Hokkaido Electric Power Co. is shutting down for repairs a nuclear reactor that suffered a primary coolant leak over the weekend, Hokkaido government officials said Wednesday.
It is the first time that the No. 2 pressurized water reactor at the Tomari nuclear power station in the village of Tomari has been shut down since it began operating in 1991, the officials said.
They said the reactor was to be gradually shut down manually starting at 6 p.m. Wednesday, with operations coming to a complete stop around midnight. The reactor is capable of producing up to 579,000 kilowatts of electricity.
Ultrasound tests found a hole of less than 1 mm in the welding that connects the regenerated heat exchanger with a pipe, the officials said.
On Saturday night, plant workers noticed an unusual rise in the fluid level in the area where liquid material is stored inside the No. 2 reactor. They later discovered that primary coolant had mixed in with the other fluid after leaking from the regenerated heat exchanger room.
The increase in fluid level stopped early Sunday afternoon 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, according to Hokkaido Electric Power officials.
About 140 liters of primary coolant had leaked inside the reactor. No radioactive material seeped out of the facility, they said.