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

O.V. Mykhailov¹, I.S. Skiter¹, O.V. Miasnykov², T.V. Tymoshenko²

¹ Institute for Safety Problems of Nuclear Power Plants, NAS of Ukraine, 36a, Kirova st., Chornobyl, 07270, Ukraine
² State Specialized Enterprise “Chornobyl NPP”, Slavutych, Kyiv Region, Ukraine, 07101

DOI: doi.org/10.31717/2311-8253.25.1.4

Abstract

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.

Keywords: Chornobyl NPP, metal waste batch, exemption from regulatory control, key nuclides, specific activity, radionuclide vector, scaling factors.

References

1. NP 306.4.159-2010. [Procedure for radioactive materials exeption from regulatory control within the framework of practical activities]. Approved by State Nuclear Regulatory
Commission order no. 84, dated 01.07.2010, registered by Ministry of Justice of Ukraine under no. 718/18013, dated 20.09. 2010. (in Ukr.)

2. SOU NNEGC260:2022. [Ensuring radiation safety. Exemption of radioactive materials from regulatory control at SE “NNEGC ‘Energoatom’”. Agreed by Letter of the State Nuclear Regulatory Commission no. 21-44/8847- 7853, dated 13.07.2023; letter of the Ministry of Health of Ukraine no. 26-04/2705/2-23, dated 03.02.2023. Kyiv, 2022, 252 p. (in Ukr.)

3. Methodology for radioactive materials exemption from regulatory control in action. Report by M. Sapon at the online seminar “Radioactive materials exemption from regulatory control”. Available at: https://sstc.ua/news/metodologiya-zvilnennya-radioaktivnih-materialiv-vid-regulyuyuchogo-kontrolyu-v-diyi. (in Ukr.)

4. Operating manual for the stationary facility of gamma spectrometric control FRM‑03. 63Е-RSS. Slavutych: SSE “Chornobyl NPP”, 2023, 49 p. (in Ukr.)

5. Determination and use of scaling factors for waste characterization in NPP. IAEA Nuclear Energy Series NW-T‑1.18. Vienna: IAEA, 2009, 142 р. 6. Mykhailov O. V., Krasnov V.O., Bezmylov V.M. (2018). [Methodology of using radionuclide vectors for characterization of NPP radioactive waste]. Nuclear Power and the Environment, vol. 12, no. 2, pp. 51−58. (in Rus.)

7. Production process control system. Methodology for the determination of radionuclide vectors for the characterization of batches of solid radioactive waste. STP 2.035-2018.
Slavutych: SSE “ChNPP”, 2018, 24 p. (revised 2020). (in Rus.)

8. Methodology for determining nuclide vectors for radioactive materials of the Chornobyl NPP. Slavutych: SSE “Chornobyl NPP”, 2019, 64 p. (in Ukr.)

9. Justification of the list of radionuclides and determination of the nuclide vector for the flow of radioactive materials sent for exemption from regulatory control. Research report. State registration no. 0119U 000602. Head A.M. Maksymenko. Slavutych, 2019, 278 p. (in Ukr.)

10. Wagstaff K. (2004). Clustering with missing values: no imputation required. Proceedings of the Meeting of the International Federation of Classification Societies, pp. 649−658,
doi.org/10.1007/978-3-642-17103-1_61.

11. 1Chi J.T., Chi E.C., Baraniuk R.G. (2016). k-POD: A method for k-means clustering of missing data. The American Statistician, vol. 70 (1), pp. 91−99, doi.org/10.1080/000313
05.2015.1086685.

12. Mykhailov O.V. (2021). [Results of comparative evaluation of algorithms for calculating scaling factors of difficult-to-measure nuclides in ChNPP wastes at 241Am example]. Nuclear Power and the Environment, vol. 2 (21), pp. 61−70. (in Ukr.)

13. Mykhailov O. V. (2022). [Results of radionuclide vector verification to characterize solid radwaste of Chornobyl Nuclear Power Plant sent for burial]. Nuclear Power and
the Environment, vol. 2 (24), рр. 43−53. (in Ukr.)

14. Mykhailov O.V., Bezmylov V.M. (2023). [Verification of Scaling Factors in Radiological Characterization of NPP Solid Radwaste Using the IAEA Procedure. Overview of
Modern Approaches]. Nuclear Power and the Environment, vol. 1 (26), pp. 24−34. (in Ukr.)

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