The U.S. government set off conventional explosives inside a tunnel deep in the Nevada desert this week in a test designed to replicate a so-called “decoupled” nuclear detonation. Data collected is now being used to help improve methods for detecting this kind of nuclear testing. Just earlier this year, American authorities accused China of using decoupling to conceal new nuclear tests despite the country’s stated moratorium on such activities.
The test, which involved the use of chemical high-explosives and radiotracers, was conducted yesterday inside P Tunnel in Area 12 of the Nevada National Security Site (NNSA), according to a press release from the National Nuclear Security Administration (NNSA). The NNSS, which is situated within the boundaries of the U.S. Air Force’s Nevada Test and Training Range (NTTR), is used for a wide variety of testing purposes today. An agency under the Department of Energy, NNSA’s main jobs are to oversee the development and production of nuclear weapons, as well as manage America’s nuclear deterrent stockpile.
“This experiment is especially focused on further enhancing the U.S. capabilities to detect a ‘decoupled’ explosion,” per NNSA’s release. “Data collected from the experiment will be used to validate scientific models and refine algorithms that are critical to U.S. nuclear explosion detection efforts.”
“Just as a stealth aircraft looks smaller on radar, decoupling can greatly muffle the signals detected by nuclear detection sensors, making a large explosion appear smaller,” the release explains. “In a conventional, or ‘coupled,’ underground nuclear test, a device is placed deep in a hole in close contact with the rock, allowing much of the explosion’s shockwave to reach sensors. In a decoupled test, by contrast, the device is detonated inside a large underground chamber, substantially reducing the explosion’s seismic signature.”
“In this experiment, researchers gathered measurements using a broad suite of advanced sensors, including accelerometers, seismometers, infrasound sensors, electromagnetic sensors, chemical and radiotracer samplers, and meteorological sensors,” it adds. ”Together, these measurements will improve scientists’ understanding of the signatures produced by underground explosions and strengthen the United States’ ability to detect and characterize nuclear explosive events.”
The U.S. already maintains a U.S. Atomic Energy Detection Systems (USAEDS) network, which is overseen by the U.S. Air Force Technical Applications Center (AFTAC). USAEDS is made up of more than 3,600 sensors positioned around the world. USAEDS is also tied in with the International Monitoring System (IMS), which is managed by the organization responsible for overseeing the Comprehensive Nuclear-Test-Ban Treaty (CTBT). AFTAC also supports the mission to monitor for potential nuclear testing globally using a fleet of specially configured WC-135R Constant Phoenix aircraft. In addition, those planes are used to help keep watch for unusual spikes in atmospheric radiation that could point to nuclear or radiological accidents or other incidents leading to the spread of potentially dangerous radioactive material.
With regard to the USAEDS network specifically, “once a disturbance is detected underground, underwater, in the atmosphere or in space, the event is analyzed for nuclear identification, and the findings are reported to command authorities,” according to AFTAC’s website.
As mentioned, the U.S. government has accused its Chinese counterparts of using decoupling to conceal new nuclear testing, and NNSA’s press release draws explicit attention to these allegations. At the annual Conference on Disarmament in Geneva, Switzerland, in February, Thomas DiNanno, Under Secretary of State for Arms Control and International Security, said that China had conducted at least one such test at Lop Nur on June 22, 2020. The Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) subsequently said the IMS had not detected an event matching that description at that location on that date. For its part, the Chinese government has denied the accusation.
The social media posts below include satellite imagery showing activity at Lop Nur that could point to new nuclear testing activities in recent years.
参考
— KAROTASU (@type36512) May 24, 2026
Satellite Imagery Analysis of China’s Alleged 2020 Nuclear Test at Lop Nurhttps://t.co/aafvU5Szh7
CSIS 20260213
ROLES SAT ANALYSIS No.7 中国に核実験実施の動き ー Lop Nur核実験場の画像分析 ーhttps://t.co/n66yYk0hLg
ROLES 20250522
While China is a signatory to the CTBT, the country has never ratified it. The Chinese government last acknowledged a critical-level nuclear test in 1996, after which a self-imposed moratorium was put in place, at least publicly. As an aside, the United States has also signed, but never ratified, the CTBT, and has a similar self-imposed moratorium on nuclear testing since 1992. It is worth noting that the treaty does not ban so-called sub-critical testing, which involves fissile material, but does not result in a full-fledged nuclear reaction.
Last week, The Wall Street Journal reported that the Trump administration has been holding new talks with the Chinese government regarding various aspects of the country’s massively and rapidly expanding nuclear arsenal, including the testing allegations. That story immediately preceded a state visit by China’s President Xi Jinping to Washington, D.C., to meet with Trump.
“The discussions between American and Chinese officials have centered on measures to reduce nuclear risks and haven’t been aimed at negotiating a formal arms-control pact, an effort Beijing has sharply rebuffed in the past,” according to that report. “The Trump administration has begun to highlight the possibility of implementing new verification measures.”
“Independent experts say seismic instruments might be placed on or near test sites,” The Journal‘s story also noted. “Another possibility, which was floated during the Biden administration, is to install radiation-detection equipment at test sites.”
NNSA’s announcement about the test at the Nevada National Security Site is certainly an example of the development underway already of new means of verification that could be deployed at sites around the world.
The United States has separately accused Russia of conducting lower-yield nuclear testing in secret in the past. Russia is a signatory to the CTBT and had previously ratified it. In 2023, President Vladimir Putin revoked that ratification in line with the provisions of a law passed by the country’s parliament, or Duma.
President Trump has also floated the idea of the resumption of U.S. nuclear testing in response to Russian and Chinese activities, though other U.S. officials have downplayed the possibility of doing so. The United States is otherwise in the midst of a huge nuclear modernization effort that impacts the air, sea, and land-based legs of the deterrent triad. American authorities are also now pursuing these efforts in an environment fully unbounded by relevant arms control agreements following the sunset of the New Strategic Arms Reduction Treaty (New START) earlier this year.
The Russian government has said it is ready to conduct new nuclear tests if the United States pursues this course of action. The last official nuclear test in Russia came in 1990 right before the fall of the Soviet Union.
“It takes nuclear expertise to detect nuclear activities and experiments like these [to] ensure America remains unmatched in detection,” NNSA Administrator Brandon Williams said in a statement yesterday in light of the test in Nevada. “The Trump Administration has made it clear that the United States will lead from a position of strength. You cannot evade American innovation. With this experiment, we are sending a clear message: under this administration, America will never be outmatched.”
Contact the author: joe@twz.com
The post U.S. Mimics “Decoupled” Nuclear Detonation By Blowing Up A Tunnel Conventionally appeared first on TWZ.
China’s Ministry of Commerce issued the warning after reports that several EU governments were discussing a mechanism modelled partly on Section 301 of US trade law, which allows Washington to investigate foreign trade practices and impose countermeasures.
Beijing described such an approach as protectionist and unilateral and warned that it could damage continuing negotiations between China and the EU.
“If the European side insists on introducing discriminatory restrictive measures against Chinese companies or products,” the ministry said, China would “resolutely respond” to defend the interests of its industries.
The warning comes as Europe’s trade relationship with China is moving further up the political agenda.
According to the European Commission’s latest EU-China trade figures, EU exports to China were worth €199.5 billion in 2025 while imports reached €559.5 billion.
The goods deficit stood at €359.9 billion, compared with €312.2 billion in 2024.
China remained the EU’s largest source of goods imports and its fourth-largest export market.
Brussels argues that the scale of the imbalance is connected not only to competitiveness but also to state support, market-access restrictions and other structural differences between the two economies.
China disputes that assessment and has repeatedly accused the EU of using industrial and security arguments to justify protectionism.
The argument is already visible in several industries.
The EU imposed countervailing duties on Chinese battery electric vehicles after an investigation concluded that state subsidies were giving Chinese manufacturers an unfair advantage in the European market.
Brussels has subsequently widened its attention to other parts of the automotive industry. Earlier this month, EU Today reported that the EU was considering restrictions affecting Chinese hybrid cars as policymakers looked for ways to contain the growing trade imbalance.
The automotive dispute is important because Europe is simultaneously trying to attract Chinese manufacturing investment.
France and Spain addressed that question during President Emmanuel Macron’s state visit to Madrid.
Macron and Spanish Prime Minister Pedro Sánchez agreed on the need for greater European unity in responding to Chinese competition. They also discussed whether Chinese investors entering strategically important European industries should be required to provide stronger commitments on issues such as technology transfer.
Macron said that companies on both sides of the Pyrenees needed protection when they faced unfair competition and argued that “the only response that works is European.”
France has generally favoured stronger European trade defences.
Germany has traditionally approached the issue more cautiously because major German manufacturers have substantial commercial exposure to China. Increasing competition from Chinese producers, particularly in industrial sectors where German companies were once dominant, has altered the debate.
Reports that Berlin and Paris are now working together on a stronger trade instrument therefore suggest a potentially important shift.
The two countries are said to be considering a European mechanism inspired by the American Section 301 process, although no final proposal has yet been adopted by the European Commission.
EU trade law already provides several instruments.
Brussels can impose anti-dumping or anti-subsidy duties following investigations, use the Foreign Subsidies Regulation to examine state-backed investment and procurement, and deploy the Anti-Coercion Instrument where another country uses economic pressure against the EU or a member state.
The discussion now concerns whether those instruments are sufficient when governments believe a problem extends across industries rather than affecting an individual product.
The debate comes only weeks after EU Today reported that Brussels was preparing additional pressure on Chinese hybrid-car imports, demonstrating how quickly EU-China trade disputes are expanding beyond the original electric-vehicle case.
At the same time, Brussels and Beijing have established a Trade and Investment Consultations mechanism, with workstreams covering trade balances, export controls, intellectual property and World Trade Organisation reform.
China’s Commerce Ministry has warned that introducing tougher measures while those talks continue would damage trust.
That leaves the EU facing two parallel choices: continue negotiations intended to narrow the trade dispute while also developing stronger instruments in case those negotiations fail.
France and Germany are increasingly arguing that Europe needs greater leverage.
Beijing’s response is that using that leverage against Chinese companies would bring countermeasures.
The next stage will depend on whether the Franco-German proposal develops into a formal EU initiative. If it does, the dispute will move beyond duties on particular products towards a broader argument over how Europe intends to manage its economic relationship with China.
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