Modelling of PWR cladding corrosion in mixed core situations

Abstract In this paper a thermal-hydraulic model for cladding corrosion recently developed in ABB Atom and used in the CORPRO3.0 code is presented. The features of the model are a subchannel geometry which consists of a 3 × 3 matrix of rods, and modelling of coolant cross-flow and coolant enthalpy mixing. The CORPRO3.0 thermal-hydraulic model is benchmarked against the TORC code, which is a 3D code for analysing the thermalhydraulics of a reactor core. In addition, results of model calculations are compared with corrosion data obtained in mixed core situations, i.e. situations where the fuel assemblies in the core have different designs (e.g. different grid and nozzle designs). Fuel assembly components in assemblies of different designs usually have unequal flow resistances. These differences result in transverse pressure gradients, which in turn increase the lateral flow velocity and thus affect the cociant mass flow rate distribution. Two different situations where this type of mismatch between fuel assemblies in the Ringhals 3 core have occurred are studied in this paper. In the first case a reload batch of fuel assemblies, with Zircaloy mixing vane grids, inserted in a core where the resident fuel assemblies have Inconel mixing vane grids is considered. In the second case cladding tubes from the same manufacturing lot that have been irradiated for the same period of time but have been situated in fuel assemblies with Zircaloy mixing vane grids of different designs are considered. The results manifest the capability of the CORPRO3.0 code to model the effects of flow resistance on cladding corrosion.