AUTOMATING CHARACTERISATION & SORTING | DECOMMISSIONING


● Data Evaluation: The acquired data is immediately analysed to determine the specific nuclide activity for each separable portion, including uncertainty values in compliance with ISO 11929.


● Classification: The results are compared against regulatory limits and classified into different categories based on customer’s requirements, typically Free Release (FR), Conditional Release (CR), Radioactive Waste (RW), and material suspected of containing hot spots (HS).


● Sorting: Based on the characterisation, the material is directed to its designated storage container via sorting belts.


● Documentation: The system automatically archives all measurement and operational data and generates the corresponding documentation in format defined by the client.


FREMES in use The FREMES has been successfully implemented in a number of large-scale nuclear decommissioning projects, such as the remediation of NUKEM’s own legacy fuel element fabrication site in Hanau, Germany, and FBFC International’s facility in Dessel, Belgium. Those consisted of materials suspected of uranium contamination, such as those typically found on enrichment and fuel fabrication plants. Here, the system successfully determined the total


uranium content in the contaminated soil using direct gamma spectrometry to measure the U-235 signature, combined with known uranium enrichment factors. The patented system’s radiological measurement in these


projects delivered: ● Certified direct proof of material release for applications in Germany,


● One of two redundant and diverse measurements required for material release in Belgium, as mandated by the Belgian nuclear authority (the second component being independent sample measurements).


● Sorting the materials into different activity/waste categories and deposition into corresponding storage containers.


● Providing all necessary measurement results and documentation required for release or disposal as waste, for regulatory compliance.


Bulk material characterisation and sorting The FREMES combines advanced measurement technology with an automated transport system to enable continuous and precise characterisation of bulk materials, such as concrete debris. The only requirement is that the material must be reduced to a sufficiently small grain size to allow for efficient transport and accurate measurement as bulk material.


The system is composed of several key components: ● Conveyor belts: Continuously transporting material under the detectors.


● Detectors: High-purity germanium detectors measure the gamma radiation emitted by the material.


● Weighing system: An integrated weighing system records the material‘s weight.


● Software: Manages the entire process, from data acquisition to evaluation and material sorting.


The core measurement process of the FREMES involves the


following steps: ● Material preparation: The material is mechanically processed (e.g. crushing, sieving) and then buffered, forming a continuous stream with a defined geometry suitable for measurement.


● Spectrum acquisition: The material is virtually divided into sorting portions, with gamma spectra captured the detectors and weight recorded for each portion.


In the Belgian project, the system processed approximately 45,000 tonnes of material, enabling the release of a substantial part of it. Sorting portions of around 100 kg were achieved with throughputs of approximately 10 –15 tonnes per hour, ensured by continuous technical supervision and system optimisation. The project was completed within the agreed quality, time and budget constraints, and the site was officially cleaned and released from nuclear supervision by royal decree in 2022. As disposal costs for higher waste categories increase


exponentially (usually by a factor of 10 per category), this precise sorting process significantly reduced overall costs – bringing the final expenditure to about 12% of the estimated cost for conventional processing methods, a demonstrable saving.


Remediation of concrete and building rubble The application of FREMES to concrete structures and buildings follows a similar approach to the projects presented above. In general, the system is highly flexible and can be tailored to specific needs: Material preparation, including tasks such as crushing and the removal of steel reinforcement, can be carried out either by NUKEM or the customer. This process can take place within controlled areas and existing buildings or be conducted outside of them. Measurement and sorting containers can be customised


to provide the required accuracy and throughput for specific needs. These containers can be designed as either containerised or free-standing systems. Estimates for achievable detection limits of the system, depending on material throughput, for the most important gamma-emitting nuclides in radiological decommissioning. In this design, the material separation size is approximately 100 kg at a bulk density of 2.0 g/cm3


. This represents


a typical example and exact parameters need to be determined from the details of any specific application. The number of sorting categories and exits can be


adjusted. While NUKEM’s standard design involves sorting into three categories, required sorting and limits can, of course, be modified to suit the requirements of the client. Material sorting is carried out by comparing activity


results against legal limits (including safety margins) for key nuclides detectable by the gamma spectrometry system. Other nuclides (e.g. those specified by nuclide vectors provided by the customer) can be incorporated into the evaluation process. The accuracy of this determination this determination specifically, the detection limit for their specific activity is designed to meet the lowest legally required sorting limits, with an adequate margin of conservatism. The detection limits for the most important nuclides in the current standard design are shown in Figure 1, overleaf.


www.neimagazine.com | October 2025 | 35


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