A fire blazed for two and a half hours on Monday during an experiment at a nuclear energy facility in central Japan, but there was no danger of radiation leakage, a spokesman said.
No one was hurt in the fire at the nuclear waste disposal facility of the Japan Atomic Energy Agency in Tokaimura, a nuclear hub located 110 kilometres (70 miles) northeast of Tokyo, agency spokesman Satoshi Waku said.
"There was no risk of radiation leakage as we have not used real nuclear waste this time," the spokesman said, noting that employees were testing a system designed to solidify nuclear ash so it can be disposable waste.
Employees were later able to douse the blaze.
Japanese nuclear energy companies have come under fire for a string of accidents in recent years blamed on human error and poor maintenance.