The successful testing of the new cores in the `` Operation Sandstone '' tests rendered Causation every component of the old weapons obsolete .

Even before the third test had been carried out Action , production of the old cores was halted Process_end , and all effort concentrated Aiming on the new Mark 4 nuclear bomb , which would become Becoming the first mass-produced nuclear weapon .

Critically , they were powering Supply the pumps that circulated coolant through the reactors ' cores to remove Removing decay heat , which continues after fission has ceased Process_end .