Two of Russia’s nuclear radiation monitoring stations went silent two days after a mysterious explosion that led to a radiation spike in northern Russia earlier this month. Russian officials say at least five nuclear engineers were killed during a rocket test involving “isotope power sources” on a platform in the White Sea, leading to outside speculation that the accident involved a nuclear-powered cruise missile. Four international stations designed to monitor nuclear activity had detected “an event coinciding with the [Aug. 8] explosion in Nyonoksa, Russia,” the world’s main nuclear test-ban body said on Aug. 10. The Dubna and Kirov stations...