Multi-layer fuel assembly design proposal for supercritical water cooled reactor

Abstract

In the current SCWR fuel assembly design, there exist some challenges for thermal hydraulic and neutron-physical behavior. For the thermal SCWR design, it is of great importance to reduce the hot channel factor and the maximum cladding temperature as far as possible. The challenging task in the fast spectrum SCWR design is to achieve sufficiently large negative void reactivity coefficient and increase the conversion ratio. To satisfy the requirements and to solve challenges mentioned above, two structures of multi-layer fuel assembly for both thermal and fast SCWR core are proposed in this paper. For the thermal core fuel assembly, the main idea is to axially divide the active zone into several sub-layers, between which inactive layers are introduced, where fluid from the previous active layer mixes well with each other and enters the next active layer with a well homogenous distribution of fluid temperature. For the fast core fuel assembly, the main idea is to introduce the axial blanket (depleted UO2) regions between the divided MOX seed regions, to achieve a higher conversion ratio, lower temperature reactivity coefficient.Both thermal hydraulic and neutron-physical performance of the proposed multi-layer fuel assembly are investigated by a subchannel code coupled with 3-D neutronics analysis. The results obtained so far have shown that the multi-layer concept is feasible and promising.