Impact of the steady state uncertainties on transient codes' RIA predictions

The need of defining new RIA safety criteria has pointed out the importance of evaluating the uncertainties affecting the transient simulation tools. The present work is devoted to analyze how the steady state uncertainties affect the transient codes predictions. For that purpose, a UA methodology based on Monte Carlo analysis supported by deterministic reduction methods (OAT and RSM) has been developed and successfully applied to the CIP0-1 experiment. To do so, the FRAPCON-3.4 (steady state) and the SCANAIR-7.2 (transient) codes have been chosen. After analyzing four transient outputs closely linked to failure criteria, the fuel and clad roughness and the Pu radial profile (burnup model) are found to be the most relevant FRAPCON-3.4 variables. The codes predictions present a suitable precision and accuracy values; however the resulting uncertainty bands still keeps estimates far away from measurements, that is, the steady state uncertainties seem not to be responsible for the deviations of SCANAIR-7.2 predictions from the experimental data available.