REPEATABILITY AND UNCERTAINTY STUDY OF STRAIN MEASURED ON COUPLED FLUID-STRUCTURE VESSELS IN RESPONSE TO HIGH INTENSITY PROTON PULSES

Spallation Neutron Source (SNS) produces neutrons through spallation reactions with the short pulse (~0.7 µs) operated at a repetition rate of 60 Hz with 1.0 GeV protons onto the mercury target in a stainless-steel vessel. Each pulse causes a distributed pressure field in the mercury, with pressures exceeding 20 MPa. Dynamic high-pressure waves created by the proton pulses interact with the stainless-steel vessel. Fluid-structure interaction causes stress cycles in the target vessel and leads to fatigue cracks and cavitation of the mercury, which leads to further damage. Strain measurements are critical for understanding and improving the lifetime of the target vessels. The measurements also allow evaluation of the efficacy of pulse mitigation techniques such as injecting small helium gas bubbles into the flowing mercury. Since 2015, researchers at SNS have used fiber-optic sensor systems to measure dynamic strain responses of the target vessels. An abundance of mercury target strain data has been collected. We would like to use these strain data to validate simulation results. It is important that the uncertainty of the measurements is quantified as part of the validation process. This paper focuses on the repeatability and uncertainty study in strain measurement data of SNS target vessels. The potential reasons causing the variance associated with measurements are investigated and discussed.