Abstract: In its Publication No.137(2017), the International Commission on Radiological Protection (ICRP) updated the dose conversion factors for radon and radon progeny exposure, replacing the value of 1.4 mSv/(mJ·h·m^-3) adopted in the 1990s with 3.3 mSv/(mJ·h·m^-3) for mines and 5.7 mSv/(mJ·h·m^-3) for indoor workplaces. This has resulted in a corresponding reduction in the control limits for radon and radon progeny concentrations in uranium mines and mills (from 2 700 to 2 000 Bq/m³ for underground mines and from 2 400 to 600 Bq/m³ for processing plants), which will significantly increase the cost of radon mitigation and protection. With advances and changes in uranium mining and milling methods, new radon contamination issues, such as high leakage and high release under high negative pressure, have emerged. Furthermore, due to the development and utilization of naturally occurring radioactive material (NORM) resources, the measurement and control of thoron and its progeny have become new challenges facing the field of radon protection.

Key words: uranium mining and milling, radon, thoron