The problems involved in buildiing a molten-salt thermalbreeder reactor are reviewed, and it is concluded that the most feasible construction is an externally-cooled reactor with the fuel salt passing through the reactcr core in graphite tubes. A reactor with 15% of the core vollume occupied by fuel salt and 5% occupied by fertile salt would have a net breeding ratio of about 1.06. The specific power is about 3.0 Mw(th) per kg of U/sup 233/, U/sup 235/, and Pa in the entire reactor and chemical processing system, The resulting doubling time is 13 fuil-power years. The cost of the fuel cycle for a 1000-Mw(e) station with this breeding performance is estimated to be 1.2 mills/kwhr, The performance in terms of material utilization is an output of 1,18 Mw(e) per kg of U/sup 233/, U/ sup 235/, and Pa, and 3.2 Mw(e) per metric ton of Th. The latter figure could be increased by a factor of two at a sacrifice of 0.01 in breeding ratio, (auth)