POSSIBILITIES FOR ASSESSMENT AND OPTIMIZATION OF NPP PHYSICAL PROTECTION SYSTEMS IN UKRAINE ON THE BASIS OF NUCLEAR SAFETY ANALYSIS

The design requirements for physical protection systems currently adopted at Ukrainian Nuclear Power Plants (NPP) were established in the middle of the nineties on the basis of deterministic analyses and expert evaluations of reactor facility vulnerabilities. At the present time the in-depth assessment of the nuclear safety of Ukrainian NPPs with the Russian version of pressurized water reactor (VVR) has been completed. The VVR-1000/B320 reactors were assessed using Probabilistic Safety Assessment (PSA). PSA has established and provided a qualitative assessment of the significance of the equipment for maintaining the integrity of a reactor core and preventing an abnormal release of radioactive material. The availability of qualitative assessments of the importance of equipment for nuclear safety allows one to assess the existing physical protection system (PPS) using (1) comparative analysis: to determine whether all equipment and zones that may be affected, as established by the nuclear safety assessment, are actually included into the vital zones protected by the existing PPS; (2) specific analysis of dominant contributors: since nuclear safety analyses provide qualitative assessment of the equipment’s importance for safety, it is easy to select a limited group of essential equipment that makes the major contribution to safety, and (3) specific equipment analysis included in dominant emergency sets: part of the components might not be included in the essential equipment group, but it might be included in the dominant emergency sets. If some equipment is found not to be covered by the PPS, it is possible, using qualitative assessment of the importance of this equipment for safety, to assess the required degree of enhancement of physical protection. Such analysis will permit an assessment of the sufficiency of the existing PPS, to define the “tight” system areas and, therefore, to develop a justified optimization of a PPS with the objective of implementing priority upgrades to enhance safety, and using limited resources in the most effective way. The application of risk-informed approaches to assessment, and subsequent optimization of the PPS will permit establishing basis for the implementation of the so-called graded-protection concept