Determination Of Uranium Enrichment Research Articles

In-field alpha spectrometry system for uranium enrichment verification of uranium hexafluoride

A portable In-Field Alpha Spectrometry (IFAS) system was developed to support on-site uranium enrichment determination for samples taken at facilities working with gaseous UF6. It consists of a modified commercial alpha spectrometer, a vacuum pump, a laptop computer, and associated connectors and cables. The IFAS uses specially designed Single-Use Destructive Assay (SUDA) samplers to capture gaseous UF6 and convert and store it as UO2F2 in a thin-film zeolite. To examine the quantitative performance of the IFAS system a large number of replicate SUDA samples was acquired for natural uranium (NU, 0.72 wt%, 23 samples), low enriched uranium 1 (LEU1, 2.33 wt% 235U, 10 samples), and low enriched uranium 2 (LEU2, 4.62 wt% 235U, 10 samples). The standard deviation (SD) values for uranium enrichment determination with the IFAS for NU, LEU1, and LEU2, in 20-hour assays, were 0.037 wt% 235U, 0.063 wt% 235U, and 0.072 wt% 235U, respectively. A separate analysis suggests that comparable SD values can be achieved in less time, approximately 8–10 h. For context, these SD values are well below the International Atomic Energy Agency’s International Target Values for the determination of uranium enrichment in non-destructive assay measurements.

Peak shape calibration of a Cadmium Zinc Telluride detector and its application for the determination of uranium enrichment

Cadmium Zinc Telluride (CZT) detectors are portable, room temperature serviceable, medium-resolution gamma-ray spectrometers. Their full-energy peak shape exhibits a low energy tail which complicates the analysis of spectra with overlapping peaks. In this paper, we determined the peak shape parameters of a CZT detector from measurements with calibrated point sources from 0.06 MeV up to 1.332 MeV. The peak shape parameters were obtained by applying a peak fitting algorithm that includes a Gaussian and a tail with energy dependent parameters in the region around the gamma-ray peak. The net peak areas were used to verify the absolute detection efficiency obtained with a Monte Carlo model of the CZT detector and the agreement in absolute terms was within 10% over the considered energy range. The peak fitting algorithm was then applied to determine the net peak areas of the full energy peak in spectra recorded with certified uranium standards. The enrichment was then determined by using the so-called ‘peak ratio’ method. We observed a systematic bias in the net peak areas of the 0.258 MeV gamma-ray which therefore was not included in the analysis. Hence, the enrichment was underestimated by about 10%.

Error reduction in gamma-spectrometric measurements of nuclear materials enrichment

The paper provides the analysis of the uncertainty in determining the uranium samples enrichment using non-destructive methods to ensure the functioning of the nuclear materials accounting and control system. The measurements were performed by a scintillation detector based on a sodium iodide crystal and the semiconductor germanium detector. Samples containing uranium oxide of different masses were used for the measurements. Statistical analysis of the results showed that the maximum enrichment error in a scintillation detector measurement can reach 82%. The bias correction, calculated from the data obtained by the semiconductor detector, reduces the error in the determination of uranium enrichment by 47.2% in average. Thus, the use of bias correction, calculated by the statistical methods, allows the use of scintillation detectors to account and control nuclear materials.

Experiments and Monte Carlo modeling of a higher resolution Cadmium Zinc Telluride detector for safeguards applications

The Belgian Nuclear Research Centre is engaged in R&D activity in the field of Non Destructive Analysis on nuclear materials, with focus on spent fuel characterization. A 500 mm3 Cadmium Zinc Telluride (CZT) with enhanced resolution was recently purchased. With a full width at half maximum of 1.3% at 662 keV, the detector is very promising in view of its use for applications such as determination of uranium enrichment and plutonium isotopic composition, as well as measurement on spent fuel. In this paper, I report about the work done with such a detector in terms of its characterization. The detector energy calibration, peak shape and efficiency were determined from experimental data. The data included measurements with calibrated sources, both in a bare and in a shielded environment. In addition, Monte Carlo calculations with the MCNPX code were carried out and benchmarked with experiments.

Enrichment determination of low – enriched uranium material by gamma spectroscopic method

In this work the non - destructive gamma spectroscopic method for determination of uranium enrichment is presented. In order to determine the uranium enrichment the activity ratios of 234U/235U and 238U/235Uwere measured. The activity ratios234U/235U and 238U/235U were determined by using intrinsic efficiency calibration. As a test of this method, low - enriched uranium standard was measured, the obtained result was in good agreement with the estimated value.

A simple method for the absolute determination of uranium enrichment by high-resolution γ spectrometry

A simple method for the determination of uranium enrichment using high-resolution γ spectrometry is presented in this paper. The method relies solely on the γ-ray emission probabilities of 235U and 234mPa, and an iterative procedure for the least squares fit of a polynomial to a set of experimentally determined data. To ensure the reliability of the 234mPa γ-ray emission probabilities employed, a new determination of these probabilities was carried out using a combination of γ spectrometry and Cerenkov counting of a purified 234Th solution. Using these new data, a maximum difference of ∼5% has been found between the experimental and declared uranium enrichment in a set of solid and liquid samples containing uranium compounds.

Results from the international evaluation exercise for uranium enrichment measurements

An international evaluation exercise for uranium enrichment measurement was organized by the ESARDA (European Safeguards Research and Development Association) Working Group on Techniques and Standards for Non-Destructive Analysis. The aim of this exercise was to test the different methods and more particularly X- and γ-ray spectrometry methods used in the determination of uranium enrichment. Sets of samples of different uranium enrichments prepared by IRMM (Institute for Reference Materials and Measurements) and BNFL (British Nuclear Fuels) were measured by 15 participants in the IRMM laboratories. A description of this exercise is given here and the final results with their uncertainties are compared to the reference values obtained from mass spectrometry measurements. The main conclusions from this exercise are proposed; in particular, it appears necessary to improve the nuclear data used in the spectral modeling of the XK α region.

Enrichment analysis of uranium in uranium oxide by gamma-ray spectrometry without using calibration standards

An analytical method for the determination of uranium enrichment in uranium oxide without using any calibration standards is described. Very good agreement between the measured and certified values was obtained in the analysis of a Standard Reference Material. Precise energies and emission probabilities were derived for two weak gamma-rays of234mPa: at 258.227±0.003 keV, (0.076±0.002)% and 742.813±0.005 keV, (0.106±0.002)%.

Gamma-spectrometric determination of uranium enrichment: A review of the method

Gamma-spectrometric determination of the uranium enrichment is reviewed and two main point are analyzed: (a) The correlation between the enrichment factor and the mass of the sample and (b) the intensity of the γ-ray used in the method, which had to be changed from previous works. Furthermore a X2 minimization has been included into the method, improving its reliability.