First studies on the Optimized Propulsion Unit System OPUSwithin the current Nuclear Space Program in CEA

摘要

Deep space missions, both for scientific and human exploration, take benefits of using a safernin-space nuclear reactor for providing both sufficient electric energy and efficient performance for arnspace propulsion. At CEA, space nuclear fission reactors have been studied in the past with the ERATOrnproject in the 80's (design of a Nuclear Electric Propulsion system of 20 to 200 kWe) and with the MAPSrnproject in the 90's (definition of a Nuclear Thermal Propulsion system of 300 MWth for 72kN of thrust).rnAccording to the recent roadmaps, CEA decided to maintain a waking state in its space nuclear activitiesrnby carrying out some conceptual design studies of NEP systems in the range of 100-500 kWe.rnThe paper presents first the basic options of the nuclear system that have been selected and the reasonsrnassociated to those choices. This nuclear power system relies on a fast gas-cooled reactor conceptrncoupled to a Brayton cycle as energy conversion system. Indeed, such a system has been identified, asrnbeing able to achieved acceptable mass to power ratio at relatively low power level (100 kWe) andrnallowing to envisage more powerful system according to the maturity of the available technologies. Thernadaptations and the possible evolutions of this concept towards a higher power level will be approachedrnstepwise by developing high temperature fuels, materials and gas technologies.rnIn a second part, the paper describes the main characteristics of an Optimized Propulsion Unit Systemrn(OPUS) and its different components: the shield units for the protection against the radiation, the designrnof the conversion system based on a small dynamic Brayton cycle, the radiator for the heat rejection.rnBased on relatively short-term technologies, the reactor is designed to provide 100 kWe. The globalrnneutronic effects are detailed (reactivity, coefficients calculation, control worths, accident scenarios atrnlaunch…). The solution is a gas-cooled reactor with 93% U235 enriched fuel aiming at minimizing thernmass of the reactor and assuring a core lifetime of 7 to 10 years.rnFinally, the integration of the major components of OPUS leads to a space power system of 100 kWe (400rnkWth) for 2400 kg, suitable to power a set of ion engine based electric thrusters. The specific mass (aboutrn24 kg/kWe) is expected to decrease significantly while increasing the unit power to 500 kWe. At the samerntime, both fuel and core materials come closer to the maximum allowable neutron fluence, thusrnsuggesting that this higher power level is best suited to the range of technologies selected in OPUS.