Development of computer program for detailed thermal-Hydraulic analysis in a fast reactor fuel subassembly (1)

Ohshima, Hiroyuki; Imai, Yasutomo*

As a thermal-hydraulic evaluation tool for high performance fast reactor fuel subassemblies, with high burn-up fuel, a numerical analysis system in which a subchannel analysis program and a detailed thermal hydraulic analysis program are utilized interactively is under development, This system enables us to clarify thermal hydraulic characteristics that cannot be revealed by experiments due to the measurement difficulty and to contribute to rational safety design and assessment. This report describes the first step of development and verification study of the detailed thermal hydraulic analysis program SPIRAL-II. SPIRAL-II adopts the finite element method from thc viewpoint of the advantage to treat precisely complicated geometry. Conservation equations of mass and momentum were discretized by Bubnov-Galerkin method. At the same time, one can choosc streamline upwind Petrov-Galerkin method or a balancing tensor diffusivity method for calculation stabilization. Semi-implicit solution scheme (fractional step method) developed by Ramaswamy is used for time integration. As the pressure equation matrix solver, ICCG or Gaussian elimination is applied. With respect to the turbulence model, k- two equation model was implemented. As to the type of calculation element, 1st/2nd order hexahedron element and 1st order pentahedron clement are available. A verification study of SPIRAL-II was carried out using the following problems: (1)2-dimensional flow in duct (laminar and turbulent flow), (2)Cavity flow, and (3)Backstep facing flow (laminar and turbulent flow) The predicted velocity profiles in the case (1)agreed with theoretical ones in both laminar and turbulent flow. In the cases of (2) and (3), it was confirmed that the SPIRAL-II has the prediction accuracy that is almost equivalent to the higher-order finite difference method.