Estimates of radioxenon released from Southern Hemisphere medical isotope production facilities using measured air concentrations and atmospheric transport modeling Paul W. Eslinger * , Judah I. Friese, Justin D. Lowrey, Justin I. McIntyre, Harry S. Miley, Brian T. Schrom Pacific Northwest National Laboratory, 902 Battelle Blvd., Richland, WA, USA article info Article history: Received 21 January 2014 Received in revised form 9 April 2014 Accepted 10 April 2014 Available online Keywords: Medical isotope production 133 Xe Source-term estimation Atmospheric modeling CTBTO abstract 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 133 Xe data from three IMS sampling locations to estimate the annual releases of 133 Xe 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  10 14 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  10 16 to 2.4  10 16 Bq, estimates for the facility in Indonesia vary from 9.2  10 13 to 3.7  10 14 Bq and estimates for the facility in Argentina range from 4.5  10 12 to 9.5  10 12 Bq. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction and background The aim of the Comprehensive Nuclear-Test-Ban Treaty (CTBT, 1996) is to eliminate nuclear explosions. One of the main verifica- tion provisions of the CTBT (CTBTO, 2013) is the International Monitoring System (IMS), which includes a network of stations that have radioactive xenon monitoring capability. As of 2013, 31 IMS stations have xenon capability in provisional operation to study and improve the performance of the verification provisions in prepa- ration for the entry into force of the treaty. In addition to nuclear explosions, nuclear power plants and medical isotope production facilities release radioxenon (Hoffman et al., 2009; Kalinowski et al., 2008; Saey et al., 2010; Wotawa et al., 2010). Medical isotope production facilities may release or- ders of magnitude more radioxenon than nuclear power plants. A typical order of magnitude release from a nuclear power plant is w10 9 Bq/d of 133 Xe, while medical isotope production facilities may release w10 11 ew10 13 Bq/d (Saey, 2009). These sources are large enough that they form a background of radioxenon that can be detected at many places around the world, and those releases could be confused with evidence of a nuclear explosion. Thus, releases from these sources must be factored into verification activities. Reduction of future releases of radioxenon from medical isotope production facilities is one way to mitigate potential impacts of background radioxenon on treaty verification activities (Bowyer et al., 2013) where one may be seeking to identify the location of a single release of the same size as the average release from the South Africa medical isotope production facility on any given day (Ringbom et al., 2009). Other methods include estimating the impact of known releases on each verification measurement in an attempt to separate the influence of background radioxenon from * Corresponding author. Pacific Northwest National Laboratory, MSIN K7-76, 902 Battelle Boulevard, P.O. Box 999, Richland, Washington, USA. Tel.: þ1 509 372 4392. E-mail addresses: paul.w.eslinger@pnnl.gov (P.W. Eslinger), Judah.Friese@pnnl. gov (J.I. Friese), Justin.Lowrey@pnnl.gov (J.D. Lowrey), Justin.McIntyre@pnnl.gov (J. I. McIntyre), harry.miley@pnnl.gov (H.S. Miley), brian.schrom@pnnl.gov (B. T. Schrom). Contents lists available at ScienceDirect Journal of Environmental Radioactivity journal homepage: www.elsevier.com/locate/jenvrad http://dx.doi.org/10.1016/j.jenvrad.2014.04.006 0265-931X/Ó 2014 Elsevier Ltd. All rights reserved. Journal of Environmental Radioactivity 135 (2014) 94e99