redundancy may be the only way to meet the overall reliability and confidence requirement. Non-redundant subsystems or components with greater than 98% reliability and confidence requirements will need hundreds or even thousands of deviceyears of testing to verify their claims. Two types of thermionic reactors can possibly be designed without mission-ending single point failure mode, thereby easing the stringent testing required to achieve reliability and confidence goals. One is the Thermionic Romashka type in which thermionic converters are mounted outside a solid carbide reactor core [1]. This type is probably the easiest to ‘debug' for mission-ending single point failure modes. The chief concern is the reactor control system, which will consist of reflector absorber rods or drums and possibly in-core shutdown rods. The reactor must be permitted to function in the case of a single stuck rod or drum (see Fig. 1).
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