<p>Radionuclide monitoring is one of the verification technologies of the global verification system of the Comprehensive Nuclear-Test-Ban Treaty (CTBT). This global network of sampling stations senses the air 24/7 for suspect noble gases and/or particulates. For noble gases this task is non-trivial due to the ever-present and highly variable background levels of the four radioxenon isotopes that are relevant for CTBT monitoring. An extensive, global effort was initiated to better estimate the civil radioxenon background based on known sources and end up with a more reliable event screening. This challenge, called &#8220;1st Nuclear Explosion Signal Screening Open Inter-Comparison Exercise 2021,&#8221; provided an assessment of a chain of multilevel, multidisciplinary scientific analyses and built on three previous atmospheric transport modelling (ATM) Challenges. It&#8217;s a first since it explored integrating both ATM and radionuclide statistical expertise to characterize the detection, time, location, and source strength of an anomalous event. The exercise ran through 2022 and was a collaboration between participants from around the world who utilized a comprehensive pre-developed test data set based on explosion release scenarios, xenon measurements and emission inventories, and atmospheric transport data provided by the ATM software FLEXPART. The data set was composed of synthetic activity concentrations of the simulated nuclear explosion signals added to the radioxenon measurements at the International Monitoring Station (IMS). Three levels of participation were offered, requiring different areas of expertise: 1) ATM expertise only, where participants simulated radioxenon background time series at the 23 IMS stations to be used as input for screening synthetic radioxenon measurements based on a set of predefined statistical methods; 2) radionuclide expertise, where participants provided their own methods and results for detection, screening, and timing powers; and 3) higher-level ATM and statistical expertise, where, in addition to Level 2, results were provided for location and magnitude estimates for a few selected test cases. This paper gives a general overview of the exercise and provides highlights and discusses the key results.</p>
Ausbreitungsmodelle liefern in der Regel Stundenwerte von Immissionskonzentrationen. Für die Geruchswahrnehmung sind jedoch Spitzen im Zeitbereich eines menschlichen Atemzuges von wenigen Sekunden entscheidend. In den letzten Jahrzehnten wurden verschiedene Ansätze zur Berücksichtigung dieser kurzfristigen Spitzenwerte in Ausbreitungsmodellen entwickelt. In dieser Untersuchung werden drei Methoden, nämlich der konstante Faktor 4 der Technischen Anleitung zur Reinhaltung der Luft (TA Luft), der stabilitätsabhängige peak-to-mean-Ansatz nach Schauberger und Piringer sowie das Konzentrations-Varianz-Modell von Öttl und Ferrero verwendet, um mit dem Ausbreitungsmodell LASAT richtungsabhängige Schutzabstände unter gegenwärtigen und zukünftigen klimatischen Bedingungen zu berechnen und zu vergleichen. Die meteorologischen Daten wurden mit einem regionalen Klimamodell für das gegenwärtige und das künftige Klima ermittelt. Betrachtet werden zwei Bereiche nördlich und südlich des österreichischen Alpenhauptkamms. Erwartungsgemäß werden mit dem Faktor 4 die größten Schutzabstände errechnet, gefolgt vom Konzentrations-Varianz-Ansatz und dem stabilitätsabhängigen peak-to-mean-Ansatz. In Österreich wird in Zukunft bei Geruchsexpertisen und in Genehmigungsverfahren der Konzentrations-Varianz-Ansatz in Kombination mit einem Lagrange-Ausbreitungsmodell verwendet werden.
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