Study of specific activity distribution of key nuclides in metal waste forwarded for exemption from regulatory control in the SSE “Chornobyl NPP”, and assessment of their compliance with the current radionuclide vector

The initiation of dismantling activities at the Chornobyl NPP Units has resulted in a significant amount of metal waste, decontamination of which can ensure the reduction of their radioactive contamination to levels that allow their removal outside the Exclusion Zone and return to economic circulation for use in the country’s metallurgical industry. To solve the problem of metal waste batches (MWB) exemption from regulatory control, FRM‑03 facility (manufactured in the Czech Republic) for gamma-spectrometry control of scrap metal in container was created at the industrial site of the SSE “Chornobyl NPP”. During the experimental and industrial operation of FRM‑03, based on the results of measurements of certain MWBs, it was found that the ratio of the activity of key nuclides (137Cs to 60Со or vice versa) in the deactivated metal differs significantly (to several times), from the scaling factors (SF), which are recommended with others SFs value for MWB radiological characterization using radionuclide vector methodology. This work aims to analyze the measurement results of specific activity of key nuclides in MWBs from the Chornobyl NPP, obtained using the FRM‑03 facility, and to determine under what conditions or by what quantitative criterion the current radionuclide vector can be applied to the waste stream exempted from regulatory control. The objects of the study were the results of measurements of 11 containers with radioactively contaminated scrap metal that underwent radiation control at the FRM‑03 facility. Statistical, regression and cluster analysis of data on the specific activity of key nuclides and the ratio of their activity in 11s MWB sent to the SSE “Chornobyl NPP” for exemption from regulatory control was carried out. A quantitative criterion for assessing the MWB compliance to the current radionuclide vector was proposed. It is recommended to compile a list of containers for which the SF value needs to be verified or new values set, corresponding to other characteristics of radioactive contamination of scrap metal that were previously unknown.