Satellite Imagery Analysis of China’s Alleged 2020 Nuclear Test at Lop Nur

Satellite Imagery Analysis of China's Alleged 2020 Nuclear Test at Lop Nur

Photo: Vantor

[Link]

[Link]

[Link]

While commercially available imagery of Lop Nur during this timeframe is limited, CSIS analyzed Vantor images from March 26, 2020, and June 25, 2020, of the northern tunnel test area. Before China's testing moratoria, China reportedly conducted underground nuclear tests with explosive yields of less than 10 kilotons in this area. Analysts have noted significant activity at Tunnel 5 since 2020. CSIS imagery analysis of Lop Nur's northern test tunnel area, including Tunnel 5, saw no significant activity or changes between March 26, 2020, and June 25, 2020. However, Lop Nur is a large facility. It is possible that China conducted an underground nuclear test at another area. It is also possible that the testing did indeed take place at this tunnel, and there are no optical indicators in these two images.

The satellite imagery did not provide any conclusive findings to support or disprove the recent U.S. allegations. Furthermore, the CSIS Project on Nuclear Issues also searched several geologic databases to determine whether there were any indicators of seismic activity around Lop Nur on June 22, 2020. No signatures of any seismic events at the Lop Nur site were found. While the U.S. Geological Survey did record a magnitude 4.1 seismic event at 6:38 p.m. local time on June 22, the epicenter was approximately 200 kilometers away at a depth of 10 kilometers-making it unlikely to be related to activity at the test site. To further confirm this point, the Comprehensive Nuclear Test Ban Treaty Organization (CTBTO) Executive Secretary Robert Floyd issued a statement on February 6th saying

The CTBTO's International Monitoring System (IMS) is capable of detecting nuclear test explosions with a yield equivalent to or greater than approximately 500 tonnes of TNT. . . . Regarding reports of possible nuclear tests with yields in the hundreds of tonnes, on 22 June 2020, the CTBTO's IMS did not detect any event consistent with the characteristics of a nuclear weapon test explosion at that time. Subsequent, more detailed analyses have not altered that determination.

CSIS's analysis yielded no indicators of a nuclear test on June 22, 2020. If the U.S. claims are true, China conducted a covert decoupling test. They would have gone to extensive effort to hide optical and seismic signatures. While satellite imagery and seismology are inconclusive in the open source, the United States intelligence community has access to many more sources of data.

Another significant part of the problem in deciphering whether China "cheated" is the lack of an international agreement on what constitutes a nuclear test. Even the Comprehensive Nuclear Test Ban Treaty (CTBT) lacks an agreed-upon definition. The United States has long championed a "zero-yield" interpretation, meaning no experiment should produce a self-sustaining chain reaction. However, in practice, this remains more of a political distinction than a purely technical one. Defining the line between spontaneous fission in a subcritical mass and a self-sustaining chain reaction is a difficult technical challenge, one that the international community chose to leave undefined in the CTBT.

Why Test? Four Possible Explanations

If China did indeed cross the supercritical threshold on June 22, 2020, then the most important question is why. What would China stand to gain from very low-yield, decoupled nuclear tests? There are at least four possible explanations.

1. To Enhance Safety and Security: The United States conducted a series of very low-yield nuclear tests to enhance the safety and security of our weapons designs. For example, Project 56, Project 57, and Project 58 shot series all sought to ensure the safety and security of the U.S. stockpile. Most of these tests were designed to ensure that our weapons are one point safe, ensuring that if one conventional explosive detonates inside the warhead, then it will not spark a chain reaction and cause the warhead to go off. China may be pursuing similar technical assurances for its modernizing arsenal. If China is conducting safety and security experiments in a decoupled manner, it is trying to hide them.
2. To Enhance Weapons Designs: The 2025 China Military Power Report from the U.S. Department of Defense states that China "is probably pursing nuclear weapons with yields below 10 kilotons," allowing for more flexible options in a regional conflict. Using a low-yield weapon on the battlefield could force adversaries to make a difficult choice-escalate dramatically with higher-yield weapons or back down. Alternatively, China may want to conduct more nuclear tests to create smaller warheads. Miniaturization of warhead technology could allow China to fit more warheads on missiles, enhancing their ability to deploy a technology called multiple independently targetable reentry vehicles (MIRV). It is worth noting that China only conducted 64 nuclear tests before its alleged moratorium. If China wants to push warhead design parameters, testing covertly would probably be beneficial for Chinese weaponeers.
3. To Detect Proliferation: If a country wanted to covertly develop a nuclear weapons program, decoupling experiments might be the best way to test a nuclear device without detection. Chinese weapons experts may have conducted a decoupling experiment to learn what the signatures of such an experiment look like. The U.S. Department of Energy's National Nuclear Security Administration conducted several experiments between 2021 and 2023 with conventional explosives to detect and characterize low-yield, evasively conducted underground nuclear explosions. Interestingly, some of those tests may have provided more conclusive evidence to support Undersecretary DiNanno's recent claims about China's nuclear testing. If these experiments provided electromagnetic or atmospheric signatures that better characterized data from China's June 22, 2020, test, then it might explain why the language in Undersecretary DiNanno's speech was so much more definitive than previous Department of State compliance reports.
4. Because It Was an Accident: The U.S. nuclear testing history is full of accidents and failures. Most famously, the largest U.S. nuclear test, Castle Bravo in 1954, had an explosive yield of 15 megatons, while its designers thought it would only yield 6 megatons. Several of the U.S. safety tests also achieved unexpected yields. For example, the Coulomb-C test in the Project 58 shot series produced an unanticipated yield of 500 tons, forcing the evacuation of significant parts of Yucca Flats on December 6, 1957. Similarly, experiment 4 in Project 56 was a safety test that produced a slight unanticipated yield. It is possible that China conducted a safety test that accidentally produced a nuclear yield. In security studies, it is easy to assume malice, but the United States should not discount the role of incompetence.
   

Ending an Era of Ambiguity

Regardless of Chinese activities, the United States should not return to the era of full-scale explosive testing. Having conducted 1,054 nuclear tests between 1945 and 1992, the U.S. possesses the most advanced data and computer modeling in the world. If the United States reopens the door to testing, its adversaries-who have far more to learn from nuclear physics than the United States does-will gain more than the United States will. Beyond the strategic rationale, widescale nuclear testing carries high costs. Legacy nuclear testing was expensive and included high environmental and humanitarian costs.

To move beyond the current test-for-test tit-for-tat rhetoric, the United States should consider the following policy pathways:

1. Establish a P5 Nuclear Testing Transparency Initiative: As the United States works with the P5 (China, France, Russia, the United Kingdom, and the United States) year, it should lead formal efforts to define nuclear testing. By negotiating a definition agreed to by the P5, the United States could fill a vital hole in the nonproliferation regime.
2. Formalize Nuclear Test Site Visit Reciprocity: President Trump or senior administration leadership could propose a program of reciprocal site visits to Novaya Zemlya, Lop Nur, and the Nevada National Security Sites. These visits could be limited in scope but would provide assurance and transparency regarding nuclear testing behavior.
3. Restrain Future Nuclear Testing: If the administration remains determined to test "on an equal basis" with its peers, the interagency should work toward an agreement where very small nuclear tests-perhaps below a 500-ton threshold-are permissible and transparently monitored. Alternatively, as other analysts have suggested, the international community could allow a caveat for tests strictly meant to enhance the safety and security of an arsenal. While this might slightly weaken the normative prohibition on testing, it is preferable to a world of unrestrained, secret, and escalatory nuclear explosions.

Joseph Rodgers is deputy director and fellow with the Project on Nuclear Issues in the Defense and Security Department at the Center for Strategic and International Studies (CSIS) in Washington, D.C. Joseph S. Bermudez Jr. is a senior fellow for imagery analysis with the iDeas Lab and Korea Chair at CSIS.

Related Content

Parading China's Nuclear Arsenal Out of the Shadows

China's Waterlogged Missiles Don't Matter