MODELING OF PWR CLADDING CORROSION IN MIXED CORE SITUATIONS

In this paper a thermal-hydraulic model for cladding corrosion recentl y developed in ABB Atom and used in the CORPRO3.0 code is presented. T he features of the model are a subchannel geometry which consists of a 3 x 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 thermalhy draulics 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 de signs (e.g. different grid and nozzle designs). Fuel assembly componen ts in assemblies of different designs usually have unequal flow resist ances. These differences result in transverse pressure gradients, whic h in turn increase the lateral flow velocity and thus affect the coola nt mass flow rate distribution. Two different situations where this ty pe of mismatch between fuel assemblies in the Ringhals 3 core have occ urred are studied in this paper. In the first case a reload batch of f uel assemblies, with Zircaloy mixing vane grids, inserted in a core wh ere the resident fuel assemblies have Inconel mixing vane grids is con sidered. In the second case cladding tubes from the same manufacturing lot that have been irradiated for the same period of time but have be en situated in fuel assemblies with Zircaloy mixing vane grids of diff erent designs are considered. The results manifest the capability of t he CORPRO3.0 code to model the effects of flow resistance on cladding corrosion.