Results of active well coincidence counter cross-calibration measurements at Argonne National Laboratory-West.

Abstract

Nondestructive Assay (NDA) of Nuclear Materials (NM) is a common tool used by inspectors involved in Material Protection, Control and Accounting (MPC&A) programs, both domestically and internationally. NDA is generally used to quantify the properties of NM, usually by determining the mass or enrichment of materials such as U-235 or Pu-240. For the NDA of Highly Enriched Uranium (HEU) metal, powder or scrap samples, Active Well Coincidence Counter (AWCC) NDA systems are routinely used. These systems bombard samples with neutrons, inducing fission events. The fissile mass of the sample is determined based upon the number of coincidence neutrons detected. To obtain accurate quantitative measurements using AWCC systems it is necessary to calibrate the instruments using physical standards representative of the unknown sample to be measured. During international inspections it is both expensive and difficult to obtain the large number of physical standards necessary to accurately assay the wide range of NM present at multiple sites. To address this issue, a cross-calibration method has been developed by Los Alamos National Laboratory (LANL) allowing the transfer of calibration parameters measured to field inspection systems without the need for physical standards. Argonne National Laboratory-West (ANLW) routinely uses AWCC systems as part of its MPC&A program to verify the fissile mass of HEU items of various enrichments. In addition, ANLW is involved in a MPC&A program initiated by the U.S. Department of Energy (DOE) to provide AWCC system support to Russia. Approximately 25 AWCCs have been delivered to Russia through this program. Before shipment to Russia, the AWCC systems measured reference standards at LANL. The results of these measurements are included in Appendix II and III. Using this data, a study of the cross calibration technique using low enriched uranium was performed by the Moscow State Engineering Physics Institute (MEPhI) with encouraging results. The purpose of the current investigation is to demonstrate the cross calibration technique as an effective method to determine calibration parameters for the assay of HEU, as well as to assess the implementation of the technique at Russian facilities.