The design, performance, and cost information on the nuclear portion of the Mixed Spectrum Superheater power plant are emphasized. The research and development programs required to ensure plant feasibility are also presented. The nuclear steam supply system, reactor auxiliary systems, radiation control systems, control and instrumentation, special test instrumentation, plant operation and maintenance, steam cycle, turbine plant, general service systems, preliminary safeguards considerations, expansion of plant power output to 150 Mw(e), and MSSR critical experiment are described. (M.C.G.)

A test to obtain data for use in determining the reactivlty wohh of Na in the Hallam reactor core is described. The test is designed to obtain information on the dry temperature coefficient of reactivity and to train operators. An evaluation of results is included. (J.R.D.)