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MICHAEL SHORT: All right.

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So like I told you guys, Friday
marked the end of the hardest

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00:00:26,270 --> 00:00:27,080
part of the course.

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And Monday marked the
end of the hardest Pset.

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00:00:30,020 --> 00:00:31,700
So because the rest
of your classes

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are going full
throttle, this one's

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going to wind down a little bit.

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So today, I'd say,
sit back, relax,

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00:00:37,080 --> 00:00:39,680
and enjoy a nuclear
catastrophe because we

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00:00:39,680 --> 00:00:43,340
are going to explain what
happened at Chernobyl now

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00:00:43,340 --> 00:00:47,030
that you've got the physics
and intuitive background

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to understand the actual
sequence of events.

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To kick it off, I
want to show you guys

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some actual footage of
the Chernobyl reactor

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00:00:56,120 --> 00:00:57,230
as it was burning.

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So this is the part that
most folks know about.

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[VIDEO PLAYBACK]

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00:01:01,534 --> 00:01:03,438
- [NON-ENGLISH SPEECH]

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MICHAEL SHORT: This is footage
taken from a helicopter

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00:01:10,930 --> 00:01:13,897
from folks that were either
surveying or dropping materials

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00:01:13,897 --> 00:01:14,605
onto the reactor.

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- [NON-ENGLISH SPEECH]

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MICHAEL SHORT: That was
probably a bad idea.

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"Hold where the smoke is."

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00:01:30,990 --> 00:01:33,165
We'll get into
what the smoke was.

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- [NON-ENGLISH SPEECH]

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00:01:49,976 --> 00:01:51,880
[END PLAYBACK]

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00:01:51,880 --> 00:01:53,860
MICHAEL SHORT: So that
red stuff right there,

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00:01:53,860 --> 00:01:57,640
that's actually glowing
graphite amongst other materials

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00:01:57,640 --> 00:02:01,510
from the graphite fire that
resulted from the RBMK reactor

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00:02:01,510 --> 00:02:06,250
burning after the Chernobyl
accident, caused by both flaws

39
00:02:06,250 --> 00:02:08,970
in the physical design
of the RBMK reactor

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00:02:08,970 --> 00:02:12,190
and absolute operator
of stupidity and neglect

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00:02:12,190 --> 00:02:15,010
of any sort of safety
systems or safety culture.

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00:02:15,010 --> 00:02:16,480
We're lucky to
live here in the US

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where our worst accident
at Three Mile Island

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was not actually really
that much of an accident.

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00:02:21,070 --> 00:02:22,870
There was a partial meltdown.

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00:02:22,870 --> 00:02:25,810
There was not that much of
a release of radio nuclides

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00:02:25,810 --> 00:02:27,760
into the atmosphere
because we do

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00:02:27,760 --> 00:02:30,910
things like build
containments on our reactors.

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00:02:30,910 --> 00:02:33,265
If you think of what a
typical reactor looks like,

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00:02:33,265 --> 00:02:36,580
like if you consider the
MIT reactor as a scaled-down

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00:02:36,580 --> 00:02:39,913
version of a normal reactor--

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let's say you have a
commercial power reactor.

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You've got the core here.

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You've got a bunch of
shielding around it.

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And you've got a dome
that's rather thick

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that comprises the containment.

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That would be the core.

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This would be some shielding.

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00:03:03,560 --> 00:03:07,670
So this is what you find in
US and most other reactors.

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For the RBMK reactors,
there was no containment

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because it was thought
that nothing could happen.

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And boy, were they wrong.

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So I want to walk you guys
through a chronology of what

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actually happened at that
the Chernobyl reactor, which

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you guys can read on the NEA, or
Nuclear Energy Agency, website,

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the same place that
you find JANIS.

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And we're going to refer to a
lot of the JANIS cross sections

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to explain why these
sorts of events happened.

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So the whole point of
what happened at Chernobyl

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was it was desire
to see if you could

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use the spinning down
turbine after you shut

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down the reactor to
power the emergency

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systems at the reactor.

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This would be
following something,

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what's called a loss
of off-site power.

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If the off-site
power or the grid

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was disconnected
from the reactor,

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the reactor
automatically shuts down.

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But the turbine, like I
showed you a couple weeks ago,

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is this enormous spinning
hulk of metal and machinery

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00:04:05,730 --> 00:04:09,370
that coasts down over a long
period of, let's say, hours.

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And as it's spinning,
the generator coils

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are still spinning and
still producing electricity,

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or they could be.

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So it was desire
to find out, can we

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use the spinning down turbine
to power the emergency equipment

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00:04:21,779 --> 00:04:23,580
if we lose off-site power?

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00:04:23,580 --> 00:04:25,650
So they had to
simulate this event.

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00:04:25,650 --> 00:04:27,810
So what they actually
decided to do

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is coast down the reactor
to a moderate power level

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or very low power and
see what comes out

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00:04:33,840 --> 00:04:37,910
of the turbine itself, or
out of the generator rather.

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00:04:37,910 --> 00:04:41,787
Now, there were a lot of
flaws in the RBMK design.

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And I'd like to bring
it up here so we

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can talk about
what it looks like

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00:04:45,770 --> 00:04:47,480
and what was wrong with it.

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00:04:47,480 --> 00:04:51,560
So the RBMK is unlike any
of the United States light

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water reactors that you
may have seen before.

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00:04:53,830 --> 00:04:55,340
Many of the components
are the same.

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There's still a light
water reactor coolant

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loop where water flows
around fuel rods,

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00:05:01,610 --> 00:05:03,530
goes into a steam
separator, better known

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00:05:03,530 --> 00:05:05,190
as a big heat exchanger.

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00:05:05,190 --> 00:05:09,500
And the steam drives a
turbine, which produces energy.

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00:05:09,500 --> 00:05:11,490
And then this coolant
pump keeps it going.

106
00:05:11,490 --> 00:05:13,400
And then the water circulates.

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00:05:13,400 --> 00:05:16,610
What makes it different, though,
is that each of these fuel rods

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was inside its
own pressure tube.

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So the coolant was pressurized.

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00:05:22,040 --> 00:05:24,410
And out here, this
stuff right here

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was the moderator
composed of graphite.

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00:05:27,700 --> 00:05:29,800
Unlike light water
reactors in the US,

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the coolant was not the only
moderator in the reactor.

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00:05:33,070 --> 00:05:34,960
Graphite also
existed, which meant

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that, if the water went away,
which would normally shut down

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a light water reactor
from lack of moderation,

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00:05:41,710 --> 00:05:44,890
graphite was still there
to slow the neutrons down

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00:05:44,890 --> 00:05:48,330
into the high-fission
cross-section area.

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00:05:48,330 --> 00:05:51,790
And I'd like to pull
up JANIS and show you

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00:05:51,790 --> 00:05:55,770
what I mean with the
uranium cross section.

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So let's go again to uranium-235
and pull up its fission cross

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00:06:00,280 --> 00:06:01,870
section.

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Let's see fission.

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I can make it a
little thicker too.

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So again, the goal
of the moderator

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is to take neutrons from high
energies like 1 to 10 MeV

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where the fission cross
section is relatively low

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and slow them down into this
region where fission is,

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00:06:23,810 --> 00:06:26,840
let's say, 1,000
times more likely.

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And in a light water
reactor in the US,

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00:06:29,030 --> 00:06:32,120
if the coolant goes away,
so does the moderation.

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And there's nothing left
to slow those neutrons down

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to make fission more likely.

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In the RBMK, that's
not the case.

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The graphite is still there.

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The graphite is cooled by
a helium-nitrogen mixture

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because the neutron interactions
in the graphite that's slowing

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down--

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00:06:48,688 --> 00:06:51,230
we've always talked about what
happens from the point of view

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00:06:51,230 --> 00:06:52,370
of the neutron.

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00:06:52,370 --> 00:06:54,950
But what about the point of
view of the other material?

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Any energy lost by
the neutrons is gained

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by the moderating material.

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00:06:59,510 --> 00:07:02,270
So the graphite gets really hot.

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00:07:02,270 --> 00:07:05,360
And you have to flow some
non-oxygen-containing gas

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00:07:05,360 --> 00:07:07,370
mixture like helium
and nitrogen, which

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00:07:07,370 --> 00:07:10,730
is pretty inert, to
keep that graphite cool.

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00:07:10,730 --> 00:07:13,460
And then in between
the graphite moderator

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were control rods, about 200
of them or so, 30 of which

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were required to be down in
the reactor at any given time

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in order to control power.

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And that was a design rule.

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That was broken during
the actual experiment.

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And then on top of here, on
top of this biological shield,

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00:07:29,840 --> 00:07:31,550
you could walk on top of it.

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00:07:31,550 --> 00:07:33,350
So the tops of those
pressure tubes,

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despite being about 350
kilo chunks of concrete,

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you could walk on top of them.

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That's pretty cool,
kind of scary too.

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So what happened in
chronological order was,

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around midnight, the decision
was made to undergo this test

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and start spinning
down the turbine.

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But the grid operator came back
and said, no, you can't just

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cut the reactor
power to nothing.

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You have to maintain at a
rather high power for a while,

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00:08:02,010 --> 00:08:05,430
about 500 megawatts electric
or half the rated power

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00:08:05,430 --> 00:08:06,690
of the reactor.

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00:08:06,690 --> 00:08:08,640
And what that had
the effect of doing

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00:08:08,640 --> 00:08:13,980
is continuing to create fission
products, including xenon-135.

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00:08:13,980 --> 00:08:16,620
We haven't mentioned
this one yet.

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00:08:16,620 --> 00:08:22,440
You'll talk about it quite a
lot in 22.05 in neutron physics.

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00:08:22,440 --> 00:08:25,800
Black shirt really
shows chalk well.

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What xenon-135 does
is it just sits there.

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It's a noble gas.

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00:08:29,540 --> 00:08:31,070
It has a half-life
of a few days.

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00:08:31,070 --> 00:08:36,380
So it decays on the slow side
for as fission products go.

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00:08:36,380 --> 00:08:41,220
But it also absorbs lots and
lots and lots of neutrons.

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00:08:41,220 --> 00:08:43,950
Let's see if I could find
which one is the xenon one.

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00:08:43,950 --> 00:08:45,100
There we go.

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00:08:45,100 --> 00:08:48,120
So here, I've plotted
the total cross-section

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00:08:48,120 --> 00:08:52,500
for xenon-135 and the
absorption cross-section.

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00:08:52,500 --> 00:08:54,690
And notice how,
for low energies,

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00:08:54,690 --> 00:08:56,580
pretty much the entire
cross section of xenon

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00:08:56,580 --> 00:08:58,042
is made up of absorption.

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00:08:58,042 --> 00:09:00,000
Did you guys in your
homework see anything that

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00:09:00,000 --> 00:09:03,030
reached about 10 million barns?

187
00:09:03,030 --> 00:09:03,970
No.

188
00:09:03,970 --> 00:09:06,850
Xenon-135 is one of the best
neutron absorbers there is.

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00:09:06,850 --> 00:09:09,130
And reactors produce
it constantly.

190
00:09:09,130 --> 00:09:12,820
So as they're operating,
you build up xenon-135

191
00:09:12,820 --> 00:09:16,270
that you have to account for
in your sigma absorption cross

192
00:09:16,270 --> 00:09:17,910
section.

193
00:09:17,910 --> 00:09:20,440
Because like you guys
saw in the homework,

194
00:09:20,440 --> 00:09:22,690
if you want to write what's
the sigma absorption cross

195
00:09:22,690 --> 00:09:26,460
section of the
reactor, it's the sum

196
00:09:26,460 --> 00:09:29,910
of every single isotope in
the reactor of its number

197
00:09:29,910 --> 00:09:34,740
density times its
absorption cross section.

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00:09:34,740 --> 00:09:39,430
And so that would include
everything for water

199
00:09:39,430 --> 00:09:42,570
and let's say the
uranium and the xenon

200
00:09:42,570 --> 00:09:44,130
that you're building up.

201
00:09:44,130 --> 00:09:47,010
When the reactor starts up,
the number density of xenon

202
00:09:47,010 --> 00:09:50,730
is 0 because you don't have
anything to have produced it.

203
00:09:50,730 --> 00:09:53,850
When you start operating, you'll
reach the xenon equilibrium

204
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level where it will build
to a certain level that

205
00:09:57,210 --> 00:10:00,960
will counteract the
reactivity of the reactor.

206
00:10:00,960 --> 00:10:03,210
And then your
k-effective expression,

207
00:10:03,210 --> 00:10:11,170
where it sources over
absorption plus leakage,

208
00:10:11,170 --> 00:10:14,830
this has the effect of
raising sigma absorption

209
00:10:14,830 --> 00:10:17,440
and lowering k effective.

210
00:10:17,440 --> 00:10:19,510
The trick is it doesn't
last for very long.

211
00:10:19,510 --> 00:10:22,670
It built decays with a
half-life of about five days.

212
00:10:22,670 --> 00:10:24,580
And when you try and
raise the reactor power,

213
00:10:24,580 --> 00:10:26,900
you will also start
to burn it out.

214
00:10:26,900 --> 00:10:29,350
So if you're operating at
a fairly low power level,

215
00:10:29,350 --> 00:10:32,325
you'll both be decaying
and burning xenon

216
00:10:32,325 --> 00:10:33,950
without really knowing
what's going on.

217
00:10:33,950 --> 00:10:36,050
And that's exactly
what happened here.

218
00:10:36,050 --> 00:10:37,775
So an hour or so later--

219
00:10:37,775 --> 00:10:40,515
let me pull up the
chronology again.

220
00:10:40,515 --> 00:10:41,890
A little more than
an hour later,

221
00:10:41,890 --> 00:10:45,970
so the reactor power stabilized
at something like 30 megawatts.

222
00:10:45,970 --> 00:10:47,810
And they were like,
what is going on?

223
00:10:47,810 --> 00:10:49,420
Why is that reactor
power so low?

224
00:10:49,420 --> 00:10:51,250
We need to increase
the reactor power.

225
00:10:51,250 --> 00:10:52,430
So what did they do?

226
00:10:52,430 --> 00:10:53,690
A couple of things.

227
00:10:53,690 --> 00:10:57,460
One was remove all but six
or seven of the control rods

228
00:10:57,460 --> 00:11:01,570
going way outside the
spec of the design

229
00:11:01,570 --> 00:11:03,520
because 30 were needed
to actually maintain

230
00:11:03,520 --> 00:11:05,350
the reactor at a stable power.

231
00:11:05,350 --> 00:11:08,710
All the while, the xenon
that had been building up

232
00:11:08,710 --> 00:11:11,500
is still there keeping the
reactor from going critical.

233
00:11:11,500 --> 00:11:14,410
It's what was the main reason
that the reactor didn't even

234
00:11:14,410 --> 00:11:16,150
have very much power.

235
00:11:16,150 --> 00:11:18,860
But it was also burning
out at the same time.

236
00:11:18,860 --> 00:11:20,780
So all the while--

237
00:11:20,780 --> 00:11:25,930
let's say if we were to show
a graph of two things, time,

238
00:11:25,930 --> 00:11:30,700
xenon inventory,
and as a solid line

239
00:11:30,700 --> 00:11:37,430
and let's say control rod
worth as a dotted line.

240
00:11:37,430 --> 00:11:39,750
The xenon inventory
at full power

241
00:11:39,750 --> 00:11:41,490
would have been at some level.

242
00:11:41,490 --> 00:11:45,020
And then it would start
to decay and burn out.

243
00:11:45,020 --> 00:11:46,560
While at the same
time, the control

244
00:11:46,560 --> 00:11:51,362
rod worth, as you remove
control rods from the reactor--

245
00:11:51,362 --> 00:11:53,820
every time you remove one, you
lose some control rod worth,

246
00:11:53,820 --> 00:11:58,560
would continue to diminish
leading to the point where

247
00:11:58,560 --> 00:12:02,010
bad stuff is going to happen.

248
00:12:02,010 --> 00:12:04,680
Let me make sure I
didn't lose my place.

249
00:12:04,680 --> 00:12:08,040
So at any rate, as they started
pulling the control rods out,

250
00:12:08,040 --> 00:12:10,800
a couple of interesting quirks
happened in terms of feedback.

251
00:12:10,800 --> 00:12:12,990
So let's look back
at this design.

252
00:12:12,990 --> 00:12:15,960
Like any reactor,
this reactor had

253
00:12:15,960 --> 00:12:18,990
what's called a negative
fuel temperature coefficient.

254
00:12:18,990 --> 00:12:22,530
What that means is that,
when you heat up the fuel,

255
00:12:22,530 --> 00:12:23,940
two things happen.

256
00:12:23,940 --> 00:12:26,640
One, the cross section
for anything, absorption

257
00:12:26,640 --> 00:12:28,290
or fission, would go up.

258
00:12:28,290 --> 00:12:30,990
But the number density
would also go down.

259
00:12:30,990 --> 00:12:34,170
As the atoms physically
spaced out in the fuel,

260
00:12:34,170 --> 00:12:35,730
their number density
would go down,

261
00:12:35,730 --> 00:12:39,000
lowering the macroscopic
cross section for fission.

262
00:12:39,000 --> 00:12:41,250
And that's arguably
a good thing.

263
00:12:41,250 --> 00:12:45,120
The problem is, at
below about 20% power,

264
00:12:45,120 --> 00:12:48,210
of the reactor had what's called
a positive void coefficient,

265
00:12:48,210 --> 00:12:50,850
which meant that, if
you boil the coolant,

266
00:12:50,850 --> 00:12:53,380
you increase the reactor power.

267
00:12:53,380 --> 00:12:54,630
Because the other thing that--

268
00:12:54,630 --> 00:12:56,560
I think I mentioned this once.

269
00:12:56,560 --> 00:13:01,175
And you calculated in the
homework the absorption cross

270
00:13:01,175 --> 00:13:05,420
section of hydrogen is not 0.

271
00:13:05,420 --> 00:13:08,120
It's small, but
fairly significant.

272
00:13:08,120 --> 00:13:09,740
Let's actually
take a look at it.

273
00:13:09,740 --> 00:13:12,850
We can always see this in JANIS.

274
00:13:12,850 --> 00:13:18,280
Go back down to
hydrogen, hydrogen-1.

275
00:13:18,280 --> 00:13:21,230
Then we look at the
absorption cross section.

276
00:13:24,520 --> 00:13:26,770
And of course, it started
us with the linear scale.

277
00:13:26,770 --> 00:13:28,140
Let's go logarithmic.

278
00:13:28,140 --> 00:13:28,780
Oh!

279
00:13:28,780 --> 00:13:30,040
OK!

280
00:13:30,040 --> 00:13:33,640
So at low energy, at 10 to the
minus 8 to 10 to the minus 7,

281
00:13:33,640 --> 00:13:35,950
it's around a barn.

282
00:13:35,950 --> 00:13:39,143
Not super high, but
absolutely not negligible,

283
00:13:39,143 --> 00:13:41,185
which meant that part of
the normal functionality

284
00:13:41,185 --> 00:13:46,865
of the RBMK depended on the
absorption of the water to help

285
00:13:46,865 --> 00:13:48,115
absorb some of those neutrons.

286
00:13:51,550 --> 00:13:54,250
With that water gone,
there was less absorption.

287
00:13:54,250 --> 00:13:57,790
But there was still a ton of
moderation in this graphite

288
00:13:57,790 --> 00:13:58,712
moderator.

289
00:13:58,712 --> 00:13:59,920
So they still could get slow.

290
00:13:59,920 --> 00:14:01,295
But then there'd
be more of them.

291
00:14:01,295 --> 00:14:03,400
And that would cause
the power to increase.

292
00:14:03,400 --> 00:14:05,680
And then that caused
more of the coolant

293
00:14:05,680 --> 00:14:09,130
to boil, which would cause
less absorption, which would

294
00:14:09,130 --> 00:14:10,387
cause the power to increase.

295
00:14:10,387 --> 00:14:10,970
Yeah, Charlie?

296
00:14:10,970 --> 00:14:14,447
AUDIENCE: So did they remove
the water from the reactor?

297
00:14:14,447 --> 00:14:16,280
MICHAEL SHORT: They did
not remove the water

298
00:14:16,280 --> 00:14:16,988
from the reactor.

299
00:14:16,988 --> 00:14:20,270
However, as the power started
to rise, some of the water

300
00:14:20,270 --> 00:14:22,360
started to boil.

301
00:14:22,360 --> 00:14:25,750
And so you can still have,
let's say, steam flowing through

302
00:14:25,750 --> 00:14:27,190
and still remove
some of the heat.

303
00:14:27,190 --> 00:14:29,920
However, you don't have
that dense or water

304
00:14:29,920 --> 00:14:31,710
to act as an absorber.

305
00:14:31,710 --> 00:14:33,460
And that's what really
undid this reactor.

306
00:14:33,460 --> 00:14:35,950
In addition, they
decided to disable

307
00:14:35,950 --> 00:14:39,330
the ECCS, or the Emergency
Core Cooling System,

308
00:14:39,330 --> 00:14:41,130
which you're just
not supposed to do.

309
00:14:41,130 --> 00:14:42,880
So they shut down a
bunch of these systems

310
00:14:42,880 --> 00:14:44,547
to see if you could
power the other ones

311
00:14:44,547 --> 00:14:46,120
from the spinning down turbine.

312
00:14:46,120 --> 00:14:48,753
And then, as they noticed
that the reactor was

313
00:14:48,753 --> 00:14:50,170
getting less and
less stable, they

314
00:14:50,170 --> 00:14:52,840
had almost all the rods out.

315
00:14:52,840 --> 00:14:57,400
Some of these pressure tubes
started to bump and jump.

316
00:14:57,400 --> 00:15:02,380
These 350-kilogram pressure
tube caps were just rattling.

317
00:15:02,380 --> 00:15:04,780
I mean, imagine
something that weighs 900

318
00:15:04,780 --> 00:15:07,000
pounds or so rattling around.

319
00:15:07,000 --> 00:15:09,225
And there's a few
hundred of them.

320
00:15:09,225 --> 00:15:11,350
So there was someone in
the control room that said,

321
00:15:11,350 --> 00:15:12,640
the caps are rattling.

322
00:15:12,640 --> 00:15:14,166
What the heck?

323
00:15:14,166 --> 00:15:16,840
And didn't quite make it
down the spiral staircase

324
00:15:16,840 --> 00:15:21,560
because, about 10 seconds
later, everything went wrong.

325
00:15:21,560 --> 00:15:23,490
And so I want to pull
up this actual timeline

326
00:15:23,490 --> 00:15:27,330
so you can see it splits
from minutes to seconds.

327
00:15:27,330 --> 00:15:30,840
Because the speed at which
this stuff started to go wrong

328
00:15:30,840 --> 00:15:33,230
was pretty striking.

329
00:15:33,230 --> 00:15:38,600
So for example, the control rods
raised at 1:19 in the morning.

330
00:15:38,600 --> 00:15:41,750
Two minutes later, when
the power starts to become

331
00:15:41,750 --> 00:15:44,240
unstable, the caps on the
fuel channels-- which, again,

332
00:15:44,240 --> 00:15:46,730
are like 350-kilogram blocks--

333
00:15:46,730 --> 00:15:48,940
start jumping in their sockets.

334
00:15:48,940 --> 00:15:50,450
And a lot of that was--

335
00:15:50,450 --> 00:15:53,330
we go back to the RBMK reactor.

336
00:15:53,330 --> 00:15:56,030
As the coolant started
to boil here, well,

337
00:15:56,030 --> 00:15:58,580
that boiling force actually
creates huge pressure

338
00:15:58,580 --> 00:16:00,740
instabilities, which
would cause the pressure

339
00:16:00,740 --> 00:16:03,530
tubes to jump up and
down, eventually rupturing

340
00:16:03,530 --> 00:16:06,950
almost every single one of
them with enough force to shoot

341
00:16:06,950 --> 00:16:09,980
these 350-kilogram caps.

342
00:16:09,980 --> 00:16:12,050
And what did they say?

343
00:16:12,050 --> 00:16:14,720
I like the language
that they used--

344
00:16:14,720 --> 00:16:16,610
jumping in their sockets.

345
00:16:16,610 --> 00:16:20,477
So 50 seconds later,
pressure fails

346
00:16:20,477 --> 00:16:22,310
in the steam drums,
which means there's been

347
00:16:22,310 --> 00:16:24,050
some sort of containment leak.

348
00:16:24,050 --> 00:16:27,260
So all the while, the
coolant was boiling.

349
00:16:27,260 --> 00:16:28,970
The absorption was going down.

350
00:16:28,970 --> 00:16:30,620
The power was going up.

351
00:16:30,620 --> 00:16:32,270
Repeat, repeat, repeat.

352
00:16:32,270 --> 00:16:35,380
And the power jumped to about
100 times the rated power

353
00:16:35,380 --> 00:16:37,840
in something like four seconds.

354
00:16:37,840 --> 00:16:39,910
So it was normally
1,000-megawatt electric

355
00:16:39,910 --> 00:16:42,610
reactor, which is about
3,200 megawatts thermal.

356
00:16:42,610 --> 00:16:47,320
It was producing
nearly half a terawatt

357
00:16:47,320 --> 00:16:50,380
of thermal power for a
very short amount of time

358
00:16:50,380 --> 00:16:52,103
until it exploded.

359
00:16:52,103 --> 00:16:53,020
Now, it's interesting.

360
00:16:53,020 --> 00:16:55,450
A lot of folks call Chernobyl
a nuclear explosion.

361
00:16:55,450 --> 00:16:57,220
That's actually a misnomer.

362
00:16:57,220 --> 00:17:00,940
A nuclear explosion would be
a nuclear weapon, something

363
00:17:00,940 --> 00:17:04,359
set off by an enormous chain
reaction principally heated

364
00:17:04,359 --> 00:17:06,579
by fission or fusion.

365
00:17:06,579 --> 00:17:09,099
That's not actually what
happened at Chernobyl,

366
00:17:09,099 --> 00:17:12,670
nor at Fukushima, nor was that
the worry at Three Mile Island.

367
00:17:12,670 --> 00:17:15,160
Not to say it wasn't
a horrible thing,

368
00:17:15,160 --> 00:17:17,950
but it wasn't an actual
nuclear explosion.

369
00:17:17,950 --> 00:17:21,730
At first, what happened
was a pressure explosion.

370
00:17:21,730 --> 00:17:25,089
So there was an enormous
release of steam

371
00:17:25,089 --> 00:17:29,560
as the power built up to 100
times normal operating power.

372
00:17:29,560 --> 00:17:31,810
The steam force was so
large that it actually

373
00:17:31,810 --> 00:17:35,820
blew the reactor lid
up off of the thing.

374
00:17:35,820 --> 00:17:38,770
And I think I have a picture
of that somewhere here too.

375
00:17:41,710 --> 00:17:43,220
It should be further down.

376
00:17:43,220 --> 00:17:46,340
Yeah, to give you a
little sense of scale.

377
00:17:46,340 --> 00:17:48,680
The reactor cover, which
weighed about 1,000 tons,

378
00:17:48,680 --> 00:17:52,430
launched into the air and
landed above the reactor

379
00:17:52,430 --> 00:17:54,380
sending most of the
reactor components

380
00:17:54,380 --> 00:17:56,600
up to a kilometer up in the air.

381
00:17:56,600 --> 00:18:00,170
Four seconds later,
that was followed

382
00:18:00,170 --> 00:18:02,630
by a hydrogen explosion.

383
00:18:02,630 --> 00:18:05,050
Let me get that down
to that chronology.

384
00:18:05,050 --> 00:18:07,550
So yeah.

385
00:18:07,550 --> 00:18:10,340
At 1:23 and 40 seconds
in the morning--

386
00:18:10,340 --> 00:18:10,840
oh, yeah.

387
00:18:10,840 --> 00:18:13,382
So I should mentioned why this
happened-- emergency insertion

388
00:18:13,382 --> 00:18:15,690
of all the control rods.

389
00:18:15,690 --> 00:18:18,240
The last part that this diagram
doesn't mention is these

390
00:18:18,240 --> 00:18:20,550
control rods-- and I'll
draw this up here--

391
00:18:20,550 --> 00:18:24,030
we're tipped with about
six inches of graphite.

392
00:18:24,030 --> 00:18:26,530
So if these were two
graphite channels--

393
00:18:26,530 --> 00:18:29,320
let's say these are carbon--

394
00:18:29,320 --> 00:18:31,620
and this is your
control rod, the goal

395
00:18:31,620 --> 00:18:37,200
was to get this control rod
all the way into the reactor.

396
00:18:37,200 --> 00:18:39,660
One part they didn't
mention was they

397
00:18:39,660 --> 00:18:42,450
were tipped with about six
inches of graphite, which

398
00:18:42,450 --> 00:18:45,210
only functions as
additional moderator.

399
00:18:45,210 --> 00:18:48,450
Graphite is one of the
lowest absorbing materials

400
00:18:48,450 --> 00:18:51,970
in the periodic table, second,
I think, only to oxygen.

401
00:18:51,970 --> 00:18:57,200
And if we pull up
graphite cross sections,

402
00:18:57,200 --> 00:18:59,850
I've plotted here the
total cross section,

403
00:18:59,850 --> 00:19:01,440
the elastic scattering
cross section.

404
00:19:01,440 --> 00:19:05,430
And down here, in
the 0.001 barn level,

405
00:19:05,430 --> 00:19:08,670
is the absorption cross
section, about 1,000 times lower

406
00:19:08,670 --> 00:19:09,510
than water.

407
00:19:09,510 --> 00:19:12,120
So you're shoving more material
in the reactor that slows down

408
00:19:12,120 --> 00:19:14,070
neutrons even
more, bringing them

409
00:19:14,070 --> 00:19:17,220
into the high-fission region
without absorbing anything.

410
00:19:17,220 --> 00:19:19,560
And they jammed
about halfway down,

411
00:19:19,560 --> 00:19:23,010
about 2 and 1/2 feet down,
leaving the extra graphite

412
00:19:23,010 --> 00:19:24,940
right in the center
of the core where

413
00:19:24,940 --> 00:19:26,510
it could do the most damage.

414
00:19:26,510 --> 00:19:28,050
And it didn't take
that much time.

415
00:19:28,050 --> 00:19:28,770
Yeah?

416
00:19:28,770 --> 00:19:31,410
AUDIENCE: So my understanding is
that, also, one of the designs

417
00:19:31,410 --> 00:19:34,270
is that the control rods
didn't immediately drop down.

418
00:19:34,270 --> 00:19:35,510
But they were slowly lowered.

419
00:19:35,510 --> 00:19:36,570
MICHAEL SHORT: Yep.

420
00:19:36,570 --> 00:19:38,205
They took 7 to 10 seconds.

421
00:19:38,205 --> 00:19:40,330
AUDIENCE: If they had a
system where they did drop,

422
00:19:40,330 --> 00:19:42,120
would that have
possibly actually set

423
00:19:42,120 --> 00:19:43,173
the system down properly?

424
00:19:43,173 --> 00:19:44,340
MICHAEL SHORT: I'm not sure.

425
00:19:44,340 --> 00:19:47,160
I don't know whether lowering
control rods into something

426
00:19:47,160 --> 00:19:49,380
that was undergoing
steam explosions

427
00:19:49,380 --> 00:19:50,610
would have actually helped.

428
00:19:50,610 --> 00:19:52,527
I mean, to me, by this
point, it was all over.

429
00:19:54,930 --> 00:19:59,732
So the extra moderator
that was dumped in

430
00:19:59,732 --> 00:20:01,440
was the last kick in
the pants this thing

431
00:20:01,440 --> 00:20:04,310
needed to go absolutely insane.

432
00:20:04,310 --> 00:20:07,370
And if we go back to the
timeline on the second level,

433
00:20:07,370 --> 00:20:11,090
control rods inserted
at 1:23 and 40 seconds.

434
00:20:11,090 --> 00:20:16,160
Explosion, four seconds later,
to 120 times full power,

435
00:20:16,160 --> 00:20:18,260
getting towards
a terawatt or so.

436
00:20:18,260 --> 00:20:22,760
One second later, the 1,000-ton
lid launches off from the first

437
00:20:22,760 --> 00:20:24,670
explosion.

438
00:20:24,670 --> 00:20:28,000
Very shortly after
that, second explosion.

439
00:20:28,000 --> 00:20:32,100
And that happened
because of this reaction.

440
00:20:32,100 --> 00:20:37,350
Well, just about anything
corroding with water

441
00:20:37,350 --> 00:20:41,380
will make pretty
much anything oxide

442
00:20:41,380 --> 00:20:44,500
plus hydrogen, the same
chemical explosion that

443
00:20:44,500 --> 00:20:47,212
was the undoing of
Fukushima and was the worry

444
00:20:47,212 --> 00:20:49,420
at Three Mile Island that
there was a hydrogen bubble

445
00:20:49,420 --> 00:20:52,242
building because of
corrosion reactions

446
00:20:52,242 --> 00:20:53,950
with whatever happened
to be in the core.

447
00:20:53,950 --> 00:20:56,620
This happens with zirconium
pretty vigorously.

448
00:20:56,620 --> 00:20:58,750
But it happens with
other materials too.

449
00:20:58,750 --> 00:21:01,330
If you oxidize
something with water,

450
00:21:01,330 --> 00:21:04,060
you leave behind the
hydrogen. And the hydrogen,

451
00:21:04,060 --> 00:21:07,030
in a very wide range of
concentrations in the air,

452
00:21:07,030 --> 00:21:08,440
is explosive.

453
00:21:08,440 --> 00:21:11,890
We're actually not allowed
to use hydrogen at about 4%

454
00:21:11,890 --> 00:21:14,530
in any of the labs here because
that reaches the flammability

455
00:21:14,530 --> 00:21:16,120
or explosive limit.

456
00:21:16,120 --> 00:21:19,510
So for my PhD, we were
doing these experiments

457
00:21:19,510 --> 00:21:22,000
corroding materials
in liquid lead.

458
00:21:22,000 --> 00:21:23,770
And we wanted to
dump in pure hydrogen

459
00:21:23,770 --> 00:21:27,040
to see what happens when
there's no oxygen. We were told,

460
00:21:27,040 --> 00:21:28,082
absolutely not.

461
00:21:28,082 --> 00:21:30,040
We had to drill a hole
in the side of the walls

462
00:21:30,040 --> 00:21:32,890
that the hydrogen would
vent outside and do

463
00:21:32,890 --> 00:21:35,500
some calculations to show if
the entire bottle of hydrogen

464
00:21:35,500 --> 00:21:37,750
emptied into the lab
at once, which it could

465
00:21:37,750 --> 00:21:40,150
do if the cap of the
bottle breaks off,

466
00:21:40,150 --> 00:21:42,970
it would not reach
4% concentration.

467
00:21:42,970 --> 00:21:45,260
So hydrogen explosions are
pretty powerful things.

468
00:21:45,260 --> 00:21:49,000
You guys ever seen people
making water from scratch?

469
00:21:49,000 --> 00:21:52,733
Mix hydrogen and oxygen in
a bottle and light a match?

470
00:21:52,733 --> 00:21:54,900
We've got a video of it
circulating somewhere around

471
00:21:54,900 --> 00:21:58,020
here because for RTC, for the
Reactor Technology Course,

472
00:21:58,020 --> 00:21:59,670
I do this in front
of a bunch of CEOs

473
00:21:59,670 --> 00:22:02,910
and watch them jump out of their
chairs to teach basic chemical

474
00:22:02,910 --> 00:22:03,520
reactions.

475
00:22:03,520 --> 00:22:06,390
But it's pretty loud.

476
00:22:06,390 --> 00:22:10,010
About enough hydrogen and
oxygen to just fill this cup

477
00:22:10,010 --> 00:22:11,460
or fill a half-liter
water bottle

478
00:22:11,460 --> 00:22:13,560
makes a bang that gets
your ears ringing.

479
00:22:13,560 --> 00:22:16,303
Not quite bleeding,
but close enough.

480
00:22:16,303 --> 00:22:18,220
So that's what happened
here, except at a much

481
00:22:18,220 --> 00:22:19,180
more massive scale.

482
00:22:19,180 --> 00:22:21,160
So there was a steam
explosion followed

483
00:22:21,160 --> 00:22:24,970
seconds later by a hydrogen
explosion from hydrogen

484
00:22:24,970 --> 00:22:27,370
liberated from the corrosion
reaction of everything

485
00:22:27,370 --> 00:22:29,800
with the water that
was already there.

486
00:22:29,800 --> 00:22:35,930
And that's when this happened.

487
00:22:35,930 --> 00:22:36,650
[VIDEO PLAYBACK]

488
00:22:36,650 --> 00:22:54,600
- [NON-ENGLISH SPEECH]

489
00:22:54,600 --> 00:22:57,100
MICHAEL SHORT: So
that smoke right there

490
00:22:57,100 --> 00:23:01,470
is from a graphite
fire, not normal smoke.

491
00:23:01,470 --> 00:23:18,350
- [NON-ENGLISH SPEECH]

492
00:23:18,350 --> 00:23:20,800
MICHAEL SHORT: Yeah.

493
00:23:20,800 --> 00:23:22,135
Spoke too soon.

494
00:23:22,135 --> 00:23:52,617
- [NON-ENGLISH SPEECH]

495
00:23:52,617 --> 00:23:53,200
[END PLAYBACK]

496
00:23:53,200 --> 00:23:55,492
MICHAEL SHORT: This actually
provides a perfect conduit

497
00:23:55,492 --> 00:23:58,360
to transition from the second to
the third parts of this course.

498
00:23:58,360 --> 00:23:59,650
A lot of you have been
waiting to find out

499
00:23:59,650 --> 00:24:01,108
what are the units
of dose and what

500
00:24:01,108 --> 00:24:03,795
are the biological and
chemical effects of radiation.

501
00:24:03,795 --> 00:24:05,170
Well, this is
where you get them.

502
00:24:05,170 --> 00:24:07,660
From neutron physics,
you can understand

503
00:24:07,660 --> 00:24:09,397
why Chernobyl went wrong.

504
00:24:09,397 --> 00:24:11,980
Honestly, you've just been doing
this for three or four weeks.

505
00:24:11,980 --> 00:24:14,740
But with your knowledge of cross
sections, reactor feedback,

506
00:24:14,740 --> 00:24:17,680
and criticality, you can start
to understand why Chernobyl

507
00:24:17,680 --> 00:24:18,942
was flawed in its design.

508
00:24:18,942 --> 00:24:21,400
And what we're going to teach
you in the rest of the course

509
00:24:21,400 --> 00:24:24,580
is what happens next, what
happens when radio nuclides are

510
00:24:24,580 --> 00:24:26,860
absorbed by animals
of the human body,

511
00:24:26,860 --> 00:24:29,680
and what was the
main fallout, let's

512
00:24:29,680 --> 00:24:34,240
say, in the colloquial
sense and the actual sense

513
00:24:34,240 --> 00:24:36,798
from the Chernobyl reactor.

514
00:24:36,798 --> 00:24:37,465
[VIDEO PLAYBACK]

515
00:24:37,465 --> 00:24:40,070
Let's look a bit at what
they did next though.

516
00:24:40,070 --> 00:25:45,898
- [NON-ENGLISH SPEECH]

517
00:25:45,898 --> 00:25:47,440
MICHAEL SHORT: That's
not quite true.

518
00:25:47,440 --> 00:25:48,190
You'll see why.

519
00:25:48,190 --> 00:25:58,573
- [NON-ENGLISH SPEECH]

520
00:25:58,573 --> 00:26:00,240
MICHAEL SHORT: That
actually did happen.

521
00:26:03,816 --> 00:26:08,027
- [NON-ENGLISH SPEECH]

522
00:26:08,027 --> 00:26:08,610
[END PLAYBACK]

523
00:26:08,610 --> 00:26:10,693
MICHAEL SHORT: I think
that pretty much summarizes

524
00:26:10,693 --> 00:26:12,420
the state of things now.

525
00:26:12,420 --> 00:26:15,690
They built a sarcophagus around
this reactor, a gigantic tomb,

526
00:26:15,690 --> 00:26:17,700
which, according
to some reports,

527
00:26:17,700 --> 00:26:20,010
is not that structurally
sound and is

528
00:26:20,010 --> 00:26:22,590
in danger of partial collapse.

529
00:26:22,590 --> 00:26:25,350
So yeah, more difficult
efforts are ahead.

530
00:26:25,350 --> 00:26:28,993
But let's now talk about
what happened next.

531
00:26:28,993 --> 00:26:31,480
I'm going to jump to
the very end of this.

532
00:26:31,480 --> 00:26:35,860
The actual way that the accident
was noticed was the spread

533
00:26:35,860 --> 00:26:41,890
of the radioactive cloud
to not-so-close-by Sweden.

534
00:26:41,890 --> 00:26:44,840
So it was noticed that folks
entering a reactor in Sweden

535
00:26:44,840 --> 00:26:46,840
had contaminants on them,
which they thought was

536
00:26:46,840 --> 00:26:48,090
coming from their own reactor.

537
00:26:48,090 --> 00:26:49,192
Good first assumption.

538
00:26:49,192 --> 00:26:50,650
When it was determined
that nothing

539
00:26:50,650 --> 00:26:52,960
was amiss at the
reactor in Sweden,

540
00:26:52,960 --> 00:26:54,760
folks started to
analyze wind patterns

541
00:26:54,760 --> 00:26:55,900
and find out what happened.

542
00:26:55,900 --> 00:26:57,910
And then it was
clear that the USSR

543
00:26:57,910 --> 00:27:00,430
had tried to cover up
the Chernobyl accident.

544
00:27:00,430 --> 00:27:02,190
But you can't cover up fallout.

545
00:27:02,190 --> 00:27:05,950
And it eventually
spread pretty wide,

546
00:27:05,950 --> 00:27:08,440
covering most of
Europe and Russia

547
00:27:08,440 --> 00:27:11,230
and surprisingly not
Spain, lucky them

548
00:27:11,230 --> 00:27:14,780
for the wind patterns that
day, or those few days.

549
00:27:14,780 --> 00:27:18,630
So what happened is a few days
after the actual accident,

550
00:27:18,630 --> 00:27:20,530
a graphite fire
started to break out.

551
00:27:20,530 --> 00:27:23,410
Because graphite, when
exposed to air, well,

552
00:27:23,410 --> 00:27:25,420
you can do the chemistry.

553
00:27:25,420 --> 00:27:32,390
Add graphite plus oxygen, you
start making carbon dioxide.

554
00:27:32,390 --> 00:27:34,130
So graphite burns when it's hot.

555
00:27:34,130 --> 00:27:35,640
And as you can see
from the video--

556
00:27:39,210 --> 00:27:43,460
where is that nice still
of burning graphite?

557
00:27:43,460 --> 00:27:43,992
Yeah.

558
00:27:43,992 --> 00:27:45,200
That graphite was pretty hot.

559
00:27:45,200 --> 00:27:48,050
So a lot of that smoke
included burning graphite

560
00:27:48,050 --> 00:27:51,290
and a lot of the materials
from the reactor itself.

561
00:27:51,290 --> 00:27:54,230
Now, when you build up
fission products in a reactor

562
00:27:54,230 --> 00:27:55,952
and they get
volatilized like this,

563
00:27:55,952 --> 00:27:57,410
the ones that tend
to get out first

564
00:27:57,410 --> 00:27:59,550
would be things like
the noble gases.

565
00:27:59,550 --> 00:28:02,630
So the whole xenon inventory
of the reactor was released.

566
00:28:02,630 --> 00:28:04,931
It's estimated at about 100%.

567
00:28:04,931 --> 00:28:08,640
And I can actually
pull up those figures.

568
00:28:08,640 --> 00:28:11,520
When we talk about how
much of which radionuclide

569
00:28:11,520 --> 00:28:13,200
was released.

570
00:28:13,200 --> 00:28:14,220
That's also a typo.

571
00:28:14,220 --> 00:28:17,670
If somebody wants to call in,
there's no 33 isotope of xenon.

572
00:28:17,670 --> 00:28:20,312
It's supposed to be 133.

573
00:28:20,312 --> 00:28:22,520
That would be interesting
if someone wants to call in

574
00:28:22,520 --> 00:28:24,560
and say the NEA
has got a mistake.

575
00:28:24,560 --> 00:28:27,000
So 100% of the
inventory released.

576
00:28:27,000 --> 00:28:29,450
That should be pretty obvious
because it's a noble gas.

577
00:28:29,450 --> 00:28:31,280
And it just kind of floats away.

578
00:28:31,280 --> 00:28:37,700
The real dangers, though, came
from iodine-131, about 50%

579
00:28:37,700 --> 00:28:41,370
of a 3-exabecquerel activity.

580
00:28:41,370 --> 00:28:43,490
So we're talking
like megacuries.

581
00:28:43,490 --> 00:28:44,255
It might be giga.

582
00:28:44,255 --> 00:28:46,160
I can't do that math in my head.

583
00:28:46,160 --> 00:28:47,600
A lot of radiation.

584
00:28:47,600 --> 00:28:49,490
The problem with that
is iodine behaves

585
00:28:49,490 --> 00:28:53,060
just like any other
halogen. It forms salts.

586
00:28:53,060 --> 00:28:54,025
It's rather volatile.

587
00:28:54,025 --> 00:28:57,610
Have any of you guys
played with iodine before?

588
00:28:57,610 --> 00:28:58,760
No one does-- oh, you have.

589
00:28:58,760 --> 00:28:59,260
OK.

590
00:28:59,260 --> 00:29:00,718
What happens when
you play with it?

591
00:29:00,718 --> 00:29:03,658
AUDIENCE: I mean, just
throw some stuff--

592
00:29:03,658 --> 00:29:08,423
like, it turns everything
yellow and it just

593
00:29:08,423 --> 00:29:10,560
reacts with acids and stuff.

594
00:29:10,560 --> 00:29:12,320
I haven't really done
very much with it.

595
00:29:12,320 --> 00:29:12,820
So--

596
00:29:12,820 --> 00:29:13,850
MICHAEL SHORT: OK.

597
00:29:13,850 --> 00:29:15,730
I happen to have
extensive practice playing

598
00:29:15,730 --> 00:29:17,800
with iodine in my home because
I did all the stuff you're not

599
00:29:17,800 --> 00:29:20,230
supposed to do as a kid, kind
of build your own chemistry

600
00:29:20,230 --> 00:29:23,260
stuff things that somehow leak
out to your local high school

601
00:29:23,260 --> 00:29:24,460
somehow.

602
00:29:24,460 --> 00:29:27,180
Iodine's pretty neat.

603
00:29:27,180 --> 00:29:29,770
Yeah, it happens sometimes.

604
00:29:29,770 --> 00:29:32,680
If you put iodine in your
hand, it actually sublimes.

605
00:29:32,680 --> 00:29:34,990
The heat from your hand
is enough to directly go

606
00:29:34,990 --> 00:29:36,910
from solid to vapor.

607
00:29:36,910 --> 00:29:39,797
And so the iodine was
also quite volatile.

608
00:29:39,797 --> 00:29:42,130
Some of it may have been in
the form of other compounds.

609
00:29:42,130 --> 00:29:43,840
Some of it may have
been elemental--

610
00:29:43,840 --> 00:29:44,740
probably not likely.

611
00:29:44,740 --> 00:29:46,930
But there was certainly
some iodine vapor.

612
00:29:46,930 --> 00:29:48,790
And about half of
that was released.

613
00:29:48,790 --> 00:29:51,820
The problem is then
it condenses out

614
00:29:51,820 --> 00:29:56,230
and falls on anything green,
anything with surface area.

615
00:29:56,230 --> 00:29:58,900
So the biggest danger to
the folks living nearby

616
00:29:58,900 --> 00:30:03,460
was from eating leafy
vegetables because leaves

617
00:30:03,460 --> 00:30:04,630
got lots of surface area.

618
00:30:04,630 --> 00:30:06,280
Iodine deposits on them.

619
00:30:06,280 --> 00:30:09,010
And it's intensely
radioactive for a month or so.

620
00:30:09,010 --> 00:30:11,290
Or depositing on the
grass that cows eat,

621
00:30:11,290 --> 00:30:14,230
which led to the problem
of radioactive milk.

622
00:30:14,230 --> 00:30:16,450
And so that's why milk
in the Soviet Union

623
00:30:16,450 --> 00:30:18,370
was banned for such a
long time because this

624
00:30:18,370 --> 00:30:22,260
was one of the major sources
of iodine contamination.

625
00:30:22,260 --> 00:30:24,330
The other one, which
we're worrying about now

626
00:30:24,330 --> 00:30:27,810
from Fukushima as
well, is cesium,

627
00:30:27,810 --> 00:30:30,750
which has similar chemistry to
sodium and potassium-- again,

628
00:30:30,750 --> 00:30:34,530
a rather salty compound,
or rather salty element.

629
00:30:34,530 --> 00:30:37,360
But it's got a
half-life of 30 years.

630
00:30:37,360 --> 00:30:40,460
And if we look it up in
the table of nuclides,

631
00:30:40,460 --> 00:30:42,580
we'll see what it
actually releases.

632
00:30:42,580 --> 00:30:43,080
Oh, good.

633
00:30:43,080 --> 00:30:45,500
It's back online.

634
00:30:45,500 --> 00:30:49,100
Anyone else notice this
broken a couple days ago.

635
00:30:49,100 --> 00:30:49,972
AUDIENCE: Yeah.

636
00:30:49,972 --> 00:30:52,180
MICHAEL SHORT: Well, luckily,
Brookhaven National Lab

637
00:30:52,180 --> 00:30:53,940
has a good version up too.

638
00:30:53,940 --> 00:30:57,860
But let's grab cesium.

639
00:30:57,860 --> 00:31:00,140
Yeah, there's plenty out there.

640
00:31:00,140 --> 00:31:02,360
Cesium-137.

641
00:31:02,360 --> 00:31:05,510
Beta decays to barium but
also gives off gamma rays.

642
00:31:05,510 --> 00:31:09,260
And most of the decays
end up giving off

643
00:31:09,260 --> 00:31:13,400
one of those gamma rays,
let's say a 660-keV gamma ray.

644
00:31:13,400 --> 00:31:15,870
So it's both a beta
and a gamma emitter.

645
00:31:15,870 --> 00:31:17,480
Now, which of those
types of radiation

646
00:31:17,480 --> 00:31:21,050
do you think it's more damaging
to biological organisms?

647
00:31:21,050 --> 00:31:23,096
The beta or the gamma?

648
00:31:23,096 --> 00:31:24,052
AUDIENCE: Gamma?

649
00:31:24,052 --> 00:31:25,427
MICHAEL SHORT:
You say the gamma.

650
00:31:25,427 --> 00:31:26,663
Why do you say so?

651
00:31:26,663 --> 00:31:28,080
AUDIENCE: Doesn't
beta get stopped

652
00:31:28,080 --> 00:31:29,690
by the skin and clothing?

653
00:31:29,690 --> 00:31:30,800
MICHAEL SHORT: It does.

654
00:31:30,800 --> 00:31:32,715
But if cesium is
better known as--

655
00:31:32,715 --> 00:31:33,590
AUDIENCE: [INAUDIBLE]

656
00:31:33,590 --> 00:31:35,540
MICHAEL SHORT: Yes.

657
00:31:35,540 --> 00:31:36,500
That's right.

658
00:31:36,500 --> 00:31:38,980
So did I get to tell
you guys this question,

659
00:31:38,980 --> 00:31:42,070
the four cookies question?

660
00:31:42,070 --> 00:31:42,920
Yeah.

661
00:31:42,920 --> 00:31:45,117
You eat the gamma cookie
because most gammas that

662
00:31:45,117 --> 00:31:47,450
are emitted by the cookie
simply leave you and irradiate

663
00:31:47,450 --> 00:31:51,330
your friend, which is going to
be the topic of pset number 8.

664
00:31:51,330 --> 00:31:51,960
You'll see.

665
00:31:51,960 --> 00:31:54,360
That's why you guys are
getting your whole body counts.

666
00:31:54,360 --> 00:31:58,910
Speaking of, who's gotten
their whole body counts at EHS?

667
00:31:58,910 --> 00:31:59,410
Awesome.

668
00:31:59,410 --> 00:32:00,850
So that's almost everybody.

669
00:32:00,850 --> 00:32:03,130
You will need that
data for problem set 8.

670
00:32:03,130 --> 00:32:06,067
So do schedule it soon,
preferably before Thanksgiving

671
00:32:06,067 --> 00:32:07,900
so that you'll be able
to take a look at it.

672
00:32:07,900 --> 00:32:12,440
Has anyone found anything
interesting in your spectra?

673
00:32:12,440 --> 00:32:14,300
Good.

674
00:32:14,300 --> 00:32:16,010
Glad to hear that.

675
00:32:16,010 --> 00:32:18,860
But you do see a potassium
peak that you can probably

676
00:32:18,860 --> 00:32:22,650
integrate and do some
problems with, right?

677
00:32:22,650 --> 00:32:23,890
Yeah, because you will.

678
00:32:23,890 --> 00:32:24,930
OK.

679
00:32:24,930 --> 00:32:25,980
Anyway, yeah.

680
00:32:25,980 --> 00:32:26,882
It's the betas.

681
00:32:26,882 --> 00:32:27,840
That's the real killer.

682
00:32:27,840 --> 00:32:31,680
The gammas are going to leave
the cesium, enter your body,

683
00:32:31,680 --> 00:32:33,780
and most likely come
out the other side.

684
00:32:33,780 --> 00:32:39,240
Because the mass attenuation
coefficient of 6-- what is it?

685
00:32:39,240 --> 00:32:41,910
Water for 660-keV gammas.

686
00:32:41,910 --> 00:32:45,040
Let's find that.

687
00:32:45,040 --> 00:32:46,540
Table 3.

688
00:32:46,540 --> 00:32:49,180
Let's say you're
made mostly of water.

689
00:32:53,420 --> 00:32:57,040
Water, liquid, that's
pretty much humans.

690
00:32:57,040 --> 00:33:01,810
660 keV is right about
here leading to about 0.1

691
00:33:01,810 --> 00:33:03,760
centimeter squared per gram.

692
00:33:03,760 --> 00:33:05,470
And with a density
of 1 gram, that's

693
00:33:05,470 --> 00:33:08,300
a pretty low
attenuation of gammas.

694
00:33:08,300 --> 00:33:10,150
So this chart actually
shows why most

695
00:33:10,150 --> 00:33:12,988
of the cesium gammas that would
be produced from ingestion

696
00:33:12,988 --> 00:33:13,780
just get right out.

697
00:33:13,780 --> 00:33:17,680
But it's the betas that
have an awfully short range.

698
00:33:17,680 --> 00:33:22,050
Anyone remember the formula
for range in general?

699
00:33:22,050 --> 00:33:24,910
So this is going to come back
up in our discussion of dose

700
00:33:24,910 --> 00:33:25,870
and biological effects.

701
00:33:30,070 --> 00:33:36,355
Integral, yep, of stopping
power to the negative 1.

702
00:33:36,355 --> 00:33:40,435
And that's stopping power
is this simple formula.

703
00:33:49,300 --> 00:33:50,640
Let's see.

704
00:33:50,640 --> 00:33:52,580
What did that come out as?

705
00:33:57,580 --> 00:33:59,600
Log minus beta squared.

706
00:33:59,600 --> 00:34:01,905
That simple little
formula, which

707
00:34:01,905 --> 00:34:03,780
I'm not going to expect
you guys to memorize.

708
00:34:03,780 --> 00:34:05,220
So don't worry about it.

709
00:34:05,220 --> 00:34:07,850
But if you integrate
this, you find out

710
00:34:07,850 --> 00:34:10,880
that the range of electrons,
even 1 MeV electrons, in water

711
00:34:10,880 --> 00:34:11,989
is not very high.

712
00:34:11,989 --> 00:34:15,500
So most of them are stopped
near or by the cells

713
00:34:15,500 --> 00:34:19,820
that absorb them doing quite
a bit of damage to DNA, which

714
00:34:19,820 --> 00:34:22,370
is eventually what causes
mutagenic effects--

715
00:34:22,370 --> 00:34:24,400
cancer, cell death,
what we're going

716
00:34:24,400 --> 00:34:28,639
to talk about for the whole
third part of the course.

717
00:34:28,639 --> 00:34:32,449
There's also a worry about
which organs actually

718
00:34:32,449 --> 00:34:34,460
absorb these radionuclides.

719
00:34:34,460 --> 00:34:37,580
And iodine in particular
is preferentially

720
00:34:37,580 --> 00:34:39,633
absorbed by the thyroid.

721
00:34:39,633 --> 00:34:41,300
So when we started
looking at the amount

722
00:34:41,300 --> 00:34:43,820
of radioactive
substances released--

723
00:34:43,820 --> 00:34:47,179
remember they said, OK, at
around the 26th of April

724
00:34:47,179 --> 00:34:50,480
or the 2nd of May or so
the release was stopped?

725
00:34:50,480 --> 00:34:52,070
Not according to our data.

726
00:34:52,070 --> 00:34:54,350
That's when the graphite
fire picked up again.

727
00:34:54,350 --> 00:34:57,600
In addition, the
core of Chernobyl,

728
00:34:57,600 --> 00:35:01,550
which had undergone a
mostly total meltdown,

729
00:35:01,550 --> 00:35:07,700
was sitting in a pool on
top of this concrete pad.

730
00:35:07,700 --> 00:35:09,540
So let's just call
this liquid stuff--

731
00:35:09,540 --> 00:35:13,810
the actual word that we use
in parlance is called corium.

732
00:35:13,810 --> 00:35:16,390
It's our tongue-in-cheek
word for every element

733
00:35:16,390 --> 00:35:19,600
mixed together in a
hot radioactive soup.

734
00:35:19,600 --> 00:35:21,640
First of all, it
started to redistribute,

735
00:35:21,640 --> 00:35:25,040
reacting with any water that was
present, flashing it to steam.

736
00:35:25,040 --> 00:35:28,340
And the steam caused additional
dispersion of radionuclides.

737
00:35:28,340 --> 00:35:30,970
And eventually, it
burrowed its way

738
00:35:30,970 --> 00:35:34,260
through and into the
ground, releasing more.

739
00:35:34,260 --> 00:35:37,270
It's the worst
nuclear thing that's

740
00:35:37,270 --> 00:35:40,900
ever happened in the
history of nuclear things.

741
00:35:40,900 --> 00:35:42,190
Quite a mess.

742
00:35:42,190 --> 00:35:46,710
And luckily, it did sort
of taper off after this.

743
00:35:46,710 --> 00:35:50,440
But let's now look
into what happens next.

744
00:35:50,440 --> 00:35:53,220
And this is the nice intro to
the third part of the course.

745
00:35:53,220 --> 00:35:57,000
Iodine is preferentially
uptaken by the thyroid gland

746
00:35:57,000 --> 00:35:59,130
somewhere right about here.

747
00:35:59,130 --> 00:36:00,630
So has anyone ever
heard of the idea

748
00:36:00,630 --> 00:36:04,740
of taking iodine tablets in
the case of a nuclear disaster?

749
00:36:04,740 --> 00:36:05,790
Anyone have any idea why?

750
00:36:09,660 --> 00:36:11,880
If you saturate your
thyroid with iodine,

751
00:36:11,880 --> 00:36:14,100
then if you ingest
radioactive iodine,

752
00:36:14,100 --> 00:36:16,740
it's less likely to
be permanently taken

753
00:36:16,740 --> 00:36:18,210
by the thyroid.

754
00:36:18,210 --> 00:36:21,240
So this actually
provided some statistics

755
00:36:21,240 --> 00:36:24,450
on the probability of
getting thyroid cancer

756
00:36:24,450 --> 00:36:27,660
from radioactive
iodine ingestion.

757
00:36:27,660 --> 00:36:29,610
Luckily, the statistics
were quite poor,

758
00:36:29,610 --> 00:36:31,785
which means that not
many people were exposed.

759
00:36:31,785 --> 00:36:36,780
It was somewhere around 1,300
or so, not like millions.

760
00:36:36,780 --> 00:36:39,630
Yeah, 1,300 people total.

761
00:36:39,630 --> 00:36:44,350
But what I want to jump to is
the dose-versus-risk curve.

762
00:36:44,350 --> 00:36:46,830
And this is going to belie
all of our discussion

763
00:36:46,830 --> 00:36:50,940
about the biological long-term
effects of radioactivity.

764
00:36:50,940 --> 00:36:56,250
What's the most striking thing
you see as part of this curve?

765
00:36:56,250 --> 00:36:57,550
AUDIENCE: Error bars.

766
00:36:57,550 --> 00:36:58,717
MICHAEL SHORT: That's right.

767
00:36:58,717 --> 00:37:00,470
That's the first thing I saw.

768
00:37:00,470 --> 00:37:04,220
There are six different models
for how dose an increased

769
00:37:04,220 --> 00:37:05,690
risk of cancer proceeds.

770
00:37:05,690 --> 00:37:09,050
And they all fall within
almost all the error

771
00:37:09,050 --> 00:37:11,330
bars of these measurements.

772
00:37:11,330 --> 00:37:13,280
I say, again, thank
God that the error

773
00:37:13,280 --> 00:37:16,220
bars are so high because that
means that the sample size was

774
00:37:16,220 --> 00:37:17,630
so low.

775
00:37:17,630 --> 00:37:19,220
So when folks say
we don't really

776
00:37:19,220 --> 00:37:23,180
know how much radioactivity
causes how much cancer, they're

777
00:37:23,180 --> 00:37:25,820
right because, luckily,
we don't have enough data

778
00:37:25,820 --> 00:37:30,090
from people being exposed to
know that really, really well.

779
00:37:30,090 --> 00:37:31,940
So some folks say we
should be cautious.

780
00:37:31,940 --> 00:37:33,530
I kind of agree with them.

781
00:37:33,530 --> 00:37:35,030
Some folks say the
jury's still out.

782
00:37:35,030 --> 00:37:37,710
I also agree with them.

783
00:37:37,710 --> 00:37:40,200
But you can start to estimate
these sorts of things

784
00:37:40,200 --> 00:37:43,440
by knowing how much
radiation energy was absorbed

785
00:37:43,440 --> 00:37:45,600
and to what organ.

786
00:37:45,600 --> 00:37:49,320
So I think the only technical
thing I want to go over today

787
00:37:49,320 --> 00:37:50,940
is the different units of dose.

788
00:37:50,940 --> 00:37:52,505
Because as you
start to read things

789
00:37:52,505 --> 00:37:53,880
in the reading,
which I recommend

790
00:37:53,880 --> 00:37:55,770
you do if you haven't
been doing yet,

791
00:37:55,770 --> 00:37:58,470
you're going to encounter a lot
of different units of radiation

792
00:37:58,470 --> 00:38:05,390
dose ranging from things like
the roentgen, which responds

793
00:38:05,390 --> 00:38:07,550
to a number of ionizations.

794
00:38:10,510 --> 00:38:13,390
You won't usually
see this one given

795
00:38:13,390 --> 00:38:15,850
in sort of biological parlance.

796
00:38:15,850 --> 00:38:17,470
Because it's the
number of ionizations

797
00:38:17,470 --> 00:38:21,220
detected by some sort of
gaseous ionization detector.

798
00:38:21,220 --> 00:38:23,410
So the dosimeters is
that you all put on--

799
00:38:23,410 --> 00:38:28,150
did you guys all bring
these brass pen dosimeters

800
00:38:28,150 --> 00:38:29,170
in through the reactor?

801
00:38:29,170 --> 00:38:33,077
Did anyone look through them to
see what the unit of dose was?

802
00:38:33,077 --> 00:38:34,910
It's going to be in
roentgens because that's

803
00:38:34,910 --> 00:38:38,150
directly corelatable to
the number of ionizations

804
00:38:38,150 --> 00:38:40,820
that that dosimeter
has experienced.

805
00:38:40,820 --> 00:38:43,490
You'll also see four
dose units, two of which

806
00:38:43,490 --> 00:38:46,030
are just factors of 100
away from each other.

807
00:38:46,030 --> 00:38:49,970
There is what's called
the rad and the gray.

808
00:38:49,970 --> 00:38:53,510
And there's what's called
the rem and the sievert.

809
00:38:57,910 --> 00:39:00,580
You'll see these
approximated as gray.

810
00:39:00,580 --> 00:39:03,370
You'll see these as
R. And these are just

811
00:39:03,370 --> 00:39:05,760
usually written as rem.

812
00:39:05,760 --> 00:39:09,070
So a rad is simple.

813
00:39:09,070 --> 00:39:10,190
Let's see.

814
00:39:10,190 --> 00:39:15,600
100 rads is the same as 1 gray.

815
00:39:15,600 --> 00:39:19,590
And 100 rem is the
same as 1 sievert.

816
00:39:19,590 --> 00:39:23,550
And for the case
of gamma radiation,

817
00:39:23,550 --> 00:39:26,270
these units are actually equal.

818
00:39:26,270 --> 00:39:28,760
I particularly like
this set of units

819
00:39:28,760 --> 00:39:33,290
because this is the kind
of SI of radiation units

820
00:39:33,290 --> 00:39:35,960
because it comes directly
from measurable calculatable

821
00:39:35,960 --> 00:39:37,010
quantities.

822
00:39:37,010 --> 00:39:40,280
Like the gray, for example,
the actual unit of gray

823
00:39:40,280 --> 00:39:45,290
is joules absorbed per
kilogram of absorber.

824
00:39:45,290 --> 00:39:47,540
It's a pretty simple
unit to understand.

825
00:39:47,540 --> 00:39:51,430
If you know how many
radioactive particles or gammas

826
00:39:51,430 --> 00:39:53,300
or whatever that
you have absorbed,

827
00:39:53,300 --> 00:39:55,940
you can multiply that
number by their energy,

828
00:39:55,940 --> 00:39:59,030
divide by the mass of
the organ absorbing them,

829
00:39:59,030 --> 00:40:01,220
and you get its dose in gray.

830
00:40:01,220 --> 00:40:07,070
Sievert is gray times
some quality factor

831
00:40:07,070 --> 00:40:12,470
for the radiation
times some quality

832
00:40:12,470 --> 00:40:17,880
factor for the specific
type of tissue.

833
00:40:17,880 --> 00:40:21,360
What this says is that
some types of radiation

834
00:40:21,360 --> 00:40:24,330
are more effective at
causing damage than others.

835
00:40:24,330 --> 00:40:27,810
And some organs are more
susceptible to radiation damage

836
00:40:27,810 --> 00:40:28,740
than others.

837
00:40:28,740 --> 00:40:31,080
Does anyone happen to know
some of the organs that

838
00:40:31,080 --> 00:40:35,358
are most susceptible
to radiation damage?

839
00:40:35,358 --> 00:40:38,107
AUDIENCE: Soft tissues.

840
00:40:38,107 --> 00:40:39,690
MICHAEL SHORT: Soft
tissues like what?

841
00:40:39,690 --> 00:40:42,536
Because there's lots of those.

842
00:40:42,536 --> 00:40:43,930
AUDIENCE: Stomach lining.

843
00:40:43,930 --> 00:40:44,650
MICHAEL SHORT: Stomach lining.

844
00:40:44,650 --> 00:40:45,190
Yep.

845
00:40:45,190 --> 00:40:46,200
Yeah?

846
00:40:46,200 --> 00:40:47,010
AUDIENCE: Lungs.

847
00:40:47,010 --> 00:40:47,530
MICHAEL SHORT: Lungs.

848
00:40:47,530 --> 00:40:48,100
Yep.

849
00:40:48,100 --> 00:40:50,043
What else?

850
00:40:50,043 --> 00:40:51,342
AUDIENCE: Thyroid.

851
00:40:51,342 --> 00:40:52,300
MICHAEL SHORT: Thyroid.

852
00:40:52,300 --> 00:40:54,430
Yep, there is definitely
one for thyroid.

853
00:40:54,430 --> 00:40:55,720
AUDIENCE: Bone marrow.

854
00:40:55,720 --> 00:40:57,690
MICHAEL SHORT: Bone marrow.

855
00:40:57,690 --> 00:40:58,530
What other ones?

856
00:41:01,750 --> 00:41:03,700
Brain, actually not so much.

857
00:41:03,700 --> 00:41:05,650
The eyes.

858
00:41:05,650 --> 00:41:07,420
And where else do
you find rapidly

859
00:41:07,420 --> 00:41:09,860
dividing cells in your body?

860
00:41:09,860 --> 00:41:10,627
AUDIENCE: Skin.

861
00:41:10,627 --> 00:41:11,460
MICHAEL SHORT: Skin.

862
00:41:11,460 --> 00:41:12,972
Yep, the dermis.

863
00:41:12,972 --> 00:41:14,187
AUDIENCE: The liver?

864
00:41:14,187 --> 00:41:16,020
MICHAEL SHORT: I don't
know about the liver.

865
00:41:16,020 --> 00:41:16,860
I would assume so.

866
00:41:16,860 --> 00:41:19,220
Yeah, it's a pretty
active organ.

867
00:41:19,220 --> 00:41:22,610
But when folks are worried
about birth defects,

868
00:41:22,610 --> 00:41:24,720
reproductive organs.

869
00:41:24,720 --> 00:41:26,310
The link here that,
for some reason,

870
00:41:26,310 --> 00:41:28,560
is not said in the reading,
and I've never figured out

871
00:41:28,560 --> 00:41:32,310
why, is the more often a cell is
dividing, the more susceptible

872
00:41:32,310 --> 00:41:35,010
it is to gaining cancer risk.

873
00:41:35,010 --> 00:41:38,880
Because every cell division
is a copy of its DNA.

874
00:41:38,880 --> 00:41:42,480
And any time that radiation
goes in and damages or changes

875
00:41:42,480 --> 00:41:44,760
that DNA by either
causing what's

876
00:41:44,760 --> 00:41:47,850
called a thiamine bridge where
two thiamine bases get linked

877
00:41:47,850 --> 00:41:51,060
together or damaging the
structure in some other way,

878
00:41:51,060 --> 00:41:53,352
that gene is then replicated.

879
00:41:53,352 --> 00:41:54,810
And the faster
they're replicating,

880
00:41:54,810 --> 00:41:59,690
the more likely cancer is
going to become apparent.

881
00:41:59,690 --> 00:42:01,230
I guess this brings
up a question.

882
00:42:01,230 --> 00:42:04,050
When does a rapidly
dividing cell become cancer?

883
00:42:04,050 --> 00:42:07,172
Is it division number 1 or
is it when you notice it?

884
00:42:07,172 --> 00:42:10,260
I guess I'll leave that
question to the biologists.

885
00:42:10,260 --> 00:42:12,280
But if you notice,
in the reading,

886
00:42:12,280 --> 00:42:16,060
you'll see a bunch of different
tissue equivalency factors.

887
00:42:16,060 --> 00:42:17,880
And you'll just see
them tabulated and say,

888
00:42:17,880 --> 00:42:18,540
there they are.

889
00:42:18,540 --> 00:42:19,770
Memorize them.

890
00:42:19,770 --> 00:42:22,590
I want you to try and think
of the pattern between them.

891
00:42:22,590 --> 00:42:24,600
The tissues that
basically don't matter,

892
00:42:24,600 --> 00:42:29,880
like the non-marrow part of the
bone, dead skin cells, muscles,

893
00:42:29,880 --> 00:42:32,070
things that basically
aren't listed that much,

894
00:42:32,070 --> 00:42:34,050
they're not dividing very fast.

895
00:42:34,050 --> 00:42:36,750
But anywhere where you
find stem cells, the lining

896
00:42:36,750 --> 00:42:38,400
of your intestine,
your lungs which

897
00:42:38,400 --> 00:42:40,430
undergo a lot of
environmental damage

898
00:42:40,430 --> 00:42:44,070
and need to be replenished,
gonads, dura, skin--

899
00:42:44,070 --> 00:42:45,570
what was the other
one that we said?

900
00:42:45,570 --> 00:42:46,950
Eyes.

901
00:42:46,950 --> 00:42:49,260
These are places that are
either sensitive tissues

902
00:42:49,260 --> 00:42:52,080
or they're rapidly dividing.

903
00:42:52,080 --> 00:42:55,790
And so the sievert is kind of in
a unit of increased equivalent

904
00:42:55,790 --> 00:43:00,650
risk so that, if you were to
absorb one gray of gamma rays

905
00:43:00,650 --> 00:43:05,420
versus one gray of alphas, you'd
be about 20 times more likely

906
00:43:05,420 --> 00:43:08,135
to incur cancer from the
alphas than the gammas because

907
00:43:08,135 --> 00:43:10,700
of the amount of localized
damage that they do to cells.

908
00:43:10,700 --> 00:43:13,880
And we'll be doing all
this in detail pretty soon.

909
00:43:13,880 --> 00:43:17,780
And then for tissue equivalency
factor, if you absorb one gray

910
00:43:17,780 --> 00:43:20,870
and your whole body, which
means one joule per kilogram

911
00:43:20,870 --> 00:43:24,560
of average body mass,
versus one gray directly

912
00:43:24,560 --> 00:43:26,090
to the lining of
your intestine by,

913
00:43:26,090 --> 00:43:29,450
let's say, drinking
polonium-laced tea

914
00:43:29,450 --> 00:43:32,420
like happened to a
poor-- who was it?

915
00:43:32,420 --> 00:43:35,680
Current or ex-KGB guy
or the Russian fellas?

916
00:43:35,680 --> 00:43:38,570
No, it was the KGB guys
that poisoned him, right?

917
00:43:38,570 --> 00:43:39,070
Yeah.

918
00:43:39,070 --> 00:43:41,530
Do you guys remember
back in 2010 or so?

919
00:43:41,530 --> 00:43:43,540
There was a Russian--

920
00:43:43,540 --> 00:43:45,033
was he a journalist?

921
00:43:45,033 --> 00:43:46,450
AUDIENCE: Actually,
he was ex-KGB.

922
00:43:46,450 --> 00:43:47,760
MICHAEL SHORT: Ex-KGB.

923
00:43:47,760 --> 00:43:50,170
So the current KGB
somehow got into London

924
00:43:50,170 --> 00:43:53,950
and slipped polonium into his
tea at a Japanese restaurant.

925
00:43:53,950 --> 00:43:57,353
AUDIENCE: [INAUDIBLE]

926
00:43:57,353 --> 00:43:58,270
MICHAEL SHORT: Really?

927
00:43:58,270 --> 00:43:59,437
AUDIENCE: I think so, right?

928
00:43:59,437 --> 00:44:01,065
[INAUDIBLE] It was unsuccessful.

929
00:44:01,065 --> 00:44:02,440
MICHAEL SHORT:
What was his name?

930
00:44:05,090 --> 00:44:05,705
Let's see.

931
00:44:09,380 --> 00:44:12,850
The polonium poisoning.

932
00:44:12,850 --> 00:44:15,070
Did he actually die?

933
00:44:15,070 --> 00:44:17,050
Poisoning of
Alexander Litvinenko.

934
00:44:20,680 --> 00:44:23,135
AUDIENCE: That's
pretty close to dead.

935
00:44:23,135 --> 00:44:24,760
MICHAEL SHORT: He's
not doing too well.

936
00:44:27,840 --> 00:44:32,850
Illness and poisoning,
death, and last statement

937
00:44:32,850 --> 00:44:34,110
at the hospital in London.

938
00:44:34,110 --> 00:44:34,763
So yeah.

939
00:44:34,763 --> 00:44:36,638
AUDIENCE: He probably
said something awesome.

940
00:44:36,638 --> 00:44:38,010
AUDIENCE: What did he say?

941
00:44:38,010 --> 00:44:40,790
MICHAEL SHORT:
Well, interesting.

942
00:44:40,790 --> 00:44:42,540
That probably has
something to do with it.

943
00:44:42,540 --> 00:44:45,037
AUDIENCE: That's a lot
of-- a really long last--

944
00:44:45,037 --> 00:44:45,870
MICHAEL SHORT: Yeah?

945
00:44:45,870 --> 00:44:48,810
Well, we're not going to
comment on the politics.

946
00:44:48,810 --> 00:44:53,280
But the radiation effect
worked, clearly, unfortunately.

947
00:44:53,280 --> 00:44:55,470
So polonium is an alpha emitter.

948
00:44:55,470 --> 00:44:57,990
And that caused a
massive dose of alphas

949
00:44:57,990 --> 00:45:00,460
to his entire
gastrointestinal tract.

950
00:45:00,460 --> 00:45:03,060
And that caused a whole lot
of damage to those cells.

951
00:45:03,060 --> 00:45:04,410
No time for cancer.

952
00:45:04,410 --> 00:45:06,900
It actually killed off a
lot of those stem cells.

953
00:45:06,900 --> 00:45:09,420
And the way that radiation
poisoning would work

954
00:45:09,420 --> 00:45:11,190
is that, if you kill
off the stem cells,

955
00:45:11,190 --> 00:45:12,660
the villi in your
intestines die,

956
00:45:12,660 --> 00:45:15,390
which are responsible
for absorbing nutrition.

957
00:45:15,390 --> 00:45:17,610
You can't uptake nutrition.

958
00:45:17,610 --> 00:45:18,690
You basically starve.

959
00:45:18,690 --> 00:45:20,310
It doesn't matter what you eat.

960
00:45:20,310 --> 00:45:22,290
It's messed up.

961
00:45:22,290 --> 00:45:24,450
Yeah.

962
00:45:24,450 --> 00:45:26,017
That's a really bad way to go.

963
00:45:26,017 --> 00:45:27,600
It's called
gastrointestinal syndrome.

964
00:45:27,600 --> 00:45:31,170
And we'll be talking about
the progressive effects

965
00:45:31,170 --> 00:45:33,480
of acute radiation
exposure where

966
00:45:33,480 --> 00:45:36,270
you have immediate
effects mostly relating

967
00:45:36,270 --> 00:45:40,200
to the death of some organ that
is responsible for either cell

968
00:45:40,200 --> 00:45:43,230
division to keep you alive
or, in extreme cases,

969
00:45:43,230 --> 00:45:44,730
your neurological system.

970
00:45:44,730 --> 00:45:47,850
And nerve function just stops
at the highest levels of dose.

971
00:45:47,850 --> 00:45:52,530
And that corresponds to
doses of around 4 to 6 gray.

972
00:45:52,530 --> 00:45:57,220
4 to 6 joules per kilogram
of villi, or body mass,

973
00:45:57,220 --> 00:45:59,880
will kill you pretty quickly
with very little chance

974
00:45:59,880 --> 00:46:02,250
of survival as
what happened here.

975
00:46:02,250 --> 00:46:03,450
And so this was the problem.

976
00:46:03,450 --> 00:46:08,010
With all the folks living around
and near Chernobyl and Ukraine

977
00:46:08,010 --> 00:46:11,040
and Belarus and everywhere
was the contamination

978
00:46:11,040 --> 00:46:13,290
was pretty extensive.

979
00:46:13,290 --> 00:46:15,990
About 4,000 people are
estimated to have died

980
00:46:15,990 --> 00:46:17,550
or contracted cancer from this.

981
00:46:17,550 --> 00:46:19,680
I can't believe how
low that number is.

982
00:46:19,680 --> 00:46:22,480
But it's still 4,000 people that
should've never happened to.

983
00:46:22,480 --> 00:46:25,905
And effects were felt far
away in towns like Gomel

984
00:46:25,905 --> 00:46:27,780
and-- can't read that
one because there's not

985
00:46:27,780 --> 00:46:29,430
enough pixels.

986
00:46:29,430 --> 00:46:32,520
Because of the way that,
let's say, rainwater--

987
00:46:32,520 --> 00:46:35,780
or let's say the vapor
cloud from the reactor was--

988
00:46:35,780 --> 00:46:37,440
the way rainwater
caused it to fall

989
00:46:37,440 --> 00:46:40,050
on certain places, which
still, to this day,

990
00:46:40,050 --> 00:46:43,080
can have a really large
contamination area.

991
00:46:43,080 --> 00:46:45,330
And this brings me a little
bit into what should we be

992
00:46:45,330 --> 00:46:47,400
worried about from Fukushima--

993
00:46:47,400 --> 00:46:49,740
a whole lot less than Chernobyl.

994
00:46:49,740 --> 00:46:52,140
And the reason why
is Fukushima did

995
00:46:52,140 --> 00:46:54,900
undergo a hydrogen
explosion and did

996
00:46:54,900 --> 00:46:59,400
and still continues to release
cesium-137 into the ocean.

997
00:46:59,400 --> 00:47:02,170
Luckily, for us,
the ocean is big.

998
00:47:02,170 --> 00:47:05,500
And except for fish caught
right near around Fukushima,

999
00:47:05,500 --> 00:47:08,680
even though concentrations
can be measured at hundreds

1000
00:47:08,680 --> 00:47:11,500
to thousands of times
normal concentrations,

1001
00:47:11,500 --> 00:47:13,510
they can still be hundreds
to thousands of times

1002
00:47:13,510 --> 00:47:16,360
lower than the safe consumption.

1003
00:47:16,360 --> 00:47:20,007
So a lot of the problems
you see in the news today,

1004
00:47:20,007 --> 00:47:21,340
I'm not going to call them lies.

1005
00:47:21,340 --> 00:47:23,320
But I'm going to call
them half truths.

1006
00:47:23,320 --> 00:47:27,670
Folks will show the radiation
plume of cesium-137 escaping

1007
00:47:27,670 --> 00:47:28,800
from Fukushima.

1008
00:47:28,800 --> 00:47:29,800
And that's true.

1009
00:47:29,800 --> 00:47:31,690
There is radiation escaping.

1010
00:47:31,690 --> 00:47:33,610
The question is,
is it high enough

1011
00:47:33,610 --> 00:47:38,623
to cause a noticeable
increased risk of cancer?

1012
00:47:38,623 --> 00:47:40,040
That's the question
that reporters

1013
00:47:40,040 --> 00:47:41,543
shouldn't be asking themselves.

1014
00:47:41,543 --> 00:47:43,460
When they only tell the
half of the story that

1015
00:47:43,460 --> 00:47:45,950
gets them viewers and they
don't tell the half of the story

1016
00:47:45,950 --> 00:47:48,440
to complete the
story and tell you,

1017
00:47:48,440 --> 00:47:49,910
should you be afraid or not?

1018
00:47:49,910 --> 00:47:52,850
Because unfortunately,
fear brings viewers.

1019
00:47:52,850 --> 00:47:53,930
This is the problem--

1020
00:47:53,930 --> 00:47:56,300
and I'm happy to go
on camera saying this.

1021
00:47:56,300 --> 00:47:59,523
This is the problem
with the media today is,

1022
00:47:59,523 --> 00:48:01,190
with a half truth and
with a half story,

1023
00:48:01,190 --> 00:48:04,820
you can incite real panic
over non-physical issues

1024
00:48:04,820 --> 00:48:07,340
that may not actually exist.

1025
00:48:07,340 --> 00:48:10,580
And so it's important that the
media tell the whole story.

1026
00:48:10,580 --> 00:48:15,790
Yes, it's true that Fukushima's
releasing cesium-137.

1027
00:48:15,790 --> 00:48:18,190
How much though is the question
that people and the media

1028
00:48:18,190 --> 00:48:19,978
should be asking themselves.

1029
00:48:19,978 --> 00:48:21,520
And in the rest of
this course, we're

1030
00:48:21,520 --> 00:48:25,280
going to answer the question,
how much is too much?

1031
00:48:25,280 --> 00:48:28,050
So I'm going to stop
here since it's 2 of 5 of

1032
00:48:28,050 --> 00:48:29,800
and ask you guys if
you have any questions

1033
00:48:29,800 --> 00:48:31,990
on the whole second
part of the course

1034
00:48:31,990 --> 00:48:33,571
or what happened in Chernobyl.

1035
00:48:37,340 --> 00:48:37,950
Yeah.

1036
00:48:37,950 --> 00:48:38,575
AUDIENCE: Yeah.

1037
00:48:38,575 --> 00:48:40,370
Could you explain the
quality factor term

1038
00:48:40,370 --> 00:48:42,610
and how you find that?

1039
00:48:42,610 --> 00:48:43,743
MICHAEL SHORT: Yeah.

1040
00:48:43,743 --> 00:48:45,160
Well, there's two
quality factors.

1041
00:48:45,160 --> 00:48:49,300
There is the quality factor for
radiation, which will tell you,

1042
00:48:49,300 --> 00:48:51,370
let's say, how much
more cell damage

1043
00:48:51,370 --> 00:48:55,120
a given amount of a given type
of radiation of the same energy

1044
00:48:55,120 --> 00:48:57,670
will deposit into a cell.

1045
00:48:57,670 --> 00:48:59,740
And the tissue
equivalency factor

1046
00:48:59,740 --> 00:49:01,840
tells you, well,
what's the added

1047
00:49:01,840 --> 00:49:06,010
risk of some sort of defect
leading to cell death or cancer

1048
00:49:06,010 --> 00:49:10,360
or some other defect from
that radiation absorption.

1049
00:49:10,360 --> 00:49:12,670
So to me, the tissue
equivalency factor

1050
00:49:12,670 --> 00:49:15,460
is roughly, but not
completely, approximated

1051
00:49:15,460 --> 00:49:17,260
by the cell division rate.

1052
00:49:17,260 --> 00:49:20,200
And the radiation
quality factor is

1053
00:49:20,200 --> 00:49:24,190
going to be quite proportional
to the stopping power.

1054
00:49:24,190 --> 00:49:29,790
You'll see a term called the
Linear Energy Transfer, or LET.

1055
00:49:29,790 --> 00:49:33,870
This is the stopping power unit
used in the biology community.

1056
00:49:33,870 --> 00:49:35,263
It's stopping power.

1057
00:49:35,263 --> 00:49:36,930
And luckily, the
Turner reading actually

1058
00:49:36,930 --> 00:49:39,360
says it's somewhere
buried in a paragraph.

1059
00:49:39,360 --> 00:49:41,400
LET is stopping power.

1060
00:49:41,400 --> 00:49:43,350
So if you start plotting
these two together,

1061
00:49:43,350 --> 00:49:45,720
you might find some
striking similarities.

1062
00:49:45,720 --> 00:49:47,840
I saw two other
questions up here.

1063
00:49:47,840 --> 00:49:50,000
Yeah?

1064
00:49:50,000 --> 00:49:52,335
AUDIENCE: Why is Chernobyl
still considered off limits

1065
00:49:52,335 --> 00:49:54,290
if most the half-lives
of these things

1066
00:49:54,290 --> 00:49:58,110
are on the range of
days to two years?

1067
00:49:58,110 --> 00:49:59,293
I mean, it happened--

1068
00:49:59,293 --> 00:50:01,210
MICHAEL SHORT: Let's
answer that with numbers.

1069
00:50:01,210 --> 00:50:05,520
So most of the half-lives were
on the range of days to hours.

1070
00:50:05,520 --> 00:50:09,090
But still, cesium-137, with
a half-life of 30 years,

1071
00:50:09,090 --> 00:50:11,940
released a third
of an exabecquerel.

1072
00:50:11,940 --> 00:50:14,100
That's one of the major
sources of contamination

1073
00:50:14,100 --> 00:50:15,210
still out there.

1074
00:50:15,210 --> 00:50:19,250
In addition, if we scroll
down a little more,

1075
00:50:19,250 --> 00:50:21,620
there was quite a bit
of plutonium inventory

1076
00:50:21,620 --> 00:50:24,620
with a half-life
of 24,000 years.

1077
00:50:24,620 --> 00:50:27,260
So on Friday, we're going
to have Jake Hecla come in

1078
00:50:27,260 --> 00:50:29,510
and give his
Chernobyl travelogue

1079
00:50:29,510 --> 00:50:32,570
because one of our seniors has
actually been to Chernobyl.

1080
00:50:32,570 --> 00:50:35,330
And his boots were so
contaminated with plutonium

1081
00:50:35,330 --> 00:50:37,010
that he could never
use them again.

1082
00:50:37,010 --> 00:50:39,030
They've got to stay
wrapped up in plastic.

1083
00:50:39,030 --> 00:50:42,570
So some of these things last
tens of thousands of years.

1084
00:50:42,570 --> 00:50:44,150
And even though
there weren't a lot

1085
00:50:44,150 --> 00:50:47,180
of petabecquerels of
plutonium released,

1086
00:50:47,180 --> 00:50:48,650
they're alpha emitters.

1087
00:50:48,650 --> 00:50:51,380
And they're extremely
dangerous when ingested.

1088
00:50:51,380 --> 00:50:55,790
So greens and things
that uptake radionuclides

1089
00:50:55,790 --> 00:50:58,940
from the soil like moss and
mushrooms are totally off

1090
00:50:58,940 --> 00:51:02,440
limits in a large
range of this area.

1091
00:51:02,440 --> 00:51:04,230
You will find the
video online, if you

1092
00:51:04,230 --> 00:51:06,263
look, of a mayor from
a nearby town saying,

1093
00:51:06,263 --> 00:51:07,680
oh, they're perfectly
safe to eat.

1094
00:51:07,680 --> 00:51:09,030
Look, I eat them right here.

1095
00:51:09,030 --> 00:51:11,070
And I just say read
the comments for what

1096
00:51:11,070 --> 00:51:13,140
people have to say about that.

1097
00:51:13,140 --> 00:51:14,580
Not too smart.

1098
00:51:14,580 --> 00:51:15,290
Yeah.

1099
00:51:15,290 --> 00:51:17,076
AUDIENCE: So what's
the process now

1100
00:51:17,076 --> 00:51:20,953
for taking care of [INAUDIBLE]?

1101
00:51:20,953 --> 00:51:23,120
MICHAEL SHORT: So the
sarcophagus around the reactor

1102
00:51:23,120 --> 00:51:24,620
has got to be shored
up to make sure

1103
00:51:24,620 --> 00:51:26,010
that nothing else gets out.

1104
00:51:26,010 --> 00:51:28,500
Because most of the
reactor is still there.

1105
00:51:28,500 --> 00:51:30,390
And let's say rainwater
comes in and starts

1106
00:51:30,390 --> 00:51:32,670
washing away more stuff
into the ground or whatever.

1107
00:51:32,670 --> 00:51:34,230
We don't want that to happen.

1108
00:51:34,230 --> 00:51:37,560
Soil replacement and
disposal as nuclear waste

1109
00:51:37,560 --> 00:51:39,540
is still going on.

1110
00:51:39,540 --> 00:51:41,520
Removal of any moss,
lichen, mushrooms,

1111
00:51:41,520 --> 00:51:43,980
or anything with a sort
of radiation exposure

1112
00:51:43,980 --> 00:51:44,980
has got to keep going.

1113
00:51:44,980 --> 00:51:48,840
But the area that it
covers is enormous.

1114
00:51:48,840 --> 00:51:51,437
I don't know if we're ever
going to get rid of all of it.

1115
00:51:51,437 --> 00:51:53,520
The question is, how much
do we have to get rid of

1116
00:51:53,520 --> 00:51:57,510
to lower our risk of cancer in
the area to an acceptable rate?

1117
00:51:57,510 --> 00:51:59,430
There will likely
be parts of this

1118
00:51:59,430 --> 00:52:01,860
that are inaccessible for
thousands to tens of thousands

1119
00:52:01,860 --> 00:52:04,080
of years unless we
hopefully get smarter

1120
00:52:04,080 --> 00:52:06,990
about how to contain and
dispose of this kind of stuff.

1121
00:52:06,990 --> 00:52:08,350
We're not there yet.

1122
00:52:08,350 --> 00:52:11,220
So right now, the methods
are kind of simple.

1123
00:52:11,220 --> 00:52:12,630
Get rid of the soil.

1124
00:52:12,630 --> 00:52:14,070
Fence off the area.

1125
00:52:14,070 --> 00:52:16,560
Some folks have been returning.

1126
00:52:16,560 --> 00:52:18,852
And they do get compensation
and free medical visits

1127
00:52:18,852 --> 00:52:20,310
because the background
levels there

1128
00:52:20,310 --> 00:52:23,530
are elevated but not that high.

1129
00:52:23,530 --> 00:52:27,640
So folks have started to move
back to some of these areas.

1130
00:52:27,640 --> 00:52:31,010
But there's a lot that
are still off limits.

1131
00:52:31,010 --> 00:52:33,720
Any other questions?

1132
00:52:33,720 --> 00:52:34,255
Yeah.

1133
00:52:34,255 --> 00:52:37,437
AUDIENCE: It's way worse
than the atomic bombs dropped

1134
00:52:37,437 --> 00:52:39,810
on Hiroshima and
Nagasaki because those

1135
00:52:39,810 --> 00:52:42,617
are full-functioning
cities at this point.

1136
00:52:42,617 --> 00:52:43,450
MICHAEL SHORT: Yeah.

1137
00:52:43,450 --> 00:52:46,720
The number of deaths
from the atomic bombs way

1138
00:52:46,720 --> 00:52:48,880
outweighed the number
of deaths that will ever

1139
00:52:48,880 --> 00:52:49,820
happen from Chernobyl.

1140
00:52:49,820 --> 00:52:51,430
AUDIENCE: But why
is the radiation

1141
00:52:51,430 --> 00:52:53,755
from those bombs not--

1142
00:52:53,755 --> 00:52:55,630
MICHAEL SHORT: Oh, not
that much of an issue?

1143
00:52:55,630 --> 00:52:57,940
There wasn't that much material.

1144
00:52:57,940 --> 00:53:00,702
There wasn't that much nuclear
material in an atomic bomb.

1145
00:53:00,702 --> 00:53:03,160
What did you guys get for the
radius of the critical sphere

1146
00:53:03,160 --> 00:53:05,070
of plutonium?

1147
00:53:05,070 --> 00:53:06,765
AUDIENCE: [INAUDIBLE]
centimeters.

1148
00:53:06,765 --> 00:53:07,890
MICHAEL SHORT: Centimeters?

1149
00:53:07,890 --> 00:53:08,390
Yeah.

1150
00:53:08,390 --> 00:53:09,820
It doesn't take a lot.

1151
00:53:09,820 --> 00:53:14,360
It takes 10, 20 kilos
to make a weapon.

1152
00:53:14,360 --> 00:53:16,690
Now, we're talking
about tons or thousands

1153
00:53:16,690 --> 00:53:18,050
of tons of material released.

1154
00:53:18,050 --> 00:53:21,640
So an atomic weapon
doesn't kill by radiation.

1155
00:53:21,640 --> 00:53:25,330
It kills by pressure
wave, the heat wave.

1156
00:53:25,330 --> 00:53:27,850
The fallout is not
as much of a concern.

1157
00:53:27,850 --> 00:53:30,700
And we'll actually be looking
at the data from Hiroshima

1158
00:53:30,700 --> 00:53:32,380
and Nagasaki
survivors to see who

1159
00:53:32,380 --> 00:53:36,100
got what dose, what increased
cancer risk did they get,

1160
00:53:36,100 --> 00:53:40,300
and is the idea that every
little bit of radiation

1161
00:53:40,300 --> 00:53:42,040
is a bad thing actually true.

1162
00:53:42,040 --> 00:53:44,930
The answer is you
can't say yes or no.

1163
00:53:44,930 --> 00:53:48,660
No one can say yes or no because
we don't have good enough data.

1164
00:53:48,660 --> 00:53:51,513
The error bars support
either conclusion.

1165
00:53:51,513 --> 00:53:53,180
So I'm not going to
go on record and say

1166
00:53:53,180 --> 00:53:54,730
a little bit of radiation is OK.

1167
00:53:54,730 --> 00:53:55,943
They data is not out yet.

1168
00:53:55,943 --> 00:53:57,110
Hopefully, it never will be.

1169
00:54:00,850 --> 00:54:03,940
Any other questions?

1170
00:54:03,940 --> 00:54:04,850
All right.

1171
00:54:04,850 --> 00:54:06,960
I'll see you guys on Thursday.