Comparisons of friction models implemented in US trace and Korean MARS-KS system TH codes

Abstract

System thermal hydraulic analysis codes such as TRACE in the US or MARS-KS in Korea are often used for nuclear power plant simulation to evaluate the safety in each country by the regulating body. In a system thermal hydraulic analysis code, the fluid field equations are used to model two phase flow. System codes typically solve mass, momentum and energy equations for multiple phases. To solve field equations, constitutive relations are needed and these correlations are often dependent on the flow regime map. The major physical models and correlation packages in the codes are the wall heat transfer, wall and interfacial friction, interfacial heat and mass transfer. TRACE and MARS-KS are very different in the implemented thermal hydraulics model and correlation even though the field equations are almost identical. Thus, it is expected that differences in the code calculations can be observed due to this difference. To compare different physical models and correlation packages of each code, each correlation package is extracted in a separate computational environment. The objective of this study is to develop a platform for comparing wall friction models of each system analysis code. The developed platform is based on MATLAB and REFPROP, and it was proven to reproduce the values of TRACE 5.0 patch5 and MARS-KS 1.5 successfully. TRACE and MARS-KS use a very different approach to evaluate friction on the wall. TRACE is based on drag coefficient model, but MARS-KS is based on Lockhart-Martinelli two-phase multiplier factor. Despite they have dissimilar wall friction models, amounts of the wall friction show almost good agreement between two codes. The regime with the greatest difference is slug and transition flow regimes related with void fraction, but this difference is not significant.