Abstract
The proposed Advanced Heavy Water Reactor (AHWR) employs double containment envelope along with many Engineered Safety Features (ESFs) to mitigate the consequences of Loss-of-Coolant Accidents (LOCA) with safety system failure, during which high enthalpy steam and radioactive fission products will be discharged into the containment. In such conditions, the pressurized containment will be the source of activity release to the environment by way of leakage. It is required to study the effect of ESFs on the source term from the AHWR containment. An analysis was performed to evaluate the release rate from the AHWR containment during a postulated accident with the in-house containment code CONTRAN and the aerosol behavior code NAUA5-M in a coupled way. Modules for simulating the engineered safety features were incorporated in the CONTRAN code and the aerosol transport behaviour was evaluated using NAUA5-M separately. The AHWR containment is divided into three nodal volumes interconnected by junctions. The blow down mass, energy discharge data and activity released into the containment from the reactor core, for a postulated LOCA case of 200% RIH break with failure of shutdown systems (1 & 2), are inputs to the CONTRAN code. Thermodynamic parameters like containment gas temperature, partial pressure of steam, air in the subdivided volumes along with the flow rates through junctions obtained from CONTRAN were supplied to NAUA5-M. An analysis was carried out for a number of cases, postulated based on availability/unavailability of ESFs. Pressure, temperature and activity concentration transients were evaluated, for 72 h, in the subdivided volumes along with the activity released out of the containment through leakages and stack discharges for all the cases. This paper highlights the importance of operation of ESF in reducing the activity release to the environment.
Kurzfassung
Der vorgeschlagene fortgeschrittene Schwerwasserreaktor (AHWR) hat ein doppeltes Containment zusammen mit einer Reihe von aktiven Sicherheitsmerkmalen (ESFs) um so die Folgen von Kühlmittelverlustunfällen (LOCA) mit Ausfall des Sicherheitssystems zu begrenzen, bei denen radioaktive Spaltprodukte in das Containment freigesetzt werden. Unter solchen Umständen wird das unter Druck stehende Containment zur Quelle von Freisetzungen von Radioaktivität in die Umgebung. Es ist deshalb erforderlich den Einfluss der ESFs auf den Quellterm für den AHWR zu untersuchen. Es wurde eine Analyse durchgeführt um die Freisetzungsrate aus dem AHWR während eines angenommenen Unfalls zu bestimmen mit Hilfe des Containment Codes CONTRAN und des Codes NAUA5-M zum Aerosolverhalten. Module zur Simulation der ESFs wurden in den CONTRAN Code integriert und das Aerosoltransportverhalten wurde mit NAUA5-M separat bestimmt. Das AHWR Containment ist in drei nodale Volumen geteilt, die durch Anschlussstellen mit einander verbunden sind. Thermodynamische Parameter wie die Temperatur des Gases im Containment, der partielle Dampfdruck, die Luft in den unterteilten Volumen zusammen mit den Strömungsraten durch die Anschlussstellen wurden auf NAUA5-M angewendet. Eine Analyse wurde durchgeführt für eine Reihe von angenommenen Szenarien auf der Grundlage des Vorhandenseins oder Nicht-Vorhandenseins von aktiven Sicherheitsmerkmalen. Druck, Temperatur und Aktivitätskonzentrationstransienten wurden bestimmt für 72 h, in den unterteilten Volumen zusammen mit der aus dem Containment freigesetzten Aktivität für diese Fälle. Diese Arbeit betont die Wichtigkeit der ESF bei der Reduzierung der in die Umgebung freigesetzten Aktivität.
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