Radiation Protection Challenges in a High-Grade Uranium Mine

Abstract

The McArthur River Project in northern Saskatchewan is the largest, highest-grade uranium ore body yet discovered. Current reserves at McArthur River are estimated at416,000,000 lb U3O8 (160,000 t U) at an average grade of 13% U. The high grade of the ore, combined with some characteristics of the structure within which it is found, presents some unusual and challenging radiation protection problems. As in any underground uranium mine, breaking the rock releases trapped radon into the mine air, increasing the radon progeny concentrations. The porous sandstone also allows rapid drainage of water into mine openings. Water that has been in contact with the ore carries high concentrations of radon-222, which is readily released into the mine air, creating very high concentrations of radon progeny, which must be controlled. Ore dust has not generally been a major source of radiation exposure in lower grade uranium mines, but the high specific activity of this ore makes it a significant problem. Finally, the direct gamma radiation from the ore makes handling even drill core an activity to be approached with caution. To complicate the work, Canada was in the process of incorporating the recommendations of ICRP Publication 60 into both the national and provincial regulations for radiation protection at the time this project was being assessed. The methods for dealing with these problems are discussed in some detail.