Japan’s nuclear sector is no longer defined only by the shutdowns that followed the Fukushima Daiichi accident. It is now entering a more difficult stage: turning a limited reactor restart program into a durable part of the national electricity system.
The government reported that 15 reactors were operating nationwide by February 2026 under the post-Fukushima regulatory framework. In April, Tokyo Electric Power Company resumed commercial operation at Kashiwazaki-Kariwa Unit 6 in Niigata Prefecture. That restart carried unusual importance because it marked the return of a TEPCO reactor to commercial service and brought nuclear generation back into the power system serving eastern Japan.
Even so, Japan remains far below the nuclear output it achieved before 2011. Many reactors have been permanently retired, others remain in regulatory review, and some face local opposition or expensive safety work. The future of nuclear energy in Japan will therefore depend less on a single political decision than on whether utilities can restart more existing plants, keep older units operating safely and eventually replace part of the aging fleet.
Fukushima Still Shapes Every Nuclear Decision
The March 2011 earthquake, tsunami and Fukushima Daiichi accident changed the legal, technical and political conditions for nuclear power. Japan’s reactors were taken offline, the former regulatory system was replaced, and the Nuclear Regulation Authority introduced new standards in 2013.
These requirements address severe accidents, flooding, earthquakes, tsunamis, loss of power and deliberate attacks. Utilities have spent heavily on seawalls, filtered venting systems, backup power, emergency control facilities and other protective measures. A reactor may return only after the regulator confirms compliance, but regulatory approval alone does not settle the issue. Support from host communities and surrounding prefectures remains central to the restart process.
Fukushima Daiichi itself will remain part of the national nuclear program for decades. Work includes managing contaminated material, removing spent fuel, retrieving fuel debris and decommissioning damaged units. Progress at the site affects public confidence in the wider industry because Japan’s case for continued nuclear use is tied to its ability to manage the consequences of its most serious nuclear accident.
The accident also created a lasting regional divide. Most early restarts took place in western Japan, particularly at plants operated by Kansai Electric Power, Kyushu Electric Power and Shikoku Electric Power. Eastern Japan remained more dependent on fossil-fuel generation. The restart of Kashiwazaki-Kariwa Unit 6 begins to narrow that gap, although one reactor cannot by itself rebalance the country’s electricity system.
Energy Security Is Driving Nuclear Policy Back Toward Expansion
Japan imports most of the fossil fuels used in its economy. The loss of nuclear generation after 2011 increased demand for imported liquefied natural gas, coal and oil, exposing electricity consumers to global fuel prices and supply disruptions.
This vulnerability now overlaps with a second pressure: electricity demand is expected to grow as Japan expands semiconductor production, data centers and other power-intensive industries. The government’s Seventh Strategic Energy Plan treats nuclear power and renewable energy as complementary low-carbon sources rather than competing alternatives. Its outlook for fiscal year 2040 assigns nuclear energy about 20% of electricity generation, compared with 8.5% in fiscal year 2023.
Reaching that level would require a large increase in reactor output. Faster restarts are part of the answer, but operating performance, maintenance outages and the remaining life of older units will also matter. Japan has revised its reactor-lifetime system so that certain long shutdown periods caused by factors outside an operator’s control can be excluded from the calculation of the normal operating limit. This may allow some reactors to remain in service beyond 60 calendar years, subject to regulatory approval and long-term management requirements.
The economic effect is also important. Restarted reactors reduce the volume of fuel that utilities must buy from abroad. Regions with more nuclear generation have generally faced lower fuel-cost pressure than areas that remain highly dependent on thermal power. However, the full cost of nuclear power also includes safety upgrades, decommissioning, accident liability, waste management and major capital investment.
Japan Must Decide How to Replace an Aging Reactor Fleet
Restarting existing plants can recover capacity, but it does not solve the long-term problem of fleet retirement. Japan has decided to decommission numerous reactors, while only two units remain formally under construction: Ohma in Aomori Prefecture and Shimane Unit 3 in Shimane Prefecture. Both projects have experienced long delays.
The government has opened a path for next-generation reactors to be developed at sites where utilities already operate nuclear plants and where other units are being decommissioned. The technologies under consideration include advanced light-water reactors, small modular reactors, fast reactors and high-temperature gas reactors. Japan also wants to preserve domestic capabilities in reactor engineering, heavy manufacturing, components, maintenance and nuclear research.
This policy is partly industrial. A long pause in new construction can weaken supply chains and reduce the number of engineers able to design, build and operate nuclear facilities. Yet replacement projects will face the same core tests as restarts: safety review, financing, local consent and a clear need within the regional power system. A policy supporting advanced reactors does not guarantee that utilities will order them.
The Fuel Cycle Remains the Weakest Link
Japan’s nuclear strategy is based on reprocessing spent fuel and reusing recovered uranium and plutonium in mixed-oxide fuel. The Rokkasho Reprocessing Plant in Aomori Prefecture is intended to serve as the center of this system, but its completion has been delayed repeatedly.
These delays affect the entire sector. Reactor sites have limited spent-fuel storage, while utilities need reliable routes for moving and managing used fuel. Japan is expanding dry-cask and interim storage options, but local acceptance is required for these facilities as well.
The final disposal of high-level radioactive waste remains unresolved. Geological disposal is national policy, yet Japan has not selected a repository site. Without progress on storage, reprocessing and final disposal, reactor restarts can continue only within a back-end system that remains incomplete.
This issue also affects public trust. Support for nuclear generation is harder to maintain when the country has no settled destination for its most hazardous waste. Technical capability is necessary, but long-term political agreements with host communities are equally important.
Japan’s Nuclear Future Depends on Execution
Japan has moved beyond the question of whether nuclear power will remain in its energy mix. National policy now clearly expects it to provide a substantial share of electricity, support industrial growth and reduce dependence on imported fossil fuels.
The harder question is whether the country can deliver enough operating capacity to meet that policy. Success will depend on additional restarts, reliable operation at existing plants, credible lifetime management, progress at Fukushima Daiichi and a workable solution for spent fuel and radioactive waste. Japan has restored nuclear generation gradually; reaching its 2040 objective will require a much faster and more coordinated program.
