Nuclear waste threatens Japan’s energy expansion

Japan’s nuclear power expansion is facing a growing challenge as the country struggles to find space for increasing volumes of spent nuclear fuel, raising fresh questions about the long-term sustainability of its energy strategy.

The issue has come into sharper focus following the restart of the No. 6 reactor at the Kashiwazaki-Kariwa Nuclear Power Station, the world’s largest nuclear power plant. The move forms part of the Japanese government’s broader effort to increase nuclear electricity generation to strengthen energy security and meet rising power demand. However, industry officials warn that storage capacity for spent fuel is becoming critically constrained.

According to the Federation of Electric Power Companies of Japan, spent fuel cooling pools at Kashiwazaki-Kariwa and two other nuclear power stations could reach full capacity within the next five years.

“Without a clear fuel management strategy, power generation could eventually face obstacles,” said Takeyuki Inagaki, general manager of the Kashiwazaki-Kariwa plant.

Japan has spent decades searching for a permanent disposal solution for highly radioactive waste but has yet to identify a final repository. The government is now examining Minamitorishima, a remote Pacific island around 2,000 kilometres south of Tokyo, as a potential disposal site, a proposal that has already triggered criticism and public concern.

Only 15 of Japan’s 54 nuclear reactors have resumed operations since the 2011 Fukushima disaster, when a powerful earthquake and tsunami caused meltdowns at three reactors and forced approximately 160,000 people to evacuate. Some affected areas remain uninhabitable.

Kashiwazaki-Kariwa, operated by Tokyo Electric Power Company Holdings (TEPCO), remained offline for years following the Fukushima accident as part of the nationwide suspension of nuclear generation.

At the newly restarted No. 6 reactor, the spent fuel storage pool is already around 88% full. TEPCO says it has introduced enhanced safety measures based on lessons learned from Fukushima, including filtered vent systems and safeguards designed to prevent hydrogen explosions.

Prime Minister Sanae Takaichi’s administration is promoting a greater role for nuclear energy in Japan’s power mix as the country seeks stable domestic electricity supplies and reduced dependence on imported fuels. However, critics argue that bringing additional reactors online will inevitably increase the volume of radioactive waste, potentially forcing future reactor closures if storage limitations are not resolved.

Japan’s nuclear policy centres on reprocessing spent fuel to recover plutonium and uranium for reuse, a strategy officials say improves energy security and reduces waste volumes. Yet the programme has faced repeated delays and technical challenges. A reactor intended to utilise recycled plutonium has struggled to achieve its objectives, while existing reprocessing facilities are not expected to handle all accumulated spent fuel.

Critics also highlight Japan’s substantial plutonium stockpile, which experts say is already large enough to produce thousands of nuclear weapons. Some specialists have therefore called for direct disposal of spent fuel to be considered alongside reprocessing.

Government figures show that by the end of 2025, storage pools at 17 nuclear power plants contained more than 17,000 tonnes of spent fuel, representing nearly 80% of total available capacity.

Experts note that Japan must manage not only routine nuclear waste generated by operating reactors but also the vast quantities of radioactive material resulting from the Fukushima disaster.

Lila Okamura, an environmental politics specialist at Senshu University, said establishing a permanent disposal facility would be a multi-generational undertaking requiring careful planning and long-term monitoring.

The debate intensified shortly after the Kashiwazaki-Kariwa restart when Industry Minister Ryosei Akazawa requested a feasibility study into the use of Minamitorishima as a final repository for high-level radioactive waste.

Akazawa described final disposal as a critical national challenge as spent fuel inventories continue to grow across the country.

The island is owned by the Japanese government and has no permanent residents. It also holds strategic significance because Japan is developing military infrastructure there, while nearby seabed areas contain valuable rare earth mineral deposits.

Supporters argue that the island’s geological stability could make it suitable for long-term storage. However, residents of neighbouring islands and local officials have raised concerns over environmental risks, safety issues and potential damage to tourism.

Opponents contend that the proposal appears politically convenient because the remote location is unlikely to face the same level of organised resistance seen elsewhere.

Despite offering substantial government subsidies, Japan has struggled for years to persuade communities to host a nuclear waste repository. Minamitorishima is only the fourth location to enter the feasibility assessment stage since the national search began in the early 2000s.

The review process is expected to take around two decades before any final decision can be made.

Meanwhile, several countries, including Britain, Germany and the United States, have largely moved away from large-scale fuel reprocessing because of its high cost and technical complexity. Finland is expected to open the world’s first permanent underground repository for spent nuclear fuel later this year.

To ease immediate storage pressures, TEPCO is transferring spent fuel to reactors with available capacity and aims to resume shipments to a dry-cask storage facility in northern Japan. Other utilities are also developing additional storage facilities.

Nevertheless, concerns remain among local residents about the growing accumulation of radioactive waste.

Civil activist Mie Kuwabara from Niigata questioned where the spent fuel would ultimately be stored.

“It is irresponsible to restart more reactors and generate additional spent fuel before deciding where it will finally be stored,” she said.

Kuwabara also criticised the Minamitorishima proposal, arguing that the island’s remoteness should not be used as justification for locating a radioactive waste facility there.

“It’s frightening to think a site could be chosen simply because there are few people around to object if something goes wrong,” she said.