Major sensitivities in FRAPCON-xt modeling of high burn-up fuel rods during dry storage to design and irradiation variables

Abstract

Thermo-mechanical performance of fuel rods is a key aspect for assessing the spent fuel safety during dry storage. There is a need of assessing fuel rod behaviour codes for dry storage stage and uncertainty quantification can be a useful tool for this assessment. As a first step of these studies, sensitivity analyses can help to understand the effects and to identify the relevant parameters for the predictions. The present work studies the effect of the scenario on sensitivity analyses focused on the cladding stress at the beginning of dry storage. To make this comparison 10 design parameter’s tolerances and 7 model biases have been studied for 2 different fuel rods in terms of design and irradiation. Cladding diameter tolerance and fuel gas release and thermal conductivity model biases are the more influencing parameters independently of the scenario chosen. Overall, moderate differences between scenarios have been obtained. Results obtained in this work are specifically related to the modelling of the code FRAPCON-xt.