Abstract
In the 2019-20 reporting period, nineteen mining operations in Western Australia were identified as having workers who were likely to be exposed to ionising radiation stemming from naturally occurring radioactive materials (NORMs), seventeen of which, known hereinafter as Reporting Entities (REs), were required to submit an annual report of the dose estimates of their workforce to the mining regulatory authority. In 2018 the International Commission for Radiological Protection published the revision of the Dose Coefficients (DCs) for occupational intakes of radionuclides of the uranium-238 and thorium-232 decay series, in ICRP-137 and ICRP-141. The 2019-20 annual reports are the first to apply the revised DCs to estimate worker doses. The mean effective dose (ED) reported by the 17 REs increased by 32.4% to 0.94 mSv in 2019-20 from 0.71 mSv reported in 2018-19, indicating that the mean ED is approaching the 1 mSv annual dose estimate at which regulatory intervention should be considered. The mean committed effective dose (CED) from inhalation of dusts containing long-lived alpha-emitting (LLα) nuclides has increased by 35% from 0.40 mSv in 2018-19 to 0.54 mSv in 2019-20. The maximum CED from LLα increased by 16.3% from 3.20 mSv in 2018-19 to 3.72 mSv in 2019-20. The authors consider that, in the absence of other explanations provided by the REs, the increase is largely attributable to the revised DC’s published in ICRP-137 and ICRP-141, but highlight that there are significant variations between REs that make a generalised conclusion problematic. The maximum reported ED in 2019-20 was 6.0 mSv, an increase of 36.4% from 2018-19 (4.4 mSv). The 2019-20 reporting period is the first time in a decade in which mine worker EDs have been elevated to the point that EDs have exceeded 5 mSv, a level at which personal monitoring and additional institutional controls are required.
