CANDU Fuel Qualification Testing in Coolant Pressure Pulse Conditions

Abstract

In Nov. 1990, fuel damage occurred during refueling in Ontario Hydro's Darlington Unit 2 Generating Station. The fatigue damage to the end plates was determined to be a result of acoustic pressure pulsations caused by the main coolant pumps. The pumps generated a pressure pulse in the coolant at 150 Hz, due to the 30 Hz pump rotation frequency multiplied by the five pump impeller vanes. Furthermore, the acoustic response of the piping amplified the pressure pulses in the headers and feeders. Thus pulsation amplitudes greater than 40 kPa (0-to-peak) reached the fuel. This system response had not been anticipated in the primary heat transport system design, nor was the fuel designed for such pressure pulse conditions. Thus, a small number of fuel channels was subject to unexpectedly high levels of pressure pulsations. The realization that all fuel channels have some potential for pressure pulsations, required that these conditions be incorporated into the tests qualifying new fuel or new channel hardware designs. As a result, methods were developed to test fuel in conditions similar to those experienced in reactor, and to develop techniques to determine acceptable fuel behavior.