Application of Selected Safety Requirements from IAEA SSR ...€¦ · EC6 Heat Transport System...

Application of Selected Safety Requirements from IAEA SSR-2/1 in the EC6 Reactor Design ›Technical Meeting on Safety Challenges for New NPPs

22-25 June 2015, Vienna, Austria

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Safety first

Remember that all

SNC-Lavalin meetings

begin with a Health

& Safety moment.

Safety doesn’t happen by accident.

SAFETY FIRST

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Outline

› EC6 Design Overview

› Requirement 7 for Level 2 defence-in-depth: Distributed Control System approach

› Requirement 53: Emergency Heat Removal System (Level 3 defence-in-depth)

› Requirements 54 and 20: Containment envelope (Levels 3 and 4 defence-in-depth)

› Requirement 20: Emergency Containment Filtered Venting System (Levels 4 and 5 defence-in-depth)

› Requirement 20: Severe Accident Heat Removal System (Level 4 defence-in-depth)

› Requirement 67: Emergency Support Centre (Levels 4 and 5 defence-in-depth)

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EC6 Design

EC6 Reactor

• Natural uranium fuel

• Heavy water moderator and coolant

• Pressure tubes; calandria not a

pressure vessel

• Coolant physically separated from

moderator

• Small/simple fuel bundle

• On-power refuelling

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EC6 Heat Transport System › The HTS comprises the heat transport

pumps, steam generators, feeders, fuel

channels, and associated piping,

arranged in two “figure eight” loops.

› Heat generated by nuclear fuel in the

fuel channels passes through the outlet

feeders to the outlet headers, then

delivered to the SGs.

› Heat is transferred to the feedwater on

the secondary side of the SGs to

generate steam.

› The primary coolant is pumped from the

SGs back to the inlet headers, then back

to the core via the inlet feeders.

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Examples of Design Approaches to Address SSR-2/1

• Safety classification

• Requirement 7: Digital Control Systems

• Requirements 53 and 25: Emergency Heat Removal System

• Requirements 54 and 20: Containment envelope

• Requirement 20: Emergency Containment Filtered Venting System

• Requirement 20: Severe Accident Heat Removal System

• Requirement 67: Emergency Support Centre

Safety Classification for EC6 Design

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Safety Class A

A system is assigned to Class A if it meets any of the following criteria:

a) Maintains pressure boundary integrity of heat transport system where a failure would lead to a non-isolatable

loss of coolant accident.

b) Performs an immediate fast reactor shutdown function to prevent an initiating event from leading to

unacceptable consequences that exceed the design bases of Heat Transport System or safety systems.

Safety Class B

A system not included in Safety Class A is assigned to Safety Class B if it meets any of the following criteria:

a) Performs the function of core cooling to prevent an initiating event from leading to unacceptable

consequences that exceed the design bases.

b) Performs the function of containment to prevent an initiating event from leading to unacceptable radioactive

releases that exceed the design bases.

Safety Class C

A system not included in Safety Class A or B is assigned to Class C if it meets any of the following criteria:

a) Supports the operation of Class A or B systems.

b) Performs safety functions in longer term as a backup.

c) Failure of the system during operation (i.e. running failure) initiates a design basis accident.

d) Provides monitoring of safety functions during a design basis accident.

Safety Class D

A system not included in Safety Class A, B or C is assigned to Safety Class D if it meets any of the following

criteria:

a) Maintains adequate operating conditions for safety systems or systems important to safety during normal

plant operation, AOO or DBAs.

b) Prevents minor releases of radioactive materials.

c) Prevents/minimizes radiation exposure of plant staff.

d) Provides monitoring that the plant remains within normal conditions.

e) Provided for mitigation or monitoring of DEC.

Not important to safety A system not included in Safety Class A, B, C or D is assigned to not important to safety.

Safety Classification for EC6 Design

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System Safety Class Code/Standard

Fuel Handling Control and Display Systems C

CSA N290.4

IEC standards or

equivalent

Essential Control Sub-System C

CSA N290.4

IEC standards or

equivalent

Emergency Heat Removal System C CSA N285 series

Containment envelope B CSA N287 series

Emergency Filtered Containment Venting

System D CSA N285 series

Severe Accident Recovery Heat Removal

System D CSA N285 series

Emergency Support Centre D CSA N290.6

Digital Control Systems

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› Control systems are designed to assure that failures and

deviations from normal operation are minimized

› EC6 improvements using distributed control systems:

› Fuel handling control and display systems: fully

separate system with independent and diverse digital

sub-system to implement protective safety interlocks

› Fully digital device control sub-systems to interface via

digital communications with the digital group controls

› Read-backs provided from the digital device control

sub-systems to the PDS, advanced alarm

annunciation system, and computer based procedures

› All important to safety mitigating functions in a

separate IEC Class 2 mitigating controller, called the

“essential control sub-system”

› Additional parameters for setback and stepback, e.g.,

end shield outlet temperature high and Shield Cooling

System pump differential pressure low

SSR-2/1

Requirement 7: Defence in depth

Clause 4.11 (a)

Clause 4.11 (b)

Clause 4.11 (b)

Clause 4.11 (c)

Clause 4.11 (c)

Emergency Heat Removal System

› With feedwater available to the steam generators,

thermosyphoning in the intact Heat Transport System

(HTS) will prevent fuel failures

› EHRS addresses design basis accidents that cause

› Loss of heat removal from the steam generators, or

› Loss of heat removal from the Emergency Core

Cooling System (ECCS) heat exchangers

› EHRS performs the following functions:

› Gravity-fed make-up to the steam generators from

the Reserve Water Tank

› Pumped make-up to the steam generators from an

external water supply

› Seismically qualified back-up cooling water for the

ECCS heat exchangers

› Water supply to HTS to make up for small leaks or

losses (as a back-up to ECCS)

› All system components required to perform on demand

for a flow permissive function are duplicated in parallel

› All system components required to perform on demand

for a flow isolation function are duplicated in series

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SSR-2/1

Requirement 53: Heat transfer to an

ultimate heat sink

Systems shall be provided to transfer

residual heat from items important to

safety at the nuclear power plant to an

ultimate heat sink. This function shall

be carried out with very high levels of

reliability for all plant states..

SSR-2/1

Requirement 25: Single failure criterion

Containment

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› Containment design pressure of 400 kPa (g)

› Design leakage rate of 0.2%/day

› Seismically qualified to design basis

earthquake with PGA of 0.3 g

› Steel liner plate on the entire inside surface

of the containment structure

› Ensures leak-tightness is within

acceptable limits and

› Prevents spalled concrete from being

generated as a result of an external impact

› Increased thickness of the containment

structure from the CANDU 6 plants

› Meets current safety requirements for

radiation shielding, missile protection,

aircraft crash, and fire protection

›SSR-2/1

›Requirement 54: Containment system for the

reactor

›A containment system shall be provided to

ensure, or to contribute to, the fulfilment of the

following safety functions at the nuclear power

plant: (i) confinement of radioactive substances

in operational states and in accident conditions,

(ii) protection of the reactor against natural

external events and human induced events and

(iii) radiation shielding in operational states and

in accident conditions.

Severe Accident Recovery and Heat Removal System

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› With removal of decay heat from the core

available, progression of core damage can be

arrested

› With removal of heat from containment

available, containment integrity can be

maintained

› SARHRS addresses design extension

conditions that cause

› Loss of heat removal from the steam

generators with intact fuel channels,

› Loss of heat removal from the calandria

vessel with failed fuel channels, and/or

› Loss of heat removal from containment

Low-flow Spray

Header

RESERVE WATER TANK

ECCS

Strainer

CALANDRIA

MODERATORHEAD TANK

Inspection Port

On-site FreshWater Source

External Water

Supply

Severe Accident Recovery and Heat Removal System

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› SARHRS performs the following functions:

› Pumped make-up to directly to the steam

generators from an external water supply

› Gravity-fed make-up from the RWT to the

calandria vessel

› Gravity-fed make-up from the RWT to the

calandria vault

› Containment low flow spray from the RWT

› Pumped make-up to the RWT from external

source to continue gravity-fed make-up and

low flow spray

› Recover water from the reactor building

basement, cool it using a heat exchanger,

and deliver it to the RWT for make up

› Drain contaminated water from RB post-

severe accident

›Requirement 20: Design extension conditions

›5.27 … to prevent accident conditions not

considered design basis accident conditions, or

to mitigate their consequences, as far as is

reasonably practicable. This might require

additional safety features for design extension

conditions, or extension of the capability of safety

systems to maintain the integrity of the

containment. …

Emergency Containment Filtered Venting System

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› With containment integrity

maintained, uncontrolled,

unfiltered releases of radioactivity

can be prevented

› ECFVS addresses design

extension conditions that cause

› Overpressurization of

containment

› ECFVS performs the following

functions:

› Controlled, filtered venting of

containment

› Monitoring of radioactive

releases

Summary

Some examples of the design approach that has been taken in the EC6

design to implement safety requirements from IAEA SSR-2/1 have been

presented:

› Level 2 defence-in-depth: improvements through the use of the Distributed Control System, addition of setback and stepback parameters and a separate system for fuel handling

› Requirement 53: EHRS for level 3 defence-in-depth

› Requirements 54 and 20: Containment envelope for levels 3 and 4 defence-in-depth

› Requirement 20: ECFVS for levels 4 and 5 defence-in-depth

› Requirement 20: SARHRS for level 4 defence-in-depth

› Requirement 67: Emergency Support Centre for levels 4 and 5 defence-in-depth

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Enhanced CANDU 6 Technical Summary

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Application of Selected Safety Requirements from IAEA SSR ...€¦ · EC6 Heat Transport System...

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