Scenario description
Assume the United States begins or funds an expanded operational effort to detect decoupled or very-low-yield nuclear explosions tied to China nuclear-risk concerns, without an earlier or simultaneous effective bilateral transparency mechanism. The initiating action is beyond the single reported National Nuclear Security Administration underground experiment at the Nevada National Security Site using chemical high explosives and radiotracers in Area 12's P Tunnel. Qualifying actions include a new funded program, additional underground or sensor-testing campaigns, deployment or procurement of detection systems, new interagency tasking, or contracts to refine detection algorithms and monitoring models. The geography includes U.S. test infrastructure and any disclosed monitoring-network or contractor sites; exact budgets, award sizes, sensor counts, test yields, and deployment schedules remain unspecified unless publicly reported by the cutoff.