Baffle jetting modelling

Abstract

Horizontal flow in the lower part of the reactor pressure vessel was found responsible for the so-called baffle jets impinging in the direction almost perpendicular to the nuclear fuel rods axes. This flow may generate flow-induced vibrations of the fuel rods that can damage the rods.As opposed to the flow-induced vibrations in a purely cross-flow situation, as in the case of e.g. heat exchanger tubes, the flow direction in the bottom part of the core barrel is of a combined axial and cross flow nature. One of peculiarities of the baffle jet and fuel rods interaction is the vicinity of the solid walls of the core barrel; also, the velocity profile impacting onto the fuel rods is non-uniform.The present study aims to further investigate the nature of flow field in the geometry relevant to the baffle jetting in the pressurized water reactors (PWRs). A separate effect study is conducted in order to assess the ability of a number of turbulent models to predict the complicated flow field in the case of baffle jets. Conclusions were drawn for the models’ ability to predict both the time-average and the transient, spectral, characteristics of the flow.An experimental program PANACHET was employed in CEA, France, for the study of baffle jetting. Flow velocity was measured for the conditions mimicking the flow field in the bottom periphery part of the core barrel. The PANACHET experiments were simulated using the models validated in the separate effects study.