Vibration Analysis of the PHT Piping System of Point Lepreau NGS

Abstract

The Point Lepreau NGS is a 600 MeW CANDU Unit and has four PHT pumps. In the course of a specific mode of operation with only two pumps running a certain amount of heavy water flows through a stability line, which has two orifice plates. During that mode of operation the PHT piping experienced a level of vibration high enough to discourage the two pump mode of operation. This paper presents the course of actions performed to establish a vibration mechanism. An extensive test program to formulate the nature of vibration and find out characteristics of the system has been implemented. Vibration accelerations, pressure pulsations, flow rates, system pressures and operating temperatures have been recorded. An impact test for structural natural frequencies was utilized. All possible solutions to remedy the problem have been discussed. The most practical solution to the PHT piping vibration problem is recommended. The design criterion, for avoiding a severe vibration caused by the vortex shedding at an orifice in the stability line of a 600 Mew Unit, is derived.