2, Université Lyon 1, CNRS/IN2P3, Lyon, , France
Nuclear grade graphite has been widely used as a neutron moderator, reflector and fuel matrix in various types of nuclear reactors since the late 1940s. Its characteristics made it a material particularly suitable for the nuclear application. Consequently, graphite represents the greatest volume of radioactive waste at the end of the reactor's life. To date, about 250,000 tons have been accumulated worldwide. This is typically the case of the French UNGG or the British MAGNOX nuclear reactors developed independently in the same period. The long-term storage or disposal of the nuclear graphite waste requires a special management strategy and the challenges for the fundamental management options are reflecting the chemical, physical and structural properties of the material itself, its retrieval from the core and the associated inventory of long lived radio-isotopes such as chlorine (36Cl) or carbon (14C) that result from neutron activation processes. Therefore, prior to select any management option for the neutron-irradiated graphite, a comprehensive understanding of the structural properties of raw and structurally modified graphite is needed, so as to provide efficient and effective solutions. Raman spectroscopy appears to be an appropriate technique to probe the structural modifications of nuclear graphite. The present paper will discuss the Raman response through the various types of defects that may appear in the nuclear graphite during its manufacturing and/or surface preparation, after being exposed to neutron bombardments and. upon ion-beam irradiation. For this latter, a special device was developed allowing in situ monitoring of nuclear graphite behavior under light ion beam supplied by a cyclotron, with conditions of temperature, pressure and chemical atmosphere similar to those of an operating UNGG reactor.