Fluid-structure interaction in a wire-wrapped rod bundle cooled with supercritical water

The Supercritical Water Reactor (SCWR) is under consideration as one of the 4th generation nuclear reactors. In a SCWR the reactor core is cooled with supercritical water (SCW), which has distinctive advantages over water at subcritical conditions as used in current light water reactors (LWRs). Main advantages are, for instance, the expected higher thermal efficiency and simplified plant design. For the design and operation of a SCWR, the characteristics of the heat transfer from the fuel rods to the SCW coolant needs to be well understood. These heat transfer characteristics are complex and cannot be captured by the correlations that are currently available in literature. First of all, the physical properties of SCW undergo strong changes near the pseudo-critical point which complicate the flow and heat transfer. Secondly, there is the complicated flow structure in the channels between the fuel rods separated by spacers. This is in particular true for the European design of the SCWR, which makes use of wire spacers that are wrapped around each fuel rod. In this respect, Computational Fluid Dynamics (CFD) analyses are essential. The present paper focuses on the analyses of flow and heat transfer in a wire-wrapped 4-rod fuel assembly that are performed within the framework of the European SCWR-FQT project. Conjugate heat transfer analyses performed with the STAR-CCM+ CFD software. In order to determine the resulting thermal stresses and deformation of the fuel rods, structural analyses have to be performed based on the temperature distribution predicted by CFD. Due to the complex geometry and boundary conditions, the FSI problem was solved using STAR-CCM+ in combination with the structural code ANSYS.