U.S. Atomic Energy Act and the ROK-U.S. Nuclear Cooperation: Exploring Legal Pathways and Policy Options

Chansong C. LEE

clee@sejong.org​

Research Fellow

Sejong Institute

1. Introduction

The question of the Republic of Korea's acquisition of nuclear-powered submarines came to the fore in earnest following the ROK-U.S. summit in October 2025. Korea indicated its intention to develop its own nuclear-powered submarines on the basis of U.S. nuclear fuel supply, while the United States signaled the possibility of cooperation on the premise that construction would take place within the United States. In November 2025, the two countries issued the following joint fact sheet:

“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.”

With the positions of the two countries remaining unresolved with respect to the specific location and modalities of construction, the following issues have emerged as subjects for research: 1) whether South Korea's development of nuclear-powered submarines conflicts with the ROK-U.S. Agreement for Cooperation Concerning Peaceful Uses of Nuclear Energy (2015); 2) whether the U.S. domestic legal pathways for civilian cooperation (enrichment and reprocessing) and military cooperation (supply of nuclear fuel) are identical; and 3) whether the transfer of U.S. nuclear fuel depends on executive decision or congressional approval. Against this backdrop, this study examines the compatibility of the ROK’s nuclear-powered submarine development with the acquisition of its enrichment and reprocessing rights, analyzes the applicable U.S. domestic legal pathways, and sets forth the available policy options for South Korea.

2. Acquisition of Uranium Enrichment and Reprocessing Rights

U.S. nuclear cooperation operates on the basis of the Atomic Energy Act of 1954, with Section 123(42 U.S.C. §2153) serving as its central provision. This section establishes a legal basis and requisite conditions for the United States to conclude civil cooperation agreements with foreign countries concerning the peaceful uses of nuclear energy, and sets forth the procedures for concluding such agreements as well as the scope of congressional oversight authority.

In the case of civilian cooperation, following the conclusion of negotiations and consultation with the Nuclear Regulatory Commission (NRC), the proposed agreement text must be submitted jointly to the President by the Secretary of State and the Secretary of Energy. The Secretary of State must submit to the President an unclassified Nuclear Proliferation Assessment Statement (NPAS) analyzing the extent to which the text of the proposed nuclear cooperation agreement is consistent with all requirements of Section 123. The President must submit the text of the proposed agreement for nuclear cooperation, together with the accompanying unclassified NPAS, to the Senate Committee on Foreign Relations and the House Committee on Foreign Affairs, with the exception of agreements concluded pursuant to 42 U.S.C. §2121(c), §2164(b), §2164(c), or §2164(d). Following a minimum consultation period of 30 days of continuous session with the relevant committees, in the case of agreements involving the transfer of a reactor capable of exceeding five megawatts of thermal power or special nuclear material (plutonium, enriched uranium-233, or enriched uranium-235) used in connection therewith, as was the case with the 2015 ROK-U.S. Agreement, the U.S. executive branch transmits the signed agreement text and accompanying documents to Congress together with the President's approval and determination. The agreement is then submitted to Congress for a period of 60 days of continuous session and referred to the House Committee on Foreign Affairs and the Senate Committee on Foreign Relations. At this time, the NPAS prepared by the Secretary of State and a classified annex prepared in consultation with the Director of the Central Intelligence Agency are also submitted concurrently.

If no resolution is reported out of committee within 45 days of continuous session, the first resolution introduced in the relevant chamber within the subsequent five days is automatically placed for floor consideration. The process follows an automatic approval mechanism under which the agreement fails to take effect only if Congress adopts a joint resolution expressing its disapproval of the agreement and that resolution is enacted into law during the 60-day period. This constitutes a system of congressional negative control or passive consent. This arrangement is relatively disadvantageous to Congress, insofar as both chambers must pass legislation to override an executive branch decision. Even if a disapproval resolution is enacted into law, the President may theoretically exercise a veto, and Congress must then secure a two-thirds majority vote in both chambers to override the veto and enact the resolution into law.

Should an amendment to the 2015 agreement be made to enable South Korea's enrichment and reprocessing activities, the congressional resolution procedures would need to be repeated. If an amendment to the existing agreement is deemed unnecessary, a separate congressional approval process may or may not be required. A letter transmitted to President Obama by the Secretary of State and the Secretary of Energy on June 1, 2015, states that sensitive nuclear technology, or information related to plutonium-bearing materials may be transferred if specifically identified through an amendment to the agreement or through a separate arrangement between the parties. It is assessed that if the U.S. executive branch adopts a negative or ambivalent posture toward South Korea's enrichment and reprocessing activities, Washington may require an amendment to the agreement, whereas if it adopts a more permissive stance, the U.S. government might proceed through a separate arrangement between the parties.

3. Acquisition of U.S. LEU for Nuclear-powered Submarines

South Korea is currently developing plans for the domestic construction of nuclear-powered submarine hulls and reactors. While no publicly available information exists regarding the technical status and developmental stages of South Korea's own reactor development for naval vessels and nuclear-powered submarines, it is assessed that the Korea Atomic Energy Research Institute(KAERI) received a transfer of small reactor technology developed by Russia's OKBM in the late 1990s to early 2000s at the laboratory design stage, and subsequently designed the SMART-P demonstration reactor based upon it.

Should South Korea seek to acquire only U.S. nuclear fuel for its submarines, a separate agreement to which 42 U.S.C. §2121(c) applies would be required. The negotiation, approval, and congressional consent procedures would differ from those applicable to civilian nuclear cooperation negotiations under Section 123 of the Atomic Energy Act. Such an agreement would also likely be linked to the provisions of 42 U.S.C. §2164(b) and (d). Section 2164 establishes the authority under which the United States may implement nuclear cooperation with foreign countries, with subsections (b), (c), and (d) specifically addressing the transfer of high-risk special nuclear material, production and utilization facilities, and sensitive nuclear technology. In this case, one additional condition applies: in addition to the principle that such transfers must "not constitute an unreasonable risk to the common defense and security," classified material transfers are permitted only when "the nation or organization concerned is participating or has agreed to participate in a program of mutual defense and security with the United States that makes a substantial and material contribution." In principle, South Korea would require a special agreement ratification process under 42 U.S.C. §2153, incorporating the exceptions provided under §2121(c) and §2164(b), (c), and (d), in order to receive nuclear fuel for nuclear-powered submarines from the United States. A notable point is that publicly documented cases in which the procedures set forth in §2153(d) have been followed on the basis of §2121(c) and §2164(b), (c), and (d) are few. With the exception of the ATOMAL Agreement concluded between the United States and NATO member states beginning in 1965, most instances of military nuclear cooperation have taken place outside the framework of §2153 (AEA §123).

South Korea may pursue U.S. nuclear fuel supply outside the framework of 42 U.S.C. §2153 through a separate agreement and applicable U.S. domestic law. Even in such a case, it is assessed that the United States would attach considerable weight to the criteria that the cooperation must promote the common defense and security without posing an unreasonable risk thereto, and that it is permissible only when South Korea is making a substantial and material contribution to mutual defense and security.

Should South Korea receive nuclear fuel for nuclear-powered submarines from the United States, a safeguards agreement with the International Atomic Energy Agency (IAEA) would need to be concluded as a prerequisite. It is assessed that the United States would strongly require South Korea, as it has with Australia, to comply with IAEA safeguards agreements and obligations under the Treaty on the Non-Proliferation of Nuclear Weapons. The IAEA Comprehensive Safeguards Agreement (INFCIRC/153) permits, through Article 14, a temporary exemption from inspections with respect to non-proscribed military activities. However, this exemption pertains to the deferral of access to reactors with nuclear fuel loaded, and transparent verification prior to the fuel-loading stage as well as of spent nuclear fuel remains necessary. At the same time, the state party must declare the inventory and composition of nuclear material exempted from safeguards and notify the IAEA Board of Governors accordingly.

4. Acquisition of U.S. Nuclear-powered Submarines and Its HEU Fuel​

South Korea may consider a scenario in which it acquires nuclear-powered submarines that are 100 percent U.S.-origin, as Australia has done. In such a case, either a §2153 agreement (123 agreement) concluded pursuant to 42 U.S.C. §2121(c) or §2164(b), (c), and (d), or a separate special legislative procedure outside that framework, could be considered. This scenario is not what the South Korean government desires, and it also presents legal, industrial, and technical challenges within the United States. Nevertheless, it is the option preferred by the Trump administration, and there are experts within the ROK who, as with Australia, favor the acquisition of U.S. nuclear-powered submarines as a means of reducing the initial costs and time required for domestic nuclear-powered submarine development.

In September 2021, AUKUS was announced by the United States, the United Kingdom, and Australia. In November 2021, the three countries concluded the "Agreement between the Government of Australia, the Government of the United Kingdom of Great Britain and Northern Ireland, and the Government of the United States of America for the Exchange of Naval Nuclear Propulsion Information (ENNPIA)," which entered into force in February 2022. This agreement provided for the exchange of information on naval nuclear propulsion during the initial 18-month scoping phase of the AUKUS submarine program. It set forth in detail the classification levels of information, access authorizations, protective measures, procedures for transmission, storage, and destruction, and security regulations. The United States places restrictions on sharing naval nuclear propulsion-related information with other countries unless appropriate agreements are in place, and the ENNPIA was necessary to overcome this constraint.

The United States incorporated and passed the AUKUS Submarine Transfer Authorization Act as part of the National Defense Authorization Act enacted in December 2023 for fiscal year 2024. The legislation set forth in subsection (d)(3) "a clear legal framework for the sole objective of Australia's acquisition of conventionally armed, nuclear-powered submarines" and stipulated that a mutual defense agreement satisfying "the most stringent nonproliferation standards with respect to the exchange of nuclear material, technology, equipment, and information" constitutes a prerequisite for this cooperation. Accordingly, in August 2024, the United States, Australia, and the United Kingdom concluded the "Agreement Among the Government of Australia, the Government of the United Kingdom of Great Britain and Northern Ireland, and the Government of the United States of America for Cooperation Related to Naval Nuclear Propulsion (NNPCA)," which entered into force in January 2025. This NNPCA supersedes the ENNPIA that had entered into force in 2022. The three countries agreed to communicate and exchange information with one another, and the United States and the United Kingdom agreed to transfer to Australia materials and equipment related to conventionally armed, nuclear-powered submarines. This agreement remains in force through December 31, 2075. A point of note is that the AUKUS agreement does not merely represent a program for the transfer of nuclear-powered submarine technology and equipment to Australia, but rather signifies the integrated operation of submarine forces.

5. South Korea's Policy Options

Seoul must draw a clear distinction between civilian and military nuclear cooperation and maintain a two-track approach. Research, personnel, facilities, and financial arrangements must be organized independently in accordance with this framework. However, in pursuing a two-track approach, Korea has encountered a complex formula of "enrichment and reprocessing for peaceful purposes combined with the military use of nuclear energy," and efforts are needed to sustain international confidence in nuclear nonproliferation through the construction of a new discourse framework. Communication with the U.S. executive branch regarding nuclear-powered submarines is currently at an impasse, and it is important to ensure that communication with the United States within the context of strategic and policy decisions does not lag behind the domestic pursuit of legislation for submarine construction. For the nuclear-powered submarine program, a framework for preparing and implementing arrangements under Article 14 of the IAEA Comprehensive Safeguards Agreement must be established.

With respect to the overarching strategic direction for the nuclear-powered submarine program, the following options merit consideration: a) maintaining the current posture of strategic autonomy; b) active participation in the U.S. regional defense architecture; c) focusing on the acquisition of civil uranium enrichment and reprocessing rights; and d) pursuing a pathway to cooperate with the third party for nuclear-powered submarine development. Whichever strategic choice the Korean government makes, it must be accompanied by unwavering leadership, an effective control tower, a realistic roadmap, and broad social consensus.

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