A nuclear research facility where workers were irradiated in a June 6 accident had previously been advised by the Nuclear Regulation Authority (NRA) to improve its radioactive material storage methods, it emerged on June 8.
Four workers at the Japan Atomic Energy Agency (JAEA)'s Oarai Research & Development Center in Ibaraki Prefecture suffered internal radiation exposure in the incident, including one man in his 50s found with up to 22,000 becquerels of plutonium-239 in his lungs. The total level of radioactive materials in the man's blood, bones, organs and other parts of his body was estimated at 360,000 becquerels, based on the amount detected in his lungs. The material was in powder form, and had been in storage at the facility since 1991.
In November 2016, the NRA apparently asked the JAEA to implement improved storage methods for radioactive materials used for nuclear fuel at a total of 12 facilities -- including at the Oarai R&D center. The demands came after it was discovered that some of the materials had been neglected in inappropriate storage conditions for over 35 years.
It has also come to light that the June 6 Oarai accident occurred while the workers were trying to carry out tasks in response to the NRA's improvement request.
Appropriate storage areas at such facilities are determined under the rules of the relevant facility -- which are in turn based on national laws and regulations. In 2016, alarm bells were raised when NRA inspectors performed safety checks at numerous facilities, and discovered that radioactive materials were being stored incorrectly.
The 12 facilities issued NRA warnings are: three facilities at the Oarai R&D center, four facilities at the Nuclear Fuel Cycle Engineering Laboratories and three facilities at the Nuclear Science Research Institute -- all in Ibaraki Prefecture -- plus two facilities at the Ningyo-toge Environmental Engineering Center in Okayama Prefecture.
With regard to the Oarai facility where the accident happened, it was discovered that 101 different radioactive materials that were not intended to be used had been left for up to around 25 years in a "glove box" designed for operations.
After the NRA improvement request, the facility's storage area was still completely full with 80 stainless steel containers of radioactive materials. The center had planned to make space by combining the materials, and began opening each container in February this year to check the contents. The June 6 accident happened during this process. The container involved in the accident had apparently not been opened once during its 26 years in storage.