Experimental simulation of selected design extension condition scenarios without core meltdown in the CODEX facility

• Published in: Progress in nuclear energy (New series) Vol. 161; p. 104720
• Main Authors: Farkas, Róbert, Hózer, Zoltán, Nagy, Imre, Vér, Nóra, Szabó, Péter, Horváth, Márta, Kostka, Pál, Lajtha, Gábor
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-07-2023
• Subjects: Core degradation; DEC-A scenarios; VVER reactor; VVER reactor; DEC-A scenarios; Core degradation
• ISSN: 0149-1970
• DOI: 10.1016/j.pnucene.2023.104720

Two DEC-A scenarios were simulated with electrically heated 7-rod bundles. The test parameters were selected on the basis of reference scenarios from VVER-440 safety analyses.
The CODEX-SBO experiment simulated a station blackout event in two separated phases. In the first phase the arrival of cold water from hydroaccumulators stopped the further heat-up of the fuel rods. In the second phase the heat-up continued up to 1900 °C and the test was terminated with the injection of emergency coolant from the recovered active injection system.
In the CODEX-NITRO experiment it was supposed that after emptying of hydroaccumulators nitrogen enters the primary coolant and the test was focused on the interaction of hot fuel rods with nitrogen. The presence of nitrogen at high temperature (up to 1700 °C) resulted in the acceleration of chemical reactions, including nitriding of zirconium components.
•Two design extension condition without core melt (DEC-A) scenarios were simulated with electrically heated fuel bundles.•High temperature conditions (up to 1900 °C) were reached.•Intense steam-zirconium, nitrogen-zirconium and zirconium-nitride re-oxidation reactions took place.•DBA safety criteria do not cover all potential fuel failure mechanisms that may take place under DEC-A conditions.