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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.

Purpose Speciation of artificial radionuclides in bottom sediments (BS) collected in the Yenisei River (Siberia, Russia) was studied, to determine temporal trends in the potential mobility of radionuclides in BS, whose releases increased ( 238, 239, 240 Pu), decreased ( 60 Co, 137 Cs), or ceased ( 152, 154 Eu) over the period of this study. Methods Integrated samples of BS whose total thickness reached 20 cm were collected in the Yenisei River in September-October 2014 and 2018–2023 downstream of a controlled radioactive effluent site. A sequential extraction technique (modified Tessier method) was applied to study speciation of radionuclides in BS. Six fractions of radionuclides were extracted from sediment samples: exchangeable, associated with carbonates, associated with oxides and hydroxides of Fe, Mn, associated with organic matter, associated with amorphous silicates, and associated with residual solids. Concentrations of γ-emitting radionuclides, plutonium, minerals, and organic matter were determined in bulk samples of BS and their fractions. Results The largest percentages of 137 Cs (83 ± 9%) and Pu isotopes (67 ± 17% of 238 Pu, 64 ± 18% of 239,240 Pu) were irreversibly bound to residual solids of BS; percentages of 152 Eu and 124 Eu in this form were less than 27% and 11%, respectively. The percentage of 60 Co in residual solids of BS was 59 ± 24%, although the proportions of species of 60 Co were quite variable, demonstrating no temporal trends. No consistent trends were revealed in the forms of Pu in BS after the upsurge of releases of Pu to the river. Easily mobilized forms of 152 Eu (up to 20%) were registered in BS for up to six years after termination of Eu releases. A decrease in the percentage of easily mobilized 137 Cs corresponded to a similar decrease in releases of 137 Cs. Conclusions This study showed considerable differences in the forms of occurrence of the artificial radionuclides 60 Co, 137 Cs, 152 Eu, 154 Eu, and isotopes of Pu deposited in BS of the Yenisei River in the vicinity of a controlled radioactive discharge site over the period of this study. Temporal trends in the forms of 137 Cs and 152 Eu in BS related to changes in controlled releases of these isotopes were revealed.

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.

This study investigated the Arctic troposphere, providing a comprehensive experimental database on nuclear aerosols that has significantly improved since 1999. The activity concentrations of 238Pu, 239+240Pu, and 241Am were measured in surface air at Hornsund, Spitsbergen, from 2007–2021. A multivariate approach, incorporating meteorological data, gamma-emitter records, and isotopic ratios, was employed to explain the dynamics of change and the provenance of transuranium elements. Levels of 238Pu and 239+240Pu were found comparable to those documented over the past decades at various locations. The highest activity concentrations were 6.61 nBq m−3 for 238Pu and 15.5 nBq m−3 for 239+240Pu, observed in 2015. Although coinciding with the resuspension and atmospheric transport of radionuclides due to the 2015 wildfires near the Chernobyl zone, a direct contribution to Hornsund remains uncertain. Further data exploration revealed a correlation between 239+240Pu and seasonal processes, including local dust redistribution and horizontal tropospheric transport of haze layers from distant areas. While similar mechanisms likely regulated a portion of 238Pu, its random enrichment relative to known nuclear events was frequently detected. As a general trend, 241Am exhibited notably high activity concentrations, reaching up to 354 nBq m−3 in 2019. Episodic signals of 237Np were identified in 2013, 2014, and 2018. All occurrences of 241Am, 237Np, and outliers of 238Pu were not linked to natural processes; hence, the possibility of recent radioactive emissions should be considered. Trajectory simulations conducted for 2019 indicated prominent transport pathways to Hornsund from northern Eurasia.

An ICP-MS method was developed to measure the actinides in autopsy brain tissue of an occupationally exposed individual. 239 Pu, 240 Pu, 241 Am, and 238 U concentrations as well as 240 Pu/ 239 Pu, 235 U/ 238 U atom ratios were measured by quadrupole ICP-MS following extraction chromatography. The 239 Pu concentrations measured in the cerebral lobe of the right side of the brain was 0.66 ± 0.08 ng/kg. The 239 Pu/ 240 Pu ratio was 0.071 ± 0.025. The 241 Am level was below the LOD. The 238 U concentration was 106.6 ± 0.29 ng/kg and the 235 U/ 238 U ratio was 0.00703 ± 0.00087.

Vertical distributions of 239Pu, 240Pu, 241Pu, 241Am, 137Cs, and 210Pb concentrations, and 240Pu/239Pu ratios were determined in seafloor sediments in the western North Pacific Ocean and the Sea of Japan to discuss the behavior of these radionuclides in the ocean and to identify the sources of anthropogenic radionuclides in the seafloor sediments. The excess 210Pb accumulation rates were greater than the predicted rates from the overlying water column. A significant amount of the Pacific Proving Grounds-derived Pu and Am has been transported by ocean currents and it has been accumulated onto the seafloor sediments by enhanced particle scavenging.

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.