Abstract
The Kudankulam NPP units contain additional and unique for VVER Quick Boron Injection System (QBIS) for beyond-design-basis accident management without scram. During the physical start-up stage at hot zero power of both Kudankulam units, special tests were performed to assess the efficiency of the system. In the course of test three out of four QBIS tanks had been promptly opened and it led to the asymmetrical injection of boric acid into the core. The scenario of the tests may address to the inhomogeneous boron dilution process that is now an essential part of safety analysis of pressurised water reactors. The simulation of the process, including ex-core ion chambers readings, has been accomplished using ATHLET/BIPR-VVER code. Behaviour of some reactor parameters in the course of the test and some results of the simulation are discussing in the paper. Authors believe the process of the asymmetrical injection of boric acid may be useful for verification and validation of coupled neutronic and thermo-hydraulic codes widely used for safety analysis, including analysis of boron dilution accident.
Kurzfassung
Die Kudankulam-Reaktoren besitzen ein zusätzliches und einzigartiges VVER-Quick-Boron-Injection-System (QBIS) zur Boreinspeisung bei der Beherrschung von Beyond Design-Basis Accidents ohne Reaktorschnellabschaltung. Während der Inbetriebnahmephase wurden im Zustand der heißen Nullleistung beider Kudankulam-Reaktoren Tests zur Beurteilung der Effizienz des QBIS durchgeführt. Dabei wurden drei von vier QBIS-Tanks prompt geöffnet, so dass es zu einer asymmetrischen Injektion von Borsäure in den Kern kam. Die Autoren glauben, dass diese Tests mit asymmetrischer Borsäureeinspeisung für die Verifikation und Validierung von gekoppelten Neutronen-Thermohydraulik Programmen und zur Analyse von Bor-Verdünnungsstörfällen nützlich sind. Der Ablauf der Tests wurde mit dem ATHLET/BIPR-VVER-Code nachgerechnet. Dabei wurden auch die Reaktivität und die Ströme in den Außendetektoren nachgerechnet. In diesem Beitrag wird der Vergleich der Test- und Rechenergebnisse für einige Reaktorparameter diskutiert. Die Autoren empfehlen die Untersuchung der asymmetrischen Borverteilung zur Verifikation und Validierung von gekoppelten Neutronenkinetik- und Thermohydraulikprogrammen.
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