Investigation on exceptional fuel CRUD samples by using radioactivity ratios of cobalt isotopes

Elemental analysis and radioactivity measurements were carried out for fuel CRUD samples obtained from a nuclear power plant. Comparisons were made for the relationship between 58Co radioactivity and Ni content and for the radioactivity ratios of 58Co to 60Co of the samples. We found a peculiar radioactivity relationship from one of the samples and were able to further evaluate this based on its unique fuel exchange history. This analysis can be useful to enhance the data credibility of CRUD samples. - Highlights: • Elemental analysis and radioactivity measurement were carried out for nuclear fuel CRUD samples. • Ratio of 58Co radioactivity to Ni content provides a means to enhance the data credibility. • Radioactivity ratio of 58Co to 60Co was used to evaluate the exposed period of CRUD in reactor core