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Chapter 3 Systems of PWR Nuclear Power Plants

Cycle steam outlet nozzle

Second stage re-heater heating tube

Relief valve nozzle

Healing steam inlet nozzle

Relief valve nozzle

Cycle steam outlet nozzle

Cycle steam inlet tube

Deck plate

First stage re-heater heating tube

First re-heater

Moisture separator drain outlet tube

Re-heater drain nozzle

I*

Chevron vane

Manifold

Chevron vane

Manhole

[Source] Mitsubishi Heavy Industries Catalog

Figure 3.5.7 Cut-away view of moisture separator reheater (example)

FVVF turbine steam supply nozzle

Cycle steam outlet nozzle

Second

Drain exhausting duct

Drain exhausting duct

4F '

feedwater pumps. Since the feedwater pumps have large capacities and high discharge heads, feedwater booster pumps are provided in the feedwater system on the suction of the feedwater pumps to maintain sufficient feedwater pump suction heads. Normally, three 50%-capacity feedwater pumps are installed in the feedwater system, two of which are used during normal operation and the third one is in a standby condition. Turbine-driven type feedwater pumps are usually used in plants with rated power larger than 800 MWe, while motor-driven pumps are employed in smaller plants. However, in order to shorten the plant startup time, a motor- driven pump is employed as the standby pump, regardless of plant size. Each of the turbine-driven feedwater pumps has its own turbine driver, which utilizes the main steam or steam extracted from the main turbine unit The exhaust steam from these turbine drivers is sent back to the main condenser.

The specifications of each type of feedwater pumps are compared in Table 3.5.3.

  1. Condensate demineralizer

The condensate demineralizer removes ionic impurities contained in the condensate. In recent

PWR plants, the condensate demineralizer is usually installed in the condensate system to prevent the secondary system components, particularly the steam generator shell side components, from corroding. The feedwater quality, including pH, is also monitored and controlled. Pure hydrazine or ammonia are added to control the pH in the secondary side water of steam generators within the range of 8.7 to 9.2.

The ion exchange resins in the condensate demineralizer are regenerated with an appropriate frequency. Corrosive materials, such as chemicals used for the resin regeneration, are prevented from flowing into the feedwater.

  1. Auxiliary feedwater system

An auxiliary feedwater system supplies water to the steam generators to remove the residual heat from the reactor when the main feedwater pumps are unavailable under abnormal plant situations such as a loss of power or a main feedwater piping rupture.

The auxiliary feedwater system consists of an auxiliary feedwater pit and two motor-driven and one turbine-driven auxiliary feedwater pumps.

i) Motor-driven auxiliary feedwater pumps

3-57

NSRA, Japan

Table 3.5.3 Comparison of feedwater pump (1200NIWe class)

Main Feedwater Pump

Auxiliary Feedwater Pump

Turbine Driven

Motor Driven

Turbine Driven

Mo ter Drive

Number

2

1

1

2

Type

Horizontal Double Volute Centrifugal

same as

left

Horizontal

2 Stage Turbine

Horizontal Multi Stage Centrifugal

Capaci ty

—4300n?/h

same as left Back-up & Start­up

—25Onr5/h

~ 1 lOnP/h

Function

Normal

Emergency

(When Main feedwater pumps are not available)