Aging Management of CANDU NPP

Concrete Structures

Julia Tcherner

Senior Civil Engineer

Candu Energy

IAEA Consultancy Meeting, Assessment and Ageing of Concrete Structures

May 29­June 1, 2012

Outline

•CANDU Plants–Multi-unit

–Single unit (CANDU 6)

•Codes and Standards–How ageing is addressed

•Ageing Management

•Condition / Life Assessments–Problem areas

•Repairs

•Monitoring1

Multi – Unit CANDU

2

•18 operating units at 3 sites in

Ontario, Canada

• Darlington

• Bruce

• Pickering

•Typically several Reactor Buildings

are connected by pressure relief

duct to the same vacuum building

• Oldest

Pickering A (1971)

• Most Recent

Darlington (1993)

• Original Design Life

30 or 40 years

CANDU 6

3

• 11 CANDU 6 Operating Reactors

• 2 in Canada, 9 around the world

• Argentina

• China

• Korea

• Romania

•Fully post­tensioned bonded

system (mat, cylinder, dome)

•Non­metallic liner system

CANDU 6 Units in Operation

CANDU 6 Containment Structure

5

Outline

•CANDU Plants–Multi-unit

–Single unit (CANDU 6)

•Codes and Standards–How ageing is addressed

•Ageing Management

•Condition / Life Assessments–Problem areas

•Repairs

•Monitoring6

Canadian Standard Association (CSA)

7

• not-for-profit membership-based association serving business, industry, government and consumers in Canada and the global marketplace.

The purpose –

• to develop standards that address real needs, such as enhancing public safety and health, advancing the quality of life, helping to preserve the environment, facilitating trade.

• to help people understand standards through education and information products and services.

Standards for Concrete Containment

Structures

• First developed in late 1970s

• Revised in early 1990s

• Another cycle of revisions started in mid 2000s

• defines requirements for concrete containment structures of

nuclear power plants including requirements for: ­ materials,

­ design,

­ construction,

­ examination and testing during construction,

­ proof pressure and leakage rate testing ,

­ in­service examination and testing.

CSA N287 Series

8

Standard for Safety Related Structures

9

CSA N291 - 08

• First edition of the Standard published in 2008

• This Standard specifies requirements for safety­related structures constructed of structural steel, reinforced concrete, and reinforced masonry

• This Standard also covers requirements for irradiated fuel storage facilities

• This Standards includes requirements for: – analysis – design– inspection– examination

10

• Consistent up-to-date standards for design and construction

of the new nuclear power plants are required.

• With aging of the nuclear power plants the necessity for

proactive approach to address emerging challenges was

recognized

• A need to allow industry to take advantage of the new level

of knowledge and experience was identified.

Recent Updates of the Standards - reasons

CSA N287 Series

CSA N287.1-93 (R2009) – currently being revised, General requirements for concrete containment structures for CANDU nuclear power plants

CSA N287.2-08, Material requirements for concrete containment structures for CANDU nuclear power plants

CSA N287.3-93 (R2009) – currently being revised, Design requirements for concrete containment structures for CANDU nuclear power plants,

CSA N287.4-09, Construction, fabrication, and installation requirements for concrete containment structures for CANDU nuclear power plants

CSA N287.5-11, Examination and testing requirements for concrete containment structures for nuclear power plants

CSA N287.6-11, Pre-operational proof and leakage rate testing requirements for containment structures for nuclear power plants

CSA N287.7-08, In-service examination and testing requirements for concrete containment structures for CANDU nuclear power plants

11

CSA N287 Series – Recently Updated Standards

N287.7 - 08

• Specifies uniform rules for

assessment of the structural

and leak­tight integrity of

concrete containment

structures through systematic

and periodic examination.

• The fourth edition of the

Standard was issued in 2008

superseding the previous

editions published in 1996,

1980, and 1975.

12

CSA N287 Series – Recently Updated Standards

N287.7 - 08

• Main updates in 2008 edition: – revisions to the reference standards

– enhancements to address the lessons learned in implementation of the

standard

– enhancements to take advantage of recent advances in in­service

examination techniques

– requirements for trending of the observations made during in­service

examinations and tests were added

– requirements for in­service examination program and acceptance criteria

were added

– requirements for pre­stressing system integrity evaluation were enhanced

– new non­mandatory annex was added to allow for alternative option for

monitoring of the pre­stressing system behaviour

– another new non­mandatory annex was added to recognize performance

based approach to determining interval between the leakage rate tests.

13

CSA N287 Series – Recently Updated Standards

N287.2 - 08

• Specifies requirements for the materials used in concrete

containment structures of containment systems designated

as class containment components, parts, and appurtenances

in CANDU nuclear power plants.

• The fifth edition of the Standard was issued in 2008

superseding the previous editions published in 1991, 1982,

1977, and 1976.

14

CSA N287 Series – Recently Updated Standards

N287.2 - 08

• Main updates in 2008 edition: – revisions to the reference standards

– the use of various types of cement and supplementary cementing

materials was allowed to take advantage of the technological

advancements

– requirements for repair materials were added

– requirements for grout and grouting of the post­tensioning system were

enhanced

– requirements for qualifications of the joint sealant materials were added

– requirements for qualifications of non­metallic liner materials were

enhanced

– an alternative for seismic qualification of post­installed mechanical anchor

bolts was included

– two non­mandatory annexes were added

15

CSA N287 Series – Recently Updated Standards

N287.4 - 09

• Specifies requirements for construction,

fabrication, and installation for concrete

containment structures.

• The fourth edition of the Standard was issued in

2009 superseding previous edition published in

1992, 1983, and 1977.

16

CSA N287 Series – Recently Updated Standards

N287.4 - 09

• Main updates in 2009 edition: ­ new requirements have been added to improve the quality of

construction to address lessons learned in recent CANDU containment construction as well as those summarized in the US NRC Information

Notice 2008­17 ­Construction Experience with Concrete Placement.

­ changes were made to incorporate industry advances and good

practices and improve interfaces with revised CSA standards

· ensuring the uniformity and traceability of concrete,

· improving quality of mechanical splices installation, · improving corrosion protection of the pre­stressing tendons.

­ requirements for tolerances and deviations in installation of the

metallic parts were refined­ requirements for installation of joint sealant material were included

­ requirements for water stops and metallic liners were added.

17

CSA N287 Series – Recently Updated Standards

N287.5 - 11

• Specifies examination and testing requirements

that will ensure that concrete containment

structures are built using techniques and work

practices that meet the quality and standards

commensurate with the safety principles

necessary to comply with the Canadian nuclear

safety philosophy.

• The third revision of the standard was issued in

2011 superseding previous editions published in

1993 and 1981.

18

CSA N287 Series – Recently Updated Standards

N287.5 - 11

• Main updates in 2011 edition: – revisions to the reference CSA standards to enhance

the clarity and consistency of the standard scope and

its linkage to other CSA standards

– lessons learned in implementation of the standard

were incorporated

– recent advances in examination and testing

techniques were captured

19

CSA N287 Series – Recently Updated Standards

N287.6 - 11

• Specifies requirements for pre­operational proof

and leakage rate testing of concrete containment

structures

• The fourth edition of the Standard was issued in

2011 superseding previous editions, published in

1994, 1980, and 1978 under the title Pre­

Operational Proof and Leakage Rate Testing

Requirements for Concrete Containment

Structures for CANDU Nuclear Power Plants

20

CSA N287 Series – Recently Updated Standards

N287.6 - 11

• Main updates in 2011 edition: – revisions to the reference CSA standards to enhance the clarity and

consistency of the standard scope and its linkage to other CSA

standards

– lessons learned in implementation of the standard as well as recent

advances in examination and testing techniques were captured

– requirements for pre­stressing system integrity evaluation were

enhanced

– new non­mandatory annex was added to address requirements

for instrumented monitoring of the post­tensioning system

21

Outline

•CANDU Plants–Multi-unit

–Single unit (CANDU 6)

•Codes and Standards–How ageing is addressed

•Ageing Management

•Condition / Life Assessments–Problem areas

•Repairs

•Monitoring 22

Canadian Nuclear Safety Commission (CNSC)

•CNSC regulates the nuclear

sector in Canada

•CNSC Regulatory Document

RD 334 – Aging Management

of Nuclear Power Plants

24

AMP Components

• Condition Assessment

• Identification of defects

• Prioritization

• Examination methods

• Evaluation criteria and frequency of periodic examinations

• Personnel qualifications

• Monitoring instrumentation

• Monitoring of environmental and operating conditions

• Monitoring performance of structure

• Repair

• Documentation requirements and data management

25

Condition Assessment

Current Condition

Health Prognosis

Assessment of construction

operation and maintenance

data against design basis

Assessment of

ARDMs and

their impact on

the ability of

structure to

meet its

functional

requirements

Assessment

of utility’s

programs to

manage

ARDMs

Obsolescence

26

Condition Assessment

To establish base

line condition

To identify

ARDMs

To identify critical

areas/components

To optimize AMP by using inspection and

monitoring techniques that are appropriate for

suspected degradation and concentrate efforts on

critical areas/components

Life Assessment / Condition Assessment

• RB Containment Structure

• RB Internal Structures

• Spent Fuel Bays

• Spent Fuel Dry Storage Facilities

• Spent Resin Tanks

• Liquid Waste Storage Tanks

• Underground Waste Storage Structures

• Turbine Block Foundation

• Cooling Water Buildings and Structures

28

Identification of Degradation

Concrete Chemical – leaching, sulphate attack,

acid attack, alkali aggregate reaction,

carbonation

Physical – freeze thaw cycles, salt

crystallization, abrasion/erosion,

temperature cycling, vibration (fatigue),

settlement, shrinkage

SteelChemical – corrosion

Physical - deformation

Physico-chemical – relaxation of

tendons

29

Identification of Degradation

Non-metallic Liners,

Sealants

Weathering, irradiation, wear,

delamination, exposure to elevated

temperatures,

ARDM Matrix

Prioritization Process

31

Periodic Evaluation

32

Examination Methods –

Visual Inspection (including ROV)

33

Advantages

•simple

•effective

Limitations

•accessibility

Objective

•To identify any visible distress

Examination Methods –

Non-Destructive Examination

34

Advantages

•non destructive

Objectives

•To identify defect

•To detect degradation

•To quantify degradation

Limitations

•accessibility

•interferences

•local effects

Examination Methods –

Laboratory Testing

35

Advantages

•quantitative

Limitations

•destructive

•accessibility / radiation

•local effects

Objectives

•To verify degradation

•To determine possible cause

•To quantify extent

Evaluation Criteria and Frequency

36

Evaluation Criteria

ACI 349.3

• Acceptance without

further evaluation

• Acceptance after

review

• Condition requiring

further evaluation

Frequency

CSA N287.7 – concrete

containment

CSA 291 – safety related

structures

Personnel Qualification

• Members of the evaluation team

–performing CA,

–conducting periodic examinations,

–evaluating results

• Knowledge (education, training, experience)

–evaluation of structure ­ material degradation / structural

integrity

–functional requirements of the nuclear civil structures

37

Monitoring Condition of the Structure and

Monitoring Stressors

38

Vibrating Wire Strain

Gauges

Fibre Optic Sensors

Thermocouples

Cast-in corrosion probes

Temperature

Humidity

Chemistry

Water level fluctuations

Problem Areas

1. Elastomeric material (i.e. joint sealant and

liner system)

2. Integrity evaluation of post-tensioning

system

3. Concrete is generally in good condition,

however:

• Parts exposed to moisture – leaching

• Ring beam and buttresses protective cover – freeze-thaw

• Areas around penetrations and fuel transfer structure – air leakage

during LRT

Examples of Liner Degradation

Examples of Joints Degradation

CSA N287.7 – In-service Examination and Testing

42

CSA N287.7­08

Pre­stressing systems used as principal reinforcement in concrete

containment structures shall be subject

to an integrity evaluation for conformance to the design

specifications to determine the effects of certain

time­related factors, such as

(a) shrinkage and creep of the concrete;

(b) stress relaxation; and

(c) deterioration.

Integrity Evaluation of Post-tensioning System

Methods for Integrity Evaluation of

Post-tensioning System

43

• Instrumented Monitoring

• Test Beams

• Lift­off test and inspection

Test Beams

•Simple beams, 6 m long

•Constructed per the same specifications as Reactor

Building containment structure

•Stored under the same conditions as Reactor Building

(exposed to the environment)

•Tested at pre­determined intervals–Tendons examination

–Flexural tests

–Lift­off tests

44

CSA N287.6 – Preoperational Proof and Leakage Rate Test

45

CSA N287.6­94

Instrumentation required in Clause

5.4.1 shall not be mandatory for non­

prototype concrete components that

are similar in design to those which

have previously passed the pressure

test requirements.

CSA N287.6­11

Instrumentation shall be provided to

(a) evaluate the behaviour of the structure and

the actual stress values during pre­operational

proof

testing; and

(b) be used for the life of the plant, as applicable,

to

(i) monitor deformation of the containment

structure at the time of leakage rate testing in

order to ensure the elastic behaviour of the

containment structure; and

(ii) verify the integrity of the prestressing system.

Integrity Evaluation of Post-tensioning System

Instrumented Monitoring

46

Vibrating Wire

Strain Gauges

Fibre Optic Sensors

Thermocouples

Instrumented Monitoring

Purpose

•To detect response of the containment

structure to the pressure loading

–Data collected during proof pressure and

leak rate tests

•To detect any unusual trends and to

monitor time­dependant changes in the

containment structure

–Data collected during operation

47

Measurements During Leakage Rate Test

48

Typical Electrical Penetration

Typical Mechanical Penetration

Outline

•CANDU Plants–Multi-unit

–Single unit (CANDU 6)

•Codes and Standards–How ageing is addressed

•Ageing Management

•Condition / Life Assessments–Problem areas

•Repairs

•Monitoring 51

Repair

• Consideration

–cause of distress

–behavior of the structure

• Case­by­case approach

• List of qualified materials

–Containment (CSA N287.2)

52

CANDU Owners Group (COG)

•COG is a not­for­profit corporation with voluntary

funding from CANDU­owning utilities and AECL.

Currently COG Membership includes 5 Canadian and 6

offshore Members

•The activities of COG cover four Programs for

collaborative research, information exchange, joint

projects and regulatory affairs.

Concrete Working Group main areas of research

•Qualification of liners and sealants

•Integrity assessment of the post­tensioning system

•Integrity of Spent Fuel Bay under elevated

temperature

•Non­destructive examination methods

Concrete Repair Example – Ring Beam, Gentilly 1

Gentilly 1 - Prototype CANDU

• 250 MW CANDU plant

• Designed in late 1960s• Currently in a safe sustainable shutdown state ­ Storage With Surveillance (SWS)

Concrete Repair Example – Ring Beam, Gentilly 1

• Visual inspection

• Concrete core analysis

• Overcore concrete stress

measurements

• In-situ stress measurement

• Inspection of cables

A study was undertaken to determine condition of

the reactor building

Investigation (cont’d)

Results

• Concrete deteriorated in the

areas of post­tensioning

anchorages (AAR and freeze­

thaw)

• The anchorage heads,

exposed tendons and rebars

were in a reasonably good

condition

• All measured stresses were

as expected –compressive,

generally in the design range

Repair Objectives

� Remove all unsound and unbonded

concrete

� Restore the concrete of the

ringbeam

� Protect pre-stressing anchorages

� Protect the repair and provide

durable solutions

� Improve aesthetics of the building

Pre-Qualification

• Material certificates and

acceptance• Production (work) procedures• Pre­qualifying workmanship test• Test repair prepared• Pull­out test

Repair Methodology

� Area of the ring-beam, with a

significant amount of

degradation should be

properly repaired and sealed

in order to prevent future

water ingress into that

structural concrete

� Application of Glass Fiber

Reinforced Polymer (GFRP)

was recommended for the

ring-beam as a long-term

solution.

Repairs

GFRP applicationConcrete repairs

Motivation for Instrumentation Program

� First GFRP repaired CANDU structure

�Promote confidence in new experimental technologies

adopted in G­1 repair

� Effectiveness and Performance of Material

�Repaired concrete

�GFRP

� Reliability and Effectiveness of Equipment

�Fiber optic sensor technology

�Remote monitoring system

Aging Management Program

• VWSG and FOS installed inside and outside of ring beam• Readings were taken during concrete pouring and hydration• Currently monitored semi­annually as part of AMP.

Vibrating Wire Strain Gauge (VWSG)

• A VWSG enables measurements of local strain of concrete in the vicinity of the gauge.

• The strain variation is calculated by measuring the change in resonant frequency of the wire, which varies with changes in its tension, against a datum value.

-800

-600

-400

-200

0

200

400

600

Date

E-300/575

E-90/575

E-90/300

W -90/560

W -330/560

N-125/250

N-50/100

N-120/250

N-50/100

S-315/500

S-90/500

S -215/600

S-90/600

S -120/275

-15

-10

-5

0

5

10

15

20

25

30

35

Date

E-300/575

E -90/575

E -90/300

W -90/560

W -330/560

N-125/250

N-50/100

N-120/250

N-50/100

S-315/500

S-90/500

S-215/600

S-90/600

S-120/275

VWSG

Results

Total

concrete

strain

Temperature

VWSG Results (cont’d)

-600

-400

-200

0

200

400

600

Date

E-300/575

E-90/575

E-90/300

W-90/560

W-330/560

N-125/250

N-50/100

N-120/250

N-50/100

S-315/500

S-90/500

S-215/600

S-90/600

S-120/275

Concrete Strain after Temperature Compensation

Fibre Optic Sensor (FOS)

Fabry-Perot (FP) Sensor• measuring a gap shift or cavity length between two

facing fibre ends contained in a glass capillary

• reflected gap is shown on a read­out screen

• FP sensors are able to provide compensated thermal

strain measurements

Protection

polyurethane protection

fast set epoxy

FRP

concrete

epoxy resin

sensor

FOS Results

Measured Strain

Measured Temperature

FOS Results (cont’d)Concrete Strain

G1 ring beam repair and monitoring results

• The structural strain in the ring beam concrete measured by

most gauges is small and indicates no cracking.

• Both VWSG and FOS technologies are practical and effective

in monitoring

• GFRP has been effective in protecting the concrete from

further AAR damage

Conclusions and Lessons Learned

74

1. Degree of Degradation depends on:

• Quality of the structure as constructed!

• Aggressiveness of environment

2. Knowledge of degradation, experienced personnel is vital

3. Condition Assessment is instrumental

4. Prioritization is useful to optimize AMP

5. Simple NDEs that cover large areas are most useful

6. Three-tier acceptance criteria needs to be customized

7. Embedded and retrofitted proven instrumentation should

be used

8. Monitoring of the stressors (environmental and operating

conditions) and performance of the structure is paramount

Thank You