Non-Contact Gas Accumulation Detection in Water Loaded Pipes Using Guided Waves

The U.S. Nuclear Regulatory Commission (NRC) issued Generic Letter 2008-01 due to the safety concern associated with gas accumulation events in emergency core cooling pipes of nuclear power plants. Since the gas accumulation may critically damage pipes, pumps, and valves, and affect the safety operation of nuclear power plants, the gas accumulation needs to be detected as well as quantified. This paper presents a quantitative gas accumulation detection method for water loaded pipes by using guided waves. To establish the detection method, we investigated the differences between guided waves in a free pipe and those in a water loaded pipe. The guided waves in both cases were measured by using a scanning laser Doppler vibrometer, and analyzed by using frequency wavenumber analysis. Analysis results show that guided wave characteristics such as wavenumbers and wave speeds are different between the free and water loaded pipes. Based on those findings, we developed a gas accumulation detection method that can also provide quantitative information of the gas accumulation. Through a proof-of-concept test, the quantitative gas accumulation detection method was verified.