The Use of Gadolinia Credit for Criticality Evaluation of a Spent-Fuel Cask

There has been a tendency recently toward a high initial enrichment grade for light water reactor (LWR) fuels and, in the future, even higher grades are anticipated. If we make a subcriticality evaluation of a cask design based on the initial enrichment of the fuel, the resulting cask wi 11 have an increased basket price and a decreased transport efficiency. This is because the cask basket wi 11 require the enriched boron or an increase of the basket thickness in order to increase the neutron absorbing performance. In order to prevent this disadvantage, an introduction of burnup credit can be very effective. But with regard to boiling water reactor (BWR) fuels, it is possible to apply the simple method by taking into consideration the negative reactivity of gadolinia contained in the fuel pellets.With this method the evaluation work will be more simplified and easily put into practice through elimination of the work to specify the burnup. In this report we have established an applicable method for using gadolinia credit for the criticality evaluation of spent fuel shipping casks.