Environmental tritium contamination from a gaseous tritium light device maintenance facility

Health Physics Unit, Queensland Health Forensic and Scientific Services, PO Box 594, Archerfield, 4108 Queensland, Australia

Abstract

An investigation was undertaken in relation to the contamination of a facility used for the servicing and refurbishment of gaseous tritium light devices. While it is generally accepted that there is minimal exposure hazard from a broken gaseous tritium light source after the tritium gas has dispersed, environmental tritium contamination displaying 'particulate' like characteristics was observed during the radiological assessment of the facility in 2003. The contamination is considered to be associated with zinc sulphide phosphor residues from damaged tritium light sources. A subsequent environmental tritium survey was conducted in 2007, in the vicinity of the affected building to determine the extent of contamination and impact on current and future occupancy and land use application. The survey was conducted by measuring both soil non-aqueous tritium and soil pore water tritium concentration. Zinc concentration, from the zinc sulphide phosphor, was also measured for the same samples to assess correlation between tritium contamination activity and the identified source material. Greater than 97% of the soil non-aqueous tritium results were observed to be less than the derived tritium residential screening level of 8.5 Bq ⋅ kg^-1, and that soil pore water tritium concentrations had decreased from 8 MBq ⋅ L^-1 to less than 2 kBq ⋅ L^-1 over a period of 5 years. Elevated elemental zinc levels in the upper surface soils correlated with increased non-aqueous tritium concentration. Ground water tritium concentrations ranged from 3 Bq ⋅ L^-1 to 20 Bq ⋅ L^-1, indicating leakage of tritium contaminated water to local aquifer systems. Natural attenuation and dilution processes have reduced environmental tritium contamination levels over a period of 5 years since the introduction of new contamination control policies and operational changes at the facility.