Russian Regulatory Approach to Evaluation of Passive Systems Used for Specific BDBA's (SBO, Loss of UHS) During Safety Review of NPP

New designs of Russian VVER NPPs that obtain license for siting or construction initially includes a set of passive systems, which are used for the management of BDBAs (including severe ones) associated with SBO and/or loss of UHS. The following technical solutions to overcome SBO (loss of UHS) scenarios are used in different NPP designs: —passive heat removal system from SG and containment; —hydro accumulator tanks (different groups are used at different stages of the accident). One of the significant issues assessed during safety review of NPP with regard to the passive systems is the requirement that innovative technical means can be used in plant design on the basis of sufficient substantiation by necessary calculations, experimental studies and operational experience. The purpose of this paper is to describe: —different design solutions of passive safety systems used in modern VVER NPP design; —Russian regulatory requirements used for evaluation of this systems; —key safety review findings regarding passive safety systems. This paper describes passive systems and approaches to their assessment, that mostly operate in BDBA with SBO and/or loss of UHS, when active systems are failed (as an example, the systems envisaged in Novovoronezh NPP-2 and Leningrad NPP-2). Passive systems used in case of a severe accident (for example core catcher, containment hydrogen removal system) are out of the scope of this paper. (author)