Laser cutting and its potential application in nuclear dismantling have gained significant attention in recent years. It is considered as a key innovation for Nuclear Dismantling. Among the techniques explored to address the challenge of retrieving fuel debris from the Fukushima Daiichi site, are conventional laser cutting, underwater laser cutting, and laser deep gouging. Unlike conventional methods, where the success of the cut can be easily monitored with surveillance cameras, laser deep gouging involves creating deep cross-grooves in the material to remove blocks. However, the depth of these grooves is difficult to observe, presenting challenges in ensuring precise cutting and process control.

The objective of this work is to present an optical device embedded within a laser cutting head, positioned inside the assist gas flat nozzle, capable of accurately measuring groove depth in real time. The device consists of a borescope made up of 30,000 optical fibers, which captures images of the molten material along the cutting front using a camera. Optics offers a key advantage in highly radioactive environments, as they are less susceptible to radiation-induced damages compared to electronics. Additionally, its integration within the assist gas flat nozzle protects the fibers from incandescent particles emitted during the process.The borescope output is connected to a high dynamic range camera. Short-pass and band-pass filters are used to block intense laser radiation at 1030 nm. By observing the emission from the molten material along the entire length of the cutting front, both the groove length and depth can be measured.