Evaluation of the criticality and reaction rate benchmark experiments utilizing UO2F2 aqueous solution of intermediate enrichment in spherical geometry at ORNL

An evaluation of the criticality and relative fission rate radial distribution experiments in an 69.2-cm diameter aluminium sphere filled with intermediately enriched UO₂F₂ aqueous solution is presented. An evaluation of the total experimental uncertainty has been performed within the framework of the International Criticality Benchmark Evaluation Project (ICSBEP) and International Reactor Physics Benchmark Evaluation Project (IRPhEP). In addition, the uncertainty due to the uncertainties in the nuclear data is evaluated in this paper. It has been determined that the highest contribution to the overall uncertainty in the effective multiplication factor k_eff is due to the uncertainty in the uranium enrichment ($\sim$550 pcm in k_eff due to the 4% uncertainty in ²³⁵U enrichment). The highest experimental uncertainties in the relative fission rate profile in terms of the relative standard uncertainty (Lrs) are 0.032, 0.016, and 0.020 due to the uncertainty in guide tube diameter, filling tubes position, and detector position, respectively. It is estimated that the uncertainty in the nuclear data contributes approximately 400 pcm–1200 pcm to the uncertainty in k_eff depending on the covariance data library used. k_eff and radial fission rates have been calculated with MCNP and COG Monte Carlo neutron transport codes and have been compared to the experimental benchmark values. In general, the various Monte Carlo codes have given similar results with deviations within uncertainties.