The 200 kWe uranium-nitride fueled lithium cooled fast reactor concept RAPID-L to be combined with thermoelectric power conversion system for lunar base power system is demonstrated. The reactor vessel is 2 m in diameter and 6.5 m in depth with lithium inlet and outlet temperatures of 1030 and 1100 degree C, respectively. It is one of the variants of RAPID (Refueling by All Pins Integrated Design) fast reactor concept, which enable quick and simplified refueling. In this small size reactor core, 2700 fuel pins are integrated altogether and encased in a fuel cartridge. Refueling is conducted by replacing the fuel cartridge. The reactor can be operated without refueling for up to 10 years. Unique challenges in reactivity control systems design have been attempted in RAPID-L concept. The reactor has no control rod, but involves the following innovative reactivity control systems: Lithium Expansion Modules (LEM) for inherent reactivity feedback, Lithium Injection Modules (LIM) for inherent ultimate shutdown, and Lithium Release Modules (LRM) for automated reactor startup. All these systems adopt lithium-6 as a liquid poison instead of conventional B4C rods or Be reflectors. These systems are effective independent of the magnitude and direction of the gravity force. In combination with LEMs, LIMs and LRMs, RAPID-L can be operated without operator. Reactor startup can be done automatically if the primary coolant temperature reaches its standby temperature. Heatup of the coolant can be made by heat release from the primary pumps. Then the freeze seal of LRM will be melt, and positive reactivity will be added very slowly. It will take 7 h to complete startup. Burnup compensation is achieved automatically by LEMs. RAPID-L is equipped with the thermoelectric energy conversion system. In spite of inferior conversion efficiency, TE system was adopted because of reliability, long-life performance, and survivability. In this paper, RAPID-L reactor concept, plant configuration and its transient characteristics are presented.
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