Numerical and experimental analyses of the behaviour of a nozzle with thermal sleeve under stratified flow Original Research Article

The load acting on a nozzle equipped with a thermal sleeve was examined in a realistic experiment under stratified flow conditions. The experiment as well as extensive calculations indicated the good protective action of the thermal sleeve against thermal shock loading. Due to the difference in the density of the water in the annulus and the reactor pressure vessel (RPV) a buoyancy flow is induced in the fluid annulus between sleeve and nozzle. This flow carries heat into the annulus, thus reducing the cooling effect on the nozzle resulting in low shock stresses. The numerical calculations produced a good agreement with the measured data.