Conceptual Design And Transient Analysis Of PRHRS For Secondary Circuit Of AP1000 Based On RELAP5

The Nuclear Power Plants require comprehensive safety systems to ensure the safety of public and environment in case of an accident. Following the shut-down of the reactor, there is some residual heat of the reactor core, arising from the delayed neutron precursors. If not removed, this heat could result in severe core damage and chemical explosions in the reactor core. The Passive Residual Heat Removal System (PRHRS) for secondary circuit could increase the safety and reliability of AP1000 by removing residual heat from the core of the reactor after an accident such as a station blackout. Therefore, as an important passive safety feature, the Passive Residual Heat Removal System (PRHRS) in secondary circuit should be designed for generation Ⅲ AP1000 Nuclear Power Plants. It is also capable of completely or partially replacing the traditional cooling system of AP1000 in said scenario.The main components of a PRHRS are the Steam Generator, Heat Exchangers, a Cooling Water Tank and the associated pipes and valves. This paper developed a model of PRHRS for AP1000 power plant based on RELAP5 code. The effects of the PRHRS on both secondary circuit and primary circuit were studied. The station blackout incident was considered as the main scenario of accident. Four different types of logics were simulated, related to the trip time of Feedwater and coolant pumps, to study the effects and heat removal capability of the PRHRS. The simulation results proved the main function of PRHRS i.e. the PRHRS was capable of removing the decay heat from the core of the reactor successfully. The results also established a single-phase natural circulation in the primary loop and a two-phase natural circulation in the PRHRS loop. The Pressure and Temperature of the PRHRS loop were shown to be increasing at the starting of the PRHRS operation. This was due to the quick opening of the PRHRS isolation valves. After fixing this issue, the results showed the decreasing pressure levels in both the pressurizer and the PRHRS loop, thus verifying the operation of PRHRS.