ICONE23-1745 IMPROVING CONFIDENCE IN CFD RESULTS FOR NUCLEAR SAFETY DEMONSTRATION : EXAMPLE OF HETEROGENEOUS INHERENT BORON DILUTION

Abstract

When using CFD for nuclear safety demonstration purposes, EDF puts industrial applications at the core of an overall methodology including physical analysis, code verification, code validation and uncertainty quantification. This methodology ensures the quality of the results and strengthens the confidence in them. By following this methodology, it must be proved that each step is consistent with the others, and with the final goal of the calculations. The physical analysis, based on a PIRT (Phenomena Identification and Ranking Table) dedicated to the specific CFD scenario, has a key role to achieve this consistency. This paper first focuses on the methodology used to fully understand a specific accidental transient by using a PIRT approach. This approach identifies the different physical phenomena (such as stratification, jets, plumes…) involved in the transient which influence the parameters of concern for the safety analysis. The parameters driving these phenomena are then listed (boundary conditions, modeling parameters...) and their level of influence on the output is quantified, thanks to numerous CFD computation sensitivities. This work enables a hierarchy of the input parameters and phenomena influences to be built. Through the example of a heterogeneous inherent boron dilution accidental transient, this paper will show how useful the quantified PIRT methodology is in increasing confidence in the quality of CFD results, and in the identification of the input parameters leading to the most severe case.