The impact of atmospheric pathways on public exposure

Abstract

This dissertation looks at the problem of radon emanating from the slime dams of mines, whether there is a cause for concern with respect to the safety of the public. It has been determined by previous work that the highest radon emanations are from tailings/slimes dams. [Ref 10, 12, 20, 27] During 1994/1995 the Council for Scientific and Industrial Research (CSIR) published a report known as the GU9301: Final report: Assessment of the radiological impact to the public from surface works on mines: radon and dust exposure pathways. It tried to assess the impact of radiation on the public from the mines in South Africa. It took three mines referred to as mine 1, mine 2, and mine three to represent the West Rand, Westem Transvaal and, the Free State gold mining regions respectively. The final data indicates that the doses from the mines were close to the 250 μSva·1 limit set by the National Nuclear Regulator. The mines conducted independent Public Hazard Assessments and their data shows that the doses from the mines are much smaller than the 250 μSva·1 limit. This dissertation tries to determine why there is a discrepancy between the GU9301 report published by the (CSIR) and the independent Public Hazard Assessments conducted by the various mines. This dissertation also tries to find an optimal method for determining radon flux from slimes dams and to characterize the slimes dams to determine the major factors (e.g. age of slimes dam, location and time of measurement etc) affecting the flux. The major factors affecting radon flux were looked at by studying two slimes dams, namely the inactive No. 2 slime dam at Kloof mine ( old) and the active No. l slime dam at Leeudorn mine (new). The flux measurements were taken around .,!he perimeter and then within the slimes dam itself. Two methods were used to determine the radon flux in this project, namely: 1. The Rad Elec dynamic/active system which requires 24 hours per measurement, and 2. The Rad Elec passive system, which required about 3 hours per measurement. Studies performed by J. Ellis on his masters' dissertation showed that there is collaboration between the dynamic and passive systems data. [Ref27] NOTE: the Rad Elec methods are not accepted by the NNR (one of the reasons being that they are not calibrated for South African slimes dams). The values obtained by the Rad Elec systems should not be taken as absolutes. They are only used to compare the readings with each other. The data obtained by this research indicates that the location of the flux measurements from slimes dams does not affect the readings (the average perimeter and internal readings were approximately the same). The time of measurement is very important. The readings from the dynamic system were higher than readings from the passive system almost by a factor of 5 (in some cases. The age of the dam appears not to play too great a role on radon flux however, the readings from the wet/young slimes dam require more scrutiny as there is a possibility of moisture formation on the electrets and causing premature discharges.