South Korea’s Uranium Enrichment Options for the Peaceful and Sustainable Use of Nuclear Energy

Bong-Geun JUN

jun2030@mofa.or.kr​

Visiting Research Fellow

Sejong Institute

1. South Korea's Early Nuclear Policy: From Nuclear Development to the Renunciation of Enrichment and Reprocessing

After North Korea's construction of nuclear facilities at Yongbyon became known in the mid-1980s and the so-called "North Korean nuclear problem" began to take shape in earnest, the U.S. and South Korean governments found themselves without effective means to persuade Pyongyang to abandon the construction of what was known as a "radiochemical laboratory," which war, in fact, a reprocessing facility. This was because Article IV of the NPT permits member states to pursue enrichment and reprocessing for peaceful purposes, provided that they accept IAEA safeguards, a right North Korea retained after joining the NPT in 1985.

South Korea therefore pursued an exceptional approach: it would unilaterally renounce enrichment and reprocessing, and use this self-imposed restraint as leverage to press North Korea for reciprocal action. To that end, President Roh Tae-woo, in his November 8, 1991 declaration "On the Denuclearization of the Korean Peninsula and the Building of Peace," stated unilaterally in Article 2 “the abandonment of enrichment and reprocessing facilities.” North Korea was called upon to take corresponding steps. When the United States subsequently notified Seoul that it had fully withdrawn all tactical nuclear weapons deployed on South Korean soil, the South Korean government announced on December 18, 1991, that "at this moment, not a single nuclear weapon exists anywhere on our soil."

Against this backdrop, the two Koreas agreed at the inter-Korean high-level talks in December 1991 on the Joint Declaration on the Denuclearization of the Korean Peninsula, Article 3 of which proclaimed that the parties "shall not possess nuclear reprocessing and uranium enrichment facilities." This provision represented a landmark nonproliferation commitment: South Korea voluntarily renounced even the peaceful enrichment and reprocessing activities permitted under Article IV of the NPT in order to prevent North Korea's nuclear development. The international community welcomed Seoul's voluntary renunciation as a historic step forward for nonproliferation. Domestically, however, proponents of "nuclear sovereignty," argued that the renunciation amounted to a one-sided concession to U.S. demands that disregarded South Korea's own nuclear energy interests.

In the end, as North Korea continued its reprocessing and enrichment activities and repeatedly conducted nuclear tests, the Joint Declaration failed to halt Pyongyang's nuclear program. Contrary to its original intent, the Declaration continued to function as a constraint on South Korea's own enrichment and reprocessing activities, and was institutionalized as a fixture of South Korean nuclear energy policy.

A domestic debate persisted over the Declaration's legal validity. Because North Korea already possessed reprocessing facilities at the time the 1991 Declaration was adopted, and had potentially extracted plutonium, the Declaration's legal validity was questionable from the outset. Moreover, since North Korea's repeated nuclear tests constituted a material breach of the Declaration's core commitments, South Korea arguably has the legal right under general principles of international law to declare the Declaration void.

Nevertheless, successive South Korean governments have refrained from formally repudiating the Declaration, citing its possible utility as a leverage against North Korea and the US preference to preserve it. Domestically, many argue that the Declaration has already been nullified by North Korea's repeated nuclear tests. At the same time, some international legal scholars maintain that, because South Korea had not explicitly declared the Declaration void, it remains in force.

Article II of the NPT establishes the nonproliferation obligations of non-nuclear-weapon states, while Article III requires all such member states to conclude safeguards agreements with the IAEA and to guarantee nuclear transparency in order to prevent the diversion of nuclear material for weapons or explosive purposes. The cases of North Korea and Iraq, however, revealed that the existing safeguards system made it difficult to detect potential diversion at an early stage. As a corrective measure, the international community in 1997 introduced the Additional Protocol, which substantially expanded the IAEA's access to nuclear facilities and related activities.

The Additional Protocol, which South Korea signed in 1999, entered into force in February 2004. In the course of preparing the initial declaration required under the Additional Protocol, the South Korean government discovered that a few researchers at the Korea Atomic Energy Research Institute (KAERI) had conducted small-scale nuclear material separation experiments without reporting them to the IAEA. In 2000, approximately 200 milligrams of uranium had been separated using laser isotope separation technology; it further emerged that natural metallic uranium that had been stored without declaration since 1984 was used in the experiments.

The IAEA dispatched two inspection teams between September and November 2004. In a Director General's report dated November 11, 2004, the IAEA acknowledged that "the amounts of nuclear material involved were small" and that South Korea had taken "active corrective measures," while expressing "serious concern" over the failure to report enrichment and plutonium separation activities. After conducting a series of consultations with the Korean government, however, the IAEA Board of Governors decided not to refer the matter to the UN Security Council, resolving it instead through a Chairman's Conclusion.

The incident prompted South Korea to announce the "Four Principles on the Peaceful Use of Nuclear Energy" on September 18, 2004, in an effort to publicly reaffirm its nonproliferation commitments. The Four Principles reaffirmed Seoul's unequivocal intention not to develop or possess nuclear weapons, pledged firm adherence to nuclear transparency, and committed the government to strict compliance with nonproliferation norms, including the NPT and the Joint Declaration on the Denuclearization of the Korean Peninsula. As a follow-up measure to strengthen domestic safeguards, export controls, and nuclear security, the National Nuclear Management and Control Agency was established in October 2004 and later reorganized and expanded into the Korea Institute of Nuclear Nonproliferation and Control (KINAC) in 2006. Despite these remedial steps, the 2004 unreported nuclear material separation incident left a lasting mark on South Korea's nonproliferation credibility.

2. The 2015 U.S.-ROK Nuclear Cooperation Agreement: the Unfinished Agenda on Enrichment and Reprocessing

The two countries concluded the revised U.S.-ROK Agreement for Peaceful Nuclear Cooperation (hereinafter "the 123 Agreement") in 2015. Its most significant achievement was that, for the first time, both sides agreed on consultation procedures for enrichment and reprocessing, leaving open the possibility of their future implementation. In doing so, the United States moved away from a standing “prior consent” approach toward a consultative framework, under which South Korea's pursuit of enrichment and reprocessing would be subject to ongoing bilateral consultation rather than an outright prohibition or automatic approval.

More specifically, the revised agreement, in addressing spent nuclear fuel management, first called for the completion of the ROK-U.S. Pyroprocessing Joint Research program(2011–2020), to be followed by a decision on the pyroprocessing path and the possibility of South Korea pursuing overseas reprocessing on a consignment basis, subject to further agreement. This provided a basis for U.S. consent regarding post-irradiation examination and electroreduction processes, areas in which the United States had previously withheld cooperation, enabling research activities to proceed at domestic facilities. It also established a pathway for further consultations on pyroprocessing technology under joint research, based on the research findings.

On the matter of a stable supply of nuclear fuel, the parties agreed that low-enriched uranium (below 20%) would be pursued through high-level consultations and written agreement procedures. This meant that a pathway for enrichment below 20% could be considered through intergovernmental consultation, without requiring revision of the current 123 Agreement.

Regarding the operation of the High-Level Bilateral Commission, following its second plenary meeting held in August 2018, the Commission did not convene for an extended period. A video conference between the two delegations' chairs was held in October 2020, but observers noted dysfunction in the ROK-U.S. nuclear cooperation channel.

At the May 2022 ROK-U.S. summit in Seoul, Presidents Yoon Suk-yeol and Biden issued a joint statement committing to nuclear cooperation for decarbonization and energy security, including cooperation on securing energy supply chains encompassing enriched uranium, managing spent nuclear fuel, and utilizing the High-Level Bilateral Commission. However, these commitments did not lead to progress in intergovernmental follow-through. Some analysts attributed this to a commercial dispute between the two countries' nuclear energy firms over nuclear exports and intellectual property rights.

To resolve this bilateral friction, the two governments agreed in January 2025 on a memorandum of understanding on "ROK-U.S. Principles on Nuclear Export and Cooperation." Around the same time, Westinghouse, the American nuclear company at the center of the intellectual property dispute, and South Korean counterparts Korea Electric Power Corporation (KEPCO) and Korea Hydro & Nuclear Power (KHNP) agreed to settle the dispute. In Korea, the settlement was criticized by some as "humiliating and unfair", while others viewed it as removing a major obstacle to ROK-U.S. nuclear cooperation.

Yet even after the long-standing intellectual property dispute between the two sides' nuclear firms was resolved, bilateral nuclear dialogue and cooperation remained stalled. In early 2025, the U.S. Department of Energy suddenly designated South Korea as a "sensitive country" without prior consultation or notification, a development that, according to observers, starkly illustrated the constrained state of ROK-U.S. nuclear cooperation. The background to, or reasons for, the Department of Energy's action still remain unknown. Some analysts suggested that the strong domestic support for nuclear armament in South Korea, including statements by political leaders, President Yoon Suk-yeol among them, suggesting that early nuclear armament was possible, had been a contributing factor.

Reflecting this strained bilateral environment, joint research and development cooperation on pyroprocessing as a solution to South Korea's spent nuclear fuel problem also stalled. During the 2015 negotiations on the revised 123 Agreement, the United States proposed conducting a ten-year joint study to verify the technical feasibility of pyroprocessing as a response to South Korea's demands. With the first phase of joint research having already concluded, the ROK-U.S. High-Level Bilateral Commission was expected to decide whether to proceed with further research, but this process has been delayed. The Moon Jae-in administration's adoption of a nuclear phase-out policy diminished domestic momentum for pyroprocessing and sodium-cooled fast reactor research. Compounding this, as discussed above, the intellectual property dispute between KHNP and Westinghouse effectively shut down bilateral dialogue channels, bringing consultations on joint research to a virtual standstill.

3. The Gyeongju ROK-U.S. Summit: Breaking the Taboo on Enrichment and Reprocessing

Until the Gyeongju ROK-U.S. summit of October 2025, "enrichment and reprocessing" were effectively a taboo subject in South Korean nuclear energy and nuclear policy circles. The terms were rarely found in government documents or research reports from the nuclear community, and actual research and development efforts were even more conspicuously absent. While the general public and commentators invoked enrichment and reprocessing nearly as often as they did "nuclear armament," those within the nuclear energy community were reluctant to mention the words in public.

The emergence of Trump’s second term and the Lee Jae Myung government in 2025 marked a significant shift in the enrichment and reprocessing policies of both countries. President Trump placed little value on traditional U.S. nonproliferation policy and the international nonproliferation regime. Against this backdrop, President Lee requested U.S. support for South Korea’s pursuit of enrichment and reprocessing and nuclear-powered submarines, as part of the package deal of a $350 billion South Korean investment fund for the United States. Trump accepted this request. The ROK-U.S. Joint Fact Sheet (dated November 14, 2025), issued as the outcome document of the Gyeongju summit, contained the following landmark commitments on nuclear policy:

Consistent with the bilateral 123 agreement and subject to U.S. legal requirements, the United States supports the process that will lead to the ROK’s civil uranium enrichment and spent fuel reprocessing for peaceful uses.

The United States has given approval for the ROK to build nuclear-powered attack submarines. The United States will work closely with the ROK to advance requirements for this shipbuilding project, including avenues to source fuel.

Domestically, the summit agreement generated high expectations that the constraints on South Korean enrichment and reprocessing would finally be lifted. At the same time, the South Korean government is well aware that it must fully observe nonproliferation norms, both in letter and in practice, if enrichment and reprocessing are to proceed smoothly. President Lee Jae Myung sought to dispel “proliferation concerns” by making clear that South Korea's own nuclear armament is not a viable path: "There is no reason for South Korea to pursue its own nuclear armament, nor is it a realistic possibility. The United States will never approve it, and South Korea cannot endure the sanctions the way North Korea does."

Despite the agreement, lingering doubts remain as to whether the US would eventually balk at giving a green light to South Korea’s quest for enrichment and reprocessing. Given that the two governments effectively exchanged South Korean investment commitments for U.S. approval of South Korea’s quest for enrichment and reprocessing, however, the United States will be under pressure to fulfill its side of the bargain if it wishes to receive South Korean investment on schedule. Furthermore, as enrichment and reprocessing were repeatedly raised throughout the summit process and publicly by the Korean government, the subject is no longer regarded as a taboo in nuclear energy and policy circles, but has entered the mainstream policy discourse.

4. South Korea's Civilian Enrichment Options: an Assessment

South Korea has thus far procured all of its enrichment services from the international nuclear fuel market, with approximately 30% supplied by Russia. With geopolitical competition intensifying as a result of the Russia-Ukraine war and U.S.-China strategic rivalry, and with the United States having legislated the phase-out of Russian enrichment services from 2028, South Korea, as a U.S. ally, must now identify new nuclear fuel supply arrangements.

First, the option with a higher near-term feasibility and energy security benefit is to pursue equity investment in and offtake agreements with the U.S. enrichment company Centrus Energy Corp., in addition to continuing existing long-term overseas procurement contracts. Negotiations by KHNP for an equity stake in Centrus are said underway; among the various enrichment options beyond market procurement, this approach is widely regarded as the most likely to secure U.S. government approval.

KHNP's 2009 equity investment of approximately 229 billion won in a French enrichment company Areva remains the first and only precedent of its kind and is understood to have been a simple financial investment. By contrast, the equity investment in Centrus that KHNP and POSCO are currently pursuing jointly would secure an ownership interest in a parts of Centrus enrichment facilities and entail offtake agreements for the enriched uranium produced, a structurally different arrangement from the earlier case. This approach is therefore assessed to offer greater practical energy security benefits than a simple financial investment. If consummated, it would also mark the first time South Korea has held an ownership interest in an overseas enrichment facility. One key limitation is that while Centrus produces High-Assay Low-Enriched Uranium (HALEU) using its own enrichment technology, its commercial-scale low-enriched uranium production facilities are not yet complete, and uncertainty remains as to whether it can achieve full-scale production by 2029.

Second, the option offering large-volume domestic enrichment supply in the short to medium term is the introduction of a black-box enrichment facility based on Centrus's enrichment technology. This option would considerable legal and practical implementation challenges. The United States has no precedent for exporting black-box enrichment facilities abroad, and such an export falls outside the scope of nuclear cooperation covered by the existing 123 Agreement, meaning its pursuit would require either amending the existing agreement or concluding a new one.

That said, U.S. agreement to this option remains plausible. The United States already envisioned the possibility of South Korea's indigenous enrichment capability in the 2015 agreement, and a black-box facility export represents the enrichment option over which the United States would retain a stronger degree of control. Moreover, since this option may serve to slow down South Korea's progress toward fully autonomous enrichment, the United States may strategically see merit in accepting it.

A relevant precedent is the so-called Washington Treaty (1992), formally the Agreement Regarding the Establishment, Construction and Operation of a Uranium Enrichment Installation in the United States, concluded between the U.S. government and the URENCO enrichment technology-holding states (the United Kingdom, Germany, and the Netherlands) to host a URENCO black-box facility in the United States. It should be noted, however, that black-box facility transfers of this kind have historically occurred between nuclear-weapon states or states already possessing enrichment and reprocessing technology, which raises questions about whether such a transfer to South Korea, a country without such sensitive nuclear technology, would proceed smoothly.

Third, enrichment cooperation with Europe, Japan, China, or others remains an option. This, however, is best treated as a fallback option, to be prepared in the event that cooperation with the United States fails, rather than as a primary pursuit. Given South Korea's nuclear cooperation structure and alliance relationships, diplomatic resources should first be concentrated on maximizing the potential for cooperation with the United States.

Fourth, equity investment in Centrus and the introduction of a U.S.-origin black-box facility are assessed to be realistic and strategically sound options for addressing South Korea's immediate energy security needs in the short to medium term.

For the long-term achievement of energy self-reliance, however, South Korea will need to actively pursue indigenous enrichment technology development in accordance with the procedures provided by the 123 Agreement. Two broad pathways exist for developing indigenous enrichment technology: one pursued within the framework of the 123 Agreement, and another pursued outside it, a U.S.-independent pathway that excludes U.S.-origin materials and equipment. In practical terms, it is advisable to concentrate on the former The latter should be considered a second-best fallback, reserved for a scenario in which the ROK-U.S. nuclear cooperation relationship has broken down and energy self-reliance for a sustainable and peaceful use of nuclear energy must be pursued without U.S. assistance.

5. Key Domestic Preparations for Enrichment and Reprocessing

First, for South Korea to pursue enrichment and reprocessing, the foremost prerequisite is to draft and present a "National Enrichment and Reprocessing Policy." There is little dispute that enrichment and reprocessing constitute the issue of greatest political and public attention in discussions of South Korea's nuclear energy policy and the 123 Agreement. Yet despite this strong public interest and the demands of the scientific, technical, and industrial communities, no formally articulated government-level enrichment and reprocessing policy exists, a gap that defines the present state of South Korean nuclear energy policy. It should be noted that, given the fact that the South Korean government declared in the 1991 Joint Declaration on the Denuclearization of the Korean Peninsula that it would renounce possession of enrichment and reprocessing facilities, it would have been difficult for anyone to publicly advocate for either capability.

Policy must precede implementation: without a declared set of goals and rationale, plans of action cannot follow. Because no national enrichment and reprocessing policy exists, the many proposals and debates surrounding the issue have produced no meaningful outcomes. This paper therefore argues that, as a first step toward introducing enrichment and reprocessing capabilities, South Korea must establish a "National Nuclear Fuel Cycle Policy" as a key component of its peaceful nuclear energy program. In formulating this policy, the government is urged to address the following questions and incorporate the answers into its policy declaration:

Why does South Korea need enrichment and reprocessing today? What are the substantive reasons that these capabilities have now become necessary, when South Korea managed without them so far ? Given that South Korea voluntarily renounced enrichment and reprocessing in the Joint Declaration on the Denuclearization of the Korean Peninsula, why should that declaration be disregarded? The United States has identified South Korea's potential pursuit of nuclear armament as the principal reason for opposing enrichment and reprocessing; how will South Korea alleviate this concern? The existing 123 Agreement requires that, if enrichment and reprocessing are introduced, the ROK-U.S. High-Level Bilateral Commission evaluate their technical, economic, safeguards, proliferation aspects and the location for those facilities; how does South Korea's enrichment and reprocessing plans satisfy these criteria?

South Korea's posture on enrichment and reprocessing has to date been defined by the 1991 Joint Declaration on the Denuclearization of the Korean Peninsula and the 2004 Four Principles on the Peaceful Use of Nuclear Energy. Pursuing enrichment and reprocessing will therefore require that South Korea either nullify or revise these frameworks. To that end, this paper proposes that the South Korean government issue a declaration on "Peaceful Use of Nuclear Energy and Nuclear Fuel Cycle Policy for Energy Security." Such a declaration should contain substantive answers to the questions above.

Second, South Korea must overcome the domestic nuclear armament debate, and to that end, this paper proposes the enactment of Basic Law on Nuclear Energy and Non-Proliferation. Given the United States' strong nonproliferation tradition, the high domestic support for nuclear armament in South Korea will constitute a serious obstacle to the introduction of enrichment and reprocessing. South Korean public support for nuclear armament is well documented: recent polling has consistently recorded support for nuclear armament at around 70%.

The Washington Declaration issued at the ROK-U.S. summit of April 26, 2023, stated that "(the South Korean government) reaffirms its longstanding commitment to its obligations under the NPT and compliance with the ROK-U.S. Nuclear Energy Cooperation Agreement." The inclusion of this language appears to have been a U.S.-requested measure to forestall the possibility of nuclear armament, after President Yoon Suk-yeol made statements, unusual for a South Korean president, suggesting the need for an independent nuclear capability. The U.S. Department of Energy's abrupt designation of South Korea as a "sensitive country" in early 2025 was widely attributed in part to South Korea's high public support for nuclear armament. For South Korea to successfully introduce enrichment and reprocessing, it needs to reduce domestic support for nuclear armament in order to alleviate U.S. concerns and opposition.

Third, President Lee Jae Myung publicly announced South Korea's intention to construct nuclear-powered submarines for the first time at the October 2025 Gyeongju summit and treated their introduction as a fait accompli, a commitment formalized in the summit's joint fact sheet. The nuclear-powered submarine program has since prompted domestic calls to produce nuclear submarine fuel independently, requiring revision of the 123 Agreement and the expedited pursuit of indigenous enrichment. This position was mostly advanced by proponents of indigenous nuclear armament or nuclear latency who envision using the submarine program as a vehicle to both supply nuclear fuel for submarines through indigenous enrichment and to acquire nuclear latency.

However, the Joint Fact Sheet stipulates that "the United States supports procedures that will result in civilian uranium enrichment and the reprocessing of spent nuclear fuel for South Korea's peaceful use, consistent with the ROK-U.S. Atomic Energy Agreement and in compliance with U.S. legal requirements," signaling U.S. opposition to amending the agreement. In fact, given the international nuclear nonproliferation regime and U.S. nonproliferation principles, it is highly unlikely that South Korea could produce naval reactor nuclear fuel for "military-use" through indigenous enrichment. When and if the United States authorizes South Korea's indigenous enrichment, it will do so strictly within the framework of the 123 Agreement, limited to civilian peaceful use, with diversion to military purposes, including naval reactors, categorically prohibited.

The argument for amending the 123 Agreement to produce naval nuclear fuel overlooks the fundamental point that the agreement is confined to "peaceful use." Even if U.S. consent for indigenous enrichment were obtained, the production of naval nuclear fuel at civilian enrichment facilities operating under the 123 Agreement would not be permitted. In practice, virtually all states that operate or develop nuclear-powered submarines separate civilian and military enrichment activities. If South Korea wishes to introduce civilian enrichment at an early stage, it must institute a legally, institutionally, and physically rigorous separation between civilian enrichment and military nuclear fuel activities. Pressing for indigenous enrichment to supply naval nuclear fuel would, in all likelihood, complicate negotiations for the acquisition of civilian enrichment and reprocessing, an outcome South Korea cannot afford.