Implementation and Development of CIAU Methodology to Cathare2 Code

The purpose of the paper is to present a tool developed for addressing the uncertainty evaluation issues, with reference to the error that the TH-SYS codes execute when predicting the operational and/or the accident transients during the deterministic safety analyses of the NPP scenarios. The availability of tools, that are able to predict how a postulated accident will evolve, allows the optimization of the parameters relevant for the NPP behavior (i.e. the fuel linear power that is connected with the maximum cladding temperature in case of a LOCA). At present, this is one of the main research objectives in the filed of the nuclear safety. Several TH-SYS codes were developed and continuously assessed with the aim of correctly simulating and predicting NPP (BWR and PWR) relevant transients. A large effort was dedicated by the scientific community to evaluate/quantify the uncertainty connected with the application of such codes in predicting the behavior of a NPP. University of Pisa contributed and developed owner methodologies: the UMAE (Uncertainty Methodology based on the Accuracy Extrapolation) and after the CIAU (Code with – the capability of Internal Assessment of Uncertainty). This paper describes the database of accuracies and uncertainties specifically developed to increase the CIAU procedure capabilities to CATHARE2 code and to allow the application of such method to the accident analyses performed with the French code. Moreover, relevance is given to the qualification issue because of the connection that it has with the safety analysis.