Abstract
Burnup Credit (BUC) is the concept which consists in taking into account credit for the reduction of nuclear spent fuel reactivity due to its burnup. In the case of PWR-MOx spent fuel, studies pointed out that the contribution of the 15 most absorbing, stable and non-volatile fission products selected to the credit is as important as the one of the actinides. In order to get a “best estimate” value of the keff , biases of their inventory calculation and individual reactivity worth should be considered in criticality safety studies. This paper enhances the most penalizing bias towards criticality and highlights possible improvements of nuclear data for the 15 FPs of PWRMOx BUC. Concerning the fuel inventory, trends in function of the burnup can be derived from experimental validation of the DARWIN-2.3 package (using the JEFF-3.1.1/SHEM library). Thanks to the BUC oscillation programme of separated FPs in the MINERVE reactor and fully validated scheme PIMS, calculation over experiment ratios can be accurately transposed to tendencies on the FPs integral cross sections.
Highlights
The issue of the acceptability by the Safety Authority of the sub-criticality demonstration of nuclear industrial facilities and applications is based on a criticality-safety study taking into account the most penalizing hypothesis
Thanks to the Burnup Credit (BUC) oscillation programme of separated FPs in the MINERVE reactor and fully validated scheme PIMS, calculation over experiment ratios can be accurately transposed to tendencies on the FPs integral cross sections
Concerning the fuel inventory biases, trends in function of the burnup can be derived from the DARWIN-2.3 package qualification
Summary
The issue of the acceptability by the Safety Authority of the sub-criticality demonstration of nuclear industrial facilities and applications is based on a criticality-safety study taking into account the most penalizing hypothesis. The concept of taking credit for the reduction of the reactivity of spent fuel due to the reduction of net fissile content, build-up of actinides and increase of fission products concentration is referred to as “Burnup Credit” (BUC) [1]. Design studies pointed out that the consideration of full BUC including fission products would enable a load increase in several fuel cycle devices (cask, storage pool).
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