ASSESSMENT OF THE UNCERTAINTIES OF MULTICELL CALCULATIONS BY THE OECD NEA UAM PWR PIN CELL BURNUP BENCHMARK
24th Symposium of AER on VVER Reactor Physics and Reactor Safety (2014, Sochi, Russia)
Advances in spectral and core calculation methods
Abstract
ASSESSMENT OF THE UNCERTAINTIES OF MULTICELL CALCULATIONS BY THE OECD NEA UAM PWR PIN CELL BURNUP BENCHMARK
István Panka, András Keresztúri
Centre for Energy Research, Hungarian Academy of Sciences Reactor Analysis Department
H-1525 Budapest 114, P.O. Box 49, Hungary istvan.panka@energia.mta.hu
ABSTRACT
It is well known that best-estimate analyses have a lot of benefits in the field of nuclear energy, although the corresponding calculations have to be supplemented by the assessment of the uncertainties. For this purpose an OECD NEA benchmark was set up. The objective of the OECD NEA Uncertainty Analysis in Best-Estimate Modeling (UAM) LWR benchmark is to determine the uncertainties of the coupled reactor physics/thermal hydraulics LWR calculations at all stages.
At the beginning, the uncertainties of the neutronic calculations at zero burnup were investigated in the frame of the UAM benchmark. That time was devoted to the elaboration of the appropriate methods quantifying the uncertainties of calculations. Later on the benchmark has been extended for the burned out case, as well. In this paper the focus is on the determination of the burnup dependent uncertainties of MULTICELL spectral calculations for a PWR pin cell defined in the benchmark.
The uncertainties of the MULTICELL calculations are discussed using Monte-Carlo type statistical analyses taking into account the energy dependent covariance matrices of the cross sections. Additionally, the impact of the uncertainties of the fission yields is also considered. The target quantities are the burnup dependent uncertainties of the infinite multiplication factor, the two-group cross sections and reaction rates and the number densities of some isotopes up to the burnup of 60 MWd/kgU. In the paper the burnup dependent tendencies of the corresponding uncertainties and their reasons are analyzed.