Much of the current congressional debate about the Clinch River Breeder Reactor (CRBR) centers around the estimated cost of designing, constructing, and operating it for a 5-year demonstration period. The Department of Energy (DOE) recently linked the revenue-generating potential of the CRBR beyond the demonstration period to the justification for continued funding. GAO presents information that points out many uncertainties in DOE's estimates of revenue and cost. GAO believes that because these estimates are based on numerous assumptions and calculations concerning events as far as 37 years in the future, they should be viewed with caution. Changes in the underlying assumptions could produce wide variance in the cost estimates. Further, GAO points out that CRBR is a research and development project and that judging its merits solely on cost and revenue estimates projected far into the future may not be appropriate.