A nuclear reactor in the Hokkaido village of Tomari sprung a coolant leak over the weekend, but no radioactive material seeped out of the facility, according to officials of Hokkaido Electric Power Co.
The primary coolant leak occurred at the regenerated heat exchanger room at the Tomari nuclear power station's No. 2 pressurized water reactor, the officials said.
It is the first time that primary coolant has leaked at this power plant.
Hokkaido Electric said Monday that the leak had been caused by a small crack in the weld connecting the heat exchanger and the piping system.
The firm said it would examine the crack in an ultrasonic wave test to see if it can be repaired while keeping the reactor in operation. The reactor will have to be shut down if the repair needs more than a week, the officials said.
At around 10 p.m. Saturday, workers noticed the fluid level was rising in the area where liquid material is stored inside the reactor and discovered that primary coolant had been mixed in, the officials said.
The increase in the fluid level stopped at around 2 p.m. Sunday after workers changed the flow inside the reactor so that the coolant could not pass through the regenerated heat exchanger, which adjusts the temperature of the coolant.
About 140 liters of primary coolant had leaked for 16 hours inside the reactor, capable of producing up to 579,000 kilowatts of electricity, the officials said.
There were no abnormalities detected during an inspection conducted at the plant by Hokkaido Electric Power between October and March, including in the regenerated heat exchanger, the officials said.