Case studies of radioactivity of drilling mud for in situ leaching uranium mining in China

The drilling mud from in situ leaching uranium mining is a type of low-radioactivity waste that contains natural nuclides and other harmful substances. In order to determine whether the drilling mud can meet the requirements of radioactive exemption management standards, field investigations and data simulations were conducted in this study. Two typical uranium mines were selected for onsite investigations. Drilling mud from different layers (i.e., the upper covering layer and ore-bearing layer) and from different stages (e.g., logging stage mud, drilling expansion stage mud, and mixed mud) was sampled. For each sample, the ²³⁸U and ²²⁶Ra concentrations of the solid components and the U and ²²⁶Ra concentrations of the supernatant were analyzed. The results revealed that the highest ²³⁸U and ²²⁶Ra concentrations of the solid components were 4122 Bq/kg and 4077 Bq/kg, while the ²³⁸U and ²²⁶Ra concentrations of the mixed drilling mud were all less than 300 Bq/kg. A radioactivity estimation model was established for scenario analysis. Exemption management screening lines of waste drilling mud, which can be used to classify and treat the drilling project according to the deposit's grade and conditions, were proposed for in situ leaching drilling projects.