Towards a Neutronic and Thermal-Hydraulic Safety Analysis of PWR Fuel Bow with SIMULATE5 and COBRA-TF

摘要

In summary, the S5 and CTF codes have been successfully used in an offline, and therefore one-way coupling scheme, to address the impact on global DNBR_(min) values for German PWR cores with bowed fuel assemblies. This coupling exercise was necessary since DNBR_(min) is one of the most important safety parameters for normal operation for these plants. Two important assumptions had to be made which justify further research in the future. First, the GROUP5 and GR0UP6 cards of CTF were used to describe the modified sub-channel sizes around a fuel assembly's periphery and experimental validation of this method for bowed fuel assembly situations is scarce. Second, the CHF correlation was applied for non-nominal gaps under the assumption that the mixing grids still exert the dominant influence on the determination of the local sub-channel properties at a fuel assembly's periphery. In a safety analysis context, this work demonstrated that bowing has comparatively little influence on global DNBR_(min) values for the cores types considered and which are characterized by pin power distributions which peak in the fuel assemblies' interiors.