Pré-Publication, Document De Travail (Preprint/Prepublication) Année : 2025

Stability threshold for stratification-induced flowrate oscillations in PLANDTL-2 sodium natural circulation experiment

Résumé

Thermal stratification in the hot and cold pools of sodium-cooled reactors during loss of flow accidental transients competes with natural circulation and might affect the reactor core cooling. One of the goals of the PLANDTL-2 facility is to study this type of issues, in an integral configuration, representative of a reactor case. In this paper, experimental results on sodium natural circulation in PLANDTL-2 are reported. Eight transient scenarios are studied. The investigated parameters are the initial state of the primary circuit, the shutdown inertia of the secondary circuit, and the operating mode of the Decay Heat Removal (DHR) system. It appears that in cases where the heat removal via the DHR circuit is the highest, flow reversals can be observed in the primary circuit, in the long-term range, more than 100 min after the transient starts. These thermalhydraulic instabilities are linked to an enhancement of stratification caused by the strong heat removal at the DHR system, leading to a cliff effect, both on thermal stratification and primary flowrate. Counterintuitively, to avoid the apparition of these instabilities, the heat removal via the DHR system should be delayed, after the full establishment of natural circulation. A novel method is introduced to estimate the delay between DHR system activation and increase in stratification. The results show that smaller power ramps favor flow stability. Finally, some guidelines for future investigations are given in order to avoid the presently described instabilities. Prospective tests are also proposed to study more in depth this cliff effect.

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Dates et versions

cea-05084224 , version 1 (26-05-2025)

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  • HAL Id : cea-05084224 , version 1

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S Renaudière de Vaux, Simon Li, Amandine Marrel, Toshiki Ezure, Masaaki Tanaka. Stability threshold for stratification-induced flowrate oscillations in PLANDTL-2 sodium natural circulation experiment. 2025. ⟨cea-05084224⟩
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