Hydrodynamics of AHWR Gravity-Driven Water Pool Under Simulated LOCA Conditions

Abstract

The advanced heavy water reactor (AHWR) employs a double containment concept with a large inventory of water within the gravity-driven water pool (GDWP) located at a higher elevation within the primary containment building. GDWP performs several important safety functions in a passive manner, and hence, it is essential to understand the hydrodynamics within this pool during a LOCA. To achieve this objective, several LOCA scenarios involving RIH break sizes ranging from 2 to 50% are postulated, and the AHWR containment system response is obtained. An in-house containment thermal hydraulics code called “CONTRAN” is used for this purpose. The blowdown mass and energy discharge data for each break size, along with the geometrical details of the AHWR containment, form the main input for the analysis. Apart from obtaining the pressure and temperature transients within the containment building, the focus of this work is on simulating the hydrodynamic phenomena of vent clearing and pool swell occurring in the GDWP. The variation of several key parameters such as pressure and temperature within the primary containment volumes V1 and V2, differential pressure, BOP rupture time, vent clearing velocity, effect of pool swell on the V2 air space pressure, GDWP water level, etc., is presented and discussed in detail, and important findings are highlighted. Further, the effect of neglecting the modeling of pool swell phenomenon on the containment transients is also clearly brought out by a comparative study. The numerical studies presented here give insight into AHWR containment transients that would be useful to both the system designer as well as the regulator.