Effectiveness of the ASVAD valve in a reactor vessel bottom leak scenario

Highlights: • Experimental and analytical evaluation of the effects of nitrogen intrusion in an RPV bottom leak scenario. • The ASVAD safety valve, an innovative passive system to avoid the injection of nitrogen from the accumulators is presented. • Benefits of avoiding the injection of nitrogen thanks to the installation of the ASVAD valve. Decay heat removal can be seriously degraded by the presence of non-condensable gases in the cooling circuits. Nitrogen gas may be pushed into the primary system after a full discharge of the accumulators. This may produce various adverse effects: the interruption of natural circulation, the limitation of the primary to secondary heat transfer during the reflux cooling and prevent the startup of the active injection by stabilization of the pressure above the injection set point. State-of-the-art system codes have proven to be capable to simulate non-condensable gas effects in accident situations. The ASVAD valve, has been designed to avoid the inflow of nitrogen into the primary system by means of passive concepts. This paper addresses the complications derived from the nitrogen and evaluates the ASVAD valve performance through the simulation of a vessel bottom leak experiment at the LSTF facility in Japan.