Flashpoints | Environment | East Asia

Japan, South Korea, and the New Logic of Nuclear Energy Security in Northeast Asia

The two neighbors are reshaping the nuclear politics of Northeast Asia – and doing so increasingly in concert with Washington.

Japan Takahama nuclear power plant units 3 and 4.

After the 2011 accident at the Fukushima Daiichi Nuclear Plant, Japan stopped all nuclear power production. Today, the country is restarting reactors, rewriting its energy law, and recasting nuclear power as a pillar of national and regional security rather than a liability to be managed. South Korea, its neighbor and rival in reactor exports, is moving along a parallel track, despite a change of government that briefly appeared to threaten the opposite. 

Together, the two countries are reshaping the nuclear politics of Northeast Asia and doing so increasingly in concert with Washington, as energy policy folds into the broader architecture of trilateral security cooperation.

The unresolved question behind both countries’ restarts is what to do with the spent fuel piling up at reactor sites. I explored one effort to solve that issue earlier this month in a visit to Japan’s Horonobe Underground Research Laboratory. There, hundreds of meters below the surface, engineers are testing whether the geological disposal methods every nuclear country is counting on actually hold up over time. Horonobe is a research site, however, not a repository, and Japan still has no designated location for permanent waste disposal. That gap has not slowed the political momentum above ground.

Before 2011, nuclear power supplied roughly 30 percent of Japan’s electricity. After the meltdown at Fukushima Daiichi, every commercial reactor in the country was taken offline, and public opinion turned sharply against nuclear power. What followed was over a decade of dependence on imported liquefied natural gas and coal, at a cost Japan, which imports about 90 percent of its primary energy, could not sustain indefinitely, especially as global gas markets tightened after Russia’s invasion of Ukraine in 2022.

The return to nuclear power began in earnest with Prime Minister Kishida Fumio’s Green Transformation (GX) policy, launched in 2022. The GX Basic Policy, approved by the Cabinet in February 2023, explicitly committed the government to restarting reactors already cleared by regulators and to building next-generation designs. 

The Seventh Strategic Energy Plan, approved by the Cabinet in February 2025 along with the accompanying GX2040 Vision, cemented nuclear power’s return as government policy rather than a temporary emergency measure. In early 2026, that policy produced its most tangible result yet: the restart of Unit 6 at Tokyo Electric Power Company’s Kashiwazaki-Kariwa plant, the world’s largest nuclear facility by capacity. Perhaps more pointedly, it’s run by the operator directly responsible for Fukushima Daiichi. Such a restart would have been politically unthinkable a decade ago.

The motivation is obvious. New public funding for data center and semiconductor facilities, worth over a trillion yen, requires that the electricity used come entirely from renewable or nuclear sources. That sends an unambiguous signal that Tokyo now considers nuclear energy to be indispensable to industrial policy, not just decarbonization.

South Korea is moving along a similar trajectory, even if it once looked to be headed in a different direction. President Lee Jae-myung took office in June 2025 after having campaigned on skepticism toward nuclear power. Lee argued that the technology was inherently dangerous and that the country’s reactor-heavy generation mix needed re-examining in favor of renewables. Seven months later, confronted with polling showing strong public support for nuclear energy and with surging electricity demand from an AI-driven data center boom, his government reversed course.

Seoul confirmed it would proceed with two new large reactors under the 11th Basic Plan for Electricity Supply and........

© The Diplomat