Starting from the end of 60s the Dipartimento di Ingegneria Meccanica, Nucleare e della Produzione was involved in setting up a system of calculation codes and related nodalization able for performing reliable safety analyses of BWR and PWR reactor.

The actual tool, CIAU (Code with the capability of Internal Assessment of Uncertainty) developed at the Dipartimento di Ingegneria Meccanica, Nucleare e della Produzione enables to make safety analyses of PWR and BWR reactors.
The internal assessment of uncertainty constitutes a capability for thermal-hydraulic system codes allowing the achievement of uncertainty bands associated with any code-calculation result. Currently, the CIAU (Code with - the capability of - Internal Assessment of Uncertainty) is derived from the UMAE (Uncertainty Methodology based on the Accuracy Extrapolation). Therefore, a system code, for example Relap5, is coupled with the uncertainty methodology and constitutes the CIAU.
The idea at the basis of CIAU is the identification and the characterisation of standard plant statuses and the association of uncertainty to each status. One hypercube and one time interval identify the plant status. “Quantity” and “Time” uncertainties are combined for each plant status.
The employ of the CIAU methodology allow to demonstrate the eventual scenario could happen in a nuclear power plant according to the possible values a system variable can assume inside its uncertainty bands.