Development of an analytical method for pump-induced pulsating pressure in a pressurized water reactor

Abstract

Analysis of the pressure pulsation load induced by the reactor coolant pump is essential in reactor design to ensure the integrity of the reactor internals. In the present thesis, an analytical method has been developed for the prediction of the pump induced-pressure distribution in the inlet pipe and downcomer annulus of a pressurized water reactor vessel. For the coupled two systems of the inlet pipe and the annulus, impedance concept is adopted by imposing the intermediate boundary conditions at both the interface and the bottom of annulus to describe a condition which is somewhere between two extremes of closed and open. While the existing methods assumed the pump-induced pressure at the annulus inlet, the present work generates the pressure at the inlet by expanding the wave equation considering the forcing at the pump discharge. When the wave equations for two one-dimensional systems coupled to each other are solved using the impedance concept, a resonance condition is found at the interface; it implies that separate analyses on each system do not produce any physically meaningful results for the pressure distribution. For the pipe-annulus-coupled system, the pressure distributions in the inlet pipe and annulus are obtained from the wave equation, and a boundary condition involving impedance is found at the interface. From the orthogonality found for the axial mode of the impedance expression for the boundary condition, it is found that the impedance expression is applicable to not only open or closed boundary but also intermediate boundary such as the bottom of annulus. The present method has been verified for its applicability using the pump discharge pressure data measured at Palo Verde Nuclear Power Generating Station Unit 1 in the United States. There are two unknowns in the expression for the pressure distribution, which are pump forcing and the boundary condition at the annulus bottom. After some trials, it is found that the boundary condition at t...