Numerical investigation of the effectiveness of radon control measures in cave mines

Ventilation is one of the radon control measures in an underground working environment. However, the dynamics related to the cave mining methods particularly in block/panel cave mines, complicate the design of effective ventilation system, and implementation. Events such as hang ups(in the drawbells),leakage from old workings, and changes in cave porosity lead to differing response of an existing ventilation designs. However, it is difficult to investigate these conditions at the mine or with a laboratory scale study. Therefore, this study develops a discrete model to investigate the impact of different radon control measures in cave mines using computational fluid dynamics techniques. We considered two ventilation conditions for a fully developed cave: with and without the undercut ventilation. For each of the two conditions, we studied four parameters: airflow distribution through the production drifts, radon distribution through the production drifts, the effect of increasing airflow on radon concentration, and the effect of a cave top negative pressure on radon distribution. The results show that: the undercut ventilation significantly increases the radon concentration in the production drift; the growth of radon concentration through the production drift is nonlinear(oscillating pattern); maintaining a negative pressure on top of the cave is more effective at mitigating radon exposure, when the undercut ventilation is active;and increase in air volume flow rate decreases radon concentration in most regions, however, there might be regions with significant radon accumulation due to pressure variation across the drifts. These findings provide vital information for designing an effective ventilation system and for proactive implementation of radon control measures in cave mines.