Dependence of laser assisted cleaning of clad surfaces on the laser fluence

The decontamination factor is studied as a function of laser fluence of three kinds of clad surfaces viz., plain zircaloy, autoclaved zircaloy and SS with the cesium as a test contamination. It has been found that the decontamination factor exhibits a maximal behaviour with the laser fluence and its maximum value occurs at different laser fluences in the three cases. The maximal behaviour is attributed to reduced coupling of energy from the laser beam to the substrate due to the initiation of surface-assisted optical breakdown. The results obtained in the experiment carried out in helium environment qualitatively support this explanation. (author)