 The handling of the chemical process for the purification of uranium is unquestionably dangerous if confronted by either human or technical thought. In the same year of the near tragic disaster of the criticality accident at the Y-12 plant, an operator at Los Alamos would not be so lucky. We're back here with yet another criticality accident. This one has been on my list for a while and I've been looking forward to having a deep dive into the Cecil Kelly incident. The late 1950s was a bad time for nuclear accidents. With windscale in 1957, kistium in 1957 as well, the NRU fuel accident, the Y-12 and the Cecil Kelly criticality accidents in 1958, just to name a few. Needless to say, if you're working back then in the nuclear industry, then you better have had good insurance. Today, we are back at the Los Alamos Laboratory, but a third and lesser known fatality from a criticality event, the first two being linked to the Demon Corps. Although not as scary sounding as the Demon Corps, the 1958 criticality that led to an operator's overexposure and subsequent death is arguably far more worrying as the time between exposure and death was just under two days. Los Alamos Post-Manhattan Project had been renamed the Los Alamos Scientific Laboratory and things had changed from the 40s when nuclear weapons were built by hand by experts. They said the laboratory had started to move towards mass production using lower skilled workers almost like a factory line. Even though bomb manufacturing had changed, the lab still undertook multiple experiments using different radioisotopes and this necessitated reprocessing and recovery. However, an unusual set of circumstances would result in a supercritical mass as the area of the incident typically only dealt with lean residues from plutonium recovery operations. These lean residues were usually sub 0.1g per litre containing plutonium and americium. The process used a chemical we've seen before in this channel, tributylphosphate, also known as TbP, which was used to separate the two radioisotopes and this was carried in an organic solvent. The solution was evaporated after being extracted to an aqueous solution to concentration resulting in a solution containing a few grams of plutonium per litre. The solution is then fed back into an earlier part of the process. The now extracted plutonium rich solids are then sent to another part of the plant for processing into smaller batches. Now that was a normal operation of the plant at Los Alamos. However, at the time of the criticality event an inventory was being undertaken. This involves stopping the normal flow of work to evaluate the residual materials in the processing machinery of plutonium content. The solution was filtered for evaluation and whilst this was undertaken, the process machinery was cleaned. On the 30th December 1958, dilute, aqueous and organic solutions from two vessels were washed into a single large vessel. The aqueous solution was removed from this vessel and the remains of approximately 200 litres of material, including nitric acid wash, was transferred to a 850 litre, 96 centimetre diameter stainless steel tank fitted with a mechanical stirrer. The kind of mixer you'd find at a bakery, albeit for mixing dangerous materials, which with my cooking skills is indistinguishable. This tank contained about 295 litres of acoustic stabilised aqueous organic emulsion and the added acid from the new material separated the liquid phases. The liquids ended up settling into two layers, the top being 160 litres organic material, containing around 3.27 kilograms of plutonium. The bottom layer consisted of around 330 litres of aqueous solution and had around 60 grams of plutonium in it. A critical mass was not achieved at this time, while the two layers being separate. The top layer was 20.3 centimetres thick and criticality would have been achieved by a thickness of 21 centimetres. Settle Kelly, a Los Alamos worker with many years of experience, was about to set off a power excursion which would end his life without even knowing it. Kelly had turned on the tank stirrer at around 4pm on the 30th December and as the agitator blades spun up to its set 60 rpm, the two layers started to mix together. To observe the mixture, the tank had a couple of viewing ports protected by thick glass. Kelly was standing on top of a small step ladder to watch the mixing in operation. The motion changed the reactivity from about $5 subcritical to super prompt critical and a power excursion occurred. Almost immediately, Kelly experienced a blue flash and a bang from within the tank. This knocked him off the ladder. Realising something was wrong, he turned off the mixer. He turned the mixer back on to hear a rumbling sound. By now, Kelly had started to feel burning over his skin and was assisted by two other operators to a shower moving back past the tank. One of the operators assisting turned off the mixer. Kelly was heard exclaiming, I'm burning. Initially it was thought that Kelly had experienced some kind of acid burn, hence the sharing. However, it was far worse than that. A radiation alarm set to go off at 10mph 175ft away was activated by the short, sharp increase from the excursion. This caused an evacuation of the site at 4.35pm. To make the tank safe again, the unknown concentration of plutonium solution had to be removed. To facilitate this, an array of small tanks was fabricated and placed 100ft away from the mixing tank. All the solution taken from the tank was analysed to figure out how much plutonium was within. A drain line was fixed to the underside to drain the fluid. As it was unknown on the level of radioisotopes in the solution, a temporary shield was set up to protect operators. A maximum reading of one REM per hour was taken from the tank reducing to 50mrems after it was fully emptied. Now back to Kelly. Within 15 minutes of exposure, he had experienced severe shock, eventually becoming unconscious. His average whole body dose was first estimated by measuring the radioactivity of his blood. This showed sodium and other light metals had activated into radioisotopes such as sodium-24. It was estimated he received 900 rad from fast neutrons and 2700 rad from gamma rays, giving a total of 3600 rad. However, in a later postmortem, this figure was closer to 4000 rad. 70 rad and above can cause acute radiation sickness. 500 rad is almost certainly a lethal dose. Six hours post-event, Kelly's white blood cells virtually disappeared from his peripheral circulation, hinting at a deadly downward spiral. 24 hours post-event, a bone marrow biopsy was taken to show watery-like substances instead of a healthy, bloody one. On the second day post-exposure, Kelly experienced hard-to-control abdomen pain, lost all color to his skin, and following an erratic pulse, passed away. What was strange was how an operator with over 11 years of experience had been in the center of an accident like this. In an AEC report, it was highlighted that Kelly had deviated from the instructions given, mixing multiple batches in the same tank, probably believing he was dealing like most other days with low concentration solutions. However, this mistake sadly bought him a slow and painful demise. Similar to the Y-12 complex, Los Alamos had employed strict administrative controls to prevent criticality of the solutions processed on site, but was planning on getting rid of the larger tanks for more safe geometry containers. Administrative controls had been used on the site for seven years successfully, and were considered acceptable for the additional six to eight months, but it would be required to obtain and install the improved equipment. Ironically, during this period, the site experienced a breakdown in controls and a fatality from a power excursion. The accident, along with Y-12 and Wood River Junction, really shows how criticality controls can't be relied upon, as human nature seems to override the strict discipline needed. All these incidents help push for geometry safe controls for fuel and waste processing. However, again, human nature has caused other events, such as the Tokimura criticality. I hope you enjoyed the video. If you'd like to support the channel financially, you can from $1 per creation, and that gets you early access to videos and access to votes. I have YouTube membership as well, and that gets you from 99 pence per month, early access to videos. 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