Neutronics Research on Annular Axial-Non-Uniform Minor Actinides Transmutation Targets in Commercial Pressurized Water Reactor

Abstract This paper introduces the thermal-fast neutron conversion material 6LiD to improve the transmutation efficiency of MAs in commercial PWR, especially the fission rate, and investigate the feasibility of using annular axial-non-uniformly transmutation targets to flatten the axial power distribution of the core and optimize the temperature reactivity effect of the moderator at high boron concentration. In this research work, four annular axial-non-uniform transmutation targets are designed and they have the same geometry structure, but axially have different MA concentration in the transmutation material which composed of MA, 6LiD and UO2. The annular transmutation targets are axially three, five and seven segments respectively, and MA concentration in the transmutation material gradually decreases from the middle to both ends. The transmutation performance of these targets is investigated while its parameters change, such as the thickness of the annular transmutation rod and the composition of the transmutation material. The results show that, compared with axially uniform rods, the annular axial non-uniform transmutation targets have high transmutation efficiency, especially the fission rate. The transmutation effect is the best while the mass ratio of 6LiD to MAs in the transmutation material is 1:9; MA fission rate of these transmutation targets can reach up to 5.05%. At the same time, these targets have good power flattening effect, especially axial power flatten results that they could reduce the axial power peak factor of the core from 1.778 to 1.388. Meanwhile, they can also optimize the temperature effect of the moderator well at high boron concentrations.