the atmosphere, only a relatively small quantity of fission products will be produced. 4.9.2.1 Example Program Concept (Molten Salt Breeder Reactor—MSBR) In operation, a MSBR breeds U(233) from thorium. In a reactor module designed primarily for power production the fuel doubling time would be approximately six years. By placing design emphasis on breeding, this time could be reduced. Bred fuels are available for later SPS's. The basic fertile fuel which is carried up is thorium. All SPS's produce radioactive wastes. These could be accumulated at the SPS's, or accelerated to a remote location by a rocket disposal system. Geosynchronous orbital velocity and altitude provides an advantageous starting condition for such a system. The breeder reactor program concept is shown in Figure 4-37. Fig. 4-37. Breeder Reactor Program Concept Table 4-26. Emphasized Reactor Types 4.9.3 Reactor Selection In addition to being a breeder, the SPS reactor should have these characteristics: 1) Compatible with energy converter system. 2) Fuel reprocessing should be capable of being accomplished nearly automatically. 3) Core temperature should be approximately that achievable in the solar systems (at least 1500K (2240°F)). 4) 30-year useful life (with refueling as required). 5) Developable by 1991. Approximately 15 reactors were investigated. Those having the greatest likelihood of achieving the above characteristics are given in Table 4-26. Note that only the RPBR has the promise of achieving very high temperatures in combination with automatic fuel processing. The other reactor types have material compatibility problems. The problem here is that while it may be possible to buffer the walls of a reactor by an inert gas, or otherwise cool them, the hot reactor material must come in contact with components of the heat exchanger which interfaces the reactor to the power cycle (Brayton, Rankine, etc.). This is true for all known potential systems with the possible exception of magnetohydrodynamic (MHD) power generation where buffering of the MHD duct may be possible, or the rotating particle bed reactor (RPBR). Buffered nuclear MHD power generation is considered to be very advanced technology within limited possiblity of achievement by 1991, however the RPBR may be achievable in the required time period. Reactor types investigated as
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