Volume 66, Issue 3

Seismological monitoring is one of the four technologies used by the International Monitoring System to verify compliance with the Comprehensive Nuclear-Test-Ban Treaty. When fully operational, two seismic networks, one primary (50 stations) and one auxiliary (120 stations), will enable global detection and event characterisation of sources with equivalent magnitude as low as 4. The basic principles of seismological theory and practice applied to verification are summarised below, with particular emphasis on the new requirements imposed by the needs of the Treaty.

Hydroacoustics is one of the four monitoring technologies of the International Monitoring System (IMS') established under the Comprehensive Nuclear-Test-Ban Treaty (CTBT). The hydroacoustic network, designed to monitor the major world oceans, contains eleven stations located with an emphasis on the vast ocean areas of the Southern Hemisphere. Two different sensing techniques are employed; hydrophone sensors, which effectively cover large ocean areas, but are quite complex and expensive, and seismic detectors on small islands which are less effective, but considerably simpler and cheaper. The hydroacoustic stations transmit data in real time via satellite to the International Data Centre (IDC). The IDC analyses the hydroacoustic data in combination with the other three technologies to produce bulletins of detected events for the States Party to the Treaty.

The infrasound component of the International Monitoring System (IMS') for Comprehensive Nuclear-Test-Ban Treaty verification will consist of 60 array stations distributed as uniformly as possible over the surface of the globe. This network will be far larger and more sensitive than any other previously operated infrasound network. In this paper, we discuss the design and performance characteristics of this monitoring network and the current status of the site survey and installation programs. A brief review of significant developments in infrasound monitoring technology in the last few years is also presented along with a summary of the various areas where data from this unique global network is likely to be of value to the scientific community.

The radionuclide monitoring network is one of the four technical components of the compliance-verification system associated with the Comprehensive Nuclear-Test-Ban Treaty (CTBT). Concentrations of radionuclides in the air are monitored at 80 stations worldwide from which spectral and counting data, together with meteorological and state-of-health data, are transmitted through a Global Communication Infrastructure to the Provisional Technical Secretariat in Vienna where the data are analyzed and reported as bulletins for States Parties. Support is provided by 16 Radionuclide Laboratories, which conduct sample analyses if necessary.

With the first version of the IDC IDC is the acronym for the International Data Centre, IMS for the International Monitoring System and CTBT for the Comprehensive Nuclear-Test-Ban Treaty. software all known radionuclides, less the natural ones and one “naturalised” man-made one, caused a spectrum measured in the IMS* network to be characterised as interesting from a CTBT* point of view. But this is really not true for the majority of nuclides, so a change has been made to let only nuclides from a limited set of so called CTBT relevant nuclides have an impact on the characterization scheme. In the present paper the concept of CTBT relevance is analysed and a set of 96 relevant nuclides are defined. Out of these 51 are fission products and 41 are neutron activation products. There are also 4 nuclides which are residues from the nuclear fuel itself or added tracers.

The radionuclide network of the IMS consists of 80 radionuclide stations monitoring radioactive airborne particulate. The air sampling systems at these stations require high technical standards regarding robustness, calibration and reliability. These systems are and will be deployed at locations where very different and often very harsh environmental conditions can dominate. An overview of sampling systems is given taking in consideration environmental and operational constraints. Because of lack of experience running radionuclide stations at the required standards, several issues are still open and need consideration for future installations and operation.

The radionuclide monitoring network enables continuous world-wide observation of airborne radionuclides in the verification regime of the Comprehensive Nuclear Test-Ban-Treaty (CTBT). The radionuclide technology – analysis of aerosol samples and xenon at 80 sites hosting radionuclide monitoring stations – contributes to the International Monitoring System (IMS). Sixteen radionuclide laboratories will support the radionuclide monitoring network. Their main function is additional analysis of aerosol samples. Samples categorised as Level 5 that contain multiple anthropogenic radionuclides, at least one of which is a fission or an activation product, will always be sent out for laboratory analysis. A number of samples will be re-analysed at the radionuclide laboratories irrespective of category. This serves the purpose of quality control for the results produced by the stations.

Global monitoring for relevant radionuclides in the atmosphere serves as part of the International Monitoring System to verify compliance with the Comprehensive Nuclear-Test-Ban-Treaty (CTBT). Atmospheric transport modelling can be applied to support these measurements and to get indications for possible source locations of detected relevant anthropogenic nuclides. This paper puts a focus on those issues that are of relevance to the International Data Centre (IDC). Possible methods of atmospheric transport modelling are outlined. The current tentative implementation at the IDC is described here.

The mission of the Comprehensive Nuclear-Test-Ban Treaty International Data Centre (IDC) is to: (a) acquire data over a Global Communications Infrastructure from a global network of 337 facilities of the International Monitoring Systems (IMS), (b) to process and analyze these data, and (c) to provide the IMS data, IDC products and services to Member States. In effect, the IDC symbolizes a new brand of arms control for the information age, leveraging Internet communications, knowledge-based data fusion, graphical decision support systems and Web-based user interfaces to achieve its mission. During 2000, the IDC was disseminating products based on data from about 90 seismic, hydroacoustic, infrasound and radionuclide stations of the future network. The number of events in the reviewed seismo-acoustic bulletins ranged from 40 to 360 each day. On average, some 200 radionuclide spectra were processed and analysed each month. Users from 45 Member States received an average of close to 18,000 data and product deliveries per month from the IDC. As the IDC continues to prepare for entry-into-force of the CTBT, it will continue to integrate the state-of-the-art in science and technology in order to meet the demands of the increasing volume of new types of IMS data, expanded IDC services, and a growing base of users.

In the paper, the technical methods to be used for the on-site inspection (OSI) are reviewed. The main purpose of the OSI is to find evidences of a nuclear explosion conducted anyplace in the world, however, the technical methods described in the paper might be employed for a suspected underground explosion. Various technical methods are described but they can be classified into two categories, namely, technical methods, 1) to identify fission products, and 2) to identify underground evidences. Fission products can be identified by conventional gamma spectrum analysis, however, for the OSI, radioactive Xe and Ar are important nuclides since they are supposed to leak to the ground surface even when the explosion is conducted in deep underground. The seismic and various other technical methods, which might be commonly used by mining industry, can identify the underground evidences, such as a cavity. However, these technical methods might be necessary to be verified to confirm the applicability and effectiveness to OSI objectives.

Evaluation and quality assurance activities of the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) are reviewed with special emphasis on radionuclide technologies. The CTBTO carries out detailed evaluation in all fields of technical verification of the Treaty. The goal is to provide States Signatories with confidence in the quality of data from the International Monitoring System and data products of the International Data Centre. The largest technical evaluation effort has been the quality assessment of the operational software. About 1.3 million lines of source code and scripts were checked. Software characteristics, such as maintainability, were assessed using automated tool-based techniques and improvements were suggested. Specific to radionuclide technologies, several methods have been developed to cope with the large amounts of spectra produced each day by 80 radionuclide monitoring stations around the world. Some of the key evaluation results, such as the peak detection capability of the operational software are presented in detail.