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It is proposed to measure the shift in the angular distribution of light charged particles (LCP) in ternary fission caused by polarized neutrons of plutonium isotopes in the resonance region with eV for the Pu target and eV for the Pu target. The reliability of interpretation of these experiments will compare favorably with measurements carried out previously at meV. The advantage is associated with a noticeable weakening of the influence of resonances, the parameters of which may raise some doubts. We are talking about resonances introduced at neutron energies eV. In addition, in the region of these two resonances, the fractions of impurity partial cross sections with a spin different from the spin of the resonance itself are small. It is important that the magnitude of the effects expected at the indicated resonance energies will be significantly greater than those previously obtained in the cold energy region. [ABSTRACT FROM AUTHOR]

This paper describes a procedure for the estimation of 241Am and 239Pu activity present in the human tissue by measuring the depth of contaminant using a portable Planar High Purity Germanium detector (HPGe). The ratios of photopeak counts of X-rays or gammas obtained with the detector coupled to collimator are calculated for the estimation of depth of the contaminant and the optimum one is determined. Since Minimum Detectable Activities (MDA) for the detector coupled to a collimator are higher than that of bare detector, activity must be estimated using bare detector, after locating the contaminant. Two methods are described for the estimation of plutonium coexisting with 241Am: (i) Abundance and isotopic correction for 239Pu (ii) and 239Pu:241Am ratio. The procedure to estimate 239Pu when plutonium isotopes alone are present is also established. An optimum monitoring period to detect the minimum value of intake for both radionuclides corresponding to chelation therapy and excision is also derived. [ABSTRACT FROM AUTHOR]

We have applied cavity ring-down spectroscopy (CRDS) to the study of the 166Er isotope in an atomic beam. These measurements were realized with an external cavity diode laser tuned to the 400.9 nm atomic transition of erbium and a customized high-finesse ring-down optical cavity under vacuum. Erbium atomic beams of different number densities were generated in a tantalum foil micro-crucible within the cavity. Absorbance values of the 166Er isotope between 3 × 10−6 and 7 × 10−5 were measured with a best-case precision on the order of 10−6, which is remarkable when considering the extreme temperatures at which the measurements were conducted, and the short detection path which is characteristic of collimated atomic beams. Number densities of erbium atoms were inferred to be between 2 × 106 and 6 × 107 cm−3. This work demonstrates for the first time the ability of studying dilute atomic beams of refractory materials with high accuracy utilizing CRDS. In these initial studies, we used erbium as a model system, but we expect to extend the proposed approach to the measurement of isotopes of uranium and plutonium for nuclear non-proliferation applications. [ABSTRACT FROM AUTHOR]

Actinide minor is a reactor waste with high toxicity and a long half-life. Minor actinides can be reduced by reusing them as fuel mixtures in reactors. This research uses PWR reactors with the primary fuel UN-PuN or Uranium Plutonium Nitride with a burning time of 5 years. The fuel consists of enriched Uranium, reactor-grade Plutonium from LWR waste, and minor actinides including Neptunium-237, Americium-241, and Curium-244. The purpose of this study was to find a design that is effective in reducing minor actinide waste. There are six designs or cases used in the addition of minor actinides. Each case has six minor actinide pins in each assembly. The addition of minor actinides is arranged in heterogeneous cores. The analysis was carried out by observing the values of k-eff, excess reactivity, and mass of minor actinides obtained from simulations using OpenMC code 0.13.2 and the ENDF/B-VIII library. The homogeneous core obtained an excess reactivity of 9.7 % with a percentage of plutonium of 8 %. The results of the homogeneous core are used as a reference for preparing a heterogeneous core. The heterogeneous core obtained an excess reactivity of 9.9 % with a percentage of plutonium F1: 5.5 %, F2: 8 %, and F3: 10.5 %. Np-237 can be reduced by 53 kg, and Am-241 can be reduced by 61 kg with minor actinide pins in case 1. Cm-244 can be reduced by 363 kilograms with minor actinide pins in case 6. Excess reactivity in the addition of Np-237 and Am-241 decreased to 5.3 %, while the accumulation of Cm-244 increased to 12.1 %. [ABSTRACT FROM AUTHOR]

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In this paper, we analyze the possibility of using 100% MOX fuel (mixed oxide uranium-plutonium fuel) in a VVER-600 reactor with nominal power of 1600 MW(t). The VVER-600 core consists of 163 fuel assemblies (FAs) similar in design to VVER-TOI fuel assemblies. MOX fuel contains tailings of uranium (99.8% 238U and 0.2% 235U) and a mixture of plutonium isotopes. A campaign with uranium oxide (UOX) fuel is also modeled to compare the neutronic characteristics with those of the MOX variant. For both MOX and UOX options, the efficiency of fuel use is analyzed at an increase in the water/fuel ratio (W/F) in comparison with the base case. The W/F ratio increases in three ways. For calculated estimates, the KASSETA-BIPR-7 software package is used. The results of calculations of individual neutronic characteristics with 100% MOX fuel when modeling the VVER-TOI variant with power of 3300 MW(t) are presented to compare with the results of calculations using other independent codes. [ABSTRACT FROM AUTHOR]

The Rocky Flats (RF) Plant was a weapons manufacturing facility that operated from the early 1950s to 1989. Its primary missions were the production of plutonium (Pu) pits for thermonuclear weapons and the processing of retired weapons for Pu recovery. The purpose of this study was to estimate radiation doses to a cohort of 4499 RF workers from an intake of 239Pu, the primary plutonium isotope handled at the site. The latest biokinetic models of the International Commission on Radiological Protection, or site-specific variations of those models, were used to estimate 239Pu intakes for each worker based on model fits to bioassay data often coupled with lung measurements. Urinary excretion and lung retention data for most 239Pu intakes could be fit reasonably well by a mixture of Pu dioxide and moderately soluble material. For some workers, better fits were obtained by application of other absorption types including Type S, 239Pu nitrate, or pure 239Pu dioxide, or by assuming intake via a wound. The lungs typically received the highest tissue doses, with fifty-year committed equivalent doses in the range of 0.5–1 Sv for 275 workers, 1–5 Sv for 115 workers, and greater than 5 Sv for 12 workers. RF was a unique site regarding a large number of lung measurements available for determining the appropriate absorption types for inhaled material. This provided higher confidence in reconstructed 239Pu doses than is generally gained from urinary data alone. [ABSTRACT FROM AUTHOR]

Accidental inhalation intake of plutonium isotopes and 241Am occurred at a Pu research facility in Japan in 2017, and the five workers involved in this accident were treated by the administration of Ca/Zn-diethylenetriaminepentaacetic acid (DTPA). For the worker who was most internally exposed, the therapy was continued over 1 y after the accident. Urinary samples collected before and after each administration were subject to bioassay to evaluate the efficacy of the dose reduction. This study performed numerical analyses using a biokinetic model dealing with 241Am-DTPA with reference to the European Coordinated Network on Radiation Dosimetry approach, which assumes that the complex of actinides and Ca/Zn-DTPA is generated in the designated compartments in the biokinetic model. The results of the model prediction well captured the trend of the observed urinary excretion in the long-term bioassay and would be useful to evaluate the efficacy of the Ca/Zn-DTPA administration for the worker involved in the accident. [ABSTRACT FROM AUTHOR]

In order to study the effect of air masses on the distribution of artificial radionuclides on both sides of the mountain range, Pu and 137Cs in forest soils of the Qinling Mountains in Shaanxi Province were determined for the first time. The 239+240Pu and 137Cs 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 240Pu/239Pu 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+240Pu activity concentrations and 240Pu/239Pu 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. [ABSTRACT FROM AUTHOR]

We present a new analytical method for accurately measuring femtogram amounts of Pu in environmental swipe samples using a high-purity 244Pu spike and multi-collector inductively-coupled-plasma mass spectrometry. The method was validated by comparative measurements of samples that were previously analysed using a 242Pu spike. The 244Pu spike allows direct normalization of all Pu isotopes to both 244Pu and 239Pu, along with online monitoring of PbAr interferences, resulting in highly-sensitive and accurate Pu assay and isotope ratio measurements. Expanded uncertainties were typically < 2.5% for Pu amounts larger than 20 fg, and < 1% for Pu isotope ratios larger than 0.08. Detection thresholds (Lc) were well below 1 fg for all Pu isotopes. [ABSTRACT FROM AUTHOR]

Quantifying soil redistribution rates is a global challenge addressed with direct sediment measurements (e.g. traps), models, and isotopic, geochemical, and radionuclide tracers. The isotope of plutonium, namely 239+240 Pu, is a relatively new soil redistribution tracer in this challenge. Direct validation of 239+240 Pu as a soil redistribution tracer is, however, still missing. We used a unique sediment yield time series in southern Italy, reaching back to the initial fallout of 239+240 Pu to verify 239+240 Pu as a soil redistribution tracer. Distributed soil samples (n=55) were collected in the catchment, and at undisturbed reference sites (n=22), 239+240 Pu was extracted, measured with inductively coupled plasma mass spectrometry (ICP-MS), and converted to soil redistribution rates. Finally, we used a generalized additive model (GAM) to regionalize soil redistribution estimates for the catchment. For the catchment sites, mean 239+240 Pu inventories were significantly reduced (16.8 ± 10.2 Bq m -2) compared to the reference inventory (40.5 ± 3.5 Bq m -2), indicating the dominance of erosion. Converting these inventory losses into soil erosion rates resulted in an average soil loss of 22.2 ± SD 7.2 t ha -1 yr -1. The uncertainties of the approach stemmed mainly from the high measurement uncertainties of some low-activity samples where samples have been bulked over depth. Therefore, we recommend taking incremental soil samples and extracting larger soil volumes (∼ 20 g). The geographic coordinates and the flow accumulation best described the spatial pattern of erosion rates in the GAM model. Using those predictors to upscale Pu-derived soil redistribution rates for the entire catchment resulted in an average on-site loss of 20.7 t ha -1 yr -1 , which corresponds very well to the long-term average sediment yield of 18.7 t ha -1 yr -1 measured at the catchment outlet and to 137 Cs-derived soil redistribution rates. Overall, this comparison of Pu-derived soil redistribution rates with measured sediment yield data validates 239+240 Pu as a suitable retrospective soil redistribution tracer. [ABSTRACT FROM AUTHOR]

This paper presents the results obtained from numerical evaluations for the possibility of large-scale 238Pu production in the light-water VVER-1000 reactor and the reactivity effect caused by the loss-of-coolant accident in the central fuel assembly of the reactor core. This fuel assembly containing the Np–Am-component of minor actinides was placed in the center of the reactor core and intended for intense production of 238Pu. Optimal conditions were found for large-scale production of plutonium with an isotope composition suitable for application in radioisotope thermoelectric generators. The reactivity effect from the loss-of-coolant accident in the central Np–Am fuel assembly was evaluated, and the perturbation theory was used to determine the contributions of some neutron processes (leakage, absorption, and moderation) to the total variation of the effective neutron multiplication factor. [ABSTRACT FROM AUTHOR]

Since the beginning of the use of nuclear energy in the twentieth century, atmospheric nuclear weapons testing, nuclear accidents, and spent fuel reprocessing have released large amounts of radioisotopes into the environment, especially plutonium isotopes. As an important anthropogenic radionuclide, plutonium is mainly produced by neutron irradiation of uranium. Plutonium isotopes and their ratios from different sources have a specific 'fingerprint', which is determined by irradiation time and intensity. Accordingly, several methods have been developed for the analysis of plutonium isotopes. As a popular new tracer in recent years, plutonium isotopes could be used for environmental tracer applications and source identification of regional environmental contamination sources. This paper summarizes and compares the pretreatment of plutonium isotopes in various samples and the detection and analysis methods in recent years. Plutonium isotopes in various environmental samples were enriched by chemical treatments, such as ashing, acid digestion, and alkali fusion. Then it was purified and separated by extraction resins to remove interfering nuclides for the subsequent mass spectrometry. The practical applications of plutonium isotopes and their related ratios in the environment are summarized, such as the determination of plutonium isotopes and their related ratios in the environment near two representative nuclear power plant accidents and the monitoring of the safe operation of nuclear power plants; the establishment of a plutonium isotope database in the vicinity of Chinese waters; and the traceability of plutonium isotopes in environmental regions through the global atmosphere and sand and dust. Finally, the outlook for subsequent research in plutonium isotope detection and applications is presented. [ABSTRACT FROM AUTHOR]

MCNPX computer code is used to design a three-dimensional model for a typical Pressurized Water reactor (PWR) core. Uranium Nitride fuel (UN) was tested for the reactor and the results were compared with a typical UO 2 fuel. Neutron spectrum, power distributions, plutonium isotopes productions, and kinetics and safety parameters were evaluated. It was found that thermal neutron spectrum is harder in UN than in UO 2. UN can achieve a longer fuel residence time in the reactor than UO 2. Kinetic and safety parameters are within the acceptable range similar to UO 2. Control rod worth is lower in UN due to thermal flux hardening. This research was carried out with the addition of three types of variations of burnable poison. [ABSTRACT FROM AUTHOR]

Ten soil cores were collected from slopes and gully bottoms in the Loess Plateau, China, and analyzed for plutonium isotopes to investigate their source, level, and distribution in the Liudaogou Catchment of the Loess Plateau. The soil 240Pu/239Pu atomic ratios (0.158–0.209) suggested that global fallout is the dominant source of Pu in this area. The 239,240Pu inventories (0.94–77.91 Bq m− 2) indicated that up to 80% of Pu was lost due to severe soil erosion in the past decades. Land use types, vegetation coverage, and topography significantly influence the preservation and redistribution of Pu, and alfalfa might be a promising restoration plant for mitigating soil erosion on the northern Loess Plateau. [ABSTRACT FROM AUTHOR]

Abstract—This paper examines the distribution of 137Cs and plutonium isotopes in the modern sediments collected from different parts of the Laptev Sea during cruises of the R/V Academik Mstislav Keldysh in 2017 and 2019. It was found that the 137Cs activity in water and sediments is within the global background level, which is typical for the Arctic seas. In all collected samples, the specific content of 239,240Pu isotopes is below the detection level. According to the results of isotope analysis of excess 210Pb, the sedimentation rates in two cores sampled in the Laptev Sea are 0.18 and 0.23 cm/year. The speciation of 239Pu introduced in samples of bottom sediments under laboratory conditions was analyzed by several methods. It was shown that the most part of 239Pu is associated with weakly dissolved organo-mineral components. 30–39% 239Pu were found in the organic easily soluble acids and humic substances, which include fulvic and humic acids of bottom sediments. [ABSTRACT FROM AUTHOR]

Information about the sources and mechanisms of plutonium release into the environment is summarized. The magnitudes and distribution of global plutonium fallout, as well as data on technogenic sources of plutonium isotope releases into the environment, are reviewed. For this purpose, the supply of plutonium as a result of nuclear explosions at test sites, such as Nevada, Semipalatinsk, Novaya Zemlya, etc., and the scale of environmental contamination as a result of tests were considered. The data on the intake of plutonium after nuclear and radiation accidents at nuclear power plants (Chernobyl nuclear power plant, Fukushima, etc.) and at enterprises of the nuclear complex (Kyshtym accident, etc.) are presented. Separately, plutonium intake into the natural environment through emissions and discharges of nuclear complex enterprises (Sellafield, MCC (Krasnoyarsk), etc.) is considered. Information about the levels and content of plutonium isotopes in various media and environmental objects, as well as information about the parameters characterizing the migration of plutonium in various media and the transition between them is generalized and presented. Forms of plutonium occurrence in soils (distribution by granulometric fractions, chemical forms, "hot" particles, etc.) are considered, and information on the characteristic levels of plutonium concentrations in soils for various objects is summarized. Data on the concentrations of plutonium in the air are given. Information on the forms of plutonium in the aquatic environment, as well as on the characteristic levels of plutonium concentrations in various water bodies, including the World's oceans, is presented. Information on the transition coefficients of plutonium isotopes in the soil–plant system is summarized. Particular attention is paid to plutonium isotopes in biological objects and the human body. [ABSTRACT FROM AUTHOR]

The Aare river system in Switzerland, with two nuclear power plants on the banks of the river, and its intermediate lakes and reservoirs, provides a unique opportunity to analyze the contribution of different sources to the radioactive contamination. Sediment cores were collected from two lakes and a reservoir, all connected by the river Aare. In order to study the influence of the Chernobyl accident, one sediment core was collected from a lake in the southern part of Switzerland. The sediment cores were sliced and analyzed with gamma ray spectrometry. Plutonium, americium, and uranium were extracted radiochemically, and their concentrations were measured with a sector field ICP-MS. The uranium isotope ratios were further measured with a multi collector ICP-MS. The maximum 137Cs activity from the Chernobyl accident and the Pu and 137Cs activities associated to the 1963 global fallout maximum were well identified in sediments from all three lakes. High-resolution records of plutonium isotopes in the zone of the sediments corresponding to the period of maximum fallout from the atmospheric nuclear weapon testing showed distinct fingerprints, depending on the different test activities. Pu isotope ratios could be used to detect non-global fallout plutonium. The ratio 241Am/241Pu was used to determine the age of the plutonium. Despite of very low 241Pu and 241Am concentrations, the calculated plutonium production dates seemed to be reasonable for the sediment layers corresponding to the NWT tests. The calculated production date of the plutonium in the upper most 15 cm of the sediment core seemed to be younger. The reason for this could be additional non-global fallout plutonium. For the lake sediments, natural ratios for 235U/238U and enriched or depleted ratios for 234U/238U were measured, depending on the lake. A small increase of the 236U/238U ratio could be recognized for the NWT zone in all three lakes and, for Lake Lugano, a further distinct increase in the Chernobyl layer. [ABSTRACT FROM AUTHOR]

This paper considers the possibility for large-scale production of plutonium isotope 238Pu in the light-water nuclear power reactor VVER-1000. 238Pu is a unique source of long-term autonomous energy supply in various devices for remote regions of the Earth and in outer space. The design of the irradiation device with 237NpO2 as a starting material is proposed, which is placed in the central zone of the VVER-1000 reactor core and makes it possible to achieve 8% of the specific Pu production (Pu/237Np) by optimizing the pitch of NpO2-rod lattice. The computations showed that the scale of 238Pu production in the irradiation device was remarkably larger (2 ÷ 7 times more) than similar values in research reactors. At the same time, the use of heavy neutron moderators with low neutron absorption (natural lead or lead isotope 208Pb) around the NpO2 fuel assembly (FA) made it possible to obtain high-purity 238Pu with the content of 236Pu below 2 ppm. The paper also shows that if the irradiation device is placed in central zone of the VVER-1000 reactor core, then the displacement damage dose in the reactor vessel remains low enough to conserve its strength properties throughout the entire period of the reactor operation (60 years). [ABSTRACT FROM AUTHOR]

Lakes are effective sentinels of global change owing to their sensitivity to land-use changes and climate variability in their catchment. Santa María del Oro Lake (SAMO, NW Mexico) is of interest both for global change studies and as a natural resource to sustain the economy of local communities. Four sediment cores were used to evaluate the temporal variations of sediment accumulation, under the hypothesis that changes in sediment input are mostly driven by anthropic activities developed in the lake surroundings. Radiocarbon (14C) dating of SAMO sediments was precluded by a large and variable reservoir effect, inducing an age offset of ~ 4000 years. Well-constrained chronologies over the past century were obtained by 210Pb dating, corroborated by the stratigraphic markers 137Cs, 239+240Pu, and 14C-fraction modern. Geochemical, magnetic susceptibility, and meteorological data were used to elucidate the main controls of sedimentation processes in the lake. Mass accumulation rates were high, likely because of the natural vulnerability of catchment soils to hydric and aeolian erosion. The highest values, observed towards the lakeshore, were attributed to the influence of seasonal runoff from the surrounding steep hills, and the proximity of human settlements and agricultural fields. Mean mass accumulation rates increased with time (from 0.03 ± 0.01 g cm−2 year−1 between 1900 and 1950, to 0.14 ± 0.10 g cm−2 year−1 after the 1950s), although the most recent values were comparable to the mean values during the pre-1950 period. Accumulation maxima across the lake, occurring mostly since the 1980s, concurred with precipitation minima and were related to terrigenous pulses associated with soil erosion, likely favored by lower soil humidity and the occurrence of wildfires during dryer years. Controls on the development of human settlement and agriculture practices should be included in the long-term environmental management plans for the conservation of the lake resources. [ABSTRACT FROM AUTHOR]

Accelerator Mass Spectrometry is the most sensitive measurement method that allows us to determine 239, 240, and 244Pu radioisotopes in environmental samples with extremely low isotopic concentrations. By measuring plutonium isotopes, we focus our research activity on two main directions, monitoring of environmental nuclear pollution and nuclear astrophysics. This report gives an overview of the progress that was made in the determination of plutonium isotopes at IFIN-HH, and it starts with the studies performed for the transport and measurement of actinides using the 1MV Tandetron Accelerator. The 238U and 232Th isotopes were used as pilot beams for the determination of ion transport parameters, after which the isotopic ratios 239Pu/242Pu, 240Pu/242Pu, and 244Pu/242Pu were measured using the new Plutonium Standard ColPuS. The results obtained for the isotopic ratios agree with the consensus values of the standard. In addition, we developed radiochemical procedures for thorium, plutonium, and uranium separation, the chemical recoveries of uranium and thorium using UTEVA and TEVA resins are presented, where we used an Agilent ICP-MS system (Inductively Coupled Plasma Mass Spectrometry). The radiochemical separation is important mainly for obtaining target materials that can provide microscopic pilot beams as U and/or Th. Finally, a short overview is provided of the molecular interference challenges that are encountered when measuring plutonium isotopes. [ABSTRACT FROM AUTHOR]

Highlights: What are the main findings? The first radiocesium and Pu isotopes data in Korean seas were present in 2011–2012; Higher 134Cs were observed in Korean seas immediately after the Fukushima accident; Fukushima-derived nuclides were introduced to Korean seas by the atmosphere for up to 2 months. What is the implication of the main finding? The residence times of 137Cs in Korean seas water is estimated to be 8–25 years; The dataset could be used to predict the dispersion of anthropogenic pollutant; The dataset could also be used to validate the model for future NPP accident around the Korean seas. The distributions of artificial radionuclides, radiocesium (134Cs and 137Cs) and plutonium isotopes (238Pu and 239+240Pu), in the surface water around the Korean seas (East/Japan Sea and Yellow Sea) in 2011–2012 and in three sections in the North Pacific between 2011 and 2014 were examined. The 137Cs activities in the surface water in the Korean seas in 2011 (immediately after the Fukushima nuclear power plant (NPP) accident on 17 March 2011) were comparable or not significantly different relative to those in 2010 and 2012. However, 134Cs, which had been not detected in the study area before the Fukushima accident (under the detection limit of 0.1 mBq kg−1 level), were detected rapidly in 2011 after the accident (in about 60% of the 72 samples) and gradually disappeared due to their short half-life (t1/2 = 2.06 years) in 2012 (detected in about 16% of the 24 samples). In addition, the highest activities of radiocesium and Pu isotopes appeared locally in some stations of the Korean Strait region (located between Korea and Japan) within 1–2 months immediately after the accident. This suggests that the radioactive nuclides released immediately after the Fukushima accident were significantly introduced through the atmosphere, based on recent studies conducted in neighboring areas. We also showed that the spatial distribution of radiocesium in the North Pacific moved eastward from 2012 to 2014, and we attempted to quantify the residence time of radiocesium (137Cs) in the Korean seas based on the long-term (tens of years scale) temporal trends of 137Cs activity data, which have been collected since the 1960s and 1970s. The estimated retention time of 137Cs in the East/Japan Sea and Yellow Sea were 25 ± 0.6 and 8.0 ± 0.1 years, respectively. These results are expected to be used as a preliminary study for a potential future event of a marine radioactive accident (which, of course, cannot be predicted) and as basic data for predicting the influences of radionuclide releases in the ocean. [ABSTRACT FROM AUTHOR]

A generalized model of scavenging of the reactive radionuclide 239,240Pu was developed, in which the sorption‐desorption processes of oxidized and reduced forms on multifraction suspended particulate matter are described by first‐order kinetics. One‐dimensional transport‐diffusion‐reaction equations were solved analytically and numerically. In the idealized case of instantaneous release of 239,240Pu on the ocean surface, the profile of concentrations asymptotically tends to the symmetric spreading bulge in the form of a Gaussian moving downward with constant velocity. The corresponding diffusion coefficient is the sum of the physical diffusivity and the apparent diffusivity caused by the reversible phase transitions between the dissolved and particulate states. Using the method of moments, we analytically obtained formulas for both the velocity of the center mass and apparent diffusivity. It was found that in ocean waters that have oxygen present at great depths, we can consider in the first approximation a simplified problem for a mixture of forms with a single effective distribution coefficient, as opposed to considering the complete problem. This conclusion was confirmed by the modeling results for the well‐ventilated Eastern Mediterranean. In agreement with the measurements, the calculations demonstrate the presence of a maximum that is slowly descending for all forms of concentration. The ratio of the reduced form to the oxidized form was approximately 0.22–0.24. At the same time, 239,240Pu scavenging calculations for the anoxic Black Sea deep water reproduced the transition from the oxidized to reduced form of 239,240Pu with depth in accordance with the measurement data. Plain Language Summary: Scavenging of particle‐reactive elements is the process of the removal of a dissolved element in seawater by adsorption onto sinking particulate matters that finally deposit on the ocean floor. Scavenging is an important pathway for the transfer of nutrients and trace elements in the ocean. The radioactive isotopes of artificial origin are useful tools to provide constraints on the scavenging and organic particle removal processes. A generalized model of scavenging of reactive radionuclide 239,240Pu was developed, in which the processes of sorption‐desorption of oxidized and reduced forms of plutonium on multifraction particulate matter are described by the first‐order kinetics. We revealed that the vertical spread out of the cloud of plutonium isotope was caused by a novel dispersion mechanism equivalent to the diffusion process. The corresponding dispersion coefficient is the sum of the physical diffusivity and the apparent diffusivity caused by the reversible phase transition between the dissolved and particulate states. It was found that apparent diffusivity for scavenging large particles was several orders of magnitude greater than physical diffusivity in the deep ocean. The model reproduces striking differences in plutonium profiles in ventilated Eastern Mediterranean and the anoxic Black Sea caused by the interplay between oxidized and reduced forms. Key Points: Novel scavenging mechanism due to the reversible phase transition results in apparent diffusivity which surpasses the ocean diffusivityIn the well‐ventilated Eastern Mediterranean, the ratio of the reduced form to the oxidized form of 239,240Pu was approximately 0.22–0.24The 239,240Pu profile in the Eastern Mediterranean has one maximum, whereas in the anoxic Black Sea it has two maximums [ABSTRACT FROM AUTHOR]

The aim of this study was to determine the distribution of alpha-emitting plutonium isotopes from arable and uncultivated soils. The effect of soils cultivation on plutonium fractionation and mobility was studied using the sequential extraction technique (modified Tessier's method). Soil samples were collected from the surface layer in the selected points. By means of reagents with increasing leaching power, the fractions were separated: readily available, carbonate bound, sesquioxide (Fe/Mn) bound and organically bound as well as residual. The content of 239+240Pu in the fractions was determined by alpha spectrometry. The sequential analysis showed that in the case of uncultivated soils, 67% of Pu was combined with organic matter, 15% was permanently bound to the matrix, but only 4% was associated with the available fraction, and 2% with the carbonate one. Arable soils revealed a different distribution: 36% of Pu was combined with the organic fraction, only 7% was bound permanently but as much as 9% was bound with the available fraction, and 11% with the carbonate one. It was proved that plutonium is bound mostly by organic matter (67% Pu—uncultivated and 36%—arable soils), however, the amounts of Pu combined with the labile fractions (ion-exchange and carbonate) are approximately 4 times higher for the arable soils than for uncultivated ones. This proves that soil cultivation can lead to the launch of plutonium in soil and its transition to more accessible forms which can cause a radiological risk. [ABSTRACT FROM AUTHOR]

As an alternative approach to the transmutation of Np, Am, and Cm in fast power reactors, the use of a specialized facility is considered, which includes a molten-salt burner reactor and module for fuel reprocessing and fabrication. Based on the requirements for the consumer properties of the installation, a comparative analysis of transmutation for LiF–NaF–KF and LiF–BeF2 salts was performed. Calculations of the transmutation characteristics were performed for model systems. The computational results show the advantages of a reactor based on the LiF–NaF–KF salt on account of the higher solubility of actinide fluorides. For a given transmutation capacity, a burner reactor based on LiF–NaF–KF consumes several-fold less power-grade plutonium, right up to its absence in the equilibrium regime, as well as lower thermal power and lower production of fission products. Of note is a particular aspect of the molten-salt incinerator reactor that is associated with the accumulation of even-numbered plutonium isotopes during its operation whereby the plutonium extracted from the facility is actually converted into long-lived radioactive waste. [ABSTRACT FROM AUTHOR]

As an alternative approach to the transmutation of Np, Am, and Cm in fast power reactors, the use of a specialized facility is considered, which includes a molten-salt burner reactor and module for fuel reprocessing and fabrication. Based on the requirements for the consumer properties of the installation, a comparative analysis of transmutation for LiF–NaF–KF and LiF–BeF2 salts was performed. Calculations of the transmutation characteristics were performed for model systems. The computational results show the advantages of a reactor based on the LiF–NaF–KF salt on account of the higher solubility of actinide fluorides. For a given transmutation capacity, a burner reactor based on LiF–NaF–KF consumes several-fold less power-grade plutonium, right up to its absence in the equilibrium regime, as well as lower thermal power and lower production of fission products. Of note is a particular aspect of the molten-salt incinerator reactor that is associated with the accumulation of even-numbered plutonium isotopes during its operation whereby the plutonium extracted from the facility is actually converted into long-lived radioactive waste. [ABSTRACT FROM AUTHOR]

Plutonium (Pu) has been used as a mid-twentieth century time-marker in various geological archives as a result of atmospheric nuclear tests mainly conducted in 1950s. Advancement of analytical techniques allows us to measure 239Pu and 240Pu more accurately and can thereby reconstruct the Pacific Pu signal that originated from the former Pacific Proving Grounds (PPG) in the Marshall Islands. Here, we propose a novel method that couples annual banded reef building corals and nearshore anoxic marine sediments to provide a marker to precisely determine the start of the nuclear era which is known as a part of the Anthropocene. We demonstrate the efficacy of the methods using sediment obtained from Beppu Bay, Japan, and a coral from Ishigaki Island, Japan. The sedimentary records show a clear Pu increase from 1950, peaking during the 1960s, and then showing a sharp decline during the 1970s. However, a constantly higher isotope ratio between 239Pu and 240Pu suggest an additional contribution other than global fallout via ocean currents. Furthermore, single elevations in 240Pu/239Pu provide supportive evidence of close-in-fallout similar to previous studies. Coral skeletal radiocarbon displays a clear timing with the signatures supporting the reliability of the Beppu Bay sediments as archives and demonstrates the strength of this method to capture potential Anthropocene signatures. [ABSTRACT FROM AUTHOR]

Plutonium, as well as fission products such as 137Cs, had been released into the earth environment in 1945 after the first atmospheric nuclear explosion of plutonium bomb in the desert of New Mexico (USA, July 16) and later over Nagasaki (August 9), followed then by many other explosions. Thus, plutonium cycling in the atmosphere and ocean has become a major public concern as a result of the radiological and chemical toxicity of plutonium. However, plutonium isotopes and 137Cs are important transient tracers of biogeochemical and physical processes in the environment, respectively. In this review, we show that both physical and chemical approaches are needed to comprehensively understand the behaviors of plutonium in the atmosphere and ocean. In the atmosphere, plutonium and 137Cs attach with aerosols; thus, plutonium moves according to physical and chemical processes in connection with aerosols; however, since plutonium is a chemically reactive element, its behavior in an aqueous environment is more complicated, because biogeochemical regulatory factors, in addition to geophysical regulatory factors, must be considered. Meanwhile, 137Cs is chemically inert in aqueous environments. Therefore, the biogeochemical characteristics of plutonium can be elucidated through a comparison with those of 137Cs, which show conservative properties and moves according to physical processes. Finally, we suggest that monitoring of both plutonium and 137Cs can help elucidate geophysical and biogeochemical changes from climate changes. • Plutonium is one of the most concerning elements because of its radio and chemical toxicity. • Both plutonium isotopes and 137Cs have been monitored for more than half a century in the atmosphere and ocean. • The environmental behaviors of plutonium and 137Cs differ from each other due to differences in their chemical relativities. • Plutonium and 137Cs are transient tracers of environmental changes accompanied by climate changes. [ABSTRACT FROM AUTHOR]

• We compare soil redistribution rates estimated by both 239+240Pu and WaTEM/SEDEM. • Rates estimated by the two methods show important discrepancies. • These discrepancies help us understand the limitations of each method. • Less uncertain conditions are needed to validate the 239+240Pu method. • Both methods predict severe soil degradation in the next decades. Soil redistribution by water and tillage soil erosion has a profound effect on the spatial variability of soil security indicators. In this study, we assess the potential of estimating long-term soil redistribution rates across a Mediterranean olive orchard catchment using two methods: 239+240Pu and the WaTEM/SEDEM model. Additionally, we identify potential sources of uncertainty explain result discrepancies, and offer guidance for reducing uncertainty. Soil sampling points were taken both in the inter-row areas and below the tree canopies and 239+240Pu inventories were converted into soil redistribution rates using MODERN. Sediment yield data measured in the catchment outlet is used to calibrate WaTEM/SEDEM. The results show a poor agreement between both methods. In this sense, these results indicate that both methods are considerably affected by several sources of uncertainty, both inherent to the methods themselves and related to the specific conditions of the study area. The latter are mainly related to anthropogenic changes in the soil surface related to soil tillage and rill filling practices and an important past land leveling effect. Despite the discrepancies, both methods convey a similar overarching message: soil security and olive production can be highly threatened in the Mediterranean in the next decades. This study demonstrates the potential advantages of combining FRN-based estimates and model simulations and highlights the importance of selecting an appropriate study area in this type of studies and the need to recognize associated uncertainties when estimating soil redistribution rates, whether employing FRN-based or modelling methods. [ABSTRACT FROM AUTHOR]

The capability of the Fixed-Energy, Response Function Analysis with Multiple Efficiency (FRAM) software to accurately determine the isotopic composition of shielded uranium and plutonium was tested by the Joint Research Centre in Karlsruhe to support the use of FRAM by safeguards inspectors in the field. More than 17,000 spectra of certified uranium and plutonium reference materials were analyzed using different FRAM parameter sets. Uranium spectra were recorded by the ORTEC Detective spectrometer and analyzed by FRAM v5.1. Plutonium spectra were recorded by the ORTEC Micro-Detective spectrometer and analyzed by FRAM v5.2. The performance of FRAM was evaluated as a function of shielding thickness, measurement time, isotopic composition, and spectrum quality. The spectrum quality was quantified using a numerical figure-of-merit constructed from the uncertainties of the peak areas relevant for the isotopic analysis. A new FRAM parameter set for analyzing uranium spectra taken by the ORTEC Detective was developed. This provided more accurate results than the default parameter sets. In the case of plutonium samples, the default parameter sets were found to be optimal and could not be further improved. It was shown how FRAM's automatic analysis option improves the plutonium isotopic results, especially in the case of lower quality spectra. The results of this work will help safeguards inspectors optimize the use of electrically cooled gamma spectrometers and improve the accuracy of isotopic composition measurements in the field. [ABSTRACT FROM AUTHOR]

The Gamma Spectrum Predictor (GSP) tool currently being developed at Virginia Commonwealth University is a gamma ray spectrum generator for large sample (>200 g) nuclear materials. As countries throughout the world develop their nuclear power industries, nuclear safeguards training becomes increasingly important. Considering that these countries are new to the nuclear industry, access to material for hands-on training may be limited. Utilizing software to substitute for this hands-on training also proves difficult as much of the software that exists is either restricted or limited in capabilities for the simulations needed. The GSP tool is open source and offers a user-friendly interface that can be effectively used by countries developing nuclear industries. Currently, the GSP tool can generate gamma spectra of nuclear materials in 200 g and 800 g cans containing the uranium isotopes 234U, 235U, 236U, and 238U. This software allows the user to select an attenuator type and thickness as well as the measurement time to cover a range of scenarios. Initial results on the development of the GSP tool has shown its effectiveness at generating the gamma spectrum while maintaining its ease of use. [ABSTRACT FROM AUTHOR]

Through high fidelity measurements of four different plutonium certified reference material standards from New Brunswick Laboratory, the mass fractionation correction factor for the 240Pu/239Pu major isotope ratio measurements by the total evaporation methodology using thermal ionization mass spectrometer instruments is shown to depend on the elapsed time since separation of the decay products from the analyzed plutonium fraction. Systematic biases arising from this matrix dependence of the mass fractionation correction factor are larger than the precision obtained in routine TE measurements of the 240Pu/239Pu major isotope ratio using thermal ionization mass spectrometry regarded as the gold standard for these measurements. LA-UR-21–21,941. [ABSTRACT FROM AUTHOR]

Sediment management is currently limited by uncertainties in the applicability of existing radionuclide tracers and the effects of urbanization. Here, we use plutonium isotopes (239+240Pu) from weapons‐testing fallout to trace sediment transport across five watersheds in an urbanizing landscape in Kansas, USA. Historic flooding in the region provided an opportunity to assess extreme connectivity of sediment sources. 239+240Pu activity of transported sediment decreased as catchments urbanized, indicating a greater contribution from subsurface bank sediment; Bayesian modeling predicted 50% (8%–80%) bank sourcing in the most rural watershed, which rose to 93% (73%–100%) in the most urban catchment. 239+240Pu activity provides explanatory information on the superposition of sediment sources, which is beyond that given by traditional organic and geochemical tracers that primarily infer vegetative and geologic sourcing, respectively. Our study demonstrates the utility of 239+240Pu as a sediment tracer for managing erosion under anthropogenic change. Plain Language Summary: Sediment is one of the most common contaminants in rivers around the globe. The susceptibility of soil to erosion increases as humans convert natural landscapes into rural and urban systems. Uncertainties remain regarding how urbanization alters sediment pathways and what tools are appropriate for quantifying this alteration. Radioactive isotopes, generated from nuclear weapons testing in the 1950s, have proven useful in this regard, although the most prominent tracer, for example, cesium, is losing some utility due to a short half‐life and extensive radioactive decay. We suggest that plutonium isotopes, which have longer half‐lives, are a viable option for tracing sediment in modern landscapes. Plutonium results suggest that in rural basins the source of sediment transitions from upland soil during low‐flows to bank material at high‐flows. On the other hand, urban streams always deliver bank sediment, regardless of storm intensity. Our study demonstrates the utility of plutonium as an alternate sediment tracer and highlights how urbanization changes the pathways and mechanisms of fluvial sediment transport. Key Points: 239+240Pu activity is a robust tracer for describing sediment sources and fluvial mixtures in a rapidly urbanizing landscapeFrequentist and Bayesian models were consistent in estimating increased bank erosion with increasing urban land useSediment sourcing is dependent on discharge in rural watersheds whereas it is independent of discharge in urban watersheds [ABSTRACT FROM AUTHOR]

Photofission cross-sections of 238,239,240,241,242,244Pu isotopes are theoretically investigated with the collective semiclassical Fermi gas model (CSCFGM) by using Talys computer code in the energy range 1 - 30 MeV. Nuclear level density has significant importance to define the structural properties of nuclei. CSCFGM is a nuclear level density model, that includes collective (rotational and vibrational) effects as well as the pairing and shell effects, and is used to analyse the (, f) reactions of plutonium isotopes. The experimental data for all reactions are taken from EXFOR library. The theoretical predictions are in agreement with the experimental data, Talys code without changing the input, and the evaluated nuclear cross-section data from TENDL 2021 library. [ABSTRACT FROM AUTHOR]

Two plutonium oxides were prepared as unique reference materials for measurement of actinide elements present as trace constituents. Each reference material unit is approximately 200 mg of PuO2 powder in a quartz glass bottle. Characterized attributes of the oxides included mass fractions of plutonium, americium, neptunium, and uranium. Isotope-amount ratios were also determined for plutonium and uranium, but neptunium and americium were observed to be monoisotopic 237Np and 241Am. Measurements for characterization and verification of the attributes show that plutonium and trace actinides are homogeneous with the exception of limited heterogeneity for uranium, primarily observed for the 238U isotope. Model purification ages calculated from measured americium and uranium attribute values are consistent with material histories and indicate that these impurities are predominantly due to the decay of plutonium isotopes. [ABSTRACT FROM AUTHOR]