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 Ingegneri. a Meccanica, Nuclea re e della Produzione (DIMNP) of the University of Pisa. Other Institutions including the nuclear regulatory body from Brazil, "Comissao Nacional de E nergia Nuclear", contributed to the development of the tool. The CIAU aims at providing the currently available Relap5/Mod3.2 system code with the int egrated capability of performing not only relevant transient calculations b ut also the related estimates of uncertainty bands. The Uncertainty Methodo logy based on Accuracy Extrapolation (UMAE) is used to characterize the unc ertainty in the prediction of system code calculations for light water reac tors and is 'internally' coupled with the above system code. Following an o verview of the CIAU development, the present paper deals with the independe nt qualification of the tool. The qualification test is performed by estima ting the uncertainty bands that should envelope the prediction of the LOBI test A1-93 (small break loss of coolant accident). The current limitation o f the 'error' database, implemented into the CIAU prevented a final demonst ration of the qualification. However, all the steps for the qualification p rocess are demonstrated.