Microstructure and dissolution of UO2 pellet after cutting by fiber laser

This study is aimed to investigate the microstructure of UO2 pellet cut by fiber laser and subsequent nitric acid solubility. A high power laser cutting system was employed to cut fuel rod which consists of stainless steel cladding and UO2 pellets. The influences of assist gas and cutting speed on the micromorphology, element distribution and phase of the cut-off surface of UO2 pellet were discussed. And the nitric acid solubility of laser cut samples was also studied. The results showed that there are defects such as shrinkage micro-pore, fragment, cave and crack on the cut-off surface of UO2 pellet, and UO2 may be converted into U3O8. However, subsequent nitric acid dissolution experiments demonstrated that the laser cut-off samples were soluble in nitric acid, and solubility and the dissolution rate were almost the same as those of the pristine UO2 pellets. This study illustrate that the laser can be employed to cut the fuel rod with the composite structure composed of stainless steel cladding and UO2 pellets with appropriate process parameters, and it has no adverse effect on subsequent nitric acid dissolution process.