I. Introduction: How Should the Legal Gap Be Addressed?

At the October 29, 2025 U.S.–ROK summit in Gyeongju, President Donald Trump accepted President Lee Jae-myung’s request regarding South Korea’s nuclear-powered submarine program, thereby moving bilateral discussions into a phase of formal strategic consultation. Subsequently, the U.S.–ROK Joint Fact Sheet released on November 14 (November 13 in the United States) stated that Washington had approved South Korea’s plan to build nuclear-powered attack submarines and that the two sides would closely consult on related requirements, including fuel-supply arrangements.1) This agreement fundamentally transformed the structure of the debate surrounding a Korean nuclear-powered submarine program. In the past, the central question had been whether such a program was possible at all. Now, the question has shifted toward how it should be designed and implemented.2) Yet the political agreement reached at the summit constitutes only a starting point, not a completed framework. Although it represents a powerful political signal, actual implementation under U.S. domestic law still requires separate legal procedures and congressional review.

In order for cooperation on naval nuclear propulsion fuel to make substantive progress, key legal challenges must first be resolved. The current 2015 U.S.–ROK Nuclear Cooperation Agreement (the so-called “123 Agreement”—the basic framework governing peaceful nuclear cooperation between the United States and partner countries) was designed for civilian nuclear use and does not directly apply to the transfer of naval nuclear propulsion fuel for military purposes. Consequently, a separate agreement—a Naval Nuclear Propulsion Cooperation Agreement (NNPCA)—is unavoidable.3) Moreover, the central challenge lies in the fact that even such a new agreement would ultimately be subject to the congressional review framework under the U.S. Atomic Energy Act (AEA).4)

In a Sejong Focus article published on December 15, 2025, the author previously outlined a six-stage U.S. approval process and proposed a U.S.–ROK naval nuclear propulsion fuel cooperation roadmap.5) Building upon subsequent research, this article focuses on two newly identified issues. First, under the AEA, there are two distinct pathways for pursuing an NNPCA. Path A involves drafting and signing a separate bilateral agreement followed by congressional review under §123(d) of the AEA. Path B involves an “AUKUS-style” approach in which enabling legislation is adopted first, followed by the conclusion of the agreement itself. Each pathway has clearly distinct advantages and disadvantages. Second, acceptance by the U.S. Congress will determine the practical success or failure of negotiations. This makes it necessary to develop tailored strategies for persuading specific congressional committees and institutional actors. This article analyzes these two issues and proposes an optimal strategic approach for South Korea.

Previous studies have largely focused on the strategic necessity of South Korean nuclear-powered submarines, the limitations of the U.S.–ROK Nuclear Cooperation Agreement, and precedents established by AUKUS and IAEA safeguards arrangements. By contrast, this study advances the discussion one step further by focusing specifically on legally viable pathways under U.S. domestic law and on strategies for securing congressional support. In particular, the article distinguishes between Path A and Path B for concluding a U.S.–ROK Naval Nuclear Propulsion Cooperation Agreement (NNPCA), compares their respective characteristics, and proposes a two-track strategy that pursues both approaches in parallel.

II. Structural Legal Obstacles to Bilateral Cooperation

1. The Two Gateways under the U.S. Atomic Energy Act

The U.S. Atomic Energy Act (AEA) strictly regulates the overseas transfer of nuclear materials and nuclear technology.6) In practical terms, the law contains two separate legal gateways. The first is the framework for civilian nuclear cooperation, commonly referred to as the “123 Agreement” system. The current U.S.–ROK Nuclear Cooperation Agreement falls within this category. The second is the gateway for military nuclear cooperation established under the special provisions of AEA §91(c) and §144(c). Matters with a clearly military character—such as naval nuclear propulsion fuel—require a separate cooperative framework operating through this second legal channel.

The principal provisions of AEA §91(c) may be summarized as follows:

The President may authorize the Atomic Energy Commission (now the Department of Energy) or the Department of Defense to cooperate with another country and, pursuant to a program approved by the President, to transfer by sale, lease, or loan the following items to that country:

In essence, §91(c) constitutes an enabling provision authorizing the President to transfer military nuclear reactors and related fuel to another country if deemed appropriate. It therefore represents the most direct legal starting point for a U.S.–ROK Naval Nuclear Propulsion Cooperation Agreement (NNPCA). The principal provisions of AEA §144(c) may be summarized as follows:

The President may authorize the Atomic Energy Commission (now the Department of Energy), with the assistance of the Department of Defense, to cooperate with another country and permit:

The central distinction between §91(c) and §144(c) may therefore be summarized as follows.

In other words, within the context of cooperation on a South Korean nuclear-powered submarine program, §91(c) functions as the legal basis for the transfer of fuel and reactor facilities and related equipment, while §144(c) serves as the legal basis for sharing reactor design and technical information. Accordingly, an NNPCA would need to invoke both provisions in parallel.

One important point must be emphasized here. Choosing the military cooperation pathway does not allow the parties to bypass congressional review. Even a separate agreement based on §§91(c) and 144(c) would ultimately fall within the congressional review framework established under AEA §123(d). Thus, the key issue in future negotiations is no longer whether the United States is willing to permit such cooperation, but rather under what legal form and through which congressional procedures such cooperation can be authorized.

Section 123(d) is not a standalone provision but rather the concluding part of §123, entitled “Cooperation with Other Nations,” which consists of subsections (a) through (d). The core procedures under §123(d) can be summarized as follows. The procedures outlined below apply to standard §123 agreements; for military agreements, the 30-day prior consultation requirement under §123(b) may not apply. In the case of cooperation on a South Korean nuclear-powered submarine program, however, the more important point is not whether the 30-day consultation requirement applies, but rather that the agreement would still enter the congressional review framework prior to taking effect and would involve both the foreign affairs committees and the armed services committees.

2. Concerns Among the U.S. Nonproliferation Community

The U.S. nonproliferation community remains concerned about the precedent effect and the potential expansion of latent nuclear capabilities. Nonproliferation refers to international efforts aimed at preventing the spread of nuclear weapons to additional states. Their concern is that if the United States grants an exception to South Korea, other allies may demand similar treatment, thereby weakening the normative authority of the global nuclear nonproliferation regime.

What makes these concerns particularly important is that they are shared across partisan lines, including by hardline nonproliferation experts such as Henry Sokolski, Director of the Nonproliferation Policy Education Center and a veteran nuclear policy expert associated with the Reagan administration. Sokolski, who is widely regarded as a leading nonproliferation hawk, has also warned that the AUKUS arrangement itself could set a negative precedent for the nonproliferation regime. South Korea must therefore address these bipartisan nonproliferation concerns directly by proactively proposing a credible verification framework.7) Accordingly, South Korea’s task is not to rely on the abstract claim that “we are trustworthy,” but rather to specify in advance what kinds of restrictions it is willing to accept and what verification mechanisms it is prepared to institutionalize.

3. The Position of the U.S. Congress

The U.S. Congress is the key actor that will determine the practical success or failure of any cooperation arrangement. The executive branch and Congress differ both in their priorities and in the language through which they are persuaded. Democratic lawmakers with strong nonproliferation views are likely to raise concerns about nuclear proliferation, whereas some Republicans may take a more favorable position from the standpoint of countering China and North Korea.

Past cases show that it is extremely rare for Congress to reject a Section 123 agreement outright. Instead, Congress has traditionally exercised influence by reshaping agreements through hearings, letters, conditional legislation, and special approval legislation that raise the political costs or impose additional requirements. The cases of Japan (1988) and India (2008) are representative examples.

South Korea’s negotiations with the United States must therefore be understood not only as diplomatic negotiations with the executive branch, but also as a process of persuading Congress. Both tracks must be designed together from the outset.

III. Two Legal Pathways for Concluding a Naval Nuclear Propulsion Cooperation Agreement and Strategies for Persuading the U.S. Congress

1. Path A: Drafting and Signing a Separate Agreement Followed by Congressional Review Under §123(d)

Path A involves drafting and signing a U.S.–ROK Naval Nuclear Propulsion Cooperation Agreement (NNPCA) under the military-use exception provisions provided in AEA §§91(c) and 144(c), and then submitting the agreement to Congress for review pursuant to AEA §123(d) before it can enter into force. An important point here is that a military agreement does not bypass congressional review. On the contrary, an agreement based on §§91(c) and 144(c) would still fall within the congressional review framework established under §123(d). Moreover, because such an agreement concerns military cooperation, the Senate and House Armed Services Committees would become major reviewing bodies alongside the Senate Foreign Relations Committee and the House Foreign Affairs Committee.

First is the stage of drafting the agreement within the executive branch and conducting interagency review. Although the Department of State (DOS) would lead the negotiations and diplomatic coordination, the substantive content would require close involvement from the Department of Energy (DOE), the National Nuclear Security Administration (NNSA), and the Department of Defense (DOD). In particular, under AEA §§91(c) and 144(c), the executive branch must determine that the proposed cooperation would promote the common defense and security between South Korea and the United States and would not constitute an unreasonable risk. Presidential approval would also be required.

Second is the stage of congressional submission and the 60-day continuous session review period. Once the agreement has received presidential approval and is formally submitted to Congress, it would be referred to the Senate Foreign Relations Committee, the House Foreign Affairs Committee, and—because of its military nature—the Senate and House Armed Services Committees as well. The term “60 days of continuous session” does not simply refer to 60 calendar days. Under the review procedures established by the Atomic Energy Act, periods during which either chamber of Congress adjourns for more than three days may be excluded from the calculation. As a result, the actual calendar period may extend beyond 60 days.8)

Third is the stage of automatic entry into force or congressional disapproval. Unless Congress succeeds in enacting a joint resolution of disapproval into law during the 60-day continuous session review period, the agreement may enter into force. This is the so-called “negative approval” structure. Importantly, any resolution of disapproval would itself be subject to presidential veto. Therefore, so long as the executive branch strongly supports the agreement, it would be structurally difficult for Congress to block it. This constitutes the greatest advantage of Path A. However, because the arrangement would proceed without prior enabling legislation, it also has an inherent weakness: if a future administration adopts a less supportive stance toward implementation, the legal and political stability of the arrangement could prove relatively fragile.

2. Path B: The AUKUS-Style “Legislation First, Agreement Later” Approach

Path B follows the AUKUS model, under which Congress first establishes the political and legal foundation for cooperation through legislation such as the National Defense Authorization Act (NDAA)—the annual statute that authorizes U.S. defense spending and defense policy—and only afterward does the executive branch sign a Naval Nuclear Propulsion Cooperation Agreement (NNPCA), which then proceeds through congressional review under AEA §123(d) before entering into force. The key point of this approach is not the avoidance of congressional review procedures. Rather, its purpose is to reduce political uncertainty after the conclusion of the agreement and to strengthen the continuity of cooperation even across changes of administration by securing legislative authorization and conditions in advance.

In the AUKUS case, Congress first established the implementation framework through Subtitle B (§§1321–1354) of the Fiscal Year 2024 NDAA, among which §§1351–1354 constitute the “AUKUS Submarine Transfer Authorization Act.” Subsequently, the trilateral Australia–United Kingdom–United States Naval Nuclear Propulsion Agreement (ANNPA) was signed on August 5, 2024, and entered into force on January 17, 2025. Even before the actual transfer of submarines, additional requirements were imposed, including certification 270 days in advance and notification 30 days prior to transfer.9) This demonstrates that the AUKUS-style pathway is not merely the conclusion of an agreement, but rather a complex process combining prior legislation, agreement conclusion, additional certification requirements, and notification obligations.

In South Korea’s case, one possible option would be to consider inserting a provision tentatively titled the “Authorization Provision for U.S.–ROK Naval Nuclear Propulsion Cooperation” into the FY2027 or FY2028 NDAA. Even in such a case, however, the actual NNPCA would still need to be separately drafted and signed, and the agreement itself would likely remain subject to congressional review procedures under AEA §123(d). Accordingly, Path B should not be understood as a complete substitute for Path A, but rather as a complementary pathway designed to reinforce the political stability and long-term continuity of Path A.

The principal advantage of this approach is that the legal basis for cooperation becomes more explicit, thereby increasing the likelihood that cooperation will continue even after a change of administration. Its disadvantage, however, is that inserting relevant provisions into the NDAA takes time, and additional conditions may be attached or the scope of cooperation narrowed during the legislative process. South Korea should therefore pursue a parallel approach: rapidly advancing agreement negotiations through Path A while simultaneously working with supportive lawmakers in the U.S. Congress through Path B to secure long-term legal and political stability.

3. Comparison of the Two Pathways and a Parallel Two-Track Strategy

In the short term, Path A offers advantages in speed, whereas Path B provides greater long-term stability. Since a nuclear-powered submarine program is inherently a long-term project extending over 10 to 15 years or more, a parallel two-track strategy represents the optimal approach. Track 1 is the pathway for securing speed. South Korea should promptly initiate negotiations under Path A, establish the basic framework of the agreement during 2026, and aim to enter the congressional review process within the term of the 119th Congress, which ends in January 2027, if possible. Track 2 is the pathway for securing long-term stability. At the same time, South Korea should work with friendly lawmakers in the U.S. Congress to pursue the insertion of authorization provisions related to U.S.–ROK naval nuclear propulsion cooperation into the FY2027 NDAA. Even if negotiations under Path A are concluded first, the subsequent addition of NDAA authorization provisions would significantly strengthen the political and institutional stability of the cooperation framework. The ATOMAL Agreement (NATO, 1965) and the AUKUS ANNPA (2025) provide precedents for Path A and Path B, respectively. However, it must be emphasized that ATOMAL concerned the sharing of classified nuclear information rather than the transfer of nuclear fuel, and therefore differs in scope from cooperation involving nuclear submarine fuel for South Korea.10)

4. Major Provisions of the U.S. Atomic Energy Act and Their Implications for South Korea’s Nuclear-Powered Submarine Program

The U.S. Atomic Energy Act structures nuclear cooperation as a system of “multiple layers of gates.” Looking at only a single provision can easily lead to misunderstanding. In practice, the AEA, DOE regulations, NRC (Nuclear Regulatory Commission) regulations, and in some cases special legislation all overlap and apply simultaneously. The table below summarizes the principal provisions relevant to cooperation on a nuclear-powered submarine program.

The following cases illustrate which legal pathways the United States has adopted under different circumstances. Understanding these precedents is essential for formulating South Korea’s negotiation strategy. In particular, the AUKUS case requires close analysis as the most recent and institutionally stable precedent for Path B.

The core message South Korea must deliver in persuading the United States consists of three components. First, the strategic message: Seoul should emphasize not “greater strategic autonomy,” but rather “greater alliance burden-sharing.” Second, the industrial message: South Korea should present itself as a partner capable of strengthening the U.S. shipbuilding and MRO (Maintenance, Repair, and Overhaul) base, supported by concrete figures on investment and job creation. Third, the nonproliferation message: Seoul should propose safeguards such as the use of LEU (Low Enriched Uranium—uranium enriched below 20 percent and therefore not directly usable for nuclear weapons production),11) ) prior consultation with the IAEA, and strict management of spent nuclear fuel, thereby presenting itself not as a state demanding exceptional treatment, but as a state seeking jointly to establish a new model framework for responsible nonproliferation governance.

In particular, for members of Congress with strong nonproliferation concerns, South Korea must clearly stress that the Korean case would constitute only a limited exception subject to strict conditions, including the North Korean nuclear threat, the unique nature of the U.S.–ROK alliance, the use of LEU, close consultation with the IAEA,12) and stringent control over spent nuclear fuel. Moreover, South Korea’s credibility would be strengthened by proactively proposing a verification framework itself—including caps on fuel enrichment levels, sealing and accountancy of fuel rods, identity verification upon return to port, retransfer of spent nuclear fuel, and institutional separation between naval fuel and the civilian nuclear fuel cycle.

IV. Roadmap for U.S.–ROK Naval Nuclear Propulsion Fuel Cooperation and Conclusion

1. Current Status of the Lee Jae-myung Government’s Initiative

The Lee Jae-myung administration has launched a Nuclear-Powered Submarine Acquisition Promotion Team under the Ministry of National Defense, a dedicated nuclear submarine team within the Ministry of Foreign Affairs, and an interagency task force. In addition, construction is underway at the Munmu Daewang Institute of Science and Technology (MARINS) in Gyeongju for a land-based demonstration facility for a naval small modular reactor (SMR), with inauguration targeted for January 2027 and completion of the radioactive waste facility scheduled for the end of 2027. The interagency task force officially held its first meeting on December 18, 2025, with participation from ten institutions, including the Ministry of National Defense, Ministry of Economy and Finance, Ministry of Foreign Affairs, Nuclear Safety and Security Commission, Ministry of Climate, Energy and Environment, Ministry of Science and ICT, Ministry of Trade, Industry and Energy, Defense Acquisition Program Administration, Joint Chiefs of Staff, and the Republic of Korea Navy. Nevertheless, substantive working-level negotiations with the United States on key issues such as nuclear fuel supply do not yet appear to have gained significant momentum. Domestic preparation is important, but the most urgent task remains the establishment of a solid legal and diplomatic foundation in advance.

2. Step-by-Step Roadmap

Phase 1 Foundation Building (2026–2028): The primary objective is to initiate NNPCA negotiations through Path A and submit the basic framework agreement to Congress within 2026. At the same time, South Korea should pursue insertion of authorization provisions into the FY2027 NDAA under Path B while simultaneously conducting consultations with the IAEA regarding special procedures. Domestically, enactment of a proposed “Naval Nuclear Propulsion System Act” and establishment of a Nuclear-Powered Submarine Program Office directly under the Office of the President should also be completed during this phase.13)

Phase 2 Agreement and Design (2028–2031): Based on the entry into force of the NNPCA, South Korea should simultaneously pursue U.S. export-control and security reviews, establishment of a dedicated domestic regulatory and safety management system, and consultations regarding IAEA verification procedures, while reaching basic agreements on fuel type, manufacturing, storage, transportation, refueling, and retrieval systems. A joint design team composed of the Korea Atomic Energy Research Institute and the Agency for Defense Development should finalize the basic design of the submarine reactor, while also developing the basic framework for IAEA verification procedures.

Phase 3 Construction (2031–2035): Construction of the lead submarine should begin with steel cutting in 2031, while MARINS completes land-based reactor demonstration testing. Following the securing and certification of the initial fuel load, the target should be launch of the lead submarine between 2034 and 2035.

Phase 4 Operational Deployment (2035–2045): Beginning with operational deployment of the lead submarine, South Korea should sequentially construct and commission four to six submarines. The key capability required at this stage is not enrichment or reprocessing capacity, but rather the gradual accumulation of fuel handling, quality assurance, safety, and security management capabilities compatible with U.S. nonproliferation conditions.

3. Conclusion: A Comprehensive Package Strategy Is Essential

The 2025 Gyeongju summit constituted an important starting point. However, substantive progress will become possible only when the NNPCA, congressional acceptance in the United States, a verification framework with the IAEA, domestic institutional preparations, and U.S. export-control and security review procedures are all established together. What South Korea seeks is not a simple revision of the existing U.S.–ROK Section 123 Agreement, but rather a new alliance-oriented framework for naval nuclear propulsion cooperation combining the military-use provisions of the AEA, Section 123 congressional review procedures, and, if necessary, additional special legislation.

First, a dual-track strategy combining the two legal pathways represents the optimal approach. Negotiations should advance rapidly through Path A, while Path B (prior NDAA legislation) should be pursued simultaneously to secure long-term legal stability.

Second, the U.S. Congress must be treated as a central negotiating counterpart from the outset. Different messages should be tailored to the Foreign Affairs Committees, Armed Services Committees, and district-based lawmakers, while members with strong nonproliferation orientations should be approached through the logic of a “limited exception.” South Korea’s credibility would be enhanced by proactively proposing the verification framework itself.

Third, negotiations with the United States should take the form of a comprehensive package proposal integrating security contributions, industrial cooperation, and nonproliferation guarantees. AUKUS demonstrates that such a path is possible, but also shows that it requires a complex combination of legislation, agreement-based arrangements, and additional certification and notification obligations. The success of a Korean model will ultimately depend on designing a structure in which U.S.-supplied nuclear fuel can be reconciled with technological autonomy, alliance burden-sharing, and nuclear nonproliferation objectives at the same time.

1. The White House, “Joint Fact Sheet on President Donald J. Trump’s Meeting with President Lee Jae Myung,” November 13, 2025. https://www.whitehouse.gov/fact-sheets/2025/11/joint-fact-sheet-on-president-donald-j-trumps-meeting-with-president-lee-jae-myung/(accessed April 20, 2026).
2. Moon Geun-sik, Korean-Style Nuclear-Powered Submarine (Seoul: Planet Media, 2026), pp. 233–235.
3. Lowell H. Schwartz, “Law and Policy for a U.S.-South Korea Nuclear Submarine Program,” Just Security, December 8, 2025.
4. See https://www.govinfo.gov/content/pkg/COMPS-1630/pdf/COMPS-1630.pdf.
5. Seong-Chang Cheong, “The Key to Opening the Era of Nuclear-Powered Submarines: A Roadmap for U.S.–ROK Naval Nuclear Propulsion Fuel Cooperation,” Sejong Focus, December 15, 2025.
6. Atomic Energy Act of 1954(AEA), 42 U.S.C. §§2011 et seq. Sections 91(c) and 144(c) provide the legal basis for military nuclear cooperation, while §2153 establishes the procedures for concluding civilian cooperation agreements (Section 123 Agreements).
7. Henry Sokolski, widely known as a nonproliferation hardliner, has warned that the AUKUS case could also set a negative precedent for the nonproliferation regime. South Korea should therefore proactively propose a verification framework capable of directly addressing these bipartisan nonproliferation concerns. IAEA, “The Structure and Content of Agreements Between the Agency and States Required in Connection with the Treaty on the Non-Proliferation of Nuclear Weapons,” INFCIRC/153 (Corrected), June 1972, paragraph 14.
8. The U.S. Congress operates on a two-year term basis, and pending legislation is automatically discarded at the end of each term. To complete the process within the term of the 119th Congress, it would be advantageous to submit the basic framework agreement to Congress during 2026.
9. FY2024 NDAA, Public Law 118-31, Subtitle B §§1321–1354 (with §§1351–1354 constituting the “AUKUS Submarine Transfer Authorization Act”); ANNPA, signed August 5, 2024, entered into force January 17, 2025. https://www.state.gov/multilateral-25-117.2(accessed April 20, 2026).
10. Agreement between the Parties to the North Atlantic Treaty for Co-operation Regarding Atomic Information (ATOMAL Agreement), signed in 1964 and entered into force in 1965. This case proceeded under the §2153 procedure, which corresponds to Section 123 of the AEA, for the sharing of classified information under AEA §144(b). However, it should be noted that ATOMAL concerned the sharing of classified nuclear information rather than fuel transfer, and therefore differs in scope from South Korea’s naval nuclear propulsion fuel cooperation issue. Lee Chan-song, “The U.S. Atomic Energy Act and the Future Direction of U.S.–ROK Nuclear Cooperation,” [§2153 corresponds to Section 123 of the AEA] Sejong Policy Brief, No. 2026-17 (April 10, 2026), p. 11.
11. According to testimony given by then-Chief of Naval Operations Kang Dong-gil before the National Assembly Defense Committee on October 30, 2025, South Korea proposed the use of LEU fuel enriched below 20 percent. France has been a representative example of LEU-based naval fuel use since the commissioning of the Rubis-class submarines. The principal advantage of LEU is its nonproliferation compatibility. See Moon Geun-sik, Korean-Style Nuclear-Powered Submarine, pp. 169–170.
12. Moon Geun-sik, Korean-Style Nuclear-Powered Submarine, pp. 252–254.
13. Moon Geun-sik, Korean-Style Nuclear-Powered Submarine, pp. 273–303. the official views of the Sejong Institute.

※ The views expressed in this Sejong Focus are those of the author and do not necessarily reflect the official position of the Sejong Institute.