Tolerances of isotopic variations of RUFIC fuel in CANDU 6 reactor

The impact of uranium isotope variations of uranium isotope in recovered uranium fuel in CANDU (RUFIC) on the average exit burnup and power distributions have been assessed to catch the Expected Maximum Variations (EMV) in channel and bundle powers. In this work, variations in U-235 content in the range of 0.92±0.02 w/o in total uranium were considered, and, for U-234 and U-236 isotopic variations, the ranges from 0.010 to 0.018 w/o and from 0.22 to 0.40 w/o were considered, respectively. 0.92 w/o U-235, 0.016 w/o U-234, and 0.34 w/o U-236 were used as the nominal isotopic contents of the isotopic contents in the reference recovered uranium fuel. It is confirmed that a coefficient of 1.933 MWh/kgU/mk was obtained as the burnup gain/loss per mk of core reactivity in RUFIC-fuelled core with 4-BS scheme. The impact on channel and bundle powers was assessed by fuelling simulations for 1 full power day, and compiling the statistics on power variations, based on the instantaneous snapshot calculation. As a result, it is shown that the effects of U-234 and U-236 are so small that the effects can be disregarded. For U-235 isotope, it is found that, for a ±0.02 w/o variation in U-235 content, the Expected Maximum Variations (EMV) in channel and bundle powers were up to 1.38 % and 3.2 %, respectively, and, for a ±0.01 w/o variation in U-235 content, the EMVs up to 0.6 % and 1.5 %, respectively