Question 14 of 19: Uranium Mine Tailings Management Strategy

Question 14: Uranium Mine Tailings Management Strategy (4 marks)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

Uranium mill tailings retain most of the ore's original radioactivity (radium-226 and its daughters, including radon gas) even after the uranium itself has been extracted, along with residual heavy metals and process reagents, so their management strategy is built around limiting three specific pathways: radon emanation to air, seepage of contaminated water to groundwater, and long-term physical stability of the impoundment. A widely-used Canadian strategy (applied at Saskatchewan operations such as Key Lake and McClean Lake) is sub-aqueous (underwater) disposal: tailings are deposited into a mined-out open pit or an engineered, lined tailings management facility and kept permanently submerged beneath a water cover. The water cover serves two purposes simultaneously — it excludes oxygen from the tailings, suppressing the oxidation of sulfide minerals that would otherwise generate acid rock drainage, and it attenuates radon emanation to the atmosphere far more effectively than a dry surface cover alone. The facility is engineered with a low-permeability liner and/or is sited in low-permeability host rock to limit seepage, with a groundwater monitoring network around the perimeter. On decommissioning, the facility is capped, contoured and revegetated, and remains under long-term institutional control and monitoring (in Canada, under CNSC licence) for as long as the residual hazard requires, since the radioactive decay series involved has half-lives on the order of centuries to millennia.