Non-destructive radiological characterization applied to fusion waste management

Highlights: • Given the amount of waste produced in fusion reactors, non-destructive characterization techniques are a valuable tool • Techniques based on semiconductor crystals allow to quantify the occurrence of several radionuclides in activated materials • Hard-to-measure activation products from fusion reactors can be quantified within a few hours by means of X spectrometry Future nuclear fusion reactors will produce radioactive waste containing both activation products and Tritium. Since Tritium can potentially be removed from the reactor components, activation products in the materials directly exposed to neutrons are the main source of the radioactive inventory. Activated structures have to be replaced during the operation of future fusion power plants. Moreover, decommissioning will generate activated metals and concrete, requiring treatment and conditioning which, in turn, will generate secondary waste. Significant portions of the waste from maintenance and decommissioning are expected to not meet clearance or low level waste requirements, therefore some underground disposal might be required. To partially address such an issue, strategies are already considered for reducing the amounts of activated waste by adopting recycling, interim storage, and clearance. These imply detailed qualitative and quantitative knowledge of radionuclides occurring in the materials involved, making it pivotal to implement appropriate measurement techniques. Radionuclides with significant impact in the long-term management of activation waste include nuclides hard to measure, given their little-to-none emission of gamma radiation. Those decaying by electron capture are traditionally detected by destructive characterization techniques, either mass spectroscopy or Liquid Scintillation Counting. Given the potential amount of fusion waste produced, non-destructive characterization techniques are preferred since they may require less time and efforts. Here the performance of solid state detectors, for the spectrometry of the X ray counterpart of the Auger electrons and for traditional $\gamma$ spectrometry, is investigated in terms of the measurement time necessary to collect a statistically significant quantification limit, as a function of the radionuclides activity concentration. An approximated deterministic model is suggested and applied to the case of the future ITER fusion reactor, providing evidence that most of the activation products can be quantified within minutes, and a few hours are needed to quantify the occurrence of the hard to measure radionuclides by means of X spectrometry.