On its 20th anniversary – Recalling Japan’s worst nuclear accident before the Fukushima nuclear reactor meltdowns on March 11, 2011
“TOKAI MURA CRITICALITY ACCIDENT”
— on 30 September 1999
“Japan’s worst nuclear accident – until 3.11”
— briefing by Greenpeace, linked here: TOKAI MURA CRITICALITY ACCIDENT 30 Sept 2019 public -1
“Twenty years ago today on 30 September 1999, Japan experienced the start of its worst nuclear
accident up until that time. Workers at the JCO nuclear fuel fabrication plant at the Conversion Test
Building in the town of Tokai-mura, in Ibaraki prefecture (north of Tokyo) were manufacturing
medium enriched uranium fuel for use in the JOYO experimental Fast Breeder Reactor. Behind
schedule, untrained and operating with a manual that had been doctored by management to increase
work rate but reduce safety margins, three workers were pouring uranyl nitrate solution that was
medium enriched uranium (around 18% U-235) into a settling tank. Instead of the specification of
2.4kg they added 16 kg of uranium to the tank. At 10.35 a.m. local time a critical chain reaction was
created – not inside a nuclear reactor building – but a steel tank, inside a conventional industrial
building in the middle of a town, a community.”