Abstract
Non-destructive assay of spent nuclear fuel assemblies using high-resolution gamma spectrometry has been developed to improve the in-situ measuring technique and the complete analytical procedure to support nuclear safeguards verification and nuclear forensics investigations. A total of 119 VVER-440 type spent fuel assemblies having individual operating histories were measured by gamma spectrometry and the activity ratios of various radionuclides were determined. The energy dependence of the detection efficiency of gamma radiation and the activities of fission products were determined by an internal calibration method. Empirical relationship between activity ratios of radionuclides, 137Cs, 134Cs, 154Eu, 144Ce, 106Ru, and 110mAg and some main fuel parameters, such as burnup, cooling time and operational history, were calculated by regression and cluster analysis. Good empirical correlation was found between the burnup and the 134Cs2/(106Ru137Cs) activity ratio, yielding burnup predictions with average deviation of 5.3% and 5.8% if the cooling time is known and unknown, respectively. The cooling time could be determined within 13.3% average deviation by using the 110mAg/134Cs activity ratio. Results of the cluster analysis of the measured data indicate a deterministic relationship between the linear combinations of the 134Cs/137Cs, 154Eu/137Cs, 144Ce/137Cs, and 106Ru/137Cs activity ratios and the operational history of the fuel assemblies.
Published Version
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