COVARIANCE WORKSHOP April 22-23, 1999 Brookhaven National Laboratory

The NCSP is a comprehensive program established to help assure continued safe, efficient operations with fissile materials in the US. The major Tasks included in the NCSP are Critical Experiments, Benchmark Evaluations, Analytical Methods, Applicable Ranges of Bounding Curves and Data (AROBCAD), Information Preservation and Dissemination, Training and Qualification, and Nuclear Data. The Nuclear Data Task provides newly measured differential data and newly evaluated nuclear data for use in analyses of fissile material systems. One feature of the effort to improve the nuclear data for criticality applications is the inclusion of covariance data and sensitivity parameters that then allows the analyst to assess the uncertainty in calculated performance parameters due to uncertainties in the nuclear data. A characteristic of currently available nuclear data libraries is a lack of such covariance information. It was felt that gathering noted experts in the field would help assess the current status and offer guidance to the NCSP Nuclear Data Task on how to proceed in developing covariance information useful for criticality safety analysts. Since many of the experts in the field are in the international community, we scheduled the Workshop to be held just prior to a meeting of the OECD Nuclear Energy Agency Working Party on Evaluation Cooperation (WPEC). Hence, the Nuclear Data Covariance Workshop, held April 22-23, 1999 at Brookhaven National Laboratory, was able to attract 28 experts from 16 institutes in 8 countries to help assess the status of nuclear data covariance information. The presentations and discussions focused on practical technical matters associated with the generation of covariance matrices, formats for covariance matrices (particularly for evaluated files), mathematical issues related to the manipulation of covariances, and applications for covariance matrices. This publication provides a means of documenting the formal and informal presentations. The chairs of the four sessions also provided a summary of the discussions and exchange of ideas that took place. The meeting provided a rekindling of interest in this important area of work and representatives of the various international cross-section libraries were supportive of the efforts being made in the NCSP to provide evaluated data files with comprehensive covariance information. It is recommended that Workshops of this kind be planned for the future and the additional activities related to nuclear data covariances be included in the program of the NEA/NCS WPEC