The EU Project MICADO, Measurement and Instrumentation for Cleaning And Decommissioning Operations, has the purpose to propose a cost-effective solution for non-destructing characterization of nuclear waste, implementing a digitization process that could become a referenced standard, facilitating and harmonizing the methodology used for the in-field waste management, dismantling and decommissioning.
Among research activities within MICADO, an integrated station for gamma measurements have been conceived. The main idea is to combine different gamma detection technologies supporting each other to a comprehensive non-destructive characterization. e.g. the cooperation of techniques to reduce the overall analysis time if results acquired from one technique can be used to direct the others, by skipping up some step in the traditional characterization procedure, or by running some measurements simultaneously when it is technically feasible.
The gamma measurement station combines, for the first time, multiple non-destructive techniques based on gamma-ray detection systems in a single device. The techniques that are taken into consideration are:
- dosimetry measurements in Open Geometry detector;
- gamma imaging in Open Geometry detector;
- Segmented Gamma
- Scanning, SGS;
- Angular Scanning, AS;
- Emission and Transmission tomography, ETC and TCT.
The characterization station will be able to provide:
- multiple Radioactive Waste Package (RWP) sizes accommodation and characterization;
- an estimate of the matrix material and density based on the evaluation of linear attenuation coefficients;
- radioactive “hot-spot” localization;
- radioisotopes identification based on high resolution gamma spectrometry.
All technologies chosen are state-of-the-art detection techniques available on the market or novel techniques near to the industrial level. They only need to be updated or integrated to get the expected results. One innovation of MICADO comes from the fact that these measurements, provided by three separate and independent systems, will be integrated to work together.
Within the MICADO project the three technologies that will perform the previously described measurements are:
- the ENEA SEA Radioactive Waste Gamma Analyzer (SRWGA) for high resolution gamma spectrometry in different geometries, from open geometry up to tomography, to complete the RWP characterization;
- the CEA Nanopix: gamma camera detector for hot spot identification and localization;
- the CAEN RadHAND for fixed dosimetry and initial spectrometry measurements in open geometry.
The integration of these technologies will make the RadHAND and the Nanopix gamma camera the starting point of the inspection phase for the assay, being those instruments able to provide input information for the following step, i.e. full radionuclides identification and quantification by means of the “gamma-scanner” system SWRGA. Another significant advantage put in place by the gamma station regards the user contribution to the whole characterization. Currently, measurements are typically run by expert user.
- dosimetry information about the RWP (magnitude and values distribution of the contact dose-rate at the side of the waste package);
- information about radionuclides identified by handheld detectors;
- information from the RWP “history”, when available;
- RWP weight compared with the expected weight of a “standard” RWP;
- some preliminary measurements of the RWP to collect information about spatial distribution of material and density of the waste matrix;
- some preliminary measurements of the RWP to collect information about spatial distribution of radioactivity,
the expert user decides about the best gamma characterization technique to apply to the complete the RWP non-destructive assay, based on his experience and judgement.
The aim of the MICADO gamma station here is to overcome this approach via an “expert system” able to autonomously controlling the gamma station. Decision parameters will be decided and set-up so that experimental values collected from real measurement could produce decision about most suitable gamma characterization technique to apply.
The “expert user decision and control option” will be still allowed for taking into account the case of particularly complex items or other special cases if the programmed expert system fails.
Here, such a conception is presented and illustrated, and the technical integration of all systems described. Given the gamma station so conceived, RWP characterization examples will be finally provided and discussed.