The nuclear accident at Fukushima Daichii Nuclear Power Plant (NPP) demonstrated the shortcomings of active safety systems once external power sources are compromised and the reactor is left vulnerable. This creates a large interest in the use of Passive Safety Systems (PSS) by the industry because they’re able to perform the same safety function as the active one without the need of external power sources, to provide an added level of safety for NPP and to help to prevent similar occurrences from reoccurring in the future. Since 2016, the DER/SESI section at the CEA in France, has been analyzing and modelling various passive safety systems. One of the systems of interest is the one from the Westinghouse © AP1000 design for water reactor. CEA proposed a new configuration for the four Automatic Depressurization System (ADS) lines introduced a Low-Pressure Water Tank (LPWT) that worked with In-Containment Refueling Water Storage Tank (IRWST) provide coolant injection in case of Loss of Coolant Accident (LOCA). In order to understand the behavior of the system, in this document is provided a Computational Fluid Dynamics (CFD) study concerned the pressurization of IRWST and LPWT made by the steam produced from evaporation of the liquid water of the primary system for the depressurization of the system caused by the breach in the primary circuit. In the study are conducted three different tests: two tests with injection in liquid and in gas with different amount of gas in the system and one with different depth of injector in liquid. The tests are conducted using the solver for diphase system NEPTUNE_CFD. It’s deduced that for accelerated the pressurization in LPWT and for decelerate it in IRWST the volume of gas in the system could be increased. In IRWST, the injection of steam pressurizes the system faster for the first seconds and then slowly if the injector is near to the interface, while pressurizes the system slowly for the first second faster then if the injector is an intermediate position in the liquid. A configuration with a lateral injector can lead to a fast pressurization for LPWT.
L'incidente nucleare alla centrale nucleare di Fukushima Daichii (NPP) ha dimostrato l'inefficienza di sistemi di sicurezza attivi una volta che le fonti di energia esterne sono compromesse. Ciò ha portato al nascere di un forte interesse nell'uso di sistemi di sicurezza passivi (PSS) in grado di svolgere la stessa funzione di sicurezza senza la necessità di fonti di alimentazione esterne, per fornire un ulteriore livello di sicurezza per NPP e per aiutare a prevenire che eventi simili si ripetano in futuro. Dal 2016, la sezione DER/SESI del CEA in Francia, analizza e modella vari sistemi di sicurezza passiva. Uno dei sistemi di interesse è quello del progetto Westinghouse © AP1000 per il reattore ad acqua. CEA ha proposto una nuova configurazione per le quattro linee del sistema di depressurizzazione automatica (ADS), ha introdotto un serbatoio di acqua a bassa pressione (LPWT) in grado di funzionare con il serbatoio di contenimento di acqua di rifornimento (IRWST) per garantire l'iniezione del refrigerante in caso di incidente con perdita di refrigerante (LOCA ). Al fine di comprendere il comportamento del sistema, in questo documento viene fornito uno studio di fluidodinamica computazionale (CFD) riguardante la pressurizzazione di IRWST e LPWT effettuata dal vapore prodotto dall'evaporazione dell'acqua liquida del sistema primario per la depressurizzazione dell’impianto causato dalla rottura del circuito primario. Per lo studio sono state condotte diverse prove atte a monitorare quantità fisiche di interesse e proporre miglioramenti nella geometria del test. I test sono condotti utilizzando il solutore per sistemi bifase NEPTUNE_CFD. I risultati hanno mostrato che per accelerare la pressurizzazione in LPWT e per decelerarla in IRWST è necessario aumentare il volume di gas nell'impianto. In IRWST, l'iniezione di vapore pressurizza il sistema più velocemente per i primi secondi e poi lentamente se l'iniettore è vicino all'interfaccia, mentre pressurizza il sistema lentamente per il primo secondo, poi più velocemente se l'iniettore è in una posizione intermedia nel liquido. Una configurazione con iniettore laterale conferisce invece una veloce pressurizzazione per LPWT.
Computational fluid dynamic's study of steam injection in a passive safety system for pressurized water reactor
PICCI, ILARIA
2020/2021
Abstract
The nuclear accident at Fukushima Daichii Nuclear Power Plant (NPP) demonstrated the shortcomings of active safety systems once external power sources are compromised and the reactor is left vulnerable. This creates a large interest in the use of Passive Safety Systems (PSS) by the industry because they’re able to perform the same safety function as the active one without the need of external power sources, to provide an added level of safety for NPP and to help to prevent similar occurrences from reoccurring in the future. Since 2016, the DER/SESI section at the CEA in France, has been analyzing and modelling various passive safety systems. One of the systems of interest is the one from the Westinghouse © AP1000 design for water reactor. CEA proposed a new configuration for the four Automatic Depressurization System (ADS) lines introduced a Low-Pressure Water Tank (LPWT) that worked with In-Containment Refueling Water Storage Tank (IRWST) provide coolant injection in case of Loss of Coolant Accident (LOCA). In order to understand the behavior of the system, in this document is provided a Computational Fluid Dynamics (CFD) study concerned the pressurization of IRWST and LPWT made by the steam produced from evaporation of the liquid water of the primary system for the depressurization of the system caused by the breach in the primary circuit. In the study are conducted three different tests: two tests with injection in liquid and in gas with different amount of gas in the system and one with different depth of injector in liquid. The tests are conducted using the solver for diphase system NEPTUNE_CFD. It’s deduced that for accelerated the pressurization in LPWT and for decelerate it in IRWST the volume of gas in the system could be increased. In IRWST, the injection of steam pressurizes the system faster for the first seconds and then slowly if the injector is near to the interface, while pressurizes the system slowly for the first second faster then if the injector is an intermediate position in the liquid. A configuration with a lateral injector can lead to a fast pressurization for LPWT.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/179877