Estimates of radioxenon released from Southern Hemisphere medical isotope production facilities using measured air concentrations and atmospheric transport modeling

• Estimate annual 133Xe releases from three Southern Hemisphere medical isotope production facilities.
• Use measured 133Xe samples from three International Monitoring System locations.
• Historical releases of 133Xe from Australia constrain estimates from the other facilities.
• Releases for Australia (ANSTO) and Indonesia match with expectations.
• Estimates of releases in South Africa are higher than anticipated.

The International Monitoring System (IMS) of the Comprehensive-Nuclear-Test-Ban-Treaty monitors the atmosphere for radioactive xenon leaking from underground nuclear explosions. Emissions from medical isotope production represent a challenging background signal when determining whether measured radioxenon in the atmosphere is associated with a nuclear explosion prohibited by the treaty. The Australian Nuclear Science and Technology Organisation (ANSTO) operates a reactor and medical isotope production facility in Lucas Heights, Australia. This study uses two years of release data from the ANSTO medical isotope production facility and 133Xe data from three IMS sampling locations to estimate the annual releases of 133Xe from medical isotope production facilities in Argentina, South Africa, and Indonesia. Atmospheric dilution factors derived from a global atmospheric transport model were used in an optimization scheme to estimate annual release values by facility. The annual releases of about 6.8 × 1014 Bq from the ANSTO medical isotope production facility are in good agreement with the sampled concentrations at these three IMS sampling locations. Annual release estimates for the facility in South Africa vary from 2.2 × 1016 to 2.4 × 1016 Bq, estimates for the facility in Indonesia vary from 9.2 × 1013 to 3.7 × 1014 Bq and estimates for the facility in Argentina range from 4.5 × 1012 to 9.5 × 1012 Bq.