Numerical analysis on inlet and outlet sections of a test fuel assembly for a Supercritical Water Reactor

The Supercritical Water Reactor (SCWR) is one of the six reactor concepts being investigated under the framework of the Generation IV International Forum (GIF). One of the major challenges in the development of a SCWR is to develop materials for the fuel and core structures that will be sufficiently corrosion-resistant to withstand supercritical water conditions. Previously, core, reactor and plant design concept of the European High Performance Light Water Reactor (HPLWR) have been worked out in substantial detail. As the next step, it has been proposed to carry out a fuel qualification test of a small scale fuel assembly in a research reactor under typical prototype conditions. Therefore design and licensing of an experimental facility for the fuel qualification test, including the small scale fuel assembly with four fuel rods, the required coolant loop with supercritical water and safety and auxiliary systems, is the scope of the project "Supercritical Water Reactor Fuel Qualification Test" (SCWR-FQT). This project is a collaborative project co-funded by the European Commission, which takes advantage of a Chinese European collaboration. As a sub-task of the SCWR-FQT project, the geometry of inlet and outlet sections of the fuel assembly has to be investigated and optimized according to thermohydraulic considerations such as expected stable and uniform inflow pattern and uniform outflow temperature field conditions. To accomplish this task three dimensional CFD analysis has been performed. During the analysis two main problems were identified. On the one hand, generation of a huge eddy was discovered in the so-called flow direction changing chamber (upstream to the inlet section) which has to be avoided or at least reduced in order to ensure stable inflow conditions. On the other hand, low velocity regions were identified directly downstream to the inlet which could cause cooling deficiency at the beginning of the heated part of fuel rods. Both problems have been solved by geometrical optimization of the inlet section. The outlet section has been analysed and it graded suitable as it is. (C) 2015 Elsevier B.V. All rights reserved.