Radioxenon Releases from A Nuclear Power Plant: Stack Data and Atmospheric Measurements

An analysis of a data set consisting of 3 years of high time resolution radioxenon stack measurements from the three nuclear reactors at the Forsmark nuclear power plant in Sweden, as well as measurements of atmospheric radioxenon in Stockholm air, 110 km away, is presented. The main causes for the stack releases, such as the function of the xenon mitigation systems, presence of leaking fuel elements, and reactor operations such as shutdown and startup, are discussed in relation to the stack data. The relation between radioxenon releases and reactor operation is clearly illustrated by the correlation between the stack measurements and thermal reactor power. In general, the isotopic ratios of the Stockholm measurements, which are shown to mainly originate from Forsmark releases, agree well with stack measurements, and with a modeled reactor operational sequence. Results from a forward atmospheric dispersion calculation agree very well with observed plume arrival times and widths, and with some exceptions, also with absolute activity concentrations. The results illustrates the importance of detailed knowledge of radioxenon emissions from nuclear power plants when interpreting radioxenon measurements for nuclear test ban verification, and provide new input to this kind of analysis. Furthermore, it demonstrates the possibility to use sensitive radioxenon detection systems to remotely detect and verify reactor operation.