Evaluation of Correction Factors for LLFP Transmutation Rate

Jin, Tomoyuki*; Oki, Shigeo 

For the design study of LLFP (Long-Lived Fission Product) transmutation core concepts in Feasibility Study on commercialized fast reactor cycle systems, correction factors for LLFP transmutation rate were evaluated by comparing the design calculation with the detailed Monte-Carlo calculation. By a step-by-step approach from design to detailed calculation, the correction factors were decomposed into the following factorial effects: (a) group collapsing effect, (b) transport effect, (c) difference between the deterministic method and the Monte-Carlo calculation, (d) detailed energy group effect (including a treatment of the thermal energy region), (e) three-dimensional effect of the core geometry, and (f) heterogeneity effect of the LLFP target assembly. As a result, the heterogeneity effect of the LLFP target assembly was turned out to be the main cause of the difference between the design and the detailed calculations. It is possible to explain the mechanism of the heterogeneity effect in connection with the cross-section shape of LLFP from resonance to thermal energy region.