Amount Of Nuclear Material Research Articles

International safeguards for the final disposal of spent nuclear fuel – why, what and how

Abstract. The objectives of international safeguards are the timely detection of diversion of significant quantities of nuclear material from peaceful nuclear activities to the manufacture of nuclear weapons (or for other purposes), and deterrence of such diversion by the risk of early detection for states with comprehensive safeguards agreements with the International Atomic Energy Agency (IAEA). Following these objectives, several studies have focused on the developments of concepts and methods for safeguarding final disposal facilities as well as on identifying the most feasible technologies that could potentially be deployed for verifying final disposal programmes (IAEA, 1998, 2010, 2018). These activities were coordinated through Member State Safeguards Support Programmes, including the joint tasks on the development of “Safeguards for Geological Repositories” (SAGOR, 1994–2004) and on the “Application of Safeguards to Geological Repositories” (ASTOR, 2005–2017). SAGOR performed a diversion path analysis for spent fuel disposal facilities, determined safeguards technical objectives and identified potential safeguards measures to meet those objectives. ASTOR supported the IAEA in assessing how safeguards measures could be effectively implemented and provided recommendations with respect to developing such measures. Specific verification technologies were developed under other Member State Support Programme tasks. A summary report on the progress and status of safeguards for spent fuel encapsulation plants and geological repositories was completed by ASTOR in 2017. ASTOR also identified areas and actions that need to be accomplished to support safeguards implementation in final disposal facilities, such as (1) establish performance requirements for the design of safeguards technologies relevant to geological disposal of spent fuel, (2) determine specific information needs of states and operators regarding safeguards implementation for geological disposal of spent fuel and develop appropriate guidance, (3) determine specific information needs of IAEA inspectors and analysts and develop a guidance document that provides recommendations for implementing safeguards for a geological repository system under the state-level concept and (4) develop and test appropriate safeguards equipment (IAEA, 2017; Moran et al., 2018). While several measures and technologies related to verifying the geological disposal of spent fuel have been used by the IAEA at other facilities or are in development or testing, other technologies still need to be developed and tested. In addition, ASTOR identified the need for approaches to how information about disposed spent fuel and high-level nuclear waste should be managed, handled, organized, archived, read, interpreted and secured for the long term (for centuries after repository closure and beyond), including an international standard for states and facility operators on information management, data-retention methods and timescales for preserving safeguards data for geological repositories. The presentation will introduce the objectives of international nuclear material safeguards for the final disposal of spent nuclear fuel, highlight the current status of developments and discussions in terms of approaches and technologies for safeguarding geological repositories, and give an outlook on implementing safeguards for final disposal in Germany.

Quantitative analysis of uranium in electro-recovery salt of pyroprocessing using laser-induced breakdown spectroscopy

The amounts of nuclear materials in the LiCl-KCl salt in pyroprocessing have to be analyzed to prevent the diversion of the nuclear material. An alternative method to the chemical analysis has been pursued, and laser-induced breakdown spectroscopy (LIBS) is one candidate. In the present work, an in situ and quantitative analysis method of electro-recovery (ER) salt was proposed and demonstrated by using LIBS combined with dipstick sampling. Two types of simulated salt samples were prepared: ER salt sample and salt obtained from the dipstick sampling, and pulsed neodymium-doped yttrium aluminum garnet (Nd:YAG) laser with a wavelength of 532 nm was focused on the salt to generate plasma. The plasma emission was measured by using an Echelle spectrometer with a resolution of 0.01 nm in conjunction with an Intensified Charge-Coupled Detector camera. The U and other rare earth peaks in the spectra were identified. The best Limit of Detection and Root Mean Square Error of Calibration of U were 38 ppm and 0.0203 wt%, respectively. Our work shows that the U in the pyroprocessing ER salt can be monitored with LIBS.

Conceptual design of neutron measurement system for input accountancy in pyroprocessing

Abstract One of the possible options for spent-fuel management in Korea is pyroprocessing, which is a process for electrochemical recycling of spent nuclear fuel. Nuclear material accountancy is considered to be a safeguards measure of fundamental importance, for the purposes of which, the amount of nuclear material in the input and output materials should be measured as accurately as possible by means of chemical analysis and/or non-destructive assay. In the present study, a neutron measurement system based on the fast-neutron energy multiplication (FNEM) and passive neutron albedo reactivity (PNAR) techniques was designed for nuclear material accountancy of a spent-fuel assembly (i.e., the input accountancy of a pyroprocessing facility). Various parameters including inter-detector distance, source-to-detector distance, neutron-reflector material, the structure of a cadmium sleeve around the close detectors, and an air cavity in the moderator were investigated by MCNP6 Monte Carlo simulations in order to maximize its performance. Then, the detector responses with the optimized geometry were estimated for the fresh-fuel assemblies with different 235U enrichments and a spent-fuel assembly. It was found that the measurement technique investigated here has the potential to measure changes in neutron multiplication and, in turn, amount of fissile material.

Assessment of the impact of diversification of uranium switching on the risk of its non-energy use

The main objective of the IAEA verification activities is the timely detection of the switching of a significant quantity of nuclear material (NM). However, from the point of nuclear security the multiple switching of "small" quantities of nuclear material with the aim of their subsequent collection also constitutes one of the main threat to ensuring the exceptionally peaceful use of nuclear materials. In this article this threat assessments were performed under the scenario of diversification of uranium switching. It is shown that diversification of 4%-uranium switching can lead to a substantial increase (up to 30 times) of the risk of uranium disuse even with carrying out proper uranium control and protection. However this effect is observed only when there are large opportunities to search for insiders (the search area is comparable to the existing set of nuclear facilities). The obtained results also prove that a reduction in the level of NM safe management at facilities could allow the collector to complete a chain of unauthorized actions with a significant probability (PSQ>0.1).

Investigation of nuclear material using a compact modified uniformly redundant array gamma camera

Abstract We developed a compact gamma camera based on a modified uniformly redundant array coded aperture to investigate the position of a UO2 pellet emitting characteristic X-rays (98.4 keV) and γ-rays (185.7 keV). Experiments using an only-mask method and an antimask subtractive method were conducted, and the maximum-likelihood expectation maximization algorithm was used for image reconstruction. The images obtained via the antimask subtractive method were compared with those obtained using the only-mask method with regard to the signal-to-noise ratio. The reconstructed images of the antimask subtractive method were superior. The reconstructed images of the characteristic X-rays and the γ-rays were combined with the obtained image using the optical camera. The combined images showed the precise position of the UO2 pellet. According to the self-absorption ratios of the nuclear material and the minimum number of effective events for image reconstruction, we estimated the minimum detection time depending on the amount of nuclear material.

Characterization of Low Level Wastes: a new design for calorimetric measurement

Calorimetry is one of the best solutions to estimate the overall quantity of nuclear material on a wide range of masses, from a few milligrams up to kilograms of radionuclides, by measuring the overall thermal power due to the radioactive decay coming from the waste contained in a metallic drum or a different type of container. It has many advantages as it features a non-destructive method which remains independent of matrix effect or the chemical composition. Until now, calorimetry allows to measure at the lowest 0.5 to 1 mW for samples up to 385 liters. But nowadays, thanks to new technological breakthroughs, KEP-Technologies calorimeters are able to measure as low as 50 μW for 40 liters samples. The μLVC is based on a new design with twin cells, a new temperature regulation loop and a heat-flow measurement system inside a vacuum chamber (Patent deposit P005299 LA/VL). The μLVC is a differential heat-flow calorimeter for precise measurement independent of the residual fluctuations caused by environmental changes. The new calorimeter is an industrial product able to work in environmental conditions with wide temperature variations. The first results have shown a great improvement in the detection of very low thermal effect thanks to the thermal noise reduction. The paper presents the developments in Large Volume Calorimetry as a new tool for quantification of nuclear material to characterize Pu-Am samples, i-graphite, and low tritium samples with high precision and reliability.

Nuclear Fuel Assay through analysis of Uranium L-shell by Hybrid L-edge/XRF Densitometer using a Surrogate Material

Assay of L-series of nuclear material solution is useful for determination of amount of nuclear materials and ratio of minor actinide in the materials. The hybrid system of energy dispersive X-ray absorption edge spectrometry, i.e. L-edge densitometry, and X-ray fluorescence spectrometry is one of the analysis methods. The hybrid L-edge/XRF densitometer can be a promising candidate for a portable and compact equipment due to advantage of using low energy X-ray beams without heavy shielding systems and liquid nitrogen cooling compared to hybrid K-edge/XRF densitometer. A prototype of the equipment was evaluated for feasibility ofthe nuclear material assay using a surrogate material (lead) to avoid radiation effects from nuclear materials. The uncertainty of L-edge and XRF characteristics of the sample material and volume effects was discussed in the article.

Nuclear Fuel Assay through analysis of Uranium L-shell by Hybrid L-edge/XRF Densitometer using a Surrogate Material

Assay of L-series of nuclear material solution is useful for determination of amount of nuclear materials and ratio of minor actinide in the materials. The hybrid system of energy dispersive X-ray absorption edge spectrometry, i.e. L-edge densitometry, and X-ray fluorescence spectrometry is one of the analysis methods. The hybrid L-edge/XRF densitometer can be a promising candidate for a portable and compact equipment due to advantage of using low energy X-ray beams without heavy shielding systems and liquid nitrogen cooling compared to hybrid K-edge/XRF densitometer. A prototype of the equipment was evaluated for feasibility of the nuclear material assay using a surrogate material (lead) to avoid radiation effects from nuclear materials. The uncertainty of L-edge and XRF characteristics of the sample material and volume effects was discussed in the article.

Optimization of hybrid-type instrumentation for Pu accountancy of U/TRU ingot in pyroprocessing

One of the final products of pyroprocessing for spent nuclear fuel recycling is a U/TRU ingot consisting of rare earth (RE), uranium (U), and transuranic (TRU) elements. The amounts of nuclear materials in a U/TRU ingot must be measured as precisely as possible in order to secure the safeguardability of a pyroprocessing facility, as it contains the most amount of Pu among spent nuclear fuels. In this paper, we propose a new nuclear material accountancy method for measurement of Pu mass in a U/TRU ingot. This is a hybrid system combining two techniques, based on measurement of neutrons from both (1) fast- and (2) thermal-neutron-induced fission events. In technique #1, the change in the average neutron energy is a signature that is determined using the so-called ring ratio method, according to which two detector rings are positioned close to and far from the sample, respectively, to measure the increase of the average neutron energy due to the increased number of fast-neutron-induced fission events and, in turn, the Pu mass in the ingot. We call this technique, fast-neutron energy multiplication (FNEM). In technique #2, which is well known as Passive Neutron Albedo Reactivity (PNAR), a neutron population's changes resulting from thermal-neutron-induced fission events due to the presence or absence of a cadmium (Cd) liner in the sample's cavity wall, and reflected in the Cd ratio, is the signature that is measured. In the present study, it was considered that the use of a hybrid, FNEM×PNAR technique would significantly enhance the signature of a Pu mass. Therefore, the performance of such a system was investigated for different detector parameters in order to determine the optimal geometry. The performance was additionally evaluated by MCNP6 Monte Carlo simulations for different U/TRU compositions reflecting different burnups (BU), initial enrichments (IE), and cooling times (CT) to estimate its performance in real situations.

Nuclear Waste Calorimeter for Very Large Drums with 385 Litres Sample Volume

For more than 40 years, large volume calorimeters developed by SETARAM Instrumentation, have been used for nuclear applications including the assay of tritium and plutonium. They have been installed in major nuclear centers all around the world.The calorimeters are used for inventory of nuclear material, or for research. In 2011 a project was launched to develop a calorimeter for the management of waste in large volume drums. A new calorimeter has been developed by Setaram Instrumentation and the CEA Valduc in France.This new calorimeter is designed for drums having a volume bigger than 100L. It guarantees high operator safety by optimizing drum handling and air circulation for cooling, and optimized software for direct measurement of the quantity of nuclear material. The system is designed to provide precise measurements independent of environmental conditions.

Study on a Re-verification Detection System for IAEA Safeguard to a Consolidated Spent Fuel Storage System

A modular type storage system that has an enhanced storage density has been developed. It has storage density more than twice larger than silo type which stands alone. The storage module can accommodates 40 cylinders in 4 rows of 10, with 24 located close to periphery of the module and 16 located internally at some distance from the peripheral walls. As for IAEA Safeguards, the module is equipped with a comprehensive set of receptacles into which the IAEA can install seals and verification equipment. The Safeguards equipment, coupled with related measures for physical protection, will facilitate the timely detection of any diversion of significant quantities of nuclear material from the spent fuels stored in the modules. Nevertheless, due to its generic design feature it makes very difficult to provide re-verification of the loaded or under loaded cylinders inside module. along with an unattended monitoring system re-verification is an IAEA safeguard requirement to measure the gamma dose rate and spectrum of each irradiated fuel basket once the storage cylinders are loaded with spent fuel. The gamma profile is read by lowering a detector inside the tube so that it can be registered at the level of each basket. For the 24 peripheral storage cylinders this method of measurement is retained on the side wall of the module. However, an alternate method is required for the 16 internal dry fuel storage cylinders since they are located some distance from the module walls and thus surrounded by storage cylinders.

Challenge to ultra-trace analytical techniques of nuclear materials in environmental samples for safeguards at JAERI: methodologies for physical and chemical form estimation

From a viewpoint of physical and chemical form estimation, ultra-trace analytical techniques of nuclear materials in environmental samples for safeguards have been investigated at Japan Atomic Energy Research Institute. This article deals with (1) an outline of the developed techniques for bulk and particle analyses of uranium and plutonium in the safeguards environmental samples; (2) current R&D on techniques relating to estimation of the physical and chemical form, such as SEM images and EDX spectra for fine particles of nuclear materials and fission track observation applicable to fissile materials; and (3) possible analytical methodologies, as future works, applicable to ultra-trace amounts of nuclear materials in environmental samples.

Fixed-wing gamma measurement for the detection of radioactive materials

Finland has the operational capability to take airborne gamma-ray measurements in emergency situations. The original purpose of airborne radiation mapping in Finland was to identify hazardous areas containing radioactive fall-out after a nuclear accident or use of nuclear weapons. Regular exercises are held annually to keep the operational functionality at a high level. The achieved capability has been well demonstrated in international INEX-2-FIN 1997 and Barents Rescue 2001 exercises. The knowledge and competence achieved can easily be applied in international radiation monitoring campaigns designed to expose undeclared nuclear materials or other clandestine nuclear activities. The essential improvements in the detection system are linked to the ability to locate point-like radiation sources rather than large areas of fall-out. This paper describes the aerial gamma-ray measurement method and its usability for the detection of nuclear material production chains and trails of fission or activation products. The ability of airborne detection systems in revealing the use of undeclared nuclear materials has been tested. Various scenarios for exposing clandestine nuclear material production, enrichment and nuclear waste trails have been considered. Based on detection capability calculations and testing in practice, it was found that the detection of one un-shielded significant quantity of natural uranium (10 tons of yellow cake in storage barrels) is possible through the daughter products, using one single 6"·4" NaI detector on the airplane. The developed fixed wing gamma measurement technique is now able to detect significant amounts of nuclear material conveniently and cost-effectively. Large areas can be screened to identify suspicious sub-areas for more detailed ground-based inspection.

Establishment of a Clean Laboratory for Ultra Trace Analysis of Nuclear Materials in Safeguards Environmental Samples

The Japan Atomic Energy Research Institute has established a cleanroom facility with cleanliness of ISO Class 5: the Clean Laboratory for Environmental Analysis and Research (CLEAR). It was designed to be used for the analysis of nuclear materials in environmental samples mainly for the safeguards, in addition to the Comprehensive Nuclear-Test-Ban Treaty verification and research on environmental sciences. The CLEAR facility was designed to meet conflicting requirements of a cleanroom and for handling of nuclear materials according to Japanese regulations, i.e., to avoid contamination from outside and to contain nuclear materials inside the facility. This facility has been intended to be used for wet chemical treatment, instrumental analysis and particle handling. A fume-hood to provide a clean work surface for handling of nuclear materials was specially designed. Much attention was paid to the selection of construction materials for use of corrosive acids. The performance of the cleanroom and analytical background in the laboratory are discussed. This facility has satisfactory specification required for joining the International Atomic Energy Agency Network of Analytical Laboratories. It can be concluded that the CLEAR facility enables analysis of ultra trace amounts of nuclear materials at sub-picogram level in environmental samples.

Radiation measurement for safeguards environmental samples by Imaging Plate

In order to contribute to the strengthened safeguards system based on the Program 93+2 of the IAEA, Japan Atomic Energy Research Institute (JAERI) constructed the CLEAR facility (Clean Laboratory for Environmental Analysis and Research) and is developing analytical technology for ultra-trace amounts of nuclear materials in environmental samples. To avoid cross-contamination among the samples and contamination of the clean rooms, radioactive materials in the samples to be introduced into the CLEAR facility will be limited to a certain amount. For this purpose the authors have examined the feasibility of Imaging-plate method, which is a kind of autoradiography and is suitable for determination on distribution of low-level radioactivity in the samples. Examination with β-ray (K-40), the linearity was obtained in the range of 0.01 - 0.2 Bq. The experiments with α-ray (Sm-147) suggested the detection limit of 0.05 Bq, which was equivalent to 2 μg of natural uranium.

Low energy gamma- and X-ray measurements by means of Compton suppression technique for safeguards environmental samples

For analyzing ultra-trace amounts of nuclear materials in safeguards environmental samples, JAERI constructed a clean room facility. To eliminate the samples with excessive amounts of radioactive materials from the facility, that is the screening, the authors need to roughly estimate actinides and radioisotopes by non-destructive analysis. In this estimation, it is very inefficient to precisely measure the actinides by using HPGe detector because the intensities of the actinides' gamma-rays are generally low and their photopeaks (mostly below 200 keV) are severely interfered by Compton continuum caused by gamma-rays of fission products etc. within the samples. For suppressing Compton scattering signals with the energy less than several hundreds of keV, the authors have examined the feasibility of planar HPGe-LEPS and “short” coaxial low-energy HPGe detectors which were symmetrically surrounded with Nal(Tl) Compton suppressor detectors.In preliminary examination by measuring 137Cs standard source, background level was reduced by a factor of about 2 in the energy range from 50 to 400 keV.

Probabilistic analysis of the inadvertent reentry of the Cassini spacecraft's radioisotope thermoelectric generators.

As part of the launch approval process, the Interagency Nuclear Safety Review Panel provides an independent safety assessment of space missions--such as the Cassini mission--that carry a significant amount of nuclear materials. This survey article describes potential accident scenarios that might lead to release of fuel from an accidental reentry during an Earth swingby maneuver, the probabilities of such scenarios, and their consequences. To illustrate the nature of calculations used in this area, examples are presented of probabilistic models to obtain both the probability of scenario events and the resultant source terms of such scenarios. Because of large extrapolations from the current knowledge base, the analysis emphasizes treatment of uncertainties.

Radiometric measurements on non-destructive assay standards fabrication for WIPP Performance Demonstration Program

The Inorganic Elemental Analysis Group of LANL has prepared several different sets of working reference materials (WRMs). These WRMs are prepared by blending quantities of nuclear materials (plutonium, americium, and enriched uranium) with diatomaceous earth. The blends are encapsulated in stainless steel cylinders. These WRMs are being measured as blind controls in neutron and gamma based non-destructive assay (NDA) instruments. Radiometric measurements on the blending homogeneity and verification on a set of sixty-three plutonium based WRMs are discussed in this paper.

Accuracy or Timeliness: A Balance in Consequence Assessments for Emergency Response

Atmospheric models are utilised by most governments to assist in assessing the consequences resulting from the inadvertent release of nuclear materials to the atmosphere. Facilities that have the potential to release large quantities of nuclear materials pose a particular concern due to the transport and dispersion of these materials over great distances. As such, it has long been recognised that there is a very real need for these models to possess a prognostic capability, and thereby provide reasonably accurate forecasts of future wind fields in a timely manner. Many such prognostic models are now available. However, there is a delicate balance between the accuracy of the model output and the timeliness with which the product is delivered to decision makers. This paper presents the problem and discusses the issues facing both the atmospheric modeler and the decision-maker.

Magnetization transfer of pure DNA and purified sperm nuclei.

Magnetization transfer (MT) imaging provides a novel opportunity to characterize interactions between tissue water and macromolecules. Although several in vitro investigations have shown that proteins and lipids are important determinants of MT, the contribution of DNA is still unknown. This study was designed to determine whether DNA and cell nuclear material exhibit MT. We measured the magnetization transfer effect of pure DNA strands and purified bovine sperm head nuclei. Although no transfer of magnetization could be detected in samples of pure DNA strands, the sperm head nuclei exhibited a strong MT effect that increased with increasing solid content of the samples. Since the purified bovine sperm head samples consist of large nuclei with only minor traces of perinuclear matrix, the measured MT effect arises from the chromatin of the nuclei. The DNA fills 90% of the nuclear volume and it is extremely tightly packed as chromatin fibers by nucleoproteins. We hypothesize that the numerous intra- and intermolecular disulfide bonds that stabilize the chromatin fibers restrict the movement of the surface water binding sites of both DNA and protamines and thus facilitate the transfer of magnetization. Therefore, the results indicate that the amount of nuclear material may positively contribute to MT in tissues.