Consideration of Low Enriched Uranium Space Reactors

摘要

The Federal Government (NASA, DOE) has recently shown interest in low enrichment uranium (LEU) reactors for space power and propulsion through its studies at national laboratories and a contract with private industry. Several non-governmental organizations have strongly encouraged this approach for nuclear non-proliferation and safety reasons. All previous efforts have been with highly enriched uranium (HEU) reactors. This study evaluates and compares the effects of changing from HEU reactors with greater than 90% U-235 to LEU with less than 20% U-235. A simple analytic approach was used, the validity of which has been established by comparison with existing test data for graphite fuel only. This study did not include cermet fuel. Four configurations were analyzed: NERVA NRX, LANL's SNRE, LEU, and generic critical HEU and LEU reactors without a reflector. The nuclear criticality multiplication factor, size, weight and system thermodynamic performance were compared, showing the strong dependence on moderator-to-fuel ratio in the reactor. The conclusions are that LEU reactors can be designed to meet mission requirements of lifetime and operability. It will be larger and heavier by about 4000 lbs than a highly enriched uranium reactor to meet the same requirements. Mission planners should determine the penalty of the added weight on payload. The amount of U-235 in an HEU core is not significantly greater in an LEU design with equal nuclear requirements. The politics of nuclear non-proliferation and safety will determine the final decision.