Neutron Flux Uncertainty and Covariances for Spectrum Adjustment and Estimations of Pressure Vessel Fluences

Results of estimations of covariance matrices of neutron spectra in VVER-1000 reactor pressure vessel and cavity positions are presented. Two-dimensional calculations with the discrete ordinates transport code DORT in r-theta and r-z-geometries are used to determine the neutron group spectrum covariances including cross-correlations between interesting positions. The new Russian ABBN-93 data set and the CONSYST code are used to supply the transport calculations with neutron group data. All possible sources of uncertainties, as neutron cross sections, fission sources, geometrical dimensions and material densities, were considered, whereas, the uncertainty of the calculation method was assumed to be negligible in view of the available precision of Monte Carlo simulation.