RELAP5 analysis of station blackout accident in RBMK-1500

Ignalina NPP is equipped with channel-type boiling-water graphite moderated reactor RBMK-1500. Results of the Level 1 probabilistic safety assessment of the Ignalina NPP have shown that in topography of the risk, the transients with failure of long-term core cooling other than LOCA are the main contributors to the core damage frequency. The total loss of off-site power with a failure to start any diesel generator, i.e. station blackout is the event, which could lead to the loss of long-term core cooling. Such accident could lead to severe conditions and should be analyzed in order to estimate the timing of the key events and the possibilities for accident management. This paper presents the results of the analysis of station blackout at Ignalina NPP with RBMK-1500 reactor. Thermalhydraulic state-of-the-art RELAP5 code was used for such analysis. In the developed model not only the elements of reactor cooling system (drum separators, main circulation pumps, pressure and suction headers, group distribution headers, fuel channels and steam lines), but also the reactor cavity, its venting system and condensing pool were modelled. The response of reactor cooling system and processes in the reactor cavity and its venting system in case of few fuel channels rupture due to overheating were demonstrated. (author)