Tokyo Electric Power Company Holdings (Tepco) has shut down the unit 6 reactor at the Kashiwazaki-Kariwa NPP in Niigata Prefecture after a malfunction was detected, just a day after the unit went online for the first time in more than 13 years. An alarm was triggered during work to withdraw control rods from the reactor as part of the restart process. The alarm sounded after 52 out of 205 rods had been extracted and the reactor had achieved criticality, Tepco said.
Tepco decided to shut down the reactor as it is expected to take time to identify the cause. An investigation is underway. The Nuclear Regulation Authority (NRA) and the Niigata prefectural government were informed of the decision. Tepco said there are no abnormalities in the condition of the reactor and no safety problems or impact outside the plant.
Plant Director Inagaki Takeyuki, told reporters the schedule for resuming commercial operations has not been decided and that Tepco will consult with NRA as the probe develops.
The start-up procedure involves removing 205 rods in batches of 26. Tepco said it suspected a malfunction in the control rod operating system but, after a component was replaced, the problem persisted.
The restart had been delayed by a day to investigate why an alarm had failed to sound during a test withdrawal of control rods.
According to a September 2025 survey, public opinion in Niigata is deeply divided with around 60% of residents opposed to the restart, of the NPP while 37% support it.
Although Kashiwazaki-Kariwa, unlike Fukushima, was unaffected by the March 2011 earthquake and tsunami, all seven of the plant’s reactors had already been offline for two to three years following the earlier 2007 Niigata-Chuetsu earthquake, which caused damage to the site. Work has since been carried out to improve the plant’s earthquake resistance.
However, earlier in January, seven groups opposing the restart submitted a petition signed by nearly 40,000 people to Tepco and NRA, saying that the plant sits on an active seismic fault zone and referring to the 2007 earthquake.
