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The Peninsula

Global Reverberations of a Nuclear South Korea

Published February 27, 2023
Category: South Korea

This piece is one of 12 contributions to KEI’s special project on South Korea’s nuclear armament debate that will run on The Peninsula blog over the next month. The project’s contributors include young, emerging, and mid-career voices, examining the debate from a historical, a domestic, and an international perspective. On Wednesday, March 15, KEI will host a conference featuring our various contributors’ work at our Washington, D.C. office and launch a compilation of all the pieces in a single, special KEI publication.

Nuclear risks are rising in East Asia in a way that may create drivers for South Korea to reconsider its nuclear weapons status. Over the last two decades, North Korea has escalated its nuclear threats and conducted a record number of missile tests. Additionally, as China becomes an increasingly revisionist global actor, the potential for clashes over territorial demarcation, such as in the Yellow Sea, is more pronounced. South Korean policymakers might perceive nuclear weapons as a means to ensure security in East Asia and the broader Indo-Pacific region.

While South Korea is under the U.S. nuclear umbrella, policymakers in Seoul may question the credibility of U.S. security guarantees as they navigate tense regional dynamics. For example, in January 2023, South Korean President Yoon stated, “It’s possible that the problem gets worse and our country will introduce tactical nuclear weapons or build them on our own.” If South Korea decides to pursue a nuclear option, the implications would stretch beyond the regional environment and reverberate throughout the global nuclear order, particularly in the context of the Nuclear Non-Proliferation Treaty (NPT).

Public polling suggests that, at least from a domestic political standpoint, nuclear acquisition is potentially feasible. A February 2022 report by the Chicago Council on Global Affairs noted that 71% of South Korean respondents favorably viewed the development of independent nuclear capabilities. When asked to choose between an independent program or the return of U.S. nuclear weapons to South Korea, 67% of respondents preferred an independent nuclear capability.

Additionally, South Korea has a high degree of nuclear latency, a term which describes “the possession of some or all of the technologies, facilities, materials, expertise (including tacit knowledge), resources, and other capabilities needed to develop nuclear weapons.” It is one of the top global producers of nuclear energy and has considerable fuel cycle infrastructure under International Atomic Energy Agency (IAEA) safeguards, including 25 nuclear power reactors. There are, however, some weaknesses in South Korea’s nuclear infrastructure and supply chain that would present challenges to developing a military nuclear capability. South Korea has an open nuclear fuel cycle and lacks uranium mining capabilities and large-scale enrichment and reprocessing facilities. Moreover, South Korea is highly dependent on imports to support its civilian nuclear program, and trade controls could cripple its nuclear activities.

South Korea is a leader in the existing nuclear order and an active member in the NPT. As a result, any scenario in which South Korea moves towards nuclear acquisition would raise difficult questions about its relationship with the NPT and nuclear norms. Yet the NPT is becoming particularly fragile due to rising nuclear risks in Europe and Asia, Iran’s possible pursuit of nuclear weapons, and deepening polarization between nuclear possessors and non-possessors. Moreover, the erosion of arms control norms and nuclear build-up by Russia and China  are at odds with the NPT’s overarching objectives. If the NPT is further weakened, there may be diminishing legal and normative pressures on South Korea to continue in its NPT leadership role – or to stay in the NPT at all. And if South Korea did leave an already-weakened NPT, it could have disastrous consequences for the treaty generally recognized as the foundation of the nuclear order.

Given these trends, what would a “nuclear South Korea” mean for the NPT? First, the term “nuclear South Korea” requires a definition which entails a spectrum of options from nuclear latency to a fully developed, operational, deployed nuclear capability. The stationing of U.S. nuclear weapons on South Korean territory is not part of this spectrum, since the U.S. would maintain control of the weapons and South Korea would continue to rely on an ally for nuclear capabilities, likely remaining in compliance with the NPT. This spectrum of options results in three potential scenarios for a “nuclear South Korea,” including: 1) increased nuclear latency; 2) a nuclear hedging strategy; and 3) an independent, operational nuclear capability. For each scenario, we hypothesize what would motivate Seoul to pursue such a strategy and what would be the implications for the NPT.

Any of these scenarios would entail a difficult trade-off for Seoul, between pursuing an independent nuclear deterrent for security reasons and risking its leadership in the global nuclear order.

Scenario 1: Increased latency

South Korea could increase its nuclear latency under the NPT. In fact, several former South Korean commanders have publicly advocated for increasing latency as “a way to deter North Korea’s nuclear threats.” The distinction between this scenario from South Korea’s current nuclear status would be the acceptance of increased diplomatic pressure and suspicions from the international community as a cost for expanding its civilian nuclear activities. Increasing latency would not necessarily be part of a strategy to create a nuclear weapons option, nor is it likely to trigger severe international sanctions and costs, but nevertheless could provide a foundation that could later be leveraged if Seoul later decided to pursue nuclear proliferation.

To increase latency, South Korea might expand existing nuclear capabilities or seek to fill fuel cycle gaps. South Korea might build up its spent fuel storage and reprocessing capabilities, as it has sought to do for decades. For example, South Korea might expand laboratory-scale research, such as the Korea Atomic Energy Research Institute’s laboratory-scale study of pyroprocessing technology in collaboration with the U.S., which has raised concerns from the U.S. nonproliferation community given the proliferation risks posed by plutonium separation technology.

Of the three scenarios considered here, this scenario would have the least impact on the NPT. The Treaty already includes countries with nuclear latency that could break out of their IAEA limits and quickly pursue a nuclear capability, such as Japan. In this scenario, the impact of South Korea’s nuclear latency would largely depend on wider political trends and atmospherics within the NPT itself. Specifically, the impact may depend on the reaction and pressure from Treaty on the Prohibition of Nuclear Weapons (TPNW) States Parties (SPs). If the TPNW gains momentum and membership in the coming years, its SPs may see South Korea’s nuclear latency as another data point in the failure of the NPT and members’ lack of commitment to Article VI, which commits them to “general and complete disarmament.” Pressure from the disarmament community could work at odds with pressure to pursue nuclear latency as it would also impact South Korean domestic politics, and could generate increased pressure on the government in Seoul to abandon nuclear deterrence and any nuclear latency posture and instead join the TPNW. While there is no evidence of this today, nuclear latency could draw attention to South Korea and exacerbate domestic and international debates about nuclear disarmament and the NPT.

Scenario 2: Hedging strategy

Alternatively, South Korea might pursue a hedging strategy. A hedging state “refrains from actively developing nuclear weapons but has not explicitly forsworn the option, putting the pieces in place for a future nuclear weapons program.” Intent is the primary distinction between scenario one (latency) and scenario two (hedging) as hedging would include deliberate steps towards creating and maintaining a nuclear option. In this scenario, South Korea would begin to accept significant economic and diplomatic costs flowing from international perceptions of violating the NPT but would maintain the flexibility to accelerate or decelerate progress towards the nuclear option as strategically necessary.

South Korea’s hedging strategy could take many shapes, likely building off increased nuclear latency or conventional defense capabilities. For example, building up conventional (and potentially dual-use) delivery systems and/or space launch capabilities could allow South Korea to creep towards a deliverable nuclear option without crossing the threshold of weaponization. South Korea’s current conventional military capabilities provide a foundation for a hedging strategy, as it possesses submarine-launched ballistic missiles (SLBMs) and dual-use technology. Given its dependence on imported nuclear materials, South Korea’s hedging strategy might also include increased involvement in proliferation networks to circumvent trade controls. South Korea could tap into existing proliferation networks that operate in East Asia to access the technologies and materials needed to achieve a nuclear option.

A hedging strategy for South Korea would raise questions about its commitment to the NPT and the wider nuclear order. Being open to nuclear development would understandably raise questions from nuclear weapons-states (NWS) and non-nuclear weapons-states (NNWS) alike about Seoul’s commitment to “general and complete disarmament,” and it might elicit condemnations from NPT states parties, being seen as preparing for an arms race rather than working to avoid one. Participation in numerous international initiatives, such as the Creating an Environment for Nuclear Disarmament (CEND), would also be jeopardized. For the NPT, this would be a test of whether or not the treaty has the restraining power it once did and whether or not its norms are still effective. It would also test the U.S.-South Korea relationship and could increase pressure on Washington to demonstrate the capability and credibility of its extended deterrence.

Scenario 3: Fully developed and deployed nuclear weapons

In the third scenario, South Korea would cross the threshold of nuclear weapons acquisition by developing and deploying a nuclear weapon with corresponding delivery systems. South Korea would incur the most significant economic and diplomatic costs in this scenario, but could achieve a more credible deterrent for ensuring its existential security via an independent nuclear capability. In a hypothetical scenario, following the development of a functional nuclear explosive device, South Korea might threaten or conduct a nuclear test if it is viewed as strategically valuable and/or technologically necessary. A South Korean nuclear test might be carried out in response to a nuclear test by North Korea or increased antagonism from China. In this case, South Korea might withdraw from the Comprehensive Test Ban Treaty (CTBT). South Korea might also test the conventional versions of its nuclear delivery systems to demonstrate the reliability and credibility of its deterrent forces.

If South Korea develops and deploys an independent nuclear weapons capability, it would assumedly withdraw from the NPT in order to do so. This would make South Korea the second country to ever withdraw from the NPT. The first country to do so, North Korea, withdrew in 2003 and was heavily sanctioned and largely treated as an international pariah as a result. South Korea may not face similar condemnation as it is more fully integrated into the international economy and is a well-functioning democracy; but it would likely face sanctions and a change in its relationship with the United States.

While South Korea might choose an independent nuclear capability to enhance its security, it could have a contradictory or even self-defeating effect at the cost of the U.S.-ROK alliance, especially if the U.S. scales back or fully abrogates the U.S.-ROK Mutual Defense Treaty. If South Korean nuclear weapons acquisition came at the cost of U.S. assurances for security on the Korean peninsula, one could easily make the argument that a South Korean nuclear weapon would be strategically counterproductive. The U.S., however, may be unwilling to sever ties with South Korea and lose a strategically located ally in East Asia given the realities of geopolitical competition and military priorities.

The impact of South Korea’s withdrawal and proliferation on the NPT would be significant, particularly in the context of follow-on treaty withdrawals. South Korean proliferation could stir distrust and spark arms racing with neighboring countries, such as Japan, China, and North Korea, as they try to navigate more complicated regional dynamics. Japan, in particular, might feel pressure to acquire nuclear weapons to balance against South Korea, further damaging the NPT. Other countries beyond East Asia may look to South Korea as a “successful” example of NPT withdrawal and subsequent nuclear proliferation. South Korean proliferation could also exacerbate current divisions between NWS and NNWS in the NPT, creating a more urgent push for progress on disarmament, especially if the response by NWS is viewed as underwhelming or insufficient.


Of all these options, scenario three would have the most significant and negative impact on the NPT as it would likely entail South Korea withdrawing from the treaty, breaking a non-proliferation norm, and potentially setting off a proliferation cascade. It would be difficult for the NPT to survive such a development without major effort on the part of States Parties, along with sufficient notice, planning, and new regulations on the part of South Korea. These scenarios should not be read as inevitable or the only options for South Korea. But they do highlight important trends and questions for leadership in Seoul, U.S. policymakers as a security guarantor, and for NPT members.

Seoul may face a difficult decision between pursuing nuclear weapons for its security and upholding its leadership role in the nuclear order. If Seoul does pursue nuclear hedging or a fully developed capability, this will indicate not only the weakening of the NPT and its norms, but also the diminishing credibility of U.S. nonproliferation policy and extended deterrence. Finally, Seoul’s decisions will be indicative of the worsening security environment and the challenge for existing disarmament and arms control tools to adapt.

Heather Williams is the director of the Project on Nuclear Issues and a senior fellow in the International Security Program at the Center for Strategic and International Studies (CSIS). Jessica Link is a program coordinator and research assistant with the Project on Nuclear Issues in the International Security Program at the Center for the Strategic and International Studies (CSIS). The views expressed here are the authors’ alone.

Photo from Shutterstock.

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