Zero cumulative fission yields in ENDF/B data

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Jaakko Leppänen
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Zero cumulative fission yields in ENDF/B data

Post by Jaakko Leppänen » Thu Jun 11, 2020 9:25 pm

The ENDF/B fission yield libraries include some metastable nuclides, for which the cumulative yield is set to zero. These values are not used in the burnup calculation, but Serpent checks them when applying a cut-off to remove insignificant fission products from the distributions. Even though the cut-off value is set to zero by default, these nuclides are removed from the distributions. There is an easy fix to the issue. On line 236 of processfissionyields.c:

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                if ((ACE[ptr + FY_INDEPENDENT_FRAC] > 0.0) &&
                    (ACE[ptr + FY_CUMULATIVE_FRAC] >
                     RDB[DATA_DEP_FP_YIELD_CUTOFF]))
change the ">" into ">=". The problem affects several meta-stable fission products, such as Y-97m at least in ENDF/B-VI.8, ENDF/B-VII and ENDF/B-VII.1. JEFF-3.1 does not contain such zero values and is unaffected.
- Jaakko

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