RADON IN THE KULOGORSKAYA — VODNAYA — TROYA KARST CAVE SYSTEM (NORTHWESTERN SECTOR OF THE RUSSIAN ARCTIC): FIRST RESULTS

The article presents the initial results of radioecological studies of the Kulogorskaya-Vodnaya-Troya cave system (Pinezhsky District, Arkhangelsk Region). The studies were conducted in October and December 2025 and included measuring radon volumetric activity (RVA) in the cave air, radon flux density (RFD) above and beyond the cave, and determining the radionuclide composition and physicochemical parameters of three clay sediment samples from the cave. High radon volumetric activity was detected in the air of Vodnaya Cave in the autumn, while the winter period was characterized by a virtual absence of radon. This is explained by natural convection of air masses due to differences in air temperature within and outside the cave. Furthermore, contrasts in radon flux density were found above and beyond the cave system, which may be due to zones of decompression in the overlying soil. According to the results of radon concentration studies in Vodnaya Cave in October 2025, significant excesses were observed, exceeding the ICRP recommended intervention levels, as well as the equivalent equilibrium radon concentrations in indoor air as specified by NRB (Radiation Safety Norms) 99-2009. The elevated radon levels in Vodnaya Cave may be associated with the saline waters of the Mezen aquifer, as well as with Vendian and Lower Cambrian terrigenous rocks. Initial study results indicate the need for periodic radiation monitoring of the caves to identify the most favorable visiting periods in terms of radiation safety.

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