Radial and Azimuthal ²³⁵U Fission and ²³⁸U Capture Distributions in BWR UO₂ Pins: CASMO-4 and MCNP4C Versus Activation Foil Measurements

In the context of the LWR-PROTEUS program, radial and azimuthal ²³⁵U fission (F₅) and ²³⁸U capture (C₈) rate distributions have been calculated for zero-burnup pins of a Westinghouse SVEA-96 Optima2 boiling water reactor fuel assembly using the stochastic MCNP4C and the deterministic CASMO-4 codes. The within-pin F₅ distributions predicted by the two codes are in very good agreement; the C₈ distributions are more pronounced, and there are significant discrepancies between the codes, both azimuthally and radially. The calculations have been compared with experimental results obtained from activation foil measurements in two pins of the assembly irradiated in the center of the PROTEUS test zone. The measurements confirm that the two codes can accurately predict the radial and azimuthal F₅ distributions but that MCNP4C within-pin C₈ distributions are much more accurate than those of CASMO-4.