Monitoring Of Nuclear Explosions Research Articles

Impact of Environmental Backgrounds on Atmospheric Monitoring of Nuclear Explosions

Impact of Environmental Backgrounds on Atmospheric Monitoring of Nuclear Explosions

Updates to the Regional Seismic Travel Time (RSTT) Model: 1. Tomography

A function of global monitoring of nuclear explosions is the development of Earth models for predicting seismic travel times for more accurate calculation of event locations. Most monitoring agencies rely on fast, distance-dependent one-dimensional (1D) Earth models to calculate seismic event locations quickly and in near real-time. RSTT (Regional Seismic Travel Time) is a seismic velocity model and computer software package that captures the major effects of three-dimensional crust and upper mantle structure on regional seismic travel times, while still allowing for fast prediction speed (milliseconds). We describe updates to the RSTT model using a refined data set of regional phases (i.e., Pn, Pg, Sn, Lg) using the Bayesloc relative relocation algorithm. The tomographic inversion shown here acts to refine the previous RSTT public model (rstt201404um) and displays significant features related to areas of global tectonic complexity as well as further reduction in arrival residual values. Validation of the updated RSTT model demonstrates significant reduction in median epicenter mislocation (15.3 km) using all regional phases compared to the iasp91 1D model (22.1 km) as well as to the current station correction approach used at the Comprehensive Nuclear-Test-Ban Treaty Organization International Data Centre (18.9 km).

Identifying the possible source regions of elevated concentrations of Xenon-133 detected at the Takasaki Radionuclide Monitoring Station (JPX38) on 2 October 2017: Malaysian CTBT National Data Centre (MY-NDC) findings

A couple of elevated concentrations of noble gas Xenon-133 were detected at the Takasaki Radionuclide Monitoring Station (JPX38) on 2 October 2017. Xenon-133 is among four relevant radioxenon isotopes that are used for monitoring and verification of nuclear explosions including Xenon-13, Xenon-133m and Xenon-131m. These radioxenon gases could be emitted either from nuclear explosion or civil nuclear facilities including medical isotopes production facilities, nuclear power reactors and nuclear research reactors. This paper presents the Malaysian CTBT National Data Centre (MY-NDC) findings in identifying the possible source regions for elevated concentrations of Xenon-133 detected at JPX38 on 2 October 2017. The findings will be useful in understanding the possible source of release for such Xenon-133 detection, whether coming from a late release of the 3 September 2017 North Korea nuclear test site or from civil nuclear facilities.

Multi-scale fracture damage associated with underground chemical explosions

Understanding rock damage induced by explosions is critical for a number of applications including the monitoring and verification of underground nuclear explosions, mine safety issues, and modeling fluid flow through fractured rock. We use core observations, televiewer logs, and thin section observations to investigate fracture damage associated with two successive underground chemical explosions (SPE2 and SPE3) in granitic rock at both the mesoscale and microscale. We compare the frequency and orientations of core-scale fractures, and the frequency of microfractures, between a pre-experiment core and three post-experiment cores. Natural fault zones and explosion-induced fractures in the vicinity of the explosive source are readily apparent in recovered core and in thin sections. Damage from faults and explosions is not always apparent in fracture frequency plots from televiewer logs, although orientation data from these logs suggests explosion-induced fracturing may not align with the pre-existing fracture sets. Core-scale observations indicate the extent of explosion-induced damage is 10.0 m after SPE2 and 6.8 m after SPE3, despite both a similar size and location for both explosions. At the microscale, damage is observed to a range distance of 10.2 ± 0.9 m after SPE2, and 16.6 ± 0.9 and 11.2 ± 0.6 in two different cores collected after SPE3. Additional explosion-induced damage, interpreted to be the result of spalling, is readily apparent near the surface, but only in the microfracture data. This depth extent and intensity of damage in the near-surface region also increased after an additional explosion. This study highlights the importance of evaluating structural damage at multiple scales for a more complete characterization of the damage, and particularly shows the importance of microscale observations for identifying spallation-induced damage.

The history and outlook for seismic monitoring of nuclear explosions in the context of the Comprehensive Nuclear-Test-Ban Treaty

ABSTRACTModern methods of nuclear-explosion monitoring are vastly more capable than they were when underground nuclear testing began in the late 1950s, in part because a cycle of improvements in explosion monitoring in the 1960–80 period led to improvements in monitoring for earthquakes and other phenomena, which then led to a general growth in monitoring assets that in turn has been applied back to explosion monitoring. Practical experiences in nuclear-explosion monitoring, acquired during the era of active testing prior to finalization of the CTBT text in 1996, laid the basis for monitoring in support of this arms-control initiative. This article elaborates on the future of nuclear-test-monitoring technology, which can build upon an additional and remarkable growth of general monitoring assets that began in the 1990s, largely unrelated to the specifics of nuclear-test monitoring. A new cycle of improvements in earthquake monitoring is likely to improve monitoring for explosions. While it is not easy to quantify the degree of monitoring improvement afforded by such new assets, an example from North Korea indicates the improvement can be substantial.

Towards global seismic monitoring of underground nuclear explosions using waveform cross correlation. Part II: Synthetic master events

Towards global seismic monitoring of underground nuclear explosions using waveform cross correlation. Part II: Synthetic master events

Development of Industrial-Scale Fission 99Mo Production Process Using Low Enriched Uranium Target

Abstract Molybdenum-99 (99Mo) is the most important isotope because its daughter isotope, technetium-99m (99mTc), has been the most widely used medical radioisotope for more than 50 years, accounting for > 80% of total nuclear diagnostics worldwide. In this review, radiochemical routes for the production of 99Mo, and the aspects for selecting a suitable process strategy are discussed from the historical viewpoint of 99Mo technology developments. Most of the industrial-scale 99Mo processes have been based on the fission of 235U. Recently, important issues have been raised for the conversion of fission 99Mo targets from highly enriched uranium to low enriched uranium (LEU). The development of new LEU targets with higher density was requested to compensate for the loss of 99Mo yield, caused by a significant reduction of 235U enrichment, from the conversion. As the dramatic increment of intermediate level liquid waste is also expected from the conversion, an effective strategy to reduce the waste generation from the fission 99Mo production is required. The mitigation of radioxenon emission from medical radioisotope production facilities is discussed in relation with the monitoring of nuclear explosions and comprehensive nuclear test ban. Lastly, the 99Mo production process paired with the Korea Atomic Energy Research Institute's own LEU target is proposed as one of the most suitable processes for the LEU target.

Towards global seismic monitoring of underground nuclear explosions using waveform cross correlation. Part I: Grand master events

Waveform cross correlation is an efficient tool for detection and characterization of seismic signals. For the purposes of the Comprehensive Nuclear-Test-Ban Treaty, cross correlation can globally reduce the threshold of detection by 0.3 to 0.4 magnitude units. However, the technique critically depends on the availability of master events. In Part I of this paper, we have demonstrated that in seismically active regions the best master events (grand-masters) replicated over a regular grid allow improving the efficiency of signal detection and event finding. In aseismic areas, there are two approaches to populate the global grid of master events for the International Monitoring System: the replication of grand-masters and calculation of synthetic seismograms for master-events in the global grid nodes. The efficiency of synthetic templates depends on the accuracy of shape and amplitude predictions controlled by focal depth and mechanism, source function, velocity structure and attenuation along the master/station path. Here we test three focal mechanisms (explosion, thrust fault, and actual Harvard CMT solution for one of the April 11, 2012 Sumatra aftershocks) and two velocity structures (ak135 and CRUST 2.0). Sixteen synthetic master events were distributed over a 1° × 1° grid covering the zone of aftershocks. We built five cross correlation standard event lists (XSEL) and compared detections and events with those built using the real and grand master events as well as with the Reviewed Events Bulletin of the International Data Centre. The XSELs were built using an explosion source and ak135 and the reverse fault with isotropic radiation pattern to demonstrate the performance similar to that of the real and grand masters. Here we have proved quantitatively that it is possible to cover all aseismic areas with synthetic masters without significant loss in seismic monitoring capabilities based on cross correlation.

Determination of the Global Coverage of the IMS Xenon-133 Component for the Detection of Nuclear Explosions

Radioxenon is an important atmospheric tracer to detect underground nuclear explosions. The International Monitoring System is designed to provide worldwide continuous physical monitoring and detection of nuclear explosions and incorporates 40 noble gas monitoring stations. They are constantly sampling the atmosphere for concentrations of radioxenon. This work analyses how effectively the network of stations is able to detect unusual xenon-133 concentrations in the atmosphere. A large multitude of nuclear explosions, evenly distributed in space and time, is simulated and the detection rate is calculated. Atmospheric transport modelling is applied to calculate the source-receptor-sensitivities for each monitoring station. The approach includes the anthropogenic radioxenon background, station-specific detection criteria, different scenarios for surface and subsurface nuclear explosions, and a spatial as well as a time dependent analysis. Recommendations are drawn for the improvement of the detection capability.

Potential impact of releases from a new Molybdenum-99 production facility on regional measurements of airborne xenon isotopes

The monitoring of the radioactive xenon isotopes 131mXe, 133Xe, 133mXe, and 135Xe is important for the detection of nuclear explosions. While backgrounds of the xenon isotopes are short-lived, they are constantly replenished from activities dominated by the fission-based production of 99Mo used for medical procedures. At present, one of the most critical locations on earth for the monitoring of nuclear explosions is the Korean peninsula where the Democratic People's Republic of Korea (DPRK) has announced that it conducted three nuclear tests between 2006 and 2013. This paper explores the backgrounds that would be caused by the medium to large scale production of 99Mo in the region of the Korean peninsula.

Ten Years of Development of Equipment for Measurement of Atmospheric Radioactive Xenon for the Verification of the CTBT

Atmospheric measurement of radioactive xenon isotopes (radioxenon) plays a key role in remote monitoring of nuclear explosions, since it has a high capability to capture radioactive debris for a wide range of explosion scenarios. It is therefore a powerful tool in providing evidence for nuclear testing, and is one of the key components of the verification regime of the Comprehensive Nuclear-Test-Ban Treaty (CTBT). The reliability of this method is largely based on a well-developed measurement technology. In the 1990s, with the prospect of the build-up of a monitoring network for the CTBT, new development of radioxenon equipment started. This article summarizes the physical and technical principles upon which the radioxenon technology is based and the advances the technology has undergone during the last 10 years. In contrast to previously used equipment, which was manually operated, the new generation of radioxenon monitoring equipment is designed for automated and continuous operation in remote field locations. Also the analytical capabilities of the equipment were strongly enhanced. Minimum detectable concentrations of the recently developed systems are well below 1 mBq/m3 for the key nuclide 133Xe for sampling periods between 8 and 24 h. All the systems described here are also able to separately measure with low detection limits the radioxenon isotopes 131mXe, 133mXe and 135Xe, which are also relevant for the detection of nuclear tests. The equipment has been extensively tested during recent years by operation in a laboratory environment and in field locations, by performing comparison measurements with laboratory type equipment and by parallel operation. These tests demonstrate that the equipment has reached a sufficiently high technical standard for deployment in the global CTBT verification regime.

High-precision Location of North Korea's 2009 Nuclear Test

On 25 May 2009, the Democratic People's Republic of Korea (North Korea) announced that it had conducted a second nuclear test, without providing information of exact time, location, and yield. On that day, the United States Geological Survey (USGS) reported detecting a magnitude 4.7 seismic tremor in an aseismic region in North Korea (http://earthquake.usgs.gov/eqcenter/recenteqsww/Quakes/us2009hbaf.php; also archived copy at http://geophysics.geo.sunysb.edu/wen/NK/usgs\_north\_korea\_2009\_test.webarchive). The seismic waveform features recorded at the seismic stations around the globe for the event exhibit characteristics of an explosion. However, the exact location of the test remains elusive. Seismic monitoring of underground nuclear explosions relies on seismic observations recorded by seismometers around the globe. Because seismic observations are influenced by the seismic properties along the paths of the wave propagation from the source to the seismometers, the accuracy of determination of an event location and time depends on the degree of our knowledge of the seismic properties in the interior of the Earth. The challenge in accurately determining the location of North Korea's nuclear tests stems from the fact that, due to the lack of seismic stations and seismicity in the region, the seismic structure is not known in enough detail that its influence can be well calibrated. For example, the horizontal uncertainty of the 2009 event location reported by the USGS is about ±3.8 km (http://earthquake.usgs.gov/eqcenter/recenteqsww/Quakes/us2009hbaf.php). While our knowledge of the seismic structure in the region is unlikely to improve soon, in this study we demonstrate a strategy that uses the forensic evidence registered by North Korea's 2006 nuclear test to determine the location of the 2009 test in high precision, and we present our determination of the location of the 2009 test. ### Scientific Evidence Registered by the 2006 Test The possible location of North Korea's 2006 test is identified by satellite images (http://cryptome.org/eyeball/dprk-test/dprktest.htm; also an archived copy at http://geophysics.geo.sunysb.edu/wen/NK/eyeball.webarchive) (Table 1). High-quality …

Using Ancillary Information to Improve Hypocenter Estimation: Bayesian Single Event Location (BSEL)

We have developed and tested an algorithm, Bayesian Single Event Location (BSEL), for estimating the location of a seismic event. The main driver for our research is the inadequate representation of ancillary information in the hypocenter estimation procedure. The added benefit is that we have also addressed instability issues often encountered with historical NLR solvers (e.g., non-convergence or seismically infeasible results). BSEL differs from established nonlinear regression techniques by using a Bayesian prior probability density function (prior PDF) to incorporate ancillary physical basis constraints about event location. P-wave arrival times from seismic events are used in the development. Depth, a focus of this paper, may be modeled with a prior PDF (potentially skewed) that captures physical basis bounds from surface wave observations. This PDF is constructed from a Rayleigh wave depth excitation eigenfunction that is based on the observed minimum period from a spectrogram analysis and estimated near-source elastic parameters. For example, if the surface wave is an Rg phase, it potentially provides a strong constraint for depth, which has important implications for remote monitoring of nuclear explosions. The proposed Bayesian algorithm is illustrated with events that demonstrate its congruity with established hypocenter estimation methods and its application potential. The BSEL method is applied to three events: 1) A shallow Mw 4 earthquake that occurred near Bardwell, KY on June 6, 2003, 2) the Mw 5.6 earthquake of July 26, 2005 that occurred near Dillon, MT, and 3) a deep Mw 5.7 earthquake that occurred off the coast of Japan on April 22, 1980. A strong Rg was observed from the Bardwell, KY earthquake that places very strong constraints on depth and origin time. No Rg was observed for the Dillon, MT earthquake, but we used the minimum observed period of a Rayleigh wave (7 seconds) to reduce the depth and origin time uncertainty. Because the Japan event was deep, there is no observed surface wave energy. We utilize the prior generated from the Dillon, MT event to show that even in the case when a prior is inappropriately applied, high quality data will overcome its influence and result in a reasonable hypocenter estimate.

Fission product ratios as treaty monitoring discriminants

The International Monitoring System (IMS) of the Comprehensive Test Ban Treaty Organization (CTBTO) is currently under construction. The IMS is intended for monitoring of nuclear explosions. The radionuclide part of the IMS monitors the atmosphere for short-lived radioisotopes indicative of a nuclear weapon test, and includes field collection and measurement stations, as well as laboratories to provide reanalysis of the most important samples and a quality control function. The Pacific Northwest National Laboratory in Richland, Washington hosts the United States IMS laboratory, with the designation “RL16.” Since acute reactor containment failures and chronic reactor leakage may also produce similar isotopes, it is tempting to compute ratios of detected isotopes to determine the relevance of an event to the treaty or agreement in question. In this paper we will note several shortcomings of simple isotopic ratios: (1) fractionation of different chemical species, (2) difficulty in comparing isotopes within a single element, and (3) the effect of unknown decay times. While these shortcomings will be shown in the light of an aerosol sample, several of the problems extend to xenon isotopic ratios. Due to the difficulties listed above, considerable human expertise will be required to convert a simple mathematical isotope ratio into a criterion which will reliably categorize an event as ‘reactor’ or ‘weapon’.

Monitoring of seismic events from a specific source region using a single regional array: A case study

In the monitoring of earthquakes and nuclear explosions using a sparse worldwide network of seismic stations, it is frequently necessary to make reliable location estimates using a single seismic array. It is also desirable to screen out routine industrial explosions automatically in order that analyst resources are not wasted upon detections which can, with a high level of confidence, be associated with such a source. The Kovdor mine on the Kola Peninsula of NW Russia is the site of frequent industrial blasts which are well recorded by the ARCES regional seismic array at a distance of approximately 300 km. We describe here an automatic procedure for identifying signals which are likely to result from blasts at the Kovdor mine and, wherever possible, for obtaining single array locations for such events. Carefully calibrated processing parameters were chosen using measurements from confirmed events at the mine over a one-year period for which the operators supplied Ground Truth information. Phase arrival times are estimated using an autoregressive method and slowness and azimuth are estimated using broadband f{-}k analysis in fixed frequency bands and time-windows fixed relative to the initial P-onset time. We demonstrate the improvement to slowness estimates resulting from the use of fixed frequency bands. Events can be located using a single array if, in addition to the P-phase, at least one secondary phase is found with both an acceptable slowness estimate and valid onset-time estimate. We evaluate the on-line system over a twelve month period; every event known to have occured at the mine is detected by the process and 32 out of 53 confirmed events were located automatically. The remaining events were classified as “very likely” Kovdor events and were subsequently located by an analyst. The false alarm rate is low; only 84 very likely Kovdor events were identified during the whole of 2003 and none of these were subsequently located at a large distance from the mine. The location accuracy achieved automatically by the single-array process is remarkably good, and is comparable to that obtained interactively by an experienced analyst using two-array observations. The greatest problem encountered in the single array location procedure is the difficulty in determining arrival times for secondary phases, given the weak Sn phase and the complexity of the P-coda. The method described here could be applied to a wide range of locations and sources for which the monitoring of seismic activity is desirable. The effectiveness will depend upon the distance between source and receiver, the nature of the seismic sources and the level of regional seismicity.

Long-range propagation and scattering of low-frequency sound pulses in the middle atmosphere

A short historical review and an analysis of the current status of both theoretical and experimental studies of long-range sound propagation in the atmosphere are given. Basic results are given on the atmospheric fine-layered structure that significantly affects the infrasonic pulse propagation and scattering in the lower and middle atmosphere. The effect of time variations (seasonal changes, tides, and both planetary and internal gravity waves) in the effective acoustic speed profile on the characteristics of infrasonic signals from different pulsed sources is discussed. The results of the studies of partial reflection (scattering) of low-frequency acoustic pulses from the fine-layered inhomogeneities of the middle atmosphere are presented. The results of the corresponding theoretical studies are also given. The potentialities of the method of long-range acoustic sounding of large-scale anisotropic turbulence in the middle atmosphere are discussed. The problems of infrasonic monitoring of nuclear low-energy explosions are also considered.

Revised Distance and Depth Corrections for Use in the Estimation of Short-Period P-Wave Magnitudes

A new short-period seismic magnitude measure based on uniform, automatic processing of digital P -wave data recorded on the standardized International Monitoring System (IMS) global network of stations has been formulated and tested. The test data consisted of over 220,000 single-station P -wave amplitude and period observations from approximately 25,000 events that were reported in the Reviewed Event Bulletin of the prototype International Data Center, which was established to evaluate various concepts proposed for use in the monitoring of nuclear explosions. Large-scale statistical analyses of these data have been used to define improved corrections for the effects of epicentral distance and focal depth, distance weighting factors for use in the estimation of a new, generalized m b measure ( m b ) that incorporates data observed over the expanded epicentral distance range extending from 2° to 180°, as well as preliminary global station corrections for a number of existing and proposed IMS station sites. The station corrections are considered to be preliminary at this time since possible maximum-likelihood effects are not explicitly considered in the present analysis. However, evidence is presented that indicates that such effects are not significantly biasing the derived distance/depth corrections and that the magnitude of their influence on the estimated station corrections is likely to be rather small with respect to the range encompassed by these corrections. Tests of this new, generalized m b magnitude measure have indicated that it can provide consistent and easily reproducible measures of seismic event magnitude, even for events that are not well recorded at traditional teleseismic distances.

Monitoring of atmospheric nuclear explosions with infrasonic microphone arrays

A review is given of the various United States programs for the infrasonic monitoring of atmospheric nuclear explosions from their inception in 1946 to their termination in 1975. The US Atomic Energy Detection System (USAEDS) monitored all nuclear weapons tests that were conducted by the Soviet Union, France, China, and the US with arrays of sensitive microbarographs in a worldwide network of infrasonic stations. A discussion of the source mechanism for the creation and subsequent propagation around the globe of long wavelength infrasound from explosions (volcanic and nuclear) is given to show the efficacy of infrasonic monitoring for the detection of atmospheric nuclear weapons tests. The equipment that was used for infrasound detection, the design of the sensor arrays, and the data processing techniques that were used by USAEDS are all discussed.

A fully global hydroacoustic monitoring system for the Comprehensive Nuclear-Test-Ban Treaty—Plans and progress

The first ever fully global hydroacoustic monitoring system is being planned and implemented for use in the verification of a new international treaty, the Comprehensive Nuclear-Test-Ban Treaty (CTBT). This system will provide hydroacoustic monitoring of all the world’s oceans for 24 h a day, every day of the year, into the indefinite future. This unique resource will utilize two types of station. One type will be based on a hydrophone at the SOFAR axis depth, cabled back to shore. The other will be based on a seismometer on a small island using detection of the T-phase signal. This latter station relies on a signal which has propagated predominantly through the ocean, but has been converted to seismic energy at the margin of the island. Although this network is being installed for monitoring of nuclear explosions, it will also be a unique resource for scientific investigation of various phenomena. Data will be available to all State Signatories to the CTBT.

Nuclear Test Ban Monitoring: New Requirements, New Resources

The authors of this article make the case for using open seismic networks in the monitoring of nuclear explosions for compliance with a global Comprehensive Test Ban Treaty (CTBT). These stations could be integrated with global communications networks to reduce the cost of monitoring for a CTBT. They would be multiuse stations not only for monitoring explosions but also for recording earthquake activity, assessment of seismic risk, and exploration of the earth's interior. Such networks now exist, but political aspects of negotiations for a CTBT have prevented them from being incorporated into the verification effort.