Autonomous in-process inspection of plasma cutting for nuclear decommissioning using air-coupled ultrasonic A0 Lamb wave

During decommissioning, there is a requirement to reduce the physical size of the range of components that are used within nuclear facilities, allowing for their safe recycling or disposal as waste. Laser and plasma cutting systems are routinely used for size reduction tasks within the nuclear decommissioning sector, and within the nuclear industry, are often robotically deployed to remove workers from radioactive environments. However, issues arise where cutting operations fail to completely sever a joint or materials, rendering further challenges related to item movement and storage. This requirement to ensure that cutting operations are fully complete drives research into in-process monitoring that can provide data on the quality of the cut, the veracity, and total severance of structures being decommissioned, such as gloveboxes. This paper introduces a robotically deployed air-coupled ultrasound in-process monitoring system that inspects cut severance during plasma cutting of 3 mm-thick 316 stainless steel plates representative of nuclear glovebox material. In this work, a plasma cutting robot is equipped with non-contact ultrasonic transducers and associated electronics to generate and detect an A0 Lamb wave mode in these metals and provide cut quality monitoring and screening. Experiments demonstrated that fully cut and uncut plate segments, as well as small uncut sections as narrow as 10 mm wide can be successfully detected. The results also show that Lamb waves remain detectable when inspecting cuts that do not fully penetrate the material.