2.3 The SP-100 With Thermoelectric Power Conversion The SP-100 thermoelectric power system (Ref. 7) shown in Figure 2.7 converts heat generated within a compact high-temperature fast-spectrum reactor directly into electricity through the use of thermoelectric conversion. The net efficiency for this system is about 4%. Although this is quite low, the system mass in the 100 kWe range is moderate, and no moving components are required for power conversion or fluid flow. For the reference 100 kWe design being pursued in the on-going SP-100 thermoelectric program, the reactor core is about 35 cm in length and diameter and consists of bundles of 0.77 cm diameter fuel pins contained in a niobium alloy pressure vessel (see Figure 2.8). The fuel pins are made up of uranium nitride fuel pellets within a rhenium-lined niobium alloy cladding. Beryllium oxide reflector segments surround the core circumference and are external to the pressure vessel. The reflector elements are hinged at one end and their radial position is adjusted at the opposite end of the reflector to control reactivity by regulating neutron leakage out of the core. In-core safety rods are also provided to maintain the reactor in the shutdown condition during potential accident scenarios. A reentry heat shield surrounds the reactor to prevent core disruption during an accidental reentry. The payload and power system electronics are protected from reactor gamma and neutron radiation by a shadow shield at the aft end of the reactor. The shield consists of layers of beryllium, tungsten, and lithium hydride. Additional attenuation of the dose to the payload is achieved by separating the payload from the reactor by a boom.
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