The Romanian nuclear regulatory authority CNCAN, supervising the ALFRED reactor licensing path, demands that software used in the plant safety demonstration be qualified for the envisaged application, meaning it can be stated that target quantities are calculated by the code with a known uncertainty in a given application domain.

ENEA, as member of the FALCON Consurtium, and in charge of all activities related to core design, is preparing the relevant tools for their qualification. Among the one exploited for the steady-state thermal-hydraulic analyses of the fuel assemblies, the ANTEO+ subchannel code is here taken as an example for showcasing the features of the undertaken validation approach, a milestone in the software qualification roadmap.
 

Based on the guidelines and best practices in place in the European context, the validation is composed of the following steps:

1. the field of application is clearly stated so to retrieve the target quantities to be calculated by ANTEO+, namely: the coolant temperature field, the clad temperature and the pressure drops through the pin bundle;
2. the main phenomena influencing the target quantities are identified;
3. the influencial parameters affecting the main phenomena are clearly listed;
4. via a comparison with the available validation database (composed of thousands experimental points), the range covered by the influencial parameters is depicted, so substantiating the validation domain;
5. both a separate (i.e., for each main phenomenon independently) and an integral (i.e., for each target quantity) validation are comprehensively performed so to retrieve the uncertainty to be associated to the target quantities for a given confidence level, feeding the successive uncertainty quantification step for completing the qualification path.

This rigorous approach, once fine tuned via a dialogue with CNCAN, will be a stepping stone for ALFRED licensing and will be applied in the future, together with the standard practices of software quality assurance, to all other computational tools envisaged for the forthcoming safety demonstration.