Miscellaneous Mechanical Components
Pressurizers are used for reactor system pressure control. The pressurizer is the
component that allows a water system, such as the reactor coolant system in a
PWR facility, to maintain high temperatures without boiling. The function of
pressurizers is discussed in this chapter.
STATE the four purposes of a pressurizer.
DEFINE the following terms attributable to a dynamic
There are two types of pressurizers: static and dynamic. A static pressurizer is a partially filled
tank with a required amount of gas pressure trapped in the void area. A dynamic pressurizer
is a tank in which its saturated environment is controlled through use of heaters (to control
temperature) and sprays (to control pressure).
This chapter focuses on the dynamic pressurizer. A dynamic pressurizer utilizes a controlled
pressure containment to keep high temperature fluids from boiling, even when the system
undergoes abnormal fluctuations.
Before discussing the purpose, construction, and operation of a pressurizer, some preliminary
information about fluids will prove helpful.
The evaporation process is one in which a liquid is converted into a vapor at temperatures below
the boiling point. All the molecules in the liquid are continuously in motion. The molecules
that move most quickly possess the greatest amount of energy. This energy occasionally escapes
from the surface of the liquid and moves into the atmosphere. When molecules move into the
atmosphere, the molecules are in the gaseous, or vapor, state.
Liquids at a high temperature have more molecules escaping to the vapor state, because the
molecules can escape only at higher speeds. If the liquid is in a closed container, the space
above the liquid becomes saturated with vapor molecules, although some of the molecules return
to the liquid state as they slow down. The return of a vapor to a liquid state is called
condensation. When the amount of molecules that condense is equal to the amount of molecules
that evaporate, there is a dynamic equilibrium between the liquid and the vapor.