Determination of the uncertainty in assembly average burnup

Pressurized water reactors maintain records of the assembly average burnup for each fuel assembly at the plant. The reactor records are currently used by commercial reactor operators and vendors for (a) special nuclear accountability, (b) placement of spent fuel in storage pools, and (c) dry storage cask design and analysis. A burnup credit methodology has been submitted to the US Nuclear Regulatory Commission (NRC) by the US Department of Energy. In order to support this application, utilities are requested to provide burnup uncertainty as part of their reactor records. The collected burnup data are used for the development of a plant correction to the cask vendor supplied burnup credit loading curve. The objective of this work is to identify a feasible methodology for determining the 95/95 uncertainty in the assembly average burnup. Reactor records are based on the core neutronic analysis coupled with measured in-core detector data. The uncertainty of particular burnup records depends mainly on the uncertainty associated with the methods used to develop the records. The methodology adopted for this analysis utilizes current neutronic codes for the determination of the uncertainty in assembly average burnup