Improving laser fume for nuclear decommissioning: gas dynamic relationships in laser cutting

Laser cutting in nuclear decommissioning and dismantling can improve speed, cost, safety, and control compared to conventional technologies such as mechanical cutting, plasma arc cutting and mechanical grinding. However, use of lasers in this application is limited due to concerns about the size, volume, and chemical composition of particulate by-products. Understanding the creation mechanisms of these by-products is needed to aid in the design of filtration systems and to reduce the risk to human health. 

One of the key mechanisms of by-product liberation, in laser cutting, is the dynamic interaction between the assist gas and molten cut front. An experimental study utilising a folded Töpler lens-type schlieren system was used to investigate gas dynamic features in a simulated laser-cutting environment. An assist gas of air was supplied via a conical nozzle with an exit diameter of 1 mm at supply pressures ranging from 4-6 barA. A material thickness of 6 mm and a kerf width of 300 µm were selected. Standoff distance of 0.5 – 5mm have been assessed.

Results show that as the stagnation bubble within the gas jet increases in size and strength, the point of boundary layer separation along the cut front shifts upwards, altering the liquid-gas interaction. Manipulation of this feature can now be further investigated to control the release of less desirably sized particles from the cut. Such advancements will aid in unlocking the potential of laser cutting as an effective nuclear decommissioning and dismantling tool.