Radio-Ecological Situation in the Area of the Uranium Legacy Site – Stepnaya Mine (Kalmykia)

Abstract

Purpose: To study the radio-ecological situation on the “uranium legacy” site of the former Stepnaya mine in the Republic of Kalmykia. Material and methods: To measure the ambient dose equivalent rate (ADER), the pedestrian gamma survey method was used using a portable spectrometric complex MKC-01A Multirad-M and dosimeter-radiometer MKC-AT6101c. The activity of gamma-emitting radionuclides in soil samples was measured using a stationary gamma spectrometer from CANBERRA. The activities of 210Po and 210Pb were measured using a radiometric installation UMF-2000 following their radiochemical separation from samples. Short-term measurements of activity concentration (AC) and equivalent equilibrium activity concentration (EEAC) of radon were carried out with an aerosol alpha radiometer for radon and thoron RAA-20P2 Poisk. Doses of radiation exposure to biological objects were estimated using dose coefficients provided by ICRP Publication 136 taking into account recommendations R52.18.820-2015. Results: Gamma ADER values at the mine site vary over the range from 0.1 to 0.36 µSv/h, and on 80 % of the area these values do not exceed the background value of 0.14 µSv/h. Along the road from the mine to Narta village the ADER values do not exceed background values with exception of the area around the dam, where in a local part of this area of about 300 m2 these values reach 0.49 µSv/h. The specific activities of natural radionuclides in the soil are below the criteria for classification as solid radioactive waste (SRW). Under the certain weather conditions, radon EEAC inside the buildings on the site reaches 13 kBq/m3, and on the territory 1-1.5 kBq/m3. Ecological risk for the terrestrial biological objects under consideration (grass, soil worm, snake and mouse-like rodents) does not exceed 0.025. Conclusions: The radiation situation at the Stepnaya mine site meets the requirements of SP LKP-91, which were in force until 2020. However, in order to transfer the facility to a local government body, reclamation work should be carried out in accordance with the Federal Law “On the Transfer of Lands or Land Plots from One Category to Another” dated December 21, 2004 No. 172-FZ and GOST R 59057— 2020 «Environmental Protection. Lands. General Requirements for Reclamation of Affected Lands». Doses of exposure to biological objects do not impact significantly on morbidity, reproduction and life expectancy of terrestrial biological objects.