Is Non-Explosive Nuclear Testing Permissible: Behind the Scenes of New Nuclear Tests by the United States and Russia

1) What is a "Nuclear Test Without a Big Explosion"?

The United States ceased nuclear weapons tests involving nuclear explosions in 1992, at the end of the Cold War. However, data on the aging of nuclear warheads and design modifications are still needed. This is where "subcritical experiments" come into play. In these experiments, plutonium samples are subjected to high pressure using chemical explosives, and the response of the materials is visualized using high-speed X-rays within the zero-yield threshold, meaning they do not reach criticality (a self-sustaining chain reaction). Literally "not causing a nuclear explosion," these experiments have been explained as consistent with the U.S. nuclear testing moratorium and the Comprehensive Nuclear-Test-Ban Treaty (CTBT).Government Accountability Office

On May 14, 2024, the Department of Energy's NNSA announced that it conducted the first in the "Nimble" series of subcritical experiments at the underground facility PULSE at the Nevada National Security Site (NNSS). Los Alamos and Lawrence Livermore National Laboratories collaborated on this experiment.The Department of Energy's Energy.gov

2) Evolving "Visualization" Underground—What SCORPIUS Brings

The key to subcritical experiments lies in diagnostic technology that allows "seeing the unseen with sufficient time resolution." U.S. research institutions have been planning to deploy the linear accelerator SCORPIUS underground to continuously capture rapid deformation of plutonium with multi-pulse X-rays. This aims to reconstruct the behavior at the end stage of the implosion of a nuclear warhead's primary stage with unprecedented resolution and to cross-verify with high-performance simulations (e.g., El Capitan-class supercomputers).News Releasesstr.llnl.gov

The full operation of SCORPIUS is expected to proceed in stages, with Los Alamos publicly sharing the assembly status from 2024 onwards. Once realized, the frequency of experiments is planned to increase to about three times a year by the end of the decade, as indicated in documents from the U.S. Congressional Research Service.lanl.gov

3) Political Fluctuations—Statements on "Resuming Nuclear Tests" and Damage Control

In early November 2025, President Trump suggested on social media that "if other countries are doing it, the U.S. should immediately resume nuclear testing," sending shockwaves through the international community. Media outlets widely reported the potential "policy shift," but the Secretary of Energy later clarified that it was not nuclear tests involving explosions, but rather non-critical, non-explosive system tests. In a sense, the "words got ahead," and the practical authorities emphasized that the plans were within the existing subcritical framework.The Washington Post

During the same period, The Washington Post and DefenseNews reported experts' views that "if the U.S. were to embark on full-scale nuclear explosion tests, it would prompt other countries to follow suit and deal a severe blow to the non-proliferation regime."The Washington Post

4) International Reactions—Russia's "Line Drawing" Statement

Interestingly, a spokesperson for the Russian Foreign Ministry acknowledged that the U.S. subcritical experiments in 2024 did not violate the CTBT (Russia withdrew its ratification of the CTBT in 2023). This implies a de facto consensus that as long as it is within the zero-yield framework, it is not easily regarded as a "nuclear explosion test" internationally.Reuters

5) Science and Ethics—How Far Can "Alternative Data" Go?

Subcritical experiments bring together the best of computational science, materials science, and radiation measurement to deepen the understanding of weapon physics without actual explosions. The advantage of reduced environmental and health risks due to non-explosive nature is significant. However, from an anti-nuclear standpoint, there is persistent ethical criticism that "even without explosions, it accelerates the modernization of weapons." Scientific journals and think tank articles are divided between the view that "cutting-edge experiments plus supercomputer verification can at least cover the current reliability assessment" and the skepticism that "eventually, updated data from actual explosions will be necessary."Science News

6) Reactions on Social Media—"Safety and Deterrence" vs. "Arms Race and Breaking Taboos"

Following the "resumption of nuclear tests" statement and subsequent clarifications by authorities, debates flared up on social media.

• Experts in security and nuclear management pointed out calmly that "NNSA's subcritical tests are as announced and are different from nuclear tests involving explosions." On X, it was also noted that "the tests were conducted as predicted, within the definition of subcritical."X (formerly Twitter)

• From local community and anti-nuclear group accounts, concerns were prominent, such as "the headline of 'resuming tests in Nevada' itself evokes trauma" and "the risk of accidents or leaks is not zero."AP News

• In political threads on Reddit, opinions emphasizing the necessity of deterrence and concerns about an arms race were evenly matched. Supporters who found it acceptable "as long as it doesn't exceed criticality" clashed with critics who argued "the line is unclear."Reddit

• In NGO and researcher threads, reports were shared stating "during a visit to NNSS, we were told there are no plans for nuclear explosion tests," which served as a brake on the heated discourse.threadreaderapp.com

7) Conditions for Maintaining "Inside the Line"

Three conditions are important for subcritical experiments to gain international understanding.
(1) Transparency: Appropriately disclose the purpose of the experiment, measurement methods, and verification methods for zero-yield (while maintaining security confidentiality).Bulletin of the Atomic Scientists

(2) Technical Robustness: Make it possible to demonstrate that "criticality has not been reached" through multiple diagnostics such as SCORPIUS.News Releases

(3) Diplomatic Consistency: Ensure that messages and actions do not undermine the norms of the CTBT. Especially in times when actions are influenced by the movements of Russia and China, it is necessary to align words with practice.The Washington Post

8) Conclusion—The Alarm Sounded by "Quiet Experiments"

"Nuclear tests without explosions" are technically wise and have minimal environmental impact. However, a single political word can easily strain the international order's taboos. Subcritical experiments are balanced on a fine line between the dual demands of maintaining nuclear deterrence and upholding disarmament norms. Whether the U.S. can strictly adhere to the conditions—transparency, robust diagnostics, diplomatic consistency—will influence the nuclear order in the latter half of the 2020s.

References and Primary Information/Reports

• NNSA Official Announcement (5/16/2024): Completion of Subcritical Experiment at Nevada PULSE.The Department of Energy's Energy.gov

• Arms Control Today (6/2024): The 34th U.S. Subcritical Experiment.armscontrol.org

• AP (9/2023 Report): Improved Diagnostic Capabilities with SCORPIUS Plan for "No Explosion."AP News

• GAO (8/2023): Definition and Safety Measures of Subcritical, SCORPIUS/ZEUS Plan.Government Accountability Office

• Sandia/LLNL/LANL Materials: Technical Explanation of SCORPIUS.News Releases

• Recent Political Reports: Energy Secretary's "No Explosion" Clarification, International Reactions in The Washington Post, Expert Opinions in DefenseNews.AP News