Radon levels after restoration of the U-mine disposal site

After cessation of the underground mining of uranium ore and production of uranium concentrate at Zirovski Vrh (Slovenia) in the period 1985-1990, two permanent surface disposal sites remained, namely, tailings pile and mine waste rock pile. Both disposal sites were of equal size of 4 hectares and were significant sources of radon. Their final restoration was designed in compliance with the condition of dose constraint for the public and authorized limits for radon exhalation from the remediated piles. In the late summer of 2008, a restoration of the mine waste pile was finished. Radon releases were reduced significantly by constructing an effective radon barrier of well compacted clayey material and a thick complex protective cover layer constructed over it. Radon exhalation rate from the mine waste area was lowered from primary level of 0.7 Bq/m(2).s to natural levels (0.01 Bq/m(2).s), and consequently, ambient radon levels also decreased on the site and nearby environment. The average radon contribution from the remaining U-mine sources was estimated on the basis of the environmental measurements of radon concentrations; they dropped from initial 7-9 Bq/m(3) to approximately 3 Bq/m(3). Further reduction of outdoor radon concentrations is expected after 2010, since the restoration of another disposal site will have been completed by the end of this year. Public exposure due to industrial radon after the first phase of restoration satisfactorily meets the dose constraint level of 0.3 mSv/y, since it decreased to less than 0.1 mSv/y.