Hypothetical conditions with deep cooling of coolant are analyzed for serial Reactor Installation (RI) with WWER-1000. The beyond design basis accident (BDBA) scenarios are specially chosen, to reveal the effectiveness of internal properties of nuclear fuel and reactor emergency protection (EP) in conditions when criterial parameters are close to the acceptance criteria or violate them. Various phases of the accident were considered: ATWS (anticipated transients without scram), repeated criticality and ‘cold slug’. Plural failures of Control Rods of Control and Protection System (CRs CPS) were modeled at the operation of EP. The analysis was carried out by the coupled code KORSAR/GP [1–3]. At the first investigation stage the individual conservative variant was considered, from which the expediency of use of BEPU method is revealed. Then at the second investigation stage the analysis of the set of variants in BE approach with uncertainty analysis on the set of statistically varied parameters — neutron-physical, thermo-physical, thermo-hydraulic and hydrodynamic was carried out with PANDA+KORSAR/GP [4] program complex. The advantages of Best Estimate Plus Uncertainty (BEPU) method for the safety margins revealing are demonstrated.

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