Nuclear Latency May Be Strategic for U.S.

U.S. President Donald Trump made headlines last October when he announced he had given South Korea approval to build nuclear-powered submarines. It’s unclear whether the United States will supply the nuclear fuel or permit South Korea to enrich its own, but the latter option would effectively give South Korea the technical capacity to produce nuclear weapons quickly—within a matter of months—if it so chooses, a condition known as nuclear latency.

To do this, Trump would theoretically need Congress to revise the bilateral U.S.-Korea nuclear cooperation agreement, known as the 123 Agreement. Last updated in 2015, this agreement allows South Korea to enrich uranium up to 20 percent and pursue pyroprocessing for civilian purposes with U.S. consent. However, it explicitly prohibits enriching or reprocessing U.S.-origin nuclear materials for military use, a category that includes fuel for nuclear-powered submarines.

U.S. President Donald Trump made headlines last October when he announced he had given South Korea approval to build nuclear-powered submarines. It’s unclear whether the United States will supply the nuclear fuel or permit South Korea to enrich its own, but the latter option would effectively give South Korea the technical capacity to produce nuclear weapons quickly—within a matter of months—if it so chooses, a condition known as nuclear latency.

To do this, Trump would theoretically need Congress to revise the bilateral U.S.-Korea nuclear cooperation agreement, known as the 123 Agreement. Last updated in 2015, this agreement allows South Korea to enrich uranium up to 20 percent and pursue pyroprocessing for civilian purposes with U.S. consent. However, it explicitly prohibits enriching or reprocessing U.S.-origin nuclear materials for military use, a category that includes fuel for nuclear-powered submarines.

But two weeks after Trump’s initial announcement, the White House released a fact sheet that laid out a way to bypass Congress altogether. “Consistent with the bilateral 123 Agreement and subject to U.S. legal requirements,” it said, “the United States supports the process that will lead to the [Republic of Korea’s] civil uranium enrichment and spent fuel reprocessing for peaceful uses.” Unlike authorizing nuclear-powered submarines, granting South Korea consent for developing those technologies for civilian purposes faces no immediate legal barriers and does not require Congressional approval.

Though plenty of uncertainties remain, if the Trump administration continues down this path, it would pave the way for South Korea’s nuclear latency. The key question, then, is whether Washington should support this development. However provocative this may sound, my answer is “yes”—not because nuclear latency comes without risk, but because all the alternatives may be even worse for U.S. interests.

Although South Korea’s acquisition of enrichment or reprocessing technology would not, in itself, violate the Nuclear Non-Proliferation Treaty (NPT), these capabilities are inherently proliferation-prone. They enable a state to produce fissile material, which is the most technically demanding step in building a nuclear weapon. Once mastered, such capabilities dramatically shorten the timeline and lower the political and economic costs of nuclear armament.

For this reason, Washington has long restricted recipients of its civilian nuclear assistance from pursuing enrichment and reprocessing technologies without explicit U.S. consent. This reluctance stems from the potential negative consequences for the global nonproliferation regime. If South Korea acquires these capabilities, other countries, such as Saudi Arabia and Turkey, may seek to do the same, and U.S. efforts to prevent their pursuit would inevitably provoke accusations of double standards. The wider diffusion of nuclear latency would, in turn, make the global security environment significantly more fragile.

These concerns are legitimate. But the United States’ alternatives are fraught as well.

1. Maintain the Status Quo

The current approach—relying on extended deterrence while restricting South Korea’s nuclear options—is increasingly untenable. South Koreans continue to question the credibility of U.S. security guarantees, and public support for nuclear armament remains high. Even after the 2023 Washington Declaration and the launch of the Nuclear Consultative Group, which demonstrated strong U.S. commitment to defending South Korea, support for an indigenous arsenal dipped only briefly before rebounding to nearly 73 percent by early 2024—and rising to more than 76 percent after Trump returned to office last year.

This suggests that no matter what the United States does to bolster its deterrence, it may not be sufficient to address South Korea’s enduring skepticism over whether the United States would truly risk New York, Los Angeles, or Chicago to defend Seoul. That concern is becoming more acute as North Korea moves closer to possessing a reliable capability to strike the U.S. homeland. Once North Korea can credibly threaten U.S. cities, the costs and risks of defending South Korea could become too high for the United States.

Against this backdrop, Washington’s mantra of strengthening “the credibility of the U.S. extended deterrence commitment” is unlikely to assuage South Korea’s sense of insecurity.

2. Deploy Tactical Nuclear Weapons to South Korea

 This option offers minimal strategic benefit. Although some in Seoul support the idea, redeploying U.S. tactical nuclear weapons is also unlikely to address South Korea’s underlying strategic concerns. While such a move might create the appearance of a stronger U.S. commitment, it would remain squarely within the traditional framework of extended deterrence, with Washington retaining full operational control.

Given the proximity of the two Koreas, Seoul would almost certainly push for shared or even pre-delegated launch authority to account for compressed decision timelines—scenarios in which a response is needed within minutes, rather than hours. Washington, however, is highly unlikely to accept such an arrangement. As a result, South Korea would remain dependent on U.S. decision-making for nuclear use, perpetuating the very vulnerability that drives its interest in nuclear autonomy.

Redeployment risks creating the worst of both worlds: South Korea would become more vulnerable, particularly for North Korean or Chinese strikes on nuclear storage facilities, while still lacking autonomous control over nuclear weapons.

At the same time, this option would impose substantial costs on the United States, both with regards to the logistical and financial burden of nuclear weapon storage and the legal concerns this would raise under Article I of the NPT, which prohibits nuclear-weapon states from transferring nuclear weapons to non-nuclear weapon states.

3. Support or Abandon a Nuclear South Korea

If Washington fails to address Seoul’s security concerns, South Korea may choose to develop its own nuclear arsenal. Once considered unthinkable, this option could become unavoidable if the perceived costs of lacking an independent deterrent begin to exceed the costs of acquiring one. The United States would then face an unenviable choice: support (or quietly condone) South Korea’s nuclearization, or sever the alliance. Neither outcome would serve U.S. interests.

Supporting a nuclear-armed South Korea would seriously undermine the global nonproliferation regime. Though the regime has arguably weathered North Korea’s and Iran’s nuclear ambitions thus far, the damage caused by a law-abiding member openly pursuing nuclear weapons—with at least tacit U.S. support—would be far more profound. If the principal architect and guarantor of the nonproliferation regime were seen as enabling such a move, the entire system’s credibility would be gravely, perhaps irreparably, damaged. The ensuing collapse of this multilateral framework would almost certainly accelerate the spread of nuclear weapons globally.

On the other hand, distancing from or abandoning a nuclear South Korea would impose enormous costs on the United States. Losing a trusted ally with substantial military, economic, technological, and industrial capabilities would significantly weaken its strategic footing in a critical region. As U.S. Forces Korea Commander Gen. Xavier Brunson recently noted, the Korean Peninsula’s geostrategic location provides cost-imposition capabilities against both Russian and Chinese forces, making the U.S. military presence there a source of “significant strategic advantage.”

Against these alternatives, permitting South Korea to maintain nuclear latency offers Washington several advantages.

First, nuclear latency could enhance stability on the Korean Peninsula by mitigating South Korea’s security fears and by reducing North Korea’s incentives for limited conventional or tactical nuclear attacks. The credible prospect that South Korea could assemble nuclear weapons within months and retaliate would diminish the appeal of aggression unless North Korea could confidently destroy the entire latent South Korean arsenal—unlikely given its weak intelligence, surveillance, and reconnaissance capabilities—or is willing to risk an all-out war.

Nuclear latency would also give South Korea leverage in future risk-reduction talks with North Korea, which has long dismissed South Korean overtures. Counterintuitive as it may seem, a controlled degree of nuclear latency could contribute greater inter-Korean stability.

Second, supporting South Korea’s nuclear latency could strengthen the United States’ broader Indo-Pacific strategy. Acknowledging its ally’s security concerns would signal trust and respect, reinforcing cohesion within the relationship. And in practical terms, preserving U.S. political support for South Korea’s pursuit of nuclear-powered submarines likely requires framing them as serving a regional security role beyond deterring North Korea, since some argue diesel-electric submarines may suffice for peninsula-focused missions. Cast as contribution to regional burden-sharing, this program, once operational, would ease pressure on U.S. submarine production capacity while strengthening deterrence against China.

Finally, South Korea’s development of enrichment capabilities would help dilute Russia’s and China’s dominance of the international nuclear fuel market. Together, Russia and China currently supply more than 60 percent of the world’s low-enriched uranium (LEU) and almost all high-assay low-enriched uranium (HALEU), essential for next-generation reactors. The United States is stepping up efforts to expand its own nuclear fuel production, but allowing South Korea to produce LEU and HALEU at scale would further bolster energy security for the United States and its partners.

None of the choices facing Washington are without risk. But the question is not whether supporting South Korea’s nuclear latency is ideal. It is whether the alternatives—South Korean nuclear armament and losing South Korea as an ally—would be better. They would not.

Allowing South Korea to develop controlled nuclear latency under strict safeguards and effective oversight may be the most tolerable option: one that strengthens deterrence, preserves the alliance, supports U.S. strategy in Asia, and still gives Washington time to address any potential South Korean breakout before it occurs.

In a world of imperfect options, the least bad choice may also be the most prudent one.

This article is adapted from Everything but the Bomb: South Korea’s Nuclear Hedging Strategy, forthcoming from Stanford University Press.