[en] This study assesses the costs and benefits of nuclear power plant life extension (NUPLEX) for the overall US under widely varying economic assumptions and compares these with alternative new coal- fired plants (NEWCOAL). It is found that NUPLEX saves future electricity consumers more than 3 cents/-kwh compared with NEWCOAL. The NUPLEX costs and benefits for existing individual US nuclear power plants under base-line, or most likely, assumptions are assessed to determine the effects of the basic plant design and plant age. While benefits vary widely, virtually all units would have a positive benefit from NUPLEX. The study also presents a cost-benefit analysis of the nuclear industry's planned advanced light water reactor (ALWR). It is concluded that ALWR offers electrical power at a substantially lower cost than NEWCOAL. 9 refs., 6 figs