FEASIBILITY STUDY ON THE APPLICATION OF THE HIGHER-ORDER NUMERICAL METHOD IN THERMAL-HYDRAULIC ANALYSIS CODE

Abstract

The existing nuclear system analysis codes which is best-estimated code such as RELAP5, TRAC, MARS and SPACE use the first-order numerical scheme in both space and time discretization. However, the first-order scheme is highly diffusive and less accurate due to the first order of truncation error. Therefore, the nuclear system analysis code needs high predictive ability. For more predictive performance and safety of nuclear reactor systems, more accurate nuclear reactor system analysis code is needed in KOREA. Thus, this study evaluated the application of the higher-order numerical scheme for the next generation nuclear system analysis code.In this study, to identify effect of numerical diffusion and dispersion problem and the decreasing error depending on the increasing mesh number, single phase pipe flow simulation with a step profile of temperature (test 01) was conducted by MARS and a separate single phase transient analysis code which is possible to calculate in the first-order and the higher-order scheme but mimics MARS solver was built in MATLAB environment. In addition, to evaluate effect of input perturbation in the first-order and second-order schemes, simplified primary loop of nuclear reactor system simulation (test 02) was performed by MARS and NTS codes.Through this study, the numerical diffusion and dispersion problem is observed in single phase transient analysis code. In addition, it is identified that the numerical diffusion and dispersion problem result in numerical instabilities and non-physical solutions. Therefore, to stabilize the numerical solutions of the higher-order scheme and to evaluate more precise solutions, a slope limiter should be applied or more stable higher-order scheme should be implemented. And then, it should be identified whether more stable and accurate solutions can be obtained in two phase condition.