SOIL AND ATMOSPHERIC AEROSOL CONTAMINATION AT THE TERRITORIES OF INFLUENCE OF FORMER URANIUM PRODUCTION FACILITIES “PRIDNIPROVSKY CHEMICAL PLANT”

Abstract

Problems Statement and Purpose. The territory of the former Uranium production facility “Prydniprovsky Chemical Plant” (“PChP”) are located in Kamensky city, Dnipropetrovsk region, occupy the area of the upper and lower terraces of the Dnieper River (more than 300 hectares), where the remained legacy facilities and residues of the former uranium ore processing are located. After 1991 the production of Uranium concentrates ceased without remediated. Thus, up to 40 million tons of radioactive and chemical mineral residues of uranium production have accumulated within its industrial site and at the adjacent territories. Systemic monitoring studies began only in 2005. The studied environment characteristics were soils contamination, the tailings facilities where Uranium ore processing residues had accumulated, as well as atmospheric contamination by airborne aerosols. The purpose of this study stage is a comprehensive analysis of the spatial distribution of radionuclides of Uranium series at the legacy site territory and factors that can lead to a significant expansion of the contaminated area and scale of chronic environmental pollution under the influence of atmospheric transport and human exposure by inhalation. Data & Methods. The field sampling and analytical methods (gamma, alpha spectrometry and liquid scintillation counting methods) for determination of radionuclides of U-Th decay series were in use for this study. Soils samples from the top layers (0–5 cm) and gamma-dose rate surveys performed. A two-week continues integrated sampling data on the radioactive aerosols ambient activity concentrations and radioactive atmospheric fallout from 7-th locations at the legacy site and adjacent areas used for the environment radioactivity site-specific analyses. For determination of radionuclides in the environment samples (aerosols, soils and in the raw ore mineral residues) the low background gamma-spectrometry method with HPGe detectors have been in use. The content of metals associated with aerosols measured on filters using atomic absorption spectrometry methods. The data analysis for longterm series of observations (2005–2017) carried out using statistical methods. The compliance environment contamination analyses for the legacy site were carried comparing averaged observed data with the established safety criteria and regional background observation data. Results. The main current sources of radiation emission to the environment at the legacy site are open dispersed residues of Uranium production accumulated at the tailings facilities and at the former U‑extraction infrastructure. The spatial analyses of the gamma dose rate at the U‑production legacy site and its soil chemical contamination showed that about 30% of its territory requires decontamination. It is shown that the effects of aerosol radioactive particles dispersion from the contaminated “hot spots” at the territory such as tailings and former U‑production infrastructure are local and do not extend significantly beyond the industrial site. The greatest effects of wind re-suspension and propagation observed during the period of earthworks during construction of the U‑tailings covers and residues management at the contaminated facilities. In worst cases during earthwork at the U‑tailings facilities specific activity concentrations of 238U, 226Ra associated with aerosols (dust) nearby the tailings facilities may exceed 100 times above background radioactivity concentrations level observed at the distance about 10 km from the legacy site in the Kamyanske city. However, the air contamination with radioactive dusts in the worst meteorological conditions (dry windy period observation) did not exceed safe level of air concentrations according national radiation safety standards of Ukraine. The content of metals associated with aerosol particles can also increase by 2–10 times, but also their transfer by wind at the site is local and does not have a significant impact on residential areas of the city. Significant inhalation risks may arise during the dismantling of production equipment and buildings of former uranium production. Therefore, during implementation of any engineering remediation works, it is advisable to provide dust suppression control and to remove all dispersed materials from the former Uranium extraction before dismantling of the contaminated buildings and U‑production equipment. The introduced methods of air sampling at the PChP legacy site and low background analytical methods for radionuclide determination in the laboratories allow to recommend them for site specific environment monitoring programs bringing the radioactive contamination PChP site in a safe state