[1A4] Non-contact pressure measurement of sealed units using an EMAT-based acoustic resonance method
S Dixon¹ and E Sharp¹,²
¹University of Warwick, UK
²National Nuclear Laboratory Ltd, UK
Some types of special nuclear material (SNM) are often stored within multiple packages, with the final external package being a welded stainless-steel container. The integrity of SNM containment is at risk of being compromised due to several arising processes that take place within the stored material: alpha decay and radiolysis can produce hydrogen and helium gas, which could lead to the internal pressurisation and even potentially depressurisation of the containment as gases are absorbed in different chemical reactions. This change in container pressure may cause material weakening and containment deformation. Hence, there is a requirement for monitoring and measurement of the internal pressure of the containment. Through a Nuclear Decommissioning Authority (NDA) PhD Bursary research project, electromagnetic acoustic transducers (EMATs) have been used to excite a range of vibrational modes of the SNM containment and detect the resulting out-of-plane displacements. This non-contact, EMAT-based acoustic resonance method has been developed to establish a measurement of internal pressure of the SNM containment, by inspecting changes to the pressure-dependent elastic properties of the container. An increase in the internal pressure of the containment is generally reflected by an effective increase in container stiffness, which in turn increases the resonant frequency of a particular resonant mode. 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. The prototype system is now being considered for use in industrial trials.
