Composition Adjustment on Direct Use of Spent Pressurized Water Reactor Fuel in CANDU

In the DUPIC fuel cycle, spent pressurized water reactor (PWR) fuel is refabricated as a DUPIC fuel by a dry process. Because the spent PWR fuel composition depends on the initial enrichment and burnup conditions of PWR fuel, the composition of DUPIC fuel is not uniquely defined. To reduce the effects of such a composition heterogeneity on core performance, an adjustment of DUPIC fuel composition was studied. The composition adjustment was made in two steps: mixing two spent PWR fuel assemblies of higher and lower ²³⁹Pu contents and blending in fresh uranium with the mixed spent PWR fuels. Because the fuel and core performances depend on both the absolute amount of fissile isotopes and the ratio of major fissile isotope contents, a parametric study was performed to determine the reference compositions of ²³⁵U and ²³⁹Pu. The reference enrichments of ²³⁵U and ²³⁹Pu were determined such that the DUPIC core performance is comparable to that of a natural uranium core with high spent PWR fuel utilization and low fuel cycle cost. Under this condition, it is possible to utilize 90% of spent PWR fuels as the DUPIC fuel formula. On average, the amounts of slightly enriched and depleted uranium used for blending correspond to 8.6 and 10.6%, respectively, of the mass of candidate spent PWR fuels.