Nuclear fusion reactors will produce activated materials containing both activation products and tritium; the former is the main source of the radioactive inventory of the generated waste, because of the reactor components that are directly exposed to neutrons. Activated structures have to be replaced during the operation of future fusion power plants, such as ITER. Decommissioning of the plants generates activated metals and concrete, that require treatment and conditioning which, in turn, will generate secondary waste. Strategies are already considered for reducing the amounts of activated waste by adopting recycling, interim storage, and clearance.
In terms of waste management processes, each single step implies detailed quantitative and qualitative knowledge of radionuclides occurring in materials and components involved, making pivotal the implementation of appropriate measurement techniques, protocols, and modeling for characterization.
Radionuclides with significant impact in the mid- and long-term management of activation waste are, among the others, Fe-55, Mn-54, Ni-59, Co-60, Zr-93 and Nb-94. With the exception of the gamma emitters such as Mn-54, Co-60 and Nb-94, which are relatively easy to detect and quantify by means of gamma spectrometry, these nuclides are hard to measure, given their little-to-none emission of gamma radiation. In particular, Fe-55 and Ni-59 decay by electron capture and are traditionally detected by destructive characterization techniques, either mass spectroscopy or Liquid Scintillation Counting, by exploiting the emitted Auger electrons. The same approach is usually adopted for the beta emitter Zr-93.
Given the potential large amount of fusion waste to be generated in the reactor lifetime, non-destructive characterization techniques are preferred since they may require less time and efforts with respect to the destructive approach and are safer from the radiation protection point of view. Techniques useful in the fusion context can be borrowed from those waste streams generated by fission, accelerators or by the industrial and the medical fields.
Here we present the case study of a decommissioned fusion research reactor which provides useful insights for quantifying advantages and drawbacks of the non-destructive characterization techniques in the context of the management of activated materials. Non-destructive techniques based on semiconductor crystals, such as CdTe, for X-ray spectrometry along with gamma spectrometry will be illustrated. Considerations for application to the case of the future ITER reactor will also be provided.