The ORNL Benchmark Experiment for Neutron Transport in Thick Sodium

Abstract

An experiment concerning deep neutron penetration in sodium was performed, and experimental results were obtained which provide a basis for verification of the accuracy of sodium cross sections to be used in transport calculations. The experiment was conducted at the Tower Shielding Facility of Oak Ridge National Laboratory and included measurements of both the neutron fluence and the neutron spectra through a large diameter sample of sodium up to 15 ft thick. Calculated results for the experiment were also compared with the experimental measurements. These results were obtained using the multigroup Monte Carlo code, MORSE, and a two-dimensional discrete ordinates code, DOT-III. One-hundred group data sets were developed from both a preliminary and the final version of the ENDF/III set (MAT-1156) for sodium for use in the calculations. Comparisons of the calculations with experiment indicate that (a) the preliminary version is slightly superior to the final version and (b) using the preliminary set, the total neutron leakage above thermal energies penetrating through 15 ft of sodium agrees to within ∼15%; and the absolute spectra penetrating through 12.5 ft of sodium, when integrated over the energy range of the measurement, agrees to within 20%. Using the final set, the corresponding comparisons are 30% and 60%.