[en] This document deals with the analysis of errors arising from application of pseudo-random signal instead of random signal in cross correlation measurements for determining system response function

[en] DNAA is a method of neutron activation analysis for detection and qualification of fissile material in various types of samples by delayed neutron counting. DNAA offers significant advantages for screening of environmental samples due to the rapid, nondestructive, sensitive and interference free analysis at relatively low cost comparing to other screening methods. Technical cooperation on the delayed neutron activation analysis (DNAA) method is being implemented pursuant to the bilateral safeguards arrangement between the United States Department of Energy and the Ministry of Science and Technology of the Republic of Korea, and the technical training was conducted at ORNL during May, 2004. The system characteristics such as reproducibility and linear range of measurement, and swipe sample screening were performed during the training. The results will be presented in this paper

[en] The control and safety analysis of a nuclear reactor strongly relies on numerical simulation of reactor dynamics, in which the neutronics computation is one of the most important tasks. It is necessary to utilize a full three-dimensional model of neutron kinetics for satisfactory results but this requires an extensive computation. The purpose of this research is to explore an efficient method for accurate solution of the spatial neutron kinetics problem. The kinetics of neutrons in a nuclear reactor of practical interest is adequately represented by the few-group diffusion equations with delayed neutron effects taken into account. For solving such a space-time equation system, finite difference methods, though the simplest, must work with a very fine-mesh grid, resulting in an extremely large algebraic system whose solution by basic numerical methods encounters inefficiency. Coarse-mesh methods increase computational efficiency by reducing the number of discretized equations. However, by adding more complexity and limitations, the coarse-mesh computation is still rather time-consuming. Multigrid methods may provide an optimal solution for a large, sparse algebraic system arising from discretization of a partial differential equation or system but have not found many applications in reactor physics due to inherent difficulties. In this research, a finite difference method is used for discretization of the kinetics equations and a multigrid solver is developed to solve the discretized equation system. The Additive Correction Multigrid, the simplest and cheapest method in the multigrid family, is used for grid coarsening, allowing for reaching the coarsest grid without any difficulties. By avoiding the singularity and indefiniteness of the discretized system, the Red-Black Gauss-Seidel method is suited for multigrid smoothing and favours an implementation of parallel computation. Numerical experiments show that our multigrid solver is not only much faster than any basic iterative method but also tends to be mesh-independent or optimal for solving a practical kinetics problem. (author)

[en] Principles of Uranium and Thorium analysis by delayed neutron are reviewed and optimal conditions for their determination are proposed: irradiation time=40 sec., decay-time=3 sec., counting time=70 sec.

[en] A delayed neutron counting (DNC) system for the analysis of special nuclear materials (SNM) has been constructed and calibrated at the Royal Military College of Canada. The polyethylene vials used to transport SNM samples have been found to contribute a time-dependent count rate, B(t), far above the system background. B(t) has been found to be independent of polyethylene mass and shows a dependence on irradiation position in the SLOWPOKE-2 reactor and irradiation time. A comparison of B(t) and the theoretical delayed neutron production from the fission of small amounts of ²³⁵U has indicated that trace amounts of uranium may be present in the DNC system tubing. (author)

[en] 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. (author)

[en] Delayed neutron data play a key role in the reactor physics analysis of safety related parameters. This is the case for any type of reactor. For existing and operating reactors the interest is for an improvement of the basic data which are used to establish the reactivity scale and the reduction of the associated uncertainties. Moreover, there is at present a strong trend towards the study and development of new reactor types. For these advanced and innovative reactor concepts, there is a need to establish complete and sound data bases. In this context delayed neutron data also plays a significant role. This paper carries out a review of the delayed neutron parameters and their uncertainties as available today. Using an exhaustive set of data, the results of an analysis focused on reactor technology are synthesized in a consistent structure having three levels of refinement. Conclusions on the quality of the data together with recommendations for improving them through modelling and measurements on each of the three levels are formulated. Improvements in delayed neutron data make it possible to establish a more precise reactivity scale for existing reactors. Increased safety margins can be achieved by reducing the current uncertainty of 10 % for two standard deviations to 5 %. (authors)

No abstract available

[en] A preliminary study was conducted to determine the amount of fissile material present in a sample. The method used consisted in irradiating the sample by means of a pulsed neutron generator and delayed neutron counting. Results show the validity of this method provided some experimental precautions are taken. Checking on the residual proportion of fissile material in leached hulls seems possible. (authors)

[en] Delayed neutron activation analysis (DNAA) is a rapid and sensitive analytical method for the determination of fissile elements in a variety of samples. The present work describes two different analytical applications of delayed neutron activation for the analysis of biological and environmental samples, respectively. In the first application, DNAA was utilized to determine the natural uranium content in NIST standard reference materials (SRM) 1547 peach leaves and 1573a tomato leaves. Measured uranium mass fractions are comparable to the non-certified values listed on the certificates for these materials. In the second application, delayed neutron activation is coupled with instrumental neutron activation analysis (INAA) for the measurement of rare earth elements (REE) (cerium, lanthanum, neodymium, and ytterbium) in NIST SRM 2586, Trace Elements in Soil Containing Lead from Paint. DNAA was utilized to determine the uranium mass fraction in SRM 2586 for the subsequent application of a correction factor to account for cerium, lanthanum, and neodymium produced as part of the INAA irradiation. Measured and corrected mass fractions for the REEs described here are all within the uncertainty limits provided on the NIST certificate for SRM 2586. These results and the demonstrated sensitivity of the DNAA system establish and validate the use of this method for the determination of REEs and for potential nuclear forensics applications. (author)