Snap 8 reactor and shield designs and operating experience

The SNAP 8 reactor is a heat source suitable for long-endurance 10to 50-kw space electric power supplies. Two tests have demonstrated its feasibility: the SNAP 8 Experimental Reactor (S8ER) and the SNAP 8 Developmental Reactor Mockup (S8DRM-1). The S8ER demonstrated stable long-term operation of the reactor core and reflector. During 500 days of nuclear operation, it operated one year in the power range 400 to 600 kwt with a 1300°F coolant outlet temperature and continuously for over 5000 hr. Post-test examination revealed cracks in ~80% of the cladding tubes, the cause of which is being investigated. Automatic control system performance and structural capabilities of the reactor design were verified in nonnuclear testing of the S8DRM-1. The reactor and shield design is summarized for manned and unmanned space applications. Curves are provided, allowing spacecraft designers to estimate shield weight for both applications rapidly as a function of pay load diameter, payload separation distance, dose rate for manned applications, and total dose for unmanned applications. The design approach to high reliability is described.