Uranium mine tailings

URANIUM MINE TAILINGS

After mining, milling and the removal of uranium from its ore, the residues are pumped to tailing piles or pools. Since the average uranium content in ore is typically about 0.1 percent to 0.15 percent, almost all of the ore winds up in the tailings. The result is very large amounts of tailings at uranium mines. For example, by 2016, Canadian mining companies had accumulated about 200 million tons of uranium mine tailings at closed mines and another 17 million tons at operating mines (excluding waste rock and contaminated water).88

Because of the large volumes of sulphuric acid used, high levels of heavy metals such as copper, zinc, nickel, and lead are mobilized, which are toxic to wildlife. Severe contamination of ground water constitutes a permanent risk. Health Canada, a department of the Canadian government, has warned that “the food chain can be contaminated unless appropriate mitigation is instituted. Fish, wildlife, vegetation, country foods, and drinking water are all at risk should spills or leakages occur. The need to manage the water from waste management areas is important, particularly if there are drinking water sources in the vicinity.” 89

Undisturbed ore contains all the radioactive daughter isotopes of uranium listed above in this section in secular equilibrium; its Becquerel amount thus remains constant. Uranium mill tailings contain all the products of the U-238 decay chain. The total radioactivity of these nuclides is approximately 80 percent of the radioactivity in the original ore, although the exact percentage depends on how long the ore has been exposed to air. Tailings can also contain significant quantities of hazardous chemicals such as copper, zinc, nickel, lead, arsenic, molybdenum, and selenium, depending upon the ore source and the reagents in the milling process.

Uranium tailings remain problematic because their radionuclides have multiple routes to living beings. Radon gas and the radioactive decay products of radon can be inhaled. Radioactive and toxic chemicals can be ingested with food and water, and external gamma radiation is emitted by the tailings. Contrary to popular belief, inhalation is the most important route as its collective doses are considerably larger than those from other exposure paths.

The existence of tailings piles and pools remains problematic because one of the decay products (thorium-230, which has a half-life 80,000 years) continues to generate the many nuclides in its decay chain for millennia. These accumulate under waste containers or they may penetrate or permeate them depending on the soil depths and the permeability of the types of containers currently in use. Such permeation means that radioactive lead-210 or polonium-210 can reach surface soils on top of tailings in high concentrations via plant uptakes (these materials have half-lives of 22.3 years and 138 days respectively).90

Few studies have quantified the risks from uranium mill tailings. In a 1983 report, the US Environmental Protection Agency estimated the lifetime excess lung cancer risk of residents living near a bare tailings pile of 80 hectares (0.8 km²) at two cases per hundred residents.91 Radon gas from mill tailings can

88 Government of Canada 2016, Inventory of Radioactive Waste in Canada 2016, viewed 24 May 2019, https://www.nrcan.gc.ca/sites/www.nrcan.gc.ca/files/energy/pdf/uranium-nuclear/17-0467%20Canada% 20Radioactive%20Waste%20Report_access_e.pdf 89 Government of Canada 2008, Canadian Handbook on Health Impact Assessment — Volume 4: Health Impacts By Industry Sector, viewed 24 May 2019, http://publications.gc.ca/collections/Collection/H46-2-04-363E.pdf 90 Pérez-Sánchez, D. and Thorne, M.C. 2014, An investigation into the upward transport of uranium-series radionuclides in soils and uptake by plants, Journal of Radiological Protection, 34(3), pp. 545. 91 US Environmental Protection Agency (EPA) 1983, “40 CFR Part 192 Environmental Standards for Uranium and Thorium Mill Tailings at Licensed Commercial Processing Sites,” in: Federal Register Vol.48, No.196, Washington D.C. October 7 1983, pp. 45940. https://www.gpo.gov/fdsys/pkg/FR-1983-10-07/content-detail.html