Radionuclide characterization studies of radioactive waste produced at high-energy accelerators

The European Laboratory for Particle Physics (CERN) has been operating accelerators for high-energy physics both on Swiss and French territory for over 50 years. Due to the interaction of the particle beams with matter, the accelerator components and the surroundings become activated and shall be treated as radioactive waste once the end of their operational lifetime is reached. For disposal towards the final repositories the radioactive waste legislation of both CERN Host-States requires the knowledge of the radionuclide inventory. This paper discusses the studies that are carried out at CERN for the characterization of the metallic radioactive waste produced every year in the several high-energy accelerators. The radionuclide inventory as well as the specific activity of radioactive waste originating from accelerators varies depending on the accelerated beam, on the location of the material with respect to the beam losses and the decay time already elapsed. The approach proposed at CERN is based on an estimate of the specific activity per radionuclide with the Monte-Carlo code FLUKA, by simulating the radiation environment to which the radioactive waste was exposed during its operational lifetime. This method has been validated for the CERN ISOLDE facility by both γ-spectrometry and Monte-Carlo simulation of the target. The use of this method in those cases where the irradiation conditions are not known with sufficient precision requires careful extrapolation based on additional dose-rate and gamma-spectrometry measurements.