PRESSURIZERSDOE-HDBK-1018/2-93Miscellaneous Mechanical ComponentsPRESSURIZERSPressurizers are used for reactor system pressure control. The pressurizer is thecomponent that allows a water system, such as the reactor coolant system in aPWR facility, to maintain high temperatures without boiling. The function ofpressurizers is discussed in this chapter. EO 1.12STATE the four purposes of a pressurizer.EO 1.13DEFINE the following terms attributable to a dynamicpressurizer system:a.Spray nozzlec.Outsurgeb.Insurged.Surge volumeIntroductionThere are two types of pressurizers: static and dynamic. A static pressurizer is a partially filledtank with a required amount of gas pressure trapped in the void area. A dynamic pressurizeris a tank in which its saturated environment is controlled through use of heaters (to controltemperature) and sprays (to control pressure).This chapter focuses on the dynamic pressurizer. A dynamic pressurizer utilizes a controlledpressure containment to keep high temperature fluids from boiling, even when the systemundergoes abnormal fluctuations.Before discussing the purpose, construction, and operation of a pressurizer, some preliminaryinformation about fluids will prove helpful.The evaporation process is one in which a liquid is converted into a vapor at temperatures belowthe boiling point. All the molecules in the liquid are continuously in motion. The moleculesthat move most quickly possess the greatest amount of energy. This energy occasionally escapesfrom the surface of the liquid and moves into the atmosphere. When molecules move into theatmosphere, the molecules are in the gaseous, or vapor, state.Liquids at a high temperature have more molecules escaping to the vapor state, because themolecules can escape only at higher speeds. If the liquid is in a closed container, the spaceabove the liquid becomes saturated with vapor molecules, although some of the molecules returnto the liquid state as they slow down. The return of a vapor to a liquid state is calledcondensation. When the amount of molecules that condense is equal to the amount of moleculesthat evaporate, there is a dynamic equilibrium between the liquid and the vapor.ME-05Rev. 0Page 30
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