Establishment of an applicable version of the CIAU methodology

The best-estimate calculation results from complex system codes are affected by approximations that are un-predictable without the use of computational tools that account for the various sources of uncertainty. The Code with (the capability of) Internal Assessment of Uncertainty (CIAU) has been proposed by the University of Pisa to realize the integration between a qualified bestestimate thermal-hydraulic system code and a suitable uncertainty methodology and to supply proper uncertainty bands each time a nuclear power plant transient scenario is calculated. In the frame of a cooperation with The Pennsylvania State University, the CIAU code has been recently extended to evaluate the uncertainty of coupled 3-D neutronics/thermal-hydraulics calculations. The result of this effort is CIAU-TN. The derivation of the methodology and the adopted qualification processes (“internal” and “external”) are described in the paper. Uncertainty, Accuracy, Best-estimate, UMAE, CIAU.