Stuff You Missed in History ClassThis 2020 episode covers the sphere of plutonium-gallium alloy that the U.S. made for use in an atomic bomb during World War II known as the Demon Core was It was the source of two fatal criticality accidents.
Happy Saturday.
Coming up, we have an episode that has some parallels to our previous episode on the Demon Core. Both of these involved a nuclear incident, and both of them also have discussions of the Cold War rush to develop nuclear technologies that led to some dangerous shortcuts. This episode came out on October twelfth, twenty twenty. Enjoy Welcome to Stuff You Missed in History Class, a production of iHeartRadio.
Hello, and welcome to the podcast. I'm Tracy B.
Wilson, and I'm Holly Frye.
My friend Adrian, who.
Is a science educator, asked me years ago at this point whether we had ever thought about doing an episode on the Demon Core, which sounds terrifying, and I kept thinking it might make a good October episode because nuclear critical accidents can be terrifying, like they expose people to possibly lethal doses of radiation and just a fraction of a second, usually completely by surprise and before anybody can react, and then that leads to just a horrifying and gruesome and sometimes prolonged death. So then every October I kept moving on in other directions and not getting to the demon Core.
Here it finally is.
The Demon Core was a sphere of plutonium gallium alloy that the United States made for an atomic bomb during World War Two, and then after the war, researchers at Los Alamos National Laboratory had two separate fatal criticality accidents while working with it. Those accidents are also part of a greater history of criticality accidents, most of which took place in the nineteen fifties and sixties. So we're going to talk about that progression today just to set some expectations. Nuclear reactor melt down like the disasters at Three Mile Island and Chernobyl and Fukushima, those are a slightly different thing from what we're talking about today. Some of them could technically be classified as criticality accidents, but they're also just a little bit bigger than the topics that were focused on. So to make sense of how these incidents play out, we need to walk through a little bit of science history. In nineteen thirty two, James Chadwick discovered the uncharged sub atomic particle known as the neutron, and soon physicists were using neutrons to study atoms, including bombarding atomic nuclei with neutrons to study the results. It was through this work that ottohon Lee's Meiitner and Fritz Strassmann discovered nuclear fission in nineteen thirty eight. Hahn had been working with uranium samples that had been bombarded with neutrons, and for reasons that he couldn't really explain, barium isotopes started appearing in his samples as well. Meiitner and Strasman made the connection that barium has about half the time mass of uranium, so the uranium atoms were splitting into two roughly equal parts. The idea that an atom could split in this way had been suggested before, but it was not really taken seriously at the time because it seemed absolutely contrary to how people understood nuclear physics at that point. This breakdown of uranium into barium didn't answer all the questions, though Meitner also calculated that the two new barium nuclei would be slightly less massive than the original uranium nucleus, with the difference converted into energy. Atto Haan was awarded the Nobel Prize in Chemistry for the discovery of nuclear fission in nineteen forty four. Although Meiitner and Strassman were mentioned in the speech, they were not included in that award. Nuclear fission can happen spontaneously in the natural world, and the details can play out a little bit differently in different elements and isotopes, but in terms of what we're talking about today, it typically starts with neutrons. Neutrons interact with the atom's nucleus, causing it to split. That split releases one or more other neutrons, and in the right conditions, those neutrons can reach the nuclei of other nearby atoms, causing them to split. That can continue on in a chain reaction. If there's enough material in one place to support a regular, ongoing, self sustaining chain reaction, that's known as critical mass. In a supercritical mass, this chain reaction unfolds at an escalating rate instead of a steady one. It's not just about how much physical material is in one place, though. The volume of the material, it's geometry, its concentration, its surroundings, and other factors all play a part. As a hypothetical example, if you have a very thin sheet of uranium two thirty five, a lot of the neutrons that are released during fission are going to fly off into the surrounding air without hitting any uranium atoms. But if you have the same amount of uranium two thirty five packed into a tight sphere, the neutrons from the interior are far more likely to interact with other nuclei as they travel, potentially starting a chain reaction. So the elements that break down and these interactions are radioactive, and the products of fission are generally radioactive as well. The energy that's released during nuclear fission, which there can be a lot of, also includes ionizing radiation, and while ionizing radiation has some beneficial uses, it can also be incredibly destructive to living cells. Criticality accidents can expose people and objects to just enormous amounts of radiation in an instant, so facilities that handle these types of materials have to take a lot of precautions to protect people from radiation and to prevent an accidental criticality, which is sometimes also called a power excursion. This includes restrictions on how much material can be in a particular place and how its to be handled. Containers to hold the material have to be shaped in a way that is unfavorable for criticality and made of materials that won't reflect too many sub atomic particles. Back into the material, and people handling the material have to be trained on how to prevent criticality accidents. Some of this can be a little counterintuitive to outside observers. For example, if you saw some plutonium rods placed near each other in a way that could potentially lead to a criticality, your first instinct might be to move them apart so that they would not do that. But a person's own body can also reflect neutrons back at the material, so that very act of trying to prevent a criticality accident could actually wind up causing one instead. This is a real example. It happened at Los Alamos National Laboratory in August of twenty eleven after somebody made an arrangement of plutonium rods for a photo op. Fortunately, while what what happened was outside the bounds of safety guidelines, it did not cause a criticality accident. Because nuclear fission releases energy, its discovery had immediate and obvious implications for both energy production and warfare, and multiple nations started trying to develop nuclear reactors and atomic bombs. In the United States, the effort to develop an atomic bomb was code named the Manhattan Project, which also involved the construction of nuclear reactors to produce the necessary radioactive materials for the bomb. For the most part, the reactors converted naturally occurring uranium into uranium and plutonium fuel. Most of the natural uranium that was used in American projects during World War II was mined in what was then the Belgian Congo, and then after the war that source shifted to the Navajo Nation and surrounding areas. The environmental, human rights, and health consequences of these uranium mining operations, some of which are extreme, are still on going today. For example, there are still hundreds of abandoned uranium mines on or near the lands of multiple indigenous nations in the US, and even though the EPA has entered into settlements totaling one point seven billion dollars, those settlements covered cleanup for fewer than half of these mines, and almost none of them have actually been addressed at this point. Although nuclear research took place at multiple facilities around the country, the primary lamb for atomic bomb development in the US was in Los Alamos, New Mexico. Simultaneously, researchers had to figure out the technology for the bomb, produced the nuclear material to power it, and figure out how to handle that material safely without accidentally allowing it to go critical or supercritical, all while trying to create a weapon that was supposed to go supercritical. One of the bombs that was created through the Manhattan Project was known as Little Boy. Then it was detonated over Hiroshima, Japan, on August six, nineteen forty five. This bomb contained a subcritical mass of enriched uranium along with a subcritical uranium projectile. A gun fired the projectile into the mass, and together the mass and the projectile were supercritical. This bomb was equivalent to about fifteen thousand tons of TNT. It killed an estimated one hundred and fifty thousand people and leveled much of the city. The Manhattan Project also produced three plutonium cores to be used in implosion style bombs during World War II. In this setup, the plutonium core is surrounded by conventional explosives. When those explosives detonate, they compress the core, causing it to go from subcritical to supercritical. One of these cores was detonated at a test at the Alamogordo Bombing and Gunnery Range also called the Trinity Site, on July sixteenth, nineteen forty five. Another was used in the bomb known as Fat Man, which was detonated over Nagasaki, Japan, on August ninth, nineteen forty five, killing an estimated seventy five thousand people. The third plutonium core was nearing completion when Japan announced its surrender on August fifteenth, nineteen forty five, meaning that it was no longer needed for World War two. Later, the US started planning Operation Crossroads, which was a test of nuclear weapons effects on warships at seed to take place off Bikini Atoll.
This third core, the one.
That would later be nicknamed the Demon Corps, was slated for use in these tests, but in the meantime it was used for criticality research. It was during that research that they nicknamed it the Demon cor even though to be clear, did not kill nearly as many people as the other two that were detonated over cities. And we're going to talk more about the Demon Corps after we first pause for a sponsor break. The plutonium core that was eventually nicknamed the Demon Core was originally nicknamed Rufus. I don't know why, but so many sources have said that that seems legitimate. It was a six point two kilogram or thirteen point seven pound sphere really two hemispheres made of refined plutonium and gallium. Under normal conditions, it was ninety five percent of a critical mass, so it's often described as having a hair trigger, although it had been created for use in a bomb. This hair trigger also made the core useful for criticality experiments. Physicists could intentionally reflect neutrons back at the core to push it close to criticality and gather data about what was happening. Physicist Richard Feynman, who's work with the Manhattan Project included helping to work out stand to prevent criticality accidents, reportedly nicknamed these types of experiments tickling the Dragon's Tail. On August twenty first, nineteen forty five, twenty four year old graduate student Harry Dallion Junior was working by himself in the lab. Because of the nature of the work that was being done at Los Alamos, like it was critical to the war effort, it involved part of the nation's nuclear material stockpile, it was standard for security guards to always be present, so even though Dallian was working alone on this experiment, there was one other person in the room that was twenty nine year old Private Robert Hemerley, who was sitting at a table about twelve feet away from the core. Dallian was using tungsten carbid bricks to build a reflective wall around the plutonium core by hand. The bricks reflected neutrons back at the core, inching it closer to criticality. The more bricks he added, the more neutrons were reflected, and the closer the core got to going critical. As Dallian was about to add the last brick in this structure, his instruments showed that doing so was going to cause the core to go critical, so he tried to pull that last brick away, but as he did, it slipped out of his hand and dropped directly onto the core. Dallian used his other hand to knock the dropped brick away, but it was too late. There was a wave of heat and a brief flash of blue light all around the exterior of the sphere. That light was probably Chirinkov radiation, which is the result of charged particles moving faster than the speed of light through a transparent medium like air. In that brief moment between when he dropped the brick and when he knocked it away, Dallian was hit with a blast of neutron radiation. He disassembled the reflector that he had built, and that continued to expose him to gamma radiation while he was doing so. Today, absorbed radiation is measured in gray, with its one gray being equivalent to one hundred rads. A sudden whole body dose of zero point seven gray is enough to cause acute radiation sickness. Sometimes symptoms can develop at as little as zero point three gray. Dallian's dose was estimated at five point one gray. He died twenty five days after the accident on September fifteenth, nineteen forty five. Private Hammerley's dose was estimated at zero point five gray. He survived this incident apparently without serious injury at the time. If you read older articles that were published before his death later on like they'll say that he wasn't seriously harmed, but he wound up dying of leukemia, which might have been related to this radiation exposure, when he was sixty two. Afterward, criticality experiments continued at Los Alamos in spite of this fatality. Although some new safety standards were put into play, the list of people allowed to do these kinds of experiments was shortened, with two sets of monitoring equipment required for each experiment. The new standards reiterated that at least two people in addition to the guard, had to be present for this kind of work. Researchers also started discussing whether it would be better to do these kinds of experiments remotely, so that if a criticality did happen, it would be too far away from people to hurt them. Operation Crossroads was scheduled to start in July of nineteen forty six, but before the core was sent to the Marshall Islands to be used there, physicists were doing one last set of criticality experiments with it. On May twenty first, nineteen forty six, Canadian physicist Lewis Slowten was using a hollow beryllium sphere to mostly cover up the core and reflect neutrons back into it. The sphere had two halves, The core was sort of resting in the bottom half, and he had his thumb threaded through a hole in the top half so that he could adjust the positioning this sort of dome with his hand. He knew that if the sphere closed completely it could cause a criticality, so he used the end of a screwdriver to keep the two halves slightly separate.
This sounds like the.
Kind of thing I would do at my house with something that is not dangerous, And even so my husband would go, are you sure that's how you want to do it?
Yes?
Yes, I have a story on this subject about myself that I will probably tell in our Friday behind the scenes fabulous.
While I have.
Some understanding of how a person might do a really foolish thing, knowing how foolish it is, I was not handling potentially critical nuclear weapons cores at the time. As he was doing this, the screwdriver slipped and the dome totally closed. There was a brief flash of blue light that was visible over the normal illumination of the room. This lasted only a moment as and flipped the dome off of the core. Slowden seems to have immediately understood that he was not going to survive this accident, saying, well, that does it. In general, a whole body radiation dose of more than ten gray is inevitably fatal, and his has been estimated at twenty one gray. At the same time, he had the presence of mind to try to document where the other seven observers in the room had been standing at the time, and then to try to calculate how large of a dose of radiation each of them received. Their doses have been estimated as ranging between zero point three seven and three point six gray. Slowden also tried to detect how much radiation was present in other objects that were in the room, but the detectors themselves had been contaminated in the accident. At the same time, he wasn't thinking entirely clearly. He asked a colleague to scatter film badges used to detect radiation exposure around the area, and that required the colleague to get close to the radioactive corps to do so. Slotin died nine days after this accident at the age of thirty five, and although he was the only person killed, three other people in the room had to be hospitalized for acute radiation exposure.
And one of them was Alvin C.
Graves, who was the closest to Slowtin physically. When this accident happened, Slowtin had actually been training Graves as his replacement. Graves was seriously injured and for a time it was not certain whether he was going to survive. He later developed cataracts and thyroid issues, and his death from a heart attack nineteen years later may also have been related. In general, people have viewed Harry Dallion Junior's accident with a bit more sympathy than Lewis Slotin's. Dallian was working alone, which was against protocol, but he was also a graduate student, so he was not as experienced as many of his colleagues. Slowtin, on the other hand, was not only as senior scientist, but had also co authored the official report on the accident that had killed Harry Dallion, so he definitely understood the risks and the potential for accident. His experiment was meant to be done with two one inch spacers between the two halves of the beryllium sphere, but Slotin had removed these and was using the screwdriver in their place. Multiple other scientists who were aware of the criticality experiment he was doing thought it was inordinately dangerous, and in general he had a reputation for being a little too cavalier around things like atomic bomb cores. Scientists nicknamed this corps the demon Corps, not just because it had been part of both of these fatal accidents, but also because of some eerie similarities between them. Both accidents took place on the twenty first of the month and on a Tuesday, and Slotin and Dallion both died in the same hospital room at the US Engineer's Hospital at Los Alamos. By this point, work had started on remote facility for criticality experiments, and after the second accident with the demon Core, hands on criticality experiments like this were banned. In nineteen forty seven, criticality experiments resumed at the newly completed critical Experiments facility at what was known as the Paharito Site. Criticality experiments there were handled with machinery and took place a quarter mile from the control room where the people doing the experiments were. Since the amount of radiation drops dramatically the farther you are away from the source, this was much safer than doing something like stacking reflective blocks with your hands. Dallian and Slotan were the only two people to die from acute radiation exposure at Los Alamos during the Manhattan Project. Although there were numerous other deaths in and around the facility during those same years, a lot of them were from accidents that had nothing to do with radioactive materials or bombs. This included motor vehicle accidents, construction accidents, and in one case, a ten year old who drowned when a canoe capsized. In nineteen forty six, three custodians also died of ethylene glycol poisoning after drinking wine that was mixed with antifreeze. In terms of the demon Core, for years after this incident happened, it was believed that it was sent on to Bikini Atoll for use in Operation Crossroads as planned, and while it was described as quote a little hot but not too hot to handle, after that second accident, it was saved for the last detonation, just in case that was going to affect the results. That last test wound up being canceled, and the demon Cor was later melted down and reintegrated into the nuclear material stockpile. At some point it was probably incorporated into other weapons. Before we move on, we should note that there have been ongoing issues with safety at Los Alamos National Laboratory in more recent years. Aside from that twenty eleven plutonium photo op that we mentioned earlier. In twenty seventeen, it was rated does not meet expectations in the Department of Energy Nuclear Criticality Safety Programs annual report that was raised up to adequate but needs improvement in twenty eighteen and twenty nineteen. Also, that second accident with the demon core is dramatized in the nineteen eighty nine film Fat Man and Little Boy, with John Cusack as a fictionalized SLOTIN who is named Michael Merriman in the film. Yeah, I watched just that scene while I was working on this, and even knowing literally what's going to happen, I found it very tense. Yeah, so we're gonna take a quick break. The two incidents that we already talked about happened during criticality experiments. The researchers were intentionally pushing the limits to do tests and gather data. But many of the other nuclear criticality accidents have happened while nuclear material was being processed in some way. So these are people working at facilities that were actively trying to avoid a criticality. However, in a lot of cases, the workers who were actually handling this material also were not nuclear physicists. In some cases, they hadn't really been trained in criticality safety at all. They didn't necessarily know that something like the size and shape of a container could be an integral part of preventing a disaster. For example, on March fifteenth, nineteen fifty three, at the Mayak Enterprise facility in Russia, two workers were transferring plutonium solution from one vessel to another. Vessels had been arranged in a row along a wall, and every other vessel was supposed to be left empty to prevent criticality. The vessels were also supposed to contain at most five hundred grams of plutonium, but neither of those limits was actually being followed. Vessels contained plutonium when they weren't supposed to, and also contained more than that five hundred grand limit, So when a criticality occurred during this plutonium transfer, workers not only did not know that it had happened, but they also did not know that it had caused a serious problem because they had not been trained on this. They just noticed that one of the vessels became warm to the touch, so they started removing the plutonium solution out of it and kept on working. They only reported the incident two days later when one of them suddenly became ill. The worker who was closer to the vessel when it went critical ultimately had to have both of his legs amputated because of extreme tissue damage from this exposure.
But in some.
Cases, the staff involved in these incidents were trained. That was the case with Cecil Kelly, who received a lethal radiation dose in a criticality accident at Los Alamos on December thirtieth, nineteen fifty eight. Kelly he had more than a decade of experience, but the tank he was working with had a concentration of plutonium that was more than two hundred times what it should have been. For reasons that are not entirely clear, this happened during a physical inventory when liquids from two holding vessels were moved into one larger vessel. So Kelly was standing on a small ladder to see into a viewing window on a tank that was being used to chemically separate plutonium from other compounds, and when he turned the stir on inside the tank, the shape of the plutonium layer inside this solution allowed it to go critical. The radiation dose to his upper body has been estimated at one hundred and twenty gray. Kelly either fell or was knocked to the floor and was completely disoriented after the criticality. He kept saying I'm burning up, and his colleagues, and a nurse who arrived thought he had sustained some kind of a chemical burn. The nurse even commented that he had nice pink skin. This was actually a sign of radiation exposure, like a mild sunburn, and not a sign of being in good health. Yeah, because of the all of the safety measures and his training and all this other stuff. Like his colleagues, it was like it took a while for them to be like, did a criticality happen and we didn't realize it. Kelly died thirty five hours after his exposure, and his death actually sparked the Human Tissue Analysis project at Los Alamos. They would keep tissue samples for further study, and that actually led to a lawsuit. Kelly's family had authorized an autopsy to determine his cause of death, but they did not imagine that that was going to include tissue samples being retained for further study through this program. Other criticality accidents during the nineteen fifties and sixties stemmed from workers intentionally bypassing safeguards meant to prevent them. Once such accident happened on July twenty fourth, nineteen sixty four, at a facility that recovered uranium from scrap metal in Wood River Junction, Rhode Island. This facility had been in operation for about four months, and part of the process involved workers manually shaking eleven liter bottles full of contaminated solvent. This was a tedious process that no one particularly enjoyed, so a worker had the idea to combine the contents of several eleven liter bottles into a large tank and to use a stir. Running Concurrently with that decision, one of the plant's evaporators had not been working properly, and it turned out that this was because it was plugged with uranal nitrate crystals, that is, a uranium salt. Fixing that problem involved filling several bottles with a concentrated ural nitrate solution. As that plug was dissolved and removed. Even though those bottles were labeled, someone mistook them for the ones that contained the contaminated solvent, which was being mixed in the large tank. When the concentrated urinal nitrate solution was dumped into the tank, it went critical, causing a blue white flash of light and splashing liquid up and out of the tank and directly onto the worker. The criticality alarm sounded and the worker ran to a nearby emergency shack. A supervisor who came in to investigate turned off the stirr in the tank, which caused a second criticality as the solution changed shape. But no one knew about the second criticality at the time because the alarm was still going off from the first one. Yet there were multiple multiple failures in the process and the safety measures that were involved in this incident. The technician who had been working the tank during that first criticality died of acute radiation exposure two days later after a radiation dose of about one hundred gray. The supervisor's dose was somewhere around one gray. Other people nearby were also exposed to lesser doses as well. A similar incident took place at the Mayac Enterprise facility on January second, nineteen fifty eight. Workers decided to drain a tank that had been used to hold material from criticality experiments faster than it was designed to drain. They removed the bolts that were holding the tank to the structure and tipped it over to drain it into containers. The shape of the material created in this process allowed a criticality which ejected a huge amount of material from the tank. Three of the four people who were doing this task died as a result, and the fourth, who was about three meters away at the time, was blinded and had long term damage to the systems and organs on the left side of her body, which was closer to the tank when it went critical.
Yeah.
I took notes on so many other incidents as I was working on this, and it's really like almost the same story over and over and over. A lot of it involves containers of the wrong size or shape being used when they should not have been. So the good news is criticality accidents like this are far less common today than they were during the nineteen fifties and sixties. Some of this is thanks to the end of the Cold War, so the rush to develop and produce nuclear weapons meant the United States and the Soviet Union in particular, had a lot of facilities that were working with these kinds of materials. As we noted earlier, the accumulation of enough material to even be able to cause a criticality, and an understanding of what it took to prevent a criticality. Those two things were happening in tandem. In some cases, these facilities were basically working out safety standards as they went, and others, though they were disregarding safety standards in order to get work done faster or more cheaply. But it's also because as these incidents happened, the governments and facilities involved got better at designing procedures and protocols to prevent them in the future, like instead of having a line of containers half of which were meant to be left empty, just not having containers arranged in a way that a criticality could ever result, or not allowing containers with geometry that could allow a criticality into the facility at all. As a result, when it comes to criticality accidents during processing and handling, the world has gone from multiple fatal accidents every year to fewer than one per decade. The other side of that progression, though, is that when criticality accidents have happened since then, a lot of times they've been just totally unexpected. In nineteen ninety nine, there was a criticality at the fuel conversion test building at the JCO Fabrication Plant Company site and Tokamura, Japan workers were using containers with unfavorable geometry because the ones they were supposed to be using were more difficult to fill, and the criticality accident that resulted from this was ongoing, with criticalities recurring over the course of twenty hours. Two of the three workers who were nearby when it started died, and radiation was released into surrounding neighborhoods around the plant. Although this nineteen ninety nine incident was similar to earlier ones in that workers had been using the wrong containers to make their jobs easier, it was also really an outlier. There were so many procedures and standards in place at the facility that people didn't think a criticality was even possible there. Because of this belief, there weren't even criticality alarms at the facility. The sensors that reported something amiss were gamma detectors. Yeah, so we're going to have to have nuclear facilities doing such work.
The good news is we're better at it now.
Glofully, as I was worried on this and I was going through all of these, all of these criticality incidents, I got to this point where I was like, man, what what's an outcome that can be here? Because just having one after another of these incidents was it just incredibly grim, and it really is like, if you look at sort of a timeline, it goes from just a block of multiple every year through the fifties and sixties to like, we get to the seventies and it's like one and then a whole long time and then one. So fingers crossed, we are past this as a society and a global world culture. Sure, thanks so much for joining us on this Saturday. If you'd like to send us a note, our email addresses History Podcast at iHeartRadio dot com, and you can subscribe to the show on the iHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows.
