Fractionation Of Thorium Research Articles

Transmutation of Plutonium and Minor Actinide in PWR Thorium-Transuranic Fuel Assembly

Long-lived radioactive waste is often considered a concerning issue on utilizing nuclear power. This waste is in the form of plutonium and minor actinides (MA), formed due to successive neutron capture of 238U. Both are not particularly hazardous radiologically, but their long half-life caused an issue in the public acceptance of radioactive waste disposal. Thereby, this issue must be resolved, either politically or technically. One of the technical solutions to address the issue of long-lived radioactive waste is the incineration of transuranic (TRU) elements in a pressurized water reactor (PWR) fuel assembly. Mixing TRU with thorium in a PWR fuel assembly can theoretically reduce TRU stockpile more effectively than uranium. This paper discusses plutonium and MA transmutation in a Thorium-Transuranic (Th-TRU) PWR fuel assembly using MCNP6 code and ENDF/B-VII library. A Westinghouse 17×17 PWR fuel assembly was chosen to determine the feasibility of TRU incineration. Three assemblies of 50:50, 55:45, and 60:40 mixture of UO2 and Th-TRU fuel rods are compared to one reference UO2 assembly from the criticality and burn-up point of view. From the calculations, the plutonium incineration rate was observed to be 9.47 %, 10.91 %, and 12.2 %, while MA incineration rates were found to be 11.5 %, 11.93 %, and 12.3 % for Th50-TRU50, Th55-TRU45, and Th60-TRU40, respectively. This observation indicates that a higher thorium fraction in the fuel assembly can increase the TRU transmutation rate. Therefore, a high thorium fraction is recommended to increase the transmutation rate of the TRU.

Transmutation of Plutonium and Minor Actinide in PWR Thorium-Transuranic Fuel Assembly

Long-lived radioactive waste is often considered a concerning issue on utilizing nuclear power. This waste is in the form of plutonium and minor actinides (MA), formed due to successive neutron capture of 238U. Both are not particularly hazardous radiologically, but their long half-life caused an issue in the public acceptance of radioactive waste disposal. Thereby, this issue must be resolved, either politically or technically. One of the technical solutions to address the issue of long-lived radioactive waste is the incineration of transuranic (TRU) elements in a pressurized water reactor (PWR) fuel assembly. Mixing TRU with thorium in a PWR fuel assembly can theoretically reduce TRU stockpile more effectively than uranium. This paper discusses plutonium and MA transmutation in a Thorium-Transuranic (Th-TRU) PWR fuel assembly using MCNP6 code and ENDF/B-VII library. A Westinghouse 17×17 PWR fuel assembly was chosen to determine the feasibility of TRU incineration. Three assemblies of 50:50, 55:45, and 60:40 mixture of UO2 and Th-TRU fuel rods are compared to one reference UO2 assembly from the criticality and burn-up point of view. From the calculations, the plutonium incineration rate was observed to be 9.47 %, 10.91 %, and 12.2 %, while MA incineration rates were found to be 11.5 %, 11.93 %, and 12.3 % for Th50-TRU50, Th55-TRU45, and Th60-TRU40, respectively. This observation indicates that a higher thorium fraction in the fuel assembly can increase the TRU transmutation rate. Therefore, a high thorium fraction is recommended to increase the transmutation rate of the TRU.

The implication of Thorium fraction on neutronic parameters of pebble bed reactor

Thorium abundance in the Earth's crust is estimated to be three to four times higher than uranium. This is one potential advantage of Thorium as a provider of attractive fuel to produce nuclear energy. Fewer transuranics produced by Thorium during the fuel burn up in the reactor may also be another advantage for reducing the long-term burden of high-level long-lived waste. The scope of this paper is to study the implication of Thorium fraction on neutronic parameters of pebble bed reactor. The reactor model of HTR-10 was selected, and the (Th, 235U)O2 fuel was used in this study. The MCNP6 code was applied to solve a series of neutron transport calculations with various Thorium fractions in (Th,235U)O2 fuel based on the ENDF/BVII library. The calculation results show that the total temperature coefficient of reactivity of Thorium-added pebble bed reactors is generally more negative than those of LEU-fuelled one, except for 10% Thorium fraction. The kinetic parameters, especially prompt neutron lifetime and neutron generation time of pebble bed reactors, are higher, which means the addition of Thorium in the fuel makes the reactor more easily controlled. However, the burn-up calculations show that the introduction of Thorium in the same fuel kernel as LEU within the pebble bed reactor is unable to lengthen the fuel residence time, except for a minimum of 40% Thorium fraction.

Trace Elemental Analysis of Bulk Thorium Using an Automated Separation-Inductively Coupled Plasma Optical Emission Spectroscopy Methodology.

Presented here is a novel automated method for determining the trace element composition of bulk thorium by inductively coupled plasma-optical emission spectroscopy (ICP-OES). ICP-OES is a universal approach for measuring the trace elemental impurities present in actinide-rich materials; however, due to the emission rich spectrum of the actinide, a separation from the trace elements is warranted for spectrochemical analysis. Here, AG MP-1 ion exchange resin was utilized for retention of the Th matrix, while allowing the trace element impurities to be separated prior to subsequent analysis using ICP-OES. After demonstrating the separation on traditional gravity-driven columns, the methodology was transitioned to an automated platform for comparison. This automated platform utilizes syringe-driven sample and solvent flow and can collect the trace element and thorium fractions in separate locations. While reducing the sample size (500 µL, 1.5 mg of Th), maintaining the overall separation efficiency (recoveries >95%), and illustrating the sample throughput ability (n = 10+), this automated methodology could be readily adopted to nuclear facilities in which the determination of trace elemental impurities in Th samples is warranted.

Ice ages: Evidence for past melting at the base of the GISP2 ice core from uranium-thorium disequilibria dating

In order to further develop 238U-234U-230Th disequilibria techniques for dating polar ice, we measured these nuclides by mass spectrometric methods for silty ice samples from the base of the GISP2 central Greenland ice core. We separated the samples by filtration and analyzed the <50 nm (truly dissolved + particulate) and >200 nm (particulate) filtered fractions. 230Th/234U activity ratios are quite low in the <50 nm fraction (0.18-0.24), and since natural liquid water is characterized by 230Th/234U activity ratios ≪1, these results suggest that recent melting/freezing event(s) have occurred at the base of the GISP2 core. The particulate fraction is characterized by 230Th/234U activity ratios of 1.12-1.23 which are also consistent with recent (<380 ka) fractionation of thorium from uranium in these ice samples.We have modeled these results using a two component mass balance calculation, with dissolved and particulate pools for each radionuclide. Although the model results vary slightly depending on assumptions, corrected dates for when the samples were last frozen range from 3500-8300 years ago, with typical 2σ uncertainties of 600-2300 years. These results are generally consistent with other geochemical and chronological data for Greenland ice cores and the notion of ice melting at the base of large continental ice sheets, even in areas that are currently frozen. Based on our U-series results and gas data in the literature, prior melting of the GISP2 ice core has evidently occurred for most of the 13 m thick silty basal layer but is most pronounced for the deepest 2 m. We also suggest that this new 230Th ingrowth method for dating previously melted ice may be more generally applicable to samples with a range of particulate matter concentrations.

Comparative study of the neutronic performance of thorium-based metallic fuel and MOX fuel in an ASTRID-like fast reactor core

As the continuation of a previous research work, in this paper the utilization of thorium-based metallic fuel is investigated in an ASTRID-like fast reactor core. The main goal of this paper is to compare the neutronic behavior and the isotopes evolution between the previously studied reference core, based on oxide fuel, and a core loaded with metallic thorium-based fuel for the same ASTRID-like reactor. The reference core, in which the fuel is a material composed of a mixture of U-Pu MOX, was compared with an equivalent core with a U-Pu-Zr metallic alloy fuel (Met-UP) and two alternative thorium-fueled strategies. For the first strategy, a combination of 232Th/233U was introduced in the fertile zone instead of the uranium isotopes, keeping the fissile zone composition unchanged (Met-UPT). For the second strategy, the fertile zone was kept with the same composition as in the first strategy, while a mix of 232Th/233U replaced the fissile fuel zone composition (Met-UT). The calculations were made with the Monte Carlo MCNP6 code and the ENDF/B-VII.0 cross section library. The parameters analyzed were: the neutron multiplication factor for a burnup of one year, the neutron energy spectrum, the Doppler effect, the coolant density reactivity effect, the delayed neutrons fraction and the control rods reactivity worth (shutdown margin). The radial power distribution and the concentration evolution of the main isotopes for each fueling strategy in the core were also analyzed. The main findings of this study were: the effective neutron multiplication factor of the reference core and that of the Met-UPT case is very close, meanwhile, the configuration Met-UT has an important loss of reactivity along the burnup. Regarding the neutron energy spectrum, it becomes harder with a higher thorium fraction in the core. Related to the fissile isotopes, in the reference core 239Pu is produced, meanwhile, 233U is bred in the fertile zone of the configuration with 232Th/233U. The Am and Cm actinides production are lower for the 232Th/233U in the fertile zone compared to the reference configuration and null in the case of the full core with 232Th/233U. Doppler constants have negative values and show similar behavior in all the core configurations. Regarding the coolant density reactivity effect, the metallic fuel configuration with 232Th/233U in the full core shows the better behavior. The power distribution is similar in all the cases, showing a region with the highest power in the outer fuel zone. The metallic fuel configurations have higher power peaks. The full 232Th/233U fuel configuration has the flattest power distribution and the lower effective delayed neutrons fraction. All core configurations show a very good shutdown margin, widely greater than 1000 pcm at the beginning of the cycle. As a result of this study, it can be concluded that the Met-UP configuration can be considered as the best option followed by the Met-UPT configuration.

Neutronic study of an ASTRID-like fast reactor core with thorium-based fuel

Abstract In this work the utilization of thorium was investigated in a sodium-cooled ASTRID-like fast reactor core. Two thorium fueled strategies were analyzed and compared with the reference core in which the fuel vector is composed of a mixture of U-Pu MOX fuel. For the first strategy, all uranium isotopes in the fertile zone (depleted uranium) were replaced by a mixture of 232Th/233U, leaving the fissile zone with the U-Pu MOX composition. For the second strategy, the whole core, that is, the fertile and fissile zones were loaded with a mixture of 232Th/233U. The Monte Carlo MCNP6 code with the ENDF/B-VII.0 cross section library was used to perform the calculations. Six neutronic parameters were analyzed for each fuel strategy: the neutron energy spectrum, the effective neutron multiplication factor (keff) for an operating cycle of 365 days, the Doppler constant, the reactivity effect of the coolant density, the effective delayed neutrons fraction (βeff) and the shutdown margin. The main isotopes evolution and the radial power distribution were also analyzed. Results show that the energy spectrum is harder with high thorium fraction, i.e. in the case with 232Th/233U in the whole core. The behavior of keff along the operating cycle of the reference core and that of the case with 232Th/233U in the fertile zone is very similar, getting the second one a slightly higher keff at the end of cycle. The keff with 232Th/233U in the whole core has a significant loss in reactivity and need further research. As for the isotopes, in the reference core 239Pu is bred, the same happens with 233U in the core with 232Th/233U in the fertile zone. This does not happen with 232Th/233U in the whole core. The Am and Cm actinides concentrations are lower with 232Th/233U in the fertile zone than in the reference core and are completely absent with 232Th/233U in the whole core. For all the configurations the Doppler constant and the reactivity effect of coolant density behave well, as the keff drops with temperature raise or with void raise. In the case of sodium voiding, a better performance is observed with 232Th/233U in the whole core. The power distribution is alike in all core configurations, having a ring with the higher power in the outer fuel region. The full 232Th/233U fuel configuration have the more even power distribution. All core configurations have similar βeff and show a satisfactory shutdown margin, as it is higher than 1% dk/k at the beginning of cycle.

Comparison of solvent extraction and extraction chromatography resin techniques for uranium isotopic characterization in high-level radioactive waste and barrier materials

The development of Deep Geological Repositories (DGP) to the storage of high-level radioactive waste (HLRW) is mainly focused in systems of multiple barriers based on the use of clays, and particularly bentonites, as natural and engineered barriers in nuclear waste isolation due to their remarkable properties.Due to the fact that uranium is the major component of HLRW, it is required to go in depth in the analysis of the chemistry of the reaction of this element within bentonites. The determination of uranium under the conditions of HLRW, including the analysis of silicate matrices before and after the uranium-bentonite reaction, was investigated. The performances of a state-of-the-art and widespread radiochemical method based on chromatographic UTEVA resins, and a well-known and traditional method based on solvent extraction with tri-n-butyl phosphate (TBP), for the analysis of uranium and thorium isotopes in solid matrices with high concentrations of uranium were analysed in detail.In the development of this comparison, both radiochemical approaches have an overall excellent performance in order to analyse uranium concentration in HLRW samples. However, due to the high uranium concentration in the samples, the chromatographic resin is not able to avoid completely the uranium contamination in the thorium fraction.

Effect of natural organic matter on the adsorption and fractionation of thorium and protactinium on nanoparticles in seawater

Laboratory experiments were carried out to examine the role of natural organic matter (NOM) in regulating the adsorption and fractionation of 234Th and 233Pa in seawater on inorganic nanoparticles (20nm), including SiO2, CaCO3, Fe2O3, Al2O3 and TiO2. Model macromolecules and natural colloidal organic matter (COM) tested in the present study included dextran with different molecular weights, acid polysaccharides (APS), humic acids (HAs), protein (bovine serum albumin, BSA), and COM isolated from river water and seawater. APS and HAs had comparable affinity and higher partition coefficients (Kd) for 234Th, with logKd values close to 7, while proteins showed weaker binding strength with 234Th and had a logKd value of 5.75. Compared to 234Th, 233Pa showed lower affinity for different organic matters, with logKd values ranging from 4.41 on APS to 5.46 on 6-kDa-dextran. In general, macromolecules and COM preferentially complexed with 234Th over 233Pa, which resulted in a fractionation between 234Th and 233Pa on different NOMs with a fractionation factor (FTh/Pa) following the order of APS>HA≥Dextran>BSA. Results from binary-sorbent experiments (nanoparticles plus NOM) indicated that NOMs evidently affected the adsorption of 234Th and 233Pa on different inorganic nanoparticles likely through the formation of organic coatings. While SiO2 preferentially adsorbed 233Pa over 234Th, the presence of APS could compete the effective sorption sites and thus reduced the adsorption of 233Pa on SiO2 nanoparticles. Based on a two end-member mixing model (Li, 2005), coating extent seemed to depend on the relative abundance and chemical composition of organic matter and inorganic nanoparticles. In addition to organic composition, NOM concentrations also affected the partitioning of 234Th and 233Pa between seawater and particles, showing a strong ‘colloidal concentration effect’. Nevertheless, there was little change in logKd values of 234Th and 233Pa on dextran with a molecular weight between 6–500kDa or 2–10nm in size, indicating negligible NOM size effect from small colloids on the adsorption of Th and Pa in seawater.

Factors affecting uranium and thorium fractionation and profile distribution in contrasting arable and woodland soils

This work investigated the vertical distribution and fractionation of uranium and thorium in soils under contrasting arable and woodland sites based on the same parent material. The effect of long-term application of phosphate fertilizer on U and Th concentrations in the arable soil was also assessed. The arable surface soils contained higher amounts of U compared with underlying layers and the woodland soil profile; by contrast, the Th distributions were very similar in both arable and woodland soils. The U and phosphate concentration profiles within the arable soil were broadly similar; U was strongly associated with Ca (r=0.94) and soil P content (r=0.86) whereas the U concentration profile in the woodland soil was virtually uniform with depth. The ‘excess’ U in arable soil, associated with long term P fertilizer application, was approximately 2.5kgha−1 with 80% in the top 30cm of the soil profile. A sequential extraction technique was used to fractionate U and discriminate between ‘reactive’ (non-residual) and ‘residual’ forms of U. The reactive U was adsorbed, mainly by organic matter and Fe–Mn oxides in the arable topsoil and there was a very strong relationship between reactive U and soil phosphate content in the arable soil (r=0.99, P<0.001). The ‘excess’ U accumulated in the arable topsoil was also considerably more reactive than the co-existing native U. Thus the reactive fraction of the excess U ranged from 29 to 42% compared with 14 to 15% reactivity of the native U. Thorium in both soils showed a very consistent, and low, reactivity down the soil profile at about 4% of total soil Th content (96% residual), bound almost completely to humus.

Adsorption and fractionation of thorium and protactinium on nanoparticles in seawater

Laboratory adsorption experiments were conducted to examine the role of particle composition in the scavenging and fractionation of 234Th and 233Pa on nanoparticles in seawater. Nanoparticles with known chemical composition and size were used, including SiO2, CaCO3, Fe2O3, Al2O3 and TiO2, representing biogenic opal, carbonate, metal oxides, and lithogenic particles, respectively. The results indicated that nanoparticles with the same size but different chemical compositions had different affinities for 234Th and 233Pa, giving rise to different partition coefficient (Kd) values. Compared to 234Th, log Kd values of 233Pa had a higher variability on different nanoparticles, ranging from 3.10 to 5.39. In general, the log Kd values for 234Th on CaCO3, Fe2O3, and Al2O3 were higher than those for 233Pa, while the opposite was true on SiO2 and TiO2 nanoparticles, resulting in a significant fractionation between 234Th and 233Pa during their adsorption on nanoparticle surfaces. Among the selected nanoparticles, Fe2O3 had the highest fractionation factor between 234Th and 233Pa (FTh/Pa) while SiO2 had the lowest, following the order of Fe2O3>CaCO3>Al2O3>TiO2>SiO2. In addition to the effect of chemical composition, the concentration of nanoparticles or micro-particles also significantly affected the partitioning of 234Th or 233Pa between dissolved and particulate phases, showing a strong particle concentration effect with a general decrease in log Kd values with increasing particle concentration. Interestingly, results from adsorption experiments with binary nanoparticles, containing both SiO2 and CaCO3, clearly demonstrated an increase in log Kd values of 233Pa with increasing SiO2/CaCO3 ratios of the adsorbent, but a decrease in the fractionation factor between 234Th and 233Pa. However, the enhanced adsorption of 233Pa on SiO2 nanoparticles or the increased log Kd value of 233Pa occurred only when the abundance of SiO2 reached 60% (in wt.) or higher. Thorium, on the other hand, was less sensitive to particle composition during its adsorption on nanoparticles in seawater. Thus, it seems that the Th/Pa ratios of oceanic particles could be largely controlled by the relative abundance of biogenic silica. Further studies are needed to examine the role of natural organic matter, which affects surface properties and chemical speciation of trace elements, in regulating the adsorption of radionuclides on nanoparticles.

Physicochemical fractionation of americium, thorium, and uranium in Chernozem soil after sharp temperature change and soil drought

AbstractA sequential extraction procedure was used to study the changes in the physicochemical forms of americium (Am), thorium (Th), and uranium (U) in laboratory-contaminated Chernozem soil as a result of sharp variations of the environmental temperature and soil moisture. The influence of freezing and soil drought on the radio-ecological hazard was evaluated three months after radioactive contamination with aqueous solutions of 241Am, 234Th, and U. The subsequent changes in the physicochemical forms of the actinides, caused by sharp increases in the environmental temperature and soil moisture, were examined for one month. The data showed that continuous freezing increased the potentially mobile forms of Am and Th but had the opposite effect on U. Prolonged soil drought did not influence the fractionation of Am and Th but led to the redistribution of U between the carbonates and organic matter and caused its immobilisation. The sharp increase in the temperature of the frozen soil caused the immobilisation of Am and Th and increased the potential mobility of U. The warming and enhanced humidity of the dry soil led to the immobilisation of Am and redistribution of U between the soil phases.

Conditions for dissolution and radiochemical isolation of U and Th from baddeleyite

Conditions of baddeleyite dissolution were examined, and an optimal method of its complete breakdown was found. A solution of 229Th tracer was prepared and used for radiochemical isolation of Th from baddeleyite. Radiochemical methds were developed for recovering the uranium and thorium fractions from a baddeleyite solution. The total chemical yield of U and Th was 71 ± 5 and 89 ± 7%, respectively.

Comparison of two sequential extraction protocols for fractionation of natural radionuclides in soil samples

Revised BCR (Bureau Communautaire de Référence) and the Schultz modification of Tessier´s sequential extraction protocols are compared for fractionation of uranium, thorium and radium in soil samples. Six soil samples were collected near to the uranium mill tailings waste pile and some of them had enhanced levels of natural radionuclides. The samples were processed by both protocols and the radionuclide content assayed by alpha spectrometric determination. The analysis revealed that results obtained by the two protocols are not fully comparable as data are mostly protocol- and element-dependent. Nevertheless, general conclusions about potential source of the particular radionuclide, which could be drawn from the specific study carried out, are mostly similar for both protocols.

Scavenging and fractionation of thorium vs. protactinium in the ocean, as determined from particle–water partitioning experiments with sediment trap material from the Gulf of Mexico and Sargasso Sea

Particle–water partition coefficients (Kd) for thorium (Th) and protactinium (Pa) were calculated for sediment trap material collected from the Gulf of Mexico (GOM) in the upper 140 m and archived sediment trap material collected in the mesopelagic and bathypelagic Sargasso Sea (500, 1500 and 3200 m sediment trap samples from the Oceanic Flux Program (OFP) site off Bermuda). Results showed that Kd values for Th were generally greater than for Pa when values were smaller, but converging to a 1:1 line at higher values. Furthermore, results showed that, though the contents of polysaccharides and calcium carbonate are significantly correlated for all samples, log Kd of Th (and Pa) values are correlated with the polysaccharide content while no correlation is apparent with CaCO 3, Mn and Fe. Since polysaccharides are not generally regarded as strongly chelating agents for actinides, we hypothesize that other co-occurring organic phases originating from the matrix of carbohydrate-rich extracellular polymeric substances (EPS), could be responsible for binding the actinides. These data provide, for the first time, direct evidence for the role of carbohydrate-rich EPS being responsible for the differential scavenging of these two radioisotopes, i.e., their fractionation.

Effects of soil pH and organic matter on distribution of thorium fractions in soil contaminated by rare-earth industries

The labilities of thorium fractions including mobility and bioavailability vary significantly with soil properties. The effects of soil pH and soil organic matter on the distribution and transfer of thorium fractions defined by a sequential extraction procedure were investigated. Decrease of soil pH could enhance the phytoavailability and the potential availability of thorium in soil. Increase of organic matter reduced the phytoavailability of thorium, but enhanced the potential availability of it. The reasons why soil pH and soil organic matter affect thorium fractions were discussed, and the behavior of the effects of soil properties on thorium fractions was elucidated. Fourier-transform infrared (FTIR) spectra were employed to reveal the positive relationship between the amounts adsorbed in humic material and/or amorphous oxides and the content of soil organic matter.

Uranium-series dating applications in natural environmental science

Uranium-series (U-series) analyses are an essential component of many research projects in Earth and environmental science, oceanography, hydrology and science-based archaeology. Topics range from magma chamber evolution and volcanic hazard prediction, global climatic change through dating of authigenic carbonate deposits, human evolution through dating of bone, to the study of groundwater evolution. The U-series decay chains contain many elements that can be fractionated in environmental and geological processes. Half-lives of radioactive isotopes of such elements range from seconds to many millennia and application depends on the natural timeframe of the process or the elapsed time. This review will be limited to some aspects of the 238U– 234U– 230Th– 226Ra system with half-lives of 245 kyr, 76 kyr and 1.6 kyr, respectively. In environmental systems, fractionation of uranium and thorium is a very efficient process because thorium is extremely insoluble while hexavalent uranium in oxidising conditions is relatively soluble. Many authigenic precipitates of calcite contain virtually no thorium and inorganic precipitates have U/Ca ratios very similar to the ratio of dissolved uranium and calcium. Almost no radiogenic 230Th in the precipitate means that the radiogenic clock starts effectively at zero. However, pure authigenic precipitates are rare and many contain some allogenic material, mostly silicate with 238U in secular equilibrium with significant 230Th. Some of the characteristics of different types of samples and various methods to accommodate or correct for ‘inherited’ 230Th will be discussed. Authigenic material should remain a ‘closed system’ with respect to the relevant isotopes but that requirement is sometimes difficult to maintain because radioactive decay results in damage to the crystal lattice of the host mineral. Consequences of this ‘recoil effect’ and correction schemes will be discussed. Dating archaeological bone based on the systematics of diffusion and adsorption to effectively model ‘open system’ behaviour is also included.

Alpha-decay from the 3.5 eV isomer of 229Th

The alpha-decay of a low energy isomer of 229Th at about 3.5 eV was sought by producing it through the (g,n) reaction on a 230Th target. Thorium isotopes in the reaction products were isolated and purified by anion exchange chromatography in a concentrated nitric acid medium to remove lanthanides fission products. The thorium fraction was further purified by samarium fluoride coprecipitation and the precipitate was mounted as a source for a-spectroscopy. Decaying a-signals were observed in the energy region that was expected for 229mTh, i.e., between 4.83 and 5.08 MeV. The half-life of the decaying component was determined from repeated experiments to be 13.9±3 hours.

A method for preparation and purification of 234Th

An improved method to recover 234Th from depleted uranium has been developed. The method is based on solvent extraction and ion-exchange separations. The final thorium fraction has a high specific activity, about 1–3 PBq/mol Th, which makes it well suited for investigations, where a low thorium concentration is essential. The method is comparably fast, with a total processing time of 2 days. Another advantage is that the uranium fraction can be used as a 234Th generator for several years.

Extraction of uranium, thorium and lanthanides using Cyanex-923: Their separations and recovery from monazite

The extraction behavior of uranium, thorium and lanthanides, represented by cerium and ytterbium, by Cyanex-923 has been investigated. The effect of different variables like the concentration of acids, metal ion and extractant, nature of diluent and temperature has been studied. A composition for the extracted U(VI) and Th(IV) species has been proposed. Based on the partition data some important binary and ternary separations involving the aforesaid metal ions have been achieved. The proposed procedure has been applied for the recovery of uranium, thorium and lanthanide fraction from monazite sand. The stability and regeneration capacity of the extractant have been evaluated.