Tokyo Electric Power Company Holdings (Tepco) has resumed power generation and transmission unit 6 of the Kashiwazaki-Kariwa NPP in Niigata Prefecture after replacing a cracked metal part found to have caused a fault signal that delayed the start of its commercial operation.
The unit resumed operation on 9 February following a false start on 21 January and was slated to begin commercial operation on 18 March before an alarm was triggered on 12 March indicating a possible electricity leak. Tepco then reduced the reactor output to 20% and halted power generation and transmission on 14 March.
A company investigation found that a metal plate, known as a grounding conductor, that connected the generator to the grounding system had been damaged by metal fatigue caused by continued vibrations from the power generator. As a result, electricity could not flow through the conductor, and the monitoring equipment interpreted this as a power leakage triggering the alarm. Tepco replaced the grounding conductor with one less prone to vibration resonance.
Tepco plans to raise output to 100% over the course of about a week and start commercial operations in April. To transition to commercial operations will require a comprehensive load performance test to verify the unit’s overall condition and a pre‑service inspection certificate must be issued by the Nuclear Regulation Authority (NRA). Tepco said it will determine the schedule for the commercial operation after consulting with the NRA’s secretariat, while taking into account the current conditions of the reactor operation and power generation.
