Japan's Nuclear Restart Hinges on Solving a Waste Problem No One Wants to Host

Japan's Nuclear Restart Hinges on Solving a Waste Problem No One Wants to Host Tokyo plans to double nuclear's share of power generation to 20% by 2040, but 18 reactors await approval and spent fuel has nowhere permanent to go. Japan's latest energy plan targets nuclear providing 20% of the electricity mix by 2040, up from under 10% last year. To reach that number, nearly all 21 reactors that have received or are awaiting safety clearances would need to restart. Japan currently has 15 operational reactors, three more with safety clearances but sitting idle, and 18 still in the regulatory queue. The rest of the fleet has been decommissioned.² That target runs into a problem that predates Fukushima and has only grown harder since: Japan has no long-term disposal site for its spent nuclear fuel. Japan NRG reported that this challenge stymies efforts for the sector's growth and hangs over the entire nuclear strategy. The question of whether a tiny Pacific island could host a waste repository has entered the discussion, though the idea faces enormous political and logistical barriers.⁵ The waste question matters now because the Hormuz crisis has made Japan's energy vulnerability impossible to ignore. Roughly 90% of Japan's crude oil comes from the Middle East. Tokyo has already released around 80 million barrels from its strategic petroleum reserves, equivalent to about 26 days of domestic oil demand. Japan covers nearly 100% of its gasoline and around 95% of its diesel through domestic refining, so the immediate fuel balance is manageable. But the structural exposure is acute.¹ Natural gas is the dominant fuel in Japan's power generation mix at around 32%, followed by coal at 28%, nuclear at 9%, and oil at 7%. About 98% of domestic gas demand is met by LNG imports, though volumes have been declining due to slower economic growth, renewables expansion, and the gradual nuclear restart. In 2025, Japan imported 66.3 million tonnes of LNG, down 1.5% year-on-year, retaining its position as the world's second-largest buyer after China.¹ The LNG supply geography provides some insulation from Hormuz. Only about 6% of Japan's LNG transits the strait, coming from Qatar and the UAE. The majority arrives from Australia at 26 million tonnes, Malaysia at 10 million tonnes, and Russia at 5.8 million tonnes via the Sakhalin-II project, in which Mitsui and Mitsubishi hold stakes under a Japanese sanctions exemption.¹ But gas remains expensive and exposed to global price volatility. The power sector absorbs roughly 55-65% of total gas consumption. Every reactor that restarts displaces gas-fired generation. Every reactor that stays offline because of unresolved waste or regulatory delays forces Japan to keep buying LNG at whatever price the market sets. The economics of nuclear restart are clear. The politics are not. Fukushima's legacy is the central obstacle. The Economist reported that the meltdown pointed to the danger of over-reliance on technology creating a false sense of security. Officials who believed sea walls would protect the Fukushima plant ignored scientists' warnings about its location near a major fault line. The government estimates a 70-80% chance of a severe earthquake and tsunami in the Nankai Trough, south of Japan's main island, within the next 30 years.⁴ That seismic risk shapes the waste debate directly. Any permanent disposal facility must survive geological timescales in one of the most tectonically active regions on earth. Japan's domestic geology makes siting a deep repository difficult, which is why offshore options, including Pacific island locations, have entered the conversation.^5,4 The renewable alternative has been slow to scale in Japan. Wind turbines are required to meet the same earthquake standards as tall apartment blocks. Land-use regulations limit the conversion of abandoned farmland for solar power. Weak transmission lines make it difficult to move renewable energy to where it is consumed. Instead of accelerating, the expansion of renewables has stalled against these regulatory and infrastructure constraints.² Technology may eventually compress the timeline. Idaho National Laboratory has partnered with NVIDIA to use artificial intelligence to speed up nuclear reactor development, aiming to cut build times by up to 50% and reduce operating costs by a similar margin. The US Department of Energy has committed $293 million in funding. Faster reactor construction would strengthen the case for new nuclear in Japan, but only if the waste question is answered first.³ The signal to watch is whether any of the 18 reactors awaiting regulatory approval receive clearance in the next 12 months. Each approval that converts to an operational restart reduces Japan's LNG import dependency and weakens gas demand at the margin. Each delay keeps Japan's power sector anchored to fossil fuel imports through a chokepoint that just demonstrated how quickly supply can disappear.^2,1