A review of radiation doses and associated parameters in Western Australian mining operations (2020-23)

Abstract

Government policies have stimulated the Western Australian (WA) mining industry to position itself as a significant global supplier of critical minerals, including lithium and rare earths. In WA the lithology that supports these minerals is often associated with elevated concentrations of naturally occurring radioactive materials (NORMs) and the increase in the number of mining operations pursuing the minerals has witnessed a commensurate increase in the number of workers potentially exposed to the radiation emitted from the NORMs. The regulatory framework for radiation protection in WA mining operations underwent significant change with the implementation of the Work Health and Safety Act 2020 and Work Health and Safety (Mines) Regulations 2022 which both came into effect on the 31 of March 2022. Under the new framework mining operations identified as having workers who were likely to receive annual effective doses (EDs) from NORMS above one mSvy-1are referenced asrelevant mines (RM). RMs are required to submit an annual report of the estimates of EDs)received by their workforce to the mining regulatory authority (WorkSafe WA: Mines Safety). This research provides an overview of the new legislative framework and updates the information in Ralph and Cattani (2022J. Radiol. Prot.42012501) to include data derived from annual occupational EDs submitted by RMs in the three-year period spanning 2020-21, 2021-22 and 2022-23. In 2022-23, 38 mining operations were identified as RMs, an increase of ten from 2021-22 which in turn had increased by six from the 2020-21 reporting period. The mean annual ED reported for the three-year period was 1.0 mSv, the level at which regulatory intervention should be considered. The maximum ED was 4.9 mSv, just below the threshold of 5 mSv above which exposed workers are considered Designated Workers and are subject to focused monitoring. The collective effective annual dose of the mine worker population reached an historical maximum of 2339 man mSv in 2022-23. Analysis of the three main exposure pathways confirms that inhalation of long-lived alpha emitting radionuclides in dust remains the most significant contributor to worker EDs. Inhalation of radon-222 and radon-220 and their short-lived progeny, once considered as a negligible contributor to worker annual EDs is the second most significant exposure pathway. A declining trend in the number of samples collected per worker is highlighted as requiring remediation to provide confidence in the reported annual EDs. The transition to the new legislative framework for radiation protection in mines has been supported by the publication of guidance materials which have been widely endorsed by the industry.