Independent qualification of the CIAU tool based on the uncertainty estimate in the prediction of the LOBI test a1-93

The Code with - the capability of - Internal Assessment of Uncertainty (CIA U) is a tool proposed by the Dipartimento di Ingegneria Meccanica, Nucleare e delta Produzione (DIMNP) of the University of Pisa. Other Institutions including the nuclear regulatory body from Brazil, Comissao Nacional de Energia Nuclear, contributed to the development of the tool. The CIAU aims at providing the currently available Relap5/Mod3.2 system code with the integrated capability of performing not only relevant transient calculations but also the related estimates of uncertainty bands. The Uncertainty Methodology based on Accuracy Extrapolation (UMAE) is used to characterize the uncertainty in the prediction of system code calculations for light water reactors and is internally coupled with the above system code. Following an overview of the CIAU development, the present paper deals with the independent qualification of the tool. The qualification test is performed by estimating the uncertainty bands that should envelope the prediction of the LOBI test A1-93 (small break loss of coolant accident). The current limitation of the error' database, implemented into the CIAU prevented a final demonstration of the qualification. However, all the steps for the qualification process are demonstrated.