Comparative studies on radon seasonal variations in various undeground environments: Cases of abandoned Beshtaugorskiy uranium mine and Kungur Ice Cave.

It is well known that one of the most important risk factors in underground environment is the harmful effects of radon. The reasons for strong seasonal fluctuations in radon content in underground environments remain not fully understood. The purpose of this article is to improve existing ideas about this phenomenon. The article presents the results of a study of radon transport in two different underground spaces - the Beshtaugorskiy uranium mine (North Caucasus) and the Kungur Ice Cave (Middle Ural). We have used the direct measurements of the equilibrium equivalent concentration (EEC) of radon progeny in air, as well as the air flow velocity. A very wide range and strong seasonal variations in the radon levels have been recorded in both cases. The EEC has a range of 11-6653 by Bq m-3 and 10-89,020 Bq m-3 in the Kungur cave and the Beshtaugorskiy mine, respectively. It has been established that seasonal fluctuations in radon levels both in the mine and in the cave are caused by the same process - convective air circulation in the underground space due to the temperature difference between the mountain massif and the atmosphere (so called chimney effect). Overall, these results indicate that due to convective air circulation, underground spaces are periodically intensively ventilated with atmospheric air, and then, on the contrary, they are filled with radon-enriched air that seeps into caves or adits from rocks and ores. In both cases, the EEC of radon progeny exceeds the permissible level for the population and workers. The results of this study highlight the need for the development of measures to limit the presence of people in the surveyed underground spaces.

Radon transport in permeable geological environments.

This article presents the results of a long-term soil radon and meteorological parameter monitoring study in the fault zone at Mt. Beshtau, North Caucasus, which for more than 3 years. Strong seasonal variations in the radon levels with maxima during summer and minima during winter were recorded. The values of radon exhalation and soil radon concentration have a range of 0.025-25 Bq m 2 s -1 and 1-170 kBq m -3, respectively. In addition, measurements of the air radon concentration, and direction of air movement at the adits mouths of the former uranium mine on the same mountain were carried out. Seasonal radon variations, similar to those observed in fault zones, were recorded at the mouths of adits. It was established that radon anomalies are associated with the periodic release of mine air from the fractures and tunnels into the atmosphere. Above an altitude of 900 m a. s. l., an abnormal release of radon occurs in winter, when the mine air is warmer than the surrounding atmosphere. At the altitudes below 900 m the cold radon rich air blows from the adit mouths in summer. During mine air discharge, radon concentrations in the open atmosphere locally around the adit mouth reach 600,000 Bq m-3, averaging 50,000-250,000 Bq m-3. The temporal pattern of radon fluctuations in fault zones and at the adit mouths is similar. A very close correlation between radon levels and atmospheric air temperature was observed both in the fault zone and at the adits mouths. It indicates that radon release in both cases are caused by a single mechanism. This mechanism probably is the atmospheric air circulation in shallow permeable zones due to the temperature difference between the inside mountain and ambient atmosphere.