Uncertainty propagation and sensitivity analysis for a better understanding of the flow excursion instability with the system code CATHARE - CEA - Commissariat à l’énergie atomique et aux énergies alternatives Accéder directement au contenu
Communication Dans Un Congrès Année : 2023

Uncertainty propagation and sensitivity analysis for a better understanding of the flow excursion instability with the system code CATHARE

Résumé

The flow excursion (or Ledinegg) instability is a limiting safety issue in research reactors, since it may lead to boiling crisis in some of the core channels. Reliable and precise simulations of this phenomenon are therefore essential. The thermal-hydraulic system code CATHARE is used for safety analysis studies, and was validated against flow excursion experiments proving good performances. In order to obtain a better understanding of the code behavior, an uncertainty propagation and sensitivity analysis was carried out. The study focuses on the simulation of a Whittle-Forgan flow excursion experiment, performed in a uniformly heated vertical narrow rectangular channel at low pressure. The input uncertain parameters associated to the geometry, the initial and boundary conditions and CATHARE closure laws were identified and quantified in terms of pdfs. An uncertainty propagation was then carried out. The obtained 95%-95% tolerance interval of the mass flow-rate predicted at flow excursion is relatively large (relative variations compared to the nominal flow-rate up to 30%) indicating a significant impact of the uncertainties on flow excursion simulations in CATHARE. Using the same set of calculations, a sensitivity analysis is performed to determine the most influential input parameters, computing the Pearson and Spearman sensitivity coefficients. The result shows that the uncertainties on the sub-cooled condensation CATHARE model and on the gap size have the largest impact. These results are compared to the ones obtained with the Sobol methodology, which gives a more reliable and complete sensitivity analysis, but more expensive in terms of number of calculations. Similar and consistent outcomes are obtained for this specific application.
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Dates et versions

cea-04191121 , version 1 (30-08-2023)
cea-04191121 , version 2 (01-09-2023)

Identifiants

  • HAL Id : cea-04191121 , version 2

Citer

Alberto Ghione. Uncertainty propagation and sensitivity analysis for a better understanding of the flow excursion instability with the system code CATHARE. NURETH 20 -20th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, Aug 2023, Washington, United States. ⟨cea-04191121v2⟩
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