Date of Award

5-2011

Degree Name

MS in Mechanical Engineering

Department

Mechanical Engineering

Advisor

Christopher Pascual

Abstract

Nuclear power plants rely on the Emergency Core Cooling System (ECCS) to cool down the reactor core in case of an accident. Occasionally, air is entrained into the suction piping of ECCS causing voids that decrease pumping efficiency, and consequently damage the pumps. In an attempt to minimize the amount of voids entering the suction side of the pump in ECCS, a Void Recirculation System (VRS) experiment was conducted for a proof of concept purpose. While many studies have been oriented in studying two-component flow behavior in ECCS, none of them propose a solution to minimize air entrainment. As a consequence, there are no simulation models that use computational fluid dynamics to address gas entrainment solutions in ECCS. The objectives of this thesis are to (1) simulate and investigate two-component air-water flow in a VRS that minimizes the amount of air in piping systems, using RELAP5/MOD3 as the computational tool, and (2) to validate the numerical results with respect to experimental results and observations.

A one-dimensional model of the VRS was built in RELAP5, in which eight different scenarios (replicating those from the VRS experiment) were simulated for a period of 150 seconds. Four Froude numbers of 0.8, 1.0, 1.3 and 1.6 were evaluated in two different pipe configurations, and the experimental data obtained from the VRS experiment was used to validate the numerical results obtained from these simulations. It was concluded that air recirculation occurs indefinitely throughout the entire 150 seconds of the simulation for Froude numbers up to 1.3; while for a Froude number of 1.6, air recirculation occurs for approximately 100 seconds and ceases after 125 seconds of the simulation. An average air reduction effectiveness of 90% was found for all simulation scenarios. The VRS model was successfully validated and can be used to investigate the effects of air entrainment in suction piping.