Experimental validation for the pin-wise isotope prediction methodology

Detail and reliable isotope assessment of spent nuclear fuels is an essential task for criticality analysis, shielding design, decay heat cooling analysis and others in the application for storage, transport and disposal. Because of time limitation and data processing issues, material assay has been evaluated in the unit of assembly. A mathematical methodology to predict pin-wise isotope inventory was developed and used for the reutilization of spent fuel pins in PWR. In this paper, validation of this method is done by comparing with experimental data published by OECD/NEA. Validation was carried out by comparing with experimental data for three reactor cases. Because quite a few data are available from experiment, calculation results were compared only for a few fuel pins in an assembly. For the most of major isotopes which has large impact, it was found that error to the experimental data is less than 5%. However, in case of minor isotopes with small number density and low importance to criticality, error exceeds over 5%, while they are within an error band of 30%. Importance of each isotope to the criticality was measured by an index of importance; as ratio of isotope contribution to total absorption or fission rates. It was found that all isotopes showing large error over 5% have very low importance compared with major isotopes. In case of short half-life fission products, calculation was overestimated because of fast radioactive decay and unknown cooling time of spent fuels. Overall estimation results are reasonably good within an acceptable range. (author)