Development of Thermal-Hydraulic Code Coupled With Heat Conduction in Structure for Thermal Striping Phenomena: Development of Calculation Module for Temperature Distribution in Structure

Thermal striping is one of the most important issues in terms of safety of Fast Breeder Reactors (FBRs). Thermal striping occurs where high temperature fluid mixes with low temperature one and it might cause structural damage. An analysis program (“MUGTHES”) for fluid-structure thermal interaction has been developed to evaluate the thermal striping phenomena and to establish the evaluation method. MUGTHES consists of two calculation modules for thermal-hydraulic analysis and for heat conduction analysis in structure and a conjugated heat transfer model that connects both modules. Thus, thermal-hydraulic field and temperature field in structure can be calculated simultaneously. Boundary Fitted Coordinate (BFC) system is employed to treat complex geometries in FBR plants. Governing equations in BFC system are discretized using the finite-volume approach to keep these conservation conditions in computation. In this paper, detailed description of the evaluation method of spatial differential terms in the equations was described. Numerical simulations were performed using fundamental problems related to one dimensional transient heat conduction in a cube and to radial transient heat conduction in a cylinder, in order to verify the discretization method in BFC system and the calculation method for thermal interaction between two calculation regions. In addition, numerical simulation of T-junction piping system was carried out to investigate characteristics of temperature fluctuation and to confirm the applicability of the program to a practical problem.