Optimization of an Integrated Neutronic/Thermal-Hydraulic Reactor Core Analysis Model

Within the context of an operating nuclear reactor core, multi-physics calculations that account for the bonded nature of the neutronic and thermal-hydraulic phenomena are of major importance in reactor safety and design. In this work, the ongoing development of a tool for neutronic/thermal-hydraulic coupled calculations is presented. OpenMC, a Monte-Carlo 3D neutronic code and COBRA-EN, a thermal-hydraulic code for sub-channel and core analysis, are integrated in a single tool for coupled calculations. This new coupled system (OpenMC/COBRA) is capable of performing coupled Neutronic/Thermal-Hydraulic analysis in both sub-channel and core level. As regards the main key parameters related to the coupled problems, these mainly include the handling of the involved feedbacks between the two physical processes, the accuracy of the Monte-Carlo calculation and the convergence behavior of such an iterative scheme. Another issue which should be considered carefully is the optimal, in terms of computational time, use of the neutronic Monte-Carlo code, since the main disadvantage of such codes is the high computational cost. This work investigates the role of these parameters in the coupled neutronic/thermal-hydraulic calculations performed by OpenMC/COBRA while it examines the direction towards which their optimization should move in order to achieve accurate results with reasonable computational cost. The results show that satisfying accuracy can be obtained in reasonable computational time when Monte-Carlo multi-processing is combined with proper selection of the Monte-Carlo parameters, as well as of the parameters concerning the coupled iterative scheme.