Benchmark analysis of unintended simultaneous opening of three main steam relief valves at Ignalina nuclear power plant

摘要

The benchmark analysis of unintended simultaneous opening of three main steam relief valves, which occurred at Ignalina nuclear power plant unit 1 on November 26 in 1986, is performed. Such an event is a beyond design basis event for the RBMK-1500 (Large Channel Type Water-cooled Graphite-moderated Reactor). The analysis performed is employing the code CONTAIN, version C11AF. The CONTAIN code is used for the prediction of thermohydraulic parameters in the accident localization system. The water backflow from the lower condensing pools to the bottom steam reception chamber and further water distribution to neighboring cells is well predicted. Nevertheless, the lack of the measured data does not allow to perform a more detailed analysis of the event. In this paper the accident localization system of Ignalina NPP, event description, results of the analysis, lessons learnt and open questions of the analysis are presented.