NEA Organised Validation of Multi-Dimensional Transport Codes and Cross-Section Sets Used Presently in Reactor Shielding

Abstract

A Task Force of the OECD/NEA Nuclear Science Committee performed benchmark calculations to validate two- and three-dimensional transport codes and cross-section sets used for radiation shielding. Based on careful measurements from the VENUS critical facility of SCK/CEN-Mol/Belgium, the Task Force started with two-dimensional benchmark calculations representing the arrangement of VENUS-1, which is a mock-up of the Westinghouse three loop reactor. About 20 different calculations were presented. Several 2D-SN-codes were used including some in-house codes and the Monte Carlo program MCNP-4A. The transport cross-sections were taken from ENDF/B-VI or JEF 2.2 and the dosimetry data mainly from IRDF-90v2. The most challenging task was the validation of the latest versions of three-dimensional transport codes with the complex arrangement of VENUS-3. Approximately 14 independent benchmark calculations were contributed world-wide. Several versions of 3D-SN-codes and the Monte Carlo code MCNP were applied. In conclusion the results of the three-dimensional benchmark (VENUS-3) are in general much closer to the experimental values than for the two-dimensional benchmark (VENUS-1). This shows the inherent deficiencies of two-dimensional transport calculations, due to approximations such as diffusion based axial buckling corrections and improper averaging of source and shielding materials, since real configurations are always three-dimensional.