In response, the company began withdrawing control rods at around 7:00 p.m. on the same day, initiating reactor startup. This marks the first time a nuclear power plant operated by TEPCO has entered operation since the accident at Fukushima Daiichi.
Following the reactor startup, control rods were withdrawn sequentially, and criticality was achieved at approximately 8:30 p.m. on January 21.
The restart of Unit 6 had originally been scheduled for January 20. However, during a control rod withdrawal test conducted on January 17, a malfunction was identified in which an alarm failed to activate, prompting the company to temporarily postpone the startup process.
According to the company, the system is designed so that when one control rod is withdrawn and another is selected, a withdrawal prevention function activates and an alarm sounds to prevent erroneous operation. During the January 17 test, however, the alarm did not activate. As a result, the test was halted, all withdrawn control rods were returned to their original positions, and power was shut off to prevent further operation of the control rods.
On the following day, January 18, confirmation tests were conducted on all control rods to check for similar issues. It was determined that the pair rod setting for the affected control rod had been incorrectly configured. After correcting the setting, the company confirmed that the withdrawal prevention function operated normally and that the alarm was properly activated, allowing the unit to return to compliance with operational limits.
On January 21, after confirming that alarms functioned normally for all control rods, the company reported the matter to the Nuclear Regulation Authority in the afternoon and subsequently received formal approval for trial reactor operation.
As Unit 6 resumes operation for the first time in approximately 14 years, the company is proceeding cautiously with equipment integrity checks. On January 22, the control rod withdrawal operation was again temporarily suspended after an alarm was triggered in the operation monitoring system for one control rod during withdrawal. The company stated that plant conditions remain stable and that there has been no impact from radioactive materials on the external environment.
