Too soon to celebrate a ‘nuclear submarine Korea’

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Too soon to celebrate a ‘nuclear submarine Korea’

Published: 11 Nov. 2025, 00:03

Audio report: written by reporters, read by AI

Chae Byung-gun

The author is the acting editor-in-chief at the JoongAng Ilbo.

The Korean government's success in securing a U.S. pledge to support the acquisition of nuclear-powered submarines is being hailed as a diplomatic triumph, but the celebration is premature. Korea has only taken its first step toward becoming a “nuclear submarine nation.”

The process of acquiring nuclear submarines can be divided into two parts. The first is the “shell,” or the hull and reactor. Korea, a major shipbuilding power, already builds its own conventional submarines but has yet to develop a fully functional reactor for submarine use. Unlike reactors that are fixed to the ground, submarine reactors must operate while constantly moving between bases, making them far more difficult to design and maintain. Still, experts say construction is not impossible, given the nation’s decadeslong investment in nuclear power infrastructure and research.

The U.S. Navy's Los Angeles-class nuclear-powered submarine USS Alexandria is seen arriving at the Busan Naval Operations Base in Busan on Feb. 10, 2025. Commissioned in 1991, the Alexandria, measuring 110 meters long and 10 meters wide, entered Busan to load supplies and provide crew rest, marking the submarine's first port call in Korea. [NEWS1]

Government and industry circles have turned their attention to small modular reactors (SMRs), which share technical similarities with submarine reactors. The power output needed for a Korean nuclear submarine — about 70 to 100 megawatts — coincidentally matches the capacity of the SMRs that the government is currently developing.

Yet technology may be less of a hurdle than politics. “It’s unclear whether the U.S. government will allow Korea to take full charge of the project,” said Yu Ji-hoon, a research fellow at the Korea Institute for Defense Analyses (KIDA). “Washington could impose conditions that ensure its control over [...] design or assembly.” Both the U.S. executive branch and Congress have long imposed strict restrictions on the export of strategic or advanced weaponry, and nuclear submarines are no exception. Domestic construction could also mean higher costs. Kim Dong-yub, a professor at the University of North Korean Studies, notes that “the United States may appear to grant Korea’s request but could, behind the scenes, demand something in return, such as additional investments in U.S. shipyards or higher defense cost-sharing.”

The ROKS Jang Yeong-sil, the first 3,600-ton submarine of the Jang Bogo-III Batch-II class, is on display at Hanwha Ocean’s Geoje shipyard in Geoje, South Gyeongsang on Oct. 21. [NEWS1]

The second obstacle is fuel. A nuclear submarine cannot operate without enriched uranium. This issue is even more sensitive than the reactor itself. The revised 2015 Korea-U.S. nuclear cooperation agreement — effective through 2035 — allows Korea to enrich uranium up to 20 percent with U.S. consultation but bans enrichment above that level. Seoul is reportedly considering importing uranium enriched to below 20 percent from the United States, but this requires addressing Article 13 of the agreement, which stipulates that nuclear materials “shall not be used for any military purpose.” To move forward, Korea must either negotiate a revision or propose a way in which fuel for naval propulsion does not qualify as military use.

Even if the U.S. administration agrees, the plan would still need approval from Congress, where amending nuclear agreements has historically faced strong scrutiny. Each step may also bring new financial burdens. Experts believe the fuel that Korea aims to acquire will likely be the high-assay low-enriched uranium used in SMRs. “For Korea to ensure a stable supply, it may need to make large-scale investments to U.S. companies such as Centrus Energy to expand production capacity,” said Ham Hyung-pil, the director of KIDA’s Center for Security and Strategy.

Even if Korea completes a prototype reactor, imports fuel and successfully demonstrates the technology, its fleet could be rendered useless if Washington later decides to halt fuel exports or restrict enrichment. While Korea could, in theory, pursue its own uranium enrichment program or import nuclear fuel from Russia, such options are unrealistic both politically and strategically.

The entire program — from reactor production and hull construction to refueling and long-term operation — depends on maintaining a stable relationship with Washington. A former military officer who once tried to persuade U.S. officials of Korea’s need for nuclear propulsion recalled being rebuffed. “They said, ‘Korea isn’t confronting China’s navy. Wouldn’t it be better to build more diesel submarines to deter North Korea?’” he said.

If the United States allows Korea to operate nuclear submarines, two conditions must logically be met. First, the submarines must serve U.S. strategic interests in East Asia. In practice, this means reducing Washington’s burden of frequent strategic deployments to counter China while strengthening the Korea-U.S. alliance. Second, the submarines must remain in the hands of a U.S. ally, signifying that a free, democratic Korea must continue to exist.

Hanwha Philly Shipyard in Philadelphia. [JOONGANG ILBO]

The Korean Navy has outlined an optimistic schedule, projecting construction in the mid to late 2030s. But experts warn that the road ahead is long. “The Trump administration’s promise is a political one,” said Lee Choon-geun, a senior adviser at the Korea Institute of S&T Evaluation and Planning. “Within a decade, the United States could see two changes of government.”

“What we have now is a political declaration. The real work begins here,” Yu said.

That assessment captures the broader reality. Korea’s nuclear submarine program hinges not only on technical success but also on the endurance of the Korea-U.S. alliance. If that alliance falters, the program could stop at any moment.

This article was originally written in Korean and translated by a bilingual reporter with the help of generative AI tools. It was then edited by a native English-speaking editor. All AI-assisted translations are reviewed and refined by our newsroom.