Mono-dimensional mechanical modelling of fuel rods under normal and off-normal operating conditions

This paper deals essentially with the mono-dimensional mechanical description of pressurised water reactor (PWR) fuel rods under normal and off-normal operating conditions for which a finite element model (MEFISTO) has been developed and integrated to the meteor fuel performance application. We describe the basic modelling hypotheses with particular attention being paid to the numerical treatment of non-linear stress relaxation phenomena such as cracking and creep of oxide fuels, cladding creep and plastic behaviour which are all accounted for. Calculation results are then shown to compare favourably over a wide range of experimental data points mainly pertaining to cladding diameter measurements of PWR rods. These results illustrate the validity of modelling hypotheses at different scales and are used to outline the areas of research that can be explored in an attempt to develop a more comprehensive and mechanistic approach to fuel rod modelling.