Core/concrete interaction scenarios for VVER-1000-type reactors

In continuation of the Austrian research program to investigate the safety behavior of VVER-type reactors, several accident scenarios for VVER-1000 reactors were analyzed. These reactors are equipped with four loops without isolation valves, horizontal steam generators, and hexagonal fuel assemblies. Safety features include a containment structure with spray-type steam suppression. The influence of this spray system on source-term behavior has already been investigated. One of the results of this work is the indication of a strong influence of the core/concrete interaction on source-term behavior. To analyze the core/concrete interaction and particularly the resulting melt layer temperatures, several accident sequences were investigated. Using the source term code package (STCP), the influence of the different water volumes available in the VVER-1000 reactor has been parametrically examined. As in most of our safety studies, a TMBL accident sequence without spray was selected as reference case. The different core interaction scenarios were obtained by variation of availability and amount of following water volumes: 1. primary coolant, which is collected in the sump; 2. accumulator water, which is collected in the cavity; 3. spray water; and 4. concrete water released during the core/concrete interaction. This paper describes the results of the different scenarios and offersmore » recommendations for further work improving accident management strategies.« less