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[00:22] All right. So, like I told you guys,
[00:24] Friday marked the end of the hardest
[00:26] part of the course and Monday marked the
[00:28] end of the hardest P set. So, because
[00:30] the rest of your classes are going full
[00:32] throttle, this one's going to wind down
[00:34] a little bit.
[00:35] So, today I'd say sit back, relax, and
[00:37] enjoy a nuclear catastrophe.
[00:39] Because we are going to explain what
[00:41] happened at Chernobyl. Now that you've
[00:43] got the physics and uh intuitive
[00:46] background to understand the actual
[00:48] sequence of events.
[00:50] To kick it off, I want to show you guys
[00:52] some actual footage
[00:54] of the Chernobyl reactor as it was
[00:56] burning. So, this is the part that most
[00:58] folks know about.
[01:09] This is footage taken from a helicopter
[01:10] from folks that were either surveying or
[01:12] dropping materials onto the reactor.
[01:25] That was probably a bad idea.
[01:29] Over where the smoke is. We'll get into
[01:31] what the smoke was.
[01:51] So, that
[01:52] red stuff right there, that's actually
[01:54] glowing graphite amongst other materials
[01:57] from the graphite fire that resulted
[01:59] from the R the RBMK reactor burning
[02:02] after the Chernobyl accident caused by
[02:04] both flaws in the physical design of the
[02:07] RBMK reactor and absolute operator
[02:10] stupidity and neglect of any sort of
[02:12] safety systems or safety culture. We're
[02:15] lucky to live here in the US where our
[02:16] worst accident at Three Mile Island was
[02:18] not actually really that much of an
[02:20] accident. There was a partial meltdown.
[02:22] There was not that much of a release of
[02:24] radionuclides into the atmosphere
[02:27] because we do things like build
[02:28] containments on our reactors. If you
[02:31] think of what a typical reactor looks
[02:32] like, like if you consider the MIT
[02:35] reactor as a scaled-down version of a
[02:37] normal reactor, or I
[02:39] let's say a commercial power reactor,
[02:41] you've got the core here. You've got a
[02:43] bunch of shielding around it.
[02:46] And you've got a dome
[02:48] that's rather thick
[02:52] that comprises the containment.
[02:57] That would be the core.
[02:59] This would be some shielding.
[03:03] So, this is what you find in US and most
[03:06] other reactors. For the RBMK reactors,
[03:10] there was no containment.
[03:14] Because it was thought that nothing
[03:16] could happen. And boy, were they wrong.
[03:19] So, I want to walk you guys through a
[03:21] chronology of what actually happened at
[03:23] the Chernobyl reactor, which you guys
[03:25] can read on the NEA or Nuclear Energy
[03:28] Agency website, the same place that you
[03:30] find Janice. And we're going to refer to
[03:32] a lot of the Janice cross sections to
[03:34] explain why these sorts of events
[03:35] happened.
[03:36] So, the whole point of what happened at
[03:38] Chernobyl was it was desired to see if
[03:41] you could use the spinning-down turbine
[03:44] after you shut down the reactor to power
[03:46] the emergency systems at the reactor.
[03:49] Uh this would be following something
[03:50] what's called a a loss of offsite power.
[03:53] If the offsite power or the grid was
[03:55] disconnected from the reactor, the
[03:57] reactor automatically shuts down. But
[03:59] the turbine, like I showed you a couple
[04:01] weeks ago, is this enormous spinning
[04:03] hulk of metal and machinery that coasts
[04:06] down over a long period of let's say
[04:08] hours. And as it's spinning, the
[04:10] generator coils are still spinning and
[04:13] still producing electricity, or they
[04:15] could be.
[04:16] So, it was desired to find out can we
[04:18] use the spinning-down turbine to power
[04:20] the emergency equipment if we lose
[04:22] offsite power?
[04:23] So, they had to simulate this event.
[04:25] So, what they actually decided to do is
[04:27] coast down the reactor to a moderate
[04:30] power level, a very low power, and see
[04:32] what comes out of the turbine itself, or
[04:35] out of the generator, rather.
[04:37] Um now, there were a lot of flaws in the
[04:40] RBMK design. And I'd like to bring it up
[04:42] here so we can talk about what it looks
[04:44] like and what was wrong with it.
[04:47] So, the RBMKs, unlike any of the
[04:50] United States light water reactors that
[04:52] you may have seen before, many of the
[04:54] components are the same. There's still
[04:56] uh light water reactor coolant loop
[04:58] where a water flows around fuel rods,
[05:01] goes into a steam separator, better
[05:03] known as a big heat exchanger, and the
[05:05] steam drives a turbine
[05:07] which produces energy, and then this
[05:09] coolant pump keeps it going, and then
[05:11] the water circulates. Uh what makes it
[05:13] different, though, is that each of these
[05:15] fuel rods was inside its own pressure
[05:18] tube. So, the coolant was pressurized,
[05:21] and out here,
[05:23] this stuff right here was the moderator,
[05:25] composed of graphite.
[05:27] Unlike light water reactors in the US,
[05:29] the coolant was not the only moderator
[05:31] in the reactor.
[05:33] Graphite also existed, which meant that
[05:35] if the water went away, which would
[05:37] normally shut down a light water reactor
[05:39] from lack of moderation, graphite was
[05:42] still there to slow the neutrons down
[05:44] into the high fission cross section
[05:46] area.
[05:48] And I'd like to pull up Janice
[05:50] and show you what I mean with the
[05:52] uranium cross section.
[05:55] So, let's go again to uranium 235
[05:58] and pull up its fission cross section.
[06:02] Z fission.
[06:08] Can make it a little thicker, too.
[06:10] So,
[06:12] again, the goal of the moderator is to
[06:14] take neutrons from high energies, like 1
[06:17] to 10 MeV, where the fission cross
[06:19] section is relatively low, and slow them
[06:21] down into this region where fission is,
[06:23] let's say, a thousand times more likely.
[06:26] And in a light water reactor in the US,
[06:28] if the coolant goes away, so does the
[06:30] moderation, and there's nothing left to
[06:33] slow those neutrons down to make fission
[06:35] more likely. In the RBMK,
[06:38] that's not the case. The graphite's
[06:39] still there.
[06:41] The graphite is cooled by a
[06:42] helium-nitrogen mixture
[06:44] because the neutron interactions in the
[06:46] graphite, that's slowing down,
[06:49] we've always talked about what happens
[06:50] from the point of view of the neutron.
[06:52] But what about the point of view of the
[06:53] other material?
[06:54] Any energy lost by the neutrons is
[06:57] gained by the moderating material. So,
[06:59] the graphite gets really hot. And you
[07:02] have to flow some non-oxygen-containing
[07:04] gas mixture, like helium and nitrogen,
[07:07] which is pretty inert, to keep that
[07:09] graphite cool.
[07:10] And then in between the graphite
[07:12] moderator were control rods, about 200
[07:15] of them or so, 30 of which were required
[07:17] to be down in the reactor at any given
[07:19] time in order to control power. And that
[07:21] was a design rule that was broken during
[07:24] the actual experiment. And then on top
[07:27] of here, on top of this biological
[07:28] shield, you could walk on top of it. So,
[07:31] those the tops of those pressure tubes,
[07:33] despite being about 350 kilo chunks of
[07:35] concrete,
[07:37] you could walk on top of them. It's
[07:38] pretty cool.
[07:40] Kind of scary, too.
[07:42] So, what happened in chronological order
[07:46] was around midnight the decision was
[07:48] made to undergo this test and start
[07:51] spinning down the turbine.
[07:53] Uh but the grid operator came back and
[07:55] said, "No, you can't just cut the
[07:57] reactor power to nothing. You have to
[07:59] maintain it at a rather high power for a
[08:01] while." About 500 megawatts electric, or
[08:04] half the rated power of the reactor. And
[08:06] what that had the effect of doing is
[08:08] continuing to create fission products,
[08:11] including xenon 135.
[08:13] We haven't mentioned this one yet.
[08:16] You'll talk about it quite a lot
[08:18] in 2205
[08:20] in neutron physics.
[08:22] Black shirt really shows chalk well.
[08:24] Okay.
[08:25] What xenon 135 does is it just sits
[08:27] there. It's a noble gas. It has a
[08:29] half-life of a few days, so it decays on
[08:32] the slow side for,
[08:34] you know, fission as fission products
[08:35] go, but it also absorbs lots and lots
[08:38] and lots of neutrons.
[08:41] Let's see if I can find which one is the
[08:42] xenon one. There we go.
[08:44] So, here I've plotted the total cross
[08:47] section for xenon 135 and the absorption
[08:51] cross section.
[08:52] And notice how for low energies, pretty
[08:54] much the entire cross section of xenon
[08:56] is made up of absorption. Did you guys
[08:58] in your homework see anything that
[09:00] reached about 10 million barns?
[09:03] No.
[09:03] Xenon 135 is one of the best neutron
[09:05] absorbers there is, and reactors produce
[09:07] it constantly. So, as they're operating,
[09:10] you'll build up xenon 135 that you have
[09:13] to account for in your sigma absorption
[09:15] cross section.
[09:17] Cuz like you guys saw on the homework,
[09:20] if you want to write what's the sigma
[09:21] absorption cross section of the reactor,
[09:24] it's the sum
[09:26] of every single isotope in the reactor
[09:28] of its number density
[09:31] times
[09:32] its absorption cross section.
[09:34] And so, that would include everything
[09:36] for
[09:37] water
[09:39] and let's say the uranium and the xenon
[09:42] that you're building up.
[09:44] When the reactor starts up, the number
[09:46] density of xenon is zero cuz you don't
[09:48] have any anything to have produced it.
[09:50] When you start operating, you'll reach
[09:52] the xenon equilibrium level where it
[09:55] will build to a certain level that will
[09:57] counteract the reactivity of the
[09:59] reactor.
[10:00] And in your K effective expression
[10:03] where it's sources
[10:06] over
[10:07] absorption plus leakage
[10:11] this has the effect of rise at raising
[10:13] sigma absorption and lowering K
[10:15] effective.
[10:17] The trick is it doesn't last for very
[10:18] long. It both decays with a half-life of
[10:20] about 5 days and when you try and raise
[10:23] the reactor power you will also start to
[10:25] burn it out. So if you're operating at a
[10:27] fairly low power level, you'll both be
[10:29] decaying and burning xenon without
[10:32] really knowing what's going on and
[10:33] that's exactly what happened here.
[10:35] So an hour or so later
[10:38] let me pull up the chronology again.
[10:40] A little more than an hour later, so the
[10:42] reactor power stabilized at something
[10:43] like 30 MW.
[10:45] And they were like, "What is going on?
[10:47] Why is the reactor power so low? We need
[10:49] to increase the reactor power." So what
[10:51] did they do? Couple things. One was
[10:54] remove all but six or seven of the
[10:55] control rods.
[10:57] Going way outside the spec of the design
[11:01] uh because 30 were needed to actually
[11:02] maintain the reactor at a stable power.
[11:05] All the while the xenon that had been
[11:07] building up is still there keeping the
[11:10] reactor from going critical. It's what
[11:11] was the main reason that the reactor
[11:13] didn't even have very much power.
[11:16] But it was also burning out at the same
[11:17] time.
[11:18] So all the while
[11:20] let's say if we were to show a graph of
[11:23] two things, time
[11:25] xenon inventory and
[11:29] as a solid line and let's say control
[11:31] rod worth
[11:35] as a dotted line.
[11:37] The xenon inventory at full power would
[11:39] have been at some level and then it
[11:42] would start to decay and burn out. Well,
[11:45] at the same time the control rod worth
[11:47] as you remove control rods from the
[11:49] reactor
[11:51] every time you remove one you lose some
[11:52] control rod worth would continue to
[11:55] diminish.
[11:56] Leading to the point where that stuff
[11:58] was going to happen.
[12:02] Let me make sure I didn't lose my place.
[12:04] So at any rate as they started pulling
[12:06] the control rods out a couple of
[12:08] interesting quirks happened in terms of
[12:10] feedback. So let's look back at this
[12:11] design.
[12:12] Like any reactor
[12:14] this reactor had what's called a
[12:16] negative fuel temperature coefficient.
[12:18] What that means is that
[12:20] when you heat up the fuel
[12:22] two things happen. One, the
[12:24] cross-section for anything absorption or
[12:26] fission would go up but the number
[12:28] density would also go down. As the atoms
[12:31] physically spaced out in the fuel, their
[12:34] number density would go down lowering
[12:36] the macroscopic cross-section for
[12:38] fission. And that's arguably a good
[12:40] thing.
[12:41] The problem is at below about 20% power
[12:45] the reactor had what's called a positive
[12:46] void coefficient
[12:48] which meant that if you boil the coolant
[12:50] you increase the reactor power.
[12:53] Because the other thing that I think I
[12:54] mentioned this once
[12:56] and you calculated in the homework
[13:00] the absorption cross-section of hydrogen
[13:03] is not zero. It's small but fairly
[13:06] significant. Let's actually take a look
[13:08] at it cuz we can always see this in
[13:11] Janus.
[13:12] Go back down to hydrogen.
[13:15] Hydrogen one.
[13:18] And we look at the absorption
[13:20] cross-section.
[13:24] And of course it started us with a
[13:25] linear scale. Let's go logarithmic. Ah.
[13:29] So at low energies at you know, 10 to
[13:32] the minus eight to 10 to the minus seven
[13:33] it's around a barn.
[13:35] Not super high but absolutely not
[13:37] negligible.
[13:39] Which meant that part of the normal
[13:40] functionality of the RBMK depending on
[13:43] depended on the absorption of the water
[13:46] to help absorb some of those neutrons.
[13:48] With those neutrons gone, I'm sorry,
[13:50] with those with that water gone
[13:53] there was less absorption but there was
[13:54] still a ton of moderation
[13:56] in this graphite moderator. So they
[13:58] still could get slow but then there'd be
[14:00] more of them and that would cause the
[14:01] power to increase. And then that caused
[14:03] more of the water the coolant to boil
[14:06] which would cause less absorption which
[14:08] would cause the power to increase. Yeah,
[14:10] Charlie? So if they removed the water
[14:12] from
[14:14] They did not remove the water from the
[14:16] reactor. However, as the power started
[14:18] to rise some of the water started to
[14:20] boil.
[14:22] And so you can still have let's say
[14:23] steam flowing through
[14:25] and still remove some of the heat.
[14:27] However, you don't have that denser
[14:29] water to act as an absorber.
[14:31] And that's what really undid this
[14:32] reactor. In addition, they decided to
[14:35] disable the ECCS or the emergency core
[14:38] cooling system which you're just not
[14:39] supposed to do.
[14:41] So they shut down a bunch of these
[14:42] systems to see if you could power the
[14:43] other ones from the spinning down
[14:44] turbine.
[14:46] And then as they noticed that the
[14:48] reactor was getting less and less stable
[14:49] they had almost all the rods out. Some
[14:53] of these pressure tubes started to bump
[14:56] and jump. These 350 kg pressure tube
[15:00] caps were just rattling. I mean imagine
[15:02] something that weighs you know, 900 lb
[15:05] or so rattling around and there's a few
[15:08] hundred of them. So there was someone in
[15:09] the control room that said, "The caps
[15:11] are rattling. What the heck?"
[15:14] Uh didn't quite make it down the spiral
[15:16] staircase because about 10 seconds later
[15:19] everything went wrong.
[15:21] And so I want to pull up this actual
[15:22] timeline so you can see
[15:24] it splits from minutes to seconds
[15:27] because the speed at which this stuff
[15:29] started to go wrong was pretty striking.
[15:33] So for example, the control rods raised
[15:35] at 1:19 in the morning.
[15:38] 2 minutes later
[15:40] when the power starts to become unstable
[15:42] the caps on the fuel channels which
[15:43] again are like 350 kg blocks start
[15:47] jumping in their sockets.
[15:48] And a lot of that was we go back to the
[15:51] RBMK reactor.
[15:53] As the coolant started to boil here,
[15:55] well that boiling force actually creates
[15:57] huge pressure instabilities which would
[15:59] cause the pressure tubes to jump up and
[16:02] down eventually rupturing almost every
[16:04] single one of them with enough force to
[16:06] shoot these 350 kilo caps
[16:09] and still what did they what did they
[16:10] say? I like the language that they used.
[16:14] Jumping in their sockets.
[16:16] So
[16:17] 50 seconds later
[16:19] pressure fails in the steam drums which
[16:21] means there's been some sort of
[16:22] containment leak. So all the while
[16:25] the coolant was boiling, the absorption
[16:27] was going down, the power was going up
[16:30] repeat, repeat, repeat and the power
[16:32] jumped to about 100 times the rated
[16:34] power in something like 4 seconds.
[16:37] So it was normally a 1000 MW electric
[16:39] reactor which is about 3200 MW thermal.
[16:42] It was producing nearly
[16:45] yeah, half a terawatt of thermal power
[16:48] for a very short amount of time until it
[16:50] exploded.
[16:52] Now this is interesting. A lot of folks
[16:53] called Chernobyl a nuclear explosion.
[16:55] That's actually a misnomer. A nuclear
[16:57] explosion would be a nuclear weapon.
[17:00] Something set off by an enormous chain
[17:02] reaction principally heated by fission
[17:05] or fusion. That's not actually what
[17:07] happened at Chernobyl nor at Fukushima
[17:10] nor was that the worry at Three Mile
[17:11] Island. Not to say it wasn't a horrible
[17:14] thing but it wasn't an actual nuclear
[17:16] explosion.
[17:17] At first what happened was a pressure
[17:20] explosion.
[17:21] So there was an enormous release of
[17:24] steam as the power built up to 100 times
[17:27] normal operating power the steam force
[17:30] was so large that it actually blew the
[17:32] reactor lid
[17:34] up off of the thing.
[17:35] And I think I have a picture of that
[17:37] somewhere here too.
[17:42] Should be further down. Yeah. To give
[17:44] you a little sense of scale
[17:46] the reactor cover which weighed about
[17:47] 1000 tons launched into the air
[17:50] and landed above the reactor
[17:52] sending most of the reactor components
[17:54] up to a kilometer up in the air.
[17:56] 4 seconds later
[17:59] that was followed by a hydrogen
[18:01] explosion.
[18:02] Let me get back down to that chronology.
[18:05] So yeah.
[18:07] At 1:23 and 40 seconds in the morning.
[18:10] Oh yeah, so I should mention why this
[18:11] happened. Emergency insertion of all the
[18:13] control rods.
[18:15] The last part that this diagram doesn't
[18:17] mention is these control rods and I'll
[18:19] draw this up here were tipped with about
[18:21] 6 in of graphite.
[18:23] So if these were two graphite channels,
[18:26] let's say these are carbon
[18:29] and this is your control rod the goal
[18:31] was to get this control rod
[18:34] all the way into the reactor.
[18:37] One part they didn't mention
[18:39] was they were tipped with about 6 in of
[18:41] graphite which only functions as
[18:43] additional moderator. Graphite is one of
[18:46] the lowest absorbing materials in the
[18:48] periodic table, second I think only to
[18:50] oxygen.
[18:51] And if we pull up graphite's
[18:53] cross-sections
[18:57] I've plotted here the total
[18:58] cross-section
[18:59] the elastic scattering cross-section and
[19:01] down here in the point 001 barn level is
[19:05] the absorption cross-section. About 1000
[19:08] times lower than water. So you're
[19:09] shoving more material in the reactor
[19:11] that slows down neutrons even more
[19:13] bringing them into the high fission
[19:14] region without absorbing anything and
[19:17] they jammed about halfway down, about 2
[19:19] and 1/2 ft down leaving the extra
[19:22] graphite right in the center of the core
[19:24] where it could do the most damage. And
[19:26] it didn't take that much time. Yeah? Um
[19:28] so my understanding is that also one of
[19:30] the designs was that the control rods
[19:32] didn't like immediately drop down but
[19:34] they were slowly lowered. Yep. Um so
[19:36] They took they took 7 to 10 seconds.
[19:38] Okay, if they had a system where they
[19:39] did drop them would that have possibly
[19:41] actually shut the system down properly?
[19:43] I'm not sure. I don't know whether
[19:45] lowering control rods into something
[19:47] that was undergoing steam explosions
[19:49] would have actually helped. I mean to me
[19:51] by this point it was all over.
[19:53] Um
[19:54] whether or not, you know, so the extra
[19:56] the extra abs- what is it? The extra
[19:58] moderator that was dumped in was the
[20:00] last kick in the pants this thing needed
[20:01] to go absolutely insane.
[20:04] And if we go back to the timeline on the
[20:06] second level, control rods inserted at
[20:08] 1:23 and 40 seconds, explosion 4 seconds
[20:12] later. Ah, to 120 times full power.
[20:16] Getting towards a terawatt, so. 1 second
[20:18] later, the 1,000 ton lid launches off
[20:22] from the first explosion.
[20:24] Very shortly after that, second
[20:26] explosion. And that happened because of
[20:29] this reaction.
[20:32] Well, any- just about anything
[20:35] corroding with water will make pretty
[20:38] much anything oxide
[20:41] plus hydrogen. The same chemical
[20:43] explosion that was the undoing of
[20:45] Fukushima and was the worry at Three
[20:47] Mile Island that there was a hydrogen
[20:49] bubble building because of corrosion
[20:51] reactions with whatever happened to be
[20:53] in the core. This happens with zirconium
[20:55] pretty vigorously, but it happens with
[20:57] other materials, too.
[20:58] If you oxidize something with water, you
[21:01] leave behind the hydrogen, and the
[21:02] hydrogen in a very wide range of
[21:05] concentrations in the air is explosive.
[21:08] We're actually not allowed to use
[21:09] hydrogen at above 4% in any of the labs
[21:12] here because that reaches the
[21:13] flammability or explosive limit.
[21:16] So, we were doing some um for my PhD, we
[21:18] were doing these experiments corroding
[21:20] materials in liquid lead, and we wanted
[21:22] to dump in pure hydrogen to see what
[21:24] happens when there's no oxygen. We were
[21:26] told absolutely not. We had to drill a
[21:28] hole in the side of the wall so that the
[21:30] hydrogen would vent outside. And do some
[21:32] calculations to show if the entire
[21:34] bottle of hydrogen emptied into the lab
[21:36] at once, which it could do if the cap of
[21:38] the bottle breaks off, it would not
[21:40] reach 4% concentration.
[21:42] So, hydrogen explosions are pretty
[21:44] powerful things. Have you guys ever seen
[21:46] people making water from scratch?
[21:48] Mix hydrogen and oxygen in the bottle
[21:50] and
[21:51] light a match?
[21:52] We've got a video of it circulating
[21:54] somewhere around here because for RTC,
[21:56] for the reactor technology course, I do
[21:58] this in front of a bunch of CEOs. Watch
[22:00] them jump out of their chairs
[22:01] to teach basic chemical reactions, but
[22:03] it's pretty loud. Enough uh about enough
[22:06] hydrogen and oxygen
[22:08] to just fill this cup or fill a half
[22:10] liter water bottle makes a bang that
[22:12] gets your ears ringing. Not quite
[22:13] bleeding, but close enough.
[22:16] So, that's what happened here, except on
[22:17] a much more massive scale. So, there was
[22:19] a steam explosion followed seconds later
[22:22] by a hydrogen explosion from hydrogen
[22:24] liberated from the corrosion reaction of
[22:26] everything with the water that was
[22:28] already there.
[22:29] And that's when
[22:33] this happened.
[22:54] So, that smoke right there
[22:57] is from the graphite fire.
[22:59] Not normal smoke.
[23:20] Spoke too soon.
[23:53] This actually provides a perfect conduit
[23:55] to transition from the second to the
[23:56] third parts of this course. A lot of you
[23:58] have been waiting to find out what are
[23:59] the units of dose and what are the
[24:01] biological and chemical effects of
[24:02] radiation. Well, this is where you get
[24:04] them. From neutron physics, you can
[24:06] understand why Chernobyl went wrong.
[24:09] With honestly, you've just been doing
[24:10] this for three or four weeks, but with
[24:12] your knowledge of cross sections,
[24:13] reactor feedback, and criticality, you
[24:15] can start to understand why Chernobyl
[24:17] was flawed in its design. And what we're
[24:19] going to teach you in the rest of the
[24:20] course is what happens next. What
[24:23] happens when radionuclides are absorbed
[24:25] by animals and the human body? And what
[24:27] was the main fallout, let's say, in the
[24:30] in the uh
[24:31] colloquial sense and the actual sense
[24:34] from the Chernobyl reactor.
[24:37] Let's look a bit what they did next,
[24:38] though.
[25:45] That's not quite true. We'll see why.
[25:58] That actually did happen.
[26:08] I think that pretty much summarizes the
[26:10] state of things now.
[26:11] They uh they built a sarcophagus around
[26:13] this reactor, a gigantic tomb, which
[26:16] according to some reports is not that
[26:18] structurally sound and is in danger of
[26:20] partial collapse.
[26:22] So, yeah, more difficult efforts are
[26:24] ahead. But let's now talk about
[26:27] what happened next.
[26:29] I'm going to jump to the very end of
[26:31] this. The actual way that the accident
[26:33] was noticed
[26:35] was the spread of the radioactive cloud
[26:37] to not so close by Sweden.
[26:41] So, it was noticed that folks entering a
[26:43] reactor in Sweden had contaminants on
[26:45] them, which they thought was coming from
[26:47] their own reactor, good first
[26:48] assumption. When it was determined that
[26:50] nothing was amiss at the reactor in
[26:51] Sweden, folks started to analyze wind
[26:54] patterns and find out what happened, and
[26:55] then it was clear that the USSR had
[26:57] tried to cover up the Chernobyl
[26:59] accident. But you can't cover up
[27:01] fallout. And it eventually spread
[27:04] pretty wide
[27:05] covering most of Europe and Russia and
[27:08] surprisingly not Spain. Lucky them for
[27:11] the wind patterns that day or those few
[27:13] days.
[27:14] So, what happened is a few days after
[27:16] the actual accident, a graphite fire
[27:19] started to break out because graphite
[27:21] when exposed to air, well, you can do
[27:23] the chemistry.
[27:25] Add graphite plus oxygen,
[27:29] you start making carbon dioxide.
[27:32] So, graphite burns when it's hot. And as
[27:34] you could see from the video,
[27:39] where is that nice still of
[27:42] mol- burning graphite? Yeah. That
[27:44] graphite was pretty hot. So, a lot of
[27:45] that smoke included burning graphite and
[27:48] a lot of the materials from the reactor
[27:50] itself.
[27:51] Now, when you build up fission products
[27:53] in a reactor and they get volatilized
[27:55] like this, the ones that tend to get out
[27:57] first would be things like the noble
[27:58] gases. So, the whole xenon inventory of
[28:00] the reactor was released. It's estimated
[28:03] about 100%.
[28:05] And I can actually pull up those figures
[28:08] when we talk about how much of which
[28:10] radionuclide was released.
[28:12] Uh that's also a typo. If somebody wants
[28:14] to call in, there's no 33 isotope of
[28:17] xenon. It's supposed to be 133.
[28:20] Um that would be interesting if someone
[28:21] wants to call in and say the NAA's got a
[28:23] mistake.
[28:24] So, 100% of the inventory released. That
[28:27] should be pretty obvious because it's a
[28:28] noble gas and it just kind of floats
[28:30] away.
[28:31] The real dangers, though, came from
[28:33] iodine 131,
[28:35] about 50%
[28:37] of a three exabecquerel activity.
[28:41] So, we're talking like megacuries or
[28:43] might be giga. I can't do that math in
[28:45] my head. Lot a lot of radiation. And the
[28:47] problem with that is iodine behaves just
[28:49] like any other halogen. It forms salts.
[28:52] It's rather volatile. Have any of you
[28:54] guys played with iodine before?
[28:57] Uh no one does Oh, you have. Okay. What
[28:59] happens when you play with it? I mean,
[29:01] it just
[29:02] absorbs the stuff like
[29:04] for instance, everything
[29:07] and it just reacts with like acids and
[29:10] stuff. I haven't done very much with it,
[29:12] so. Okay.
[29:13] I happen to have extensive practice
[29:15] playing with iodine in my home cuz I did
[29:17] all the stuff you're not supposed to do
[29:18] as a kid. Going to build your own
[29:19] chemistry stuff, things that somehow,
[29:21] you know, leak out of your local high
[29:22] school, somehow.
[29:24] Iodine's pretty neat.
[29:27] Yeah, it happens sometimes. Um if you
[29:29] put iodine in your hand, it actually
[29:31] sublimes. The heat from your hand is
[29:33] enough to directly go from solid to
[29:35] vapor. And so, the iodine was also quite
[29:39] volatile. Some of it may have been in
[29:40] the form of other compounds, some of it
[29:42] may have been elemental, probably not
[29:44] likely, but there was certainly some
[29:45] iodine vapor, and about half of that was
[29:47] released. The problem is then it
[29:50] condenses out and falls on anything
[29:53] green, anything with surface area. So,
[29:56] the biggest danger to the folks living
[29:57] nearby was from eating leafy vegetables
[30:01] because the the leaves that leaves got
[30:03] lots of surface area, iodine deposits on
[30:05] them, and it's intensely radioactive for
[30:07] a month or so or depositing on the grass
[30:10] that cows eat, which led to the problem
[30:12] of radioactive milk.
[30:14] And so, that's why milk in the Soviet
[30:16] Union was banned for such a long time
[30:17] because this was one of the major
[30:19] sources of iodine contamination.
[30:22] The other one which we're worrying about
[30:23] now from Fukushima as well is cesium
[30:27] which has similar chemistry to sodium
[30:29] and potassium, again a rather salty
[30:31] compound
[30:33] or rather salty element, but it's got a
[30:34] half-life of 30 years.
[30:37] And if we look it up in the table of
[30:38] nuclides
[30:40] we'll see what it actually releases. Oh,
[30:42] good. It's back online.
[30:45] Anyone else notice this broken couple
[30:47] days ago?
[30:48] Yeah.
[30:50] Well, luckily Brookhaven National Lab
[30:52] has a good version up, too. But, let's
[30:54] grab cesium.
[30:57] Yeah, there's plenty out there.
[31:00] Cesium 137
[31:02] beta decays to barium, but also gives
[31:04] off gamma rays, and most of the decays
[31:07] end up giving off one of those gamma
[31:10] rays. Let's say a 660 keV gamma ray. So,
[31:13] it's both a beta and a gamma emitter.
[31:15] Now, which of those types of radiation
[31:17] do you think is more damaging to
[31:18] biological organisms?
[31:20] The beta or the gamma?
[31:24] You say the gamma. Why do you say so?
[31:27] Doesn't beta get stopped by like skin or
[31:28] clothing? It does.
[31:30] But, if cesium is better known as
[31:33] Yes.
[31:35] That's right. So Did I get to tell you
[31:37] guys this question, the four cookies
[31:39] question?
[31:41] Yeah.
[31:42] You eat the gamma cookie because most
[31:44] gammas that are emitted by the cookie
[31:46] simply leave you and irradiate your
[31:47] friend, which is going to be the topic
[31:48] of piece at number eight.
[31:51] You'll see. That's why you guys are
[31:52] getting your whole body counts. Speaking
[31:54] of, who's who's gotten their whole body
[31:56] counts at DHS?
[31:58] Awesome. So, that's almost everybody.
[32:00] You will need that data for problem set
[32:02] eight. So, do schedule it soon.
[32:04] Preferably before Thanksgiving so that
[32:06] you'll be able to take a look at it. Has
[32:08] anyone found anything interesting in
[32:09] your spectra?
[32:12] Good.
[32:14] Glad to hear that.
[32:15] But, you do see a potassium peak that
[32:18] you can probably integrate and do some
[32:20] problems with, right?
[32:22] Yeah, cuz you will. Okay.
[32:24] Anyway, yeah, it's the betas. That's the
[32:27] real killer. The gammas are going to
[32:29] leave the cesium, enter your body, and
[32:31] most likely come out the other side.
[32:33] Because the mass attenuation coefficient
[32:37] of six What is it? Water for 660 keV
[32:41] gammas, let's find that.
[32:44] Table three.
[32:46] Let's say you're made mostly of water.
[32:53] Water, liquid. That's pretty much
[32:55] humans.
[32:56] 660 keV is right about here leading to
[32:59] about 0.1 cm squared per gram, and with
[33:03] a density of 1 g, that's a pretty low
[33:06] attenuation of gammas. So, this chart
[33:08] actually shows why most of the cesium
[33:10] gammas that would be produced from
[33:12] ingestion just get right out, but it's
[33:13] the betas that have an awfully short
[33:15] range.
[33:17] Anyone remember the formula for range
[33:20] in general?
[33:22] Cuz it's going to come back up in our
[33:23] discussion of dose and biological
[33:25] effects.
[33:29] Integral of
[33:32] Yep, of stopping power to the negative
[33:33] one.
[33:36] And that stopping power
[33:38] is this simple formula.
[33:49] Let's see. What did that come out as?
[33:57] log minus beta squared. Ah, simple
[34:00] little formula.
[34:01] Which I'm not going to expect you guys
[34:03] to memorize, so don't worry about it.
[34:05] But
[34:06] if you integrate this, you find out that
[34:07] the range of electrons, even 1 MeV
[34:09] electrons in water, is not very high.
[34:11] So, most of them are stopped near or by
[34:14] the cells that absorb them doing quite a
[34:17] bit of damage to the DNA, which is
[34:19] eventually what causes mutagenic
[34:21] effects, cancer, cell death what we're
[34:24] going to talk about for the whole third
[34:25] part of the course.
[34:28] There's also
[34:29] a worry about which organs actually
[34:32] absorb these radionuclides, and iodine
[34:35] in particular is preferentially absorbed
[34:38] by the thyroid.
[34:39] So, when we started looking at the
[34:40] amount of radioactive substances
[34:43] released, remember they said, "Okay, at
[34:44] the round
[34:46] 26th of April or the 2nd of May or so,
[34:48] the release was stopped." Not according
[34:50] to our data. That's when the graphite
[34:52] fire picked up again. In addition, the
[34:55] core of Chernobyl which had undergone a
[34:58] mostly total meltdown
[35:01] was sitting in a pool
[35:04] on top of this concrete pad.
[35:07] So, let's just call this liquid stuff
[35:09] The actual word that we use in parlance
[35:11] is called corium.
[35:13] It's our tongue-in-cheek word for every
[35:15] element mixed together in a hot
[35:17] radioactive soup.
[35:19] It's First of all, it started to
[35:20] redistribute reacting with any water
[35:22] that was present, flashing it to steam,
[35:24] and the steam caused additional
[35:26] dispersion of radionuclides, and
[35:28] eventually
[35:29] it burrowed its way through and into the
[35:31] ground
[35:32] releasing more. You know, it's it's uh
[35:35] it's the worst nuclear thing that's ever
[35:37] happened in the history of nuclear
[35:38] things.
[35:40] Quite a mess.
[35:42] And luckily, it did sort of taper off
[35:44] after this.
[35:46] But, let's now look into
[35:48] what happens next. And this is the nice
[35:51] intro to the third part of the course.
[35:53] Iodine is is preferentially uptaken by
[35:55] the thyroid gland somewhere right about
[35:57] here.
[35:58] Um so, has anyone ever heard of the idea
[36:00] of taking iodine tablets in the case of
[36:02] a nuclear disaster?
[36:04] Anyone have any idea why?
[36:09] If you saturate your thyroid with
[36:11] iodine, then if you ingest radioactive
[36:13] iodine, it's less likely to be
[36:15] permanently uptaken by the thyroid. So,
[36:18] this actually provided some statistics
[36:21] on the probability of getting thyroid
[36:23] cancer from radioactive iodine
[36:26] ingestion.
[36:27] Luckily, the statistics were quite poor,
[36:29] which means that not many people were
[36:31] exposed. It was somewhere around 1,300
[36:34] or so.
[36:35] Not like millions. Yeah, 1,300 people
[36:38] total.
[36:39] But, what I want to jump to is the dose
[36:42] versus risk curve. And this is going to
[36:44] apply all of our discussion about the
[36:47] biological long-term effects of
[36:49] radioactivity.
[36:50] What's the most striking thing you see
[36:53] as part of this curve?
[36:56] That's That's right. That's the first
[36:58] thing I saw.
[37:00] There are six different models for how
[37:03] dose and increased risk of cancer
[37:05] proceeds, and they all fall within
[37:07] almost all the error bars of these
[37:09] measurements.
[37:11] I'll say again, thank God that the error
[37:13] bars are so high because that means that
[37:15] the sample size was so low.
[37:17] So, when folks say we don't really know
[37:19] how much radioactivity causes how much
[37:22] cancer, they're right because luckily,
[37:24] we don't have enough data from people
[37:26] being exposed to know that really,
[37:28] really well.
[37:29] So, some folks say we should be
[37:31] cautious. I kind of agree with them.
[37:33] Some folks say the jury's still out. I
[37:35] also agree with them.
[37:37] But, you can start to estimate these
[37:39] sorts of things by knowing how much
[37:41] radiation energy was absorbed and to
[37:44] what organ.
[37:45] So, I think the only technical thing I
[37:47] want to go over today
[37:49] is the different units of dose because
[37:51] as you start to read things in the
[37:52] reading, which I recommend you do if you
[37:54] haven't been doing yet, you're going to
[37:55] encounter a lot of different units of
[37:57] radiation dose ranging from things like
[38:00] the roentgen
[38:04] which responds to a number of
[38:06] ionizations.
[38:10] You won't usually see this one
[38:12] given in sort of biological parlance
[38:15] because it's the number of ionizations
[38:17] detected by some sort of gaseous
[38:19] ionization detector. So, the dosimeters
[38:21] that you all put on the Did you guys all
[38:23] bring these uh
[38:25] these like brass
[38:27] pen dosimeters into the reactor? Anyone
[38:29] look through them to see what the unit
[38:30] of dose was?
[38:33] It's going to be in roentgens cuz that's
[38:34] directly correlatable to the number of
[38:37] ionizations that that dosimeter has
[38:39] experienced. You'll also see four dose
[38:42] units, two of which are just factors of
[38:44] 100 away from each other. There is
[38:46] what's called the rad and the gray
[38:49] and there's what's called the rem
[38:52] and the sievert.
[38:57] You'll see these approximated as gray.
[39:00] You'll see these as R, and these are
[39:03] just usually written as rem.
[39:05] So, a rad is simple.
[39:08] Let's see.
[39:10] 100 rads
[39:13] is the same as 1 gray.
[39:15] And 100 rem
[39:17] is the same as 1 sievert. And for gamma
[39:20] for the case of gamma radiation
[39:23] these units are actually equal.
[39:26] I particularly like this set of units
[39:28] because
[39:30] this is the kind of SI of radiation
[39:32] units because it comes directly from
[39:34] measurable, calculatable quantities.
[39:36] Like the gray, for example, the actual
[39:38] unit of gray
[39:40] is joules absorbed
[39:42] per kilogram of absorber.
[39:45] It's a pretty simple unit to understand.
[39:47] If you know how many radioactive
[39:49] particles or gammas or whatever that you
[39:52] have absorbed, you can multiply that
[39:54] number by their energy, divide by the
[39:56] mass of the organ absorbing them, and
[39:59] you get its dose in gray.
[40:01] Sievert
[40:02] is gray
[40:04] times some quality factor for the
[40:07] radiation
[40:10] times some quality factor
[40:14] for the specific type of tissue.
[40:17] What this says is that some types of
[40:20] radiation are more effective at causing
[40:22] damage than others, and some organs are
[40:25] more susceptible to radiation damage
[40:27] than others. Does anyone happen to know
[40:29] some of the organs that are most
[40:31] susceptible to radiation damage?
[40:38] Soft tissues like what? Cuz there's lots
[40:40] of those.
[40:43] Stomach lining, yep. Yep. Huh?
[40:46] Lungs? Yep. What else?
[40:51] Thyroid. Yep, there there is definitely
[40:53] one for thyroid.
[40:55] Bone marrow.
[40:57] What other ones?
[41:00] Y'all,
[41:01] brain actually not so much. Eyes.
[41:05] And where else do you find rapidly
[41:07] dividing cells in your body?
[41:10] Skin? Yep, the dermis.
[41:14] I don't know about the liver. I would
[41:16] assume so. Yeah, it's a pretty active
[41:17] organ.
[41:19] But when folks are worried about birth
[41:20] defects
[41:22] reproductive organs.
[41:24] The link here that for some reason is
[41:26] not said in the reading and I've never
[41:28] figured out why is the more often a cell
[41:30] is dividing the more susceptible it is
[41:33] to gaining cancer risk because every
[41:35] cell division is a copy of its DNA.
[41:38] And anytime that radiation goes in and
[41:41] damages or changes that DNA by either
[41:44] causing what's called a thymine bridge
[41:45] where two thymine bases get linked
[41:47] together or damaging the structure in
[41:49] some other way, that gene is then
[41:52] replicated and the faster they're
[41:54] replicating the more likely cancer is
[41:56] going to become apparent.
[41:59] I guess that this brings up a question,
[42:01] when does a rapidly dividing cell become
[42:03] cancer? Is it division number one or is
[42:05] it when you notice it?
[42:07] I guess I'll leave that question to the
[42:08] biologists.
[42:10] But if you notice in the reading you'll
[42:12] see a bunch of different tissue
[42:13] equivalency factors.
[42:15] And you'll just see them tabulated and
[42:17] say there they are, memorize them. I
[42:19] want you to try and think of the pattern
[42:21] between them. The tissues that basically
[42:23] don't matter like the non-marrow part of
[42:26] the bone, dead skin cells, muscles,
[42:29] things that basically aren't listed that
[42:31] much, they're not dividing very fast.
[42:33] But anywhere where you find stem cells,
[42:35] the lining of your intestine, your lungs
[42:38] which undergo a lot of environmental
[42:40] damage need to be replenished, gonads,
[42:42] dermis, what was the other one that we
[42:44] said? Eyes.
[42:46] These are places that are either
[42:47] sensitive tissues or they're rapidly
[42:49] dividing.
[42:51] And so the sievert is kind of an a unit
[42:54] of increased equivalent risk. So that if
[42:57] you were to absorb one gray of gamma
[42:59] rays versus one gray of alphas, you'd be
[43:03] about 20 times more likely to incur
[43:05] cancer from the alphas than the gammas
[43:07] because the amount of localized damage
[43:09] that they do to cells. And we'll be
[43:10] doing all this in detail pretty soon.
[43:13] And then for tissue equivalency factor,
[43:15] if you absorb one gray in your whole
[43:18] body, which means one joule per kilogram
[43:20] of average body mass
[43:22] versus one gray directly to the lining
[43:24] of your intestine by let's say drinking
[43:27] polonium-laced tea
[43:29] like happened to a poor ex was it
[43:32] current or ex-KGB guy? One of the
[43:34] Russian fellows?
[43:35] No, it's the KGB guys that poisoned him,
[43:37] right?
[43:38] Yeah, you guys remember back in 2010 or
[43:40] so?
[43:41] There was a Russian
[43:43] Was he a journalist?
[43:46] Ex-KGB. So the current KGB somehow got
[43:49] into London and slipped polonium into
[43:51] his tea at a Japanese restaurant.
[43:56] Uh, really?
[44:01] What was his name?
[44:04] Let's see.
[44:08] Then polonium
[44:12] poisoning. Did he actually die?
[44:14] Poisoning of Alexander Litvinenko.
[44:23] He's not doing too well.
[44:27] Illness and poisoning, death and last
[44:29] statement.
[44:32] At the hospital in London. So, yeah.
[44:37] Well
[44:39] interesting. That probably has something
[44:42] to do with it.
[44:44] Yeah? Well
[44:46] all right, we're not going to comment on
[44:48] the politics, but the the radiation
[44:49] effect worked clearly, unfortunately. So
[44:53] polonium is an alpha emitter and that
[44:55] caused a massive dose of alphas to his
[44:58] entire gastrointestinal tract. And that
[45:00] caused a whole lot of damage to those
[45:02] cells. No time for cancer. It actually
[45:04] killed off a lot of those stem cells.
[45:06] And the way that radiation poisoning
[45:08] would work is that if you kill off the
[45:10] stem cells, the villi in your intestine
[45:12] die which are responsible for absorbing
[45:14] nutrition. You can't uptake nutrition.
[45:17] You basically starve. Doesn't matter
[45:19] what you eat. It's messed up.
[45:22] Yeah.
[45:24] That's a really bad way to go. It's
[45:26] called gastrointestinal syndrome. And
[45:27] we'll be talking about the progressive
[45:30] effects of acute radiation exposure
[45:33] where you have immediate effects mostly
[45:35] relating to the death of some organ that
[45:38] is responsible for either cell division
[45:40] to keep you alive or in extreme cases
[45:43] your neurological system and nerve
[45:45] function just stops at the highest
[45:46] levels of dose. And that corresponds to
[45:48] doses of around 4 to 6 gray. 4 to 6
[45:53] joules per kilogram of villi or body
[45:56] mass will kill you pretty quickly with
[45:59] very little chance of survival as what
[46:00] happened here.
[46:02] And so this was the problem with all the
[46:03] folks living around and near Chernobyl
[46:06] and Ukraine and Belarus and everywhere
[46:09] was the contamination was pretty
[46:11] extensive. Uh, about 4,000 people are
[46:14] estimated to have died or contracted
[46:16] cancer from this. I can't believe how
[46:18] low that number is, but it's still 4,000
[46:20] people that it should never happen to.
[46:22] And effects were felt far away in towns
[46:25] like Gomel and I can't read that one cuz
[46:27] there's not enough pixels. Um, because
[46:29] of the way that let's say rainwater
[46:32] whisked or let's say um, the vapor cloud
[46:34] from the reactor was whisked away,
[46:36] rainwater caused it to fall on certain
[46:37] places which still to this day can have
[46:40] a really large contamination area.
[46:42] And this brings me a little bit into
[46:44] what should we be worried about from
[46:46] Fukushima? A whole lot less than
[46:48] Chernobyl. And the reason why is
[46:51] Fukushima did undergo a hydrogen
[46:53] explosion and did and still continues to
[46:55] release cesium 137 into the ocean.
[46:59] Luckily for us the ocean is big.
[47:01] And except for fish caught right near
[47:04] around Fukushima, even though
[47:05] concentrations can be measured at
[47:08] hundreds to thousands of times normal
[47:10] concentrations, they can still be
[47:12] hundreds to thousands of times lower
[47:14] than the safe consumption. So a lot of
[47:17] the problems you see in the news today,
[47:20] I'm not going to call them lies, but I'm
[47:21] going to call them half-truths. Folks
[47:23] will show the radiation plume of cesium
[47:26] 137 escaping from Fukushima and that's
[47:28] true. There is radiation escaping. The
[47:31] question is is it high enough to cause a
[47:34] noticeable increased risk of cancer?
[47:38] That's the question that reporters
[47:40] should be asking themselves. When they
[47:42] only tell the half of the story that
[47:43] gets them viewers and they don't tell
[47:45] the half of the story to complete the
[47:46] story
[47:47] and tell you should you be afraid or not
[47:49] cuz unfortunately fear brings viewers.
[47:52] This is the problem and I'm happy to go
[47:54] on camera saying this. This is the
[47:56] problem with the media today
[47:58] is with a half-truth and with a
[48:00] half-story you can incite real panic
[48:03] over non-physical issues that may not
[48:05] actually exist. And so it's important
[48:08] that the media tell the whole story.
[48:10] Yes, it's true that Fukushima's leasing
[48:12] releasing cesium 137.
[48:15] How much though is the question that
[48:17] people and the media should be asking
[48:18] themselves.
[48:20] And in the rest of this course we're
[48:21] going to answer the question how much is
[48:23] too much.
[48:25] So I'm going to stop here
[48:26] since it's 2 of 5 of and ask you guys if
[48:28] you have any questions on
[48:30] the whole second part of the course or
[48:31] what happened in Chernobyl.
[48:37] Yeah. Yeah, uh, could you explain the
[48:39] quality factor or determine how you find
[48:41] that? Yep, the quality factor Well,
[48:43] there's two quality factors. There's the
[48:45] quality factor for radiation which will
[48:47] tell you how much let's say how much
[48:49] more cell damage a given amount of a
[48:52] given type of radiation of the same
[48:54] energy will deposit into a cell.
[48:57] And the tissue equivalency factor tells
[49:00] you, well, what's the added risk of some
[49:03] sort of defect leading to cell death or
[49:05] cancer or some other defect
[49:07] from that radiation absorption.
[49:10] So to me the tissue equivalency factor
[49:12] is roughly but not completely
[49:14] approximated by the cell division rate
[49:17] and the radiation quality factor is
[49:20] going to be quite proportional to the
[49:21] stopping power.
[49:23] You'll see a term called the linear
[49:27] energy transfer or LET.
[49:29] This is the stopping power unit used in
[49:32] the biology community. It's stopping
[49:34] power. And luckily the Turner reading
[49:36] actually says it somewhere buried in a
[49:38] paragraph. LET is stopping power. So, if
[49:41] you start plotting these two together,
[49:43] you might find some striking
[49:44] similarities.
[49:45] I saw two other questions up here.
[49:47] Yeah. Can I ask uh
[49:49] Why is Chernobyl still considered like
[49:51] off-limits if most of the half-lives of
[49:53] these things were like
[49:55] on the range of like days to
[49:57] like 2 years? I mean, it happened in
[49:59] Let's answer that with numbers. So, most
[50:01] of the half-lives were on the range of
[50:03] days to hours.
[50:05] But, still, cesium 137 with a half-life
[50:08] of 30 years released a third of an
[50:10] exabecquerel. That's one of the major
[50:12] sources of contamination still out
[50:14] there. In addition, if we scroll down a
[50:16] little more,
[50:19] there was quite a bit of plutonium
[50:20] inventory with a half-life of 24,000
[50:23] years.
[50:24] So, on on Friday, we're going to have
[50:26] Jake Heckler come in and give his
[50:28] Chernobyl travelogue, cuz one of our
[50:29] seniors has actually been to Chernobyl.
[50:32] And his boots were so contaminated with
[50:34] pluto- with plutonium that he can never
[50:36] use them again. They got to stay wrapped
[50:37] up in plastic. So, some of these things
[50:39] last tens of thousands of years. And
[50:42] even though there weren't a lot of
[50:44] petabecquerels of plutonium released,
[50:47] they're alpha emitters. And they're
[50:48] extremely dangerous when ingested.
[50:51] So,
[50:52] uh greens and things that uptake
[50:54] radionuclides from the soil, like moss
[50:56] and mushrooms, are totally off-limits in
[50:59] a large range of this area.
[51:02] You will find a video online, if you
[51:04] look, of a mayor from a nearby town
[51:06] saying, "Oh, they're perfectly safe to
[51:07] eat. Look, I eat them right here." And I
[51:09] just say read the comments for what
[51:11] people have to say about that.
[51:13] Not too smart.
[51:14] Yeah. So, what what's like the process
[51:16] now for like taking care of Chernobyl?
[51:18] Like, what do they
[51:19] do there?
[51:21] The so so the sarcophagus around the
[51:22] reactor has got to be shored up to make
[51:24] sure that nothing else gets out, cuz
[51:26] most of the reactor is still there.
[51:28] And let's say rainwater comes in and
[51:29] starts washing away more stuff into the
[51:31] ground or whatever. We don't want that
[51:33] to happen. Soil replacement and disposal
[51:36] as nuclear waste is still going on.
[51:39] Uh removal of any moss, lichen,
[51:40] mushrooms, or anything with a sort of
[51:42] radiation exposure has got to keep
[51:44] going. But, this the area that it covers
[51:47] is enormous. I don't know if we're ever
[51:49] going to get rid of all of it. The
[51:51] question is, how much do we have to get
[51:53] rid of to lower our risk of cancer in
[51:55] the area to an acceptable rate? There
[51:57] will likely be parts of this that are
[51:59] inaccessible for thousands to tens of
[52:01] thousands of years, unless we hopefully
[52:03] get smarter about how to contain and
[52:05] dispose of this kind of stuff.
[52:06] We're not there yet. So, right now, the
[52:08] methods are
[52:09] kind of simple. Get rid of the soil.
[52:12] Fence off the area.
[52:14] Some folks have been returning, and they
[52:16] do get compensation and free medical
[52:18] visits because the background levels
[52:20] there are elevated, but not that high.
[52:23] So, folks have started to move back to
[52:25] some of these areas,
[52:27] but there's a lot that are still
[52:28] off-limits.
[52:30] Any other questions?
[52:33] Yeah. It's like way worse than the
[52:36] atomic bombs dropped on Hiroshima and
[52:38] Nagasaki, because those are like fully
[52:40] functioning cities at at this point.
[52:43] Yeah, the number of deaths from the
[52:45] atomic bombs way outweighed the number
[52:47] of deaths that will ever happen from
[52:49] Chernobyl. But, like, why is the
[52:50] radiation from those bombs not
[52:54] Oh, not that much of an issue? Yeah.
[52:55] There wasn't that much material. The not
[52:57] There wasn't that much nuclear material
[52:59] in an atomic bomb.
[53:00] What did you guys get for the radius of
[53:02] the critical sphere of plutonium?
[53:04] 4.7
[53:06] cm.
[53:06] Centimeters? Yeah. Yeah.
[53:08] Doesn't take a lot. It takes, you know,
[53:10] 10, 20 kilos to make a weapon.
[53:14] Now, we're talking about tons or
[53:16] thousands of tons of material released.
[53:18] So, an atomic weapon doesn't kill by
[53:20] radiation. It kills by pressure wave,
[53:23] the heat wave.
[53:25] The fallout is not as much of a concern.
[53:27] And we'll actually be looking at the
[53:29] data from Hiroshima and Nagasaki
[53:31] survivors to see who got what dose, what
[53:33] increased cancer risk did they get, and
[53:36] is this the
[53:37] is the idea that every little bit of
[53:39] radiation is a bad thing actually true?
[53:41] The answer is, you can't say yes or no.
[53:44] No one can say yes or no, because we
[53:46] don't have good enough data.
[53:48] The error bars support either
[53:49] conclusion.
[53:51] So, I'm not going to go on record and
[53:52] say a little bit of radiation is okay.
[53:54] The data's not out yet.
[53:56] Hopefully, it never will be.
[54:00] Any other questions?
[54:03] All right. I'll see you guys on
[54:05] Thursday.