A reactor at Kansai Electric Power Co.'s Takahama nuclear power station in Fukui Prefecture was automatically halted Monday after an alert went off warning of a rapid decrease in the number of neutrons within the unit, the complex's regulator and operator said.
The No. 4 reactor was halted at 3:21 p.m., the Osaka-based utility said, adding that there has been no indication of the incident causing environmental contamination. The reactor's cooling function is normal, according to the Nuclear Regulation Authority.
The No. 4 reactor restarted in November after being shut down for routine inspections.
The seaside plant has four reactors and faces the Sea of Japan.