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 keff for each core configuration and the effect of uncertainties on keff 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 keff of the benchmark model was reproduced within the difference of 0.05% δkeff for the water-reflector cores and 0.17% δkeff for the unreflected cores