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The performance of the spectral shift control (SSC) method is evaluated and compared to the conventional poison method in the VVER-1000 fuel assembly design. The SSC method can be implemented by gradually adjusting the ratio of heavy water to light water moderator ( D 2 O/H 2 O ) during the fuel cycle. In this study, the efficiency of using the SSC design with or without a thermal absorber (gadolinium) is investigated. We apply the SSC with both 12 burnable absorber rods containing 4.0 wt.% Gd 2 O 3 (Case 1) and without Gd 2 O 3 (Case 2). The neutronic calculations indicate that the discharge burnup is enhanced by 60% and the conversion ratio (CR) is increased by 64.4% at the beginning of the cycle (BOC) compared to the benchmark data. The breeding of Pu 239 and Pu 241 is extended to 33.7% and 29.5%, respectively, for the SSC design case (2), and better utilization of U-235 and U-238 has been achieved compared to BM.
Ashraf et al. (Mon,) studied this question.