Japan's nuclear output climbs but stalled capacity leaves 2030 target exposed
Nuclear generation hit 101.0 TWh in 2025 but flat capacity through 2029 leaves Japan's 20-22% target dependent on clearing a regulatory backlog of 18 idled reactors.
Japan's nuclear generation recovered to 101.0 terawatt-hours in 2025, according to a GlobalData report published on Tuesday (2026-08-18), but capacity is expected to remain mostly flat through 2029, with only modest gains beginning in 2030. GlobalData projects output rising to 123.3 TWh by 2035, a trajectory that depends entirely on regulatory approvals that have moved slowly for years.5
The government's latest energy plan targets nuclear at 20% of the electricity mix by fiscal 2040, up from 9.4% in fiscal 2024. Japan currently has 15 operational reactors. Three more have received safety clearances but remain idle, while 18 others are still awaiting regulatory approval, the Economist reported in May (2026-05-19). To reach 20%, nearly all 21 eligible reactors would need to restart, leaving almost no margin for further delays or community vetoes.1,2
GlobalData power analyst Attaurrahman Ojindaram Saibasan said reactors from the pre-2011 fleet are being requalified alongside safety upgrades. But three constraints are pulling against that process: community mistrust, slow radiation safety reviews, and the absence of a resolved plan for nuclear waste storage. "Nonetheless, community mistrust, slow radiation safety reviews, and unresolved decisions on waste storage remain significant barriers to what should otherwise be swift progress," Saibasan said.5
Saibasan added that Japan could reach a 20-22% nuclear generation share by 2030 if requalification proceeds well, stabilising the energy mix, lowering emissions, and reducing exposure to imported fuel costs. The conditional carries significant weight. If those measures stall, he said, nuclear will struggle to fulfill that role in the country's energy balance.5
KEPCO's fiscal 2026 numbers illustrate how quickly utilization can erode even at plants already cleared to operate. The utility said its nuclear capacity utilization rate for fiscal 2026 will be 70.5%, a 10.4 percentage-point drop year on year, driven by extended inspections at Takahama — where internal structures in units 1 and 2 are being replaced and steam generator replacement work is underway in units 3 and 4.4
The industry ministry has drafted a plan to rebuild between two and five reactors by the 2040s, the first such proposal since Fukushima, with up to 14 replacements potentially authorized by 2050. Officials estimate Japan will need between 2.2 million and 5.5 million kilowatts of replacement capacity to prevent a supply shortfall after 2040.2
The Iran conflict has tightened the supply security calculus for Japan, one of the world's largest LNG importers. Much of the LNG transiting the Strait of Hormuz served South Korea and Japan, both of which import nearly all their energy needs, Newsday reported in June (2026-06-29). That dependence makes nuclear expansion a supply hedge as much as a decarbonization policy. JKM Asian LNG was priced at $21.88 per MMBtu on Wednesday (2026-08-19).3
Waste storage is the constraint least amenable to engineering timelines or political momentum. Radiation safety reviews can in principle be accelerated with additional regulatory resources. Community resistance may soften as memories of Fukushima recede. But Japan has yet to select a permanent disposal site, and without that decision, every new licensing process faces the same objection cycling back into the queue.5
Progress on regulatory approvals for the 18 reactors still awaiting clearance is what separates the 20-22% scenario from a miss. If those approvals do not begin arriving in volume before 2030, the 123.3 TWh projection for 2035 starts to look like a ceiling rather than a floor.5,1