The measurement of radon emanation rates in a Canadian cut-and-fill uranium mine

CIM Bulletin, Vol. 74, No. 825, 1981

K.C. CHENG, Radiation Engineer, Elliot Lake Laboratories, Mining Research Laboratories, CANMET, Energy, Mines and Resources Canada, J.W.M. PORRITT, Geologist, Bondar-Clegg & Co., Ltd. Ottawa, Ontario

Knowledge of radon emanation rates from uranium-bearing rocks is essential to the design of mine ventilation systems for uranium mines. Measurements of equilibrium ratio between radon and its daughters in mine air are important for a better control of mine radiation conditions. The concentrations of radon and daughters were monitored at cut-and-fill slopes in the Beaverlodge Mine of Eldorado Nuclear Ltd. during all phases of the mining cycle. The radon emanation rates of ore and rock samples were measured at the laboratory and the results were compared with in-situ emanation tests in an isolated ore drift. Samples of backfill solution, backfill drainage and ground seepage water were measured for radon and analyzed for radium and uranium. The results showed that discharges of backfill solution and daily shift-end blasts were the two major sources for a rapid release of radon gas in the ventilation air. Other mining operations, such as drilling, mucking, etc., contributed little effect on radon release to the mining environment. Radon emanation rates of the Beaverlodge ore samples ranged from 13 x 10-18 to 600 x 10-18 Ci/cm2/sec and that of waste rock samples from 0.54 x 10-18 to 13.4 x 10-18 Ci/cm2/sec. The in-situ emanation rate of mine walls with ore-to-rock ratios of 1 to 7 was 60 x 10-18 Ci/cm2/sec. The average equilibrium ratio of radon and its daughters in slopes was 32.6%. Under a normal ventilation condition, the average background levels of radon concentration in cut-and-fill slopes ranged from 13 to 80 pCi/L. The discharges of backfill solution during backfill operations at 100 tons solids per hour released approximately 1.8 x 1O6 pCi/min of radon and elevated radon concentration in slopes 2 to 5 times above the background levels.

Keywords: Underground mining, Uranium mining, Radon emanation rates, Cut-and-fill mining, Radiation, Ventilation, Beaverlodge Mine, Backfilling, Environmental control.