Mars 2011: Kärnkraftverket i Fukushima - utbruten och sammanfogad tråd

TOKYO, April 8

While the spent fuel pools at the Onagawa plant and the Higashidori nuclear power station in Aomori Prefecture, both operated by Tohoku Electric Power Co., lost their cooling functions for 20 to 80 minutes after the quake, the temperature hardly rose, the Nuclear and Industrial Safety Agency said.

A small amount of contaminated water spilled on the floor was observed inside the buildings at all three reactors at the Onagawa plant, which has suspended operations since the mega earthquake and tsunami last month, according to the agency.

In all, water spilled or leaked at eight sections of the plant as a result of the 11:32 p.m. quake, according to Tohoku Electric.

As much as 3.8 liters of water leaked at one of them, with the highest level of a radioactive isotope -- 5,410 bequerels per kilogram -- found in the spilled water on the floor beside a spent fuel pool in the building housing the No. 1 reactor.

A spent nuclear fuel disposal facility in the village of Rokkasho, Aomori Prefecture, lost external power supply and switched to an emergency generator but power was restored at 9:44 a.m. Friday, according to the agency.

The Higashidori nuclear power plant in Aomori also got power from an emergency generator after the Thursday quake, but its external power supply was restored at 3:30 a.m. Friday, according to Tohoku Electric and the government's countermeasure headquarters.

No changes in radiation readings have been observed at any of the facilities, including Fukushima Daini, a nuclear power plant just south of Daiichi, both operated by Tokyo Electric Power Co. Nor is there any information that radioactive materials have leaked outside due to the aftershock.

Higashidori's only reactor was undergoing regular maintenance at the time of the temblor, and its fuel rods were not inside the core but were stored in a spent fuel pool, the agency said.

The Onagawa nuclear plant lost three of its four external power connections but one of them was restored on Friday morning, with its cooling system for the spent nuclear fuel pools temporarily stopped.