In-situ structural integrity evaluation for high-power pulsed spallation neutron source by using a laser Doppler method

High-power pulsed spallation neutron sources are being developed in the world. Mercury is used as a target material to produce neutrons. At the moment of the proton beams bombard the mercury target, the mercury target vessel is impulsively excited resulting from the interaction between mercury and solid wall due to the pressure waves. The vibrational velocity on the outer surface of the target vessel was measured by a laser Doppler vibrometer to diagnose the structural integrity of the vessel. Measured vibrational signals, were applied for evaluating the damage inside the target vessel that is induced by the cyclic loading and cavitation bubble collapsing due to the pressure waves. A technique, the Wavelet Differential Analysis (WDA), was applied to clearly indicate the effects of damages on the impulsive vibration behavior. Moreover, in order to reduce the effects of superimposed noise on the vibration signals on the WDA, the statistical methods, the Analysis of Variance (ANOVA) and the Analysis of Covariance (ANCOVA), were applied. The lab-experimental results, numerical simulation results with manually added random noise, and field data were analysed by the statistic methods. The results demonstrated that the established in-situ diagnostic technique can effectively evaluate the structural integrity. Nomenclature WDA Wavelet Differential Analysis WDI Wavelet Differential Image Img Wavelet Image f frequency Hz t time s Ia average intensity of WDI D diameter of damage mm V(t,f) value of intensity of the WDI at time t and frequency f dB SST total sum of square n total number of samples y�� jth sample value of the ith group M sample mean of all samples h number of samples in each group y�� sample mean of the ith group 3.2.5 76 JAEA-Conf 2015-002