Preparation of a Global Radioxenon Emission Inventory: Understanding Sources of Radioactive Xenon Routinely Found in the Atmosphere by the International Monitoring System for the Comprehensive Nuclear-Test-Ban Treaty
Last updated: October 21, 2008
Authors
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Martin B. Kalinowski |
Published by Program in Arms Control, Disarmament, and International Security (ACDIS), University of Illinois at Urbana-Champaign
ACDIS Research Report series
December 2005
Full text [PDF]Summary
The Comprehensive Nuclear-Test-Ban Treaty (CTBT) was opened for signature in 1996. In 1997 the Provisional Technical Secretariat began building up the verification system as part of the International Monitoring System (IMS). When completed, forty to eighty stations will monitor the atmosphere for radioactive xenon.Four radioactive xenon isotopes are the best indicators of nuclear weapon tests: Xe-135, Xe-133m, Xe-133 and Xe-131m. The challenge for verification of compliance with the CTBT based on atmospheric radioxenon is created by the fact that all nuclear reactors are constantly emitting these isotopes as normal operational releases. The background concentration of Xe-133 in the northern hemisphere is in the order of the detection limit at about 1 mBq/m3. The other three isotopes have typical concentrations below the detection limit and are seen only during the passage of a plume with elevated concentrations over the detector site.
In order to improve the interpretation of measurements as possible indications of a nuclear test in the presence of high background caused by civilian facilities, it is crucial to establish an understanding of what levels of concentrations could be expected as normal at the radionuclide station sites, which may vary depending upon seasonal and weather related conditions.
The goal of the project described in this research paper is to prepare a database on global radioxenon emissions from nuclear reactors. There are more than 400 power reactors and about fifty large research reactors that have to be taken into consideration. The most accurate data are based on effluent data reported by the respective facility operator. The emissions of those reactors for which no reported data are available are estimated from suitable reactor parameters such as fuel inventory or power output. Various reactor parameters are investigated and the ones providing the most precise relationships with fission gas activity releases are used for scaling.
The resulting emission inventory shall be used as input to global atmospheric transport models to determine the global distribution of the four relevant radioactive xenon isotopes. Their atmospheric background concentration as well as the deviations from their averages shall be determined climatologically, i.e. depending on seasonal weather patterns. The background concentration at all IMS measurement sites is particularly of high interest. These stations have a time resolution of eight, twelve, or twenty-four hours. This is much better than the current standard of taking weekly samples, and it will be possible to resolve passages of fresh plumes with sharp concentration gradients. This time resolution will allow the application of methods for atmospheric transport modeling in order to determine the source location.