Evaluation of Relap5 Reactor Core Modeling Capability

of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science EVALUATION OF RELAP5 REACTOR CORE MODELING CAPABILITY By Vincent J.-P. Roux August 2001 Chairman: Professor Samim Anghaie Major Department: Nuclear and Radiological Engineering RELAP5 is a one-dimensional reactor-system simulation code with additional cross-flow calculation capability to include two- and three-dimensional effects in light water nuclear reactor cores. The code is used to model the core, steam generator, and the balance of the Surry reactor, which is a three-loop Westinghouse Pressurized Water Reactor (PWR) system. A detailed RELAP5 model including full nodalization of the system is developed and implemented for this study. The RELAP5 Surry core model uses one or several parallel channels to compare and assess the performance of the cross-flow model. Several inlet flow rates and core power distributions are considered and modeled. Results of the analysis showed the significant contribution of cross-flow in overall temperature and flow distributions in the core. Results of the study also showed that the RELAP5 predictions of cross-flow, at least for single-phase cases, are not consistent with the theory. xi To evaluate the accuracy of RELAP5 cross-flow model, an industry standard Computational Fluid Dynamics code, FLUENT, is used to perform two- and threedimensional calculations. Initial and boundary conditions for the RELAP5 model are used to develop a high-resolution FLUENT model for a pair of parallel reactor core channels. Two models were developed for FLUENT calculation of cross-flow. The first model is a simple tube with axisymmetric non-uniform inlet flow velocities. The second model included differen..