How nuclear submarines could pave the way for nuclear weapons in South Korea

Bulletin, By Sharon Squassoni | December 12, 2025

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The mystique of nuclear-powered submarines has been captured by at least half a dozen popular Hollywood films. Some have centered on the drama of undersea warfare and the risk of global nuclear apocalypse should the nuclear-tipped missiles aboard most of them be launched. Others confront the issues of rogue submarine commanders or the dilemmas of decision-making when out of communication with national leadership. One or two, including Kathryn Bigelow’s K-19 Widowmaker, portray real-world disasters of a reactor meltdown aboard submarines. (Bigelow is also the director of the new film, A House of Dynamite, which depicts the last 20 minutes before a nuclear-armed missile of unknown origin falls on an American city.)

The underlying message of these fictional works is that nuclear submarines—powered by reactors and armed with atomic missiles—are a tightrope act. One misstep could endanger many, many lives.

The United States’ recent nuclear submarine deal with South Korea is a tightrope act for a different reason. Lost in the noise about nuclear submarines, the Trump administration has agreed to let South Korea enrich uranium and reprocess commercial nuclear spent fuel. This step—which could give South Korea a virtual or latent nuclear weapons capability—is needlessly destabilizing.

US nuclear technology exports. In the last five years, the United States has made deals with Australia and South Korea to hasten the day when some countries will deploy nuclear-powered submarines that don’t carry nuclear missiles. Under the 2021 AUKUS deal (a partnership between Australia, the United Kingdom, and the United States), Australia will build nuclear-powered submarines using UK reactors and US highly enriched uranium fuel at the latest estimated cost of $368 billion. And in October, South Korea scored a political coup in convincing US President Donald Trump to allow its pursuit of nuclear-powered submarines.

South Korea has sought nuclear-powered submarines for more than 30 years. Sparked by the first international crisis over North Korea’s nuclear weapons program, Seoul has dabbled in the relevant technologies in an on-again, off-again fashion. Past forays included a 1994 directive to the Korean Atomic Energy Research Institute to design a nuclear-powered submarine (cancelled in 1998) and the so-called “362” covert task force formed in 2003 that reportedly utilized Russian help to design a submarine reactor. This task force was disbanded in 2004 after South Korean officials revealed that scientists had enriched uranium without declaring it to the International Atomic Energy Agency.

More recently, Moon Jae-in campaigned on South Korea acquiring nuclear-powered submarines in 2017, and Korean officials since 2020 have suggested that their next generation of submarines would be nuclear-powered. Speculation persists over whether South Korean efforts to develop small modular reactors fueled with 19.5 percent high-assay low-enriched uranium could be adapted or modified for naval applications.

Many details about South Korea’s nuclear submarines are still unknown— when, where, and how they will be built. Those details will matter a great deal in terms of the proliferation implications. Allowing South Korea to indigenously produce its own nuclear submarines could be riskier than if South Korea were to purchase US subs or the reactors that go into these subs.

Nuclear-powered vs. nuclear-armed. Nuclear-powered submarines make total sense to nuclear weapon states, which weigh the risks and costs of these vehicles against the benefits of stealth, range, and having a platform for assured, nuclear retaliation. (In theory, such submarines can enhance stability because they provide assured destruction in case an opponent seeks advantage by striking first—the so-called delicate balance of terror.) Already engaged in high-cost and high-risk nuclear projects, nuclear-powered submarines are not a huge step up for countries with nuclear weapons.

For countries without nuclear weapons, however, the costs far outweigh the benefits.

Per unit, a single modern diesel-electric attack submarine with air-independent propulsion costs between $500 million and $900 million. A modern nuclear-powered attack submarine will cost between $3 billion and $4 billion each, based on the current cost of Virginia-class nuclear attack submarines in the United States, a country with experience in building such ships. This is on top of the considerable investment in shipbuilding that countries like South Korea and Australia would have to make. For instance, South Korea has vowed to invest $350 billion in the United States, of which half will be spent on US shipbuilding…………………………………………………………………………………………………………………………………………… https://thebulletin.org/2025/12/how-nuclear-submarines-could-pave-the-way-for-nuclear-weapons-in-south-korea/