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Inventory estimation of long-lived fission products (LLFPs) in high-level radioactive wastes (HLW) from spent nuclear fuels of light water reactors is important for a safety assessment of their disposal. In order to develop an inventory estimation method of difficult-to-measure LLFPs (Se-79, Tc-99, Sn-126, and Cs-135), a parametric study was carried out by using a sophisticated burnup calculation code and data. In the parametric study, fuel specifications and irradiation conditions are changed in the conceivable range. The considered parameters are fuel assembly types (PWR / BWR), U-235 enrichment, moderator temperature, void fraction, power density, and so on. From the calculated results, we clarify the burnup characteristics of the target LLFPs and their possible ranges of generations. Finally, candidates of the key nuclide are proposed for the scaling factor method of HLW.

For accurate inventory estimation of long-lived fission products in LWR spent nuclear fuels, a new burn-up chain model was developed, and the latest nuclear data were employed for neutron cross sections, fission yields, half-lives, and so on. Most of them are taken from JENDL-4.0. MVP-BURN with the latest nuclear data was applied to four destructive assay data of spent nuclear fuels including inventory measurements of 79

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