Uncertainty and Sensitivity Analyses of Emergency Cooling Systems in BNPP During the Small Break-LOCA in the Primary Circuit

In this paper, uncertainty and sensitivity of emergency cooling systems of the primary and secondary circuits are investigated in the VVER1000/V446 nuclear reactor during the small break
(SB)-LOCA. The emergency systems include accumulators, high pressure and low pressure injection systems and emergency feed-water system. The analysis is performed using the RELAP5/Mod 3.2 Code for nodalization and simulation of the nuclear power plant. The GRS method is used for the calculation of the minimum number of the code to achieve 95% of the tolerance limit and confidence level. For a conservative analysis of the accident, the loss of power to the NPP and the failure of the two diesel generators are considered when SB-LOCA occurs. These limitations cause the malfunctioning of the two channels of the emergency cooling systems. Also, by considering the single failure criteria, one accumulator is failed throughout the accident process. The results show that the accumulators deuelop the most sensitivity of the maximum clad temperature. Also, the HPIS pumps have relatively little influence on the SB-LOCA. When all emergency cooling setpoints are altered, a new set is achieved, which causes to lower the maximum clad temperature, in comparison with a default setpoint of the emergency cooling systems.