Material Requirements, Selection And Development for the Proposed JIMO SpacePower System

NASA is proposing a major new nuclear Space initiative—The Jupiter Icy Moons Orbiter (JIMO). A mission such as this inevitably requires a significant power source both for propulsion and for on‐board power. Three reactor concepts, liquid metal cooled, heat pipe cooled and gas cooled are being considered together with three power conversion systems Brayton (cycle), Thermoelectric and Stirling cycles, and possibly Photo voltaics for future systems. Regardless of the reactor system selected it is almost certain that high temperature (materials), refractory alloys, will be required. This paper revisits the material selection options, reviewing the rationale behind the SP‐100 selection of Nb‐1Zr as the major cladding and structural material and considers the alternatives and developments needed for the longer duty cycle of the JIMO power supply. A side glance is also taken at the basis behind the selection of Uranium nitride fuel over UO2 or UC and a brief discussion of the reason for the selection of Lithium as the liquid metal coolant for SP‐100 over other liquid metals.