Not taking anything for granted, the Tohoku Electric Power Company has conducted a drill in its Higashidori nuclear plant in Aomori Prefecture (in northeastern Japan) to prepare for a potential total loss of external power to one of its reactors in an emergency.
The owner of the nuclear plant, Tohoku Electric Power Co., Inc. is an electric utility, servicing 7.6 million individual and corporate customers in 6 prefectures in the Tohoku region (including Aomori prefecture). It is the fourth-largest electric utility in Japan in terms of revenue behind Tokyo Electric Power Co., Inc. (TEPCO), Kansai Electric Power Co., Inc., and Chubu Electric Power.
The reason for the power loss drill was the fact that the Higashidori nuclear power station in Aomori Prefecture lost all its external power supply in an aftershock on April 7, 2011. An emergency diesel backup generator began cooling the reactor, but the generator failed shortly after external power was restored.
The Higashidori Nuclear Power Plant is located in the town of Higashidori in eastern Aomori Prefecture on the Shimokita Peninsula. Just like any other nuclear plants near the sea, the Higashidori Nuclear Power Plant is facing the Pacific Ocean. It is unique in Japan in that in its four-unit site, two units are run by the Tohoku Electric Power Company while the two units are run by the embattled TEPCO. The reactors are all of Toshiba design.
The construction of Tohoku Electric's Higashidori Unit-1 began in November 2000 and was completed in December, 2005. The design was based on Tohoku Electric's Onagawa Nuclear Power Plant Unit-3 in Ishinomaki City in Miyagi (with improvements to the reactor vessel to allow for greater ease in inspection and maintenance). A separate building, apart from the containment structure, is dedicated specifically for the heat exchanger system based on seawater to provide primary coolant for the reactor.
The April 20, 2011 drill was held based on the scenario that both the external power and the backup generator had been lost. The workers confirmed the procedures for starting up an emergency power truck and connecting its cables to the plant's facilities. The emergency power truck was deployed late last month. Tohoku Electric Power Company says the power truck works for only 2-and-a-half hours before it needs to be refueled with light oil. Higashidori Nuclear Plant chief Shun Tsubata pledged to improve the plant's safety in the light of the recent Fukushima nuclear plant disasters.