Abstract
A hypothetical main steam line break transient in a VVER-1000 core with multiple equipment faults was simulated with the coupled COBAYA4/CTF and COBAYA3/FLICA4 nodal core models. The objective was to test recent versions of the models developed in the EU NURISP and NURESAFE projects and to analyze the thermal-hydraulic conditions in the hot assembly at the pin-cell level. The accident scenario was specified as an aggravated variant of the OECD/NEA VVER-1000 MSLB benchmark with eight peripheral control rod clusters stuck out of the core after scram, all of them in the overcooled sector. Coarse-mesh models and a realistic cross-section library were used to compute the full-core behavior with pre-calculated MSLB boundary conditions and to identify the hot assembly. Then a sub-channel thermal-hydraulic analysis of the hot assembly was performed with the CTF code, using time-dependent assembly boundary conditions from the coarse-mesh vessel and core simulation. The results show that the predicted values of the safety parameters do not exceed the safety limits.
Kurzfassung
Mit den gekoppelten Knotenmodellen COBAYA4/CTF und COBAYA3/FLICA4 wurde ein hypothetischer Hauptdampfleitungsbruch in einem WWER-1000-Kern mit mehreren Gerätefehlern simuliert. Ziel war es, aktuelle Versionen der in den EU-Projekten NURISP und NURESAFE entwickelten Modelle zu testen und die thermohydraulischen Bedingungen im heißen Brennelement auf der Eben der Brennstoffzellen zu analysieren. Das Unfallszenario wurde als verschärfte Variante des OECD/NEA WWER-1000-MSLB-Benchmarks spezifiziert, wobei acht periphere Steuerstabcluster nach dem Scram aus dem Kern herausragen, alle im unterkühlten Bereich. Grobmaschige Modelle und eine realistische Querschnittsbibliothek wurden verwendet, um das Vollkernverhalten mit vorberechneten MSLB-Randbedingungen zu berechnen und die heiße Baugruppe zu identifizieren. Anschließend wurde mit dem CTF-Code eine thermohydraulische Unterkanalanalyse der heißen Baugruppe unter Verwendung zeitabhängiger Baugruppen-Randbedingungen aus der Grobmaschen- und Kernsimulation durchgeführt. Die Ergebnisse zeigen, dass die berechneten Werte der Sicherheitsparameter die Sicherheitsgrenzen nicht überschreiten.
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