assigned to degradation of the various heat rejection radiators due to micrometeoroid damage to heat pipes and the other 2.5% to the balance of the system. Thus, since there would be a large number of heat pipes whose failure would only reduce system power incrementally, there is a 97.5% probability of the system producing a significant percentage of system power after 10 years. We assumed 10% redundancy in the power conditioning subsystem and 20% for the transmission lines. In the case of turboalternators and Stirling conversion systems, we assumed 20% redundancy, which means these systems would use six conversion units operating at reduced power; five units would be able to supply 100% power. Using a large number of conversion units may or may not practical, but the assumption is adequate for mass estimation purposes. 3.23 Component Mass Estimates Our power system mass estimates include the reactor, shield, power conversion, power conditioning, power transmission, heat exchanger, and radiator subsystems plus the structure required to interface with the user satellite, but they do not include the satellite itself. Area estimates include radiators to dump the waste heat from the power conversion and power conditioning subsystems, but do not include a satellite electronics radiator. The mass estimates for the reactors were obtained based on the following considerations. The structural mass associated with the reactor such as cladding and TFE internal structure is explicitly included. In addition a number of miscellaneous structural components such as reflector supports, fittings, springs, etc. are included by multiplying the core volume by a core-average miscellaneous structural density that was obtained by dividing the miscellaneous structural mass for the SP-100 100 kWe reactor core by its volume. Safety system mass estimates are based on the assumption that all reactors will require a redundant reactivity control safety system plus a re-entry aeroshell. The reactor core volumes are arbitrarily increased by 20% to account for the in-core redundant reactivity control system unless they already have enough space for this system. The mass of the redundant reactivity control system is assumed to be directly proportional to the core effective radius; it is estimated for all concepts by multiplying the resultant core radius by a number obtained by dividing the redundant reactivity control system mass for the SP-100 100 kWe design by its core radius. The mass of the re-entry aeroshell is taken from the SP-100 program and scaled to other systems based on reactor geometry. In addition to these two safety system components, all concepts except the OTRs include an auxiliary coolant loop to prevent meltdown in case of a loss of coolant accident. The mass of a rhenium barrier is also included to provide negative reactivity for core flooding accidents in all concepts except the OTRS. The OTRs are excluded because their tungsten emitter could conceivably be replaced with a rhenium emitter that would meet this requirement. The instrumentation and control mass is broken down into three components: 1) fixed items that change very little with power level or reactor size, e.g., controllers and multiplexers; 2) size dependent items that increase appreciably with power level or reactor size, e.g., control and safety drives and actuators; and 3) items dependent on boom length, e.g., I&C cabling. The mass
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