On the Influence of Wire-Wrap Spacer in a Four Rod-Bundle cooled with Supercritical Water using CFD

摘要

The High Performance Light Water Reactor (HPLWR) uses supercritical water (SCW) as coolant for the innovative three-pass reactor core. The reference design of the HPLWR includes wire-wrap as a spacer around the fuel rods in the fuel assembly. The thermophysical properties of SCW exhibit strong changes with temperature near the pseudocritical point at a given pressure. Literature reveals that such changes in thermo-physical properties result in special heat transfer behaviour, e.g. Enhanced or deteriorated heat transfer. Empirical correlations are not available for SC conditions and combined with the presence of a wire wrap as spacer. Therefore, CFD is used to predict the heat transfer coefficient and to investigate the effect of the wire wrap on the heat transfer rate. Numerical simulations have already demonstrated the feasibility of the Reynolds Averaged Navier-Stokes (RANS) based Computational Fluid Dynamics (CFD) approach in computing the heat transfer to supercritical fluids, such as SCW. In this paper, the influence of the selected HPLWR wire-wrap spacer on the heat transfer in a four rod-bundle is demonstrated using SCW. The flow in the considered four rodbundle is analyzed using a tested RANS approach at an operating pressure of 25 Mpa with a mass flux of 1332 kg/m2s and a inlet temperature of 310° C. Using hydraulically fully developed flow conditions, the heat transfer rate for the rod-bundle with and without wire-wrap spacer is analysed. The results demonstrate the enhanced cross flow and mixing in case of the bundle with wire wrap. This results in an improvement of the heat transfer rate and a more uniform distribution of the surface temperature of the rods.