Pressure studies in water jet simulations

Abstract

This thesis studies the forces on a coolant pipe in wetwell from waterjets after a full scale loss-of-coolant-accident(LOCA) in a nuclear reactor. The waterjets are part of a pressure suppression system constructed to be able to take care of ruptures in the reactor. Thermodynamical simulations in RELAP5 show that, at the bottom of dry- well, there is an initial pressure wave in drywell during the first 20ms. After this the pressure rises almost linearly during the first second to 324 kPa gauge pressure. Fluid flow simulations in FLUENT show that the water initially standing in the blowdown pipes is blown out 570ms after the LOCA with a final speed of 14 m/s. As the coolant pipe is hit by the jet it experiences oscillating forces with a maximum of 13 kN/m after 900ms. The simulations were per- formed using the k − ε model. These forces are satisfactory low for the pipe not to break during a LOCA.