Update and improvement of the global krypton-85 emission inventory
Highlights
► Krypton-85 is mainly produced in nuclear reactors and released during reprocessing. ► Krypten-85 can be possibly used as an indicator for clandestine reprocessing. ► This work provides an up-to-date global krypton-85 emission inventory. ► The inventory includes emissions from all possible artificial sources.
Introduction
Extensive atmospheric emission inventories with historic data have various applications in meteorology and environmental sciences. They can be used for monitoring of air pollution, climate research or evaluation of atmospheric transport models. Important inventories are for example the Aerosol Comparisons between Observations and Models database (AeroCom) (Textor et al., 2006), the Emission Database for Global Atmospheric Research (EDGAR) (Olivier et al., 2005), the European Monitoring and Evaluation Programme (EMEP) (EMEP, 2010) and the Global Emission Inventory Activity (GEIA) (GEIA, 2011). So far, none of these inventories includes noble gases. A global emission inventory for radioactive xenon isotopes was provided by Kalinowski and Tuma (2009). The aim of the present article is to provide an emission inventory for 85Kr.
The radioactive noble gas isotope 85Kr is produced by fission of uranium or plutonium in nuclear reactors and mainly released into the atmosphere during chopping and dissolution of spent fuel in nuclear reprocessing facilities. The only significant sink for this gas is radioactive decay with a half-life of 10.76 years. Its solubility in water in the equilibrium is only 1.85 × 10−10 g/g (Izrael et al., 1982).
With these characteristics 85Kr is suited for evaluation of atmospheric transport models (Zimmermann et al., 1989) and other environmental tracer studies like groundwater age indicator (Cook and Solomon, 1995). The radioisotope is also qualified as an indicator of clandestine plutonium separation (Kalinowski et al., 2004; Kemp and Schlosser, 2008). A recent study for the German Member State Support Programme for the IAEA demonstrated how it could be used as a novel safeguard technology to expand IAEA’s existing verification tools under the Additional Protocol to the Nuclear Nonproliferation Treaty (Roß, 2010, Klingberg et al., 2010). A comprehensive emission inventory is required for an adequate simulation of the atmospheric background of 85Kr and its variability. Knowledge of the background variability is necessary for an estimation of the detectability of clandestine activities in the framework of novel technologies for IAEA safeguards (Ross et al., 2008). A historic example for the application of 85Kr in this context is the assessment of the Soviet plutonium stockpile in the 1980s (von Hippel and Levi, 1986).
The most comprehensive compilation of emission data for known reprocessing plants for the time period 1945–2000 (temporal resolution of one year) is given by Winger et al. (2005). The inventory presented in the present article is an update of that work and contains emission data of the known reprocessing sites with annual resolution from the beginning of their operation until 2009. Smaller quantities of 85Kr contributed by power reactors, naval reactors and isotope production facilities are also estimated (Sections 2 Emission inventory, 3 Assessment of the total global). In Section 4, emission characteristics of the reprocessing facilities La Hague (France) and Tokai (Japan) are investigated by analysis of hourly and daily emission data respectively. The main results are summarized in Section 5.
Section snippets
Emission inventory
A comprehensive emission inventory for 85Kr has to cover all anthropogenic sources since the beginning of nuclear activities. The most relevant source of 85Kr in the atmosphere is reprocessing of nuclear fuel. In fact, 85Kr is also produced naturally by cosmic neutrons in the atmosphere, but this contributes only 0.15 TBq per day to the global inventory and is therefore 4 orders of magnitude lower than current anthropogenic emissions (Styra and Butkus, 1991). Less than 1% of the krypton
Assessment of the total global 85Kr inventory
Nuclear reprocessing facilities contribute most of the global 85Kr background. Other small sources are power reactors, naval reactors and isotope production plants. The worldwide emissions from all power reactors are comparable to one small reprocessing plant, while the other two sources cause even lower emissions (at most a few TBq worldwide per year compared to approximately 372 TBq produced to get one significant quantity of reactor-grade plutonium, i.e. 8 kg) (Stanoszek and Kalinowski, 2009
Emission characteristics of the reprocessing facilities La Hague and Tokai
In this section the emission characteristics of the reprocessing facilities La Hague and Tokai are determined by evaluation of emission data with high temporal resolution. La Hague is the largest 85Kr emitter in Europe and therefore knowledge of emission characteristics is important for simulation of 85Kr background variability in Europe. For La Hague reprocessing facility hourly emission data are available for the years 2007 and 2008 (Schneider, 2009). Daily 85Kr emissions are available for
Conclusion
The possibility of using 85Kr for the detection of clandestine plutonium separation makes this isotope especially interesting with regard to the development of novel safeguard technologies (Ross et al., 2010; Klingberg et al., 2010). The present work provides the first comprehensive emission inventory, which is necessary to evaluate the atmospheric background of 85Kr. It is concluded that nuclear reprocessing facilities represent the most important contributors for the current background. Apart
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