Burnup effect on 95Nb/95Zr ratio-cooling time correlation

The axial 95Nb/95Zr ratio distribution in a fuel assembly of the typical research reactor (IRT) was determined experimentally by gamma scanning. The results showed that this ratio is stable along the fuel assembly axis regardless of the position of the scanned section. This allows to limit gamma scanning of the whole assembly on the measurement of the central section only. This will save time, efforts and experimentalist’s exposure to radiation. In addition, the effect of burnup on the 95Nb/95Zr-cooling time correlation was investigated. The results showed that, using this correlation to determine cooling time, will include a systematic error of about 12%.