Nuclear Power Plant Instrumentation and Control

Installed throughout a nuclear power plant, instrumentation and control (I&C) is an essential element in the normal, abnormal and emergency operation of nuclear power plants (International Atomic Energy Agency [IAEA], n.d.). Through their equipment, modules, sensors, and transmitters, I&C systems measure thousands of variables and processes the data to activate pumps, valves, motors, and other electromechanical equipment that control the plant. The I&C system senses basic physical parameters, monitors performance, integrates information, and makes automatic adjustments to plant operations to keep process variables within the plant design limits. By reacting appropriately to failures and abnormal events, I&C ensures the plant’s safety and efficient production of power (U.S. Nuclear Regulatory Commission [U.S. NRC], 2011). All of these roles can be reduced to three basic functions (IAEA, 1999). First, as the plant’s nervous system, I&C provides plant operators with accurate and relevant information so they can make the appropriate actions during normal as well as abnormal operation. Second, I&C provides plant operators with the capacity to exercise automatic control over the plant and its associated systems so they can take whatever actions are needed to maintain efficient and safe operation. Finally, I&C serves the critical function of protecting the plant from faults in the system or errors made by the operator as well as abnormal or extreme external events that threaten the plant’s operation. More specifically, I&C should enable the plant to operate safely for an extended period without operator intervention following an accident (IAEA, 1999). Nuclear plant I&C systems must be accurate to properly sense and communicate the process variables and reasonably fast to provide timely display, adjustment, and protection against upsets in both the main plant and its ancillary systems. For example, temperature sensors such as resistance temperature detectors (RTDs), which are key elements in the safety system instrumentation of nuclear power plants, may be expected to provide 0.1 percent accuracy and respond to a step change in temperature in less than 4 seconds. Nuclear plant I&C is more complex and varied than the control instrumentation in other industrial applications because of the special nature of nuclear power. A nuclear plant’s production must remain continuous because of its high capital costs, direct access to and control over the nuclear plant’s reactor is impossible, and the potential risks of nuclear energy production require greater redundancy and reliability in plants’ control infrastructure (IAEA, 1999). Although I&C is a relatively small component in a typical plant’s maintenance and