Japan is rebuilding its nuclear fleet with renewed urgency, marking a decisive shift more than 15 years after the Fukushima disaster transformed national energy policy.
Reactor restarts now sit at the center of the country's campaign to strengthen energy security, curb fossil fuel imports, and meet climate targets.
Before March 2011, nuclear stations supplied roughly one third of Japan's electricity.
A magnitude 9.0 earthquake, tsunami, flooding, and reactor meltdowns at Fukushima Daiichi led authorities to shut all 54 reactors and impose a far more demanding regulatory system.
The recovery has been cautious, technically intensive, and politically sensitive.
Each returning unit must satisfy strict Nuclear Regulation Authority requirements while operators attempt to rebuild public confidence through plant upgrades, inspections, emergency planning, and engagement with surrounding communities.
Tokyo Electric Power Co., known as TEPCO, has now returned Unit 6 at the Kashiwazaki Kariwa Nuclear Power Station in Niigata Prefecture to commercial operation.
The restart is especially significant because Unit 6 is the first TEPCO reactor to resume service since Fukushima.
Kashiwazaki Kariwa had remained entirely offline since March 2012. Before its shutdown, the seven reactor complex was recognized as the world's largest nuclear power station, with total nameplate capacity of approximately 8.2 GW.
Unit 6 is an advanced boiling water reactor with 1,356 MW of generating capacity.
Its return helped bring Japan to 15 nuclear plants in operation, representing combined generating capacity of about 33 GW at the time of reporting.
The government wants nuclear generation to provide at least 20 percent of national electricity by 2030.
Nuclear power currently supplies about 8 percent to 9 percent, leaving a substantial gap that will require additional restarts and sustained regulatory progress.
Japan leaned heavily on imported liquefied natural gas after its reactors closed. LNG fired generation now represents about 30 percent of the national electricity mix, while coal fired power and renewable resources, primarily solar and hydropower, also hold major shares.
That dependence has exposed Japan to volatile global fuel prices, shipping risks, and persistent economic pressure.
According to estimates cited by the United States Energy Information Administration, Unit 6 could displace approximately 1.3 million tons of LNG, equal to 62 billion cubic feet of natural gas imports each year.
The restart did not proceed without difficulty. Unit 6 initially started in January but shut down within hours after an equipment issue involving a monitoring alarm occurred during the withdrawal of control rods, although officials said the reactor remained stable and posed no leakage risk.
Following inspections and corrective work, Unit 6 achieved criticality in February.
Additional equipment integrity checks and Nuclear Regulation Authority inspections cleared the reactor to begin commercial operation in April, completing a closely watched return for a plant that first entered service in 1985.
TEPCO emphasized the unusual scale of the verification campaign, stating, “As it has been approximately 14 years since the power station was in operation, we will carefully verify the integrity of each and every plant facility while suitably addressing any issues that arise and conveying information to the public during each step of the startup process.”
Physical protections at Kashiwazaki Kariwa have expanded substantially.
TEPCO installed a seawall about 50 feet high and one kilometer long, added flood barriers and watertight doors, strengthened critical piping and electrical equipment, and improved protection for reactor buildings and essential equipment rooms.
Electrical resilience also received major attention. The site now has five external transmission lines across three routes, new emergency diesel generators, mobile power vehicles, gas turbine generator trucks, and elevated batteries intended to preserve essential functions during severe emergencies.
Cooling resources include a new 20,000 ton water reservoir designed to support at least one week of cooling.
Mobile heat exchanger vehicles can provide another heat removal route for roughly 10 days, while passive catalytic recombiners and filtered containment venting address hydrogen and radioactive material risks.
The stakes extend beyond engineering. Kashiwazaki Kariwa once supplied substantial electricity to the region between Niigata and metropolitan Tokyo, and Unit 6 again provides meaningful domestic generation for millions of customers while reducing exposure to overseas fuel markets.
TEPCO continues to present safety as the foundation of the revival.
“There is no end to safety,” the company said, while plant superintendent Takeyuki Ingaki offered an even more direct pledge: “We will never compromise [on safety], because we have experienced the Fukushima accident firsthand.”
Unit 6 is therefore more than another reactor restart.
It is a high visibility test of whether rigorous regulation, hardened infrastructure, operational discipline, and transparent community engagement can carry nuclear power back into a central role in Japan's electricity system.
