2 Août 2017
August 2, 2017
Japan rates severity of June nuclear exposure accident as level 2
TOKYO (Kyodo) -- The Nuclear Regulation Authority said Wednesday that it assessed the severity of a nuclear exposure accident in June in eastern Japan provisionally as level 2 on the zero-to-seven international scale.
The June 6 accident at the Japan Atomic Energy Agency's Oarai Research and Development Center in Ibaraki Prefecture, east of Tokyo, left five workers internally exposed to radiation although no harmful consequences were detected for the surrounding environment.
Level 2 on the International Nuclear and Radiological Event Scale is a stage defined as an "incident." The Fukushima nuclear accident, triggered by the huge earthquake and tsunami in March 2011, was rated at the maximum level 7, on a par with the 1986 Chernobyl disaster.
When one of the five workers, a male in his 50s, opened a container in a storage room at the facility, a plastic bag inside it with plutonium and uranium powder samples ruptured.
The worker continued the check even when the plastic bag swelled, resulting in the inhalation of radioactive substances. Tests have found a small amount of radioactive materials -- plutonium and americium -- in the urine of the five workers, confirming they suffered internal radiation exposure.
It was estimated one of the workers will be internally exposed to a radiation dose from 100 to 200 millisieverts in total over 50 years, a level that could slightly increase the risk of cancer.
NRA Chairman Shunichi Tanaka urged the JAEA to take measures to prevent further accidents, saying it is "responsible for ensuring the safety of workers."
Japan previously assessed as level 2 a critical-state accident at the No. 1 reactor of Hokuriku Electric Power Co.'s Shika nuclear plant in 1999. The utility hid the accident, which occurred while the unit's operation was suspended for regular checkups, until 2007.
Tokyo also rated as level 2 a 1991 accident at the No. 2 reactor in the Mihama plant run by Kansai Electric Power Co., in which one of a steam generator's tubes snapped, activating the emergency core-cooling system for the first time in the country.
Oarai nuclear accident rated as Level 2
Japanese nuclear regulators have provisionally assessed an accident at a research facility north of Tokyo as Level 2 on an international scale.
In June, 5 workers at the Oarai Research and Development Center of the Japan Atomic Energy Agency were exposed to radioactive substances when a bag containing them burst open.
The agency reported to the Nuclear Regulation Authority that the highest possible level of exposure would be 100 to 200 millisieverts over a 50-year period.
The authority made the announcement on Wednesday.
Level 2 accident is third from the bottom on the 8-level nuclear and radiological event scale.
The last Level 2 accident in Japan was at Onagawa No.2 reactor in Miyagi Prefecture, where the tsunami triggered by the March 2011 earthquake flooded the reactor building basement and caused key pieces of equipment to stop operating.
The accident at Fukushima Daiichi nuclear plant caused by the same tsunami was rated far higher, at Level 7.
The sodium leak at the Monju fast-breeder reactor in 1995 was assessed as Level One.