SENSITIVITY ANALYSIS ON THE RANKING OF INPUT UNCERTAINTIES WITH RESPECT TO PEAK CLADDING TEMPERATURE UNCERTAINTY IN A PWR LBLOCA ANALYSIS

U. Rohde, Y. Kozmenkov, Helmholtz-Zentrum Dresden-Rossendorf, Institute of Resource Ecology, Germany

23rd Symposium of AER on VVER Reactor Physics and Reactor Safety (2013, Štrbské Pleso, Slovakia)
Reactor dynamics and safety analysis

Abstract

An uncertainty analysis of a large break loss-of-coolant accident (LBLOCA) for a German PWR
Konvoi was performed using a statistical method, which is based on the Wilks? theory. The
evaluated output parameter is the peak cladding temperature (PCT). The primary goal of this
paper is a ranking of the input uncertainties, according to their contributions to the PCT
uncertainty in the ATHLET simulation of PWR LBLOCA, by performing a sensitivity analysis.
It was shown, that the starting (extended) set of varied parameters can be considerably reduced
without any statistically significant influence on the uncertainty analysis results.
The statistical t-test was used to minimize the number of varied parameters. A set of uncertainty
parameters with significant impact on the uncertainty of the PCT was identified. The main
contribution to the uncertainty of the first cladding temperature maximum during the blowdown
phase of the accident is produced by the core parameters that affect the fuel?s stored energy at
the beginning of the accident. However, the major contributors to the uncertainty of the second
PCT maximum are the uncertainties in the code models, and first of all the uncertainties in the
heat transfer coefficients for dispersed and pure steam flows.
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