The U.S. Supreme Court’s ruling June 17 that state regulators acted properly in restricting uranium mining shuts the door on Virginia Uranium Inc.'s proposed underground mine. Had it moved ahead, the underground dig would have required action to manage distinct worker risks like radon exposure.

The mine operator pushed for years to open a new underground mine in Pittsylvania County, Va., in the south-central part of the state, to unlock an estimated 119 million pounds of the mineral. The company...