Japanese utility Tokyo Electric Power (Tepco) has decided to postpone the reactivation of its long-idled 1,356MW No.6 reactor at the Kashiwazaki-Kariwa nuclear power plant because of a technical issue.
Tepco had originally aimed to reactivate the No.6 reactor on 20 January. But on 17 January, the company detected that an alarm designed to ensure the safe management of the control rods — which are key to regulate nuclear fission — was not working correctly. Tepco identified errors in the control rod settings and completed repairs on 18 January.
It plans to take one to two days to inspect and ensure safety of all control rods before reactivation. The utility is unsure when it can reactivate the No.6 reactor as it will depend on whether the company can obtain permission from Japan's nuclear regulation authority (NRA). Tepco also said that it can absorb this unexpected delay to restart the plant's commercial operation on 26 February as initially planned, but it could also depend on permission from NRA.
The errors in the control rods settings had been present since the No.6 reactor first entered service in 1996.
Restarting the Kashiwazaki-Kariwa No.6 reactor would represent a milestone for Tepco's efforts to return nuclear power generation after the 2011 Fukushima disaster, marking the utility's first reactor to be resume operations since the meltdown.
The Kashiwazaki-Kariwa plant comprises of seven reactors with a combined capacity of 8,212MW. The No.6 and No.7 units have cleared the stricter post-Fukushima safety inspections. The No.7 unit will be required to remain shut until August 2029 for the installation of anti-terrorism facilities.
Under Japan's stricter nuclear regulations, operators are required to build dedicated anti terrorism facilities — known as specified severe accident response facilities or Tokuju — designed to serve as an independent backup in case of deliberate attacks such as an aircraft crash, ensuring reactors can be safely shut down even if main control systems are compromised. The No.7 unit must remain offline until August 2029 to complete installation of these systems, in line with NRA requirements.

