A significant numbr of older U.S. nuclear power plants are approaching the end of their useful lives and must be decommissioned , a process with profound environmental consequences, because the innards of reactors become radioactive during decades of operation. The central questions in decommissioning involve how clean the sites are going to be and how to dispose of the radioactive waste. Tens of billion of dollars are at stake, because current standards apply to some 70 nuclear power plant and waste disposal sites in America.