A modified accumulator method for measuring surface radon flux from a uranium tailings pile

CIM Bulletin, Vol. 75, No. 843, 1982

N.K. DAVE, Research Scientist, and T.P. LIM, Physical Scientist, Elliot Lake Laboratory, Mining Research Laboratories, CANMET, Energy, Mines and Resources Canada

A modified accumulator method was devised to measure surface radon flux from porous media. It consists of a collector hood type of accumulator with a homogenizer pump and a pressure balancer. The latter was used to compensate any pressure changes produced during sample withdrawal and hence eliminate additional radon transport from the media. Errors resulting from radon back diffusion due to decreasing concentration gradient with time across the interface were also eliminated by measuring radon concentrations in the accumulator for two different periods of time and calculating the true radon flux, J(o), from the solution of a time-dependent radon transport equation in the absence of any pressure and temperature gradients.Core samples from the observation site were also withdrawn for laboratory determination of porosity, moisture content, bulk and grain densities, Ra-226 source concentration and the fraction of Rn-222 produced in the void volume. The data were used to calculate the radon diffusion coefficient for the media.Using the present method, the true value of surf ace radon flux for an abandoned uranium tailings pile was obtained as J(o) = 2020.2 mBq/m2/sec (54.6 pCi/m2/sec) compared to the value J = 1406.0mBq/m2/sec (38.0pCi/m2/sec) obtained by the conventional method. The bulk diffusion coefficient of radon for the media was obtained as 1.2 x 10-7 m2/sec.
Keywords: Environmental control, Radon flux, Accumulator methods, Uranium tailings, Porosity, Moisture content.