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

moisture separator heater

main stop valve control valve

to high pressure feedwater beater X intercept valve I cross-around pipe | II

stop valve

high pressure feed water heater

low pressure turbine

generator

pressure turbine

condenser

extraction line

gland evaporator

from condensate storage pool

high pressure condensate pump

circulating waterpump

from condensate storage pool

steam from turbine extraction

turbine bypass line

to low pres s u re # 1 feed walerhearer extraction turbine

turbine bypass , , valve

H

to condenser >ow P^urepeater

I turbine driven reactor feedwater pump||

i

r I water pump

vacuum pump

steam

condensate feed water

sea waler

drain

1 drain tank

exhaust

to off gas system

steam Jet ; Ejector . intercept

gland steam condenser

turbine extraction to turbine gland

Motor driven reactor feedwater pump

A

high pressure drain pump

low pressure

drain pump (0 control rod drive condensate storage pool

(SJAE:steam jet air ejection)

Figure 2.12.7 Schematic configuration of turbine system

| boiling-water type ♦large self controllability

♦ large natural circulation capability

| easy operation control | ♦easy power control

♦ water-level instrumenlion capability

primary containment vessel

|rcic

water

water

direct cycle~| ♦simple system configuration ♦increased feed water supply

level , meter

Isafely relief

control rod

(FMCRD-)

| pressure suppression type containment vesseF]

♦ increased cooling-water capability

Figure 2.12.8 abwr safety features

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NSRA, Japan

Chapter 2 Systems of BWR Nuclear Power Plants

unit The reactor safety can be assured even if such an event occurs, since the BWR has the inherent features of controlling the induced reactivity feedback by the negative reactivity due to the void and Doppler effects in the reactor.

  1. Enhanced reactor cooling capability

By dispensing with the external recirculation piping, the ABWR has no large-diametric pipes below the core level, as shown in Figure 2.12.9.

This vertical arrangement ensures the reactor core is constantly covered with water, even when a single system failure in the ECCS is assumed in a LOCA

The ECCS has a sufficient cooling capability over short, as well as long periods after a LOCA by the use of three lines of the high-pressure system with strengthened redundancy (Table 2.12.2 and Figure 2.12.10).

The ECCS cooling capability has been fully verified by the utilities-manufacturers joint study experiments using a full-size fuel bundle (one bundle). It has also been confirmed that the test results can be conservatively reproduced by analytical codes which were developed based on the extensive test results obtained by the joint studies.

  1. Enhanced capability for containing radioactive materials

The ABWR is safely shutdown against any postulated accidents by the full use of its inherent safety features in the design.

Even when an accident should have occurred, the RCCV inner pressure can be reduced by condensing the steam in the suppression pool in the RCCV. The RCCV contains the radioactive materials released in the RCCV in an accident long enough to let them fully decay, and prevents any leaks to the outside. The ABWR RCCV is designed as small by the adoption of the internal pumps, the RPV size reduction, and other improvements. Hie cylindrical RCCV using the structural features and being integrated with the reactor building improves the earthquake resistance due to its low center of gravity.

  1. Overall safety

The ABWR has achieved strengthened safety, by ensuring the core is constantly covered with water in any pipe breaks of the reactor coolant pressure boundary, and by enhancing the redundancy of the high pressure ECCS and the RHR system to deal with for multiple failures.

Figure.2.12.9 Elevation of postulated pipe breaks(Conventional BWR-5 and ABWR)

2- 125

NSRA, Japan

Table 2.12.2 Comparison of safety features

functions

ABWR

conventional BWR

contents

features

reactivity shutdown

Improved CRD (hydraulic and electric) Manual injection of boric acid water

•Multiple drive mechanisms

Hydraulically driven CRD

Manual injection of boric acid water

reactor

depressurization

automatic depressurization system

automatic depressurization system

core cooling

[high pressure ECCS]

RCIC: 1 line

HPCF: 2 lines [low pressure ECCS] LPCF: 3 lines

■ Strengthened high-pressure system [increased to 3 lines]

•Reduced ECCS capacity by eliminating large-diameter pipe breaks

• Continuous core coverage under water during accident

[high pressure ECCS] HPCS: 1 line

[low pressure ECCS] LPCS: 1 line

LPCI: 3 lines

residual heat removal

RHR: 3 systems

• Strengthened redundancy

RHR: 2 systems