A Japanese state-run nuclear fuel laboratory near Tokyo said Wednesday it detected a radiation leak in its plutonium handling facility, but no workers were exposed.
The Japan Atomic Energy Agency said a radiation alarm went off after nine workers changed plastic covers on two canisters containing MOX, a mixture of plutonium and uranium, and removed them from a sealed compartment.
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 in Tokai Village, Ibaraki Prefecture. 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.
JAEA has been reprimanded repeatedly by Japanese nuclear authorities for its poor safety record in recent years. A bag of plutonium broke during an inspection at another facility operated by the agency in 2017, contaminating five workers. A plutonium-burning fast breeder reactor, Monju, is being scrapped after suffering an accident in 1995.
Japan's possession of large plutonium stockpiles from its struggling nuclear spent-fuel recycling program has raised international concerns. Critics say Japan should stop extracting plutonium, citing risks of it being used to develop nuclear weapons. JAEA possesses about half of the 10.5 tons of separated plutonium that Japan has at home, 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.