Mass optimization of the radiation shadow shield for space nuclear power system

Abstract

The mass of a space nuclear power system is a critical parameter due to limitation and high cost of transportation. In such systems, a considerable part of the mass is contributed by the radiation shadow shield. Therefore, it is necessary to study the shielding optimization for minimizing the mass of space nuclear power system. In this work, the optimization of shielding design for unmanned lithium cooled space reactor from the aspect of the selection, composition optimization and layout configuration of materials/composite materials has been carried out using the Super Multi-functional Calculation Program for Nuclear Design and Safety Evaluation (SuperMC). Firstly, the shielding performance of the traditional shielding materials for space reactor has been evaluated and was found that interaction of the tungsten (W), a gamma shielding material, with neutrons is a source of high energy secondary gamma due to neutron capture and inelastic scatter reactions. As secondary gamma seriously affects the mass of shield, so new developed potential composite material W–B4C was adopted for gamma shielding to reduce the generation of secondary gamma. The choice of W–B4C (10B enriched) as gamma shield lowered the gradient of curve for required mass versus distance from reactor face, shifted the place of gamma shield toward the reactor and reduced the mass of gamma shield by 7.4% as compared to traditional gamma shield W. Finally, a comprehensive optimization with the new composite material has been performed from the aspect of cutting the unnecessary shield through the observation of gamma dose/neutron flux on dose plane and reduced the mass of shield by 20.4% as compared to the initial shielding design.