CHAPTER 5 - Power Reactor Control Systems

Abstract

This chapter discusses power reactor control systems. A reactor has four main control systems, including a protection system to initiate safety devices, a radiation monitoring system, and a process plant system for secondary items, such as deionizing make-up water. Control of the reactor and its plant, such as turbines and coolant circulators, depends significantly on the reactor type. Light water reactors employ water with its good heat transfer properties and neutron-moderating properties in the reactor core. As the water heats up, it expands or even forms steam bubbles, and to ensure a safe design, it is fundamental to require the core to be undermoderated so that a loss of moderator leads to a fall in reactivity offsetting any potential accident situation. Heavy water, with equally good heat transfer properties and nearly as good neutron-moderating properties as ordinary water, has substantially better neutron absorption ties. Thus, heavy water reactors can be designed with larger spacing between fuel elements that in turn enables pressure tubes to be provided around individual fuel elements rather than the pressure vessel of light water reactors. Pressure tubes can be thinner and, therefore, cheaper than the large diameter pressure vessel for the same duty. Coolant within the tubes can be either heavy or ordinary water.