Category: Nuclear Safety
Tags: Chernobyldisasterradiationreactorsafety
Entities: Alexander Litvinenkocesium-137ChernobylFukushimaiodine-131RBMK reactorThree Mile Islandxenon-135
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visit mit opencourseware at ocw.mit.edu all right so like i told you guys friday marked the end of the hardest part of the course and monday marked the end of the hardest pset so because the rest of your classes
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are going full throttle this one's going to wind down a little bit so today i'd say sit back relax and enjoy a nuclear catastrophe because we are going to explain what happened at chernobyl now that you've got the physics and intuitive background to understand the
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actual sequence of events to kick it off i want to show you guys some actual footage of the chernobyl reactor as it was burning so this is the part that most folks know about
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this is footage taken from a helicopter from folks that were either surveying or dropping materials onto the reactor
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was probably a bad idea hold where the smoke is we'll get into what the smoke was
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so that red stuff right there that's actually glowing graphite amongst other materials from the graphite fire that resulted from the rbmk reactor burning after the chernobyl accident caused by both flaws in the physical design of the rbmk
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reactor and absolute operator stupidity and neglect of any sort of safety systems or safety culture we're lucky to live here in the u.s where our worst accident at three mile island was not actually really that much of an accident there was a partial meltdown there was
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not that much of a release of radionuclides into the atmosphere because we do things like build containments on our reactors if you think of what a typical reactor looks like like if you consider the mit reactor is a scaled down version of a normal reactor all right
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let's say a commercial power reactor you've got the core here you've got a bunch of shielding around it and you've got a dome that's rather thick that comprises the containment
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that would be the core this would be some shielding so this is what you find in u.s and most other reactors for the rbmk reactors there was no containment
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because it was thought that nothing could happen and boy were they wrong so i want to walk you guys through a chronology of what actually happened at the chernobyl reactor which you guys can read on the nea or nuclear energy agency website the same place that you find
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janus and we're going to refer to a lot of the janus cross sections to explain why these sorts of events happened so the whole point of what happened at chernobyl was it was desired to see if you could use the spinning down turbine after you shut down the reactor to power
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the emergency systems at the reactor this would be following something what's called a loss of off-site power if the off-site power or the grid was disconnected from the reactor the reactor automatically shuts down but the turbine like i showed you a couple weeks
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ago is this enormous spinning hulk of metal and machinery that coasts down over a long period of let's say hours and as it's spinning the generator coils are still spinning and still producing electricity or they could be so it was desired to find out can we use the
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spinning down turbine to power the emergency equipment if we lose offsite power so they had to simulate this event so what they actually decided to do is coast down the reactor to a moderate power level or very low power and see what comes out of the turbine itself or
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out of the generator rather now there were a lot of flaws in the rbmk design and i'd like to bring it up here so we can talk about what it looks like and what was wrong with it so the rbmk is unlike any of the united states light water reactors that
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you may have seen before many of the components are the same there's still a light water reactor coolant loop where water flows around fuel rods goes into a steam separator better known as a big heat exchanger and the steam drives a turbine
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which produces energy and then this coolant pump keeps it going and then the water circulates what makes it different though is that each of these fuel rods was inside its own pressure tube so the coolant was pressurized and out here
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this stuff right here was the moderator composed of graphite unlike light water reactors in the us the coolant was not the only moderator in the reactor graphite also existed which meant that if the water went away which would normally shut down a light water reactor
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from lack of moderation graphite was still there to slow the neutrons down into the high fission cross section area and i'd like to pull up janus and show you 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 section z fission can make it a little thicker too
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so again the goal of the moderator is to take neutrons from high energies like 1 to 10 mev where the fission cross section is relatively low and slow them down into this region where fission is let's say a thousand times more likely
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and in a light water reactor in the u.s if the coolant goes away so does the moderation and there's nothing left to slow those neutrons down to make fission more likely in the rbmk that's not the case the graphite's still there the graphite is cooled by a helium
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nitrogen mixture because the neutron interactions in the graphite that's slowing down we've always talked about what happens from the point of view of the neutron but what about the point of view of the other material any energy lost by the neutrons is gained by the moderating material so the
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graphite gets really hot and you have to flow some non-oxygen containing gas mixture like helium and nitrogen which is pretty inert to keep that graphite cool and then in between the graphite moderator where control rods about 200
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of them or so 30 of which were required to be down in the reactor at any given time in order to control power and that was a design rule that was broken during the actual experiment and then on top of here on top of this biological shield you could walk on top
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of it so those the tops of those pressure tubes despite being about 350 kilo chunks of concrete you could walk on top of them it's pretty cool kind of scary too so what happened in chronological order
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was around midnight the decision was made to undergo this test and start spinning down the turbine but the grid operator came back and said no you can't just cut the reactor power to nothing you have to maintain at a rather high power for a while about 500
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megawatts electric or half the rated power of the reactor and what that had the effect of doing is continuing to create fission products including xenon 135 we haven't mentioned this one yet you'll talk about it quite a lot
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in 2205 in neutron physics this black shirt really shows chalk well okay what xenon 135 does is it just sits there it's a noble gas it has a half-life of a few days so it decays on the slow side for
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you know fission fission products go but it also absorbs lots and lots and lots of neutrons let's see if i can find which one is the xenon one there we go so here i've plotted the total cross section for xenon 135 and the absorption
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cross section and notice how for low energies pretty much the entire cross-section of xenon is made up of absorption did you guys in your homework see anything that reached about 10 million barns no xenon-135 is one of the best neutron absorbers there is and reactors produce
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it constantly so as they're operating you build up xenon 135 that you have to account for in your sigma absorption cross section because like you guys saw in the homework if you want to write what's the sigma absorption cross section of the reactor
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it's the sum of every single isotope in the reactor of its number density times its absorption cross section and so that would include everything for water
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and let's say the uranium and the xenon that you're building up when the reactor starts up the number density of xenon is zero because you don't have any anything to have produced it when you start operating you'll reach the xenon equilibrium level where it
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will build to a certain level that will counteract the reactivity of the reactor and in your k effective expression where its sources over absorption plus leakage
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this has the effect of rise raising sigma absorption and lowering k effective the trick is it doesn't last for very long it both decays with a half-life of about five days and when you try and raise the reactor power you will also start to burn it out so if you're
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operating at a fairly low power level you'll both be decaying and burning xenon without really knowing what's going on and that's exactly what happened here so an hour or so later let me pull up the chronology again a little more than an hour later so the reactor power stabilized at something
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like 30 megawatts and they were like what is going on why is the reactor power so low we need to increase the reactor power so what do they do couple things one was remove all but six or seven of the control rods going way outside the spec of the design
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because 30 were needed to actually maintain the reactor at a stable power all the while the xenon that had been building up is still there keeping the reactor from going critical it's what was the main reason that the reactor didn't even have very much power but it was also burning out at the same
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time so all the while let's say if we were to show a graph of two things time xenon inventory and as a solid line and let's say control rod worth
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as a dotted line the xenon inventory at full power would have been at some level and then it would start to decay and burn out while at the same time the control rod worth as you remove control rods from the reactor
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every time you remove one you lose some control rod worth would continue to diminish leading to the point where bad stuff was going to happen let me make sure i didn't lose my place so at any rate as they started pulling
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the control rods out a couple of interesting quirks happened in terms of feedback so let's look back at this design like any reactor this reactor had what's called a negative fuel temperature coefficient what that means is that when you heat up the fuel
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two things happen one the cross section for anything absorption or fission would go up but the number density would also go down as the atoms physically spaced out in the fuel their number density would go down lowering the macroscopic cross
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section for fission and that's arguably a good thing the problem is at below about twenty percent power the reactor had what's called a positive void coefficient which meant that if you boil the coolant you increase the reactor power
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because the other thing that i think i mentioned this once and you calculated in the homework the absorption cross section of hydrogen is not zero it's small but fairly significant let's actually take a look
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at it because we can always see this in janus we go back down to hydrogen hydrogen one and we look at the absorption cross section
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and of course it started us with a linear scale let's go logarithmic ah okay so at low energies that you know 10 to the minus 8 to 10 to the minus seven it's around a barn not super high but absolutely not negligible which meant that part of the normal
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functionality the rbmk depending up depended on the absorption of the water to help absorb some of those neutrons with those neutrons gone i'm sorry with those with that water gone there was less absorption but there was still a ton of moderation
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in this graphite moderator so they still could get slow but then there'd be more of them and that would cause the power to increase and then that caused more of the water the coolant to boil which would cause less absorption which would cause the power to increase yeah charlie
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they did not remove the water from the reactor however as the power started to rise some of the water started to boil and so you can still have let's say steam flowing through and still remove some of the heat however you don't have that denser water to act as an absorber
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and that's what really undid this reactor in addition they decided to disable the eccs or the emergency core cooling system which you're just not supposed to do so they shut down a bunch of these systems to see if you could power the other ones from the spinning down turbine and
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then as they noticed that the reactor was getting less and less stable they had almost all the rods out some of these pressure tubes started to bump and jump these 350 kilogram pressure tube caps were just rattling i
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mean imagine something that weighs you know 900 pounds or so rattling around and there's a few hundred of them so there was someone in the control room that said the caps are rattling what the heck didn't quite make it down the spiral staircase because about 10 seconds later
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everything went wrong and so i want to pull up this actual timeline so you can see it splits from minutes to seconds because the speed at which this stuff started to go wrong was pretty striking so for example the control rods raised
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at 1 19 in the morning two minutes later when the power starts to become unstable the caps on the fuel channels which again are like 350 kilogram blocks start jumping in their sockets and a lot of that was we go back to the
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rbmk reactor as the coolant started to boil here well that boiling force actually creates huge pressure instabilities which would cause the pressure tubes to jump up and down eventually rupturing almost every single one of them with enough force to shoot
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these 350 kilo caps and what did that what did they say i like the language that they used jumping in their sockets so 50 seconds later pressure fails in the steam drums which means there's been some sort of
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containment leak so all the while the coolant was boiling the absorption was going down the power was going up repeat repeat repeat and the power jumped to about a hundred times the rated power in something like four seconds so it was normally a thousand megawatt
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electric reactor which is about 3200 megawatts thermal it was producing nearly yeah half a terawatt of thermal power for a very short amount of time until it exploded now the it's interesting a lot of folks called chernobyl a nuclear explosion
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that's actually a misnomer a nuclear explosion would be a nuclear weapon something set off by an enormous chain reaction principally heated by fission or fusion that's not actually what happened at chernobyl nor at fukushima nor was that the worry at three mile
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island not to say it wasn't a horrible thing but it wasn't an actual nuclear explosion at first what happened was a pressure explosion so there was an enormous release of steam as the power built up to 100 times normal
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operating power the steam force was so large that it actually blew the reactor lid up off of the thing i think i have a picture of that somewhere here too it should be further down yeah to give
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you a little sense of scale the reactor cover which weighed about a thousand tons launched into the air and landed above the reactor sending most of the reactor components up to a kilometer up in the air four seconds later that was followed by a hydrogen
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explosion let me get back down to that chronology so yeah at 123 and 40 seconds in the morning oh yeah so i should mention why this happened emergency insertion of all the control rods the last part that this diagram doesn't
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mention is these control rods and i'll draw this up here we're tipped with about six inches of graphite so if these were two graphite channels let's say these are carbon and this is your control rod the goal was to get this control rod
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all the way into the reactor one part they didn't mention was they were tipped with about six inches of graphite which only functions as additional moderator graphite is one of the lowest absorbing materials in the periodic table second i think only to
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oxygen and if we pull up graphite's cross sections i've plotted here the total cross section the elastic scattering cross section and down here in the 0.001 barn level is the absorption cross
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section about a thousand times lower than water so you're shoving more material in the reactor that slows down neutrons even more bringing them into the high fission region without absorbing anything and they jammed about halfway down about two and a half feet down leaving the extra graphite right in
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the center of the core where it could do the most damage and it didn't take that much time yeah um so my understanding is that also one of the designs was that the control rods didn't like immediately drop down but they were slowly lowered yep so they took they took seven to ten seconds okay if they had a system where
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they did drop them would that have possibly actually shut the system down properly i'm not sure i don't know whether lowering control rods into something that was undergoing steam explosions would have actually helped me to me by this point it was all over um whether or not you know so the extra the
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extra abs what is it the extra moderator that was dumped in was the last kick in the pants this thing needed to go absolutely insane and if we go back to the timeline on the second level control rods inserted at 123 and 40 seconds explosion four
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seconds later ah to 120 times full power getting towards a terror water so one second later the thousand ton lid launches off from the first explosion very shortly after that second explosion
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and that happened because of this reaction well any just about anything corroding with water will make pretty much anything oxide plus hydrogen the same chemical explosion that was the
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undoing of fukushima and was the worry at three mile island that there was a hydrogen bubble building because of corrosion reactions with whatever happened to be in the core this happens with zirconium pretty vigorously but it happens with other materials too if you oxidize something with water you
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leave behind the hydrogen and the hydrogen in a very wide range of concentrations in the air is explosive we're actually not allowed to use hydrogen at about four percent in any of the labs here because that reaches the flammability or explosive limit so we were doing some for my phd
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we were doing these experiments corroding materials in liquid lead and we wanted to dump in pure hydrogen to see what happens when there's no oxygen we were told absolutely not we had to drill a hole in the side of the wall so that the hydrogen would vent outside and do some calculations to show if the
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entire bottle of hydrogen emptied into the lab at once which it could do if the cap of the bottle breaks off it would not reach four percent concentration so hydrogen explosions are pretty powerful things have you guys ever seen people making water from scratch mix hydrogen and oxygen in a bottle and
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light a match we've got a video of it circulating somewhere around here because for rtc for the reactor technology course i do this in front of a bunch of ceos watch them jump out of their chairs to teach basic chemical reactions but it's pretty loud enough
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about enough hydrogen and oxygen to just fill this cup or fill a half liter water bottle makes a bang that gets your ears ringing not quite bleeding but close enough so that's what happened here except on a much more massive scale so there was a steam explosion followed seconds later
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by a hydrogen explosion from hydrogen liberated from the corrosion reaction of everything with the water that was already there and that's when this happened
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is so that's smoke right there
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from a graphite fire not normal smoke [Music]
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spoke too soon [Music]
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foreign this actually provides a perfect conduit to transition from the second to the third parts of this course a lot of you have been waiting to find out what are the units of dose and what are the biological and chemical effects of radiation well this is where you get
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them from neutron physics you can understand why chernobyl went wrong with honestly you've just been doing this for three or four weeks but with your knowledge of cross-sections reactor feedback and criticality you can start to understand why chernobyl was flawed in this design and what we're going to
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teach you in the rest of the course is what happens next what happens when radionuclides are absorbed by animals of the human body and what was the main fallout let's say in the in the colloquial sense and the actual sense from the chernobyl reactor
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let's look a bit what they did next though
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[Music] foreign
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[Music]
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foreign
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i think that pretty much summarizes the state of things now the uh they built a sarcophagus around this reactor a gigantic tomb which according to some reports is not that structurally sound and is in danger of partial collapse so yeah more difficult efforts are ahead
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but let's now talk about what happened next i'm going to jump to the very end of this the actual way that the accident was noticed was the spread of the radioactive cloud to not so close by sweden
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so it was noticed that folks entering a reactor in sweden had contaminants on them which they thought was coming from their own reactor good first assumption when it was determined that nothing was amiss at the reactor in sweden folks started to analyze wind patterns and find out what happened and then it was clear that the ussr had tried to cover
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up the chernobyl accident but you can't cover up fallout and it eventually spread pretty wide covering most of europe russia and surprisingly not spain lucky them for the wind patterns that day or those few days
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so what happened is a few days after the actual accident a graphite fire started to break out because graphite when exposed to air well you can do the chemistry add graphite plus oxygen
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you start making carbon dioxide so graphite burns when it's hot and as you can see from the video where is that nice still of mold burning graphite yeah that graphite was pretty hot so a lot of that smoke
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included burning graphite and a lot of the materials from the reactor itself now when you build up fission products in a reactor and they get volatilized like this the ones that tend to get out first would be things like the noble gases so the whole xenon inventory of the reactor was released
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it's estimated about a hundred percent and i can actually pull up those figures when we talk about how much of which radionuclide was released uh that's also a typo if somebody wants to call in there's no 33 isotope of xenon it's supposed to be 133.
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um that would be interesting if someone wants to call in and say the nea's got a mistake so 100 of the inventory release that should be pretty obvious because it's a noble gas and it just kind of floats away the real dangers though came from iodine 131
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about 50 percent of a three exo-becquerel activity so we're talking like mega curies or might be giga can't do that math in my head a lot a lot of radiation and the problem with that is iodine behaves just like any other halogen it forms salts
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it's rather volatile if any of you guys played with iodine before no one does oh you have okay what happens when it you play with it i mean like yeah and it just reacts with like acids and stuff
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okay i happen to have extensive practice playing with iodine in my home because i did all the stuff you're not supposed to do as a kid kind of build your own chemistry step things that somehow you know leak out of your local high school somehow iodine is pretty neat yeah it happens sometimes
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um if you put iodine in your hand it actually sublimes the heat from your hand is enough to directly go from solid to vapor and so the iodine was also quite volatile some of it may have been in the form of other compounds some of it may have been elemental probably not
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likely but there was certainly some iodine vapor and about half of that was released the problem is then it condenses out and falls on anything green anything with surface area so the biggest danger to the folks living nearby was from eating leafy
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vegetables because the loads that leaves got loss of surface area iodine deposits on them and it's intensely radioactive for a month or so or depositing on the grass that cows eat which led to the problem of radioactive milk and so that's why milk in the soviet
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union was banned for such a long time because this was one of the major sources of iodine contamination the other one which we're worrying about now from fukushima as well is cesium which has similar chemistry to sodium and potassium again a rather salty
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compound a rather salty element but it's got a half-life of 30 years and if we look it up in the table of nuclides we'll see what it actually releases oh good it's back online anyone else notice this broken a couple
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days ago well luckily brookhaven national lab has a good version up too but let's grab cesium yeah there's plenty out there cesium-137
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beta decays to barium but also gives off gamma rays and most of the decays end up giving off one of those gamma rays let's say a 660 kev gamma ray so it's both a beta and a gamma emitter now which of those types of radiation do you think is more
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damaging to biological organisms the beta or the gamma you say the gamma why do you say so doesn't beta get stopped by it does but if cesium is better known as
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yes that's right so did i tell you guys this question the four cookies question yeah you eat the gamma cookie because most gammas that are emitted by the cookie simply leave you and irradiate your friend which is going to be the topic of
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piece at number eight you'll see that's why you guys are getting your whole body counts speaking of who's gotten their whole body counts at ehs awesome so that's almost everybody you will need that data for problem set eight so do schedule it soon
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preferably before thanksgiving so that you'll be able to take a look at it has anyone found anything interesting in your spectra good glad to hear that but you do see a potassium peak that you can it probably integrate
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and do some problems with right yeah because you will okay anyway yeah it's the betas that's the real killer the gammas are going to leave the cesium enter your body and most likely come out the other side because the mass attenuation coefficient
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of six what is it water for 660 kev gammas let's find that table three let's say you're made mostly of water
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water liquid that's pretty much humans 660 kv is right about here leading to about 0.1 centimeters squared per gram and with a density of 1 gram that's a pretty low attenuation of gammas so this chart actually shows why most of
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the cesium gammas that would be produced from ingestion just get right out but it's the betas that have an awfully short range anyone remember the formula for range in general because it's going to come back up in our discussion of dose and biological
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effects integral of yup of stopping power to the negative one and that stopping power is this simple formula
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let's see what did that come out as log minus beta squared that simple little formula which i'm not going to expect you guys to memorize so don't worry about it but
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if you integrate this you find out that the range of electrons even one mev electrons in water is not very high so most of them are stopped near or by the cells that absorb them doing quite a bit of damage to the dna which is eventually what causes
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mutagenic effects cancer cell death what we're going to talk about for the whole third part of the course there's also a worry about which organs actually absorb these radionuclides and iodine in particular
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is preferentially absorbed by the thyroid so when we started looking at the amount of radioactive substances released remember they said okay at around 26th of april or the 2nd of may or so the uh release was stopped not according to our data that's when the graphite
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fire picked up again in addition the core of chernobyl which had undergone a mostly total meltdown was sitting in a pool on top of this concrete pad so let's just call this liquid stuff the
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actual word that we use in parlance is called corium it's our tongue-in-cheek word for every element mixed together in a hot radioactive soup it's first of all it started to redistribute reacting with any water that was present flashing it to steam
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and the steam caused additional dispersion of radionuclides and eventually it burrowed its way through and into the ground releasing more you know it's it's uh it's the worst nuclear thing that's ever happened in the history of nuclear things
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quite a mess and luckily it did sort of taper off after this but let's now look into what happens next and this is the nice intro to the third part of the course iodine is is preferentially uptaken by
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the thyroid gland somewhere right about here so has anyone ever heard of the idea of taking iodine tablets in the case of a nuclear disaster anyone have any idea why if you saturate your thyroid with iodine
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then if you ingest radioactive iodine it's less likely to be permanently uptaken by the thyroid so this actually provided some statistics on the probability of getting thyroid cancer from radioactive iodine ingestion
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luckily the statistics were quite poor which means that not many people were exposed it was somewhere around 1300 or so not like millions yeah 1300 people total but what i want to jump to is the dose versus risk curve and this is going
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to belie all of our discussion about the biological long-term effects of radioactivity what's the most striking thing you see as part of this curve that's that's right that's the first thing i saw
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there are six different models for how dose and increased risk of cancer proceeds and they all fall within almost all the error bars of these measurements i say again thank god that the error bars are so high because that means that the sample size was so low
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so when folks say we don't really know how much radioactivity causes how much cancer they're right because luckily we don't have enough data from people being exposed to know that really really well so some folks say we should be cautious i kind of agree with them some folks say
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the jury's still out i also agree with them but you can start to estimate these sorts of things by knowing how much radiation energy was absorbed and to what organ so i think the only technical thing i want to go over today
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is the different units of dose because as you start to read things in the reading which i recommend you do if you haven't been doing yet you're going to encounter a lot of different units of radiation dose ranging from things like the renkin
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which responds to a number of ionizations you won't usually see this one given in sort of biological parlance because it's the number of ionizations detected by some sort of gaseous
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ionization detector so the dosimeters that you all put on the did you guys all bring these uh these like brass pendocimeters into the reactor did anyone look through them to see what the unit of dose was it's going to be in renkins because
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that's directly correlatable to the number of ionizations that that dosimeter has experienced you'll also see four dose units two of which are just factors of 100 away from each other there's what's called the rad and the gray
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and there's what's called the rim and the sievert you'll see these approximated as gray you'll see these as r and these are just usually written as rem
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so a rad is simple let's see 100 rads is the same as one gray and 100 rem is the same as one sievert and for gamma for the case of gamma
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radiation these units are actually equal i particularly like this set of units because this is the kind of s i of radiation units because it comes directly from measurable calculatable quantities like
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the gray for example the actual unit of gray is joules absorbed per kilogram of absorber it's a pretty simple unit to understand if you know how many radioactive particles or gammas or whatever that you have
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absorbed you can multiply that number by their energy divide by the mass of the organ absorbing them and you get its dose in gray sievert is gray times some quality factor for the radiation
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times some quality factor for the specific type of tissue what this says is that some types of radiation are more effective at causing damage than others and some organs are more susceptible to radiation
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damage than others does anyone happen to know some of the organs that are most susceptible to radiation damage soft tissue is like what because there's lots of those
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stomach lining yep yeah huh lungs yup what else thyroid yep there there is definitely one for thyroid bone marrow what other ones
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your brain actually not so much eyes and where else do you find rapidly dividing cells in your body skin yep the dermis i don't know about the liver i would
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assume so yeah it's a pretty active organ but when folks are worried about birth defects reproductive organs the link here that for some reason is not said in the reading and i've never figured out why is the more often a cell is dividing the more susceptible it is
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to gaining cancer risk because every cell division is a copy of its dna and anytime that radiation goes in and damages or changes that dna by either causing what's called a thymine bridge where two thymine bases get linked together or damaging the structure in
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some other way that gene is then replicated and the faster they're replicating the more likely cancer is going to become apparent i guess this brings up a question when does a rapidly dividing cell become cancer is it division number one or is
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it when you notice it i guess i'll leave that question to the biologists but if you notice in the reading you'll see a bunch of different tissue equivalency factors and you'll just see them tabulated and say there they are memorize them i want you to try and think of the pattern
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between them the tissues that basically don't matter like the non-marrow part of the bone dead skin cells muscles things that basically aren't listed that much they're not dividing very fast but anywhere you find stem cells the lining of your intestine your
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lungs which undergo a lot of environmental damage need to be replenished gonads what was the other one that we said eyes these are places that are either sensitive tissues or they're rapidly dividing and so the sievert is kind of in a unit
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of increased equivalent risk so that if you were to absorb one gray of gamma rays versus one gray of alphas you'd be about 20 times more likely to incur cancer from the alphas than the gammas because the amount of localized damage that they do to cells and we'll
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be doing all this in detail pretty soon and then for tissue equivalency factor if you absorb one gray in your whole body which means one joule per kilogram of average body mass versus one grade directly to the lining of your intestine by let's say
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drinking polonium-laced tea like happened to a poor was it current or xkgb guy one of the russian fellows no it's the kgb guys that poisoned them right yeah do you guys remember back in 2010 or so there was a russian
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was he a journalist xkgb so the current kgb somehow got into london and slipped polonium into his tea at a japanese restaurant uh really i think so right
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it was like what was his name let's see poisoning did he actually die
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poisoning of alexander lidovenko he's not doing too well illness and poisoning death and last statement
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at the hospital in london so yeah well interesting that probably has something to do with it yeah well uh we're not going to comment on the
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politics but the uh the radiation effect worked clearly unfortunately so polonium is an alpha emitter and that caused a massive dose of alphas to his entire gastrointestinal tract and that caused a whole lot of damage to those cells no time for cancer it actually
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killed off a lot of those stem cells and the way that radiation poisoning would work is that if you kill off the stem cells the villi in your intestine die which are responsible for absorbing nutrition you can't uptake nutrition you basically starve doesn't matter what you eat it's messed up
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yeah that's a really bad way to go it's called gastrointestinal syndrome and we'll be talking about the progressive effects of acute radiation exposure where you have immediate effects mostly relating to the death of some organ that
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is responsible for either cell division to keep you alive or in extreme cases your neurological system and nerve function just stops at the highest levels of dose and that corresponds to doses of around four to six gray four to six joules per
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kilogram of villi or body mass will kill you pretty quickly with very little chance of survival as what happened here and so this was the problem with all the folks living around and near chernobyl and ukraine and belarus and everywhere was the
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contamination was pretty extensive about 4 000 people are estimated to have died or contracted cancer from this i can't believe how low that number is but it's still 4 000 people that it should never happen to and effects were felt far away in towns like amel and can't
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read that one because there's not enough pixels because of the way that let's say rain water wist or let's say um the vapor cloud from the reactor was whisked away rain water caused it to fall on certain places which still to this day can have a really large contamination area
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and this brings me a little bit into what should we be worried about from fukushima a whole lot less than chernobyl and the reason why is fukushima did undergo a hydrogen explosion and did and still continues to release cesium-137 into the ocean luckily for us
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the ocean is big and except for fish caught right near around fukushima even though concentrations can be measured at hundreds to thousands of times normal concentrations they can still be hundreds to thousands of times lower than the safe consumption
47:16
so a lot of the problems you see in the news today i'm not going to call them lies but i'm going to call them half truths folks will show the radiation plume of cesium-137 escaping from fukushima and that's true there is radiation escaping
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the question is is it high enough to cause a noticeable increased risk of cancer that's the question that reporters should be asking themselves when they only tell the half of the story that gets them viewers and they don't tell the half of the story to complete the
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story and tell you should you be afraid or not because unfortunately fear brings viewers this is the problem and i'm happy to go on camera saying this this is the problem with the media today is with a half truth and with a half story you can incite real panic over
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non-physical issues that may not actually exist and so it's important that the media tell the whole story yes it's true that fukushima's leasing releasing cesium-137 how much though is the question that people and the media should be asking
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themselves and in the rest of this course we're going to answer the question how much is too much so i'm going to stop here since it's two of five of and ask you guys if you have any questions on the whole second part of the course or what happened in chernobyl
48:37
yeah yeah could you explain the equality factor term and how you find that yep the quality fat well there's two quality factors there's the quality factor for radiation which will tell you how much let's say how much more cell damage a given amount of a given type of radiation of the same
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energy will deposit into a cell and the tissue equivalency factor tells you well what's the added risk of some sort of defect leading to cell death or cancer or some other defect from that radiation absorption
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so to me the tissue equivalency factor is roughly but not completely approximated by the cell division rate and the radiation quality factor is going to be quite proportional to the stopping power you'll see a term
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called the linear energy transfer or let this is the stopping power unit used in the biology community it's stopping power and luckily the turner reading actually says it's somewhere buried in a paragraph let is stopping power so if you start
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plotting these two together you might find some striking similarities i saw two other questions up here yeah it's gonna ask uh why is chernobyl still considered like off limits of most the half-lives of these things are like on the range by days to
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let's answer that with numbers so most of the half-lives were on the range of days to hours but still cesium-137 with a half-life of 30 years released a third of an exo-becquerel that's one of the major sources of contamination still out there in addition if we scroll
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down a little more there was quite a bit of plutonium inventory with a half-life of 24 000 years so on on friday we're going to have jake heckler come in and give his chernobyl travelogue because one of our seniors has actually been to chernobyl and his
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boots were so contaminated with plutonium that he can never use them again they got to stay wrapped up in plastic so some of these things last tens of thousands of years and even though there weren't a lot of petabeckerals of plutonium released they're alpha emitters and they're
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extremely dangerous when ingested so greens and things that uptake radionuclides from the soil like moss and mushrooms are totally off limits in a large range of this area you will find a video online if you look
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of a mayor from a nearby town saying oh they're perfectly safe to eat look i eat them right here and i just say read the comments for what people have to say about that not too smart yeah so what's like the process now for like taking care of what are they
51:19
doing so the sarcophagus around the reactor has got to be shored up to make sure that nothing else gets out because most of the reactor is still there and let's say rain water comes in and starts washing away more stuff into the ground or whatever we don't want that to happen soil replacement and disposal as nuclear
51:36
waste is still going on uh removal of any moss lichen mushrooms or anything with a sort of radiation exposure has got to keep going but this the area that it covers is enormous i don't know if we're ever going to get rid of all of it the question is how
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much do we have to get rid of to lower our risk of cancer in the area to an acceptable rate there will likely be parts of this that are inaccessible for thousands to tens of thousands of years unless we hopefully get smarter about how to contain and dispose of this kind of stuff we're not there yet so right now the
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methods are kind of simple get rid of the soil fence off the area some folks have been returning and they do get compensation and free medical visits because the background levels there are elevated but not that high so folks have started to move back to some
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of these areas but there's a lot that are still off limits any other questions yeah it's like way worse than the atomic bombs dropped on hiroshima and nagasaki because those are like fully functioning
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cities at this point yeah the number of deaths from the atomic bombs way outweighed the number of deaths that will ever happen from chernobyl like why is the radiation from those bombs not oh not that much of an issue there wasn't that much material that not there
52:57
wasn't that much nuclear material in an atomic bomb what did you guys get for the radius of the critical sphere of plutonium centimeters yeah doesn't take a lot it takes you know 10 20 kilos to make a weapon now we're talking about
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tons or thousands of tons of material released so an atomic weapon doesn't kill by radiation it kills by pressure wave the heat wave the fallout is not as much of a concern and we'll actually be looking at the data from hiroshima and nagasaki
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survivors to see who got what dose what increased cancer risk did they get and is this the is the idea that every little bit of radiation is a bad thing actually true the answer is you can't say yes or no no one can say yes or no because we
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don't have good enough data the error bars support either conclusion so i'm not going to go on record and say a little bit of radiation's okay data is not out yet hopefully it never will be any other questions
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all right i'll see you guys on thursday
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you