Alight water-cooled nuclear power plant rated at 1000 mw(el) would require approximately 3100 mw of thermal input from the fuel. estimate the mass of fuel that has fissioned during a year of operation at 80 percent plant capacity factor. the plant capacity factor is the ratio of energy gen- erated in a given period to the amount that could be produced if the plant operated continuously. note that the mass fissioned is not the loss in mass as a result of fission since each atom fissioned forms fission product nuclides.