Hydrodynamic loads on a PWR primary circuit due to a LOCA Original Research Article

The safety analysis of the PWR plants requires to assess the consequences of a hypothetical Loss Of Coolant Accident (LOCA) occuring in the primary circuit. This paper is dedicated to the study of the depressurisation phase immediately following the break opening. The primary circuit of a 3-loop PWR is represented with a pipe-model. We suppose that the LOCA occurs in a reactor working at nominal rating. A first calculation is carried out at nominal rating in order to validate the numerical model by comparing the computed pressures, volumic flows and pump working conditions with the estimated nominal rating ones. A second calculation is performed in accidental operation, from the previous initial conditions. A guillotine rupture is applied to one of the cold legs, just downstream the pump. We analyse the evolution versus time of the pressure, volumic and massic flows, void fraction, density, temperature, sound speed and the mass of water lost by the break. The pipe-model used here is able to provide a global idea of the blowdown progress in the PWR primary circuit in case of a guillotine rupture. However, as the 3D components of the circuit are described with pipes, the results are only indicative.