Seoul has long debated building nuclear-powered attack submarines, arguing they are needed to track North Korea’s growing missile and submarine forces. As of late 2024, Washington had not publicly approved any transfer of naval nuclear propulsion technology to South Korea; if that changes, it would carry major technical, legal, and regional implications.

Where the debate stands and why it’s back now

South Korea’s navy has pushed for nuclear-powered submarines for years, saying they are better suited than diesel-electric boats for shadowing North Korean submarines and operating for long periods without surfacing. The idea gained steam after Pyongyang accelerated missile testing and unveiled a refurbished missile-carrying submarine in September 2023, while North Korean leader Kim Jong Un has repeatedly said he wants a nuclear-powered submarine. In 2021, the AUKUS deal showed the United States and the United Kingdom were willing to share nuclear propulsion with Australia, a close ally, which fueled arguments in Seoul that a similar path should be on the table. Still, U.S. and South Korean officials have, in public, stopped short of announcing any agreement to transfer propulsion technology or change the rules governing South Korea’s use of nuclear material. The 2023 Washington Declaration emphasized U.S. strategic asset deployments, including visits by U.S. ballistic missile submarines, not technology transfer.

The main hurdle is the U.S.–South Korea civil nuclear cooperation pact, updated in 2015, which restricts South Korea from enriching uranium or reprocessing spent fuel without U.S. consent. Most nuclear submarines use highly enriched uranium fuel; even low-enriched options raise complex safeguard questions. The Nuclear Non-Proliferation Treaty allows naval propulsion as a non-explosive military use, but it requires tailored arrangements with the International Atomic Energy Agency to manage oversight. No such arrangement exists today for South Korea. On the engineering side, building a nuclear-powered attack submarine is a decade-scale effort requiring reactor design, a land-based prototype for testing, specialized shipyard infrastructure, and a trained cadre of nuclear-qualified sailors and maintainers. South Korea’s yards—home to the KSS-III conventional submarine program—would be starting from a strong industrial base, but nuclear propulsion demands a different level of safety, regulation, and workforce training.

Regional ripple effects and likely reactions

Any U.S. green light would reverberate across Northeast Asia. North Korea would likely use it to justify further missile and submarine development, and to harden its nuclear posture. Japan, already investing heavily in anti-submarine warfare and long-range strike, would probably accelerate tracking and basing upgrades and ask for even tighter trilateral coordination with Seoul and Washington. China criticized AUKUS in 2021 as destabilizing and would almost certainly denounce a similar move for South Korea, arguing it erodes nonproliferation norms and fuels an arms buildup. The broader context is tense: North Korea and Russia signed a security pact in June 2024, and U.S., South Korean, and allied officials have accused Moscow and Pyongyang of expanding military cooperation in violation of U.N. sanctions. While analysts have speculated about Russian technical help to North Korea’s naval programs, there is no verified evidence that Pyongyang has acquired nuclear propulsion.

What it would mean at home in South Korea

For ordinary South Koreans, the implications are practical as much as strategic. A nuclear-submarine program would command a large share of the defense budget for years, affecting other priorities. It would also create high-skill jobs in shipbuilding centers and across a supplier network of thousands of small and medium-sized firms. Communities near naval bases and shipyards would see new safety rules, emergency planning, and environmental oversight typical of nuclear propulsion. Politically, public support for stronger deterrence has risen alongside North Korea’s missile advances, but a nuclear-powered fleet would trigger debates over cost, timing, and whether it meaningfully changes deterrence compared to expanding high-end conventional submarines, maritime patrol aircraft, and undersea sensors.

What’s to come

The clearest signals to watch are official: any joint U.S.–South Korea statement referencing naval nuclear propulsion, talks to amend or interpret the 2015 nuclear cooperation agreement, or IAEA discussions on safeguards for naval fuel. In Seoul, look for budget lines in the Mid-Term Defense Plan, contracts for land-based reactor testing, and workforce training initiatives. Regionally, track North Korea’s submarine construction via commercial satellite imagery, Japan’s ASW investments, and statements from China. In Washington, congressional notifications or hearings would likely precede any technology transfer. Until those pieces move, the debate remains just that—a debate with high stakes for alliance strategy, nonproliferation norms, and the security balance in Northeast Asia.