1 Study of Algorithmic Requirements for a System - to - Cfd Coupling Strategy

Over the last decades, the analysis of transients and accidents in nuclear power plants has been performed by system codes. Though they will remain the analyst’s tool of choice for the foreseeable future, their limitations are also well known. It has been suggested that an improvement in the simulation technology can be obtained by “coupling” system codes with Computational Fluid Dynamics (CFD) calculations. This is usually attempted in a domain decomposition fashion: the CFD simulation is only performed in a selected subdomain and its solution is “matched” with the system code solution at the interface. However, another coupling strategy can be envisioned. Namely, CFD simulations can be used to provide closures to a system code. This strategy is based on the following two assumptions. The first assumption is that there are transients which cannot be simulated by system codes because of the lack of adequate closures. The second assumption is that appropriate closures can be provided by CFD simulations. In this paper, such a coupling strategy, inspired by the Heterogeneous Multiscale Method (HMM), is presented. The philosophy underlying this strategy is discussed with the help of a computational example.