Impacts of revised dose coefficients for the inhalation of NORM-containing dusts encountered in the Western Australian Mining Industry

Abstract

The aim of this paper is to evaluate the impact of recent revisions to the dose coefficients published in ICRP-137 and ICRP-141 for members of the²³²Th,²³⁸U and²³⁵U decay series on radiation doses received by Western Australian mine workers via the inhalation of insoluble dusts containing long-lived alpha particle emitting radionuclides.Whilst some dose coefficients for individual members of the decay series have decreased, the nett effect is that the sum of all dose coefficients in all three decay series have increased as a result of the revisions. The increase is inversely related to Activity Median Aerodynamic Diameter.Assuming the radionuclides in the inhaled dusts are in secular equilibrium, the dose conversion factors (the mean committed effective dose per unit intake of alpha activity) will increase by a factor between 1.9 and 2.9 times.In 2019, 11 mining operations in Western Australia submitted an annual report of worker radiation exposures to the regulatory authority. The reports indicate that between 35% and 60% of the committed effective doses to workers arises from inhalation of insoluble radioactive dusts. Applying an AMAD of 5 μm and a²³²Th decay series to^238+235U decay series ratio of 10:1, committed effective doses to the workforce are greater by a factor of between 0.74 and 1.26 times from those reported in 2018-19 as a result of the revised DCs published in ICRP-137 and ICRP-141.Guidance on how to calculate doses from the inhalation of radioactive dusts is provided in the regulatory authority's Guideline 'NORM-5: Dose Assessment', which will need revision to incorporate the revised dose coefficients. The Guideline has been widely distributed outside of Western Australia, and those jurisdictions which have adopted all, or sections of it, into their legal framework for radiation protection may need to consider the impact of the revision.

Keywords: ICRP-137; ICRP-141; dose coefficients; dose from inhaled dusts; mining industry; naturally occurring radioactive materials.