Gamma-spectrometry measurements of filtration media from an Advanced Gas-cooled Reactor.

Filtration media used to quantify particulate and gaseous releases have been collected from Hartlepool Power Station in the United Kingdom and measured using high-sensitivity gamma-spectrometry systems. Radionuclides that are relevant to the monitoring regime of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) have been detected. Results are reported and compared to detections recorded on the International Monitoring System (IMS). Time series activity plots have been produced and results interpreted with respect to known plant activities. The reported results improve the understanding of trace-level radionuclide emissions from Advanced Gas-cooled Reactors (AGRs) and aid interpretation of IMS measurements. This work is being performed as part of the Xenon Environmental Nuclide Analysis at Hartlepool (XENAH) collaboration between the Atomic Weapons Establishment (AWE, UK), EDF Energy (UK), Pacific Northwest National Laboratory (PNNL, US) and the Swedish Defence Agency (FOI, Sweden).

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.

SAUNA III - The next generation noble gas system for verification of nuclear explosions.

The SAUNA III represent the next generation of the SAUNA systems designed for detection of low levels of radioactive xenon in the atmosphere, with the main purpose of detecting underground nuclear explosions. The system automatically collects, processes and measures 40 m3 atmospheric samples every 6 h, increasing both the sensitivity and time resolution as compared the systems currently in use. The higher sensitive increases the number of detections, especially for samples were more than one isotope of xenon are detected. This improves the understanding of the background and the possibility to screen out signal from civilian sources. The increased time resolution of the new system also provides a more detailed picture of the plumes, especially important for near-by sources. The design of the system as well as data from the first two years of operation are presented.

Impact of the noble gas system NEX48 in Niger on the radioxenon global network coverage for the International Monitoring System of the comprehensive nuclear-test-ban treaty.

The radioxenon measurement components of the International Monitoring System (IMS) of the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) play a significant role in uncovering clandestine nuclear weapons tests. The radioxenon network coverage is a critical component of the IMS capabilities. NEX48 is one of the still to-be-certified radioxenon stations and it will be the only IMS station with radioxenon measurement capabilities in the Sahara desert in Central Africa. Therefore, it may increase the radioxenon global coverage in a vast region. Seasonal contributions from NEX48 (in Niger) on the 133Xe global coverage of the IMS have been investigated in current and complete (39 stations) networks for a hypothetical one-kt subsurface nuclear explosion using atmospheric transport modelling. Adding NEX48 to the stations currently operating increased the daily global coverage by about 1.1 percent on average with most of the improvement between 15-45 N latitudes and 0-40 E longitudes. The improvements from adding NEX48 vary greatly by the seasons of the year. Removing NEX48 from the complete network leads to a daily coverage deterioration of about 0.2 percent, and the cumulative minimum coverage has a significant change.

SAUNA field - A sensitive system for analysis of radioxenon in soil gas samples.

A high throughput system for processing and detection of low levels of radioxenon in soil gas samples has been developed. Processing and analysis of sub-soil noble gas samples puts high demands on the gas separation part of the system since the samples might contain high levels of Rn, CO2 as well as other gases. The gas process is optimized to remove all CO2, H2O and Rn with a high recovery yield of the xenon in the sample to ensure a high sensitivity even for small samples. The system is designed to handle multiple samples per day with a high level of automation and sample traceability to be suitable for use in an on-site inspection (OSI) an important component in the verification of the Comprehensive Nuclear Test Ban Treaty. To ensure a rapid deployment the system could be pre-installed in a flight container.

Measurement of radioxenon and radioargon in soil gas collected in the region of Kvarntorp, Sweden.

Over 40 soil gas samples were collected both in post-industrial areas as well as in undisturbed areas in the region of Kvarntorp, Sweden. Radioxenon (133Xe) was detected in 15 samples and radioargon was detected in 7 from 10 samples analysed. The concentration of radioxenon and radioargon in soil gas ranged up to 109 mBq/m3 and 19 mBq/m3, respectively. During sample collection other soil gases such as radon, CO2 and O2 were also measured and soil samples were taken along with dose rate measurements. The field experiment presented here shows that it is possible to detect naturally occurring radioxenon and radioargon in soil gas simultaneously.

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.

Design and development of radioactive xenon gas purification and analysis system based on molecular sieves.

The dynamic adsorption of xenon on molecular sieve packed columns was investigated. The modified Wheeler-Jonas equation was used to describe adsorption parameters such as adsorption capacity and adsorption rate coefficient. Different experimental conditions were accomplished to study their effects and to touch appropriate adsorbing circumstances. Respectable consistency was reached between experimental and modeled values. A purification and analysis setup was developed for radioactive xenon gas determination. Standard sample analysis results approved acceptable quantification accuracy.

The 2014 Integrated Field Exercise of the Comprehensive Nuclear-Test-Ban Treaty revisited: The case for data fusion.

The International Monitoring System of the Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) uses a global network of radionuclide monitoring stations to detect evidence of a nuclear explosion. The two radionuclide technologies employed-particulate and noble gas (radioxenon) detection-have applications for data fusion to improve detection of a nuclear explosion. Using the hypothetical 0.5 kT nuclear explosive test scenario of the CTBTO 2014 Integrated Field Exercise, the intrinsic relationship between particulate and noble gas signatures has been examined. This study shows that, depending upon the time of the radioxenon release, the particulate progeny can produce the more detectable signature. Thus, as both particulate and noble gas signatures are inherently coupled, the authors recommend that the sample categorization schemes should be linked.

SPALAX new generation: New process design for a more efficient xenon production system for the CTBT noble gas network.

The SPALAX (Système de Prélèvement Automatique en Ligne avec l'Analyse du Xénon) is one of the systems used in the International Monitoring System of the Comprehensive Nuclear Test Ban Treaty (CTBT) to detect radioactive xenon releases following a nuclear explosion. Approximately 10 years after the industrialization of the first system, the CEA has developed the SPALAX New Generation, SPALAX-NG, with the aim of increasing the global sensitivity and reducing the overall size of the system. A major breakthrough has been obtained by improving the sampling stage and the purification/concentration stage. The sampling stage evolution consists of increasing the sampling capacity and improving the gas treatment efficiency across new permeation membranes, leading to an increase in the xenon production capacity by a factor of 2-3. The purification/concentration stage evolution consists of using a new adsorbent Ag@ZSM-5 (or Ag-PZ2-25) with a much larger xenon retention capacity than activated charcoal, enabling a significant reduction in the overall size of this stage. The energy consumption of the system is similar to that of the current SPALAX system. The SPALAX-NG process is able to produce samples of almost 7 cm(3) of xenon every 12 h, making it the most productive xenon process among the IMS systems.

High resolution monitoring system for IRE stack releases.

The main activity of IRE (Institute for Radio-Element) is radioisotope production of bulk (99)Mo and (131)I for medical application (diagnosis and therapy). Those isotopes are chemically extracted from HEU (High Enriched Uranium) targets activated in reactors. During this process, fission products are released from the targets, including noble gases isotopes (Xe and Kr). Like any nuclear plant, IRE has release limits which are given by the Belgium authority and moreover IRE is in the process of continuously reducing the level of its releases. To achieve this mission, the need of an accurate tool is necessary and IRE has developed a specific monitoring system using a high resolution detector in order to identify and accurately estimate its gaseous releases. This system has a continuous air sampling system in the plant main stack. The sampled gases cross charcoal cartridges where they are slowed down and concentrated for higher detection efficiency. In front of those cartridges is installed an HPGe detector with a detection chain connected to a specific analysis system allowing on-line spectrum analysis. Each isotope can be separately followed without interferences, especially during the production process where high activity can be released. Due to its conception, the system also allows to measure iodine isotopes by integration on the charcoal cartridges. This device is of great help for accurately estimate IRE releases and to help for understanding specific releases and their origin in the production or maintenance process.

The determination of trace amounts of natural 133Xe in gas under high radon activity concentration levels.

Radioxenon monitoring has become one of the major concerns in both international monitoring systems and on-site inspection. The most important technical specifications for radioxenon system are the radon removal coefficient and the minimum detectable activity concentration. We have developed one kind of on-site radioxenon sampling, separation and measurement system, and have tested it under high radon activity concentration levels. The result shows the natural (133)Xe background activity concentration, the (133)Xe/(222)Rn ratio and the radon removal coefficient to be in the ranges 0.73-1.6 mBq/m(3), (1.5-3.5) × 10(-8) and (2.3-57) × 10(-8), respectively.

An automated multidimensional preparative gas chromatographic system for isolation and enrichment of trace amounts of xenon from ambient air.

The monitoring of radioactive xenon isotopes is one of the principal methods for the detection of nuclear explosions in order to identify clandestine nuclear testing. In this work, a miniaturized, multiple-oven, six-column, preparative gas chromatograph was constructed in order to isolate trace quantities of radioactive xenon isotopes from ambient air, utilizing nitrogen as the carrier gas. The multidimensional chromatograph comprised preparative stainless steel columns packed with molecular sieves, activated carbon, and synthetic carbon adsorbents (e.g., Anasorb®-747 and Carbosphere®). A combination of purification techniques--ambient adsorption, thermal desorption, back-flushing, thermal focusing, and heart cutting--was selectively optimized to produce a well-defined xenon peak that facilitated reproducible heart cutting and accurate quantification. The chromatographic purification of a sample requires approximately 4 h and provides complete separation of xenon from potentially interfering components (such as water vapor, methane, carbon dioxide, and radon) with recovery and accuracy close to 100%. The preparative enrichment process isolates and concentrates a highly purified xenon gas fraction that is suitable for subsequent ultra-low-level γ-, ß/γ-spectroscopic or high-resolution mass spectrometric measurement (e.g., to monitor the gaseous fission products of nuclear explosions at remote locations). The Xenon Processing Unit is a free-standing, relatively lightweight, and transportable system that can be interfaced to a variety of sampling and detection systems. It has a relatively inexpensive, rugged, and compact modular (19-inch rack) design that provides easy access to all parts for maintenance and has a low power requirement.

Isotopic noble gas signatures released from medical isotope production facilities--simulations and measurements.

Radioxenon isotopes play a major role in confirming whether or not an underground explosion was nuclear in nature. It is then of key importance to understand the sources of environmental radioxenon to be able to distinguish civil sources from those of a nuclear explosion. Based on several years of measurements, combined with advanced atmospheric transport model results, it was recently shown that the main source of radioxenon observations are strong and regular batch releases from a very limited number of medical isotope production facilities. This paper reviews production processes in different medical isotope facilities during which radioxenon is produced. Radioxenon activity concentrations and isotopic compositions are calculated for six large facilities. The results are compared with calculated signals from nuclear explosions. Further, the outcome is compared and found to be consistent with radioxenon measurements recently performed in and around three of these facilities. Some anomalies in measurements in which (131m)Xe was detected were found and a possible explanation is proposed. It was also calculated that the dose rate of the releases is well below regulatory values. Based on these results, it should be possible to better understand, interpret and verify signals measured in the noble gas measurement systems in the International Monitoring of the Comprehensive Nuclear-Test-Ban Treaty.

Notes on radioxenon measurements for CTBT verification purposes.

The verification of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) includes, beside three different waveform techniques, global monitoring of radioactive aerosols and noble gases. The noble gases are difficult to contain for the illicit tester and are therefore of particular importance to identify signals from underground or underwater nuclear tests. Several isotopes of xenon are sufficiently produced in fission and a few have suitable half-lives and radiations to be detected. These are (131m)Xe, (133m)Xe, (133)Xe and (135)Xe and they have been selected for continuous monitoring. Four different systems have been developed to sample and measure them. Three of them use cryogenic or room-temperature gas chromatography processes and one a membrane technology. One measures by gamma spectroscopy, two by beta-gamma coincidence spectroscopy and one by beta-gated gamma spectroscopy. These systems are now undergoing trials at worldwide locations in the so-called International Noble Gas Experiment (INGE). In parallel, specific analytical software is being developed to examine the spectra produced by these different systems. This paper presents results from data acquired both from regions having a high radioxenon background and from remote low background stations.

133Xe contamination found in internal bacteria filter of xenon ventilation system.

OBJECTIVE: We report on (133)Xe contamination found in the reusable internal bacteria filter of our xenon ventilation system. METHODS: Internal bacteria filters (n = 6) were evaluated after approximately 1 mo of normal use. The ventilation system was evacuated twice to eliminate (133)Xe in the system before removal of the filter. Upon removal, the filter was monitored using a survey meter with an energy-compensated probe and was imaged on a scintillation camera. The filter was monitored and imaged over several days and was stored in a fume hood. RESULTS: Estimated (133)Xe activity in each filter immediately after removal ranged from 132 to 2,035 kBq (3.6-55.0 micro Ci), based on imaging. Initial surface radiation levels ranged from 0.4 to 4.5 micro Sv/h (0.04-0.45 mrem/h). The (133)Xe activity did not readily leave the filter over time (i.e., time to reach half the counts of the initial decay-corrected image ranged from <6 to >72 h). The majority of the image counts (approximately 70%) were seen in 2 distinctive areas in the filter. They corresponded to sites where the manufacturer used polyurethane adhesive to attach the fiberglass filter medium to the filter housing. CONCLUSION: (133)Xe contamination within the reusable internal bacteria filter of our ventilation system was easily detected by a survey meter and imaging. Although initial activities and surface radiation levels were low, radiation safety practices would dictate that a (133)Xe-contaminated bacteria filter be stored preferably in a fume hood until it cannot be distinguished from background before autoclaving or disposal.

A method for determining leakage of 133Xe gas from septum-sealed glass vials.

We have developed a method for determining the leakage of 133Xe gas from septum-sealed glass vials that are supplied for medical examinations. Twenty vials each originally containing 370 MBq of 133Xe and 20 vials each originally containing 740 MBq 133Xe were measured daily for 26 d. Retention of 133Xe within the vial was modeled as a first order process with a constant rate coefficient, lambdaT. The value of lambdaT was estimated for each vial using a regression analysis. The leakage rate, lambdaL, was then determined assuming that lambdaT = lambdaL + lambda(r) where lambda(r) represents the physical decay of 133Xe. Monte Carlo simulations were performed using uncertainties in the estimates of each vial to obtain the mean and tails of the distribution for the average leakage rate, lambdaL. The average leakage rate for the complete sample of vials was 0.00007 d(-1) with an upper, one-sided, 95% confidence limit of 0.0011 d(-1). Uncertainties in the published values of lambda(r) for 133Xe made a significant contribution to the uncertainties of the leakage rate for this sample of vials. The methods described can be applied to other situations where leakage of radioactive materials may be of concern.

Effect of major surgery on absorption rate of NPH insulin injected s.c.

The absorption rate of NPH insulin injected s.c. was evaluated before operation and on the day of surgery by continuous measurements of residual radioactivity of 125I-labelled insulin in 10 patients undergoing major abdominal surgery. The results show that major surgery has no effect on rate of absorption of intermediate acting insulin.