Plutonium Ratios Research Articles

137Cs and 239,240Pu activity concentrations distribution in waterlogged and non-boggy soils of Lithuania

Vertical distributions of 239,240Pu and 137Cs activity concentrations in the waterlogged and non-boggy soil cores sampled in the vicinity of Vilnius City and in the Varėna District were analyzed. The radionuclides appeared in the soils mainly as a result of the fallout after the nuclear weapon testing in atmosphere in 1960s and due to the Chernobyl NPP accident in 1986. The deposited radionuclides on the surface of waterlogged soils on the shores of lakes experienced processes of translocation and accumulation, therefore their total activity in the column differs from the activity in non-boggy soils. The mobility of plutonium is the highest in waterlogged organic-rich soils. Clay in the waterlogged soil significantly limits the migration of radiocesium and does not affect noticeably the mobility of plutonium. Compared with radiocesium, the mobility of plutonium in non-boggy soils is somewhat limited. So, in waterlogged and non-boggy soils, the radionuclide mobilizing factors act in the opposite directions for radiocesium and plutonium. A clear correlation between the radionuclide activity and soil organic matter content was not observed. The investigation showed that radionuclide mobility can be determined by studying radionuclide physicochemical forms in the soil, vertical profiles of radiocesium to plutonium ratios, soil composition as well as its oxidation regime.

Plutonium isotopes in Northern Xinjiang, China: Level, distribution, sources and their contributions

Plutonium in the environment has drawn significant attentions due to its radiotoxicity in high concentration and source term linked with nuclear accidents and contaminations. The isotopic ratio of plutonium is source dependent and can be used as a fingerprint to discriminate the sources of radioactive contaminant. 239Pu, 240Pu and 137Cs in surface soil and soil cores collected from Northern Xinjiang were determined in this work. The concentrations of 239,240Pu and 137Cs are in the range of 0.06–1.20 Bq kg−1, and <1.0–31.4 Bq kg−1 (decay corrected to Sep. 2017), respectively, falling in the ranges of global fallout in this latitude zone. The 240Pu/239Pu atomic ratios of 0.118–0.209 and 239,240Pu/137Cs activity ratios of 0.039–0.215 were measured. Among the investigated sites, distinctly lower 240Pu/239Pu atomic ratios of 0.118–0.133 and higher 239,240Pu/137Cs activity ratios of 0.065–0.215 compared to the global fallout values were observed in the northwest part, indicating a significant contribution from other source besides the global fallout. This extra source is mainly attributed to the releases of atmospheric nuclear weapons testing at Semipalatinsk Nuclear Test Site, which was transported by the west and northwest wind through the river valley among mountains in this region. This contribution is estimated to account for 28–43% of the global fallout in the northwest part of Northern Xinjiang. The contribution from the Chinese atmospheric nuclear weapons testing to this region is negligible due to the lack of appropriate wind direction to transport the radioactive releases to this region.

Neutron-neutron angular and energy-angle correlations of plutonium samples with varying α-ratio

Abstract Accurate and timely characterization of physical properties pertinent to plutonium bearing materials is important for fulfilling nuclear nonproliferation and safeguards goals. Physical properties include the fissile mass, leakage multiplication, and the α -ratio, defined as the ratio of ( α ,n) neutrons to spontaneous fission neutrons. Traditionally, these properties can be inferred by relating the measured neutron multiplicity count rates to the well-established point kinetics moments equations; the current state-of-the-art utilizes 3 He-based detection systems. Organic scintillators have been used extensively to study and measure characteristic signatures in the neutron angular and energy distributions. Previous work has proposed techniques that independently leverage the energy and angle sensitivity of organic scintillators to estimate the α -ratio of plutonium bearing material; however, it is expected that the energy and angular distributions are correlated to one another due to the underlying physics of fission and ( α ,n) neutron emissions. This work presents experimental results that characterize neutron-neutron angular distribution and subsequently the neutron-neutron energy-angle correlations for plutonium samples of similar mass and multiplication, but varying α -ratio due to the type of low-Z impurity. Full neutron-neutron angular distributions are presented using a low-energy detection threshold of 0.10, 0.15, and 0.20 MeVee (0.73, 0.96, 1.16 MeV neutron-equivalent energy). Neutron anisotropy was quantified by taking the ratio of neutron-neutron coincidences at 180°to those at 90°, where a value of unity indicates a purely isotropic source. The results show that the observed neutron-neutron correlations transition away from fission-induced signal to the cross-talk signal associated with single ( α ,n) neutrons with increasing α -ratio. Energy-angle correlations are characterized by calculating the neutron anisotropy at various detection thresholds and show positive correlation between the observed anisotropy and the energy of the neutrons.

Experimental validation of a nuclear forensics methodology for source reactor-type discrimination of chemically separated plutonium

Abstract An experimental validation of a nuclear forensics methodology for the source reactor-type discrimination of separated weapons-useable plutonium is presented. The methodology uses measured values of intra-element isotope ratios of plutonium and fission product contaminants. MCNP radiation transport codes were used for various reactor core modeling and fuel burnup simulations. A reactor-dependent library of intra-element isotope ratio values as a function of burnup and time since irradiation was created from the simulation results. The experimental validation of the methodology was achieved by performing two low-burnup experimental irradiations, resulting in distinct fuel samples containing sub-milligram quantities of weapons-useable plutonium. The irradiated samples were subjected to gamma and mass spectrometry to measure several intra-element isotope ratios. For each reactor in the library, a maximum likelihood calculation was utilized to compare the measured and simulated intra-element isotope ratio values, producing a likelihood value which is proportional to the probability of observing the measured ratio values, given a particular reactor in the library. The measured intra-element isotope ratio values of both irradiated samples and its comparison with the simulation predictions using maximum likelihood analyses are presented. The analyses validate the nuclear forensics methodology developed.

Fingerprinting commercial nuclear reactor forensics using the ORIGEN-S simulation code

The ability to determine the origin of a specific spent-fuel sample from a commercial nuclear reactor was studied using the Origen-S simulation code by calculating the plutonium and uranium isotopic concentration data for a range of nuclear power reactors. This range of reactors is based on a typical Westinghouse PWR fuel assembly with a fuel type of W17 X 17, having individual operating histories. Isotopic ratios of plutonium in nuclear reactors during the fuel-cycle period provide information on how the plutonium grows into the fuel as a function of burnup, as well as its attractiveness to proliferators. Using the results from the calculation of uranium and plutonium isotopic ratios, the origin of each spent-fuel assembly for a particular reactor can be predicted and documented for a future nuclear forensics reference database.

Room temperature ionic liquid system for the mutual separation of Pu(IV) from other actinides using 2-hydroxy acetamide extractant

Abstract N , N -dioctyl-2-hydroxyacetamide (DOHyA) in 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ([C 4 mim][NTf 2 ]) was employed for the extraction of actinides from nitric acid medium. The extraction of Pu(IV) was studied as a function of various parameters such as concentration of nitric acid, extractant concentration, temperature, alkyl chain length attached to amidic nitrogen of the extractant etc. The distribution ratio of plutonium(IV) (D Pu(IV) ) obtained in DOHyA/[C 4 mim][NTf 2 ] was compared with that obtained in DOHyA/ n -dodecane ( n -DD). Extraordinary extraction of Pu(IV) was achieved when ionic liquid was employed as a diluent. D Pu(IV) in DOHyA/[C 4 mim][NTf 2 ] decreased marginally with increase in nitric acid concentration up to 3 M nitric acid, and there after the D Pu(IV) remained constant. A significant separation was achieved for Pu(IV) over U(VI) and Am(III) from the employed mixture of actinides at various nitric acid concentrations using DOHyA/[C 4 mim][NTf 2 ]. Stripping of metal ion (Pu(IV)) from the loaded ionic liquid phase was carried out using aqueous soluble complexing agents such as oxalic acid and acetohydroxamic acid.

Determination of isotopic ratios of plutonium and uranium in soil samples by thermal ionization mass spectrometry

Isotopic ratios of plutonium and uranium in soil samples were investigated, in order to understand the level of contamination with plutonium and uranium released at the accident of Fukushima Daiichi nuclear power plant. At first, plutonium and uranium were recovered from the standard reference soil/sediment materials by extraction/ion-exchange chromatography, and their isotope compositions were analyzed by TIMS. By applying our analytical technique to soil samples obtained from Fukushima prefecture, a possibility of atmospheric release of nuclear fuel material during the accident of FDNPP was discussed. The contamination with uranium was under detection limit, while that with plutonium was observed.

Ultra-trace analysis of plutonium by thermal ionization mass spectrometry with a continuous heating technique without chemical separation

Thermal ionization mass spectrometry (TIMS) with a continuous heating technique is known as an effective method for measuring the isotope ratio in trace amounts of uranium. In this study, the analytical performance of thermal ionization mass spectrometry with a continuous heating technique was investigated using a standard plutonium solution (SRM 947). The influence of the heating rate of the evaporation filament on the precision and accuracy of the isotope ratios was examined using a plutonium solution sample at the fg level. Changing the heating rate of the evaporation filament on samples ranging from 0.1fg to 1000fg revealed that the influence of the heating rate on the precision and accuracy of the isotope ratios was slight around the heating rate range of 100–250mA/min. All of the isotope ratios of plutonium (SRM 947), 238Pu/239Pu, 240Pu/239Pu, 241Pu/239Pu and 242Pu/239Pu, were measured down to sample amounts of 70fg. The ratio of 240Pu/239Pu was measured down to a sample amount of 0.1fg, which corresponds to a PuO2 particle with a diameter of 0.2μm. Moreover, the signals of 239Pu could be detected with a sample amount of 0.03fg, which corresponds to the detection limit of 239Pu of 0.006fg as estimated by the 3-sigma criterion. 238Pu and 238U were clearly distinguished owing to the difference in the evaporation temperature between 238Pu and 238U. In addition, 241Pu and 241Am formed by the decay of 241Pu can be discriminated owing to the difference in the evaporation temperature. As a result, the ratios of 238Pu/239Pu and 241Pu/239Pu as well as 240Pu/239Pu and 242Pu/239Pu in plutonium samples could be measured by TIMS with a continuous heating technique and without any chemical separation processes.

Trace Fission Product Ratios for Nuclear Forensics Attribution of Weapons-Grade Plutonium from Fast and Thermal Reactors

The growing concern about nuclear terrorism threats has enhanced the need to develop fast and accurate nuclear forensics analysis techniques for nuclear material source attribution and to create a credible nuclear deterrence. Plutonium produced as a by-product in nuclear reactor fuel, especially in fuel discharged at low burn-up (1 to 2 MWd/kg), is potentially weapons usable material. In the event of plutonium interdiction from a smuggling act, its origin has to be established through nuclear forensics attribution methods before any response is initiated against this malicious act. The characteristics of separated plutonium from discharged reactor fuel and the associated fission product traces depend on factors such as the reactor type (thermal or fast reactor), fuel burn-up, irradiation history, and the chemical process used to separate plutonium. A new methodology of using trace fission product to plutonium ratios for nuclear forensics attribution of plutonium to the type of reactor used for its production is presented along with results obtained for case studies of a fast neutron spectrum breeder reactor and a thermal neutron spectrum reactor using open literature design information of these two types of nuclear reactors.

Long-range tropospheric transport of uranium and plutonium weapons fallout from Semipalatinsk nuclear test site to Norway

A combination of state-of-the-art isotopic fingerprinting techniques and atmospheric transport modelling using real-time historical meteorological data has been used to demonstrate direct tropospheric transport of radioactive debris from specific nuclear detonations at the Semipalatinsk test site in Kazakhstan to Norway via large areas of Europe. A selection of archived air filters collected at ground level at 9 stations in Norway during the most intensive atmospheric nuclear weapon testing periods (1957–1958 and 1961–1962) has been screened for radioactive particles and analysed with respect to the concentrations and atom ratios of plutonium (Pu) and uranium (U) using accelerator mass spectrometry (AMS). Digital autoradiography screening demonstrated the presence of radioactive particles in the filters. Concentrations of 236U (0.17–23nBqm−3) and 239+240Pu (1.3–782μBqm−3) as well as the atom ratios 240Pu/239Pu (0.0517–0.237) and 236U/239Pu (0.0188–0.7) varied widely indicating several different sources. Filter samples from autumn and winter tended to have lower atom ratios than those sampled in spring and summer, and this likely reflects a tropospheric influence in months with little stratospheric fallout. Very high 236U, 239+240Pu and gross beta activity concentrations as well as low 240Pu/239Pu (0.0517–0.077), 241Pu/239Pu (0.00025–0.00062) and 236U/239Pu (0.0188–0.046) atom ratios, characteristic of close-in and tropospheric fallout, were observed in filters collected at all stations in Nov 1962, 7–12days after three low-yield detonations at Semipalatinsk (Kazakhstan). Atmospheric transport modelling (NOAA HYSPLIT_4) using real-time meteorological data confirmed that long range transport of radionuclides, and possibly radioactive particles, from Semipalatinsk to Norway during this period was plausible. The present work shows that direct tropospheric transport of fallout from atmospheric nuclear detonations periodically may have had much larger influence on radionuclide air concentrations and deposition than previously anticipated.

Simultaneous determination of plutonium and uranium isotope ratios in individual plutonium–uranium mixed particles by thermal ionization mass spectrometry

Simultaneous determination of plutonium (Pu) and uranium (U) is preferred for analyzing the isotope ratio in Pu and U mixed samples such as the particles formed from MOX (mixed U–Pu oxide) fuels. In this study, we developed a method for the simultaneous measurement of all the plutonium and uranium isotopes without the need for chemical separation, using thermal ionization mass spectrometry (TIMS) with a continuous heating method. The MOX particles with sizes of 0.6–2.3μm used in this study were made from a mixed solution of plutonium (SRM947) and uranium (U500, 50% 235U enriched). The isotope ratios of plutonium and uranium obtained for all the MOX particles, including the ones in the sub-micrometer size range, were in good agreement with the certified values within the range of error. In particular, the determination of the 238Pu/239Pu isotope ratio, which is difficult because of the isobaric interference of 238U, was performed accurately. The 238Pu/239Pu ratios were obtained by using a correction in which the background of 238U intensity at the 238Pu peak was estimated from the peak fitting of the 238U signal profile. In addition, the 241Pu/239Pu isotope ratio could be accurately measured without being influenced by the 241Am formed by the decay of 241Pu. For the MOX particles with diameters of 1.12μm, the relative standard deviations (2RSDs) of the 238Pu/239Pu, 240Pu/239Pu, 241Pu/239Pu, and 242Pu/239Pu isotope ratios were 15.2%, 3.4%, 12.5%, and 5.1%, respectively. The relative standard deviations (2RSDs) of the 234U/238U, 235U/238U, and 236U/238U isotope ratios were 7.0%, 3.0%, and 41.2%, respectively. It is expected that the method developed in this study will become a powerful tool for the analysis of Pu and U mixed samples because of its ability to measure simultaneously even the minor isotopes of plutonium and uranium without any chemical separation.

Application of a continuous heating method using thermal ionization mass spectrometry to measure isotope ratios of plutonium and uranium in trace amounts of uranium–plutonium mixture sample

A method for measuring isotope ratios of plutonium and uranium in plutonium or uranium–plutonium (Pu/U) mixture samples was developed by using a continuous heating method of thermal ionization mass spectrometry, which was previously shown to be effective in measuring isotope ratios of trace uranium. In this method, temperature of an evaporation filament is increased sequentially. This leads to measure the ratios of Pu and U at different temperatures in which each element is evaporated efficiently. Under optimal measurement conditions, the intensity of 239Pu and the ratio of 240Pu/ 239Pu were measured down to sample amounts of 0.1 fg and 0.3 fg, respectively. In Pu/U mixture samples with pg-level masses and 0.01–10 Pu/U ratios, isotope ratios of 240Pu/ 239Pu and 235U/ 238U were measured simultaneously without chemical separation of samples. The relative standard deviation of the isotope ratios of 240Pu/ 239Pu and 235U/ 238U in the sample containing each 1 pg of plutonium and uranium were better than 2% and 4%, respectively. Moreover, 238Pu/ 239Pu ratios were obtained by using a correction in which the 238U intensity was estimated from the 235U intensity and the 235U/ 238U ratio. The results in this study suggest that the continuous heating method of thermal ionization mass spectrometry will be effective tool as a method for measuring isotope ratios in the Pu/U mixture samples.

Neutron constants verification by nonstationary experiments with multiplying systems

The arrangement of nonstationary experiments with multiplying systems whose results can be used to verify neutron constants libraries is described. For two multiplying systems with different ratio of plutonium and highly enriched uranium, the experimental results are compared with the computational results obtained using the BAS and ENDF-BVI neutron constants.

Ionic Liquid Extractants in Molecular Diluents: Extraction Behavior of Plutonium (IV) in 1,3-Diketonate Ionic Liquids

Room temperature ionic liquids (RTILs) containing β-diketonate anions have been prepared and studied for the extraction of 239Pu(IV), 233U(VI), and 241Am(III) from nitric acid medium. The ionic liquids such as alkylquaternaryammonium thenoyltrifluoroacetonate (R4NTTA), and 1-alkyl-3-methylimidazolium thenoyltrifluoroacetonate (amimTTA), with methyl, butyl, hexyl, heptyl, and octyl moieties have been prepared and characterized by 1H and 13C nmr and IR spectroscopy. The distribution ratio of plutonium(IV) (D Pu(IV)) in a solution of tri-n-octylmethylammonium thenoyltrifluoroacetonate (TOMATTA) present in tri-n-octylmethylammonium bis(trifluoromethylsulfonyl)imide (TOMANTf2) and amimTTA in amimNTf2 was studied as a function of various parameters. The unique property of β-diketonate ionic liquids, namely, the miscibility in molecular diluents, was exploited to elucidate the mechanism of Pu(IV) extraction in these ionic liquids.

ANALYSIS OF THE VARIABILITY OF BIOKINETIC MODEL PARAMETERS DUE TO INTER-INDIVIDUAL VARIATION

Biokinetic models for the assessment of individual internal doses represent the physiological processes of a standardized human, which affect the internal distribution of the radionuclide of interest. The flow from one compartment into another is specified by transfer rates, which may vary from person to person. The rate constants are then representing the mean values for the population as a whole, around which individual parameters fluctuate according to given probability densities. Analytical distribution propagation can be calculated only for very simple models. The influence of inter-individual variation can be studied with Monte Carlo simulations, which compare the simulated compartment content distributions using different initial distributions for the parameters. The simulations indicate that the form of test distributions affect the distributions of compartment contents only for very simple models in the early stages. Later on, the distributions converge to a lognormal shape. The coefficients of variation of the initial distributions can be adjusted so that the resulting distributions resemble each other. Due to the lack of significant differences, lognormal distributions--which are found in most measurable body parameters--were used for further studies. The range of inter-subject variability can be estimated by comparing data generated with Monte Carlo simulations with observed data. For the plutonium model, data retrieved long times post intake are most suitable for this purpose when the redistribution of the radionuclide in the compartments is in a state of quasi-equilibrium and the ratio of plutonium in different compartments is nearly constant. For the estimation of inter-individual variability, the ratios of the main excretion paths and the organs of main burden can be used. The comparison of observed and simulated standard deviations indicates a value of 0.6 for the coefficient of variation for all transfer rates. The generated distributions show good agreement with the available data and thus confirm that the simulations can represent the inter-individual variation in the biokinetic plutonium model.

Ionisation efficiency improvements for AMS measurement of actinides

Measurements of the isotopic ratios of plutonium and uranium are utilised by the safeguards community, environmental radioactivity and remediation studies, oceanography research, and in the U-series dating of geological samples. Accelerator Mass Spectrometry offers the advantages of high selectivity and sensitivity for such ratio measurements, but suffers from a poorer ionisation and transmission efficiency than some other mass spectrometric techniques. In addition, the ionisation efficiency achieved in caesium-sputter ion sources can be variable depending on the chemical form and geometry of the target used, yielding actinide negative ion beam rates with efficiencies ranging from 0.05% to 0.5%. In this paper we investigate the impact of the crystal structure of the target material, chemical composition and the geometry of the target in order to determine conditions which will allow us to maximise beam output and increase the efficiency of AMS measurements in future. We also examine target stability and “burn in time” (the time taken to generate a stable beam current) in conjunction with these measurements in order to maintain a high precision of measurement during the measurement period.

Determination of activity concentrations and activity ratios of plutonium, americium and curium isotopes in radioactive waste samples

This paper presents a rapid and quantitative radiochemical separation method for the Pu, Am and Cm isotopes with an anion exchange resin and a TRU resin. After the Pu isotopes were purified with an anion exchange resin method and the Am and Cm isotopes were purified with the TRU resin method, micro-coprecipitation method was applied for an alpha-source preparation. The activity concentrations and activity ratios for the Pu, Am and Cm isotopes in a radioactive sample were measured by radiation counting methods such as an alpha-spectrometry and a liquid scintillation counting as well as by a mass spectroscopic method such as a thermal ionization mass spectrometry.

High sensitivity analysis of plutonium isotopes in environmental samples using accelerator mass spectrometry (AMS)

This article presents a methodology for the determination of the concentration and isotopic ratio of plutonium occurring at femtogram levels in environmental matrices such as soils and sediments by accelerator mass spectrometry (AMS). Results on analyses of a number of reference materials (IAEA-375, IAEA-135, IAEA-300, IAEA-327, NIST 4350, NIST 4353b) are presented as validation of the method in reproducibly measuring the plutonium isotopic ratio 240Pu : 239Pu in a variety of environmental sample matrices.

Method for determining plutonium in air filters in detection of nuclear activities

Summary A method was developed to determine activities and isotope ratios of plutonium and uranium. The method includes dry and wet ashing of air filters and separation of plutonium and uranium from each other and from other nuclides on Eichrom®´s extraction chromatography resins UTEVA and TRU. Interferences in plutonium separation caused by thorium and polonium were investigated and eliminated. A field trial was performed in Kurchatov, Kazakhstan, to test the aerosol sampling and radiochemical methods developed for plutonium and uranium. In the air samples collected, the activity of 239,240Pu varied between 0.67 and 228 Bq/kg of dust, the activity of 238Pu from 0.20 Bq/kg to 16.4 Bq/kg of dust, and the isotopic ratio 238Pu/239,240Pu between 0.011 and 2.4. Concentrations of Pu isotopes in the air were 13.4-2490 nBq/m3 for 239,240Pu and 7.2-960 nBq/m3 for 238Pu. Radioactivity of 239,240Pu in air filters from Astana varied between 0.075 and 0.72 Bq per kg of dust and that of 238Pu between 0.038 and 0.14 Bq/kg of dust. Activity concentration of 239,240Pu in the air of Astana was 5.0-130 nBq/m3.

The Ratio of Plutonium Isotopes Depending on the Burnup of the Fuel from the Fourth Block of the Chernobyl Nuclear Power Plant

The ratio of plutonium isotopes can be used for determining the burnup of nuclear fuel in the fuel-containing masses from the fourth block of the CNPP. The burnup values obtained by two independent methods using cesium and plutonium isotopes are in satisfactory agreement.