Development and test of a transient fine-mesh LWR Multiphysics solver in a CFD Framework

Paper in proceeding, 2015

We present a framework for fine-mesh, transient simulations of coupled neutronics and thermal- hydraulics for Light Water Reactor (LWR) fuel assemblies. The framework includes models of single- phase fluid transport for the coolant and conjugate-heat transfer between the coolant and the fuel pins, complemented by a neutronic solver. The thermal-hydraulic models are based on a CFD approach, resolving the pressure and velocity coupling via an iterative algorithm. Similarly, the neutronics is for- mulated in a fine-mesh manner with resolved fuel pins. The neutronic and thermal-hydraulic equations are discretized and solved in the same numerical framework (foam-extend-3.1). A test case of a quarter of a fuel pin is used to test the transient behavior of the code for a set of different initial reactivities. The same geometry is used to simulate a decrease of the inlet temperature, which demonstrates the response both in the CFD and the neutronics for an increase in reactivity. Furthermore, a system of 7x7 fuel pins is simulated with the same inlet temperature decrease and we present the temporal development of the temperature as well as an analysis of the heterogeneities captured by the fine-mesh approach. The solver is shown to capture the transient multiphysics couplings and demonstrates the numerical and computational applicability based on the presented cases.