JIIA Strategic Comments (2026-14) Preserving the Nuclear Test Moratorium at the NPT Review Conference

Mao Takahata (Research Fellow, The Japan Institute of International Affairs)
JIIA Strategic Comments (2026-14) Preserving the Nuclear Test Moratorium at the NPT Review Conference
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Papers in the "JIIA Strategic Commentary Series" are prepared mainly by JIIA research fellows to provide comments and policy-oriented analyses of significant international affairs issues in a readily comprehensible and timely manner.

Introduction

At the Nuclear Non-Proliferation Treaty (NPT) Review Conference that started in New York on April 27, 2026, attention is focused on the possibility that a final document will again not be adopted, given that no consensus agreement was reached on final documents at the last two conferences (in 2015 and 2022). However, we must not forget that the importance of a moratorium on nuclear testing has continued to be highlighted at NPT Review Conferences even when final documents were not adopted. A moratorium on nuclear testing refers to the temporary suspension of nuclear explosion tests. In many cases, nuclear-weapon states (NWSs) have voluntarily suspended nuclear explosive testing, and this “de facto pause” has been viewed as a step toward building international trust and promoting disarmament and non-proliferation.1

Amid growing concerns that the expiration of the New Strategic Arms Reduction Treaty (New START) in February of this year may have a negative impact on the NPT regime, the question of whether the nuclear test moratorium will continue to serve as a normative framework for nuclear disarmament and non-proliferation at the NPT Review Conference has garnered increasing consideration. In particular, the United States announced in 2025 that it would immediately resume nuclear testing due to concerns that China and Russia are not adhering to the nuclear test moratorium.2 Having voted for the first time against a resolution supporting the Comprehensive Nuclear-Test-Ban Treaty (CTBT) in last year’s UN First Committee session, the United States is likely to adopt a negative stance at this year’s NPT Review Conference as well.3 There are various views on why President Trump announced the resumption of nuclear testing, including that he intended to influence negotiations with China ahead of the US-China summit, and that he was reacting to Russia’s testing of nuclear-capable operational systems (such as the Burevestnik cruise missile and the nuclear-powered Poseidon torpedo).4 These circumstances make it an urgent priority for NPT state parties to recognize the importance of the nuclear test moratorium and exert stronger pressure to ensure its continued observance. This paper focuses on the significance of upgrading nuclear test detection capabilities, arguing that such capabilities contribute to maintaining the nuclear test moratorium.

The relationship between the NPT and the CTBT

To preserve the moratorium on nuclear testing, it is crucial that all state parties to the NPT reaffirm their commitment to complying with the CTBT. The relationship between the NPT and the CTBT stems from the very beginning of negotiations on the NPT, which states in its own Preamble: “Recalling the determination expressed by the Parties to the 1963 Treaty banning nuclear weapons tests in the atmosphere, in outer space and under water in its Preamble to seek to achieve the discontinuance of all test explosions of nuclear weapons for all time and to continue negotiations to this end.”5 Furthermore, Article VI of the NPT calls for state parties to “pursue negotiations in good faith on effective measures relating to cessation of the nuclear arms race at an early date and to nuclear disarmament, and on a treaty on general and complete disarmament under strict and effective international control.”6 In this regard, non-nuclear-weapon states (NNWSs) view the CTBT as a benchmark to measure if the nuclear powers are genuinely working toward disarmament, while NWSs value its contribution to nuclear non-proliferation since the CTBT was adopted by the United Nations in 1996.7

At past Cluster 1 meetings, NPT Preparatory Committee (PrepCom) meetings and NPT Review Conferences, many state parties, including NWSs, have issued statements regarding the importance of the CTBT. For example, at the 2015 and 2022 NPT Review Conferences where no final document was adopted, both the United States and Russia released statements directly supporting the CTBT.8 Although Russia withdrew its ratification of the CTBT in 2023, it announced at the 2024 NPT PrepCom that “Nevertheless, we continue to take full part in the CTBT process and have recently completed our segment of the International Monitoring System (IMS), the largest certified segment to date. We stand ready to return to the issue of CTBT ratification as soon as the United States ratifies it.”9 However, the United States limited its remarks at the 2025 PrepCom to the prohibition of fissile material production for nuclear weapons or other nuclear explosive devices, stating that “For more than 30 years, we have implemented a moratorium on the production of fissile material for use in nuclear weapons or other nuclear explosive devices. These are effective measures that concretely advance the goals of Article VI.”10 Russia made no mention of the nuclear test moratorium. Given these circumstances, there is no guarantee that the United States and Russia will present statements emphasizing the ban on nuclear testing at this year’s NPT Review Conference, raising concerns about the survival of the moratorium on nuclear testing.

Low-yield nuclear testing and stepped-up verification

In the 2025 edition of its annual report titled “Adherence to and Compliance with Arms Control, Non-Proliferation, and Disarmament Agreements and Commitments”, the United States declared that “Due to the lack of transparency with regard to their respective nuclear testing activities and previously identified adherence issues, the United States remains concerned about China and Russia’s adherence to their respective moratoria.”11 Furthermore, in February 2026, the United States expressed its suspicions that China had conducted low-yield nuclear testing in 2020 in violation of the moratorium on nuclear testing,12 prompting debate – not for the first time – over an accusation of low-yield nuclear testing. The CTBT stipulates in Article I that “Each State Party undertakes not to carry out any nuclear weapon test explosion or any other nuclear explosion, and to prohibit and prevent any such nuclear explosion at any place under its jurisdiction or control,”13 and detecting extremely small nuclear explosion would have been scientifically challenging. During negotiations over the CTBT at the Conference on Disarmament, concerns were raised that trying to technically define what counts as a nuclear weapon test could reveal sensitive information and slow down negotiations; negotiators therefore decided early on not to include a formal definition of a nuclear weapon test explosion in the treaty.14 The lack of a clearly defined zero-yield standard has led to differing interpretations among NWSs on subcritical experiments or very low-yield testing. For instance, the United States accused Russia of conducting such testing in 2019, which Russia denied.15

These cases serve as a reminder of the importance of scientific verification and fact-based dialogue in building trust. For instance, the IMS, the CTBTO’s nuclear test monitoring mechanism, initially did not detect any unusual activity when the accusation was made in 2019, yet a nuclear explosion was detected three months later at Russia’s State Central Naval Testing Range at Nyonoksa through seismic and infrasound stations in the region.16 Concluding that a particular explosion was a nuclear explosion relies on detecting radioactive materials, so the IMS’s ability to detect radioactive xenon is key to identifying low-yield nuclear tests because it is uncertain how much xenon escapes from each nuclear explosion, meaning that yields close to low levels could potentially be detected.17 The IMS is the only facility capable of detecting radioactive xenon on a global scale.

Improving xenon detection technology could enhance the ability to identify these tests, while combining radionuclide data with other sources such as satellite imagery and seismic data could further improve detection accuracy for state parties and enhance their analyses.18 For instance, the latest radioactive xenon monitoring system (SAUNA III) developed in Sweden can collect xenon gas at less than half the concentration needed for conventional methods.19 By analyzing data more quickly, it plays a noteworthy role in providing accurate analysis results. Such ongoing technological advancements and expanding radionuclide monitoring capacity are expected to reinforce verification efforts and build international trust in the system. Even though the CTBT has not entered into force, the CTBTO’s existing monitoring mechanisms, made possible by the contributions of the treaty’s signatories and ratifying states, already collect relevant scientific data from more than 90% of the Earth’s surface.20 In conducting good-faith negotiations on nuclear disarmament under Article VI of the NPT, more accurate scientific data and reliable information are helpful in promoting greater transparency and facilitating dialogue among state parties.

Conclusion and recommendations

There are concerns that the 2026 NPT Review Conference will face difficulties in adopting a final document, as was the case with the two previous conferences. Regardless of whether a final document is adopted, though, the fact that the norm of a nuclear test moratorium has been consistently supported at previous conferences should not be overlooked. On the other hand, the expiration of the New START treaty, wavering support for the CTBT, and growing mutual distrust regarding low-yield nuclear tests are having a significant impact on the sustainability of the nuclear test moratorium. In particular, the existence of low-yield nuclear tests, which are difficult to verify, amplifies suspicions of nuclear testing and serves as a structural factor that increases the risk of the moratorium’s collapse. Therefore, it is essential to regard as top priorities for this year’s NPT Review Conference the continued issuance of political declarations by all states affirming their adherence to the moratorium and the strong reaffirmation of its importance through joint statements and other means for the sake of sustaining the de facto norm of a nuclear test moratorium.

In light of the above, the following recommendations can be considered.

  • Undertake diplomatic efforts to emphasize the nuclear test moratorium: Even if the outcome of the NPT Review Conference is unfavorable toward the nuclear test moratorium, it does not necessarily mean that countries will immediately resume nuclear testing. For Japan, it is important to engage with other nations at the Ministerial level to ensure that the nuclear test moratorium continues to be addressed, particularly in preparation for the meeting for the Friends of the CTBT scheduled for 2026 in collaboration with Australia, the Netherlands, Canada, Finland, and Germany.
  • Enhance detection and monitoring capabilities centered on the CTBT: Since the key to maintaining the nuclear test moratorium lies in trusting that no nuclear test will go unnoticed, it is important to conduct diplomacy based on facts derived from analyses of accurate scientific data. To this end, it is essential to continue bolstering existing nuclear test verification capabilities. Above all, investing in the advancement and development of radionuclide monitoring capabilities for detecting low-yield nuclear tests, as well as enhancing the IMS’s observational capabilities, will help ensure that the nuclear test moratorium functions as a substantive norm supporting nuclear disarmament and non-proliferation. Specifically, in addition to continuing to contribute to the CTBTO’s IMS, I propose considering implementing measures such as establishing Japan’s own monitoring system for radioactive xenon.
  • Support enhanced detection in the Southeast Asia, the Pacific, and the Far East (SEAPFE): To maintain the functionality of the existing verification system, it is crucial that CTBT state parties transmit high-quality data and that each country conducts its own analysis. Therefore, it is vital to maintain and improve local detection and analysis capabilities, particularly in developing countries in the SEAPFE region and not allow them to decline. Japan and Australia should collaborate and demonstrate leadership, for example, by utilizing the CTBTO’s National Data Center (NDC) capacity-building scheme, to support the development of observation stations and human resources in this region, thereby boosting the detection and analysis capabilities of the entire international network.
  1. Kimball, Daryl, “Nuclear Testing and Comprehensive Test Ban Treaty”, CTBT Timeline, Arms Control Association, April 2026.
  2. Trevor Hunnicutt, Ismail Shakil and Kanishka Singh. “Trump tells Pentagon to resume testing US nuclear weapons.” Reuters, October 30, 2025. https://www.reuters.com/world/china/trump-asks-pentagon-immediately-start-testing-us-nuclear-weapons-2025-10-30/
  3. “Diplomats Prepare for Difficult Nonproliferation Treaty Conference,” Arms Control Association, April 17, 2026.
  4. Williams, Heather. “Can the United States Immediately Return to Nuclear Testing?” CSIS, October 30, 2025.
  5. The Treaty on the Non-Proliferation of Nuclear Weapons, United Nations, https://www.un.org/en/conf/npt/2005/npttreaty.html
  6. Ibid.
  7. Dahlman, O., J. Mackby, S. Mykkeltveit, and H. Haak. 2011. “Detect and Deter: Can Countries Verify the Nuclear Test Ban?” Springer Science & Business Media, p.27.
    2010 Review Conference’s final document, adopted with consensus, also reiterated the importance of the CTBT and the moratorium on nuclear test explosion (2010 Review Confernce on the parties to the treaty on the non-prolfieration of nuclear weapons, final document, 2010. https://www.nonproliferation.org/wp-content/uploads/2015/04/2010_revcon_action_plan_only.pdf)
  8. Statement by the United States, General Debate, NPT RevCom, April 27, 2015: “We have pledged not to pursue new nuclear warheads or support new military missions or military capabilities for the weapons that we do have, and we haven’t tested a nuclear weapon in 23 years. We have clearly demonstrated our commitment to abide by the Comprehensive Nuclear Test Ban Treaty.”
    Statement by the Russian Federation, General Debate, NPT RevCom, April 27, 2015: “We are deeply concerned by the lack of any tangible progress in the Comprehensive Nuclear-Test-Ban Treaty (СTBT) coming into force. We recall that our country ratified the CTBT in 2000, and we are working hard to make it universal both in bilateral and multilateral formats.”
    Statement by the United States, General Debate, 2022 NPT RevCom, August 1, 2022: “To cap the growth of nuclear arsenals anywhere in the world, we continue to support the entry into force of the Comprehensive Nuclear-Test Ban Treaty. “
    Statement by the Russian Federation, General Debate, NPT RevCom, August 2, 2022: “We note the unacceptable situation around the Comprehensive Nuclear Test-Ban Treaty (CTBT). It has been more than a quarter of a century since the Treaty was opened for signature, but it has never evolved into a living international legal instrument. Responsibility for this lies with the eight Annex 2 states of the CTBT that have not yet acceded to the Treaty.”
  9. Statement by Russia, General Debates, Second PrepCom for the 11th NPT RevCon, July 23, 2024.
  10. Sato, Mao. "Advancing Nuclear Test Verification without Entry into Force of the CTBT." Journal for Peace and Nuclear Disarmament 4.2 (2021): 251-267., p.264.
  11. U.S. Department of State, “Adherence to and Compliance with Arms Control, Nonproliferation, and Disarmament Agreements and Commitments,” April 2025, p. 29. https://www.state.gov/wp-content/uploads/2025/04/2025-Arms-Control-Treaty-Compliance-Report-1.pdf
  12. Please refer to https://www.jiia.or.jp/jpn/report/2026/03/strategic_comment_2026-5.html on Chinese nuclear testing.
  13. Comprehensive Nuclear-Test-Ban Treaty (treaty booklet), https://www.ctbto.org/sites/default/files/2023-10/2022_treaty_booklet_E.pdf, p.2.
  14. Dahlman, O., J. Mackby, S. Mykkeltveit, and H. Haak. 2011. “Detect and Deter: Can Countries Verify the Nuclear Test Ban?” Springer Science & Business Media, p.21.
  15. Borger, Julian. “Russia 'probably' violating nuclear test ban treaty, top US official says.” The Guardian. May 29, 2019.
    https://www.theguardian.com/world/2019/may/29/russia-nuclear-test-ban-treaty-probably-violating-us
  16. Sato, Mao. "Advancing Nuclear Test Verification without Entry into Force of the CTBT." Journal for Peace and Nuclear Disarmament 4.2 (2021): 251-267, p.256.
  17. Dahlman, O., J. Mackby, S. Mykkeltveit, and H. Haak. 2011. “Detect and Deter: Can Countries Verify the Nuclear Test Ban?” Springer Science & Business Media, p.86.
  18. Ibid., p.87.
  19. SAUNA III, https://scientaenvinet.com/images/produkte/sauna/Data_Sheet_SAUNAIII.pdf
  20. Sato, Mao. "Advancing Nuclear Test Verification without Entry into Force of the CTBT." Journal for Peace and Nuclear Disarmament 4.2 (2021): 251-267, p.264.