Development of computer program for detailed thermal-hydraulic analysis in a fast reactor fuel subassembly (2); Incorporation of turbulence models

Ohshima, Hiroyuki; Ohshima, Hiroyuki; Imai, Yasutomo*

As a thermal-hydraulic evaluation tool for fast reactor fuel subassemblies with high burn-up ratio, a numerical analysis system in which a subchannel analysis program and a detailed thermal hydraulic analysis program are utilized interractively is under development. This system enables us not only to clarify thermal hydraulic characteristics that cannot be revealed by experiments due to measurement difficulty but also to contribute to the rational safety design and assessment. This report describes the incorporation of turbulence models to the detailed thermal hydraulic analysis program SPIRAL-II and its verification study. In addition to the standard k- two-equation model, Renormalization Group(RNG) k- model and Algebraic Stress Model(ASM) were incorporated to SPIRAL-II as turbulence models. The former utilizes fewer empirical constants than the standard k- model and is believed to be more accurate especially in low Reynolds number regions. The latter treats Reynolds stresses directly and therefore has applicability to anisotropic turbulent flow. It is common for three models that similar transport equations for turbulent kinetic energy k and dissipation rate are discretized and solved by galerkin method. With respect to ASM, Daly-Harlow model is applied to the diffusion terms of the transport equations and algebraic expressions related to Reynolds stresses are solved by Newton-Raphson method using calculated k and . A wall function (Reichardt function) is applied to each model as the boundary condition treatment. A verification study of improved SPIRAL-II was carried out using three kinds of problems: turbulent flow between parallel walls, backstep facing turbulent and turbulent flow in a square duct. From these calculation results, the validity of the improved program was confirmed and prediction characteristics of each turbulent model were clarified.