[en] A microcomputer program called the Replacement Energy Cost Analysis Package (RECAP) has been developed to assist the US Nuclear Regulatory Commission (NRC) in determining the replacement energy costs associated with short-term shutdowns or deratings of one or more nuclear reactors. The calculations are based on the seasonal, unit-specific cost estimates for 1988-1991 that were previously published in NRC Report NUREG/CR-4012, Vol. 2 (1986), for all 117 US reactors, with updates that were made in July 1988. The program is menu-driven, allowing the user to define specific case studies in terms of such parameters as the units to be included, the length and timing of the shutdown or derating period, the unit capacity factors, and the reference year for reporting cost results. In addition to simultaneous shutdown cases, more-complicated situations, such as overlapping shutdown periods or shutdowns that occur in different years, can be examined through use of a present-worth calculation option