Radiological characterization for research reactor decommissioning: Application of lessons learned from the VVR-S reactor to the WWR-M facility

Radiological characterization is a key element of the decommissioning of any nuclear facility, providing the information required for dismantling planning, radiation protection, radioactive waste management, and final site release. This paper presents a characterization strategy developed for the decommissioning of the WWR-M research reactor in Ukraine, integrating historical records, radiological surveys, in situ measurements, laboratory analyses, activation assessments, and radionuclide inventory determination. The proposed approach covers three main stages of decommissioning: dismantling, radioactive waste management, and final cleaning of premises. Particular attention is given to the characterization of activated structures, contaminated systems and components, radioactive waste streams, and residual contamination in building materials. The methodology incorporates lessons learned from the successful decommissioning of the VVR-S research reactor in Romania, including activation assessment, dose-rate mapping, radionuclide inventory determination, and waste classification. By combining direct measurements with analytical and modelling techniques, the proposed program provides the information necessary for safe and efficient decommissioning implementation while reducing uncertainties and optimizing characterization efforts. The approach may serve as a practical framework for other research reactors undergoing decommissioning.