A thermoelastic analysis of the laser scabbling of concrete

The process of scabbling is used in the decommissioning of nuclear power stations and consists of the removal of the radioactive surface layer of the shielding concrete. It is proposed that the process can be analyzed in terms of a thermoelastic model. Point solutions can be used in the study of such problems. We describe the method and present the relevant solutions for semi-infinite homogeneous media with a plane boundary. The method is applied with particular reference to the problem of laser scabbling of concrete but can be applied much more generally, for example to the stresses induced during surface heat treatment of metals or, at a certain level of approximation, in welding. In the case of the scabbling of concrete there is only a very thin thermal layer at the surface, resulting in a simplification of the analysis. Three special solutions are obtained in the two-dimensional approximation and they show that the strength of the tendency to fragmentation depends on the maximum rate of decrease of incident intensity at the rear of the scanning beam and that the depth of penetration depends on the overall front-to-backwidth of the beam. A broad beam is preferable in order not to reduce the penetration possible with the chosen overall depth of beam. These general characteristics are consistent with the results of experiments.