Management of the SBLOCA sequences with HPIS failure in VVER-1000/V320 reactors; comparison with Westinghouse PWR strategies

In small break LOCA sequences with failure of the high-pressure safety injection system, the reactor coolant system pressure can stagnate at a high value making the medium and low-pressure safety injection systems unable to inject water into the core before its peak cladding temperature exceeds the safety limit. In this work, a review and comparison of different strategies presented in the Emergency Operating Procedures for managing these sequences in VVER-1000/V320 and Westinghouse PWR has been carried out. For this purpose, the Integrated Safety Assessment methodology, developed by the Spanish Nuclear Safety Council has been applied. The results show that the strategy related to the controlled SGs depressurization at a primary side cooling rate of 60 K/h in VVER-1000/V320 reactors and 55 K/h in Westinghouse PWR provides a wide safety margin. In cases where the Inadequate Core Cooling temperature is reached, the fast SGs depressurization strategy is also effective to avoid the core damage.