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Chapter 3 Systems of PWR Nuclear Power Plants

Primary makeup wa ter

Secondary makeup water

Figure 3.11.1 Water supply and treatment system diagram

the auxiliary steam system.

The auxiliary steam supply lines to these two groups and drain return lines from them can be separated from each other to give flexibility to the auxiliary steam system operation.

  1. Compressed Air Systems

There are two compressed air systems in a plant, an instrument air system and a station service air system.

(1) Instrument air system

The instrument air system supplies clean and dry compressed air to air-operated valves, controllers, instruments, etc. A schematic diagram of an example instrument air system is shown in Figure 3.11.3.

Each of two full-capacity instrument air units consists of a compressor, a cooler, a reservoir and a drier; each unit supplies air to one of two headers. If necessary, the two units and headers can be separated from each other. Vertical reciprocating air compressors of a non-lubricated type are used to supply oil-free clean compressed air to instruments. Each of the two compressors is able to satisfy the plant needs during normal plant operation and

after accidents. As a backup for the instrument air system, compressed air can also be supplied from the station service air system through a connection line, which is located upstream from the air drier and is normally closed by valves.

A small part of the instrument air flow is supplied to the control valves inside the containment vessel, and discharged to the containment vessel atmosphere after being used to operate the valves. The discharged air increases the containment vessel pressure and consequently the containment vessel air purge frequency. Therefore, in some PWR plants, dedicated compressed air units which take suction from the inside of the containment vessel are installed for supplying air to air-operated valves in the containment vessel.

(2) Station service air system

The station service air system is located in the reactor auxiliary building and it supplies service air for components inside the containment vessel, the reactor building, the turbine building and other buildings. The station service air compressors are a non-lubricated type. This system serve as a backup system for the instrument air system.

3- 121

NSRA, Japan

7thX extraction

Main stea

High 4 Low pressure turbine gland

Auxiliary steam drain cooler

Others

1

Steam convertor feedwater tank

Aux, steam drain tank

Aux. steam drain trap

Radiation control room air feeding unit

Steam convertor feedwater

pump

Boric acid makeup tank

Containment air feeding unit

Auxiliary building air feeding unit

Steam convertor

to Low pressure feedwater heater

Boron recycle device

Liquid waste evaporator

Volume reduction solidification facility

Others

Deaerator

Auxiliary steam condensate monitor

Aux. steam drain tank pump

Makeup water

Auxi1i ary boiler

Auxi1iary boi1 er