Critical Experiments on 10% Enriched Uranyl Nitrate Solution Using an 80-cm-Diameter Cylindrical Core

The third series of the critical experiments on 10% enriched uranyl nitrate solution has been performed at the Static Experiment Critical Facility (STACY) of the Japan Atomic Energy Research Institute. Water-reflected and unreflected 80-cm-diam cylindrical cores were used to obtain the systematic data of critical solution height and differential reactivity for various uranium concentrations from 190 to 240 g/l. The numerically evaluated extrapolation length of neutron flux distribution was in good agreement with the experimental result. The effective neutron multiplication factor k_eff for each core configuration and the effect of uncertainties on k_eff were also numerically evaluated with both the detailed experimental configuration of critical cores and a benchmark model provided for the validation of nuclear calculation codes. The MCNP 4B was used for the evaluation calculations with JENDL-3.2 cross-section library, and the value of the k_eff of the benchmark model was reproduced within the difference of 0.05% k_eff for the water-reflector cores and 0.17% k_eff for the unreflected cores.