Setting the baseline for estimated background observations at IMS systems of four radioxenon isotopes in 2014

Abstract

Worldwide monitoring of radionuclides is an essential part of the verification system of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) as it can provide a direct evidence of the nuclear nature of an explosion. In the case of underground nuclear testing, the radioactive noble gases, specifically radioxenon, have the highest probability to escape to the atmosphere. The detection capability of the CTBT noble gas network, which is being built, is weakened due to the presence of a worldwide civilian radioxenon background. Improving the understanding and knowledge of civilian radioxenon sources and their impact on the noble gas systems background is crucial to strengthen their verification capabilities. Two major civilian radioxenon sources have been identified in past research, namely: Medical Isotope Production Facilities (MIPFs) and Nuclear Power Plants (NPPs). In this study, a 2014 baseline radioxenon emission inventory is proposed for all four CTBT relevant radioxenon isotopes (Xe-131m, Xe-133m, Xe-133 and Xe-135) on the basis of a literature review for both the Medical Isotopes Productions Facilities and Nuclear Power Plants. This 2014 baseline radioxenon emission inventory relies on peer-reviewed information on the facility location and corresponding radioxenon emission. The baseline radioxenon emission inventory is used along with Atmospheric Transport Modelling (ATM) to estimate the radioxenon activity concentrations at the noble gas systems. The results reveal the complexity and the geographical dependence of the civilian radioxenon background. The estimations are compared to the observations for CTBT noble gas systems that were operational in 2014. It is demonstrated that the estimated Xe-133 activity concentrations are, for most systems, in the same order of magnitude than observed detections. Non-detections of Xe-131m, Xe-133m, Xe-133 and Xe-135 are, for most samples, well reproduced by the estimation. To our best knowledge, this study is the first attempt to propose, a baseline emission inventory for all four CTBT relevant radioxenon isotopes and compare the estimated Xe-131m, Xe-133m, Xe-133 and Xe-135 activity concentrations with all observations at CTBT noble gas systems during the full 2014 calendar year.

Global Radioxenon Emission Inventory from Nuclear Power Plants for the Calendar Year 2014

“…The paper of Gueibe et al (2017) uses an emission inventory that is a first simple update to Kalinowski/Tuma (2009). It still uses estimates for a generic year but takes into account which reactor were in operation in 2014.…”

“…Depending on the IMS location, NPPs contribute between zero and 80% of all observed radioxenon concentrations (Achim et al 2016). Other papers cover the release of radioxenon from nuclear research reactors (Kalinowski et al 2020) and medical isotope production facilities (Gueibe et al 2017) in the year 2014. A few medical isotope production facilities (MIPFs) are the strongest sources but all NPPs together contribute as much as one strong MIPF (Kalinowski et al 2014).…”

“…The results of Kalinowski and Tuma (2009) are supposed to be valid for a generic year. Gueibe et al (2017) adapts them to the situation in 2014 by taking the operational status of the NPPs in 2014 into consideration. The numbers of operational reactor units per site is retrieved from the IAEA (2015) database.…”

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

“…Another, complementary approach is the use of statistical methods of optimization, likely well suited for characterization of radioxenon atmospheric background. Finally, in the continuation of the work by Gueibe et al (2017), there is a need to carry on the characterization of the atmospheric background of the other radioxenons of interest (Xe-135, Xe-133m, and Xe-131m) for the monitoring of nuclear tests. Although they are less frequently detected than Xe-133, better knowledge could help anticipate issues arising with decreasing detection limits of measurement systems.…”

Radioxenon net count calculations revisited

“…(2), to properly calculate the net counts of a specific isotope, counts from other xenon isotopes and 214 Pb (interference effects) must be accounted for and subtracted. If one does not account for all the interference effects, they can bias activity concentration results [30]. To accurately determine the sample activity, interference terms must be determined during detector calibration, and implemented in the analysis equations.…”