Slag Capture and Removal During Laser Cutting

It has been found expedient to separate the casings of spent nuclear reactor fuel rods from the fuel-containing elements held therein by cutting the casings with a laser beam. Metal melted by the laser beam has heretofore been removed from the cutting point on a fuel rod casing by means of a gas jet which sweeps the melted metal into a suction duct located adjacent the cutting point. The suction ducts required in this type of slag removal system are undesirably bulky, and it would also be advantageous to eliminate the cost of operating the blower associated therewith.

It is therefore an object of this invention to provide an improved means for collecting slag generated by laser cutting of nuclear reactor fuel rod casings.

Another object is to provide a compact and economically operated slag collection means for a nuclear fuel rod cutting apparatus of the laser type.

These objects are attained by (1) directing a gas jet toward a point on a nuclear fuel rod casing, thereby blowing particles of melted metal, or slag, away from the cutting point, and (2) capturing the thus propelled slag on a magnet.

The drawing is a diagrammatic representation of a preferred embodiment of the invention.

In the drawing, reference number 10 designates a workpiece such as the casing of a nuclear fuel rod. A laser beam 12 is directed against workpiece 10 by means of a conventional laser mirror 14 to cut it in accordance with known technology, and a gas jet 16 is aligned adjacent the workpiece so that a high velocity gas stream 18 discharged therefrom blows molten metal particles sputtering from the cut in the workpiece along a divergent path 20. A frustum slag guide tube 22 intercepts the jet-propelled particles and deflects them onto an electromagnet 24, the particles being cooled by spattering on the guide tube.

The applicant has discovered that when the normally nonmagnetic metal (a 300 series austinetic stainless steel) used in nuclear fuel assembly is cut by using a laser beam, the material is melted and then rapidly quenched so that a ferritic and probably a martensitic slag is formed. Therefore the slag becomes ferromagnetic below its Curie temperature.

Thus slag particles removed from a workpiece 10 that is part of a nuclear fuel assembly made of a normally nonmagnetic stainless steel will be retained on electromagnet 24 after being directed thereto by the gas jet discharged from gas jet 16. After a cut in workpiece 10 has been made, captured slag can be released from the electromagnet by de-energizing it. In some cases the electromagnet can advantageously be moved to a dump region remote from workpiece 10 before slag is released therefrom.

Slag guide tube 22 and electromagnet 24 occupy considerably less space than the ductwork included in the suction-type slag collectors now used with laser cutting systems. Furthermore, electromagnet 24 costs less to operate than a blower of a suction-type slag collector.