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ROK-U.S. Agreement on Nuclear-Powered Submarine Construction: Key Issues and Challenges — Construction Location and the Question of Uranium Enrichment and Reprocessing |
| November 28, 2025 |
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Seong-Chang CheongVice President, Sejong Institute | softpower@sejong.org
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The agreement reached at the ROK-U.S. summit in Gyeongju on October 29 on the construction of nuclear-powered submarines represents a historic turning point with the potential to transform the paradigm of South Korean naval power. After more than three decades of starts and stops, the nuclear-powered submarine (SSN) program has finally acquired a realistic prospect of realization, having secured explicit approval from a U.S. president. Yet some observers have characterized the agreement as incomplete on the grounds that the construction location was not specified, while others have argued that securing enrichment and reprocessing (ENR) rights must be a prerequisite. What, precisely, does this agreement contain, and what challenges lie ahead for South Korea?
South Korea's consideration of SSN development as a response to North Korea's nuclear threat dates to the Kim Young-sam administration, when the government first began studying the possibility. The Roh Moo-hyun administration sought to advance the program in earnest but was forced to suspend it due to funding constraints and the absence of the necessary technical personnel and infrastructure. The Moon Jae-in administration subsequently attempted to revive the program, but without U.S. cooperation it was left with no option but to proceed as a covert effort.
The landscape changed at the Gyeongju summit on October 29, when President Lee Jae-myung publicly requested that President Donald Trump agree to supply fuel for South Korea's nuclear-powered submarines, and Trump consented, injecting new momentum into the program. The joint fact sheet released by the two governments on November 14, however, formally titled "Joint Fact Sheet from the Meeting between President Lee Jae-myung and President Donald Trump," did not specify a construction location, prompting a wave of critical commentary to the effect that Trump had not approved South Korea's independent construction of nuclear-powered submarines and that the agreement was incomplete.
These assessments are premature and reflect a failure to properly weigh the respective significance of the diplomatic fact sheet against President Trump's social media statements. An accurate understanding of the substance of the agreement requires a comprehensive reading of the statements made by both leaders on October 29, Trump's social media post on October 30, and the fact sheet taken together. This paper analyzes the key issues surrounding the ROK-U.S. agreement on nuclear-powered submarine construction and identifies the tasks that lie ahead for the South Korean government.
A terminological note is in order. The vessel the Lee Jae-myung government intends to build, a Submersible Ship, Nuclear-powered (SSN), has been referred to in Korean variously as a haekjam (nuclear-powered submarine) or wonjam (atomic-powered submarine). This paper uses the term haekjam. President Lee used this term at the October 29 summit. On November 5, however, Minister of National Defense Ahn Gyu-baek publicly stated that "the government's official designation is wonjam," explaining that the term haekjam might connote the carriage of nuclear weapons and invite objections from the international community, and that the change was intended to keep the focus on peaceful use. The Ministry of National Defense then reversed course on November 11, announcing through interagency deliberation that the term haekjam would be used again, citing the need to use terminology with which the public is familiar. This produced a whipsaw effect within the space of barely ten days: haekjam on October 29, wonjam on November 5, and haekjam again on November 11. This paper respects the government's final decision and uses the term haekjam throughout. -
At the ROK-U.S. summit held at the Gyeongju National Museum on October 29, President Lee Jae-myung requested that President Donald Trump "make the decision to allow us to receive fuel for nuclear-powered submarines." President Lee added that "it seems there may have been some misunderstanding due to insufficient explanation on our part previously; we are not seeking to build submarines armed with nuclear weapons." This was an explicit clarification that the submarine South Korea intends to build is not a ballistic missile submarine (SSBN) carrying nuclear weapons, but a nuclear-powered attack submarine (SSN) that carries no nuclear armament.
President Lee further explained that "diesel submarines have limited submerged endurance, which constrains their ability to track North Korean and Chinese submarines," and emphasized that "if you permit us to receive fuel, we will use our own technology to construct several submarines armed with conventional weapons to conduct defensive operations in waters around the Korean Peninsula, which would also reduce the burden on U.S. forces."
In response, President Trump expressed agreement that South Korea requires nuclear-powered submarine capabilities given changed circumstances, including North Korea's construction of ballistic missile submarines, and indicated his willingness to proceed with follow-on consultations, according to a post-summit briefing by National Security Director Wi Sung-lac.
On October 30, President Trump stated via his Truth Social account that "the ROK-U.S. military alliance is stronger than ever," and on that basis announced that he had "approved South Korea to build nuclear-powered submarines to replace the outdated and less mobile diesel submarines it currently operates." Trump went further, stating that "South Korea will build the nuclear-powered submarines right here at the great Philadelphia Shipyard," and that "American shipbuilding will soon make a Big Comeback," remarks that brought the question of construction location into contention.
The joint fact sheet released by the two governments on November 14, however, states: "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." The document reflects precisely what President Lee had requested at the summit, namely U.S. cooperation on nuclear fuel supply, and contains no reference to the Philadelphia Shipyard mentioned in Trump's social media post.
What the Structure of the Fact Sheet Reveals
The fact sheet states unambiguously that "the United States has given approval for the ROK to build nuclear-powered attack submarines." The sentence structure warrants close attention: the formulation "ROK to build" explicitly identifies the Republic of Korea as the party responsible for construction.
Had the United States been firmly insisting on construction in the United States, the document would have contained language such as "the two countries agreed to cooperate closely for South Korea to acquire nuclear-powered submarines" or a specific reference to construction at a U.S. shipyard. Neither appears.
The more significant textual indicator is the phrase "avenues to source fuel." If construction in the United States were the underlying premise, fuel supply would be handled automatically at the U.S. shipyard and would require no separate provision. The fact that the document specifies cooperation on fuel sourcing as a distinct item presupposes construction in South Korea, making it necessary to address how fuel will be procured and delivered.
A diplomatic fact sheet and a presidential social media post cannot be treated as documents of equivalent authority. The official record of a summit is the written document; a social media post is closer to political rhetoric. President Trump's emphasis on the "revival of American shipbuilding" was directed at a domestic American audience and served to highlight his achievements for U.S. voters.
In sum, the fact sheet can be read as an accurate reflection of the South Korean government's position: that nuclear-powered submarines will be built in South Korea, with nuclear fuel to be supplied by the United States. -
The most important factor behind President Trump's approval of South Korea's nuclear-powered submarine program is economic. Trump has consistently favored a transactional approach to diplomacy that links security decisions to economic exchanges.
Economic Exchange: Modernizing the U.S. Shipbuilding Industry
In the joint fact sheet, the U.S. approval of South Korea's SSN program appears under the heading "Advancing the Maritime and Nuclear Energy Partnership." That section opens with the following: "The United States welcomed the ROK's commitment to contribute to modernizing and expanding the capacity of the U.S. shipbuilding industry, including through investments in U.S. shipyards and U.S. workers. The ROK welcomed U.S. support for South Korea's civilian and naval nuclear programs."
The sequencing is deliberate: South Korea's commitment to contribute to the modernization and expansion of U.S. shipbuilding capacity is stated first, followed by U.S. support for South Korea's civilian nuclear program, covering uranium enrichment and spent fuel reprocessing, and naval nuclear program, meaning SSN construction. This ordering suggests that U.S. approval of the SSN program was extended as a reciprocal arrangement in exchange for South Korea's commitment to invest in the U.S. shipbuilding sector.
The section identifies two specific areas in which the United States expects South Korea to deliver. First, the two countries are to advance cooperation through a bilateral shipbuilding working group in areas including maintenance, repair and overhaul, workforce development, shipyard modernization, and supply chain resilience. Second, South Korea is expected to contribute to increasing the number of U.S. commercial vessels and combat-capable naval vessels as rapidly as possible, including through the potential construction of U.S. vessels in South Korea.
The close linkage in the fact sheet between South Korea's contribution to U.S. shipbuilding modernization and U.S. support for South Korea's civilian and naval nuclear programs is unmistakable. Trump's social media announcement of SSN approval, accompanied by the declaration that "the revival of American shipbuilding will begin," reflects the same logic. If South Korea is to secure active U.S. cooperation on enrichment, reprocessing, and SSN construction, contributing to the modernization and expansion of the U.S. shipbuilding industry is not optional. It is a prerequisite.
Trump's Burden-Sharing Conception of Alliance
A second important factor is Trump's burden-sharing conception of alliance. Throughout his presidency, Trump has consistently maintained that South Korea and Japan must shoulder greater responsibilities for their own defence. He has favored a model of alliance cooperation in which partners develop their own capabilities and reduce the burden on the United States, rather than one in which Washington provides all strategic assets.
In this context, South Korea's proposal to build its own submarines using its own technology, requiring only fuel supply from the United States, aligned precisely with the burden-sharing philosophy Trump has championed. A South Korean fleet of nuclear-powered submarines would reduce the operational burden of continuous U.S. Navy SSN deployments to the region, directly serving the model of efficient alliance management Trump has sought to advance.
Shifts in the Northeast Asian Security Environment
The rapid deterioration of the Northeast Asian security environment constitutes another significant factor. North Korea is building ballistic missile submarines capable of carrying nuclear warheads, and China has been steadily expanding its SSN and SSBN force. Against this backdrop, it has become increasingly apparent that South Korea's existing submarine force, based on diesel-electric vessels, is ill-suited to the sustained submerged operations required to track North Korean and Chinese submarines over extended periods.
When President Lee explained at the summit that diesel submarines make it difficult to reliably track North Korean and Chinese submarine activities, Trump's immediate expression of agreement reflects a shared recognition of this operational reality.
U.S. Indo-Pacific Strategy
At a broader strategic level, the evolution of U.S. maritime strategy has also been a contributing factor. Since the launch of AUKUS, the United States has come to regard the expansion of allied SSN capabilities as a central instrument of its strategy to counter China, with Australia's acquisition of nuclear-powered submarines serving as the defining precedent.
From the U.S. perspective, a South Korean SSN capability would substantially enhance maritime surveillance across the Yellow Sea, the East China Sea, and the Sea of Japan, providing meaningful support for U.S. efforts to counter China's growing SSBN force. South Korea's acquisition of nuclear-powered submarines is thus not simply a bilateral cooperative arrangement but a decision that serves U.S. Indo-Pacific strategic interests directly.
Trump's Decision-Making Style
Finally, Trump's personal approach to decision-making is a relevant consideration. He has consistently favored decisive action when he judges it necessary over deference to complex normative frameworks or bureaucratic procedures. When U.S. industrial interests, alliance burden-sharing, the North Korean nuclear threat, and Chinese maritime power converged simultaneously around a single decision, Trump moved quickly and decisively on an issue that previous administrations had approached with considerable caution. -
Some have argued that the ROK-U.S. Atomic Energy Agreement (the so-called 123 Agreement) must first be revised to secure uranium enrichment and reprocessing (ENR) rights before nuclear-powered submarine construction becomes possible, contending that it is premature to discuss SSN acquisition without first establishing ENR sovereignty. This argument, however, rests on a misunderstanding of the international norms governing nuclear fuel supply for naval propulsion.
Naval Reactor Fuel Operates Under a Separate Regulatory Framework
SSN acquisition and the securing of ENR sovereignty are not sequential steps on the same track. They are entirely separate tracks. More fundamentally, the supply of naval reactor fuel is governed by a distinct body of norms that has no bearing on ENR agreements.
Safeguards issues relating to highly enriched uranium (HEU) or low-enriched uranium (LEU)-based fuel used for nuclear submarine propulsion are addressed within the framework of the Comprehensive Safeguards Agreement (CSA) concluded pursuant to Article III of the NPT, while the procedures for the withdrawal and reapplication of safeguards in connection with non-prohibited military nuclear activities are set out in paragraph 14 of INFCIRC/153. These matters therefore give rise to legal and institutional questions distinct from those governing enrichment and reprocessing for civilian nuclear power.
In other words, South Korea can receive naval reactor fuel through normal international procedures without possessing ENR rights. Australia is the illustrative case: it has no indigenous enrichment or reprocessing capability whatsoever, yet under the AUKUS arrangement it is to receive complete reactor systems and fuel from the United States and the United Kingdom. South Korea could apply the same model, or a variant adapted to its own circumstances.
SSN Acquisition Strengthens South Korea's ENR Negotiating Position
ENR rights are not a prerequisite for SSN acquisition. The logic runs in the opposite direction. It is precisely the successful acquisition of nuclear-powered submarines that will strengthen South Korea's negotiating position in the nuclear fuel and reactor domains going forward. If South Korea takes on a larger role in undersea security in Northeast Asia, the United States will naturally be compelled to treat South Korea's requests for nuclear technology and fuel cooperation with considerably greater seriousness than before.
The strategic sequencing South Korea should pursue is accordingly clear. First, a dedicated ROK-U.S. consultative mechanism for SSN acquisition should be activated in earnest to finalize the naval reactor fuel supply model. Second, a special safeguards agreement with the IAEA covering non-explosive military use reactors should be concluded to establish international legal standing. Third, building on this foundation, South Korea should pursue what might be termed an indirect ENR approach, expanding research into small modular reactors (SMRs) and the nuclear fuel cycle to incrementally broaden its practical influence in these domains.
SSN acquisition is, in the end, the path South Korea must travel first, even for the sake of its own ENR sovereignty. It is not the case that ENR rights must precede SSN construction; rather, it is SSN acquisition that builds the negotiating leverage needed to advance South Korea's broader nuclear sovereignty.
The two leaders reaffirmed at the end of October the agreement on South Korea's approximately 150 billion dollar investment in the U.S. shipbuilding sector, an astronomically large figure sufficient to construct roughly 33 Virginia-class nuclear-powered submarines, each estimated to cost approximately 4.5 billion dollars to build.
It is precisely because South Korea committed to such a substantial investment in U.S. shipbuilding that the Trump administration extended its support for the procedures that could lead to South Korea's civilian uranium enrichment and spent fuel reprocessing for peaceful purposes. While U.S. approval of South Korea's SSN construction has attracted the greater share of public attention, the fact sheet addresses the ENR question before the SSN issue. As South Korea's shipbuilding investment in the United States takes concrete shape, meaningful progress on ENR rights can be expected to follow. -
For South Korea to construct nuclear-powered submarines domestically with U.S.-supplied fuel, two sets of requirements must be met concurrently: U.S. domestic legal procedures and international nonproliferation norms. The model most likely to apply is the one used for Australia under AUKUS, in which the United States enacted dedicated legislation.
U.S. Congressional Legislation
Revising the ROK-U.S. 123 Agreement is not a realistic path forward. As the foundational framework governing all U.S. nuclear cooperation arrangements, amending it to accommodate a single partner country's specific requirements would carry a prohibitive political cost.
Country-specific legislation enacted by the U.S. Congress, as in the AUKUS case, has clear precedent and is far more feasible. Such legislation would define South Korea's nonproliferation obligations, the scope of nuclear fuel provision, and technology protection requirements under the SSN program.
Three conditions are essential for such legislation to pass. First, Congress must be satisfied that South Korean SSNs would make a tangible contribution to U.S. strategic interests in East Asia. Second, South Korea must be seen as a reliable adherent to nonproliferation norms. Third, the arrangement must generate clear economic benefits for U.S. shipbuilding and nuclear industries.
Examining a Hybrid Construction Model
President Trump has expressed a preference for South Korea to build nuclear-powered submarines in the United States as part of his vision for reviving the American shipbuilding industry. This issue is likely to feature prominently in the bilateral shipbuilding cooperation consultative body between the two countries' National Security Councils.
South Korea's requirements, however, extend well beyond a single vessel. A hybrid model, under which South Korea pursues independent domestic construction while simultaneously undertaking joint construction with the United States, warrants serious consideration. South Korea would develop an autonomous construction capability while closing the technology gap through U.S. shipyard cooperation. The United States would gain both the political dividend of a shipbuilding revival and the strategic benefit of a strengthened undersea deterrent on the Korean Peninsula.
IAEA Special Safeguards Agreement
Naval reactor fuel falls under the category of non-explosive military use under Article 14 of the NPT, which requires South Korea to conclude a special safeguards agreement with the IAEA. Negotiations under this framework involve technical agreement on fuel loading, removal, and verification arrangements. The AUKUS parties are already engaged in this process.
Projected Timeline and Phased Tasks
The full set of required procedures constitutes a long-term project. Drawing on the AUKUS experience, the following phased timeline can be projected.
Year 1-2: Enactment of U.S. congressional legislation and conclusion of the IAEA safeguards agreement. Year 2-3: Finalization of reactor design and establishment of the fuel supply system. Year 3-5: Commencement of construction and integration of major systems. Year 5-7: Testing and operational deployment.
Australia is not expected to receive its first nuclear-powered submarine for approximately ten years or more. South Korea's existing capability to design and build medium-sized submarines independently suggests a shorter timeline may be achievable.
Delivering on the U.S. Shipbuilding Investment Commitment
South Korea must faithfully fulfill its commitment, as specified in the fact sheet, to contribute to U.S. shipbuilding modernization. This is not simply an economic cooperation arrangement. It is the political foundation on which the sustainability of the SSN program rests.
Concrete measures include investment by South Korean shipbuilders in the United States, technology cooperation for U.S. shipyard modernization, and joint ROK-U.S. naval vessel construction. Tangible progress on these fronts is the condition for sustaining the support of the U.S. Congress and the American defense industrial base over the long term. -
The agreement on nuclear-powered submarine construction reached at the ROK-U.S. summit in Gyeongju last October marks a historic turning point for a program that has cycled through advancement and frustration for more than three decades. Analysis of the joint fact sheet confirms that the South Korean government's position, namely independent domestic construction with U.S. fuel supply, is clearly reflected in the document.
Several factors converged to make this agreement possible: President Trump's transactional approach to diplomacy, his burden-sharing conception of alliance, and the rapidly shifting security environment in Northeast Asia. The linkage of South Korea's investment in the U.S. shipbuilding industry with U.S. approval of the SSN program as a package arrangement carries significant implications for the implementation process ahead.
The argument advanced in some quarters that ENR rights must be secured first stems from a misreading of the international nonproliferation regime. Naval reactor fuel is governed under a separate framework pursuant to Article 14 of the NPT, and it is precisely the successful acquisition of nuclear-powered submarines that will strengthen South Korea's negotiating position in future ENR discussions, not the other way around.
The tasks before the South Korean government are clear: sustained diplomatic engagement to secure U.S. congressional legislation, conclusion of a special safeguards agreement with the IAEA, faithful fulfillment of the U.S. shipbuilding investment commitment, and serious examination of a hybrid model combining independent domestic construction with joint ROK-U.S. construction.
Translating this historic opportunity into operational capability will require strategic consistency and disciplined execution. In a security environment defined by North Korea's expanding submarine-based nuclear force and China's growing maritime assertiveness, South Korea's acquisition of nuclear-powered submarines has ceased to be a matter of choice. Converting this agreement into a deployable capability stands as one of the most consequential security tasks facing the current government.
| Five Key Features of the 'Kim Jong-un 2.0 Era' and Power Elite Reshuffling
| Is There a Disagreement Between the ROK and the United States on the Construction Location?
| Trump's Decision to Approve South Korea's Nuclear-Powered Submarine Program
| The Relationship Between Securing ENR Rights and Nuclear-Powered Submarine Development
| Future Tasks for the South Korean Government
| Conclusion: Fulfilling a Thirty-Year National Aspiration
※ The contents published on 'Sejong Focus' are personal opinions of the author and do not represent the official views of Sejong Institue
