China might be secretly conducting nuclear tests with very low explosive power despite Beijing’s assertions that it is strictly adhering to an international accord banning all nuclear tests, according to a new arms-control report to be made public by the State Department. US concerns about Beijing’s possible breaches of a “zero yield” standard for test blasts have been prompted by activities at China’s Lop Nur nuclear test site throughout 2019, the State Department report said. Zero yield refers to a nuclear test in which there is no explosive chain reaction of the type ignited by the detonation of a nuclear warhead. “China’s possible preparation to operate its Lop Nur test site year-round, its use of explosive containment chambers, extensive excavation activities at Lop Nur and a lack of transparency on its nuclear testing activities … raise concerns regarding its adherence to the zero yield standard,” the report said, without providing evidence of a low-yield test. Beijing’s lack of transparency included blocking data transmissions from sensors linked to a monitoring centre operated by the international agency that verifies compliance with a treaty banning nuclear test explosions. Notably, the 1996 Comprehensive Test Ban Treaty (CTBT) allows activities designed to ensure the safety of nuclear weapons.