Babcock and Wilcox experiments interpretation

This work consists of enlargement of critical experiments used for the pin power distribution calculation validation by the EDF industrial methodology. The Babcock and Wilcox critical experiments have measured the pin by pin radial power distribution in UO{sub 2} assemblies with and without glass or gadolinium absorber rods. The EDF scheme calculates two energy groups collapsed and homogenized neutron cross-sections and diffusion coefficients for the different pins types present in the mock-up, using the APOLLO2 cell code, based on the Pij collision probability modelling, fed with the 99 energy groups CEA93V6 data base library. These cross sections are then corrected by the HERMES transport-diffusion equivalence and used as entry data by the COCCINELLE core calculation code using finite difference method with one mesh for each calculation cell. The comparison between measured and calculated pin power values has confirmed the very satisfactory accuracy level of EDF industrial scheme for the treatment of assemblies without and with gadolinium pins. It exists a margin of improvement: the future calculation methodology currently under development will have the benefit of more accurate transport calculations for generating the two groups cross-sections used by the core diffusion code. (authors)