Japan's nuclear restart exposed as spent fuel storage nears capacity

Japan’s nuclear comeback is colliding with the part of the industry officials have delayed for decades: what to do with the spent fuel after the reactors run. As of December 2025, cooling pools at 17 nuclear power plants held more than 17,000 tons of spent fuel, filling nearly 80% of total storage capacity and leaving the system increasingly exposed to a shortage of room.

That pressure is most visible at Kashiwazaki-Kariwa Nuclear Power Station in Niigata Prefecture, the world’s largest nuclear plant. Its No. 6 spent-fuel pool was reported to be 88% full, and Tokyo Electric Power Company Holdings has already been shifting spent fuel from that reactor to other pools with more space. Kashiwazaki-Kariwa General Manager Takeyuki Inagaki warned that without solid fuel-management plans, power generation could stall sooner or later.

The restart of No. 6 earlier this year was meant to help bring more reactors back online, but it also sharpened a structural contradiction in Japan’s energy policy. Only 15 of the country’s 54 reactors have restarted since the March 2011 Fukushima disaster, when a 9.0 earthquake and tsunami triggered meltdowns at three TEPCO reactors, forced about 160,000 people to flee and left some areas still unlivable. TEPCO has added filtered venting systems and hydrogen-explosion prevention measures at Kashiwazaki-Kariwa based on Fukushima lessons, but public trust remains fragile as officials press for more restarts.

Prime Minister Sanae Takaichi is pushing to bring more nuclear plants online to meet rising electricity demand, including from AI data centers, and to reduce fossil-fuel imports. The Federation of Electric Power Companies of Japan says three plants’ spent-fuel pools will be full within five years, underscoring how quickly expanded generation could run into physical limits if storage capacity does not grow at the same pace.

The government’s long-term answer still rests on a fuel cycle that has lagged for years. The Rokkasho Reprocessing Plant in Aomori Prefecture remains in its final stage of completion and is intended to process about 800 tons of spent fuel a year when fully operating. Yet Japan still lacks a durable disposal route for highly radioactive waste, and its main policy framework has moved only in increments: the Final Disposal Act has been in force since 2000, setting out a three-stage site-selection process for geological disposal at depths greater than 300 meters, and the basic policy on final disposal was updated in 2015 and again in 2023.

Officials have even looked at Minamitorishima, a remote Pacific island south of Tokyo, as a possible repository site, a sign of how unresolved the issue remains. International and Japanese nuclear bodies still describe geological disposal as the endpoint, but local opposition and the need to consult municipalities at each stage have kept Japan’s nuclear expansion tied to a waste problem it has not solved.