[2A5] Non-contact pressure measurement of sealed units using acoustic methods
E Sharp¹, S Dixon¹, R Bernard² and G Bolton³
¹University of Warwick, UK
²Sellafield Ltd, UK
³National Nuclear Laboratory, UK
The structural integrity of special nuclear material (SNM) containment is at risk of being compromised due to radioactive decays or the chemical reactions that take place inside the SNM storage can. Alpha decay and radiolysis pose a significant issue due to the production of hydrogen and helium gas, leading to the internal pressurisation of the containment. This pressurisation may cause material weakening over time and lead to containment elastic and plastic deformation. Regular monitoring and measurement of the internal pressure is therefore required to ensure that the pressure within the containment does not exceed a certain threshold that would threaten the structural integrity of the can.
A non-contact acoustic method has been developed to establish a measurement of the internal pressure of the can, measuring changes to the elastic properties of the can indicated by changes in the resonant frequencies of vibration of the container. An increase in the internal pressure of the containment will generally stiffen the elastic response and will alter the vibrational resonant frequencies. Electromagnetic acoustic transducers (EMATs) have been used to excite the vibrational modes of the SNM containment and to separately detect the resulting out-of-plane displacements as the container wall vibrates. A calibrated pressure field microphone has also been used to detect the airborne acoustic displacements produced by the containment wall, several centimetres away from the container. A frequency profile of the containment has been constructed from measurements collected at atmospheric pressure to 20 bar, to inspect changes to the vibrational frequencies as a function of internal pressure. Finite element modelling has been used to aid the experimental work, by estimating the vibrational resonant frequencies and their corresponding mode shapes. Laser vibrometer measurements taken from the containment wall have confirmed the presence of the modes predicted by the finite element model.
A non-contact acoustic method has been developed to establish a measurement of the internal pressure of the can, measuring changes to the elastic properties of the can indicated by changes in the resonant frequencies of vibration of the container. An increase in the internal pressure of the containment will generally stiffen the elastic response and will alter the vibrational resonant frequencies. Electromagnetic acoustic transducers (EMATs) have been used to excite the vibrational modes of the SNM containment and to separately detect the resulting out-of-plane displacements as the container wall vibrates. A calibrated pressure field microphone has also been used to detect the airborne acoustic displacements produced by the containment wall, several centimetres away from the container. A frequency profile of the containment has been constructed from measurements collected at atmospheric pressure to 20 bar, to inspect changes to the vibrational frequencies as a function of internal pressure. Finite element modelling has been used to aid the experimental work, by estimating the vibrational resonant frequencies and their corresponding mode shapes. Laser vibrometer measurements taken from the containment wall have confirmed the presence of the modes predicted by the finite element model.
