A Brief History of: The Tokaimura Criticality Incident (Short Documentary)

the towing industry puts a great deal of focus on the safety of nuclear reactors as is on a disposal of waste products from fission and on the hull this focus has created a safe clean source of energy however one part of the fuel cycle was much less regulated and VC's the processing of fuel this is due to a lower potential for widespread harm because of its many countries historically have not been as far in the laws and checks required for such an operation and Japan was one of those countries in 1999 Japan's largest civil nuclear industrial accident took place at a fuel reprocessing plant into chimera and it would hold it on our until 2011 [Music] tako village is located 120 kilometres northeast of Tokyo about here on a map the village had become a center for the Japanese nuclear industry since 1956 the opening of the Japan Atomic Energy Research Institute there are several nuclear related sites in Sakai for example with Japan atomic power company nuclear power plant the Japan Atomic Energy Research Institute establishment and a fuel reprocessing plant owned by jco the Japan nuclear fuel conversion company or jco was a wholly owned subsidiary of sure Ito metal mining company limited and ran free reprocessing palms on the site at taco Mora within 10 kilometers was a population of around three hundred and ten thousand inhabitants with 150 residents living within 350 meters in June 1984 permission for a change in the jco licensing conditions to encompass a new conversion milling was given by the prime minister after a review by the Japanese Science and Technology Agency in total the jco operated free conversion buildings on the site Sakai the conversion building was on the western side of the site nearest boundary were the municipalities of Takei and nakanishi the building was commissioned in 1988 and had an annual capacity of around 3 tons of uranium-235 with an enrichment of up to 20% this level of enrichment was much higher than needed for regular reactors but instead supplied various research and specialist reactors one such being the Jo fast research reactor the jato plant had a particular approved method of fuel preparation this involves dissolving uranium oxide powder into nitric acid in a tank and then transferred as pure renal nitrate solution to a storage column for mixing followed by transfer to a precipitation tank this tank was surrounded by a water cooling jacket to remove excess heat generated by the chemical reaction the facility was not operated constantly but instead and when needed for short production runs of less than 200 kilograms for licensing conditions limiting the volume and mass of the facility production helped reduce the risk of criticality incidents as well as the process itself a key part of the design of the process was in the storage tank with a criticality safe layout which allowed control of the amount transferred to the precipitation tank due to be type of facility Japanese legal requirements didn't have a need for periodic inspections and obviously this would turn out to be a big mistake as corners would get cut the allowed working procedures was modified in 1996 without the permission from the regulating authorities instead of dissolving the uranium oxide in nitric acid inside a disillusioned tank stainless steel buckets were used further still the procedure was modified by the operators to speed up the process by pouring the solution directly into the precipitation tank completely cutting out the mixing column and his criticality controls mechanical Stara was used in the precipitation tank to mix up the solution this also meant that there weren't proper controls FLIR mount tipped into the hundred liter precipitation tank but tanks dimensions or 45 by 61 centimeters increase the chance of criticality also as a cherry on a glowing cake of screw-ups the IAEA would later find bet management provisions for the Prevention of accidents showed no clear and specific qualification and training to have been established this leads us on to the accident on the 30th of September 1999 three staff members at a jco facility have been preparing fuel for the joy a fast reactor and had been working to the modified unregulated process previously when the new method had been devised the fuel being prepared was at a level of around five percent enrichment much lower than the 18.8% they were working on this time no another facility really understood the increased chance of criticality clearly as they wouldn't have done what they had per day before around 26 liters of solution had been poured into the precipitation tank you four batches and on the morning of the 30th the workers carried on as they had before by 10:30 a.m. another free batches had been prepared and poured into the tank resulting in about 40 litres residing aside the equivalent of around 16 kilograms of uranium this was what was needed to create a critical mass the nuclear fission chain reaction became self-sustaining and began to emit intense gamma a neutron radiation triggering a number of alarms the criticality incident didn't create an explosion however fission products were released into the building the free workers evacuated and were treated on site by emergency service workers and the rest of the site workers gathered at a muster zone at around 11:40 a maximum gamma radiation was measured as 0.85 millisieverts an hour in an area around the facility and at 5 p.m. the maximum Neutron dose rates at the site boundaries were measured to be around 4 millisieverts an hour due to it being a wet process the water in a solution acted as a moderator prolong in the reaction for the next 20 or so hours criticality continued intermittently with monitors outside the building gradually recording levels down to background radiation the reason why it lasted so long was due to the solution boiling creating voids halting the criticality but as soon as it cooled down the voice disappeared starting up the reaction again the erection was stopped once coolant water was drained away as it was acting as a neutron reflector enhancing fission it took the opening of valves and the cutting of a pipe to get rid of some of the coolant water however argon gas was pumped through the system to get out as much as possible at the same time as a water removal efforts were taking place to repair for injection of aqueous boric acid into the precipitation tank so it would remain subcritical at 8:19 on the 1st of October the boric acid solution was pumped in completed at 8:30 9:00 a.m. at oh 9 18 after an inspection criticality was confirmed over during the initial response and bore an injection 27 workers were exposed to varying levels of radiation after criticality had ceased focus shifted to shielding the surrounding area from gamma radiation on a second of October sandbags were placed around the facility building and concrete walls were erected in other parts of the site due to no explosion Fisher materials were not ejected from the rim and even more importantly the building had been compromised structurally this meant that the facility's exhaust filtration system was still intact and thus limiting contaminated particles from leaving the containment building however some noble gases did escape conversion facilities such as this one are kept under negative pressure meaning the air leaks into the building rather than escape out I was found by workers pumping in the borage solution that the system was intact he was confirmed with a smoke test on the 5th of October it was later decided to stop the exhaust system and instead rely on a passive confinement of the facility building five hours after the initial incident 161 people had been evacuated who lived in around 39 properties within a 350 meter radius of the jco facility however these people were allowed to return after the installation of the shielding and residence within 10 kilometers of the site were asked to stay indoors however a restriction was lifted the next afternoon the free workers present at the tyranny accident Hisashi al Chi yutaka Yoko Kawa and Masato Sheena Hara were transferred to hospital two of which were in a serious condition each worker received a full-body dose of radiation the worst of which receiving between 16 and 20,000 millisieverts a fatal dose is considered around 8,000 the second worker received between 6 to 10,000 millisieverts and a final work have received between one and five thousand his lower dose was due to being behind a desk doing paperwork at the start of the incident 24 more workers received a dose of up to 48 millisieverts it was also estimated that one member of the public received a dose of 24 millisieverts with several others receiving 15 or for the worst of the exposed workers Hisashi the prognosis was not looking good having drifted in and out of consciousness before getting to the hospital tests on out cheese vomit showed signs of isotopes sodium 24 confirming that he received a dose of neutron radiation in October he was transferred to the University Hospital Tokyo where he received a blood stem cell transplant however on a 21st of December he died after intensive treatment including multiple blood transfers and skin grafts I won't show him here but the photos of Hisashi post accident are absolutely harrowing the second marker Masato Shinohara was not in the best shape with radiation damage to his lungs causing him to contract pneumonia in the incidence I am appalled it was stated that his prognosis was unknown her Vashon Hara sadly passed away on the 27th of April 2000 due to multiple organ failure the third worker Yutaka Yoko Kawa survived after six months of intensive hospital care examinations of activation materials in items such as coins in the immediate area near the facility showed that during the incident around a hundred millisieverts of radiation would have been exposed to nearby residents if it wasn't for the Swift evacuation it was estimated that around 160 Terra becuse of noble gases and 2 terabyte fuels of gaseous iodine were released from the criticality incident however it was thought that not much had escaped the building by October I am a germans of the residential area around the facility showed levels on piled expected natural background rate measurements of iodine-131 in the soil showed to be no problem for the levels allowed for food the Japanese authorities class the incident as a level 4 on the ine s scale essentially saying it was an event we have no off site significant risk the IAEA report pegged the blame for the incident on operator error which it essentially is lack of knowledge by the workers and shortcuts to the process were also important factors the event had an economic impact on the area affecting house prices and the cost of local produce the accident was a wake-up call for the Japanese nuclear industry with six jco employees including Yokogawa charged with negligence resulting in death all six pled guilty for charges were issued due to the dangerous corner-cutting in the license process for the creation of the solution the jco received six thousand eight hundred and seventy five cases for compensation and paid out a hundred and twenty-one million dollars on the 30th of september 2000 the Japanese government created new laws and the institutional changes to try and prevent such an accident from happening again for example regular visits and more stringent checks on facilities as well as giving the Prime Minister more power in calling a general emergency for license for the facility was revoked by a regulator and in 2000 afraid to jco facility ceased uranium conversion activities moving forward most reprocessing facilities are now automated and many use dry processes essentially ruling out the type of accident that took the lives of two workers in September 1999 thank you for watching what do you think should have the 6j co-employees been charged let me know in the comments below if you're too small be financially I have a merch store and a patreon page if you want to help to channel money free then like subscribe and share my videos and all that's left to say is thank you for watching [Music]

Channel: Plainly Difficult

Views: 1,332,899

Keywords: tokaimura, history, Chernobyl, nuclear, atomic history, Japanese, Fukushima, a brief history of, plainly difficult, demon core

Id: acpz3CG1xi4

Length: 13min 33sec (813 seconds)

Published: Thu Dec 12 2019