Effect of spacer grid mixing vanes on coolant outlet temperature distribution

Abstract

In Loviisa VVER-440-type NPP the coolant outlet temperature of the hot subchannel is constantly monitored during the operation. According to the authority requirement the maximum subchannel outlet temperature must not exceed the saturation temperature. Coolant temperature distribution inside the fuel assembly is affected by the efficiency of the coolant mixing. In order to enhance the coolant mixing the fuel manufacturer is introducing the additional mixing vanes on the fuel bundle spacer grids. In the paper the effect of the different mixing vane modifications is studied with computational fluid dynamics (CFD) simulation. Goal of the modelling is to find vane modifications with which sufficient mixing is reached with acceptable increase in the spacer grid pressure loss. The results of the studies are discussed in the paper.

Calculation of Stress and Deformation in Fuel Rod Cladding During Pellet-Cladding Interaction

“…The outer diameter of the cladding was 9.1 mm and its thickness was 0.685 mm [1]. The spacer grid, with a thickness of 0.25 mm and a height of 10 mm [7], was placed on the interface of the 2nd and 3rd pellets. The external conditions correspond to the conditions in the VVER 440 reactor during normal operation (coolant temperature: 297°C; pressure: 12.26 MPa [4]).…”