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A Task Force ofthe OECDINEA Nuclear Science Committee performed benchmark calculations to validate two-and threedimensional transport codes and cross-section sets used for radiation shielding. Based on careful measurements from the VENUS critical facility of SCKlCEN-Mol/Belgium, the Task Force started with two-dimensional benchmark calculations representing the arrangement of VENUS-I , which is a mock-up of the Westinghouse three loop reactor. About 20 different calculations were presented. SeveraI2D-S N -codes were used including some in-house codes and the Monte Carlo program MCNP-4A. The transport cross-sections were taken from ENDFIB-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 ofVENUS-3. Approximately 14 independent benchmark calculations were contributed world-wide. Several versions of3D-S N -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-I). This shows the inherent deficiencies oftwo-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.

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