RHR heal exchanger

on site ■ power system p

emergency diesel generator

feed waterline

F

| reactor building cooling water system (RCW)

reactor )

pressure.

vessel

primary containment vessel

safety relief valve

residual heat ’ removal system I (RHR) | heat exchanger.

ZJ1

LPCF pump

[reactor building cooling water system (RCW)

condensate water .storage lank

onsite power system

emergency diesel generator

emergency diesel

generator

main steam line

to turbine

reactor core isolation

cooling system resdualleM reaocal i .

(RCIC) pump sjsen) (RHR) ba ( |

exchanger ■*’

RCW j LPFL J pump

1

~T~ ¹ from

——feed water pump

Figure 2.7.6 ECCS network (ABWR)

high pressure

core flooder

) (HPCF) pump

high pressure

reactor internal pump (RIP)

low pressure

flooder

J (LPFL)

* pump

3. Reactor Containment Facility

1. Roles of reactor containment facility

As explained in the previous sub-section, the ECCS can prevent the release of fission products due to a large number of fuel failures even when the coolant is lost (LOCA).

However, from the “Defense-in-Depth” viewpoint, the reactor containment facility is installed and controls the fission product release to the environment to sufficiently low levels.

To this end, the reactor containment facility has the following systems: the PCV to hold fission products, the containment spray system (CSS) to cool the atmosphere and to remove radioactive iodine, the flammable gas control system (FCS) to prevent combustion, in the PCV, of flammable gases produced by metal-water reactions, the reactor building (secondary containment) to prevent leaked fission products from the PCV from being directly released to the environment, and the standby gas treatment system (SGTS) to remove the fission products from the atmosphere of the building before releasing the treated atmosphere from the stack.

2. Primary containment vessel (pcv)

The PCV prevents and controls the release of radioactive materials to the environment from the reactor core in an accident

Typical examples of the BWR PCV are: Type Mark- f (Figure 2.7.7), Type Mark- II (Figure 2.7.8), and their improved types (Figure 2.7.9 and Figure 2.7.10). Their design peak pressures are 0.435 Mpa [gauge] and 0.315 Mpa [gauge], respectively. All these containment vessels are made of steel.

The PCV consists of a drywell that accommodates the RPV, the recirculation loops and other primary system components, and a suppression chamber that has a suppression pool therein. Hie drywell and the suppression chamber are connected by steel vent piping.

The steam-water mixtures released to the drywell in a LOCA are transported to the pool in the suppression chamber through the vent piping, where the steam is cooled and condensed. Thus, the pressure increase of the PCV can be effectively controlled. The isolation valves installed on the PCV piping penetrations hold the released fission products in the PCV. The PCV is designed,

2-87

NSRA, Japan

~T

Figure 2.7.8 PCV Type Mark-Il

Figure 2.7.9 PCV Type Mark-1 (improved)

Figure 2.7.10 PCV Type Mark-Il (improved)

NSRA, Japan

2 88