Use of AWCC in evaluation of unknown fissile materials

An important technological problem in the sphere of non-proliferation and safeguards is nondestructive analysis (NDA) methodology for qualitative and quantitative characterization of nuclear materials. Additionally, NDA tends to be labor and time intensive. Two NDA techniques used at KIPT included Gamma Spectroscopy (for qualitative analysis) and Neutron activation (for quantitative analysis). Gamma Spectroscopy was used to confirm the presence of radionuclides within the samples, whereas an Active Well Coincidence Counter (AWCC) in the active mode was used to quantitatively determine the 235U content in particular types of fissile materials at KIPT. This paper describes the usage of the AWCC at NSC KIPT for characterizing nuclear materials for IAEA safeguards. It was also an opportunity to estimate fissile materials of unknown composition. The equipment used was a model JCC-51 AWCC using a shift register model JSR-12 from Canberra and two neutron sources [AN-HP (241AmLi)]. A Compaq Presario computer using Windows version of NCC (Los Alamos software) was used to operate the AWCC. Materials studied in this project included highly enriched nuclear material in the form of powder, compacts (tablets, microspheres, rods), salt and scrap. The chemical composition of nuclear material included uranium metal, uranium dioxide, uranium nitride, uranium carbonitride, thorium dioxide, and mixtures of these compounds. New standards were used to recalibrate the AWCC using material obtained at KIPT with documented compositional values more similar to the materials to be measured, and in similar containers as well. During this study, the AWCC calibration curves were obtained for uranium metal and uranium dioxide with different enrichments up to 90 % for 235U. A broad spectrum of other fissile materials of unknown composition with differing enrichments has also been studied, and the items' isotopic and quantitative compositions have also been determined. Using the new calibration curves, 235 U was determined with accuracy of ∼1.2% for samples <100g and with accuracy of ∼3.5% for samples <2kg compared to original values, that are confirmed by results of destructive analysis in IAEA Safeguard Analytical Laboratory