A Depletion Evaluation of PLUS7 16X16 Nuclear Fuel Assembly using TRITON

A nuclear criticality safety evaluation that applies burnup credit (BUC) to a DSC is performed mainly through a two-step process: (1) the determination of isotopic compositions within UNFs to be loaded into a DSC by a depletion analysis and (2) the determination of the k_eff value with respect to the DSC by a criticality analysis . In particular, isotopic compositions by a depletion analysis should be estimated accurately because the nuclides, especially major actinides such as uranium or plutonium, contained in a UNF has a significant influence on a depletion analysis and the subsequent criticality analysis. One way for an accurate estimation of isotopic compositions is to apply accurate cross section libraries to a depletion analysis. In this work, the new one-group cross section libraries of the ORIGEN code were generated with respect to a domestic nuclear fuel assembly (NFA), PLUS7, with and without gadolinia rods using the SCALE 6.1/TRITON code. Then, one of the new libraries was applied to the SCALE 6.1/STARBUCS code to evaluate the effect of the k_eff value. From the results calculated in these conditions, the following conclusions are drawn. (1) The fission and absorption cross-sections of two fissile nuclides generated from burnups of low-enriched NFAs had higher values than those of high-enriched NFAs, while the fission and absorption cross-sections of U-238 generated from burnups of low-enriched NFAs had lower values than those of high-enriched NFAs. (2) The fission and absorption cross-sections below approximately 15,000 MWD/MTU depended on the amount of gadolinia rods and the initial enrichment, while those above approximately 15,000 MWD/MTU depended on the only initial enrichment. (3) The applications of the new PLUS7 16X16 cross section library gave larger k_eff values than the CE 16X16 cross-section library, except for a few cases. The effects of the new library on the k_eff values ranged from -135 to 434 pcm in reactivity.