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Chapter 2 Systems of BWR Nuclear Power Plants

in operation

Figure 2.3.23 ABWR power-flow operating map

  1. Primary Coolant System

  1. System Summary

Figure 2.4.1 shows a schematic diagram of the primary coolant system. It consists of the RPV, primary loop recirculation (PLR) system, main steam (MS) system and feed water (FDW) system. The RPV is a high pressure cylindrical vessel and houses the core, core support structures and other internal structures (core internals) (See Section 2.3). The steam generated in the core is transported to the turbine system, flowing through the steam separator and the steam dryer assemblies and through the main steam piping after leaving the RPV via steam outlet nozzles located at the upper part of the RPV. The PLR system forcibly circulates the reactor coolant inside the RPV for removing the heat by recirculation pumps and jet pumps, before returning it into the core. Hie reactor power (the amount of steam generated by the reactor) is controlled by adjusting the core flow rate by controlling the speed of the recirculation pumps. Hie MS system, in addition to its primary function of carrying the steam from the RPV upper dome

to the turbine system, has two additional functions: (1) it prevents any abnormal system over-pressure during the transient or accident conditions by releasing the steam from the safety relief valves (SRVs), and, (2) it limits the steam release from the RPV and the PCV by means of the main steam flow limiters and the main steam isolation valves. The FDW system transports condensed water from the turbine condenser back into the in-vessel feed water spargers. It consists of the related piping and valves. Table 2.4.1 shows a typical example of key specifications of the primary coolant system.

  1. Primary loop recirculation (plr) system

The following are the design philosophies of the PLR system.

  1. It provides slightly sub-cooled water (slightly lower than the saturation temperature) into the core during normal operation and removes the heat generated in the core.

  2. It controls the reactor thermal power by controlling the coolant flow rate.

  3. It has a required flow decreasing (pump coast down) characteristic, upon a pump trip, and

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NSRA, Japan

from reactor feed waterline

loRCIC

MSIV

from reactor feed water line

from reactor water cleanup sysrem(CUW)

main steam line, _ L matn steam

.line

main steam line

Tn from other main steam lines

(CUWtreactor water cleanup system) (RHR:residual heal removal system) (MSLVtmain sleam isolation valve)

(RCICrreactor core isolation cooling system)

Msrv

MS drain liner

injection line

header

reactor feed water line

safely

relief valve

reactor feed waler line

§

§’

purge system of recirculation pump seal

main steam line

lo pressure suppression chamber

from recirculation

pump

lo main steam line

toRHR

toCUW

suction

I me

from control rod

drive system

sampling line

riser line

f to turbine

to MS drain line

lo condenser

Figure 2.4.1 Reactor primary coolant system

Table 2.4.1 Key specifications of a reactor primary coolant system (1,100MWe class)

] Reactor Thermal Power

3,293MWt

Reactor Coolant Flow

48,300ton/h

Main Steam Flow

about 6,400ton/h

In-diameterabout

6.4m

Reactor Pressure Vessel

Height

about 22m (inside measurement)

Material

low alloy steels, low alloy steel forgings (basic materials) stainless steel, Ni-based alloys (Inconel) (lining)

Type

vertical single stage centrifugal pump

Flow

10,000 m3/h/unit

Recirculation Pump

Head

about 240m

Diameter

600A (nominal)

Material

stainless steel castings

Type

back pressure balancing (with an actuator)

No.

15

Safety Relief Valve

Inlet-diameter

150A (nominal)

Outlet-diameter

250A (nominal)

Capacity

about 400ton/h (safety valve function)

Material

carbon steel (main body)

Type

air (or nitrogen)/spring driven Y-shaped groove valve

Main Steam Isolation Valve (MSIV)

Diameter

650A (nominal)

Closing speed

about 3 - 5s

Material

carbon steel (main body)

Design

Pressure

8.62 MPa [gauge] (87.9kg/cm2 g)

Temperature

302t

NSRA, Japan

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