The Japan Atomic Energy Agency says a tiny hole in a plastic bag may have been responsible for a leak of radioactive substances at one of its laboratories in Tokai village, north of Tokyo, last month.
The president of the agency, Toshio Kodama, on Friday reported the theory to a science ministry task force investigating the matter.
The leak occurred as workers were packing a container of nuclear fuel materials into special plastic bags at the agency's Nuclear Fuel Cycle Engineering Laboratories in Ibaraki Prefecture on January 30. The workers realized there was a problem when an alarm went off.
The agency says no one was exposed to radiation, and the leak had no impact on the surrounding environment.
Kodama said officials found a roughly five-millimeter-wide hole in one of the plastic bags, and they believe the radioactive substances leaked from there.
The trouble occurred less than two years after five workers were exposed to radiation at another facility run by the agency in the prefecture. On that occasion, a bag that the workers were handling burst open. The agency responded by introducing preventive measures.
The head of the science ministry task force, State Minister Keiko Nagaoka, said the latest case has eroded public trust in the agency.
Nagaoka said the ministry will consider whether the agency took sufficient measures to prevent the leak.