Two energy conversion technologies were considered in the present study, and size and mass constraints were chosen to make the reactor system suitable for space shuttle launch. During the optimization process, certain essential subsystems and design constraints were found to effect system mass strongly and these are pointed out to clarify technology efforts required in the next design phase. There are three major sections to this paper-one presenting overall design requirements and top level requirements for the design study; the second describing the basic concepts and subsystem design procedures for a space nuclear powerplant; and the third presents the result of the optimization process and discusses the values chosen for the independent variables and design constraints. Overall Design Considerations Top level requirements for this design study are summarized in Table I. In addition, the following requirements were addressed in the design: • guaranteed safety during transport and launch; • guaranteed safety at end of life; • core disintegration in case of inadvertent re-entry; • containment of fission product gases in the system; • assembly completed on the ground; • requires only a single shuttle launch; • not rendered useless by any single point failure. Fission product gases are retained in the core in this design to ensure environmental acceptability regardless of where in space the reactor is used. The system is fully assembled on the ground and launched in a single shuttle flight. A boron plug was centred in the core to ensure the reactor does not accidentally achieve criticality before normal operation begins. At the end of the reactor's life it will be separated from the associated payload and boosted to an orbit with a 300-year life-long enough for radiation to decay to an acceptable level before re-entry. One megawatt design output was selected because Japanese space development in the 21st Century will require hundreds of kilowatts of baseload power for applications such as experimental facilities, manned space stations, and electric propulsion systems. In particular, nuclear-electric propulsion is one of the most promising propulsion technologies for deep space missions where nuclear power is the only realistic energy
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