Health Hazard Evaluation Report: HETA-2011-0090-3161, July 2012. Evaluation of Exposure to Radon Progeny During Closure of Inactive Uranium Mines - Colorado.

摘要

In June 2011, NIOSH received an HHE request from managers of a federal agency in Colorado. NIOSH was asked to evaluate employees' exposure to ionizing radiation hazards during construction of various types of closures at abandoned uranium mines. The primary health concern at these sites involved inhalation of naturally occurring short-lived radon progeny (i.e., polonium-218, lead-214, bismuth-214, and polonium-214) at mine entrances (adits). Also of concern, but to a lesser extent, was exposure to gamma radiation emitted from mine waste and nearby geological formations. On September 12-15, 2011, we visited several abandoned mines on Wedding Bell Mountain in southwest Colorado and the Vanadium Queen mine in Utah. We observed the construction of a native stone and mortar closure on Wedding Bell Mountain. We also conducted continuous monitoring of radon progeny at several mine openings at Wedding Bell Mountain and at the Vanadium Queen mine. We reviewed the state inactive mine reclamation program's pre-bid radon monitoring protocol. Monitoring results and onsite observations suggest that employee exposures to radon during mine closure activities are generally low. However, radon concentrations at mine openings are greatly affected by changing environmental conditions such as wind velocity, moisture, and barometric pressure. Results of NIOSH exposure monitoring did not exceed the average pre-bid PAEC values obtained during previous monitoring by state inactive mine reclamation program staff. Nevertheless, PAEC results from the CWLMs varied widely over the sampling period because of constant fluctuations in ventilation patterns. Given this variability, it is unlikely that short-term sampling, as conducted by state inactive mine reclamation program staff, is sufficient to derive long-term average concentrations that form the basis of protective actions. Control measures are needed in some instances to keep exposures as low as reasonably achievable (ALARA). Gamma radiation is likely to be measureable at the surface of waste rock piles near mine adits. Occupancy to these areas should be limited to minimize exposures to radon. The use of simple engineering controls (e.g., barriers, ventilation), along with the use of respiratory protection when needed, are recommended to keep radon exposures ALARA.