Delayed neutron activation analysis (DNAA) presents a fast, accurate, and reliable method for quantification of fissile material.
The method has relatively few sources of error and may be accomplished nondestructively. The need for a fast, accurate screening
of materials stems from the necessity to protect cleanroom facilities from widely varying fissile quantities in samples and
from desired gains in efficiency of mass spectrometric analysis by assisting in spike level selection and by removing from
the sample set those materials that are not of interest. During the last several years, many different materials have been
screened or analyzed in support of international safeguards, internal process control for actinide separations, and in uranium
contamination assessments. Swipes from a variety of sources have been analyzed, either before or after dissolution, and comparison
of the DNAA results to mass spectrometry results is generally favorable. A facility characterization of the High Flux Isotope
Reactor was performed using filter paper swipes to demonstrate the utility of the DNAA technique.
Recent attention to international safeguards has stimulated interest in nondestructive analysis techniques. These NDA techniques include high- and low-resolution gamma-ray spectrometry, active and passive neutron counting, and physical measurements. Often, the NDA measurements are made abroad under field conditions, and in these cases, portability is important. In other cases, the measurements are made under laboratory conditions but no calibration materials are available. This paper describes several NDA applications in support of international safeguards projects, all involving international cooperation.
Authors:Owen Drury, Miguel Velazquez, Jonathan Dreyer, and Stephan Friedrich
We are developing superconducting ultrahigh resolution gamma-detectors for non-destructive analysis (NDA) of nuclear materials,
and specifically for spent fuel characterization in nuclear safeguards. The detectors offer an energy resolution below 100 eV
FWHM at 100 keV, and can therefore significantly increase the precision of NDA at low energies where line overlap affects
the errors of the measurement when using germanium detectors. They also increase the peak-to-background ratio and thus improve
the detection limits for weak gamma emissions from the fissile Pu and U isotopes at low energy in the presence of an intense
Compton background from the fission products in spent fuel. Here we demonstrate high energy resolution and high peak-to-background
ratio of our superconducting Gamma detectors, and discuss their relevance for measuring actinides in spent nuclear fuel.
Authors:C. Lee, K. Iguchi, J. Inagawa, D. Suzuki, F. Esaka, M. Magara, S. Sakurai, K. Watanabe, and S. Usuda
An improved method of fission track (FT) sample preparation was developed, in which the detector of fission track and the
layer containing particles are separated, in order to apply the FT-thermal ionization mass spectrometry (TIMS) for particle
analysis of safeguards environmental samples. The developed FT sample enabled us to detect the particle of interest simply
by observing the fission tracks. The process of particle identification was difficult due to the discrepancy between the position
of the particles and fission tracks, which were observed in the conventional FT sample. The proposed method has significantly
resolved this problem.
Authors:J. H. Buchmann, J. E. S. Sarkis, M. H. Kakazu, and C. Rodrigues
The use of environmental monitoring as a technique to identify activities related to the nuclear fuel cycle has been proposed
by international safeguards organizations. The elements specific for each kind of nuclear activity, or “nuclear signatures”,
inserted in the ecosystem can be intercepted by different live organisms. This work demonstrates the technical viability of
using pine needles as bioindicators of nuclear signatures associated with uranium enrichment activities. Additionally, it
proposes the use of HR-ICP-MS to identify the signature corresponding to that kind of activities in the ecosystem. Nitric
acid solutions, used to wash pine needles sampled near nuclear facilities and containing only 0.1 mg . kg-1 of uranium, exhibit a n(235U)/n(238U) isotopic abundance ratio of 0.0092±0.0002, while solutions originated from samples collected at places located more than
200 km far from activities related to the nuclear fuel cycle exhibit a value of 0.0074±0.0002. Similar results were obtained
for sample solutions prepared using the acid leaching process. The different values of n(235U)/n(238U) isotopic abundance ratio obtained permit to confirm the presence of anthropogenic uranium and demonstrate the viability
of using the methodology proposed in this work.
Environmental sampling (ES) is one of the measures applied in international nuclear safeguards. The detection capability of
safeguards ES relies on a combination of highly sensitive analytical techniques and resourceful data evaluation. The evaluation
process is dynamic, employing a variety of tools, information and analytical results. While the presence of uranium or plutonium
may be a significant finding in itself, high quality isotopic measurements are essential to associate the material with a
specific nuclear activity. This is illustrated in cases where the uranium detected appears to be “natural” or “near-natural”,
but in fact can be identified with various nuclear processes.
The purpose of this study was twofold: the identification of some uranium compounds and a measurement of mixed U/Pu particles with different ratios of these elements. We used a Philips XL-30 scanning electron microscope equipped with an EDAX energy dispersive spectrometer with a Si(Li) detector and a super ultra-thin polymer window and with a Microspec wavelength dispersive spectrometer. A number of WDXRF and EDXRF spectra of U and Pu containing particles were accumulated and evaluated. The software package provided by the manufacturer was used for EDXRF spectra evaluation and calculation of the weight and atomic composition. Eight different U compounds were identified with a different degree of confidence. Several different types of U and Pu particles were measured using the WDXRF spectrometer and the results of the measurements are discussed. The measurement of mixed U-Pu particles showing large differences in the concentration of both elements can best be carried out with the use of WDXRF because the deconvolution of the M lines of U and Pu in the energy dispersive spectra is only possible over a relatively small concentration range. The results of particle analysis are very useful for verifying the absence of undeclared nuclear activities.
Authors:O. Farmer, K. Olsen, M. Thomas, and S. Garofoli
A method for the separation and determination of total and isotopic uranium and plutonium by ICP/MS was developed for IAEA
samples on cellulose-based media. Preparation of the IAEA samples involved a series of redox chemistries and separations using
TRU® resin (Eichrom). The sample introduction system, an APEX nebulizer (Elemental Scientific, Inc.), provided enhanced nebulization
for a several-fold increase in sensitivity and reduction in background. Application of mass bias (ALPHA) correction factors
greatly improved the precision of the data. By combining the enhancements of chemical separation, instrumentation and data
processing, detection levels for uranium and plutonium approached high attogram levels.
Authors:A. Bosko, S. Croft, S. Philips, and R. Gunnink
Nondestructive measurements of γ-ray and X-ray emissions are often made to characterize special nuclear materials. Various
computer codes are available to determine the relative isotopic composition of uranium or plutonium (along with certain other
associated nuclides) from analysis of the spectra resulting from such measurements. MGA (Gunnink, Proceedings of the 9th ESARDA
symposium on safeguards and nuclear management 167, 1987) and MGAU (Gunnink et al., Proceedings of the IAEA symposium on international
safeguards 541, 1994) are among the major isotopic codes. The purpose of this study was to investigate MGA and MGAU performance
versus energy resolution of the counting system.