Integrated control system responses during load rejection transient for Lungmen ABWR Plant

The RETRAN model of Lungmen ABWR Plant was used to evaluate the load rejection with bypass transient of the start-up test program. There are three major control systems implemented in Lungmen RETRAN Model, including recirculation flow control, feedwater control, steam bypass and pressure control system. The responses of the control systems are important to help the reactor operate smoothly in the test, and credited to mitigate the transient impact. A brief description about the Lungmen RETRAN Model and the design feature of control systems is included in this article. The predicted analysis of load rejection test was conducted by using RETRAN-3D code to verify the dynamic responses of the reactor and control systems to protective trips in the generator, and also to demonstrate the capability of the plant to withstand against a generator load rejection without reactor scram. The analysis results show that the reactor has not been scrammed due to the proper control system responses, and sustained stable operation under the condition of the minimum station house load. The sensitivity studies show that there will be no significant pressurization in load rejection transient as long as activating bypass capacity functions in time. While, the sensitivity study cases of other settings in the mitigation facilities have no outstanding impact on the system response.

► The Lungmen RETRAN model was used to evaluate the load rejection with bypass start-up test.
► The purpose is to verify the capability of the plant withstand a load rejection without scram.
► The responses of the control systems are important to help mitigate the transient impact.
► The analysis show that the reactor is not scrammed due to the proper responses of the control systems.
► As long as bypass capacity functions in time, there is no significant pressurization in transient.