The operator of the Tsuruga nuclear power station in central Japan said Monday a "minute amount" of radiation leaked from the plant, a news report said.
Japan Atomic Power Co said the radiation was released from its Tsuruga nuclear power plant, a week after the operator found higher levels of radioactive substances in coolant water, Kyodo News reported.
The two incidents at Tsuruga in eight days took place amid growing public concern about another possible nuclear accident and demands to review nuclear energy policy, dpa reported.
Since the Fukushima Daiichi nuclear plant was damaged by the March 11 earthquake and tsunami, it has leaked radioactive substances into the air and sea.
The Tsuruga plant is located on the west coast of Japan, some 500 kilometres south-west of Fukushima and was not affected by the disaster.