One of three emergency diesel generators for the No. 1 reactor at the Shika Nuclear Power Station in Ishikawa Prefecture, which has been hit by a series of problems in the wake of the Noto Peninsula earthquake, stopped automatically during a test run, operator Hokuriku Electric Power Co. announced on Jan. 17.
The emergency generators are designed to operate pumps that circulate seawater to cool nuclear fuel stored at the plant in the town of Shika when external power is lost. The failure means trouble has hit part of the plant’s last line of safety defense. The company is investigating the cause as it tries to restore operations.
The seismic intensity of the Jan. 1 Noto Peninsula Earthquake registered an upper 5 on the 7-point Japanese scale on the grounds of the nuclear power plant, where the reactors are currently offline. The quake caused transformers to malfunction, rendering two of five external power lines unusable. Electricity continues to be supplied through the remaining lines, and a company representative stated that the halt of the generator poses “no safety issues.”
On Jan. 16 another quake measuring a lower 5 on the Japanese scale hit the town of Shika. The following day Hokuriku Electric conducted a test run of the emergency generators. It found no issues with two of the generators. It then started the third generator at around 5 p.m. and increased output, but the generator automatically stopped at 5:13 p.m.
The utility had conducted a test run of the emergency power sources for reactor Nos. 1 and 2 on Jan. 3, and no problems were found at the time.
The company has not identified the cause of the automatic shutdown this time, but it confirmed that procedures were followed according to the manual, and an official in charge stated, “The possibility of human error is low.”
Under new regulatory standards required by the government for nuclear power plants, aseismic performance levels are categorized into three stages, and emergency generators need to meet the strictest criteria.
In addition to the loss of the two external power sources in the wake of the New Year’s Day quake, some 23,400 liters of oil leaked when transformers for both the No. 1 and 2 reactors were damaged.
(Japanese original by Junichi Tsuchiya, Lifestyle, Science & Environment News Department)
Source: The Mainichi
