Whip restraint for a steam pipe rupture event on a nuclear power plant

Abstract

One of the requirements of a safe nuclear power plant design is the postulation of the dynamic effects of a steam pipe rupture. The dynamic effects are the discharging fluid and pipe whip on structures, systems or components. A pipe rupture can be caused in the steam pipe system where a defect such as a crack exists. Multiple factors contribute to the initiation of pipe cracks during the plant’s life. Cracks may start microscopically small and over time, with the assistance of cyclic operation, fatigue may elongate the crack. When a steam pipe is cooled by water during an accident, steam condensate may accumulate and form slugs of water. This water will have an effect on the system termed condensation induced water hammer. The cause of the pipe rupture is not addressed in this dissertation. Pipe rupture can be considered to be either a circumferential or longitudinal break. For the purpose of this dissertation only a circumferential break will be considered. This research is based on the development of a pipe whip restraint structure to protect the plant environment during a steam pipe rupture event in a nuclear power plant. It focuses on a structural component required to restrain the dynamic energy to an acceptable level. Whip restraints used in the nuclear industry are typically honeycomb, U-bar and crush pipe types. In this dissertation only the U-bar and crush pipe whip restraints will be considered. The plant environment, with regards to pipe layout, plays a large role in determining the type of restraint to be used, whether it is U-bar or crush pipe. A whip towards the wall/structure will favor a crush pipe; a whip away from the wall/structure will favor a U-bar restraint. In this project the crush pipe is selected where the whip is towards a wall/structure. The crush pipe also represents a simpler design. First-order analysis is performed using the energy method to determine the conceptual geometry of the whipping component and the restraint geometry. Second-order analysis includes finite element analysis to verify the first-order results. In this dissertation the concept validation is done using LS-PrePost. for the pre- and post-processing while the analysis is performed using LS-DYNA ®. During the second-order analysis it was demonstrated that the energy is successfully absorbed by the crush pipe and thus the first-order analysis is considered adequate.