Shutdown, functional diagram

Detecting transducers at the measuring points are electrical, pneumatic, or hydraulic. The resultant circuits and sequences can be seen from the typical functional diagram in Figure 4-34. An emergency shutdown immediately triggers the following operations ... 

Figure 4-34. Function diagram of the safety systems for emergency and slow shutdowns, and of the speed regulating devices.

Figure 13-3 shows a block diagram of the proposed design for the safety instrumented function of the high line pressure. It consists of two separate and independent shutdown functions in two separate and independent systems (ESDI and ESD2). The components associated with the two systems for this function are ... 

The control rooms provide the control and displays necessary for the operator to carry out actions required during normal and shutdown operations of the plant. In some NPPs, including WWER NPPs, it follows the classical division by subsystems with an "active mimic" diagram of each subsystem shown with controls for pumps and valves in their appropriate functional position on the diagram. This type of organization has led to operational problems, most notably the Three Mile Island Unit 2 accident in the USA, because the operator s attention is focused on a specific item and he tends to disregard the interactions between the subsystems. An action that is taken at one point to solve one problem may create other problems in related subsystems. 

Figure 1-2 shows the simplified schematic diagram of the SMART nuclear steam supply system (NSSS) and exhibits the safety systems and the primary system as well as auxiliary systems. The engineered safety systems designed to function passively on demand consist of a reactor shutdown system, passive residual heat removal system, emergency core cooling system, safeguard vessel and reactor overpressure protection system. 

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