INAA of Zr,La, Ce and Nd in geological samples in the presence of different uranium concentratios

Rock samples which contain relatively high concentrations of uranium may create problems of interference produced by fission products, when instrumental neutron activation analysis is used. The isotopes⁹⁵Zr,¹⁴⁰La,¹⁴¹Ce, 143Ce and 147Nd, which are commonly used in the neutron activation analysis of the corresponding elements, are also produced as fission products of²³⁵U. For each of these radioisotopes, a contribution factor is calculated theoretically and meaured experimentally using geological samples with different uranium contents.     

Multielement analysis of uraniferous rocks by INAA: Special reference to interferences due to uranium and fission of uranium

The presence of uranium in a sample enhances the true values of La, Ce, Nd, Sm determined by INAA if appropriate corrections are not made for the interference. The enhancement of the true values comes about because the (n, γ) activation products of these elements, viz.¹⁴⁰La,¹⁴¹Ce,¹⁴⁷Nd,¹⁵³Sm, are also produced from the fission of²³⁵U (～0.72% natural isotopic abundance) even when La, Ce, Nd, Sm are totally absent in the given sample. In a 5 hour irradiation 1 μg of U is found to be equal to 0.28 μg of Ce and 0.23 μg of Nd while the equivalent La is found to be dependent upon the delay from end of irradiation to sample counting time. A numerical procedure is given to correct for these interferences. Spectral interferences from fission and (n, γ) β products of uranium in the determination of other trace elements by INAA is also investigated. Uranium is found to be determined best using the 278 keV gamma-ray of²³⁹Np.     

Chromatographic isolation of144Ce and144Pr from the wastes of irradiated uranium treatment

A two-step chromatographic technique was elaborated to isolate¹⁴⁴Ce,¹⁴⁴Pr from a solution of uranium fission products in 6M HNO₃. The oxidation to Ce(III) by bromate and selective adsorption of¹⁴⁴Ce(IV) on anion exchange column were used to concentrate and purify¹⁴⁴Ce. Some impurities of uranium,⁹⁵Zr,⁹⁵Nb,¹⁰⁶Ru remain in¹⁴⁴Ce solution after the first step of its isolation. The final purification is achieved by passing the 6M HNO₃ solution of¹⁴⁴Ce(IV) through the HDEHP-coated teflon column. The decontamination factors of¹⁴⁴Ce from main fission products are given. 7.2 mCi of (¹⁴⁴Ce+¹⁴⁴Pr) are recovered from each gram of irradiated uranium trioxide with the yield greater than 99%. An improvement of known generator was carried out to elute a purer¹⁴⁴Pr from maternal¹⁴⁴Ce(IV) adsorbed on the anion exchange column.     

Production of99Mo and its application in nuclear medicine

Molybdenum-99 is produced in large quantities as the parent radioisotopes of^99mTc, which has been used recently in nuclear medicine. The neutron capture reaction on molybdenum and the nuclear fission of uranium are used for the large scale production of⁹⁹Mo. The products by these methods are used properly according to the objects of diagnosis. In this paper, the production of⁹⁹Mo is reviewed and the development of the production in JAERI is outlined.     

Interference in neutron activation analysis of rocks by uranium fission

Interferences by uranium fission for⁹⁵Zr,⁹⁹Mo,¹⁰³Ru,¹⁴⁰La,¹⁴¹Ce and¹⁴⁷Nd have been studied using a single comparator method with two monitors. The effect of the neutron energy spectrum on the interference factor was examined by using the effective activation cross section. All the activities of¹⁴⁰La produced during neutron irradiation of uranium were included in the calculation of the factor for lanthanum. The calculated and experimental interference factors are in good agreement within 10% deviation. The results have been applied for the analysis of several rock samples containing uranium in a wide concentration range.     

Separation of gram quantities of uranium from fission products by extraction chromatography

The separation of gram quantities of uranium from fission products has been investigated by extraction chromatography. The separation which is based on the difference in distribution coefficients between uranium and the fission products on a tributyl phosphate (TBP) resin in nitric acid medium, was carried out by means of high acidity feed and stepwise elution on a TBP chromatography column. The results show that this technique is capable to separate 5 g of uranium from a large quantity of fission products. The recovery of uranium is more than 99%. The decontamination factors of g- and b-activities were 2.1^.10³ and 2.3^.10³, respectively.     

Comparative study of cesium adsorption on dioctahedral and trioctahedral smectites

Bentonites which are characterized by good rheological, mineralogical and chemical stability is considered used as sealing barriers in multibarrier Slovak system of deep geological repository for high-level radioactive waste and spent nuclear fuel. In Slovak Republic there are several significant deposits of bentonite, which are characterized by appropriate adsorption properties and meet the geotechnical requirements for this type of barriers. Study of adsorption properties of bentonites and other smectites is an essential step for developing the migration model long-lived corrosion and activation products, and fission products of uranium. Nuclear wastes contain the most important nuclear fission products, radioisotopes ¹³⁴Cs and ¹³⁷Cs. The present paper investigates and compares the cesium adsorption properties of Slovak and North America bentonites composed mainly of dioctahedral smectite montmorillonite (J, L, SAz-1 and STx-1) and trioctahedral smectites saponite (SapCa-2) and hectorite (SHCa-1).     

Intereferences from uranium fission in neutron-activation analysis in an Argonaut-type Low Flux Reactor

The interferences by uranium fission on the determination by neutron activation analysis of Zr, Mo, Ru, La, Ce, Nd and Sm are investigated for the Argonaut-type Low Flux Reactor at ECN, Petten, The Netherlands. In addition, the spectral interference of the determination of Sm by²³⁹Np is considered. The experimental values for fission yields are found to be in good agreement with calculated values based on recent cross-section compilations.     

Fission product yields in the fast-neutron fission of238U

The fission yields of 38 fission products in the fast-neutron induced fission of²³⁸U have been determined using a rapid, multiscaling gamma-ray spectroscopic method. To obtain absolute yields for fission products having half-lives ranging from 32 s to 40 d, a total of 56 multi-scaling gamma-ray spectra were collected using various irradiation and cooling periods. Gamma-rays and photopeak areas of interest were assigned to the fission products by their energies and half-lives. Fission product activities were evaluated from spectral data using growth and decay calculations and fission yields were determined by normalizing the¹⁴⁰Ba yield to the average value from reported data. The depleted uranium target, covered with a boron-cadmium thermal neutron shield, was used to keep interference from the fission of²³⁵U minimal. Results for the cumulative fission yields, including 17 mostly short-lived fission products measured for the first time, are compared with previous measurements and with the recommended yields in recent evaluations. The agreement, and some discrepancies, in the comparisons are discussed. No explicit even-odd pairing effects are observed in the fission yield data for fast-neutron induced fission of²³⁸U.     

Correcting for uranium fission in instrumental neutron activation analysis of high-uranium rocks

Failure to correct for fission products of²³⁵U is shown to result in significant errors in the measured concentrations of La, Sm, Nd, Ba, Zr, and Mo by Instrumental Neutron Activation Analysis of high uranium rocks. Measured and calculated correction factors are presented as the ratio of the fission product to parts per million by weight of uranium in the rock. Potential errors in petrogenetic interpretations of uncorrected data are outlined.     

Neutron activation analysis of pure uranium: Preconcentration of impurity elements

We have developed a radiochemical neutron activation analysis technique (RNAA) of pure uranium with using extraction chromatographic separation of ²³⁹Np from impurity elements in TBP-6M HNO₃ media. The estimation of influence of fission products of ²³⁵U on the results by radiochemical neutron activation analysis has been carried out. For it we have performed NAA with preconcentration of impurity elements. Experiments show that in this case the apparent concentration of Y, Zr, Mo, Cs, La, Ce, Pr, Nd exceeds the true concentration by 2500–3000 times. Therefore, determination of these elements is not possible by RNAA. This technique allowed to use the determination of 26 impurity elements with detection limit 10⁻⁵–10⁻⁹% by mass. This developed technique may be used for the determination of impurities in uranium and its compounds.     

New concepts for radiometric measurements of environmental samples

The Radiation Detection and Nuclear Sciences Group at Pacific Northwest National Laboratory has a long history in conducting measurements of radioisotopes for various applications. This experience includes ultra-low background measurements, arrays of germanium detectors, automated sampling and measurement systems and coincidence measurement systems. A recent lab-supported effort has been studying how these capabilities, both in terms of hardware and experience, can be leveraged to enable environmental sampling measurements. One area of interest is the release of fission products and actinides into the environment from a reactor incident. While the initial survey of this area is still under way, one isotope of interest that surfaced early in the study is ²³⁸Pu. Existing techniques to assay this isotope suffer from measurement challenges. In alpha counting, there can be significant interference with ²⁴¹Am, while in mass spectrometry, there can be interference with ²³⁸U. The authors are developing the concept for a detector that through coincidence counting techniques can distinguish ²³⁸Pu and ²⁴¹Am. In addition, we will design the system to conduct radiometric measurements of other plutonium isotopes to enable a direct comparison of those isotopes. We will present our concept of the detector system for ²³⁸Pu, as well as discuss other radiometric measurements of fission products and actinides with which we intend to advance the state of the art for environmental measurements.     

Determination of uranium,plutonium and selected fission products in the coolant of the KS-150 reactor

The method of monitoring of U, Pu and some fission products (^103,106Ru,^134,137Cs and^141,144Ce) in gaseous CO₂ coolant is described. The method is based on the retention of the radionuclides studied by membrane filters built in by-pass of the burst-cartridge detection (BCD) system. The purpose of the present study was the determination of U, Pu in CO₂ and the verification of the possibility of the indirect monitoring of U and Pu contents in the coolant, using the gamma-spectrometric determination of selected fission products retained by the filter. For calibration of the proposed method after decomposition of the filters, uranium was determined spectrophotometrically using Arsenazo III, plutonium was determined radiometrically after its separation by extraction with 2-thenoyltrifluoracetone and the fission products were determined by gamma-spectrometry. From the results obtained it follows that a correlation exists between the U and Pu content in the coolant and the activity of certain fission products retained on the filter.     

Comparison of portable detectors for uranium enrichment measurements

Uranium enrichment and holdup measurements require a detector capable of accurately obtaining the 186-keV peak area. NaI detectors have been widely used for these tasks. However, for recycled uranium, the interference of the 239-keV peak from the ²³²U decay chain challenges the capabilities of the NaI detectors to accurately extract the area of the 186-keV peak. Using CZT detectors, which have much better resolution than the NaI detectors, has temporarily solved this interference problem. However, the CZT detectors have setbacks in that they are generally small and have low efficiencies, which require long acquisition times for reasonable statistics. Recently, two new types of scintillator detectors have become available commercially, LaCl₃(Ce) and LaBr₃(Ce). These cerium-doped lanthanum halide detectors, with comparable resolution but better efficiency than the CZT detectors, appear to permanently solve the interference problem for recycled uranium measurements. In this report, we compare the uranium enrichment measurement performances of a portable NaI detector, a large coplanar-grid CZT detector, and a LaBr₃ detector.     

低浓缩铀靶辐照后溶液中铀的化学种态及主要裂变元素的影响

利用化学种态分析软件CHEMSPEC计算了低浓缩铀靶辐照后溶液中铀(U)的化学种态分布及其主要裂变元素对U化学种态的影响。结果表明,在单组分体系中,pH值和铀酰浓度都会显著影响U的化学种态分布。随着铀酰浓度的增大,溶液中将会生成多核配合物;在较高的NO₃^-浓度下,U在溶液中主要以UO₂²⁺和UO₂NO³⁺的形式存在。CO₂对不同浓度铀的种态分布影响结果表明,当铀酰浓度较低时,铀的化学种态多以碳酸铀酰的形式存在;当铀酰浓度较高时,铀的化学种态多以氢氧铀酰或柱铀矿沉淀的形式存在。计算发现,当裂片元素Tc、I、Mo的浓度小于0.01mol·L^-1并分别以TcO₄^-、I^-、MoO₄^2-的种态存在时,这些裂片元素不改变铀的各化学种态的分布。     

Sequential separation of transuranic elements and fission products from uranium metal ingots in electrolytic reduction process of spent PWR fuels

A sequential separation procedure has been developed for the determination of transuranic elements and fission products in uranium metal ingot samples from an electrolytic reduction process for a metallization of uranium dioxide to uranium metal in a medium of LiCl-Li₂O molten salt at 650 °C. Pu, Np and U were separated using anion-exchange and tri-n-butylphosphate (TBP) extraction chromatography. Cs, Sr, Ba, Ce, Pr, Nd, Sm, Eu, Gd, Zr and Mo were separated in several groups from Am and Cm using TBP and di(2-ethylhexyl)phosphoric acid (HDEHP) extraction chromatography. Effect of Fe, Ni, Cr and Mg, which were corrosion products formed through the process, on the separation of the analytes was investigated in detail. The validity of the separation procedure was evaluated by measuring the recovery of the stable metals and ²³⁹Pu, ²³⁷Np, ²⁴¹Am and ²⁴⁴Cm added to a synthetic uranium metal ingot dissolved solution.     

低浓缩铀靶辐照后溶液中铀的化学种态及主要裂变元素的影响

利用化学种态分析软件CHEMSPEC计算了低浓缩铀靶辐照后溶液中铀(U)的化学种态分布及其主要裂变元素对U化学种态的影响。结果表明,在单组分体系中,pH值和铀酰浓度都会显著影响U的化学种态分布。随着铀酰浓度的增大,溶液中将会生成多核配合物;在较高的NO₃^-浓度下,U在溶液中主要以UO₂²⁺和UO₂NO₃⁺的形式存在。CO₂对不同浓度铀的种态分布影响结果表明,当铀酰浓度较低时,铀的化学种态多以碳酸铀酰的形式存在;当铀酰浓度较高时,铀的化学种态多以氢氧铀酰或柱铀矿沉淀的形式存在。计算发现,当裂片元素Tc、I、Mo的浓度小于0.01 mol·L^-1并分别以TcO₄^-、I^-、MoO₄^2-的种态存在时,这些裂片元素不改变铀的各化学种态的分布。     

Application of neutron activation analysis in a fission molybdenum separation study

The separation of⁹⁹Mo from low-enriched uranium (LEU, 19.5%²³⁵U) targets was evaluated using natural uranium (NU) and non-radioactive tracers. Neutron activation analysis was used to determine (1) the efficiency of molybdenum recovery and (2) the decontamination factor of numerous fission product elements from the molybdenum product. Using NU and non-radioactive elements simplified procedures and allowed tests to be completed in a fume hood instead of a shielded cell. During activation of the non-radioactive tracers, uranium fission occurs, which can interfere with subsequent gamma-ray analysis. A comparison was made of the interferences caused by these fission products from both NU and LEU.     

Experimental measurements of short-lived fission products from uranium,neptunium, plutonium and americium

Fission yields are especially well characterized for long-lived fission products. Modeling techniques incorporate numerous assumptions and can be used to deduce information about the distribution of short-lived fission products. This work is an attempt to gather experimental (model-independent) data on short-lived fission products. Fissile isotopes of uranium, neptunium, plutonium and americium were irradiated under pulse conditions at the Washington State University 1 MW TRIGA reactor to achieve ~10⁸ fissions. The samples were placed on an HPGe (high purity germanium) detector to initiate counting in less than 3 min post irradiation. The data was analyzed to determine which radionuclides could be quantified and compared to the published fission yield data.     

Radiochemical analyses for the defense waste processing facility startup at the Savannah River Site

Highly radioactive waste from defense-related activities at the Savannah River Site in South Carolina are to be incorporated into a borosilicate glass in the Defense Waste Processing Facility (DWPF) for long-tem geological isolation. Processing and repository safety considerations require the determination of 24 radioisotopes that meet the reporting criteria. These isotopes include fission products, activation products, and daughter nuclei that grow into the waste. Four isotopes,¹³⁷Cs,⁹⁰Sr,²³⁸Pu and²³⁸U will be routinely measured in the DWPF operation for process control. This work shows that the concentrations of the other 20 reportable radioisotopes in the final glass product can be predicted from a thorough characterization of the high level waste (HLW) tanks and a knowledge of the concentrations of the major non-radioactive components in the vitrification process.