In the lush, misty valleys of southwest China, satellite imagery reveals the country\u2019s accelerating nuclear buildup, a force designed for a new age of superpower rivalry.<\/p>\n
One such valley is known as Zitong, in Sichuan Province, where engineers have been building new bunkers and ramparts. A new complex bristles with pipes, suggesting the facility handles highly hazardous materials.<\/p>\n
Another valley is home to a double-fenced facility known as Pingtong, where experts believe China is making plutonium-packed cores of nuclear warheads. The main structure, dominated by a 360-foot-high ventilation stack, has been refurbished in recent years with new vents and heat dispersers. More construction is underway next to it.<\/p>\n
Above the Pingtong facility entrance, a hallmark exhortation of China\u2019s leader, Xi Jinping, appears in characters so large they are visible from space: \u201cStay true to the founding cause and always remember our mission.\u201d<\/p>\n
These are among several secretive nuclear-related sites in Sichuan Province that have expanded and undergone upgrades in recent years.<\/p>\n
China\u2019s buildup complicates efforts to revive global arms controls<\/a> after the expiration of the final remaining nuclear arms treaty between the United States and Russia. Washington argues that any successor agreements must also bind China, but Beijing has shown no interest.<\/p>\n \u201cThe changes we see on the ground at these sites align with China\u2019s broader goals of becoming a global superpower. Nuclear weapons are an integral part of that,\u201d said Renny Babiarz<\/a>, a geospatial intelligence expert who has analyzed satellite images and other visual evidence of the sites and shared his findings with The New York Times.<\/p>\n He likened each nuclear location across China to a piece of a mosaic that, seen as a whole, shows a pattern of rapid growth. \u201cThere\u2019s been evolution at all of these sites, but broadly speaking, that change accelerated starting from 2019,\u201d he said.<\/p>\n China\u2019s nuclear expansion has been a growing source of tension with the United States. Thomas G. DiNanno, the State Department\u2019s under secretary for arms control and international security, this month publicly accused China of secretly conducting<\/a> \u201cnuclear explosive tests\u201d in contravention of a global moratorium. Beijing has rejected the claim<\/a> as untrue, and experts have debated<\/a> how strong the evidence is for Mr. DiNanno\u2019s assertions.<\/p>\n China had more than 600 nuclear warheads by the end of 2024<\/a> and is on a track to have 1,000 by 2030, according to the Pentagon\u2019s latest annual estimate. China\u2019s stockpile is much smaller than the many thousands held by the United States and Russia, but its growth is still troublesome, said Matthew Sharp<\/a>, a former State Department official who is now a senior fellow at the Center for Nuclear Security Policy at the Massachusetts Institute of Technology.<\/p>\n \u201cI think without a real dialogue on these topics, which we lack, it\u2019s really hard to say where it\u2019s going, and that, for me, is dangerous,\u201d he said, \u201cbecause now we\u2019re forced to react and plan around the worst-case interpretation of a concerning trend line.\u201d<\/p>\n The sites in Sichuan were built six decades ago<\/a> as part of Mao Zedong\u2019s \u201cThird Front,\u201d a project to shield China\u2019s nuclear weapons production labs and plants from strikes by the United States or the Soviet Union.<\/p>\n Tens of thousands of scientists, engineers and workers labored in secret to carve into the mountainous interior what Danny B. Stillman, an American nuclear scientist who visited the area, later called, in a coauthored book, \u201can inland nuclear empire.\u201d<\/p>\n When China\u2019s tensions with Washington and Moscow subsided in the 1980s, many \u201cThird Front\u201d nuclear facilities closed or shrank, and often their scientists moved to a new weapons lab in the nearby city of Mianyang. Sites like Pingtong and Zitong continued operating, but change in the years that followed was piecemeal, reflecting China\u2019s policy then of keeping a relatively small nuclear arsenal, said Dr. Babiarz.<\/p>\n That era of restraint faded from about seven years ago. China began rapidly building or upgrading many nuclear weapons facilities, and construction at the sites in Sichuan also accelerated, Dr. Babiarz said. The buildup includes a vast laser ignition lab<\/a> in Mianyang that could be used to study nuclear warheads without detonating actual weapons.<\/p>\n The design of the Pingtong complex suggests that it is being used to make the pits of nuclear warheads \u2014 the metal core, usually containing plutonium \u2014 according to Dr. Babiarz. He noted that its architecture was similar to that of pit making facilities in other countries, including the Los Alamos National Laboratory in the United States.<\/p>\n In Zitong, the new bunkers and ramparts are likely being used to test \u201chigh explosives,\u201d experts say, referring to the chemical compounds that detonate to create the conditions for a chain reaction in nuclear materials.<\/p>\n \u201cYou have a layer of high explosives and the shock wave at the same time implodes into the center. This needs blast tests to perfect them,\u201d said Hui Zhang<\/a>, a physicist who researches China\u2019s nuclear programs at the Kennedy School of Government of Harvard University, who examined Dr. Babiarz\u2019s findings.<\/p>\n The complex includes an oval area about the size of 10 basketball courts.<\/p>\n The precise objective of these upgrades remains a subject of debate. Dr. Zhang said satellite imagery alone offers limited information. \u201cWe don\u2019t know how many warheads have been produced, but we just see the plant expansion,\u201d he said.<\/p>\n Some of the recent changes may simply reflect upgrades for safety, said Dr. Zhang, the author of a new book<\/a>, The Untold Story of China\u2019s Nuclear Weapon Development and Testing. Chinese nuclear engineers may also need more facilities and test areas at Zitong to modify warhead designs for new weapons, such as submarine-launched missiles, he said.<\/p>\n One major concern for Washington is how this larger, more modern arsenal might change China\u2019s behavior in a crisis, particularly over Taiwan.<\/p>\n