Direct determination of uranium in sintered deeply depleted uranium oxide pellets by wavelength dispersive X-ray fluorescence spectrometry

This paper presents studies on direct non-destructive determination of uranium in sintered deeply depleted (DD) uranium oxide (UO₂) pellets by wavelength dispersive X-ray fluorescence (WDXRF) spectrometry. A special collet was designed and fabricated for holding the sintered DDUO₂ pellets for direct analysis, thus avoiding the sample preparation steps. The samples were analyzed using a calibration plot obtained from WDXRF spectra of matrix matched calibration standards. The WDXRF determined uranium values were found to be in very close agreement with titrimetric values and has reproducibility better than 0.05% (RSD, 1 s, n = 10) for the sintered DDUO₂ pellets having U: 86.81–88.04 wt%.

     

Rapid determination of 237Np and Pu isotopes in water by inductively-coupled plasma mass spectrometry and alpha spectrometry

A new method that allows rapid preconcentration and separation of plutonium and neptunium in water samples was developed for the measurement of ²³⁷Np and Pu isotopes by inductively-coupled plasma mass spectrometry (ICP-MS) and alpha spectrometry. ²³⁸U can interfere with ²³⁹Pu measurement by ICP-MS as ²³⁸UH⁺ mass overlap and ²³⁷Np via peak tailing. The method provide enhanced removal of uranium by separating Pu and Np initially on TEVA Resin, then moving Pu to DGA resin for additional removal of uranium. The decontamination factor for uranium from Pu is almost 100,000 and the decontamination factor for U from Np is greater than 10,000. This method uses stacked extraction chromatography cartridges and vacuum box technology to facilitate rapid separations. Preconcentration is performed using a streamlined calcium phosphate precipitation method. Purified solutions are split between ICP-MS and alpha spectrometry so that long and short-lived Pu isotopes can be measured successfully. The method allows for simultaneous extraction of 20 samples (including QC samples) in 4?C6 h, and can also be used for emergency response. ²³⁹Pu, ²⁴²Pu and ²³⁷Np were measured by ICP-MS, while ²³⁶Pu, ²³⁸Pu, and ²³⁹Pu were measured by alpha spectrometry.     

An improved method for determination of uranium isotopic composition in urine by alpha spectrometry

A comparative study of source preparation techniques to determine uranium isotopic composition by alpha spectrometry, namely electrodeposition and chemical stripping with polymeric membranae containing trioctylphosphine oxide (TOPO), is presented. The mean yield obtained for electrodeposition and TOPO deposition were 85% and 74%, respectively. The mean activity ratio²³⁵U/²³⁸U were 0.044 and 0.042 and the ratio²³⁴U/²³⁸U were 0.994 and 1.009, using electrodeposition and TOPO deposition techniques, respectively. The method of uranium separation from urine using an ion-exchange resin Dowex 1×8, chloride form and citrate form, was also studied. The obtained global yields of these methods were 50% and 41%, respectively.     

Determination of (236)U and transuranium elements in depleted uranium ammunition by alpha-spectrometry and ICP-MS

It is well known that ammunition containing depleted uranium (DU) was used by NATO during the Balkan conflict. To evaluate the origin of DU (the enrichment of natural uranium or the reprocessing of spent nuclear fuel) it is necessary to directly detect the presence of activation products ((236)U, (239)Pu, (240)Pu, (241)Am, and (237)Np) in the ammunition. In this work the analysis of actinides by alpha-spectrometry was compared with that by inductively coupled plasma mass spectrometry (ICP-MS) after selective separation of ultratraces of transuranium elements from the uranium matrix. (242)Pu and (243)Am were added to calculate the chemical yield. Plutonium was separated from uranium by extraction chromatography, using tri- n-octylamine (TNOA), with a decontamination factor higher than 10(6); after elution plutonium was determined by ICP-MS ((239)Pu and (240)Pu) and alpha-spectrometry ((239+240)Pu) after electroplating. The concentration of Pu in two DU penetrator samples was 7 x 10(-12) g g(-1) and 2 x 10(-11) g g(-1). The (240)Pu/(239)Pu isotope ratio in one penetrator sample (0.12+/-0.04) was significantly lower than the (240)Pu/(239)Pu ratios found in two soil samples from Kosovo (0.35+/-0.10 and 0.27+/-0.07). (241)Am was separated by extraction chromatography, using di(2-ethylhexyl)phosphoric acid (HDEHP), with a decontamination factor as high as 10(7). The concentration of (241)Am in the penetrator samples was 2.7 x 10(-14) g g(-1) and <9.4 x 10(-15) g g(-1). In addition (237)Np was detected at ultratrace levels. In general, ICP-MS and alpha-spectrometry results were in good agreement.The presence of anthropogenic radionuclides ((236)U, (239)Pu,(240)Pu, (241)Am, and (237)Np) in the penetrators indicates that at least part of the uranium originated from the reprocessing of nuclear fuel. Because the concentrations of radionuclides are very low, their radiotoxicological effect is negligible.     

Isotopic uranium analysis in urine samples by alpha spectrometry

Urine assay is the preferred method for monitoring accidental or chronic internal intake of uranium into the human body. A new radiochemical separation procedure has been developed to provide isotopic uranium analysis in urine samples. In the procedure, uranium is co-precipitated with hydrous titanium oxide (HTiO) from urine matrix, and is then purified by anion exchange chromatographic column. Alpha spectrometry is used for isotopic uranium analysis after preparation of a thin-layer counting source by cerium fluoride micro-precipitation. Replicate spike and procedural blank samples were prepared and measured to validate the procedure. The ²³²U tracer was utilized for chemical recovery correction, and an average recovery of 76.2 ± 8.1% was found for 1400 mL urine samples. With 48 h of counting, the minimum detectable activity concentrations were determined to be 0.43, 0.21 and 0.42 mBq/L for ²³⁸U, ²³⁵U and ²³⁴U, respectively.     

Comparative determination of uranium in rock phosphates and columbite by ICP-OES,alpha &; gamma spectrometry

During this work selective separation of uranium from rock phosphate and columbite mineral was done before its quantitative estimation by using Inductively Coupled Plasma Optical Emission Spectrometery (ICP-OES). Uranium from the rock phosphate and columubite was extracted by sodium peroxide fusion followed by leaching in 2 M HNO₃. To avoid spectral interference in the estimation of uranium by ICP-OES, the selective separation of uranium from the leachate was carried out by using two different extractants, 30% Tributyl Phophates (TBP) in CCl₄ and a equi-volume mixture of Di(2-ethylhexyl) phosphoric acid (D2EHPA) & TBP in petrofin. Uranium was stripped from the organic phase by using 1 M ammonium carbonate solution. Determination of uranium by ICP-OES was done after dissolving the residue left after evaporation of ammonium carbonate solution in 4% HNO₃. The concentration of the uranium observed in the rock phosphates samples was 40–200 μg g⁻¹ whereas in columbite samples the concentration range was 100–600 μg g⁻¹. Uranium concentration evaluated by ICP-OES was complimented by gamma & alpha spectrometry. Concentration of uranium evaluated by gamma spectrometry in case of rock phosphate and coulmbite was in close agreement with the uranium content obtained by ICP-OES. Uranium determination by alpha spectrometry showed only minor deviation (1–2%) from the results obtained by ICP-OES in case of rock phosphates whereas in case of coulmbites results are off by 20–30%.     

High precision determination of uranium in ore by gamma-ray spectrometry

A new approach for the determination of elemental uranium in uranium bearing ore, using high resolution -ray spectrometry, was applied. Using a variant of the enrichment technique an agreement of better than 1% has been obtained between -ray measurement results and a certified value obtained by other analytical methods. For the calibration of the -ray spectrometer uranium reference samples have been used which are made available jointly in Europe and the USA as Certified Reference Materials for Gamma-Ray Spectrometry (EC NRM 171 and NBS SRM 969, respectively). The measured ore has been put in a special designed container which ensured in all directions seen from the radiation window an uniform degree of infinite thickness of about 95%. The results can be taken as an example for the applicability of -ray spectrometry when high accuracy is required and under conditions were homogeneously distributed elemental uranium is embedded in larger amount of matrix material.     

Neptunium-237 in the marine environment determination in animal and plant species in the English Channel: Biological indicators and trophic relationships

We have studied the uptake of²³⁷Np in marine plants and animals belonging to several phyla, and collected samples from the end of January 1986 to March 1986, in a sampling station situated near the outlet of the irradiated fuel reprocessing plant at La Hague.We determined the²³⁷Np by neutron activation analysis. This method is very sensitive, with a limit of detection of 5×10^–10 mg, 1.3×10^–2 mBq. The method consists of the following steps:Reduction of the neptunium to the tetravalent state by treatment with a mixture of hydrazine sulfate and ferrous iron-chromatographic separations on Dowex 1×10 resin in a nitric medium, then in a hydrochloric medium-neutron irradiation in a nuclear reactor-purification of the neptunium by chromatography on Dowex 1×10 resin in a nitric then hydrochloric medium-measurement of the isotope²³⁸Np by gamma ray spectrometry using a Ge(Li) detector. The species were collected at Goury, at the northwest extremity of the Cotentin Peninsula, 5 km from the outlet of the reprocessing plant at La Hague. The levels of²³⁷Np were as follows: red algaeCorallina officinalis 64 mBq kg^–1 wet weight; andChondrus crispus 18 mBq kg^–1 wet weight; the spongeHalichondria panicea 14 mBq kg^–1 wet weight; the ascidianDendrodoa grossularia 12 mBq kg^–1 wet weight. The bivaive molluscsPatella vulgata andGibbula umbilicalis (the flesh ofP. vulgata andG. umbilicalis: 4 and 7 mBq kg^–1 wet weight respectively) also prove to be interesting biological indicatorsThe transfer modes of²³⁷Np to the various species as a function of their trophic levels are discussed as well as the distribution among the organs in the species consumed and the radiological impact of human consumption.     

Rapid determination of 237Np in soil samples by multi-collector inductively-coupled plasma mass spectrometry and gamma spectrometry

A radiochemical procedure is developed for the determination of ²³⁷Np in soil with multi-collector inductively-coupled plasma mass spectrometry (MC-ICP-MS) and gamma-spectrometry. ²³⁹Np (milked from ²⁴³Am) was used as an isotopic tracer for chemical yield determination. The neptunium in the soil is separated by thenoyl-trifluoracetone extraction from 1 M HNO₃ solution after reducing Np to Np(IV) with ferrous sulfamate, and then purified with Dowex 1 × 2 anion exchange resin. ²³⁹Np in the resulting solution is measured with gamma-spectrometry for chemical yield determination while the ²³⁷Np is measured with MC-ICP-MS. Measurement results for soil samples are presented together with those for two reference samples. By comparing the determined value with the reference value of the ²³⁷Np activity concentration, the feasibility of the procedure was validated.     

Rapid determination of radium isotopes by alpha spectrometry

An efficient analytical method for the determination of low-levels of²²⁶Ra and²²⁴Ra by alpha spectrometry is described. A cation exchange column was used to separate the analyte from other constituents in the sample (1–50 mL). After preconcentration and separation, the radium was electrodeposited onto a stainless steel disc from a solution of ammonium oxalate and hydrochloric acid. The electrodeposition was accomplished by the addition of platinum in microgram amounts. Linear responses were greater than two orders of magnitude. Detection limits of the procedure, taken as three times the standard deviation of several reagent blank analyses, were (1.8±0.3)×10^–4 Bq and (2.9±0.3)×10^–4 Bq for²²⁶Ra and²²⁴Ra, respectively. Recoveries of²²⁶Ra and²²⁴Ra ranged from 90% to 100% when samples of drinking water, well water, and dissolved bones were analyzed. Precision was calculated to be less than 5% for the determination of²²⁶Ra. Matrix effects were studied for salts of barium, magnesium, iron, and calcium.     

Determination of alpha activity ratios by alpha spectrometry in the presence of large amounts of uranium

A direct evaporation method is described for the preparation of sources using stainless steel as the backing material and tetraethylene glycol (TEG) as a spreading agent in the presence of large amounts of uranium. It is shown that FWHM and tail contribution at the low energy peak due to energy degradation of the high energy peak can be optimized by heating the source under controlled conditions in a furnace at 500–600°C for about 15 min. An accuracy of 0.5–1% is demonstrated for the determination of²³⁸Pu/(²³⁹Pu+²⁴⁰Pu) alpha activity ratio in the U/Pu range of 10 to 1500 generally encountered in dissolver solution of irradiated fuel.     

The determination of uranium in rocks by inductively coupled plasma-optical emission spectrometry

A method for the determination of uranium in rock samples by emission spectrometry is presented. The rock is dissolved and the uranium content determined by nebulizing the solution into an inductively coupled-plasma optical excitation source. Various spectral lines were investigated. The uranium emission at 378.28 nm -was chosen because of its relative freedom from matrix element spectral interferences. For this emission, a practical detection limit of 0.1 p.p.m. in solution was achieved by optimizing source parameters (power, flow-rate, observation height). Results are compared with those obtained by a number of other techniques.     

Isotope dilution alpha spectrometry with spike enriched in233U for the determination of uranium in geological samples

Isotope dilution alpha spectrometric /IDAS/ method has been developed for the determination of uranium in geological materials. The spike employed as uranium enriched in the isotope 233. The results of the analysis for rock and ore samples show that the precision and accuracy of the method are comparable to other analytical techniques and the method can be employed for routine analysis.     

Analytical techniques for the separation and determination of transuranium element ultratraces in depleted uranium ammunitions

It is well known that ammunition containing depleted uranium (DU) was used by NATO during the Balkan conflict. To evaluate the DU origin (natural uranium enrichment or spent nuclear fuel reprocessing) it is necessary to check the presence of activation products (²³⁶U, ^239+240Pu, ²⁴¹Am, ²³⁷Np, etc.) in the ammunition.

Every transuranium element (TRU) was separated from the uranium matrix by extraction chromatography with microporous polyethylene (Icorene) supporting suitable stationary phases. Plutonium was separated by tri-n-octylamine (TNOA). ²⁴¹Am was separated by TNOA and di(2ethylhexylphosphoric) acid (HDEHP). Neptunium also was separated by tri-n-octylamine using different conditions. After elution, the TRU elements were electroplated and counted by alpha spectrometry. The TRU decontamination factors from uranium were higher than 10⁶.

The final chemical yields ranged from 50 to 70%. The detection limit was 1?Bq?kg^?1 for 0.10?g ammunition; ^{239 + 240}Pu and ²⁴¹Am concentrations in two penetrators were 26 and 70?Bq?kg^?1 and <1 and 3.4?Bq?kg^?1, respectively; the ²³⁷Np concentration in one penetrator was 30.1?Bq?kg^?1.

The presence of these anthropogenic radionuclides in the penetrators indicates that at least part of the uranium originated from the reprocessing of nuclear fuel, although because of their very low concentrations, the radiotoxicological effect is negligible.     

Characterization of uranium isotopic abundances in depleted uranium metal assay standard 115

Certified reference material (CRM) 115, Uranium (Depleted) Metal (Uranium Assay Standard), was analyzed using a TRITON Thermal Ionization Mass Spectrometer to characterize the uranium isotope-amount ratios. The certified ²³⁵U/²³⁸U “major” isotope-amount ratio of 0.0020337 (12) in CRM 115 was determined using the total evaporation (TE) and the modified total evaporation (MTE) analytical techniques. In the MTE method, the total evaporation process is interrupted on a regular basis to allow correction of background from peak tailing, internal calibration of the secondary electron multiplier detector versus the Faraday cups, peak-centering, and ion source re-focusing. For the “minor” ²³⁴U/²³⁸U and ²³⁶U/²³⁸U isotope-amount ratio measurements using MTE, precision and accuracy comparable to conventional analyses are achieved, without compromising the quality of the ²³⁵U/²³⁸U isotope-amount ratios. Characterized values of the ²³⁴U/²³⁸U and ²³⁶U/²³⁸U isotope-amount ratios in CRM 115 are 0.000007545 (10) and 0.000032213 (84), respectively. The ²³³U/²³⁸U isotope-amount ratio in CRM 115 is estimated to be <5 × 10^?9. The homogeneity of the CRM 115 materials is established through the absence of any statistically significant unit-to-unit variation in the uranium isotope-amount ratios. The measurements leading to the certification of uranium isotope-amount ratios are discussed.     

Determination of uranium and radium concentrations in the waters of the Grand Canyon by alpha spectrometry

In order to establish baseline information for current and future mining operations, water samples from the Colorado River and its tributaries have been analyzed for Ra-226 and uranium isotopes. Ra-226 was separated by coprecipitation on BaSO₄ followed by alpha spectrometry. Ba-133 was used as a tracer for yield determination. Uranium was separated by a combination of BaSO₄ precipitation and solvent extraction followed by coprecipitation on CeF₃ for alpha spectrometry.Results indicate that radium and uranium levels in the Colorado River and its tributaries, except the Little Colorado River, are below the EPA specifications [1] for drinking water of 185 mBq/liter (5 pCi/1) for Ra-226 and 433 mBq/liter (11.7 pCi/1) for U-238. However, the specific sources for elevated uranium and Ra-226 concentrations in the Little Colorado River should be identified, and the potential impacts from leaching of the naturally exposed mineralization inside the Grand Canyon should be investigated.     

On the determination of226Ra in soils and uranium ores by direct gamma-ray spectrometry

The evaluation of the source term in facilities related to the first stages of nuclear fuel involves the determination of radium concentration, as well as those from other radionuclides members of the uranium series. These activities are often required within a short time period, making impossible the use of radiochemical methods or the gamma-ray spectrometry of radium daughters. In those situations it can be very convenient to determine the²²⁶Ra activity by means of its 186 keV gamma-ray line. For this purpose it is necessary to estimate the interference due to²³⁵U, also present in natural samples. This method has been applied successfully to several soil samples from an old uranium factory in Southern Spain.     

Mass spectrometry determination of the isotopic composition of uranium hexafluoride

An absolute method for the determination of isotopic composition of substances in multiple collector mass spectrometers was proposed. The detailed analysi of terms used in the method for the determination of the isotopic composition of uranium hexafluoride was given. Parabolic nature of occurring constant measurement error, obtained in theory, was proved by test data for ²³⁵U within a wide range of its concentrations. In order to use the method of measurements in practice, the registration of constant error, through linear discriminatory relations Δc _i (c _i ), preliminary determined using uranium hexafluoride with standard isotopic composition, was proposed. The advantages of the developed method in comparison with the traditional analysis procedures, applied at present, were considered.