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Proceedings of the conference

Kozlachkov A.N. Laptev S.G.

Combination of deterministic and probabilistic approaches for assessment of realistic success criteria of VVER RP emergency protection system

The paper is devoted to assessment of realistic success criteria of mechanical part of reactor emergency protection system. The data obtained are necessary for making the analysis of its reliability.

By the realistic success criteria of CPS mechanical part when implementing the emergency protection function we mean the minimum number of CPS CR having actuated (considering their position) at which the safety criteria are met. Respectively, in this case the failure criterion of CPS mechanical part will be the minimum number of failed CPS CR resulting in violation of acceptance criteria.

The paper deals with the calculational analysis of the accident with the initiating event "steamline rupture". The condition is determining for a group of conditions with an increase in heat removal from the primary circuit from the viewpoint of core cooling, the possibility of reaching recriticality and meeting the acceptance safety criteria.

We used the results given in [1] where the accident under study was analyzed from the viewpoint of risk – the various accident sequences considering their conventional probability and consequences were considered. We determined a number of the accident sequences with a various combination of the most meaningful failures of systems and interlockings for the given accident.

Thermal-hydraulic calculations with the various number of failures of the most meaningful CPS CRs have been performed. An assessment of realistic success criteria of emergency protection for the various emergency sequences is presented.

We considered both a danger of recriticality occurrence and a danger of local power increase (and, as a consequence, violations of the acceptance safety criteria characterizing the integrity of physical barriers).

An assessment of conventional probability of violation of acceptance criteria with the various number of CPS CR failures was performed as well. This assessment is based on the multi-variant calculations performed with simulation of a random arrangement of CPS CR failures.

The given approaches are based on the combined combination of the deterministic and probabilistic approaches.

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