Radon as a natural tracer for gas transport within uranium waste rock piles

Abstract

Acid mine drainage (AMD) has been identified as the main cause for outflow of acid water and radioactive/non-radioactive contaminants. AMD encompasses pyrites oxidation when water and oxygen are available. AMD was identified in uranium waste rock piles (WRPs) of Indústrias Nucleares do Brasil-Caldas facility (Brazilian uranium mine), resulting in high costs for water treatment. AMD reduction is the main challenge, and scientific investigation has been conducted to understand oxygen and water transportation within WRPs, where 222Rn is used as natural tracer for oxygen transportation. The study consists of soil radon gas mapping in the top layer of WRP4 using active soil gas pumping, radon adsorption in active charcoal and 222Rn determination using high-resolution gamma-ray spectrometry. A sampling network of 71 points was built where samples were collected at a depth of 40 cm. Soil radon gas concentration ranged from 33.7 to 1484.2 kBq m(-3) with mean concentration of 320.7±263.3 kBq m(-3).

Evaluation of single- and dual-porosity models for reproducing the release of external and internal tracers from heterogeneous waste-rock piles

“…In WRPs, tracer tests can be used to characterize complex unsaturated flow and transport patterns, which are controlled by physical and chemical heterogeneities (e.g. Blackmore et al, 2014;Marcoline, 2008;Neuner et al, 2013;Nichol et al, 2005;Peterson, 2014;Silva et al, 2014). Although our work mainly focuses on conservative tracer tests, reactive compounds can also be used to identify geochemical processes within the waste rock at both laboratory and field scales (e.g.…”