Numerical investigation on cavitation within letdown orifice of PWR nuclear power plant

The present study numerically investigates the influence of three parameters (including outlet pressure, the circular bead of orifice inlet and the shape change of orifice outlet induced by cavitation erosion) on the cavitation characteristics within letdown orifice of pressurized water reactor (PWR) nuclear power plant. In order to understand the determinants of cavitation within letdown orifice, the influences of the mentioned parameters on cavitation characteristics are revealed. Correspondingly, the formation and variation of low pressure zones are analysed. Meanwhile, areas with high risk of cavitation erosion are displayed and confirmed through the examination in nuclear power plant. From the above, it can be concluded: Cavitation would not occur within letdown orifice unless the outlet pressure decreases to a certain value when inlet pressure remains unchanged; once cavitation has been formed within letdown orifice, the degree of cavitation would increase with the decrease of outlet pressure. The variation of circular bead could change both the location and the degree of cavitation. The shape change of orifice outlet induced by cavitation erosion would enhance the degree of subsequent cavitation around the discharge end of letdown orifice; in addition, this effect would be strengthened with the increase of shape change.