APOLLO: Analysis of hexagonal critical experiments

Three groups of slightly enriched UO2 fueled, hexagonal light-water moderated lattice critical experiments were analyzed with the APOLLO code at the Hungarian Academy of Sciences KFKI AEKI Reactor Analysis Laboratory, in collaboration with CEA. The work was a part of the NURESIM project where KFKI undertook to develop and qualify some calculation schemes for hexagonal problems using APOLLO2 version 2.7. In the first step non-perturbed asymptotic lattices characterized by material buckling, regular lattice perturbed by different content of gadolinium and reactivity coefficient measurements were chosen for simulation. The modeling approaches used in this analysis are discussed for selected cases. Generally the results performed by the French code using the JEF 2.2 based CEA93.V7 group library were compared to the measurements but in some cases inter-comparisons were performed to both Monte Carlo solutions as well as against results of the Hungarian lattice transport code MULTICELL based on ENDF-B/VI nuclear data. Even if the agreement between calculations and measurements differs for different codes using different nuclear data and methods the overall agreement among measured and calculated figures are good.