Thermal-Mechanical Behavior of Fuel Element in SCWR Design

Abstract

This paper presents a study on thermal-mechanical behavior of fuel elements proposed for the Canadian Supercritical Water Cooled Reactor (SCWR). In the Canadian SCWR, the coolant pressure is 25 MPa, and the temperature is 350°C at the inlet and 625°C at the outlet of the reactor core. A critical design decision for fuel design was the selection of fuel cladding material and its design options. Due to high operating pressures and temperatures, a collapsible cladding was selected. This paper presents an analysis of the Canadian SCWR fuel with collapsible cladding. Typical conditions for the evaluation of the fuel behavior, such as linear heat generation rate, coolant temperature and cladding surface heat transfer coefficient, were extracted from core and fuel channel designs. The temperature distribution on the fuel element is predicted by a thermal model and then the thermal model is coupled sequentially with a structural model to predict the fuel cladding deformation under temperature distribution and external pressure. Nonlinear thermo-mechanical simulations include nonlinear buckling instability with elastic-plastic deformation such that three known cladding collapse phenomena can be modelled: (1) plastic collapse by yielding, (2) elastic collapse by buckling, and (3) ridging. The numerical models are validated against analytical and experimental data. The presented results show the temperature distribution, deformed shape, stress and strain of the fuel element, allowing the designers to select appropriate cladding material and the cladding thickness for the SCWR fuel element design.