An alarm was triggered at a onetime nuclear fuel manufacturing facility Wednesday after radioactive substances leaked from materials that were being transferred at the facility operated by the Japan Atomic Energy Agency in Tokai, Ibaraki Prefecture, company officials said.
All nine of the workers who were in the room when the radiation leak occurred were cleared with no ill effects to their health, JAEA official Shinichi Nishikawa told a news conference.
JAEA said the workers, each wearing a mask, escaped radiation exposure after running into another room. No leak was detected outside the Nuclear Fuel Cycle Engineering Laboratories. The facility ended nuclear fuel production in 2001 and is being decommissioned.
The cause of the leak is under investigation. The agency suggested possible damage to the plastic covers during the routine change.
Officials told the news conference that they would begin assessing the site as soon as possible to determine how much radioactive material had been leaked and if it was still leaking.
The agency will file a report of its findings to the Nuclear Regulation Authority and come up with preventive measures.
The warning alarm that detects radioactive materials went off at around 2:30 p.m. as workers were removing radioactive materials — which were contained in a plastic bag — from sealed-up equipment that had been used for experiments.
The mixed oxide fuel (MOX) and plutonium was being kept in a sealed glove box container for future research.
The alarm is set up in an area of the facility once used for the production of MOX nuclear fuel made by mixing uranium with plutonium extracted from spent nuclear fuel.
In June 2017, a JAEA research facility in the town of Oarai, Ibaraki Prefecture, was the scene of another leak of radioactive substances, including powdered plutonium, when a plastic bag containing nuclear fuel remnants exploded. Five workers who were handling the materials were exposed to the substances.
JAEA possesses about half of the 10.5 tons of separated plutonium that Japan stores domestically, while an additional 37 tons have been reprocessed and are stored overseas. To reduce the stockpile, Japan burns plutonium as MOX fuel in conventional reactors.
Restarts of halted nuclear plants have proceeded slowly amid persistent anti-nuclear sentiment since the 2011 Fukushima nuclear power plant disaster.