SYMPOSIA PAPER Published: 01 January 2001

Improved Covariance Analysis and Spectrum Adjustment for VVER-1000 Pressure Vessel Fluences


The assessment of the uncertainties of neutron transport calculation results caused by uncertainties of the input data is important for the direct use of the calculated fluences and even indispensable for the further improvement of the data by spectrum adjustment on the basis of experimental results. A former work of two of the authors has approached this topic first for a VVER-1000 using a one-dimensional reactor model and applying spectrum adjustment in a single spectrum approximation. In the present work 2D/lD-SN-synthesis calculations have been used to determine the neutron group spectrum covariances including cross-correlations between interesting positions. As possible sources of uncertainties neutron data and reactor model parameters were considered, whereas the uncertainties caused by the calculational method were considered negligible in view of the now available precision of Monte Carlo simulations. The input data uncertainties have been updated including newer information.

The calculated absolute group fluence spectra have been adjusted to measured exvessel cavity activation rates with the help of the COSA3 generalized least squares multi spectrum adjustment code. Adjusted fluences for different detector positions have been compared with corresponding fluences obtained with single spectrum adjustments. The results are discussed and conclusions have been drawn. Results obtained with Russian LUND- and ENDF/B-VI-based cross section and fission spectrum covariance data have been compared.

Author Information

Boehmer, B
Forschungszentrum Rossendorf e.V., Dresden, Germany
Borodkin, GI
Scientific and Engineering Centre for Nuclear and Radiation Safety of Russian GOSATOMNADZOR, Moscow, Russia
Manturov, GN
SSC RF Institute of Physics and Power Engineering, Obninsk, Kaluga Region, Russia
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Developed by Committee: E10
Pages: 508–515
DOI: 10.1520/STP13636S
ISBN-EB: 978-0-8031-5450-6
ISBN-13: 978-0-8031-2884-2