Japan Atomic Energy Agency announced Thursday that a pool of radioactive water was found in the radiation uncontrolled area of its materials testing reactor in Oarai, Ibaraki Prefecture.
The amount of radiation in the water was small and posed no threat to the environment or people, the agency said.
According to the agency, a worker was patroling the ground floor of a building that stores below it water and resin used to produce water for cooling a nuclear reactor, and found some 66 liters of water on the floor. The ground floor has a pump to send contaminated water from underground to another facility.
The testing reactor has not been in operation.