621 00:27:18,180 --> 00:27:20,040 is as brittle as glass. 622 00:27:20,040 --> 00:27:23,100 This is actually a talk I saw yesterday. 623 00:27:23,100 --> 00:27:26,430 We had a summer visitor in our lab from Kazakhstan. 624 00:27:26,430 --> 00:27:28,518 And most of their radioactive materials 625 00:27:28,518 --> 00:27:30,060 came from this reactor that shut down 626 00:27:30,060 --> 00:27:34,080 in 1999 on one side of Kazakhstan, 627 00:27:34,080 --> 00:27:36,150 and they wanted to transport those materials 628 00:27:36,150 --> 00:27:37,590 to the other side. 629 00:27:37,590 --> 00:27:39,840 So they hired the cheapest truck drivers 630 00:27:39,840 --> 00:27:41,580 to go on the bumpy roads. 631 00:27:41,580 --> 00:27:44,700 And the scientists were freaking out, because only 632 00:27:44,700 --> 00:27:47,873 they knew that all of the metal that all those guys thought 633 00:27:47,873 --> 00:27:49,290 was going to be ductile like metal 634 00:27:49,290 --> 00:27:51,300 was more brittle than glass. 635 00:27:51,300 --> 00:27:55,890 And any sort of bump would cause just complete shattering 636 00:27:55,890 --> 00:28:00,090 of this metal and catastrophic release 637 00:28:00,090 --> 00:28:01,920 of radioactive material. 638 00:28:01,920 --> 00:28:03,510 So this took them-- 639 00:28:03,510 --> 00:28:06,510 let's see-- I think Kazakhstan is smaller than the US. 640 00:28:06,510 --> 00:28:09,780 So who here has done a cross-country trip? 641 00:28:09,780 --> 00:28:10,850 How long it take you? 642 00:28:10,850 --> 00:28:12,807 AUDIENCE: Six days from Seattle to here. 643 00:28:12,807 --> 00:28:14,890 MICHAEL SHORT: OK, and did you stop along the way? 644 00:28:14,890 --> 00:28:15,515 AUDIENCE: Yeah. 645 00:28:15,515 --> 00:28:18,080 MICHAEL SHORT: OK, so this trip took them 13 days 646 00:28:18,080 --> 00:28:19,940 because they went slow. 647 00:28:19,940 --> 00:28:21,818 And I don't think the roads in Kazakhstan 648 00:28:21,818 --> 00:28:24,360 are as good as they are in most of the middle of the country. 649 00:28:24,360 --> 00:28:27,950 The coasts are terrible, but the middle is pretty good. 650 00:28:27,950 --> 00:28:30,260 So this trip went slow because the scientists 651 00:28:30,260 --> 00:28:31,980 said this happens. 652 00:28:31,980 --> 00:28:32,917 You should be careful. 653 00:28:32,917 --> 00:28:35,000 And luckily, there were no problems and no release 654 00:28:35,000 --> 00:28:36,890 of radioactive material. 655 00:28:36,890 --> 00:28:39,320 Pretty cool. 656 00:28:39,320 --> 00:28:41,930 What you want to happen is for dislocations 657 00:28:41,930 --> 00:28:44,640 to move on the easiest planes. 658 00:28:44,640 --> 00:28:46,460 And so what I have redrawn here is, 659 00:28:46,460 --> 00:28:48,770 let's say you've got a bar of some metal, 660 00:28:48,770 --> 00:28:53,540 some face-centered cubic metal, as you pull on it, like this, 661 00:28:53,540 --> 00:28:57,440 it will actually deform at about a 45 degree angles. 662 00:28:57,440 --> 00:28:59,967 You might wonder, why does that happen? 663 00:28:59,967 --> 00:29:01,550 But if you look carefully here, what's 664 00:29:01,550 --> 00:29:04,850 the closest packed plane of atoms that you can see? 665 00:29:04,850 --> 00:29:08,150 It's not this plane normal to the stress direction. 666 00:29:08,150 --> 00:29:11,390 It's like this one or like this one, 667 00:29:11,390 --> 00:29:13,760 and so you actually end up getting deformation 668 00:29:13,760 --> 00:29:17,000 in what's called slip plains, or the easiest directions 669 00:29:17,000 --> 00:29:18,570 for things to deform. 670 00:29:18,570 --> 00:29:20,870 And without going into any of the math or atomistics, 671 00:29:20,870 --> 00:29:23,120 I just want to show you some examples pulled out 672 00:29:23,120 --> 00:29:25,040 of, again, the fusion reactor. 673 00:29:25,040 --> 00:29:28,690 So this is a piece of rotor steel from the same Alcator 674 00:29:28,690 --> 00:29:30,950 rotor where we found that inclusion. 675 00:29:30,950 --> 00:29:33,410 We were pulling it in this direction, and look 676 00:29:33,410 --> 00:29:34,850 what formed. 677 00:29:34,850 --> 00:29:38,815 All of these slip bands at 45 degree angles, 678 00:29:38,815 --> 00:29:40,190 showing you that just because you 679 00:29:40,190 --> 00:29:41,690 pull in something in one direction, 680 00:29:41,690 --> 00:29:44,090 doesn't mean it deforms in that direction. 681 00:29:44,090 --> 00:29:47,180 It deforms and little slices in the direction 682 00:29:47,180 --> 00:29:49,755 that dislocations can move the easiest. 683 00:29:49,755 --> 00:29:51,380 So when you actually pull on something, 684 00:29:51,380 --> 00:29:55,590 to show you diagrammatically, it deforms something like that. 685 00:29:55,590 --> 00:29:58,250 You get a mixture of bending and rotation 686 00:29:58,250 --> 00:30:01,570 to make it look like the bar is bending uniformly straight, 687 00:30:01,570 --> 00:30:04,930 but on the microscale, it's not. 688 00:30:04,930 --> 00:30:08,190 So this is a pretty slick image of a single crystal of cadmium 689 00:30:08,190 --> 00:30:11,700 being pulled in this direction, and you can actually 690 00:30:11,700 --> 00:30:15,300 see every plane there, that's a slip plane. 691 00:30:15,300 --> 00:30:16,710 That's a plane where dislocations 692 00:30:16,710 --> 00:30:20,055 have been moving all the way to the outside of the material, 693 00:30:20,055 --> 00:30:21,930 which is pretty cool, and this is the process 694 00:30:21,930 --> 00:30:24,120 that you want to happen. 695 00:30:24,120 --> 00:30:26,490 Anything in the way of those dislocations, 696 00:30:26,490 --> 00:30:28,680 you don't start forming these slip bands, 697 00:30:28,680 --> 00:30:31,050 and you'd make it more preferable that the thing will 698 00:30:31,050 --> 00:30:33,500 just break and fracture. 699 00:30:33,500 --> 00:30:36,440 To show you some extreme examples of slip, 700 00:30:36,440 --> 00:30:38,330 that's when you have to go nano. 701 00:30:38,330 --> 00:30:40,360 So these are some pillar compression test 702 00:30:40,360 --> 00:30:42,260 that used a focused ion beam, which 703 00:30:42,260 --> 00:30:45,260 we will be using to top off our study of electron 704 00:30:45,260 --> 00:30:48,080 interactions with matter and ion interactions 705 00:30:48,080 --> 00:30:52,220 to take a piece of metal and carve out a little cylinder. 706 00:30:52,220 --> 00:30:54,020 And all they did is smash. 707 00:30:54,020 --> 00:30:57,290 They came down and compressively pushed on the cylinder, 708 00:30:57,290 --> 00:30:59,250 and look how it deformed. 709 00:30:59,250 --> 00:31:01,980 Not in the way you might intuitively expect, 710 00:31:01,980 --> 00:31:04,440 if you don't know any material science. 711 00:31:04,440 --> 00:31:06,750 So it deformed all on 45 degree angles 712 00:31:06,750 --> 00:31:10,200 and very weird compression. 713 00:31:10,200 --> 00:31:13,553 Not actually weird, if you know what's going on. 714 00:31:13,553 --> 00:31:15,220 there's lots more neat examples of this. 715 00:31:15,220 --> 00:31:17,590 If you don't push too hard, you can actually 716 00:31:17,590 --> 00:31:21,880 see these perfectly symmetrical slip planes at 45 degree angles 717 00:31:21,880 --> 00:31:23,870 to the axis of compression, and you 718 00:31:23,870 --> 00:31:27,040 know every one of these pillars you see this happening. 719 00:31:27,040 --> 00:31:30,605 And this is what you want to happen to nuclear materials 720 00:31:30,605 --> 00:31:32,230 because you're really trying to balance 721 00:31:32,230 --> 00:31:37,045 this between slip and fracture towards the direction of slip. 722 00:31:37,045 --> 00:31:39,545 That means that something will deform a little bit before it 723 00:31:39,545 --> 00:31:45,338 just shatters like those channel boxes from the Russian reactor. 724 00:31:45,338 --> 00:31:46,880 Any questions on what I said before I 725 00:31:46,880 --> 00:31:49,071 go on to the macroscale properties? 726 00:31:53,130 --> 00:31:55,410 All right, and let's get into the real world stuff. 727 00:31:55,410 --> 00:31:57,900 What actually causes this embrittlement? 728 00:31:57,900 --> 00:32:00,000 Well, there's a few things. 729 00:32:00,000 --> 00:32:04,600 Remember we saw videos of those dislocations in a traffic jam. 730 00:32:04,600 --> 00:32:08,210 If not, then I'll refresh your guy's memory. 731 00:32:08,210 --> 00:32:13,430 It's a phenomenon called pileup, let's see. 732 00:32:13,430 --> 00:32:16,850 There is the traffic jam. 733 00:32:16,850 --> 00:32:18,570 Do you guys remember this video now-- 734 00:32:18,570 --> 00:32:21,850 I know it's been a week, but these dislocations 735 00:32:21,850 --> 00:32:24,430 are moving and feeling each other's stress, 736 00:32:24,430 --> 00:32:27,340 and so they can't move as easily as they would want to, 737 00:32:27,340 --> 00:32:29,710 so you end up with a phenomenon called pileup. 738 00:32:29,710 --> 00:32:33,250 This happens both near other dislocations 739 00:32:33,250 --> 00:32:37,860 and near any other defect that gets in the way, 740 00:32:37,860 --> 00:32:39,520 like a grain boundary. 741 00:32:39,520 --> 00:32:43,980 So for smaller materials you end up with more of this pileup, 742 00:32:43,980 --> 00:32:49,050 and they tend to be of a fair bit stronger, and a fair bit-- 743 00:32:49,050 --> 00:32:51,680 they can be less ductile, with some exceptions. 744 00:32:51,680 --> 00:32:53,438 I won't say they're always less ductile, 745 00:32:53,438 --> 00:32:55,230 but if you put anything in the way, notice, 746 00:32:55,230 --> 00:32:57,180 this just says barrier. 747 00:32:57,180 --> 00:33:00,250 Any other defect can act as a barrier. 748 00:33:00,250 --> 00:33:01,710 And this ends up shifting what we 749 00:33:01,710 --> 00:33:05,070 call the ductile-brittle transition temperature. 750 00:33:05,070 --> 00:33:07,260 This is the property that people worry 751 00:33:07,260 --> 00:33:09,670 about for reactor pressure vessels, 752 00:33:09,670 --> 00:33:12,310 because you would want the pressure vessel, which in cases 753 00:33:12,310 --> 00:33:15,040 the entire core of the reactor, to always 754 00:33:15,040 --> 00:33:18,870 be ductile in the worst possible situation. 755 00:33:18,870 --> 00:33:21,990 The worst possible situation is on the absolute last day 756 00:33:21,990 --> 00:33:24,600 of operation at the coldest temperature 757 00:33:24,600 --> 00:33:26,400 it could possibly be. 758 00:33:26,400 --> 00:33:29,040 As you guys know, or you probably know, 759 00:33:29,040 --> 00:33:31,620 when you make something colder, it tends to be more brittle. 760 00:33:31,620 --> 00:33:35,130 So who's frozen stuff in liquid nitrogen and broken it before? 761 00:33:35,130 --> 00:33:35,630 Good. 762 00:33:35,630 --> 00:33:37,010 I'm glad to see a few hands, so what 763 00:33:37,010 --> 00:33:38,218 do you guys freeze and break? 764 00:33:42,310 --> 00:33:45,790 So just like froze a bottle of Pepto Bismol and shattered it? 765 00:33:45,790 --> 00:33:46,570 Nice. 766 00:33:46,570 --> 00:33:48,973 That must have been a fun mess to clean up. 767 00:33:48,973 --> 00:33:50,140 Yeah, what about you, Sarah? 768 00:33:50,140 --> 00:33:52,290 AUDIENCE: A banana and a coin. 769 00:33:52,290 --> 00:33:53,300 MICHAEL SHORT: Cool, OK. 770 00:33:53,300 --> 00:33:55,180 And we're able to break the coin? 771 00:33:55,180 --> 00:33:56,110 There you go. 772 00:33:56,110 --> 00:33:58,720 So normally you'd be able to bend a coin, 773 00:33:58,720 --> 00:34:01,390 or if it's a one yen coin, you can bite through it. 774 00:34:01,390 --> 00:34:03,760 Not when immersed in liquid nitrogen. What about you, 775 00:34:03,760 --> 00:34:04,480 Charlie? 776 00:34:04,480 --> 00:34:05,230 AUDIENCE: Flowers. 777 00:34:05,230 --> 00:34:05,890 MICHAEL SHORT: Flowers, OK. 778 00:34:05,890 --> 00:34:06,400 Classic. 779 00:34:06,400 --> 00:34:08,710 So take a rose and shatter it. 780 00:34:08,710 --> 00:34:09,489 Yeah. 781 00:34:09,489 --> 00:34:12,909 All these normally ductile materials become extremely 782 00:34:12,909 --> 00:34:14,320 brittle when they get colder. 783 00:34:14,320 --> 00:34:16,330 So do reactor pressure vessels. 784 00:34:16,330 --> 00:34:18,190 The problem is, they don't just get brittle 785 00:34:18,190 --> 00:34:20,290 when they get to liquid nitrogen temperatures. 786 00:34:20,290 --> 00:34:21,707 At the end of their life, they can 787 00:34:21,707 --> 00:34:25,030 be brittle at room temperature from radiation damage. 788 00:34:25,030 --> 00:34:27,280 So there is what's called a ductile-brittle transition 789 00:34:27,280 --> 00:34:31,570 temperature before a pressure vessels are irradiated, 790 00:34:31,570 --> 00:34:35,050 there's about this 50% line, whatever this temperature was 791 00:34:35,050 --> 00:34:38,650 where you have let's say, 50%, or 10%, or 0% ductility. 792 00:34:38,650 --> 00:34:40,420 Whatever measure you're using, you 793 00:34:40,420 --> 00:34:42,190 say, OK, we always want to make sure 794 00:34:42,190 --> 00:34:45,219 that it's got a certain amount of energy absorption 795 00:34:45,219 --> 00:34:49,159 capability, toughness, at a certain temperature. 796 00:34:49,159 --> 00:34:51,159 And as you irradiate that vessel, 797 00:34:51,159 --> 00:34:55,810 this shifts over this way, and this upper amount of energy, 798 00:34:55,810 --> 00:34:58,240 this USE, or what we call upper shelf energy, 799 00:34:58,240 --> 00:35:01,650 because this looks like a shelf, goes down. 800 00:35:01,650 --> 00:35:04,990 What you want to make sure is that this change 801 00:35:04,990 --> 00:35:07,360 in ductile-brittle transition temperature 802 00:35:07,360 --> 00:35:10,390 never reaches room temperature. 803 00:35:10,390 --> 00:35:13,510 You might think, oh, it's OK, reactors run at 300 Celsius, 804 00:35:13,510 --> 00:35:16,512 and things are pretty ductile right there. 805 00:35:16,512 --> 00:35:18,970 Well, you usually have to shut the reactor down once you're 806 00:35:18,970 --> 00:35:22,120 done with it to refuel, and if something goes wrong, 807 00:35:22,120 --> 00:35:23,920 there's a pressure spike, you can 808 00:35:23,920 --> 00:35:27,140 have a condition called pressurized thermal shock, 809 00:35:27,140 --> 00:35:28,710 or PTS. 810 00:35:28,710 --> 00:35:32,570 In that case, you would have a sudden pressure wave from, 811 00:35:32,570 --> 00:35:35,180 let's say, from steam explosion or whatever you could have, 812 00:35:35,180 --> 00:35:37,790 and you want that vessel to be able to absorb that energy 813 00:35:37,790 --> 00:35:40,670 instead of breaking in half, because if you break it half, 814 00:35:40,670 --> 00:35:43,210 that's a radioactive release. 815 00:35:43,210 --> 00:35:46,180 The way you test ductile-brittle transition temperature 816 00:35:46,180 --> 00:35:48,850 is what's called a Charpy impact test. 817 00:35:48,850 --> 00:35:54,220 It's probably the highest tech, lowest tech test I've seen. 818 00:35:54,220 --> 00:35:56,650 You simply hit things with a hammer. 819 00:35:56,650 --> 00:36:00,520 A very well calibrated, precise hammer. 820 00:36:00,520 --> 00:36:04,000 Let me pause so you can see what the sample looks like. 821 00:36:04,000 --> 00:36:06,710 You have these little bars with a notch in them. 822 00:36:06,710 --> 00:36:09,700 The notch is to make sure that acts as a stress concentrator, 823 00:36:09,700 --> 00:36:11,810 and you know where the breaks going to happen. 824 00:36:11,810 --> 00:36:16,180 So in a Charpy test, you line up this little sample, 825 00:36:16,180 --> 00:36:19,930 and you've got-- actually in your reactors, usually, 826 00:36:19,930 --> 00:36:21,850 you've got pieces of the pressure vessel 827 00:36:21,850 --> 00:36:25,330 in this form lining the inside rim of the reactor pressure 828 00:36:25,330 --> 00:36:26,110 vessel. 829 00:36:26,110 --> 00:36:27,880 So every time you refuel your reactor, 830 00:36:27,880 --> 00:36:31,340 you take off another few of these out 831 00:36:31,340 --> 00:36:34,820 and you hit them with a very well calibrated hammer. 832 00:36:34,820 --> 00:36:38,760 And you can measure by actually turning this dial 833 00:36:38,760 --> 00:36:40,920 and letting the hammer turn it as it moves 834 00:36:40,920 --> 00:36:42,780 through the material, you can see 835 00:36:42,780 --> 00:36:45,390 how much energy was absorbed by the material 836 00:36:45,390 --> 00:36:47,040 as the hammer comes back up. 837 00:36:49,940 --> 00:36:52,190 So it breaks right through the material, in this case, 838 00:36:52,190 --> 00:36:55,850 it's in a quenched or brittle condition, and for some reason, 839 00:36:55,850 --> 00:36:57,950 they have a lot of footage of the guy standing 840 00:36:57,950 --> 00:36:59,750 and not breathing, but what I want 841 00:36:59,750 --> 00:37:05,040 to show you is what actually happens here. 842 00:37:05,040 --> 00:37:08,790 I didn't make the video, I just got it. 843 00:37:08,790 --> 00:37:10,330 There we go. 844 00:37:10,330 --> 00:37:12,850 So what you can see is that if the hammer were 845 00:37:12,850 --> 00:37:15,880 to move through air with absolutely no drag, 846 00:37:15,880 --> 00:37:18,280 it would come back to the zero position. 847 00:37:18,280 --> 00:37:20,170 If they had encountered some resistance, 848 00:37:20,170 --> 00:37:22,210 like with a piece of steel in the way, 849 00:37:22,210 --> 00:37:25,390 it then measures the amount of energy in joules 850 00:37:25,390 --> 00:37:28,930 that piece of steel absorbs from the hammer blow. 851 00:37:28,930 --> 00:37:30,910 The larger that is, the better. 852 00:37:30,910 --> 00:37:32,950 And by doing this test at a number 853 00:37:32,950 --> 00:37:35,290 of different temperatures, you can 854 00:37:35,290 --> 00:37:38,170 recreate this ductile-brittle transition temperature curve. 855 00:37:38,170 --> 00:37:40,540 So they'll take a few Charpy coupons, 856 00:37:40,540 --> 00:37:43,510 they will test them at, let's say, every 25 Celsius, 857 00:37:43,510 --> 00:37:47,050 get a bunch of points, draw the line through the points, 858 00:37:47,050 --> 00:37:49,210 and decide where is the material brittle. 859 00:37:49,210 --> 00:37:53,760 At what temperature will it become brittle? 860 00:37:53,760 --> 00:37:57,127 To show you what something looks like when it's not brittle. 861 00:37:57,127 --> 00:37:58,710 The same test is done in what's called 862 00:37:58,710 --> 00:38:01,200 the normalized condition, where you simply heat 863 00:38:01,200 --> 00:38:03,480 the steel to a high temperature, relaxing out 864 00:38:03,480 --> 00:38:06,180 most of the defects, and bringing back as much 865 00:38:06,180 --> 00:38:08,850 of the perfect crystal structure as possible, which 866 00:38:08,850 --> 00:38:11,820 is really good for letting dislocations move through it. 867 00:38:11,820 --> 00:38:15,540 So the same test is done by the same awkward feller who 868 00:38:15,540 --> 00:38:18,540 likes to stand there and not breathe, 869 00:38:18,540 --> 00:38:23,212 but you'll notice a very different result of this test. 870 00:38:23,212 --> 00:38:24,920 Doesn't look like it, but if you actually 871 00:38:24,920 --> 00:38:28,910 look at how much energy was absorbed, much, much higher. 872 00:38:28,910 --> 00:38:31,910 So something like 18 times more energy, 873 00:38:31,910 --> 00:38:34,430 and you can qualitatively see the difference 874 00:38:34,430 --> 00:38:36,230 between these two conditions by looking 875 00:38:36,230 --> 00:38:38,450 at the fractured surfaces, and this is where 876 00:38:38,450 --> 00:38:40,070 it starts to get intuitive. 877 00:38:40,070 --> 00:38:41,900 Something that's ductile would tear more 878 00:38:41,900 --> 00:38:45,140 like taffy, where something that's brittle 879 00:38:45,140 --> 00:38:47,240 would cleave or break in half much more 880 00:38:47,240 --> 00:38:49,767 smoothly, so these are the two pieces of metal 881 00:38:49,767 --> 00:38:50,600 that we just showed. 882 00:38:50,600 --> 00:38:55,010 You the one that absorbed 180 joules by lots of defamation, 883 00:38:55,010 --> 00:38:58,220 and the one that absorbed 10 joules by fracture 884 00:38:58,220 --> 00:38:59,720 in a brutal way. 885 00:38:59,720 --> 00:39:04,040 This is what you want your reactor vessel to behave like, 886 00:39:04,040 --> 00:39:06,500 but the problem with these ductile-brittle transition 887 00:39:06,500 --> 00:39:08,450 temperature curves, is this not just this part 888 00:39:08,450 --> 00:39:11,270 that you're worried about, it's that part. 889 00:39:11,270 --> 00:39:15,320 So even at high temperatures, things get less ductile. 890 00:39:15,320 --> 00:39:17,840 So it's a combination of temperature and number 891 00:39:17,840 --> 00:39:18,980 of defects. 892 00:39:18,980 --> 00:39:21,230 And if either one of these criteria fails, 893 00:39:21,230 --> 00:39:23,900 if you become too brittle at low temperature, 894 00:39:23,900 --> 00:39:27,950 or your total ductility at high temperature goes down too much, 895 00:39:27,950 --> 00:39:30,500 that's the end of life of your reactor vessel, 896 00:39:30,500 --> 00:39:33,740 and this is one of the biggest problems in life extensions 897 00:39:33,740 --> 00:39:35,450 of light water reactors. 898 00:39:35,450 --> 00:39:37,640 They were built for 40 years and they originally 899 00:39:37,640 --> 00:39:39,035 had license for 40 years. 900 00:39:39,035 --> 00:39:41,660 How many of you guys have heard of the license extensions going 901 00:39:41,660 --> 00:39:43,970 on now, to 60 or 80 years? 902 00:39:43,970 --> 00:39:45,610 Yeah, so a few of you guys. 903 00:39:45,610 --> 00:39:48,050 I've heard heard, why not run the reactor longer. 904 00:39:48,050 --> 00:39:49,610 Not build a new one, but keep getting 905 00:39:49,610 --> 00:39:52,220 all this clean green cheap nuclear energy? 906 00:39:52,220 --> 00:39:53,660 This is why. 907 00:39:53,660 --> 00:39:57,350 You have to be absolutely sure that your vessel, 908 00:39:57,350 --> 00:40:00,380 your primary containment, will survive. 909 00:40:00,380 --> 00:40:06,370 And we're not so sure because well, we 910 00:40:06,370 --> 00:40:11,080 jump to the part of the video that's got the Charpy coupons. 911 00:40:11,080 --> 00:40:12,610 Those. 912 00:40:12,610 --> 00:40:14,970 We ran out. 913 00:40:14,970 --> 00:40:17,190 We only plan to put these vessels in service 914 00:40:17,190 --> 00:40:21,300 for 40 years, and folks put 40 years worth of these coupons, 915 00:40:21,300 --> 00:40:24,700 plus some extras, in the reactor vessel. 916 00:40:24,700 --> 00:40:26,550 Now, in order to prove that it's actually 917 00:40:26,550 --> 00:40:28,950 safe to continue operation, you have 918 00:40:28,950 --> 00:40:32,190 to have some amount of material to test 919 00:40:32,190 --> 00:40:34,270 and say, OK, this vessel is still ductile, 920 00:40:34,270 --> 00:40:35,417 it's still going to work. 921 00:40:35,417 --> 00:40:36,000 What happened? 922 00:40:36,000 --> 00:40:38,923 What do you do when you run out of coupons? 923 00:40:38,923 --> 00:40:40,340 Anyone have any ideas, because I'm 924 00:40:40,340 --> 00:40:42,480 sure the industry would love to hear them. 925 00:40:42,480 --> 00:40:44,480 AUDIENCE: Would you have to start using material 926 00:40:44,480 --> 00:40:45,810 from the vessel itself? 927 00:40:45,810 --> 00:40:48,600 MICHAEL SHORT: You could start using material from the vessel. 928 00:40:48,600 --> 00:40:52,170 That's actually what I plan to do too, but with some very 929 00:40:52,170 --> 00:40:52,950 strong caveat. 930 00:40:52,950 --> 00:40:56,580 So if you were to scoop out a piece of the vessel, 931 00:40:56,580 --> 00:40:58,920 you then create a stress concentration. 932 00:40:58,920 --> 00:41:02,910 In addition, reactor vessel looks like a gigantic forging 933 00:41:02,910 --> 00:41:10,720 of really thick carbon steel with a very thin liner 934 00:41:10,720 --> 00:41:11,770 of stainless steel. 935 00:41:15,430 --> 00:41:18,820 And the stainless steel is there to prevent corrosion 936 00:41:18,820 --> 00:41:21,490 from the reactor water. 937 00:41:21,490 --> 00:41:25,960 That thin, quarter inch bit of stainless steel 938 00:41:25,960 --> 00:41:27,420 is what actually saved what could 939 00:41:27,420 --> 00:41:29,503 have been one of the worst nuclear accidents in US 940 00:41:29,503 --> 00:41:31,810 history, the Davis Bessie plant, where there 941 00:41:31,810 --> 00:41:33,280 was a crack in the vessel. 942 00:41:33,280 --> 00:41:38,980 Boric acid actually ate through a whole chunk 943 00:41:38,980 --> 00:41:41,950 of the pressure vessel, leaving the stainless steel intact. 944 00:41:41,950 --> 00:41:44,200 And it's that little quarter inch stainless steel that 945 00:41:44,200 --> 00:41:45,418 saved the plant. 946 00:41:45,418 --> 00:41:46,960 But if you were to take something out 947 00:41:46,960 --> 00:41:49,377 from the inside of the vessel, the part that gets the most 948 00:41:49,377 --> 00:41:54,800 damage, you'd be taking out some of the stainless steel, which 949 00:41:54,800 --> 00:41:56,090 is a problem. 950 00:41:56,090 --> 00:42:00,640 You could take a piece out from here, maybe the outside, 951 00:42:00,640 --> 00:42:02,860 but then you've got a stress concentrator. 952 00:42:02,860 --> 00:42:05,080 Any sort of chunk that is missing 953 00:42:05,080 --> 00:42:07,600 is where a crack is going to preferentially form, 954 00:42:07,600 --> 00:42:10,690 so you would weaken that vessel by taking a piece out. 955 00:42:10,690 --> 00:42:12,050 Anyone else have any ideas? 956 00:42:12,050 --> 00:42:12,550 Yeah? 957 00:42:12,550 --> 00:42:14,860 AUDIENCE: Is it impossible to just replace the vessel? 958 00:42:14,860 --> 00:42:15,652 MICHAEL SHORT: Yes. 959 00:42:15,652 --> 00:42:17,620 A new vessel means a new reactor. 960 00:42:17,620 --> 00:42:19,570 So the license for the plant is intimately 961 00:42:19,570 --> 00:42:21,940 tied to the license for the vessel. 962 00:42:21,940 --> 00:42:23,530 Any other ideas? 963 00:42:23,530 --> 00:42:24,440 Yeah? 964 00:42:24,440 --> 00:42:27,690 AUDIENCE: The creation of the vessel, just put extra in there 965 00:42:27,690 --> 00:42:29,110 and then take that out. 966 00:42:29,110 --> 00:42:31,360 MICHAEL SHORT: That's what they did, right? 967 00:42:31,360 --> 00:42:33,850 So that's why these Charpy coupons were there, 968 00:42:33,850 --> 00:42:36,560 but what do we do about the vessels that we already have? 969 00:42:36,560 --> 00:42:37,060 Yeah? 970 00:42:37,060 --> 00:42:39,100 AUDIENCE: Can you make Charpy coupon or coupons 971 00:42:39,100 --> 00:42:43,630 that are similar to the status of the ones most recently taken 972 00:42:43,630 --> 00:42:46,540 out of the vessel, and then just put them in? 973 00:42:46,540 --> 00:42:48,320 MICHAEL SHORT: That's what they're doing. 974 00:42:48,320 --> 00:42:51,160 So they're taking these Charpy coupons, which this 975 00:42:51,160 --> 00:42:53,230 is bigger than actual size. 976 00:42:53,230 --> 00:42:57,070 They break them, so let's say this region's all garbage, 977 00:42:57,070 --> 00:43:00,712 and then they cut a little mini Charpy coupons out 978 00:43:00,712 --> 00:43:02,920 of the last piece, and they're putting those back in. 979 00:43:02,920 --> 00:43:04,180 So that's absolutely right. 980 00:43:04,180 --> 00:43:07,210 You've just probably recreated a year's worth of licensing work 981 00:43:07,210 --> 00:43:08,965 and ideas and in a class. 982 00:43:08,965 --> 00:43:10,840 But I just want to get back to Charlie's idea 983 00:43:10,840 --> 00:43:12,670 because that's what I think has to happen 984 00:43:12,670 --> 00:43:15,040 is you'd like to be able to take a piece out 985 00:43:15,040 --> 00:43:18,170 from the actual vessel and run a test on it. 986 00:43:18,170 --> 00:43:20,710 The only way to do that is to go nano. 987 00:43:20,710 --> 00:43:23,410 Take the tiniest, tiniest little piece out, 988 00:43:23,410 --> 00:43:26,720 and perform some other sort of measurement. 989 00:43:26,720 --> 00:43:28,850 So this is the idea that our group 990 00:43:28,850 --> 00:43:32,180 has had in using what's called stored energy of radiation 991 00:43:32,180 --> 00:43:35,580 damage, so I don't mind telling you about it, 992 00:43:35,580 --> 00:43:38,910 even though it's not like funded or papered yet 993 00:43:38,910 --> 00:43:42,940 because it's educational, and it's cool. 994 00:43:42,940 --> 00:43:46,750 So every kind of defect takes energy to create. 995 00:43:46,750 --> 00:43:48,670 Defects don't just create themselves. 996 00:43:48,670 --> 00:43:50,920 You either have to raise the temperature of a material 997 00:43:50,920 --> 00:43:52,720 or in our case, irradiate it. 998 00:43:52,720 --> 00:43:55,690 And it's the energy of those incoming neutrons that 999 00:43:55,690 --> 00:43:58,450 bounces around different atoms and creates 1000 00:43:58,450 --> 00:44:00,770 all these different types of defects. 1001 00:44:00,770 --> 00:44:03,668 So those defects are storing energy in the material. 1002 00:44:03,668 --> 00:44:05,710 And so if you think about how much energy does it 1003 00:44:05,710 --> 00:44:07,168 take to destroy something, it would 1004 00:44:07,168 --> 00:44:10,870 have to be the energy that it's already stored plus the energy 1005 00:44:10,870 --> 00:44:13,000 that you put into it during the test 1006 00:44:13,000 --> 00:44:15,220 can reach the failure energy. 1007 00:44:15,220 --> 00:44:17,410 What if you could measure the stored energy? 1008 00:44:17,410 --> 00:44:18,967 What if there was a way to know how 1009 00:44:18,967 --> 00:44:20,800 many of each of those defects there actually 1010 00:44:20,800 --> 00:44:22,570 were in a material? 1011 00:44:22,570 --> 00:44:23,710 We think there is. 1012 00:44:23,710 --> 00:44:24,880 Well, we know there is. 1013 00:44:24,880 --> 00:44:28,000 It's called differential scanning color imagery. 1014 00:44:28,000 --> 00:44:30,370 It's a way of measuring the change 1015 00:44:30,370 --> 00:44:33,970 in heat capacity of a material, where you take two 1016 00:44:33,970 --> 00:44:35,782 very small furnaces-- 1017 00:44:35,782 --> 00:44:37,990 you don't have to put this in your notes, by the way, 1018 00:44:37,990 --> 00:44:40,040 this is just for fun. 1019 00:44:40,040 --> 00:44:45,080 You take two small furnaces, put your chunk of your material 1020 00:44:45,080 --> 00:44:51,000 on one, and you apply a lot of heat to both of them. 1021 00:44:54,430 --> 00:44:58,030 And you look at the difference in the amount of heat 1022 00:44:58,030 --> 00:45:01,300 you have to put in to keep the two at the same temperature. 1023 00:45:01,300 --> 00:45:03,790 So normally, you would get the heat capacity 1024 00:45:03,790 --> 00:45:07,690 of a material, how much heat can extort per degree Kelvin. 1025 00:45:07,690 --> 00:45:11,560 If this material's got a bunch of defects already in it, 1026 00:45:11,560 --> 00:45:14,440 then you should release that defect energy by heating it 1027 00:45:14,440 --> 00:45:18,160 and that would take a little less energy to heat it up, 1028 00:45:18,160 --> 00:45:20,770 but there's a lot of problems with calorimetry, 1029 00:45:20,770 --> 00:45:23,740 so we're actually using what's called nanocalorimetry. 1030 00:45:23,740 --> 00:45:27,460 We're doing this process on nanograms of material 1031 00:45:27,460 --> 00:45:29,740 and seeing if you can irradiate something and measure 1032 00:45:29,740 --> 00:45:31,660 its stored energy because if you could, 1033 00:45:31,660 --> 00:45:33,910 you could take a tiny little razor blade, 1034 00:45:33,910 --> 00:45:36,820 take out the smallest sliver of the vessel-- 1035 00:45:36,820 --> 00:45:38,200 smaller than a grain of sand. 1036 00:45:38,200 --> 00:45:40,150 Not enough to cause a crack-- 1037 00:45:40,150 --> 00:45:42,165 enough to measure its stored energy. 1038 00:45:42,165 --> 00:45:44,540 And I want to show you guys what this process looks like. 1039 00:45:44,540 --> 00:45:47,080 So I'm just going to deviate from the actual lecture, 1040 00:45:47,080 --> 00:45:50,880 and jump into the topic I'll give tomorrow. 1041 00:45:50,880 --> 00:45:52,910 I think it's more interesting and more relevant. 1042 00:46:00,660 --> 00:46:01,310 There we go. 1043 00:46:04,705 --> 00:46:06,580 I'm going to skip through some of this stuff, 1044 00:46:06,580 --> 00:46:08,560 but it's within the last five minutes, 1045 00:46:08,560 --> 00:46:10,810 I'll try to get through this, see if this is a record. 1046 00:46:10,810 --> 00:46:12,780 It's what we call the ultimate snipe hunt. 1047 00:46:12,780 --> 00:46:15,260 Has anyone here been on a snipe hunt? 1048 00:46:15,260 --> 00:46:16,208 What's a snipe hunt? 1049 00:46:16,208 --> 00:46:18,500 AUDIENCE: People bringing you in the woods and tell you 1050 00:46:18,500 --> 00:46:20,750 you're looking for a bird that doesn't exist. 1051 00:46:20,750 --> 00:46:22,280 MICHAEL SHORT: That's right. 1052 00:46:22,280 --> 00:46:23,690 Pretty much this, right? 1053 00:46:23,690 --> 00:46:25,640 They say bang a bunch of sticks, get a bag, 1054 00:46:25,640 --> 00:46:26,630 and go look for snipes. 1055 00:46:26,630 --> 00:46:28,310 They don't exist, right? 1056 00:46:28,310 --> 00:46:30,540 They actually do. 1057 00:46:30,540 --> 00:46:31,785 Snipes are real. 1058 00:46:31,785 --> 00:46:33,865 You pretty much have to be British to know it, 1059 00:46:33,865 --> 00:46:35,490 because they hunt them there for sport, 1060 00:46:35,490 --> 00:46:37,290 and apparently, they're delicious. 1061 00:46:37,290 --> 00:46:39,920 That's actually where we get the term snipe 1062 00:46:39,920 --> 00:46:42,950 because the actual size of the sniper compared to the sniper 1063 00:46:42,950 --> 00:46:44,030 is about that. 1064 00:46:44,030 --> 00:46:45,830 If you can shoot that bird with a gun, 1065 00:46:45,830 --> 00:46:49,700 you are an expert marksman and deserve the delicious and tiny 1066 00:46:49,700 --> 00:46:52,480 treat that you've then blown apart with your bullet-- 1067 00:46:52,480 --> 00:46:54,080 AUDIENCE: [INAUDIBLE] 1068 00:46:54,080 --> 00:46:55,970 MICHAEL SHORT: Yeah, exactly. 1069 00:46:55,970 --> 00:46:59,120 So you can you know rain bird dust on whatever meal 1070 00:46:59,120 --> 00:47:00,770 you've already prepared. 1071 00:47:00,770 --> 00:47:03,290 That's what I like in finding these radiation damage 1072 00:47:03,290 --> 00:47:04,753 defects too. 1073 00:47:04,753 --> 00:47:06,170 Because some experiments have been 1074 00:47:06,170 --> 00:47:10,580 done to plot the number of defects versus their size. 1075 00:47:10,580 --> 00:47:13,670 And as the defects get bigger, the number of them decrease. 1076 00:47:13,670 --> 00:47:17,960 So most defects are very, very small, and it turns out that-- 1077 00:47:17,960 --> 00:47:21,168 first of all, the resolution of the screen is funny. 1078 00:47:21,168 --> 00:47:22,460 I think I know how to fix that. 1079 00:47:25,830 --> 00:47:28,490 Clone the screen and then jump back to presenter mode. 1080 00:47:28,490 --> 00:47:31,350 That usually-- that's not what I wanted. 1081 00:47:31,350 --> 00:47:33,810 That's what I wanted, great. 1082 00:47:33,810 --> 00:47:36,690 Most of the defects that cause these reductions in material 1083 00:47:36,690 --> 00:47:39,930 properties are too small to see, even in the transmission 1084 00:47:39,930 --> 00:47:42,070 electron microscope. 1085 00:47:42,070 --> 00:47:45,490 So I don't have to tell you this stuff again, that I don't like 1086 00:47:45,490 --> 00:47:47,590 the DPA, I showed you that. 1087 00:47:47,590 --> 00:47:49,540 What we want is that. 1088 00:47:49,540 --> 00:47:51,070 We took some inspiration directly 1089 00:47:51,070 --> 00:47:52,660 from the Manhattan Project. 1090 00:47:52,660 --> 00:47:55,570 Luckily, I have an uncle who works at the DuPont Library 1091 00:47:55,570 --> 00:47:59,740 and Dupont was quite responsible for the Manhattan Project. 1092 00:47:59,740 --> 00:48:02,200 So this memo between Eugene Wigner and Leo Szilard-- 1093 00:48:02,200 --> 00:48:04,210 one of whom won the Nobel Prize, the other one 1094 00:48:04,210 --> 00:48:05,710 probably should have-- 1095 00:48:05,710 --> 00:48:08,320 said, hey, radiation stores energy 1096 00:48:08,320 --> 00:48:12,160 by neutron collisions like cold working and amorphization. 1097 00:48:12,160 --> 00:48:15,160 So we've dug up this original memo from the 40s, and said, 1098 00:48:15,160 --> 00:48:18,370 let's do this for everything because every defect has 1099 00:48:18,370 --> 00:48:20,500 its unique amount of energy that it stores 1100 00:48:20,500 --> 00:48:22,570 and creating it in some different amount 1101 00:48:22,570 --> 00:48:27,120 of eV per defect, and we've done some molecular dynamics 1102 00:48:27,120 --> 00:48:29,670 simulations to show that this amount of energy stored 1103 00:48:29,670 --> 00:48:31,200 is pretty universal. 1104 00:48:31,200 --> 00:48:34,140 When you irradiate something, we predict that it stores about 2% 1105 00:48:34,140 --> 00:48:36,832 of its energy in radiation defense. 1106 00:48:36,832 --> 00:48:38,790 So if you know the number of neutrons that hit, 1107 00:48:38,790 --> 00:48:41,340 and you know that the amount of energy per neutron, 1108 00:48:41,340 --> 00:48:43,480 you know how much you're looking for. 1109 00:48:43,480 --> 00:48:46,900 You know what your signal should be. 1110 00:48:46,900 --> 00:48:50,650 And to jump through to the whole idea of differential scanning 1111 00:48:50,650 --> 00:48:52,450 calorimetry, it's like what I drew here, 1112 00:48:52,450 --> 00:48:54,190 but a lot more legible. 1113 00:48:54,190 --> 00:48:56,920 You simply heat two materials, one of which 1114 00:48:56,920 --> 00:48:59,800 contains your sample, measure their temperature, 1115 00:48:59,800 --> 00:49:02,830 and look how much energy it takes between them to keep them 1116 00:49:02,830 --> 00:49:04,870 at the same temperature. 1117 00:49:04,870 --> 00:49:06,505 We did some of these measurements 1118 00:49:06,505 --> 00:49:08,380 on a piece of steel from the nuclear reactor, 1119 00:49:08,380 --> 00:49:10,005 and we got a whole bunch of interesting 1120 00:49:10,005 --> 00:49:12,502 looking peaks for the red curve compared 1121 00:49:12,502 --> 00:49:14,710 to the blue curve in the other irradiated conditions, 1122 00:49:14,710 --> 00:49:16,990 so we think there's something there. 1123 00:49:16,990 --> 00:49:19,750 So we tried a more controlled experiment irradiating 1124 00:49:19,750 --> 00:49:22,300 aluminum with helium ions and the accelerator 1125 00:49:22,300 --> 00:49:24,420 in Northwest 13. 1126 00:49:24,420 --> 00:49:27,250 And we were encouraged because the initial time 1127 00:49:27,250 --> 00:49:30,070 that we heated this material, we got some stored energy 1128 00:49:30,070 --> 00:49:32,260 out of it in some funky spectrum that might tell us 1129 00:49:32,260 --> 00:49:33,910 what the defects are. 1130 00:49:33,910 --> 00:49:36,990 The bad news is we got that with the control heat too, 1131 00:49:36,990 --> 00:49:39,472 and the really bad news is that when you normalize 1132 00:49:39,472 --> 00:49:40,930 all these curves, you get something 1133 00:49:40,930 --> 00:49:44,520 that you can't tell if I drew it or my son drew it. 1134 00:49:44,520 --> 00:49:46,200 Looks suspiciously like the doodles 1135 00:49:46,200 --> 00:49:49,480 that he does, not scientific data. 1136 00:49:49,480 --> 00:49:52,190 And the problem is that DSC, differential scanning 1137 00:49:52,190 --> 00:49:55,190 calorimetry, induces a lot of artifacts in the signal 1138 00:49:55,190 --> 00:49:58,150 that we couldn't separate from the noise. 1139 00:49:58,150 --> 00:50:00,580 So our solution was to go nano. 1140 00:50:00,580 --> 00:50:03,580 To use a nano a DSC, or nano differential scanning 1141 00:50:03,580 --> 00:50:06,730 calorimeter, that can heat about 10,000 times 1142 00:50:06,730 --> 00:50:09,430 faster than a traditional DSC. 1143 00:50:09,430 --> 00:50:12,400 So you can get your energy out from smaller materials 1144 00:50:12,400 --> 00:50:15,970 way faster than these artifacts can manifest themselves. 1145 00:50:15,970 --> 00:50:17,883 What we think is going to happen is 1146 00:50:17,883 --> 00:50:19,300 that every one of these peaks here 1147 00:50:19,300 --> 00:50:23,290 is going to correspond to one type of defect that's released 1148 00:50:23,290 --> 00:50:25,090 at a certain temperature. 1149 00:50:25,090 --> 00:50:28,990 And by extrapolating, or say, integrating the area 1150 00:50:28,990 --> 00:50:32,410 under those curves, you get the energy in each type of defect. 1151 00:50:32,410 --> 00:50:35,530 And by extrapolating to a zero heating rate, 1152 00:50:35,530 --> 00:50:37,960 you should know which type of defect they are. 1153 00:50:37,960 --> 00:50:39,820 And if you know which defects you have 1154 00:50:39,820 --> 00:50:42,850 and how many of each one, you know the full defect 1155 00:50:42,850 --> 00:50:44,500 properties and material, you should 1156 00:50:44,500 --> 00:50:46,302 know it's material properties. 1157 00:50:46,302 --> 00:50:48,760 Because we already know if you have this many dislocations, 1158 00:50:48,760 --> 00:50:53,060 it's this brittle, the question is how many dislocations. 1159 00:50:53,060 --> 00:50:55,185 So we start off by-- 1160 00:50:55,185 --> 00:50:56,810 we use a different kind of calorimeter. 1161 00:50:56,810 --> 00:50:58,760 It actually fits on a chip. 1162 00:50:58,760 --> 00:51:00,500 In fact, there's two on a chip. 1163 00:51:00,500 --> 00:51:02,960 There's one that we put our material on, 1164 00:51:02,960 --> 00:51:05,750 and one as a reference that we both put 1165 00:51:05,750 --> 00:51:08,450 in the accelerator being irradiated at the same time 1166 00:51:08,450 --> 00:51:10,672 to control for that effect, and this is 1167 00:51:10,672 --> 00:51:11,880 what they actually look like. 1168 00:51:11,880 --> 00:51:14,370 The scale bar here is 100 microns, 1169 00:51:14,370 --> 00:51:16,880 and that transparent spot is a little bit of aluminum 1170 00:51:16,880 --> 00:51:21,140 that we vapor deposited onto the calorimeter. 1171 00:51:21,140 --> 00:51:22,880 Right there. 1172 00:51:22,880 --> 00:51:27,080 And so the way this process works, is we take our DSC chip, 1173 00:51:27,080 --> 00:51:30,470 we put a mask over it, vaporize some aluminum 1174 00:51:30,470 --> 00:51:33,020 to deposit on one of the calorimeters, 1175 00:51:33,020 --> 00:51:37,090 take the mask away, and irradiate the whole thing, 1176 00:51:37,090 --> 00:51:39,930 and then finally put it in the nanocalorimeter, 1177 00:51:39,930 --> 00:51:41,680 and I'll show you what happens slowed down 1178 00:51:41,680 --> 00:51:43,240 by a factor of 1,000. 1179 00:51:43,240 --> 00:51:44,500 That pulse right there. 1180 00:51:44,500 --> 00:51:48,832 That whole thing just went from zero to 450c a millisecond. 1181 00:51:48,832 --> 00:51:50,790 And the reason it took a second is because I've 1182 00:51:50,790 --> 00:51:54,180 slowed down the video by 4,000 or by 5,000 times, 1183 00:51:54,180 --> 00:51:56,790 and that little pulse of heat actually 1184 00:51:56,790 --> 00:51:59,550 released some of the defect energy. 1185 00:51:59,550 --> 00:52:02,460 We were able to see very clearly, the first time we 1186 00:52:02,460 --> 00:52:04,740 heated the sample, this extra area 1187 00:52:04,740 --> 00:52:08,400 corresponds to some sort of energy release. 1188 00:52:08,400 --> 00:52:11,605 We then heated that same sample a whole bunch of times, 1189 00:52:11,605 --> 00:52:13,980 and made sure that it was always the same, which meant we 1190 00:52:13,980 --> 00:52:16,940 had a fully relaxed material. 1191 00:52:16,940 --> 00:52:18,493 And it shows some sort of a trend. 1192 00:52:18,493 --> 00:52:20,660 If you note this data was taken like two months ago, 1193 00:52:20,660 --> 00:52:21,830 it's pretty fresh. 1194 00:52:21,830 --> 00:52:24,050 Not published yet, so hopefully by the time 1195 00:52:24,050 --> 00:52:26,250 this video comes out, it will be. 1196 00:52:26,250 --> 00:52:28,250 And we see some sort of trend between the amount 1197 00:52:28,250 --> 00:52:30,542 of irradiation it gives and the amount of stored energy 1198 00:52:30,542 --> 00:52:31,560 you can get out of it. 1199 00:52:31,560 --> 00:52:34,620 So this is what we hope can be used instead of those Charpy 1200 00:52:34,620 --> 00:52:35,730 coupons. 1201 00:52:35,730 --> 00:52:37,710 We can go much, much smaller and just take out 1202 00:52:37,710 --> 00:52:40,890 tiny pieces of the vessel and get the same information 1203 00:52:40,890 --> 00:52:44,790 as you would from a Charpy test but on the nanoscale. 1204 00:52:44,790 --> 00:52:47,680 So the question then is, where is the defect fingerprints? 1205 00:52:47,680 --> 00:52:49,360 Where are those individual defects 1206 00:52:49,360 --> 00:52:51,260 that we were looking for? 1207 00:52:51,260 --> 00:52:55,520 Well, I think they're just popping up right here. 1208 00:52:55,520 --> 00:52:59,080 The reason for that is we picked a very fast heating rate 1209 00:52:59,080 --> 00:53:01,870 for our experiments, and doing these sorts of measurements 1210 00:53:01,870 --> 00:53:05,738 on other materials shows that at 10,000 Kelvin per second-- 1211 00:53:05,738 --> 00:53:07,030 think about that for a second-- 1212 00:53:07,030 --> 00:53:09,570 10,000 Kelvin per second. 1213 00:53:09,570 --> 00:53:11,730 So in a millisecond, something heats up 1214 00:53:11,730 --> 00:53:17,210 by 10 K, which is ridiculous. 1215 00:53:17,210 --> 00:53:18,440 Yeah, something like that. 1216 00:53:18,440 --> 00:53:21,310 You don't really see any peaks. 1217 00:53:21,310 --> 00:53:24,410 The heating is so fast that the defects don't even 1218 00:53:24,410 --> 00:53:27,350 have time to find each other, annihilate, and release 1219 00:53:27,350 --> 00:53:28,670 their stored energy. 1220 00:53:28,670 --> 00:53:30,800 So we need to repeat the experiments at some lower 1221 00:53:30,800 --> 00:53:33,630 temperatures, see what the peaks are, 1222 00:53:33,630 --> 00:53:36,920 but if you go too low, you end up getting a lot of noise 1223 00:53:36,920 --> 00:53:37,803 in your signal. 1224 00:53:37,803 --> 00:53:40,220 So there's going to be some sweet spot that we haven't yet 1225 00:53:40,220 --> 00:53:43,520 found in order to see this stored energy. 1226 00:53:43,520 --> 00:53:46,880 So we're just at the very first experimental stage 1227 00:53:46,880 --> 00:53:49,820 of trying to see can we extend reactor lifetimes. 1228 00:53:49,820 --> 00:53:51,375 After doing simulations for a year 1229 00:53:51,375 --> 00:53:53,000 that probably no one believes until you 1230 00:53:53,000 --> 00:53:56,270 do an experiment, including me. 1231 00:53:56,270 --> 00:53:58,950 But for now, it actually shows some sort of a trend, 1232 00:53:58,950 --> 00:54:01,370 so it's just enough justification for us 1233 00:54:01,370 --> 00:54:02,870 to buy one of these nanocalorimeters 1234 00:54:02,870 --> 00:54:05,158 and start looking for real. 1235 00:54:05,158 --> 00:54:07,700 So if you want to see, now I've taken you from basic material 1236 00:54:07,700 --> 00:54:09,890 science, to where's the field going to, 1237 00:54:09,890 --> 00:54:13,457 how do we keep our reactors running in about two hours. 1238 00:54:13,457 --> 00:54:15,290 I think that's the most compact introduction 1239 00:54:15,290 --> 00:54:19,110 to nuclear materials I can possibly give you. 1240 00:54:19,110 --> 00:54:21,170 So any questions on what you've seen today? 1241 00:54:21,170 --> 00:54:23,580 AUDIENCE: Is that roughly the trend you would expect? 1242 00:54:23,580 --> 00:54:25,530 MICHAEL SHORT: Yes, I would expect an up. 1243 00:54:25,530 --> 00:54:27,060 That's the best I can say. 1244 00:54:27,060 --> 00:54:28,990 As far as is it actually a line? 1245 00:54:28,990 --> 00:54:30,330 Is it a curve? 1246 00:54:30,330 --> 00:54:34,537 I am not as brave or stupid as some of the other folks that 1247 00:54:34,537 --> 00:54:36,870 will draw an arbitrary shaped line through a single data 1248 00:54:36,870 --> 00:54:37,950 point. 1249 00:54:37,950 --> 00:54:41,127 So I'm not drawing a trend line yet. 1250 00:54:41,127 --> 00:54:42,210 Yeah, any other questions? 1251 00:54:42,210 --> 00:54:43,190 Yeah? 1252 00:54:43,190 --> 00:54:45,630 AUDIENCE: Is it-- or I guess you're making the assumption 1253 00:54:45,630 --> 00:54:48,620 that one little spot in the reactive pressure vessel 1254 00:54:48,620 --> 00:54:53,140 to say what the rest of the vessel has been exposed to? 1255 00:54:53,140 --> 00:54:54,390 MICHAEL SHORT: Oh, not at all. 1256 00:54:54,390 --> 00:54:55,980 Take a whole bunch. 1257 00:54:55,980 --> 00:54:58,980 Then, instead of just doing Charpy coupons 1258 00:54:58,980 --> 00:55:02,610 of one place, which is what we do now, you can get a map. 1259 00:55:02,610 --> 00:55:04,230 We don't have that information now, 1260 00:55:04,230 --> 00:55:06,230 but if you take pieces from all over the vessel, 1261 00:55:06,230 --> 00:55:09,840 then you get an actual 3D map instead of a single point 1262 00:55:09,840 --> 00:55:11,340 of saying all right, well, we picked 1263 00:55:11,340 --> 00:55:13,750 what we think is going to be the worst condition. 1264 00:55:13,750 --> 00:55:14,910 How do you know? 1265 00:55:14,910 --> 00:55:16,550 You don't. 1266 00:55:16,550 --> 00:55:17,890 How do you know for sure? 1267 00:55:17,890 --> 00:55:19,265 You make measurements like these. 1268 00:55:22,430 --> 00:55:24,420 Any other questions? 1269 00:55:24,420 --> 00:55:24,920 Yeah? 1270 00:55:24,920 --> 00:55:27,260 AUDIENCE: What would a peak in this graph 1271 00:55:27,260 --> 00:55:31,100 correspond to in terms of like-- 1272 00:55:31,100 --> 00:55:34,640 How does it relate to some sort of damage effect? 1273 00:55:34,640 --> 00:55:36,640 MICHAEL SHORT: We would expect that a peak would 1274 00:55:36,640 --> 00:55:40,090 relate to a certain type of defect reaction occurring. 1275 00:55:40,090 --> 00:55:43,060 When some type of defect gets high enough in temperature 1276 00:55:43,060 --> 00:55:47,170 that it goes from stuck to mobile, and as that moves, 1277 00:55:47,170 --> 00:55:49,750 it encounters anything else it will in the material, 1278 00:55:49,750 --> 00:55:52,540 and will react with all the other defects nearby, 1279 00:55:52,540 --> 00:55:54,640 decimating the population of that defect 1280 00:55:54,640 --> 00:55:56,890 and slightly depressing that of the others. 1281 00:55:56,890 --> 00:55:58,890 And as you go higher, and higher in temperature, 1282 00:55:58,890 --> 00:56:00,910 the slower and slower defects start to move. 1283 00:56:03,600 --> 00:56:04,100 Yeah? 1284 00:56:04,100 --> 00:56:05,892 AUDIENCE: So you can get rid of the defects 1285 00:56:05,892 --> 00:56:07,545 by heating it quickly? 1286 00:56:07,545 --> 00:56:08,420 MICHAEL SHORT: Mm-hmm 1287 00:56:08,420 --> 00:56:12,380 AUDIENCE: Would there be a way to self repair our radiation 1288 00:56:12,380 --> 00:56:14,298 damage to pressure vessels themselves? 1289 00:56:14,298 --> 00:56:15,840 MICHAEL SHORT: That would be awesome. 1290 00:56:15,840 --> 00:56:19,310 But the properties of the vessel are highly dependent on, 1291 00:56:19,310 --> 00:56:22,490 not just its composition, but the heat treatment 1292 00:56:22,490 --> 00:56:23,840 that went to make it. 1293 00:56:23,840 --> 00:56:25,310 If you heat that vessel, you both 1294 00:56:25,310 --> 00:56:28,820 remove the radiation damage and remove the strengthening put 1295 00:56:28,820 --> 00:56:32,020 in by the forging and heating process. 1296 00:56:32,020 --> 00:56:34,300 So you would have, if-- again, if you 1297 00:56:34,300 --> 00:56:39,010 let's say, replace the vessel you have a new reactor. 1298 00:56:39,010 --> 00:56:41,590 If you heat the vessel too much, it's 1299 00:56:41,590 --> 00:56:45,590 no longer a code stamp vessel. 1300 00:56:45,590 --> 00:56:48,110 Pretty tricky spot that we're in, huh? 1301 00:56:48,110 --> 00:56:51,103 But we're trying to science our way out of it. 1302 00:56:51,103 --> 00:56:52,520 Well, it's a couple minutes after. 1303 00:56:52,520 --> 00:56:58,300 I don't want to keep you longer, but I'll open on Thursday 1304 00:56:58,300 --> 00:57:01,270 with a little story about how mass attenuation 1305 00:57:01,270 --> 00:57:04,880 coefficients can get you out of apartheid South Africa. 1306 00:57:04,880 --> 00:57:06,080 I'm serious. 1307 00:57:06,080 --> 00:57:10,000 And then we'll move into dose and biological effects.