WAFER-2, a code for thermal and mechanical LWR fuel performance modelling

The Danish LWR fuel performance model WAFER-2 is designed to analyze one pellet-size segment of a fuel rod throughout an arbitrary power history. Both pellet and clad mechanics are rigorously dealt with. Fuel thermal behaviour, fission gas release, and clad irradiation growth are analyzed by means of detailed empirical models based on physical concepts. Special attention is paid to the fuel-clad mechanical interaction. Detailed local stress-strain analysis of the clad area close to a pellet interface is achieved through the use of an energy principle. This paper gives a brief description of WAFER-2 and reports on the application of the model to a well-documented experimental case of severe ridging. It is demonstrated that the code predictions, especially regarding ridge heights, are in good agreement with the observed values, the code concepts thereby being verified. (orig.)