Molten-salt reactor technology, urdar development since 1947, has led to a concept of a high-temperature, thermal-nei-tron breeder reactor that operates on the thorium-^*" ? U fuel cycle. A connected processing plant that continuously removes protactinium and fission products from the fuel salt is a basic feature of the system. The success of the Jfclten-Salt Reactor Experiment that was operated befve.'.n 1965 and 1969, the development of a nev processing method that allowed simplification of

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... e breeder desiga, and the potential breed ing performance, economics, and safety of the concept, are cited in this report as arguments for the continued development of MSBR's. The report reviews the status of the technology, identifies further development needs for an MSBR, and gives the program staff's assess ments of the uncertainties and the likelihood of success. Separate chapters are devoted to reactor physics, chemistry, graphite, reactor metals, reactor components and systems, cells and building, control and instrumentation, fuel processing, maintenance, design studies, and environmental effects and safety.