International Conference on Opportunities and Challenges for Water Cooled Reactors in the 21st

Century, Vienna, 27th – 30th October 2009

AP1000TM Nuclear Power Plant - Passive Safety System

Actuation using Explosively Opening “Squib Valves”

• Actuation provided by three independent igniters.

• Simple design

• Few ways to fail

• Failure probability (failure to operate)

~ 5.8E-04 per demand

• Redundant configuration (four valves in ADS)

• Provide diversity to motor operated valves

• Leak-before-break criteria fulfilled

The ultimate heat sink of the AP1000TM safety systems is the

environment. Steam is condensed at the containment vessel

wall and heat is removed to the atmosphere via natural

convection.

Containment Cooling System of AP1000TM

Piston

Nipple

Nipple shear cap

Charge

Squib Valve

(principle sketch)D. Freis, Dr. W. Tietsch

Westinghouse Electric Germany

The Passive Core Cooling System (PXS) of the AP1000TM

plant performs:

• Emergency core decay heat removal

• Reactor coolant system emergency makeup and boration

• Containment pH control

• Safety injection

All safety functions of the AP1000TM rely on natural forces

like natural circulation, gravity, convection, evaporation,

condensation and compressed gas.

Passive Core Cooling System of AP1000TM

Passive Core Cooling System

Passive Safety Injection with Squib Valves (marked by red circles)

CLHL

N2

PRESSURIZER

IRWST

ACCUM.

(1 OF 2)

CORE

REACTOR

VESSEL

CORE MAKEUP

TANK (1 OF 2)

#3

#2

#1

FAI

REFUEL

CAVITY

FO

RNS

SPARGERS

M

RNS

PUMPS

LOOP

COMPART.

RECIRC

SCREEN

(1 OF 2)

M

DVI CONN.

(1 OF 2)

PRHR

HX

(1 OF 2)

ADS

STAGES 1-3

(1 OF 2)

ADS

STAGE 4

(1 OF 2)

PUMPS

CONTAINMENT

M M

MM

M M

M

M

M

M

(1 OF 2)

IRWST

SCREEN

Safety injection from passive low pressure systems can only

be provided after depressurization of the primary circuit.

The Automatic Depressurization System (ADS) releases the

pressure from the reactor coolant system using motor

operated valves and Squib Valves, which open on actuation

of an explosive charge. Safety injection from the In-

containment Refueling Water Storage Tank and Sump

Recirculation are activated by Squib Valves.

Squib Valves in Safety Systems

Design Features of Squib Valves

Passive Containment Cooling System