Study on methods for decontaminating concrete surface by laser treatment

Unlike the deep radio-activation of biological shield concrete of nuclear power reactors, the concrete surfaces at JRTF (JAERI's Reprocessing Test Facility) are contaminated by radioactive material including α-nuclide up to depth of about 10mm from the top surface. Two methods of decontamination of such concrete are described here. In the first method, laser irradiation at high energy density and low scanning speed is made to cause instantaneous melting of the elements of the concrete (mainly oxides of silicon, aluminum, and calcium) by intense heat, resulting in the formation of a glass layer, which is then removed easily and collected by appropriate means. In the second method, using lower energy density and higher scanning speeds, instantaneous evaporation of the water in the concrete is induced and rapid build-up pressure occurs without surface melting. This phenomenon causes spalling of the contaminated surface layer. Debris are collected by appropriate means. (author)