Some remarks about engineering factor determination
20th Symposium of AER on VVER Reactor Physics and Reactor Safety (2010, Hanasaari, Espoo, Finland)
Engineering factors
Abstract
The problem of the power distribution uncertainties is in general a multidimensional
problem of random vector and problem of multidimensional Probability Density Function
(PDF). The standard methodology of derivation VVER engineering factors is based on
representation of analyzed power peaking in the linear form of random factors and on
presumption about their normal PDF.
In this paper is presented the derivation of locally defined engineering factors and for
mechanical factors has been performed their reformulation. Final formulation of engineering
factors as a statistics of relative deviations involves new parameter ? mean.
Engineering factors definition from so called endpoints of uncertainty tolerance
interval is recommended. Approach (95%/95%) for normal PDF is discussed in detail, the
relation to present standard uncertainty methodology of power distribution is found and
problem of optimality in tolerance factor finding including limitation of sample size is
discussed.
On the bases of statistically based uncertainty kinf analysis for linear model has been
shown that multivariate outputs vector of power peaking has nearly normal PDF
independently on the PDF character of input multivariate vector from under its small
dimension (lower than number of FAs in 1/6 core symmetry).
Finally the development of the methodological part of the engineering factors for
VVER-1000 design macrocode MOBY-DICK is described and their calculation direct on the
bases of SPD experimental data of Temelin NPP and Volgodonsk NPP has been performed
with inclusion the variability of detector (SPD).