Boyan D. Ivanov

Simulation of the flow rotation and mixing in the downcomer of a VVER-1000 reactor

Flow rotation and mixing in a VVER-1000 reactor is investigated using two system codes with three-dimensional fluid-dynamics modeling capabilities (RELAP5-3D and TRACE) and a computational fluid-dynamics (CFD) code (FLUENT). Coarse-mesh models were developed for the system codes, and their applicability is evaluated using the test data as well as the detailed CFD results obtained. Two different temperature zone mapping schemes for comparison with the measured data are proposed and discussed. The test is very informative when used to examine the real loop mixing taking place at a nuclear reactor. The results can be used to improve code input data for correct simulation of the phenomenon. Correctly predicting the flow mixing is very important in regard to the prediction of the local three-dimensional feedback effects depending on the vessel mixing in coupled three-dimensional neutron-kinetic/thermal-hydraulic safety analysis of reactivity insertion accidents such as the main steam line break accident.

Development of a Three-Dimensional Pseudo Pin-by-Pin Calculation Methodology in ANC

Advanced cores and fuel assembly designs have been developed to improve operational flexibility and economic performance and to further enhance safety features of nuclear power plants. The simulation of these new designs, along with strong heterogeneous fuel loading, have brought new challenges to the reactor physics methodologies currently employed in the industrial codes for core analyses. Control rod insertion during normal operation is one operational feature in the AP1000® plant of Westinghouse next-generation pressurized water reactor design. This design improves its operational flexibility and efficiency but significantly challenges the conventional reactor physics methods, especially in pin power calculations. The mixture loading of fuel assemblies with significant neutron spectra causes a strong interaction between different fuel assembly types that is not fully captured with the current core design codes. To overcome the weaknesses of the conventional methods, Westinghouse has developed a state-of-the-art three-dimensional (3-D) pin-by-pin calculation methodology (P3C) and successfully implemented it in the Westinghouse core design code ANC. The new methodology has been qualified and licensed for pin power prediction. The 3-D P3C methodology along with its application and validation are discussed in the paper.