Assessment of the radiological impact of gamma and radon dose rates at former U mining sites in Central Asia

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Abstract

An assessment of the radiological situation due to exposure to gamma radiation, radon and thoron was carried out at selected former uranium mining and processing sites in the Central Asian countries of Kazakhstan, Kyrgyzstan, Uzbekistan and Tajikistan. Gamma dose rate measurements were made using various field instruments and radon/thoron measurements were carried out using discriminative radon (222Rn)/thoron (220Rn) solid state nuclear track detectors (SSNTD). The detectors were exposed for an extended period of time, including at least three seasonal periods in a year, in different outdoor and indoor public and residential environments at the selected uranium legacy sites. The results showed that gamma, Rn and Tn doses were in general low, which consequently implies a low/relatively low radiological risk. The major radiation hazard is represented by abandoned radioactive filtration material that was being used as insulation by some Minkush residents (Kyrgyzstan) for a longer period of time. Annual radiation doses of several hundred mSv could be received as a consequence of using this material domestically. In addition, the gamma and Rn/Tn dose rates at Digmai, Tajikistan, could reach values of several 10 mSv/a. The doses of ionizing radiation deriving from external radiation (gamma dose rate), indoor radon and thoron with their short-lived progenies in several cases exceeded the recommended annual effective dose threshold level of 10 mSv. At none of the sites investigated did the individual annual effective doses exceed 30 mSv, the internationally recommended value for considering intervention. Current doses of ionizing radiation do not represent a serious hazard to the health of the resident public, but this issue should be adequately addressed to further reduce needless exposure of the resident public to ionizing radiation.

Introduction

Uranium ore mining and processing started in the former Soviet Republics of Kazakhstan, Kyrgyzstan, Tajikistan and Uzbekistan after the Second World War and lasted for half a century. Extensive mining and milling activities resulted in large amounts of uranium tailing materials and waste rock deposits, often dumped in inhabited areas or in their close vicinity. Both materials may have a potential radiological impact on the environment and on the local populations.

A NATO Science for Peace project RESCA (Radioactivity Environment Security Central Asia) and a Joint Norwegian–Kazakhstan–Kyrgyzstan–Tajikistan (JNKKT) project to secure the effective management of uranium industry wastes in the Central Asian republics of Kazakhstan, Kyrgyzstan, Tajikistan and Uzbekistan were initiated in 2006/2007 in order to prevent health and environmental damage. The participating institutions included Jožef Stefan Institute, Slovenia; Norwegian University of Life Sciences and Norwegian Radiation Protection Authority; Joint Stock Company Volkovgeologiya and Al-Farabi Kazakh National University from Kazakhstan; Chu Laboratory of Ecology, Kyrgyzstan; State Owned Company Vostokredmet, Tajikistan; and the Institute of Nuclear Physics, Uzbekistan.

The objectives of the NATO RESCA project included:

  • the characterization of the source-terms and determination of local radioactive contamination in selected uranium tailing sites in Kazakhstan, Kyrgyzstan, Tajikistan and Uzbekistan;

  • radiation dose and impact assessment; and

  • identification of appropriate mitigation/remediation countermeasures.

The objectives of the Joint Norwegian–Kazakhstan–Kyrgyzstan–Tajikistan project (JNKKT) were: to assess long term consequences from radioactive and trace metal contamination associated with uranium mining and tailing at selected sites, especially at sites where run-off to rivers may significantly influence drinking water and river qualities, with the following sub-goals:

  • to utilize state-of-the-art technology for assessing potential mobility and ecosystem transfer;

  • to perform dose and impact assessments for man and the environment;

  • to evaluate the needs for countermeasures; and

  • to strengthen the scientific competence in Kazakhstan, Kyrgyzstan and Tajikistan with respect to sampling strategy, measurements, ecosystem transfer models and environmental impact assessments, and the framework/infra-structure with respect to management of radiation protection.

In the NATO RESCA study, an assessment of the radiological situation was conducted at former uranium mining and processing sites in the Central Asian countries of Kazakhstan, Kyrgyzstan, Tajikistan and Uzbekistan. To make a reliable assessment of current radiation doses received by the resident population living at or in the close vicinity of the uranium tailings and radioactive waste rock deposits, gamma dose rates, indoor radon (222Rn) and thoron (220Rn) measurements were carried out, including several measurements of 226Ra, 210Pb and 210Po in selected environmental samples at some of the investigated uranium legacy sites (UMB/JSI Draft Report, 2011).

At all investigated sites, mine rock deposits and uranium mill tailings were located within or in the close vicinity of residential areas. At all investigated sites, members of the resident public might have used radioactive materials, i.e. mine rock deposits for building and street coverings, and tailings residues as material for construction purposes, which could significantly contribute to elevated radiation doses in the living (indoor) environment.

The measurements started in spring 2006 and concluded in summer of 2009. The study aimed at a reliable assessment of radiation doses due to indoor 222Rn/220Rn and gamma exposure to ionizing radiation at the investigated uranium legacy sites in Central Asia. A preliminary radiological risk assessment for the resident public was made on the basis of the results obtained. A total of 19 field visits and expeditions were performed during the period.

Section snippets

Description of the sites investigated

The locations of the sites investigated within the NATO SfP RESCA project and the Joint collaboration between Norway, Kazakhstan, Kyrgyzstan and Tajikistan (JNKKT) project are shown in Fig. 1.

Gamma dose rates

In Kurday, the gamma dose rates in air were measured at the Pit Lake and in the area covered by waste rock piles. Based on a total of 40 measurements, the gamma dose rate ranged from 0.14 to 0.95 μGy/h 1 m above ground and 0.15–1.14 μGy/h at ground level. The readings obtained with two different field survey scintillation counters were in good agreement. In general, the gamma dose rates varied according to the site, with peak concentrations identified at the pit lake and at the top of the

Conclusions

The U legacy sites studied in Central Asian countries of Kazakhstan, Kyrgyzstan, Uzbekistan and Tajikistan represent sources of potential contamination of the living environment by naturally occurring radionuclides. The majority of legacy sites are only partly or not at all remediated, which allows unrestricted access to the sites by the resident public. The unfavorable radiological situation is to a large extent a consequence of inappropriate management of the former U sites, mainly due to the

Acknowledgments

The authors gratefully acknowledge the assistance of the NATO SfP programme in funding the RESCA project. Technical support in the field missions, overall co-operation, collaboration and assistance, particularly of young specialists involved in the NATO RESCA and to the Norwegian Ministry of Foreign Affairs for funding the JNKKT projects is also highly appreciated.

References (13)

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