Russia, the United States and China have all built new facilities and dug new tunnels at their nuclear test sites in recent years, satellite images obtained exclusively by CNN show, at a time when tensions between the three major nuclear powers have risen to their highest in decades.
While there is no evidence to suggest that Russia, the US or China is preparing for an imminent nuclear test, the images, obtained and provided by a prominent analyst in military nonproliferation studies, illustrate recent expansions at three nuclear test sites compared with just a few years ago.
https://www.cnn.com/2023/09/22/asia/nuclear-testing-china-russia-us-exclusive-intl-hnk-ml/index.html: Satellite images show increased activity at nuclear test sites in Russia, China and US