Medical Isotope Production Facility Research Articles

Investigation of Radioxenon Probability Density Functions at IMS Radionuclide Stations Using a Monte Carlo Method for Background Estimation

Abstract The International Monitoring System, the primary means of verification of the Comprehensive Nuclear-Test-Ban Treaty, monitors the planet for any sign of a nuclear explosion. Regarding the International Monitoring System radionuclide stations, it is known that radioxenon released from nuclear facilities such as medical isotope production facilities and nuclear power plants influences the stations. For the purposes of monitoring nuclear explosions, it is important to better understand the radioxenon background based on these nuclear facilities. The probability density functions of background activity concentration at IMS radionuclide stations are estimated using a Monte Carlo method based on emissions from known nuclear facilities and source receptor sensitivity data. This paper describes two case studies of radioxenon detections at radionuclide stations applying the developed approach. This method could be one of several prospective approaches to predict the activity concentrations of isotopes of radioxenon at radionuclide stations in Comprehensive Nuclear Test-Ban Treaty Organization’s (CTBTO’s) prototype xenon background estimation tool software. It can also be used in characterization of CTBT-relevant nuclear events for expert technical analysis. Plain Language Summary Civil nuclear power stations and medical isotope production facilities release radioisotopes of xenon during their normal operations. These emissions would make it harder to detect xenon produced from any nuclear weapon test that might occur. A method is described that starts with information about civil releases and produces a statistical description of the concentrations of isotopes measured at stations designed to detect nuclear tests. This information makes it possible to enhance nuclear explosion detection performance.

Examining the potential for detecting simultaneous noble gas and aerosol samples in the international monitoring system radionuclide network

The purpose of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) is to establish a legally binding ban on nuclear weapon test explosions or any other nuclear explosions. The Preparatory Commission for the CTBT Organization (CTBTO PrepCom) is developing the International Monitoring System (IMS) that includes a global network of 80 stations to monitor for airborne radionuclides upon entry into force of the CTBT. All 80 radionuclide stations will monitor for particulate radionuclides and at least half of the stations will monitor for radioxenon. The airborne radionuclide monitoring is an important verification technology both for the detection of a radionuclide release and in the determination of whether the release event originates from a nuclear explosion as opposed to an industrial use of nuclear materials.Nuclear power plants and many medical isotope production facilities release radioxenon into the atmosphere. Low levels of a few particulate isotopes, such as iodine, may also be released. Detections of multiple isotopes are useful for screening the radionuclide samples for relevance to the Treaty. This paper examines the anticipated joint detections in the IMS of noble gas and particulate isotopes from underground nuclear explosions where breaches in the underground containment vents from low levels to up to 1% of the radionuclide inventory of the resulting fission products to the atmosphere. Detection probabilities are based on 844 simulated release events spaced out at 17 release locations and one year in time. Six different release (venting) scenarios, including two fractionated scenarios, were analyzed.When ranked by detection probability, 11 particulate isotopes and one noble gas isotope (133Xe) appear in the top 20 isotopes for all six release scenarios. Using the 11 particulate isotopes and the one noble gas isotope, the IMS has nearly the same detection probability as when 45 particulate and 4 noble gas isotopes are used. Thus, a limited list of relevant radionuclides may be sufficient for treaty verification purposes. The probability that at least one particulate and at least one radioxenon isotope would be detected in the IMS from the release events ranged from 0.15 to 0.86 depending on the release scenario.

Short-lived noble gas effluent trends from a research reactor

An understanding of anthropogenic sources of radioactive noble gases in the atmosphere is needed to enhance the discrimination ability of the International Monitoring System's sensors. These sources include commercial and research nuclear reactors and medical isotope production facilities. While abiding by local environmental ordinances these facilities all emit noble gas radioisotopes through normal operation. This research presents measurements and analysis of noble gas isotopes (41Ar, 135Xe, 135mXe, 137Xe, 138Xe, 87Kr, 88Kr, and 89Kr) made directly at the stack of the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory. The Xe and Kr noble gases are concurrently observed with 41Ar, a neutron activation product, when the reactor is operational. The magnitude of the Xe and Kr noble gases released is not constant over the HFIR cycle, but they temporally match the 41Ar trend. An isotope activity ratio analysis of these shorter lived isotopes combined with the observation of the cycle's temporal trend helps understand the noble gas production mechanism at the HFIR. Isotopes with short half-lives are not useful for long-range environmental monitoring. However, these measurements could potentially be combined with atmospheric modeling to predict the background source term of the longer-lived Xe ratios at a monitoring station.

Addressing the quantification of meteorological uncertainties in the atmospheric transport simulations of the 133Xe industrial background

The French National Data Center (NDC) uses an automated simulation of the 133Xe worldwide atmospheric background as one of the means to categorize the radionuclide measurements of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) International Monitoring System (IMS). These simulations take into account 133Xe releases from the known or assumed major industrial emitters in the world and global-scale meteorological data. However, a quantification of the simulation uncertainties in this operational set up is yet to be addressed. This work discusses the benefits of meteorological ensemble data as available from National Centers for Environmental Prediction (NCEP) for that purpose. For this study, the daily dispersion of releases from the Institute for Radio Elements (IRE), a medical isotope production facility located in Fleurus (Belgium), was calculated over one year with emissions measured in-site and ensemble meteorological data. The ensemble contains 31 members, which resulted in as many predictions of activity concentration for any given time and place. The resulting distribution statistics (mean, median and spread), and the control run, were confronted to the deterministic run and to measurements at one IMS-like station near Paris (France) and one IMS station in Freiburg (Germany). Overall, the ensemble results have decreased the simulation performance, as expected given the use of meteorological analyses only. However, contrasting patterns were found with a detailed analysis of daily activity concentration over two one-month-and-a-half periods. Noticeably, outlier results were found to carry the best forecast in some significant detections, proving their relevance for the measurement categorization, despite their isolated character. Importantly, the ensemble has allowed the quantification of meteorological uncertainties, which was beneficial in all cases. It either has improved the confidence of IMS data categorization or has pointed to low confidence predictions. A criterion to identify the latter is suggested, based on information provided by the ensemble distributions. In addition, maps of probability of detections and of relative spread are suggested to show additional benefits of ensemble meteorology.

Detection of anomalous radioxenon concentrations: A distribution‐free approach

AbstractThe detection of anomalous atmospheric radioxenon concentrations plays a key role in detecting both underground nuclear explosions and radioactive emissions from nuclear power plants and medical isotope production facilities. For this purpose, the CTBTO's International Data Centre uses a procedure based on descriptive thresholds. In order to supplement this procedure with a statistical inference‐based method, we compared several non‐parametric change‐point control charts for detecting shifts above the natural radioxenon background. The results indicate that the proposed methods can provide valuable tools for the institutions responsible for the verification and classification of anomalous radioxenon concentrations.

Source Term Analysis of Xenon (STAX): An effort focused on differentiating man-made isotope production from nuclear explosions via stack monitoring

An overview of the hardware and software developed for the Source Term Analysis of Xenon (STAX) project is presented which includes the data collection from two stack monitoring systems installed at medical isotope production facilities, infrastructure to transfer data to a central repository, and methods for sharing data from the repository with users. STAX is an experiment to collect radioxenon emission data from industrial nuclear facilities with the goal of developing a better understanding of the global radioxenon background and the effect industrial radioxenon releases have on nuclear explosion monitoring. A final goal of this work is to utilize collected data along with atmospheric transport modeling to calculate the contribution of a peak or set of peaks detected by the International Monitoring System (IMS) to provide desired discriminating information to the International Data Centre (IDC) and National Data Centers (NDCs). Types of data received from the STAX equipment are shown and collected data was used for a case study to predict radioxenon concentrations at two IMS stations closest to the Institute for RadioElements (IRE) in Belgium. The initial evaluation of results indicate that the data is very valuable to the nuclear explosion monitoring community.

First STAX detector installation at the National Institute for Radioelements (IRE)

The Source Term Analysis of Xenon (STAX) project has been installing stack detectors at medical isotope production facilities to measure radioxenon emissions to investigate the effect of radioxenon releases on nuclear explosion monitoring. This paper outlines the installation of the first STAX detection system at the National Institute for Radioelements (IRE) in Fleurus, Belgium which has been operating for over three years and transferring collected data to the STAX repository. Information about the equipment installed, the data flow established, and calculations for determination of radioxenon releases from the facility are presented. Data quality was investigated to confirm values reported by STAX automated data processing and in a comparison of collected STAX data with data collected by IRE for regulatory reporting.

Use of STAX data in global-scale simulation of 133Xe atmospheric background

A global-scale simulation of the 133Xe atmospheric background is automated at the French National Data Center (NDC) for the purpose of categorizing the radionuclide measurements of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) International Monitoring System (IMS). These simulations take into account 133Xe releases from all known major industrial emitters in the world, compiled from the literature and described as constant values. Emission data measured directly at the stack of the Institute for Radio Elements (IRE), a medical isotope production facility located in Fleurus (Belgium), were implemented in the simulations with a time resolution of 15 minutes. This work discusses the contribution of real (measured) emissions to the prediction of the 133Xe atmospheric background at IMS noble gas stations and at a location near Paris, for which IMS-like 133Xe measurements were available. For the purpose of this study, simulations initiated with the IRE measured emissions were run in parallel to those with the a priori emissions used to date. The benefits of including actual emissions in the simulations were found as a function of the distance between the station and the source of the release. At the closest stations, i.e., near Paris (France) and at Schauinsland, Freiburg (Germany), respectively 250 and 400 km from Fleurus, the simulated activity concentrations differed by a factor greater than 2 more than one third of the time, and by a factor of more than 5 about 10% of the time. No significant or detectable differences were found beyond 1500–2000 km. Furthermore, at the Paris station, the timing of the measured peaks was better reproduced with the actual emission data. However, not all peak amplitudes were correctly reproduced even though the real emissions were used, highlighting the remaining uncertainties, primarily in the meteorological data and transport modeling.

Using STAX data to predict IMS radioxenon concentrations

The noble gas collection and measurement stations in the International Monitoring System (IMS) are heavily influenced by releases from medical isotope production facilities. The ability to reliably model the movement of radioxenon from the points of release to these IMS samplers has improved enough that a routine aspect of the analysis of IMS radioxenon data should be the prediction of the effect of releases from industrial nuclear facilities on the sample concentrations. Predicted concentrations at IMS noble gas systems in Germany and Sweden based on measured releases from Institute for Radioelements (IRE) in Belgium and atmospheric transport modeling for a four-month period are presented and discussed.

Application of silver-exchanged zeolite for radioxenon mitigation at fission-based medical isotope production facilities

Atmospheric radioxenon releases from fission-based medical isotope production facilities are the main contributors to the radioxenon background being observed in the International Monitoring System (IMS) for the verification of the Comprehensive Nuclear-Test-Ban Treaty. This background is impacting the detection capability of the IMS network for potential nuclear explosions. Reducing the radioxenon emissions from these facilities requires the optimization of the corresponding filtration process. The investigation of more efficient Xe adsorption materials than Activated Carbon (AC), which is currently used for this application, can play an important role for such an optimization. In this work, the Xe adsorption capacity of silver-exchanged zeolites (AgZs) is compared to the one of ACs in relevant conditions for fission-based medical isotope production facilities. The most promising AgZ candidate, a silver-exchanged titanosilicate (Ag-ETS-10), is investigated in more detail for its application to further reduce radioxenon releases. As operational conditions depend on the production and off-gas treatment processes, the effect of Xe concentration, flow rate, temperature and moisture on the Xe adsorption in Ag-ETS-10 is reported. Furthermore, since AgZs are far more expensive than ACs, it is crucial to be able to regenerate the material, whilst maintaining its full Xe adsorption properties for successive reuse. Accordingly, the durability of Ag-ETS-10 is investigated with regard to desorption and adsorption cycles but also with regard to gamma irradiation.

Global Radioxenon Emission Inventory from Nuclear Research Reactors

To monitor compliance with the Comprehensive Nuclear-Test-Ban Treaty (CTBT), the International Monitoring System (IMS) is being established which will include 40 sensor systems for atmospheric xenon radioactivity. Radioactive isotopes of the noble gas xenon provide the most likely observable radioactive signatures of underground nuclear explosions. These isotopes are frequently detected by IMS noble gas systems as a result of normal operational releases from different types of nuclear facilities including nuclear power plants (NPPs), medical isotope production facilities (MIPFs), and nuclear research reactors (NRRs). Improved knowledge of the contribution of different emission sources on IMS observations strengthens the screening of radioxenon measurements to exclude observations not relevant to emissions from a nuclear explosion. The contribution of NPPs and MIPFs to the global radioxenon emission inventory is fairly well understood. NRRs have yet to be systematically assessed. This paper is the first attempt to assess the total emission inventory of NRRs expressed as annual total discharges. The results can enhance understanding of those sources most likely to impact IMS background observations and to guide future studies on contributions to IMS station background.

Analysis of environmental radioxenon detections in the UK

Radioxenon activity concentrations are monitored globally using the International Monitoring System (IMS) of the Comprehensive Nuclear-Test-Ban Treaty Organisation, improving the monitoring community's ability to detect radionuclide signatures from an underground nuclear test (UNT). An IMS-like noble gas system is in operation at AWE (Aldermaston, UK) and can collect and measure radioxenon isotopes in environmental air samples. When operated in this mode, data produced is analysed at the UK National Data Centre (NDC) and significant detection events are flagged for further investigation. This work discusses a number of significant detection events analysed using the operational system deployed at the UK NDC, which includes atmospheric transport simulations and a real-time stack-monitoring data feed from the nearest medical isotope production facility in Belgium. A comparison of the expected radionuclide contributions with measured detections is presented, including a comparison of the isotopic ratios for the radioxenon isotopes of interest (133Xe, 131mXe, 133mXe, 135Xe).

6 months of radioxenon detection in western Europe with the SPALAX-New generation system – Part 2: Atmospheric transport modelling

Atmospheric transport modeling has been used to interpret the unprecedented number of multi-isotope detections of radioxenons observed during the six months of the qualification process by the Comprehensive Nuclear-Test-Ban Treaty Organization of the new SPALAX-NG system (Système de Prélèvement Automatique en Ligne avec l’Analyse du Xénon - Nouvelle Génération). Highest 133Xe activity concentrations were found to be systematically associated with the concomitant measurement of several other radioxenons at the prevailing wind direction of north/northeast pointing to the Institute for Radio Elements (IRE), a medical isotope production facility located in Fleurus (Belgium). The lowest 133Xe activity concentrations were not associated with a prevailing wind direction or other radioxenons, indicating the contribution of distant sources (global background). The IRE's average source terms for 133mXe and to a lesser extent for 133Xe (slightly overestimated by a factor of 1.7) showed good agreement with the literature values, while corrections by a factor of ~23 and ~53 were proposed for 131mXe and 135Xe since the initial values were underestimated. However, detections of 131mXe alone and some low-activity concentrations of 133Xe associated with only one of the other radioxenons could not be linked to the IRE releases. Analysis of these cases suggests the contribution of local source releases that have been difficult to identify to date. In addition to the global background, releases from such local sources, if not identified, could affect the analysis of the isotopic ratios measured following a nuclear test. The characterization of these local contributions is now possible owing to the capacity of the SPALAX-NG and other new generation measurements systems.

Source type estimation using noble gas samples

A Bayesian source-term algorithm recently published by Eslinger et al. (2019) extended previous models by including the ability to discriminate between classes of releases such as nuclear explosions, nuclear power plants, or medical isotope production facilities when multiple isotopes are measured. Using 20 release cases from a synthetic data set previously published by Haas et al. (2017), algorithm performance was demonstrated on the transport scale (400–1000 km) associated with the radionuclide samplers in the International Monitoring System. Inclusion of multiple isotopes improves release location and release time estimates over analyses using only a single isotope. The ability to discriminate between classes of releases does not depend on the accuracy of the location or time of release estimates. For some combinations of isotopes, the ability to confidently discriminate between classes of releases requires only a few samples.

A Consideration of Radioxenon Detections Around the Korean Peninsula

The detection of radioxenon isotopes from an underground nuclear test using the International Monitoring System of the Comprehensive Nuclear Test-Ban Treaty is complicated by a radioxenon background, largely originating from the civil radioxenon emissions of medical isotope production facilities and nuclear power plant reactors. Much of the background is measured as single isotopes near the detection threshold, limiting the use of isotopic ratios which could differentiate between the possible sources. Here we introduce the UK Radionuclide National Data Centre methodology to approach the problem of radioxenon detections and source identification. Using automated analysis of radiometric data and atmospheric transport simulations, the detectability of radioxenon isotopes $${^{133}\hbox {Xe}}$$, $${^{131\mathrm{m}}\hbox {Xe}}$$, $${^{133\mathrm{m}}\hbox {Xe}}$$ and $${^{135}\hbox {Xe}}$$ from North Korea is estimated for the Takasaki radionuclide station JPX38, and the possibility of detecting $${^{133}\hbox {Xe}}$$ from selected locations across the Korean Peninsula and extended region is investigated.

Cavity-melt partitioning of refractory radionuclides and implications for detecting underground nuclear explosions

Isotopic ratios of radioxenon captured in the atmosphere can be indicators of the occurrence of an underground nuclear explosion. However, civilian sources of xenon isotopes, such as medical isotope production facilities and nuclear reactors, can interfere with detection of signals associated with nuclear testing, according to a standard model of the evolution of radioxenon isotopic abundances in a nuclear explosion cavity. We find that this standard model is idealized by not including the effects of physical processes resulting in the partitioning of the radionuclide inventory between a gas phase and rock melt created by the detonation and by ignoring seepage or continuous leakage of gases from the cavity or zone of collapse. Application of more realistic assumptions about the state of the detonation cavity results in isotopic activity ratios that differ from the civilian background more than the idealized standard model suggests, while also reducing the quantity of radioxenon available for atmospheric release and subsequent detection. Our simulations indicate that the physical evolution of the detonation cavity during the post-detonation partitioning process strongly influences isotopic evolution in the gas phase. Collapse of the cavity potentially has the greatest effect on partitioning of the refractory fission products that are precursors to radioxenon. The model allows for the possibility that post-detonation seismicity can be used to predict isotopic evolution.

Source term estimation using multiple xenon isotopes in atmospheric samples

Algorithms that estimate the location and magnitude of an atmospheric release using remotely sampled air concentrations typically involve a single chemical or radioactive isotope. A new Bayesian algorithm is presented that makes discrimination between possible types of releases (e.g., nuclear explosion, nuclear power plant, or medical isotope production facility) an integral part of the analysis for samples that contain multiple isotopes. Algorithm performance is demonstrated using synthetic data and correctly discriminated between most release-type hypotheses, with higher accuracy when data are available on three or more isotopes.

Source term estimation in the presence of nuisance signals

Many source-term estimation algorithms for atmospheric releases assume the measured concentration data are influenced only by the releases of interest. However, there are situations where identifying a short-term release from an unknown location in the presence of long-term releases from a different location is of interest. One such example is determining if part or all of a typical magnitude concentration of a radioactive isotope in a sampler came from a nuclear explosion, such as the explosion announced by DPRK in 2013, while medical isotope facilities and nuclear power plants were also operating in the region.An estimation algorithm has been developed for the case where a short-duration release is confounded by a long-term nuisance signal associated with an additional release location. The technique is demonstrated using synthetic release data for a hypothetical medical isotope production facility and a hypothetical puff release from a different location. The algorithm successfully determines the location (within 30 km) and time-varying release rate (within a factor of 2) for the medical isotope production facility and the location (within 60 km), time (within 6 h), and release magnitude (within a factor of 4) of the puff release.

Spectroscopic noble gas stack monitor with continuous unattended operation and analysis

A spectroscopic stack monitoring system for the measurement of noble gasses discharged from medical isotope production facility and nuclear power plant stacks has been designed and a prototype constructed. The prototype is based on a Marinelli beaker style HPGe measurement operating in a continuous acquisition mode. Continuous acquisition is accomplished with novel software and hardware which allows for unattended acquisition, analysis, and storage of data over multiple workflow definitions. As a direct result of the multiple averaging times and the use of the transistor reset preamplifier, the dynamic range of the system covers nearly 8 orders of magnitude.

Radiation Attenuation and Stability of ClearView Radiation Shielding TM-A Transparent Liquid High Radiation Shield.

Radiation exposure is a limiting factor to work in sensitive environments seen in nuclear power and test reactors, medical isotope production facilities, spent fuel handling, etc. The established choice for high radiation shielding is lead (Pb), which is toxic, heavy, and abidance by RoHS. Concrete, leaded (Pb) bricks are used as construction materials in nuclear facilities, vaults, and hot cells for radioisotope production. Existing transparent shielding such as leaded glass provides minimal shielding attenuation in radiotherapy procedures, which in some cases is not sufficient. To make working in radioactive environments more practicable while resolving the lead (Pb) issue, a transparent, lightweight, liquid, and lead-free high radiation shield-ClearView Radiation Shielding-(Radium Incorporated, 463 Dinwiddie Ave, Waynesboro, VA). was developed. This paper presents the motivation for developing ClearView, characterization of certain aspects of its use and performance, and its specific attenuation testing. Gamma attenuation testing was done using a 1.11 × 10 Bq Co source and ANSI/HPS-N 13.11 standard. Transparency with increasing thickness, time stability of liquid state, measurements of physical properties, and performance in freezing temperatures are reported. This paper also presents a comparison of ClearView with existing radiation shields. Excerpts from LaSalle nuclear power plant are included, giving additional validation. Results demonstrated and strengthened the expected performance of ClearView as a radiation shield. Due to the proprietary nature of the work, some information is withheld.