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The 200 kWe, uranium nitride fuelled, lithium-cooled, fast reactor concept "RAPID-L" for a lunar base power system, and the 1000 kWe, U -Pu -Zr metal fuelled, sodium-cooled, fast reactor concept "RAPID" for a terrestrial power system have been demonstrated. These reactors are characterized by the RAPID (Refuelling by All Pins Integrated Design) refuelling concept, which enables quick and simplified refuelling. The essential feature of the RAPID concept is that the reactor core consists of an integrated fuel assembly (IFA) instead of conventional fuel subassemblies. In this small-size reactor core, all the fuel pins are integrated altogether and encased in a fuel cartridge. Refuelling is conducted by replacing an IFA. The reactor can be operated without refuelling for up to 10 years. Unique challenges in reactivity control system design have been addressed in these reactors. They have no control rod, but involve the following innovative reactivity control systems: lithium expansion modules (LEMs) for inherent reactivity feedback, lithium injection modules (LIMs) for inherent ultimate shutdown and lithium release modules (LRMs) for automated reactor start-up. All these systems adopt lithium-6 as a liquid poison instead of B4C rods. In combination with LEMs, LIMs and LRMs, RAPID-L and RAPID can be operated without an operator. Another characteristic of RAPID-L and RAPID is a thermoelectric (TE) power conversion system instead of the conventional steam turbine generator. In this paper, design characteristics of RAPID-L and RAPID power system concepts are discussed.

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A conceptual design of the thermoelectric power conversion system combined with open rack type LNG (liquefied natural gas) vaporizer to make use of cold heat of LNG is presented. The system performance analysis has been made based on the thermoelectric module performance data obtained at the cryogenic thermoelectric (CTE) test rig which could realize temperature and fluid dynamic condition of the open rack type LNG vaporizer. Conventional bismuth-telluride thermoelectric modules were tested, however, each module is encapsulated in the stainless steel container to achieve water proof. Electricity production cost evaluation of the system is also discussed.