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

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.

CIEMAT response to challenges on fuel safety research during dry storage

The research on safety of dry stored nuclear fuel poses a number of challenges related to understand and predict its performance under the anticipated conditions. The ultimate goal is the development of analytical capabilities for predicting the integrity of the fuel rod. In this regard, the research carried out by the Unit of Nuclear Safety Research of CIEMAT is enabling the use of predictive tools and analysis methodologies whereby safety conditions can be assessed. To do so, the experience gained in fuel rod thermal-mechanics in reactor is used as a basis; particularly, the fuel performance code FRAPCON is being extended to the dry storage technology, called FRAPCON-xt. This paper shows the work carried out so far, including some applications on aspects related to cladding embrittlement due to hydrides as one of the main concerns.