As global tensions rise among nuclear powers, observers are concerned about the prospect of renewed nuclear weapons testing and a new arms race (Economist, AP, Politico, Arms Control Association). For the purposes of this question, a "nuclear device" is one that is designed to produce a nuclear explosion utilizing the fission and/or fusion of nuclear fuel (e.g., Uranium-235, lithium deuteride). A radiological device (aka "dirty bomb") would not count (Nuclear Regulatory Commission). Whether China, Russia, and/or the US has detonated a nuclear device in their respective territories will be determined using credible open source reporting. A detonation by China, Russia, or the US must occur within that country's internationally recognized boundaries (including territorial waters and airspace) to count.
Part of the Economist: The World Ahead 2024 superforecaster prediction series.