Weapons-grade Plutonium Research Articles

Uniqueness, Reproducibility and Discrimination of Nuclear Warhead Gamma Signatures

Nuclear verification includes confirmation measures of nuclear weapons and fissile material, which often rely on the detection of radiation signatures. It is an open research question whether these signatures are unique. Or in reverse, could a malicious actor imitate these signatures and compromise verification of disarmament processes by using hoax objects instead of real warheads? This article presents several warhead emission models and a simulation framework to assess the uniqueness of their passive gamma radiation signatures. A red team approach includes detailed simulations of three proposed confirmation systems: The Information Barrier eXperimental, and the Information Barrier eXperimental II, both developed at Princeton University, and the Trusted Radiation Identification System, developed at the Sandia National Laboratories. For these simulations, various hoaxes are analyzed: warheads using reactor-grade plutonium instead of weapon-grade plutonium, combinations of different gamma emitting isotopes, and combinations of neutron sources with radioactive isotopes. Our findings reveal that numerous radioactive signatures are not unique and may be susceptible to imitation. Moreover, confirmation systems based on passive gamma radiation signatures using low bin numbers demonstrate a limited ability to accurately handle warheads of varying ages.

Applied radiation tags for warhead dismantlement transparency

This study explores the feasibility of applying radiation tags as a Chain of Custody tool to confirm the dismantlement of individual warheads by investigating time dependent emissions from special nuclear material. Precedents of photon and neutron sources that have been used to irradiate warhead components are presented. Measurements of irradiated Highly Enriched Uranium (HEU) are used to benchmark simulations with the CINDER90 depletion code module within MCNP. Delayed gamma emissions are simulated as a function of time since irradiation of moderated HEU and Weapons Grade Plutonium with photon and neutron sources. Models of commercial 9 MV and 15 MV linacs were found to induce ∼109fissions/g and ∼1011fissions/g, respectively, creating 3 to 4 orders of magnitude more delayed gammas than neutron sources, modeled at 1010n/s. However, a DT neutron source was found to induce sufficient fissions, ∼107fissions/g, to create quantifiable signatures relative to intrinsic emissions. Applied radiation tagging is determined to be technically feasible, but its operational context and practical implementation requires significant development.

Age Dating of Repurified and Mixed Plutonium Using Machine Learning

Age dating a sample of nuclear material is a key part of predetonation technical nuclear forensics. As plutonium stockpiles age, they are more likely to require repurification and mixing to remove in-grown daughter products and maintain a consistent product. Existing age-dating techniques do not adequately address this problem. Four models were trained using machine learning techniques to determine (1) if a sample of weapons-grade plutonium had been repurified, (2) the elapsed time after repurification, and (3) the minimum and maximum elapsed times between repurification and its initial separation/purification/fabrication. The trained models predicted the repurification status with 99% accuracy, the age after repurification with a root-mean-square error (RMSE) of 0.34 years, and the minimum and maximum ages before repurification with RMSEs of 4.66 and 9.34 years, respectively. Age dating plutonium provides valuable insight into the country and possibly the facility of origin of the material, which is one tool to deter state-sponsored nuclear terrorism.

A multi-collector ICP-MS method for quantification of plutonium, uranium, and americium in hair and nails of occupationally or medically exposed individuals

The 239Pu, 238U, and 241Am concentrations and 239Pu/240Pu, 235U/238U, and 236U/238U atom ratios were measured in the hair and nail samples using a new method utilized TEVA, UTEVA, and DGA extraction chromatography and multi-collector ICP-MS. Samples were collected from individuals who donated their bodies to the United States Transuranium and Uranium Registries. The concentration of 239Pu ranged from 0.22 to 15.8 ng/kg. The 240Pu/239Pu isotopic ratios ranged from 0.026 to 0.127 which is consistent with weapons-grade plutonium. Concentration of uranium fell between 1.84 μg/kg and 29.5 μg/kg and 235U/238U ratios ranged from 4.8 × 10−3 to 7.6 × 10−3. Elevated 236U/238U atom ratios were measured in two cases and ranged from 5.0 × 10−6 – 2.4 × 10−5 indicating exposure to spent or reprocessed uranium material. The concentration of 241Am was measured in four hair samples and ranged from 0.02 to 0.21 ng/kg.

New data on mobility of transuranium elements in sediments of the Yenisei River

The inflow of transuranium elements to the Yenisei River was previously associated with the production of weapons-grade plutonium at the Mining-and-Chemical Combine (MCC, Zheleznogorsk, Russia), but the source of transuranium elements in the River today is fabrication of MOX fuel that started recently at the MCC. The current study presents results of sequential chemical extraction of radionuclides from sediment samples collected in 2014 and 2020 in two areas near the MCC discharge site and compares these results with the data obtained previously by sequential extraction of sediments collected during 1999–2007. Over the study period, the strength of binding of 137Cs and 60Co in the Yenisei River sediments was high (up to 100%) and remained so, while the percentages of 241Am and 152Eu in residual solids after sequential extraction increased considerably and the percentage of 239,240Pu in residual solids decreased in samples from all study areas. In samples collected at the position located close to the MCC discharge site, the percentages of the strongly bound 241Am and 152Eu as well as 239,240Pu were lower than in the samples from the other positions. The study demonstrated an enormous increase in 239,240Pu activity concentration in the top sediment layers collected at all positions in 2020 relative to 2014. In the same period, as literature data suggest, 239,240Pu activity concentrations also increased in aquatic organisms of the Yenisei River, which can be indicative of the growing potential bioavailability of plutonium in the aquatic ecosystem, which could be caused by the presence of the mobile form of plutonium in the routine discharges from the MCC.

НЕЙТРОННО-ФИЗИЧЕСКИЙ РАСЧЕТ РЕАКТОРА ВВЭР-1000 НА МОКС-ТОПЛИВЕ

The use of mixed uranium-plutonium fuel in thermal reactors makes it possible to effectively use highly toxic weapons-grade plutonium for peaceful purposes. The world's reserves of such plutoni-um are a serious problem. The use of this fuel in thermal reactors significantly reduces the amount of enriched uranium needed, as well as to dispose of plutonium-239. The plutonium processed in this way can be reused in fast reactors. In that way, a significant part of nuclear waste can be used in the process of energy release, and the number of potential radioactive waste that would otherwise be buried in the soil will also decrease. The paper presents the results of the neutron-physical calculation of the VVER-1000 reactor on mixed uranium-plutonium fuel for three fuel assemblies: 30%, 50% and 70% MOX fuel from the total amount of the produced substance. The total enrichment is 5%, which will not make critical changes to the reactor operation. Effective multiplication coefficients are obtained for all variations in several approximations: the 4-factor method, the multigroup approximation. The neutron spectrum for the multigroup approximation is obtained. Xenon and samarium poisoning of the reactor was calculated. The analysis of the kinetics of the reactor and the change in the neutron flux at different input reactivity is presented. The possibility of using the selected assemblies on real power plants and the degree of plutonium reproduction during reactor operation are evaluated

Simulating the Passive Neutron and Gamma Signatures of Containerized Nuclear Warheads for Disarmament Verification

For nuclear disarmament verification, measuring passive neutron and gamma signatures is discussed for confirming the presence of weapons-grade plutonium. Using the Geant4 code, the effects of neutron and photon interactions with the various materials of containerized items are explored for (i) notional fission and thermonuclear warheads waiting for dismantlement, (ii) intentionally shielded plutonium in a scrap container. Due to strong neutronic linking of the various warhead materials neutron multiplicity measurements can not be expected to give correct results. Gamma emissions of the plutonium may even be completely shielded by a tamper. Gamma spectrometry could verify the presence of explosives from (n,γ) activation of hydrogen and nitrogen as well as of fission processes from their prompt fission gamma emissions. Limiting diameters of scrap containers together with long-time gamma measurements of the absence of photons produced by (n,γ) activation of shielding materials will provide an effective approach for detecting an intentional diversion of plutonium.

Elodea Canadensis (Submerged Macrophyte of the Yenisei River) and Actinides: Properties, Accumulation, Regularities and Interactions

Radioactive contamination of the Yenisei River bottom and (including the contamination with actinides) is the result of long-term operation of the Mining and Chemical Combine, which manufactures plutonium for weapons. The study considers the behavior of a submerged macrophyte Elodea Canadensis, one of the most widely spread species of aquatic plants in the River Yenisei. The values of the accumulation coefficients obtained for 242Pu, 13100 ± 2100 L·kg-1, were close to the concentration factor for 241Am–17100 ± 4300 L·kg-1, obtained for the Elodea shoots. Studies on the potential adaptation of one of the common aquatic macrophytes Elodea canadensis when immersed in a medium containing actinide. It was found that almost all the studied 241Am and 242Pu do not show a clear external effect on the solid fragments of the plant (cell membranes). Thus, it was shown that Elodea canadensis is tolerant of anthropogenic radio nuclides that differ in nature, physico-chemical properties, etc.

Development and Calibration of an Indigenous Spectroscopic System for Radiation Portal Monitor Application

Abstract The growing terrorism threat based on the use of special nuclear materials (SNMs), which includes highly enriched uranium (HEU), weapons-grade plutonium (WGPu), or high-activity radiological sources has reinforced the need for improved population protection mechanisms. The motivation for the development of a radiation portal monitor is the need for inspecting cargo at various entry points of the country. This inspection process requires scanning many containers for the presence of SNMs such as Uranium, Thorium, and Plutonium. In this study, we have worked on designing a system with eight NaI (Tl) detectors for the detection of any gamma-emitting radioactive source. The multichannel analyzer for collecting the data from the detectors has also been indigenously developed using PXIe-6386 data acquisition system with a sampling rate of 14 MS/s. The system is automated using labview platform. The system is capable of detection as well as identification of the SNMs passing through it in static conditions. The energy spectra of various radionuclides, such as 137Cs, 60Co, and 54Mn, measured using our RPM have been used for the validation of the identification of sources with unknown energy lines.

Improved Disposition of Surplus Weapons-Grade Plutonium Using a Metallic Pu-Zr Fuel Design

The United States and the Russian Federation have agreed to dispose of their excess weapons-grade plutonium, with consuming the material as nuclear fuel in light water reactors for electricity generation often discussed as the best option. Lightbridge Corporation has several thermal reactor fuel designs that offer very high burnups, in the range of 21 at. % or approximately 190 900 MWd/tonne of heavy metal, which make them well suited for consuming excess weapons-grade plutonium. MCNP6.2 computer simulations were performed to quantify the mass of plutonium consumed in a Lightbridge-designed fuel rod compared to traditional mixed-oxide (MOX) fuel, as well as the attractiveness of the plutonium in the used fuel for weapons purposes. The results of these simulations show that the Lightbridge plutonium disposition fuel variant consumes approximately 5.5 times more plutonium per fuel rod than MOX fuel and that the material attractiveness of the Lightbridge-used plutonium is noticeably less than that of MOX fuel.

China's New Breeder Reactors May Produce More Than Just Watts: They Could Also Make Weapons-Grade Plutonium

Jutting out from the coast of China's Fujian province, Changbiao Island may seem small and unremarkable. It is anything but. This is where the China National Nuclear Corp. is building two fast-neutron nuclear breeder reactors, the first of which is slated to connect to the grid in 2023, the second in 2026. So China could start producing weapons-grade plutonium there very soon.

Nondestructive and destructive assay for forensics characterization of weapons-grade plutonium produced in LEU irradiated in a thermal neutron spectrum

A post-irradiation examination (PIE) of an enriched uranium sample was performed to advance a nuclear forensics methodology, based on intra-elemental nuclide ratios. The PIE was carried out on a few milligrams of low enriched uranium dioxide (LEUO2) sample, irradiated to a burnup of 1 GWd/MTU. The PIE of the LEUO2 sample provided the concentration of selected plutonium and fission product nuclides (239Pu, 240Pu, 241Pu, 91Y, 95Zr, 95Nb, 103Ru, 133Cs, 134Cs, 135Cs, 137Cs, 136Ba, 138Ba, 140Ba, 140La, 141Ce, 144Ce, 149Sm, 150Sm, 152Sm, 153Eu, and 154Eu). The PIE supported validation of the MCNP (Monte Carlo N-Particle neutronics simulation code) predicted concentration of these nuclides in the irradiated LEUO2 sample. This study showed that most of the MCNP predicted nuclide concentrations were within 15% and several within 10% compared to the PIE results. Gamma and mass spectrometry of nuclides in irradiated LEUO2 enabled the determination of uranium burnup and time since irradiation.

Multiphysics thermo-mechanical behavior modeling for annular uranium-plutonium mixed oxide fuels in a lead-cooled fast reactor

Understanding and predicting nuclear fuel behavior is the cornerstone for fuel design and optimization, and the safe and economic operation of nuclear reactors. Due to the excellent neutronic economy and safe operational characteristics of lead/lead-bismuth-based liquid metal coolant, lead-cooled fast reactor (LFR) has received much attention and has been regarded as one of the top candidate reactors for Generation IV nuclear power plants. Mixed oxide (MOX) fuel is beneficial to improve fuel cycle utilization and consume weapons-grade plutonium, among which hollow MOX fuel has excellent heat transfer advantages, which can further improve fuel economy and safety, and has good development prospects. In this work, an annular uranium-plutonium mixed oxide (MOX) fuel operating in a liquid lead/lead-bismuth cooled fast reactor is modeled and simulated to predict its behavior under transient and steady-state operation. This model has several modules working in a fully coupled approach based on COMSOL Multiphysics, such as heat transfer, fuel burnup, oxygen redistribution, plutonium redistribution, porosity evolution, fission gas release, JOG growth, and grain size evolution. The modeling results were benchmarked with the existing codes and experimental data, and the results were in satisfactory agreement. The parameters analysis was carried out in this work. Consistent with the solid MOX fuel, the O/M ratio (or deviation from the stoichiometry of oxygen) significantly affects temperature evolution, fission gas migration and release behavior, and plutonium redistribution. Linear power also has a significant influence on fuel performance.

Mining for the Bomb: The Vulnerability of Buried Plutonium to Clandestine Recovery

Efforts by the United States and Russia to bilaterally reduce their weapons plutonium stockpiles are currently stalled following a U.S. decision to dilute and bury excess plutonium in a geologic repository. Russia has derided this approach as impermanent and easily reversible. Conversely, many analysts contend that the recovery of buried plutonium would require large-scale mining operations, rendering it observable and preventable. Here, we show that the use of advanced mining techniques overlooked in prior analysis (namely, salt solution mining and in situ leaching) would enable the rapid, clandestine recovery of buried plutonium. Burial would therefore yield a novel plutonium geologic resource. We attribute the persistence of international technical controversy over the permanence of plutonium burial to state-level divergence in U.S. and Russian technological framings of plutonium and geologic repositories—distinct socially constructed understandings of the meanings, uses, and risks of these technologies.

Simulation study of neutron multiplicity of plutonium samples of different shapes

In this paper, an optimized boron-coated straw tube neutron multiplicity counter is used to simulate neutron multiplicity for six different shapes of weapons-grade plutonium samples. It was found that under the point model equation, the mass simulation results for samples of different shapes showed different degrees of negative deviations with increasing mass, and the deviations increased with increasing mass. On this basis, the reasons for the deviation are analyzed and a multilayer perceptron is introduced, and three counting rates and preset qualities of samples of different qualities under six shapes are trained. The results showed that the multi-layer perceptron could better fit the relationship between the counting rates of different shapes and the preset quality. The sparrow search algorithm was introduced to optimize the initial weights and thresholds of the multilayer perceptron, and the optimized model was used to predict another four samples of different shapes. The results show that the optimized multilayer perceptron can better fit the relationship between the counting rate and the mass of samples with different shapes. When the sample mass is less than 3 kg, the relative deviation of the three counting rates for samples with four shapes to the sample mass prediction is less than 2%, which meets the requirements of neutron multiplicity measurement.

Disposal, Destruction and Disarmament: Comparative Analysis of US Chemical Weapon and Weapons Plutonium Stockpile Reductions

The elimination of stockpiled weaponry constitutes a key step in arms control and disarmament processes, lending permanence and irreversibility to arms reductions. Yet it has proven challenging in practice. The destruction of advanced weapon components, like lethal chemical agents and the fissile materials from which nuclear weapons are constructed, is often technically complex and costly. To elucidate the dynamics of this back-end of arms control and disarmament processes, this article compares two representative cases involving analogous challenges but divergent outcomes: the nearly complete elimination of the US chemical weapon stockpile and stalled efforts to shrink the US weapons plutonium stockpile. Drawing from both engineering and organisation theory, technical and social distinctions between these efforts are assessed to identify key factors governing their outcomes. This analysis shows that the technical bases for stockpile reductions were broadly analogous between the two cases, and thus fail to explain their divergence. Rather, differing organisational characteristics among the responsible institutions proved decisive. These fostered either adaptive (in the chemical weapon case) or path-dependent (in the weapons plutonium case) organisational planning, influencing the ability of the responsible entities to pivot from stockpile maintenance to an unfamiliar reductions mission.

Israeli nuclear weapons, 2021

ABSTRACT The Nuclear Notebook is researched and written by Hans M. Kristensen, director of the Nuclear Information Project with the Federation of American Scientists, and Matt Korda, a senior research associate with the project. The Nuclear Notebook column has been published in the Bulletin of the Atomic Scientists since 1987. This issue’s column examines Israel’s nuclear arsenal, which we estimate includes a stockpile of roughly 90 warheads. Israel neither officially confirms nor denies that it possesses nuclear weapons, and our estimate is therefore largely based on calculations of Israel’s stockpile of weapon-grade plutonium, its inventory of suspected nuclear-capable delivery systems, and declassified or leaked government documents.

Nondestructive and Destructive Assay for Forensics Characterization of Weapons-Grade Plutonium Produced in Leu Irradiated in a Thermal Neutron Spectrum

Nondestructive and Destructive Assay for Forensics Characterization of Weapons-Grade Plutonium Produced in Leu Irradiated in a Thermal Neutron Spectrum

Nondestructive and Destructive Assay for Forensics Characterization of Weapons-Grade Plutonium Produced in Leu Irradiated in a Thermal Neutron Spectrum

Nondestructive and Destructive Assay for Forensics Characterization of Weapons-Grade Plutonium Produced in Leu Irradiated in a Thermal Neutron Spectrum

Toward an Agent-Based Blackboard System for Reactor Design Optimization

The field of reactor design is rich with opportunities for applications of computational optimization algorithms; these applications can range from preliminary core design to reactor shuffling patterns. Many of these schemes rely on sets of previously generated solutions (sometimes referred to as “generations”) to inform future decisions. While it is important to build upon prior knowledge, this process requires a full generation of solutions to be formed before future solutions can be examined. Rather than relying on a generational scheme to perform an optimization, we propose using an agent-based approach in conjunction with a blackboard framework for performing reactor design optimizations. Utilizing an agent-based approach allows agents to perform tasks independently, while retaining the ability to build off of previous solutions. We develop an agent-based blackboard system (ABBS) for determining the Pareto front (PF) in sodium fast reactor design optimization problems and compared this with the Non-Dominated Sorting Genetic Algorithm II (NSGA-II). Our goal is to evaluate the viability of the ABBS in producing a PF that is comparable with the NSGA-II algorithm. The design space consists of the fuel height, fuel smear, and plutonium fraction in the core, and we seek to minimize the reactivity swing and plutonium mass, while maximizing the burnup. The diversity, coverage, and spread of the PFs generated by the two methods are examined, and the ABBS is able to converge to the same PF as the NSGA-II algorithm. These results show that the ABBS is able to find optimal designs that are similar to those found by the NSGA-II algorithm. We conclude our study by applying the ABBS to the design of a sodium-cooled fast reactor to dispose of weapons-grade plutonium. The ABBS finds a core design that can burn upwards of 17.5 kg of weapons-grade plutonium per year and degrade an additional 195 kg of weapons-grade plutonium per year into non-weapons-grade material.