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The correlation relations for determining the [sup.242]Pu mass fraction which are used in the MGA and FRAM computer codes are compared with the relations proposed in the present article for plutonium stored in the RT-1 plant of the Industrial Association Mayak. The need to determine the [sup.242]Pu mass fraction using the correlations arises in nondestructive analysis of plutonium. The MGA and FRAM codes use correlations which are based on data on the isotopic composition of the plutonium that has accumulated in American reactors so that the possibility of using these codes for Russian plutonium must be checked. This check was based on an analysis of data obtained on more than 6000 isotopic compositions during certification of the RT-1 plutonium. A characteristic of the relation proposed in this article is that it takes account of the change in the isotopic composition of plutonium over time.

An understanding of the phase diagram of elemental plutonium (Pu) must include both, the effects of the strong directional bonding and the high density of states of the Pu 5f electrons, as well as how that bonding weakens under the influence of strong electronic correlations. Here we present electronic-structure calculations of the full 16-atom per unit cell α-phase structure within the framework of density functional theory together with dynamical mean-field theory. Our calculations demonstrate that Pu atoms sitting on different sites within the α-Pu crystal structure have a strongly varying site dependence of the localization-delocalization correlation effects of their 5f electrons and a corresponding effect on the bonding and electronic properties of this complicated metal. In short, α-Pu has the capacity to simultaneously have multiple degrees of electron localization/delocalization of Pu 5f electrons within a pure single-element material.

Advances in nuclear power reactors include the use of mixed oxide fuel, containing uranium and plutonium oxides. The high-temperature behaviour and structure of PuO 2– x above 1,800 K remain largely unexplored, and these conditions must be considered for reactor design and planning for the mitigation of severe accidents. Here, we measure the atomic structure of PuO 2– x through the melting transition up to 3,000 ± 50 K using X-ray scattering of aerodynamically levitated and laser-beam-heated samples, with O/Pu ranging from 1.57 to 1.76. Liquid structural models consistent with the X-ray data are developed using machine-learned interatomic potentials and density functional theory. Molten PuO 1.76 contains some degree of covalent Pu–O bonding, signalled by the degeneracy of Pu 5 f and O 2 p orbitals. The liquid is isomorphous with molten CeO 1.75 , demonstrating the latter as a non-radioactive, non-toxic, structural surrogate when differences in the oxidation potentials of Pu and Ce are accounted for. These characterizations provide essential constraints for modelling pertinent to reactor safety design. The molten structure of plutonium oxide—a component of mixed oxide nuclear fuels—is measured, showing some degree of covalent bonding. Its atomic structure is similar to that of cerium oxide, which could be a non-radioactive structural surrogate.

The biokinetic and dosimetry models recommended by the International Commission on Radiological Protection do not incorporate dosimetric uncertainty. Recently, Bayesian approach—offering distribution of dose estimates rather than a single point value—has been applied in epidemiological risk modeling. Although the true dose is unknown, Bayesian analysis is assumed to provide information on the true dose through a posterior distribution. This study presents a unique opportunity to validate that assumption. Radiation dose is directly related to the time-dependent radionuclide activity deposited or retained in organs and tissues. Therefore, uncertainties in organ activity predictions derived from biokinetic modeling can serve as proxies for the uncertainties in dose estimation. In this study, uncertainties in model predictions of 239 Pu organ activities were evaluated for 20 former nuclear workers with known plutonium inhalation. Ten individuals from Los Alamos were primarily exposed to soluble Pu-nitrate, while ten from Rocky Flats were exposed to insoluble PuO 2 . All individuals were volunteer tissue donors to the United States Transuranium and Uranium Registries. Urine bioassay data and post-mortem measurements of 239 Pu in the liver, skeleton and respiratory tract were used in the analysis. Latin hypercube sampling was employed to generate parameter sets for each realization, varying only two parameters of the human respiratory tract model: the rapidly dissolved fraction, f r and slow dissolution rate, s s . For each realization: (i) intake was estimated using maximum likelihood fitting of the urine bioassay data, and (ii) post-mortem organ activities, used as surrogates of true doses, were predicted based on the estimated intake. Predicted distributions of 239 Pu organ activities were compared to point estimates based on default parameters for soluble and insoluble plutonium, as well as to the measured post-mortem values. Results showed that in most cases, the predicted distributions did not cover the measured values (75% for liver, 90% for skeleton, and 50% for the respiratory tract), indicating a need to improve current biokinetic models. Additionally, in some cases, the model predictions were not conservative, which raises concerns from a radiation protection standpoint.

In order to study the effect of air masses on the distribution of artificial radionuclides on both sides of the mountain range, Pu and 137 Cs in forest soils of the Qinling Mountains in Shaanxi Province were determined for the first time. The 239+240 Pu and 137 Cs activity concentrations ranged from 0.001 ± 0.001 to 0.501 ± 0.031 Bq/kg and 0.27 ± 0.06 to 7.82 ± 0.34 Bq/kg, respectively. The 240 Pu/ 239 Pu atom ratios in samples ranged from 0.160 ± 0.024 to 0.218 ± 0.037 with an average value of 0.188 ± 0.014, indicated that Pu isotopes from the Qinling Mountains mainly came from global fallout. The results of this research add the 239+240 Pu activity concentrations and 240 Pu/ 239 Pu atom ratio of the Qinling Mountains, the atmospheric circulation in the Qinling Mountains did not significantly affect the Pu content. Also, it provides significant data on the radioactivity of Chinese soils.

The assessment of nuclear safety and the potential risks associated with proliferation is a critical area of research in the context of nuclear energy utilization. This study focuses on evaluating the Material Attractiveness (ATTR) in several light water-based reactor designs, specifically NuScale, ESBWR, BWRX-300, and PWR, both during reactor operation and post-operation. The analysis employed Origen 2.2 for modeling radioactive decay and MCNP4C for assessing material attractiveness. The findings reveal an increase in the production of plutonium isotopes, with the exception of Pu-239, which decreases as a result of the fission. Initially, the Pu-240 composition across all four reactors is classified as Super-grade plutonium. However, with increased burnup, the Pu-240 composition transitions to a reactor-grade plutonium level. At the initial of irradiation, the ATTR values were determined to be 0.19 for the ESBWR, 0.20 for the PWR, 0.16 for the BWRX-300, and 0.21 for NuScale, categorizing them within the weapon-grade range. By the end of reactor operation, these values had significantly decreased, with ESBWR at 0.0125, PWR at 0.0148, BWRX-300 at 0.0111, and NuScale at 0.0133, placing them in the un-usable grade category. This marked reduction in ATTR values, correlated with increased burnup, indicates an effective decrease from weapon-grade to un-usable grade by the end of the reactor^s operational period. This trend is primarily influenced by the increased production of isotopes Pu-238, Pu-240, Pu-242, and the corresponding decrease in Pu-239, the primary fissile material.

While many transnational histories of the nuclear arms race have been written, Kate Brown provides the first definitive account of the great plutonium disasters of the United States and the Soviet Union. She draws on official records and dozens of interviews to tell the extraordinary stories of Richland, Washington and Ozersk, Russia--the first two cities in the world to produce plutonium. To contain secrets, American and Soviet leaders created plutopias--communities of nuclear families living in highly-subsidized, limited-access atomic cities. Plutopia was successful because in its zoned-off isolation it appeared to deliver the promises of the American dream and Soviet communism; in reality, it concealed disasters that remain highly unstable and threatening today.

Based on density functional theory, a first-principles study of the adsorption behavior of hydrogen atoms on the PuO2(111) surface is carried out in this work. Models for three different surface morphologies of PuO2(111) are established. It is found that the surface with the outermost oxygen atom (sub outer Pu atom) morphology has the best stability. Based on this model, the adsorption energy, bader charge, and electronic density of the states of a hydrogen atom at different adsorption sites are calculated. Finally, we analyzed the process of hydrogen dissociation into hydrogen atoms on the surface using the cNEB method. The results indicate that the top position of the outermost oxygen atom and the bridge position of the second outermost plutonium atom are relatively stable adsorption configurations, where hydrogen atoms lose electrons and release heat, forming O-H bonds with oxygen atoms. The density of states of O-p orbital electrons will undergo significant changes, reflecting the hybridization of O-p and H-s orbital electrons, forming a stable bonding effect. The dissociation of hydrogen molecules into two hydrogen atoms adsorbed on the top of oxygen atoms requires crossing an energy barrier of 1.06 eV. The decrease in total energy indicates that hydrogen tends to exist on the PuO2(111) surface in a hydrogen atom state. The research results lay the foundation for theoretically exploring the hydrogenation corrosion mechanism of the PuO2(111) surface, providing theoretical support for exploring the corrosion aging of plutonium oxide, predicting the material properties of plutonium oxide under extreme and special environments.