Ageing Management of Civil Structures: Some Aspects of · PDF file| 15 AAR on EDF NuclearPower Plants : ~12 slightlyaffectedby AAR (almost pop outs and AAR gels only) Pop out : crackedcoating

Ageing Management of Civil

Structures:

Some Aspects of eDF's In-

Service Inspection Program and

Risk Informed Approach

Alexis COURTOIS ([email protected]), Frederic

COPPEL ([email protected]), Etienne

GALLITRE, Frederic TAILLADE

4th International Conference on Nuclear Power Plant Life Management

Lyon, France

23-27 October 2017

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CONTENT

PLIM 2017 - Some Aspects of eDF's ISI - ID 087

1. OVERVIEW OF THE EDF’S AGEING MANAGEMENT PROGRAM

2. LONG TERM BEHAVIOR MONITORING OF CONTAINMENTS

FEATURES OF PWR FRENCH CONTAINMENTS

SURVEILLANCE PRINCIPLES

MONITORING SYSTEM

DATA MANAGEMENT : FROM IN-SITU MEASUREMENT TO DIAGNOSIS

3. APPREHENSION OF RISKS OF INTERNAL EXPANSION OF THE CONCRETE ON EDF OPERATING

NUCLEAR POWER PLANTS

RISK OF INTERNAL EXPANSION DUE TO DEF OR AAR

METHODOLOGY USED BY EDF

APPLICATION

4. CONCLUSION AND PERSPECTIVES

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AGEING MANAGEMENT PROGRAM FOR CIVIL

STRUCTURES AT EDF

� Ageing management has been implemented on civil

structures at eDF since the 1990’

� Comparison with IAEA NS-G-2.12:

� “Régles Nationales de Maintenance” is close to what is called

“Ageing Management Program” (AMP) by IAEA standards

� “Fiche d’Analyse du Vieillissement” is equivalent to “Ageing

Management Review”. 66 mechanisms related to 11 generic

systems (containment, pools, anchoragesD) are addressed.

� “Dossier d’Aptitude à la Poursuite d’Exploitation” is close to

Time Limited Ageing Analysis “TLAA”


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AGEING MECHANISMS ANALYSIS

The analysis consists in answering to the questions:

� What is the design life time hypothesis?

� Is it a potential threat or a phenomenon already observed?

� Did we encounter difficulties that could affect a safety function?

� Is the maintenance program adapted?

� Is a possible repair easy to implement?

� Is there any risk of obsolescence of the system?

Additional questions for Long Term Operation:

� Is there any regulation or qualification requirements that could affect operation time?

� Is there any additional inspection or maintenance to perform for LTO?

� What is the expected life time of the items and what is the assessment basis?

Two ageing mechanisms that have to be followed-up:

� Concrete creep of prestressed containment vessel

� Internal expansion reactions in concrete structures (AAR and DEF)


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PHENOMENON:

CREEP OF CONCRETE CONTAINMENT


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WHY A CONTAINMENT MONITORING SYSTEM IN

OPERATION?� eDF made the choice of PWR with prestressed concrete containment

� French containment prestressing systems are cement grouted

(bonded tendons):

• effective protection against corrosion

• additional strength for overdesign situation

• no direct inspection

• no re-tensioning


Grouting with special grout Anchorage systemTendons ducts

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SURVEILLANCE PRINCIPLES

� “Allowable” creep concrete strains and displacement are assessed by

design (consistent with acceptable prestressing lossess)

� Monitoring of concrete strains/displacement to assess prestressing

losses over time

� Monitoring the actual structural behavior under pressure

� Use of specific instrumentation

� Periodic monitoring reports (2 or 5 year period)

Monitoring data

Pressure

Strain

In operation

In pressure test

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STANDARD MONITORING SYSTEM


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VWSG AND PENDULUM


Embedded VWSG layout, vertical cross section of

containment

Vibrating Wire Strain Gages (VWSG, embedded within concrete wall)

Elongation of the wire is linked to wire Eigen frequency

Temperature probe

(Pt100)

Pendulum for horizontal displacement

measurement

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IN CASE OF VWSG FAILURE, MIND THE

SURFACE EXTENSOMETERS!


7 years for designing and testing the system on operation conditionsD

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COMPARISON EMBEDDED / SURFACE

EXTENSOMETERS


Surface sensor

Embedded sensor

Strain

Time

Pressure

Strain

Surface sensor

Embedded sensor

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DATA GENERATION AND MANAGEMENT WITH

KOALA SOFTWARE


Raw dataPerioddicity

depends upon

operation

rules

Operatorof measurements

of structural behaviour

Storageof data (temperature effect)

Corrected data

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PHENOMENON:

CONCRETE INTERNAL EXPANSION


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Environmental effects and various others phenomena can cause

ageing of NPP structures.

One of these phenomena is the internal expansion of concrete

which can be caused by alkali aggregate reaction (AAR) and / or

internal sulfate attack (Delayed Ettringite Formation=DEF).

Aggregates

DEF

Cement paste

Sound

AAR AND DEF APPRAISAL FOR EXISTING


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AAR on EDF Nuclear Power Plants : � ~12 slightly affected by AAR (almost pop

outs and AAR gels only )

Pop out :

cracked coating



DEF on EDF Nuclear Power Plants�2 slightly affected structures, discovered around 2008

• Precast concrete columns cast in the early 1980’s

• Mass concrete underground structure , cast in the late 1980

- Very slow swelling (< 10µm/m/year)

- Detected by sensor monitoring only

AAR Gel (silicone and

alkalis – calcium poor)

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No prevention of AAR and DEF was

existing at the time of construction for

power plants built before 1985.

This is why EDF has since defined a

methodology for the AAR and DEF

appraisal on these power plants.



The EDF methodology is based

on IFSTTAR recommandations

“Management of structures

affected by internal expansive

reactions of concrete”

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- 6 levels of theoretical risk are defined : MB0 (negligible) , MB1 (low),

MB2 (medium), MB3 (high) and MB4 (very high)

- The parameters required to determine the theoretical risk of AAR are

illustrated below :Alkali content in

concrete

MB risk

Humidity exposure

Aggregate reactivity

Methodology developed by EDF in order to estimate the

theoretical risk of AAR



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� 5 levels of theoretical risk are defined : OB0, OB1, OB2, OB3, OB4

� The parameters required to determine the theoretical risk of DEF are

illustrated below :

Maximum temperature

reached during hydration

OB risk

Humidity/water exposure

Concrete sensitivity:

-Alkali content in concrete

-Cement or binder composition

Methodology to estimate the theoretical risk of DEF



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For the reactor building, depending on the availability of data :

o level 1 : building = internal containement of the reactor building

o level 2 : part of the building = dome, raft, containment wall

o level 3 : concrete layer

ex : NPP 2

ex : NPP 1

1

Application to EDF Nuclear Power Plants buildings

NPP Dome Contain. wall Gusset Raft

Max. DEF

risk

OB0 OB0 OB1 OB2

Fiability poor poor poor poor



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Precisely defined in a civil works preventive maintenance policy

(made available for safety authorities)

Surveillance strategy based on the MBi / OBi classification of each

building, in application of the general methodology

IN SITU ASSESSMENT

- MB0/OB0 classification: no specific action

- MB1-MB2/OB1-OB2 classification: simplifiedsurveillance

- 3 zones by building

- MB3-MB4/OB3-OB4 classification: complete surveillance

- 6 zones by building

Counting of pop outs

Fluorescence using

uranyl acetate

0

200

400

600

800

1000

1200

1400

0 4 8 12 16 20 24 28 32 36 40 44 48 52

Exp

an

sio

n (µ

m/m

)

Age (semaines)

B1 sain 1017 K4B

B1 fissuré 1017 K8B

B1 très fissuré 1017 K12B

B2 879 K3 sain

B2 879 K5A sain

B2 879 K12 fissuré

B2 879 K14 A fissuré

B2 879 K18 fissuré

B2 879 K20 A très fissuré

B2 879 K27 A très fissuré

B3 sain 1018 K4B

B3 fissuré 1018 K8B

B4 sain 1019 K4B

B4 très fissuré 1019 K9B

Residual

expansion

test

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Step 1: in situ detection

Step 3:

enhanced

surveillance

Step 2: diagnosis

on samples

IN SITU ASSESSMENT

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CONCLUSION AND PERSPECTIVES� As an illustration of eDF’s AMP, two examples have been presented:

� Containment concrete creep monitoring

� AAR and DEF appraisal for existing structures

� Approach fully consistent with NS-G 2.12 IAEA standard

� Collecting useful records (design, construction, inspection and monitoring) is a

key point for an effective AMP:

� Provide appropriate database since the beginning of the projects is highly

recommended.

� Data management in the eDF’s Vercors project may be considered as an example of

good practice.

� New tools and new methods are needed to improve structural health monitoring

for LTO:

� Knowledge on behavior at different scales (materials, specimen, real structures)

� Non Destructive Tests / monitoring devices for cracking, steel rebars or tendons

corrosion, concrete water contentD

� Methods to combine all the records to build a relevant diagnosisPLIM 2017 - Some Aspects of eDF's ISI - ID 087

Thank you for your attention

Documents

Ageing Management of Civil Structures: Some Aspects of · PDF file| 15 AAR on EDF NuclearPower Plants : ~12 slightlyaffectedby AAR (almost pop outs and AAR gels only) Pop out : crackedcoating