Abstract
AP1000 nuclear power plant adopts several severe accident management strategies aiming at terminating the core melting process and maintaining the containment integrity, thus limiting the risk of significant radioactive releases to the environment. Analyses are carried out to evaluate the effectiveness of these management strategies using integral severe accident computer code MIDAC. Simulations and analyses of severe accidents initiated by 1-in, 2-in and 5-in LOCAs are performed first, then 1-in LOCA is selected to assess the severe accident management strategies. Different assumptions are defined in different cases for a specific management strategy. Results show that ADS can significantly reduce the primary system pressure, thus resulting in the injection of cold water from CMTs and ACCs into the core rapidly. In addition, high-pressure melt ejection is prevented due to low in-vessel pressure and the hydrogen generation in-vessel is significantly decreased. After cavity injection system operates at core exit temperature 1367 K, water from IRWST will flood the cavity up to the hot legs level. Consequently, heat in-vessel is removed by external reactor vessel cooling (ERVC) and the goal of in-vessel melt retention is achieved. As the final heat sink, PCCS can significantly decrease the containment pressure and gas temperature to ensure the containment integrity. Igniters arranged at different locations of the containment will lead to local hydrogen combustion, therefore, the fraction of hydrogen in each compartment is maintained less than 6% and hydrogen deflagration or hydrogen detonation is consequently avoided.
