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01 POWER ISLAND / Overview of Light Water.docx
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main steam header

Cl

turbine stop valve

reactor

3 u 5’ a

S

1 turbine control valve

cross around pipe

moislure separaior

SJAE

I to off-gas system

from condensate

storage tank

intermediate stop valve intercept valve

j generator vacuum pump -^> to stack

to sea

low- pressure feed water beater.

circulating waterpump

to control rod drive hydraulic system and condensate storage tank

high pressure turbine

feed water condensate water line steam line = = exhaust line drain line sea water line

SJAE for

r and own

turbine bypass valve' —X|

steam tram turbine

steam from turbine

turbine driven reactor feed water

motor driven reactor feed waler pump

high pressure feed water heater]

Figure 2.5.1 Outline of turbine system (example)

low pressure

turbine

condenser

low pressure

condensate pump

turbine grand steam condenser

drain cooler

Lj-] ! I high pressure SJAE

drain I I | I condensate intermediate

tank | pump cooler

-— J I ►- to condenser

demineralizer. Some plants do not adopt the low pressure drain pump up system.

  1. Main Turbine System and Auxiliary Equipment

  1. Iypes of nuclear plant steam turbines

The tandem-compound type turbine is widely adopted for nuclear plant steam turbines. Conventional BWR plants in Japan mainly use the non-reheat type.

A schematic of a typical turbine is shown in Figure. 2.5.2.

In this turbine type, after driving the high pressure turbine, the steam is sent to the moisture separator. The exhaust steam of the high pressure turbine usually has about 12% wetness (i.e. about 88% dryness). The moisture is removed from the steam by the moisture separator. An example of a Mollier chart for the steam of a nuclear reactor turbine is shown in Figure. 2.5.3.

In the reheat type turbines, inlet steam of the low pressure turbine is superheated by the moisture separator and heater.

Hie thermal efficiency of a BWR turbine plant is 33-35%.

Figure 2.5.2 Outline of typical turbine structure (tandem-compound 6 flow)

NSRA, Japan

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Chapter 2 Systems of BWR Nuclear Power Plants

Figure 2.5.3 Example of Mollier chart for the steam of the nuclear reactor turbine

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NSRA, Japan

  1. Steam turbine

Since the steam generated in the reactor is saturated steam, the volume flow rate of the steam is high. Therefore, large diameter low speed rotators (1,500 or l,800rpm) are needed. Since the heat drop between the main steam conditions and the condenser vacuum is small, the turbine system has a high pressure turbine and a low pressure turbine.

For the high pressure rotor, a solid forged mono­block rotor has been adopted. On the other hand, the low pressure rotor has a larger size and it was at an early stage made by shrink-fitting of a rotor shaft and disks shaved separately. However, a solid forged mono-block rotor has recently been in use. The solid forged mono-block rotor has an advantage that stress corrosion cracking which may occur at shrunk-on disks is prevented.

Materials which have high corrosion resistance are used for the turbine. Moisture is intensively removed inside the turbine, too, by a moisture separation diaphragm or moisture separation blades

with slits.

The last stage blade of the turbine is selected from standard components, which have various combinations of number of flows and blade lengths, with consideration of the power rate and the best thermal efficiency. Generally in the case of a l,500rpm turbine, a 35-inch or a 41-inch blade length is adopted for the 800MWe class plants, and a 41-inch or a 52-inch blade length is adopted for the 1,100-1,3OOMWe class plants. In the case of a l,800rpm turbine, the 38-inch blade is used for the 800MWe class and the 43-inch or the 52-inch blade is used for the 1,100-1,300MWe class plants.

Since the steam generated in the reactor flows directly into the turbine in a BWR system, radiation shield plates cover the high pressure turbine and the main valves to reduce the radiation dose rate. A schematic drawing of a TC6F- 41 type 1,100-1,300MWe steam turbine is shown in Figure 2.5.4.

Figure 2.5.4 Outline of TC6F- 41 type 1,100-1,300MWe steam turbine

NSRA, Japan

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