Assessment of expected maximum doses from the El Sherana airstrip containment, South Alligator River valley, Australia

Department of Sustainability, Environment, Water, Population and Communities, 2013

Internal Report 618
Supervising Scientist Division
Andreas Bollhöfer, Che Doering, Peter Medley, Linda da Costa

Executive summary

The El Sherana airstrip containment is a near-surface disposal facility located in the South Alligator Valley area in the south of Kakadu National Park. The containment was constructed, filled and covered in the 2009 dry season. It is currently in the institutional control period. This is the period following closure of the facility during which public access to, or alternative use of, the site must be restricted (NHMRC 1993). The containment is managed by Parks Australia with regulatory oversight by the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA). An inspection of Parks Australia by ARPANSA on 27–28 September 2011 highlighted that dose constraints for the containment had not been established. Parks Australia subsequently requested that SSD conduct an assessment of potential doses to workers and the public from the containment that could be used to guide decision making on dose constraints.

Two scenarios were considered. The occupational scenario assumed that a Park Ranger spends 80 hours per year working onsite at the containment for routine maintenance. The member of the public scenario assumed that a tourist camped for four nights (40 hours in total) next to the boundary fence of the containment.

The dose from external gamma radiation was calculated by multiplying the 99th percentile of the above background dose rate with the time spent on site. The dose from radon progeny inhalation was calculated using the RESRAD-Offsite computer model, with the 99th percentile of the above background radon exhalation flux density used to determine the radon progeny concentration in air on and downwind of the containment for highly stable atmospheric conditions. The ingestion and dust inhalation pathways have not been considered. The expected maximum doses to a worker and a member of the public from the containment for the assumed exposure scenarios is less than 10 µSv per year for the current radiological characteristics of the containment.