China nuclear test allegation reignites US testing moratorium debate

The State Department claims that China conducted a fruitful nuclear test In 2020, there is renewed debate in Washington over whether the United States can continue a decades-long moratorium on nuclear weapons testing.

US officials have warned that Beijing may be setting up tests in the “hundreds of tons” range – a range that highlights China’s accelerating nuclear modernization and complicates efforts to draw Beijing into arms control talks.

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Under Secretary of State for Arms Control and International Security Thomas DiNano recently said the United States has evidence that China conducted an explosive nuclear test at the Lop Nor site.

“I can reveal that the US government is aware that China has conducted nuclear explosive tests, including preparing for tests with a specified power of hundreds of tons,” DiNano said during his statements at the United Nations Conference on Disarmament.

He added, “China conducted a productive nuclear test of this type on June 22, 2020.”

DiNano also accused Beijing of using “separation” — detonators in ways that dampen seismic signals — to “hide its activities from the world.”

The Chinese Foreign Ministry denied these accusations, accused Washington of politicizing nuclear issues, and reiterated that Beijing maintains a voluntary moratorium on nuclear testing.

But the accusation has sharpened questions about verification and deterrence and whether the US stockpile management program – which relies on advanced simulations rather than live explosions – remains adequate in an era of renewed nuclear competition between great powers.

The State Department’s claim that China conducted a productive nuclear test in 2020 reignites debate in Washington over whether the United States can continue a decades-long moratorium on nuclear weapons testing. (Ken Ishii-Pool/Getty Images)

Why are small nuclear tests so difficult to detect?

Detecting small underground nuclear tests has long been one of the thorniest problems in arms control.

Unlike the massive air explosions of the Cold War, modern nuclear testing takes place deep underground. If a country used so-called “decoupling” techniques — detonating a device inside a large underground cavity to dampen the seismic shock — the resulting signal could be dramatically reduced, making it more difficult to distinguish from normal seismic activity.

This vulnerability has been discussed for decades in discussions about Comprehensive Nuclear Test Ban TreatyWhich China signed but never ratified. Even a relatively small underground detonation can provide valuable weapons data while remaining difficult to detect.

“If you detonate a device inside a large underground cavity, you can significantly mitigate the seismic signature,” said Chuck DeVore, senior national initiatives officer at the Texas Public Policy Foundation and a former Pentagon official. “This makes it difficult to detect with confidence.”

Are simulations sufficient?

China signed the Comprehensive Nuclear-Test-Ban Treaty in 1996, but did not ratify it, and the treaty never entered into force. It has maintained a voluntary moratorium on testing, a commitment that is contradicted by any explosion that produces results.

As China expands its nuclear arsenal and key arms control frameworks falter, the Cold War principle of “trust but verify” is under increasing pressure.

A US State Department official said that China may be conducting low-yield nuclear tests. (Tingshu Wang/Archive Photo/Reuters)

“The arms control community should feel completely discredited at this point,” Devore said, arguing that policymakers should not assume that Western restraint will be reciprocated by Beijing.

For decades, the United States has relied on stockpile management software — advanced computer modeling and simulation — to ensure its weapons remain reliable without explosive testing. Devore cautioned that this approach may not be sufficient if competitors conduct live bombings.

“The question assumes we live in a purely technical world,” he told Fox News, arguing that relying solely on simulations while “competitors cheat on every treaty they’ve ever signed” risks leaving the United States behind.

Devore also pointed to what he described as a growing institutional challenge.

“Almost everyone who had direct experience with live testing is now retired,” he said. “Rebuilding that experience will take years.”

But not all nuclear experts agree that resuming testing is the solution.

Henry Sokolsky, executive director of the Center for Nonproliferation Policy Education, warned that a return to live detonations would be more complicated and costly than critics of the current system suggest.

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“The yield test is not a magic key,” Sokolsky said. “If you want meaningful reliability data, don’t run one test, run many tests.”

He noted that the United States conducted more than 1,000 nuclear tests during the Cold War, building a deep database that now supports the program. He said restarting this process would likely require years of preparation and significant funding before it would yield strategic benefits.

“The debate is not pro-nuclear versus anti-nuclear,” Sokolsky said. “It’s about what is technically necessary and what is economical.”

For now, US laboratory directors continue to certify that the US arsenal remains safe and reliable without explosive testing. (Press Service of the Russian Ministry of Defense via AP)

Discussion inside the weapons complex

Sokolsky said that the dispute extends even within the US nuclear weapons complex.

“Certainly in one of our big labs that likes to use calculations — which is Livermore — they would say you’re home,” he said, indicating confidence in advanced simulations and hydrodynamic modeling.

Others place more weight on experimental verification and maintain the option of direct testing.

He said that the conflict is not ideological but technical – centered around levels of trust, costs, and long-term strategic planning.

Allies and the issue of credibility

The repercussions extend beyond Washington and Beijing.

Sokolsky warned that the credibility of “extended deterrence” — the US commitment to defending its allies under its nuclear umbrella — could come under pressure if doubts about American design or capability grow.

“Do they think you’ll come to their defense?” Sokolsky said. “If they don’t, it doesn’t matter how reliable your weapons are, extended deterrence won’t work well.”

Allies like Japan South Korea has long relied on US nuclear guarantees rather than seeking independent arsenals. Any perception that the balance is shifting could complicate regional stability and long-term efforts to prevent the spread of nuclear weapons.

Policy crossroads

For now, US laboratory directors continue to certify that the US arsenal remains safe and reliable without explosive testing. But Heather Williams, director of the Nuclear Issues Project at the Center for Strategic and International Studies, said continued testing by competitors — especially a lack of transparency — could change that calculus.

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She added: “If Russia and China continue their nuclear testing activities without providing some kind of transparency, the technical community may make a different assessment.”

The debate facing US policymakers is not simply whether to conduct testing, but under what conditions testing might enhance deterrence rather than accelerate competition.

Trump has previously suggested that the United States should ensure testing is conducted “on an equal footing” with competitors, although his administration has not formally announced a shift in policy.

Trump suggested in October 2025 that the United States should consider resuming nuclear weapons testing “on an equal footing” with other powers, and at one point said that if others were testing, “then I think we should test.”

The president did not clarify whether he meant full nuclear explosions, which the United States has not conducted since 1992, or other forms of testing such as evaluations of launch systems that do not involve nuclear explosions. Any return to explosive testing would represent a major shift in US policy.

The White House did not immediately respond to a request for comment.