Results of Monitoring of Equivalent Dose of γ-Radiation in the Shelter Object Rooms

O. V. Mykhailov¹ , M. V. Saveliev^1,2, M. A. Pantin²

¹ Institute for Safety Problems of Nuclear Power Plants, NAS of Ukraine, 36a, Kirova st., Chornobyl, 07270, Ukraine
² Institute of Mathematical Machines and Systems Problems NAS of Ukraine, 42, Akademika Glushkova ave, Kyiv, 03680, Ukraine

DOI: doi.org/10.31717/2311-8253.24.2.6

Abstract

After the construction of the Shelter object (SO), also known as Chornobyl Sarcophagus, several research measurement systems were created to understand and monitor the fuel-containing materials behaviour. Within the framework of the SO, transformation into environmentally safe system by the construction of the New Safe Confinement (NSC), and prior to the protective Arch was set into design position, integrated automated monitoring system (IAMS), was created. One of components of the IAMS is the Stationary Radiation Monitoring System (SRMS), designed for monitoring of such parameters of the radiation situation in the SO rooms and the industrial site as gamma equivalent dose rate (GDR) and volumetric activity of α-, β- aerosols in the air. This work is devoted to the analysis of the SRMS data in terms of the GDR measurements results. The analysis of the GDR data in the SO rooms for 34 monitoring point, received during the years 2018–2023, was carried out. It was established that only one type of GDR dynamics is observed in the SO rooms — a constant decrease in the average monthly value against the background of pronounced seasonal fluctuations. The average annual decrease of GDR is estimated as — 2.12±0.57%/year, which is 8% lower than the rate of radioactive decay of ¹³⁷Cs. Compared to the rate of radioactive decay of ¹³⁷Cs in rooms that meet the conditions for permanent staff presence, the GDR decrease more slowly than in rooms categorized as periodic and limited stay. The results of SRMS data approximation obtained in the work make it possible to reliably predict the GDR levels in the controlled SO rooms and can be used to plan works and estimate the time when, under conditions of high GRD levels, such works can be performed by personnel in the places where they are carried out.

Keywords: : Chornobyl NPP, New Safe Confinement, Shelter object, Stationary Radiation Monitoring System, gamma equivalent dose rate, dynamic, regression analysis.

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