July-August 2018 NPJ

24 NuclearPlantJournal.com Nuclear Plant Journal, July-August 2018 of-four division safety actuation logic. This is a digital system that provides all the safety-related control in the plant. The AP1000 plant also has a backup defense-in-depth, hardwired system called the diverse actuation system (DAS). It includes certain functions to allow key safety responses even in the case of a postulated failure of the digital system. When you look at the main fluid systems, there is the passive core cooling system or PXS, which is designed to remove decay heat safely from the reactor core and includes both the automatic passive depressurization and water makeup functions. We also have the passive containment cooling system, which removes heat from containment and ensures the capability to operate the passive core cooling system indefinitely without any water injection into containment. Another key passive system is the main control room habitability system: Our main control room is designed to remain habitable without power by using stored air and DC batteries, even in the case of multiple events leading to an extended, complete loss of power. Then, of course, we have the spent fuel cooling system, which is another fully passive safety system to provide for effective long-term cooling of the spent fuel pool. Those are essentially the main categories of safety systems: the I&C safety systems, the core cooling, spent fuel pool cooling and containment cooling systems and the main control room habitability system. One important aspect to understand is that the AP1000 plant also has two high-quality, high reliability onsite diesel generators. They provide defense in depth, and support normal plant operations, as well as the normal response to most events in case of a loss of AC power, with the passive safety systems providing the plant with the unique capability to manage events even when all AC power sources, onsite and offsite, are lost. 6. Are the AP1000 controls user- friendly to the younger generation? The answer to that is, yes, it is more user-friendly than the current generation of nuclear power plants because the modern control systems allow a level of man-machine interface that was not possible for previous generations of nuclear power plants designed in the 1970s or earlier. One quality that allowed us to improve the man-machine interface is the excellent synergy between the passive systems and the digital control systems. When we were designing the controls, we wanted to develop a system that would be more natural to a generation that has grown up on digital technology, both in a professional and personal environment. The main control room is mostly designed as a soft interface work environment – with displays and soft controls, allowing operators to control the plant primarily through interaction Passively Safe... ( Continued from page 23) (Continued on page 44)