Safety analysis of beyond design basis accidents in RBMK-1500 reactors

At present the design basis accidents for RBMK-1500 are rather thoroughly investigated. The performed analyses helped to develop and implement a number of safety modifications. Further plant safety enhancement requires developing emergency procedures that would enable beyond design basis accidents management by preventing core damage or mitigating consequences of severe accidents. This paper presents results of Ignalina NPP Level 1 and Level 2 probabilistic safety assessment and their use for development of beyond design basis accidents list. The most important phenomena for RBMK type reactor severe accident management are described. The paper also presents physical processes that occur in an overheated reactor core and discusses its cooling capabilities. The discussion also includes processes that occur in the reactor and primary circuit surrounding compartments, i.e. confinement. A number of recommendations on accident processes management are presented.