Characterization of Xe‐133 global atmospheric background: Implications for the International Monitoring System of the Comprehensive Nuclear‐Test‐Ban Treaty

Abstract

Monitoring atmospheric concentrations of radioxenons is relevant to provide evidence of atmospheric or underground nuclear weapon tests. However, when the design of the International Monitoring Network (IMS) of the Comprehensive Nuclear‐Test‐Ban Treaty (CTBT) was set up, the impact of industrial releases was not perceived. It is now well known that industrial radioxenon signature can interfere with that of nuclear tests. Therefore, there is a crucial need to characterize atmospheric distributions of radioxenons from industrial sources—the so‐called atmospheric background—in the frame of the CTBT. Two years of Xe‐133 atmospheric background have been simulated using 2013 and 2014 meteorological data together with the most comprehensive emission inventory of radiopharmaceutical facilities and nuclear power plants to date. Annual average simulated activity concentrations vary from 0.01 mBq/m3 up to above 5 mBq/m3 nearby major sources. Average measured and simulated concentrations agree on most of the IMS stations, which indicates that the main sources during the time frame are properly captured. Xe‐133 atmospheric background simulated at IMS stations turn out to be a complex combination of sources. Stations most impacted are in Europe and North America and can potentially detect Xe‐133 every day. Predicted occurrences of detections of atmospheric Xe‐133 show seasonal variations, more accentuated in the Northern Hemisphere, where the maximum occurs in winter. To our knowledge, this study presents the first global maps of Xe‐133 atmospheric background from industrial sources based on two years of simulation and is a first attempt to analyze its composition in terms of origin at IMS stations.

Seasonal Variability of Xe‐133 Global Atmospheric Background: Characterization and Implications for the International Monitoring System of the Comprehensive Nuclear‐Test‐Ban Treaty

“…Annual average activity concentrations of Xe‐133 calculated from 2 years of simulated data, at ground level (in the layer 0–100 m AGL), from Achim et al (). Location of the main facilities releasing radioxenon in the atmosphere considered in this study: yellow circles for medical isotope production facilities (MIPs); white circles for nuclear power plants (NPPs).…”

“…However, in the case of the Xe‐133 industrial background, global emission evolutions are not known to be modeled on such long periods of time. Therefore, seasonal trends were studied based on 2 years of simulations (2013–2014) as the major sources are known over this period of time (Achim et al, ). The number of detections per month at many IMS stations is, however, too small to have significant monthly estimates.…”

“…IMS measurements include 12 h or 24 h average activity concentrations, MDC, and the critical limit (below which no amount of Xe-133 can be detected). Detections from all operational IMS stations across the globe have been used in Achim et al (2016) to validate the simulation data set for the period 2013-2014, the same one used in the present study. The overall agreement in terms of annual averages, distributions of measured activity concentrations, and variability from one station to another one (shown in Achim et al, 2016) is an indication that the dominant sources influencing the IMS network over the 2 year period are taken into account in the simulations (although large uncertainties remain in particular on the release hours).…”

“…Given this setup, it is possible to identify the dominant origin of the Xe-133 simulated at the location of IMS stations (as group of NPPs or individual MIPs). Achim et al (2016). Location of the main facilities releasing radioxenon in the atmosphere considered in this study: yellow circles for medical isotope production facilities (MIPs); white circles for nuclear power plants (NPPs).…”

“…The description of time and duration of releases in the simulations follows the available information (state-ofthe-art compiled in Achim et al (2016)). Releases of NPPs have been considered to be continuous over 24 h (following the study of Kalinowski and Tuma (2009)).…”