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International Journal of Pressure Vessels and Piping 83 (2006) 756–766

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Lifetime management for mechanical systems, structures andcomponents in nuclear power plants

E. Roos�, K.-H. Herter, X. Schuler

Materials Testing Institute (MPA), University of Stuttgart, Pfaffenwaldring 32, D-70569 Stuttgart, Germany

Received 2 March 2006; received in revised form 29 June 2006; accepted 3 July 2006

Abstract

Guidelines, codes and standards contain regulations and requirements with respect to the quality of mechanical systems, structures and

components (SSC) of nuclear power plants. These concern safe operation during the total lifetime (lifetime management), safety against

ageing phenomena (ageing management) as well as proof of integrity (e.g. break exclusion or avoidance of fracture). Within this field the

ageing management is a key element. Depending on the safety-relevance of the SSC under observation including preventive maintenance

various tasks are required in particular to clarify the mechanisms which contribute system-specifically to the damage of the components

and systems and to define their controlling parameters which have to be monitored and checked. Appropriate continuous or

discontinuous measures are to be considered in this connection. The approach to ensure a high standard of quality in operation and the

management of the technical and organisational aspects are demonstrated and explained.

r 2006 Published by Elsevier Ltd.

Keywords: Lifetime management; Ageing management; Proof of integrity; Damage mechanisms; Basis safety concept; In-service monitoring;

Technological ageing; Material-related (physical) ageing; Deming-process

1. Introduction

In most countries it has been stipulated that the licensing ofnuclear power plants and their subsequent operation is basedmainly on proof of the plant safety (e.g. strength analysis foroperational conditions, postulated accidents, etc.). In Ger-many the atomic energy act [1] requires that ‘‘every necessary

precaution has been taken in the light of existing scientific

knowledge and technology to prevent damage resulting from

construction and operation of the installation’’. This has beenrealised in guidelines and in the nuclear standards [2–4] withtheir indications and requirements for plant safety. Accordingto these documents it has to be ensured that:

�

safety with respect to the quality of the systems,structures and components (SSC) is provided by thedesign, the material and the manufacture;

e front matter r 2006 Published by Elsevier Ltd.

vp.2006.07.008

ing author. Tel.: +49 711 685 2604; fax: +49 711 685 3144.

ess: eberhard.roos@mpa.uni-stuttgart.de (E. Roos).

�

the quality of the SSC has to be guaranteed anddocumented throughout the lifetime (extensivequality assurance during design, manufacture, andoperation); � the operational parameters (damage mechanisms) rele-

vant for the integrity of the SSC are monitored and

� operational experience is recorded continuously and

safety-related information is evaluated.

Therefore, the guidelines and standards contain all therequirements for a safe operation throughout the lifetime(lifetime management), for the control of ageing phenom-ena (ageing management) as well as for proof of integrity(e.g. with the aim to demonstrate break exclusion) formechanical SSC, Fig. 1.In Germany the discussions on ageing of mechanical

SSC to be included in a structured ageing managementprocess for nuclear power plants started at the beginning ofthe 1990s [5,6], Fig. 2.

ARTICLE IN PRESSE. Roos et al. / International Journal of Pressure Vessels and Piping 83 (2006) 756–766 757

2. Definitions and methodology

2.1. Lifetime management and classification of the

components

Lifetime management, Fig. 1, stands for the integrationof ageing management and economic planning for SCC inorder to

�

Fig

and

optimise the operation, the maintenance and the lifetimeof the plants,

� maintain an accepted level of safety and performance, � maximise return on investment over the lifetime of the

plant.

Various engineering measures are required depending onthe safety relevance of the SSC or for reasons of preventive

for mechanicalcomponents

. 1. Correlation between lifetime management, ageing management

proof of integrity for mechanical systems, structures and components.

Fig. 2. Relevant ageing management act

maintenance [7–10]. Consequently, the SSC have to bedivided into three groups, Fig. 3.The first step within the scope of lifetime management of

mechanical components is to select and arrange the SSCand to assign these to group 1, 2 or 3. The classification isaccording to the requirements of the nuclear codes andstandards (RSK-guidelines, KTA) and if necessary accord-ing to plant-specific and safety-related factors. The plantoperator is responsible for the classification and an experthas to check it on the basis of the current codes, standardsand the state-of-the-art.

�

iviti

Group 1: Failure of the SSC shall be excluded to avoidsubsequent damage, e.g. reactor pressure vessel(RPV) and main coolant lines (MCL). The requiredquality shall be guaranteed for subsequent operation.The causes of possible in-service damage mechanismsshall be monitored and controlled (proof of integrity)[11]. Implementing this ‘‘proactive approach’’ preventsdamage.

� Group 2: For redundant SSC the failure of a single

part is allowable from a safety relevant point ofview. However, common mode failure shall beexcluded. The present quality shall be maintainedfor subsequent operation. The consequences ofpossible in-service damage mechanisms shall be mon-itored (preventive maintenance, time- or condition-oriented).

� Group 3: There are no defined standards for the quality

of the SSC concerning subsequent operation (failure-oriented maintenance).

es in Germany—an overview [6].

ARTICLE IN PRESS

LifeTim e

Management

Age

ing

Man

agem

ent

Inte

grit

Failure of a single SSC is allowed,

common-mode-faiure must be excluded (group 2)

Failure of a SSCmust be excluded

(group 1)

No specificrequirement for the quality of the

SSC for the ongoing operation(group 3)

LifeTime

Management

Age

ing

Man

agem

ent

Proo

f of

Inte

grity

Failure of a single SSC is allowed,

common-mode-faiure must be excluded (group 2)

Failure of a SSCmust be excluded

(group 1)

No specificrequirement for the quality of the

SSC for the ongoing operation(group 3)

Fig. 3. Application of lifetime management, ageing management and proof of integrity for mechanical systems, structures and components of groups 1–3.

E. Roos et al. / International Journal of Pressure Vessels and Piping 83 (2006) 756–766758

2.2. Aging phenomena and engineering measures

Ageing stands for the time-dependent gradual change offeatures and properties related to their function, e.g.regarding

�

the engineering (mechanical SSC, buildings, electricalequipment), � the systems and control devices relevant to the operation

of the plant,

� the specifications and the documents, � the plant operating staff.

This also takes into consideration the development of thestate-of-the-art (science and technology). Furthermore, it ispossible that conceptual design and engineering methods aswell as administration rules may become obsolete com-pared to the state-of-the-art.

Ageing management, Fig. 1, covers all engineering andorganisational actions for the plant operator to guaranteesafe operation during the lifetime including control of theageing phenomena.

Ageing management of mechanical SSC is the entirety oftechnical and organisational measures that guarantee thesafe operation of the SSC for the lifetime by engineeringmeasures and maintenance actions including ageing phe-nomena within acceptable limits. It has to be distinguishedbetween

�

conceptual aspects (modification of requirements, mod-ification of safety philosophy), � technological aspects (latest results on possible in-

service damage mechanisms, on material properties ofcomponents, on test methods, on analysis methods, onassessment methods, etc.),

� material-mechanical or physical aspects (in-service

damage mechanisms caused by changes in materialcharacteristics, by in-service loads and by in-serviceenvironmental conditions, Fig. 4).

The terms technological and material-mechanical ageingare used as a synonym for all technical and organisational

measures that guarantee the recording, monitoring andcontrol of all possible in-service damage mechanisms.Causes and consequences of the in-service damagemechanisms are to be monitored or supervised. Further-more, follow-up actions have to be carried out and anychanges in current knowledge have to be recorded. Thesedefinitions and considerations are also in accordance withinternational procedures and methodologies, e.g. in [12].Within the proof of integrity, Fig. 1, it has to be

demonstrated that the load-bearing capacity is maintainedfor all relevant operational loads as well as accidental loadsfor the lifetime taking into account the specified ormonitored number of load-cycles.The proof of integrity for SSC assigned to group 1 is

according to the fundamentals of the German basis safetyconcept (concept of break exclusion or avoidance offracture) [13,14], Fig. 5. Consequently, ‘‘independentredundancies’’ will be effective since they are included inthe basis safety concept to consider also any possiblechanges in operational conditions influencing the integrityof the SCC and to guarantee quality after manufacture,Fig. 6. A systematic procedure which is oriented on thebasis safety concept, requires the following points to beconsidered to guarantee the integrity of components (forsubsequent operation) such as, Fig. 7:

�

The actual (as-built) state of quality (performance,design, loading) shall be in accordance with theparticular requirements (guidelines, codes, standards).There has to be sufficient knowledge about thepossible in-service damage mechanisms in the SSC,Table 1. � This state of quality shall be guaranteed for subsequent

operation byJ in-service monitoring of the causes of possible in-

service damage mechanisms and assessment of thedata recorded (continuous measures),

ARTICLE IN PRESS

Basis Safety Concept:Exclusion of Catastrophic Failure

R & DW ork Continuous/Repeated

In-seviceMonitoringSurveillanceNonD estructiveExamination

Codes and

Design andOperationFractureMechanicsIrradiationNon DestructiveExamination

Incredibility of Catastrophic FailurePrinciple

•

Codes andStandards

OptimisationQualificationControl

DesignMaterialManufacturing

IndependentQualityAssurance

PlantMonitoring

DocumentationPrinciple

Multiple PartiesTestingPrinciple

QualityThroughProductionPrinciple

Worst CasePrinciple

ValidationPrinciple

Basis Safety Independent Redundancies

•

•

•

•

••

• ••

•

••

FailureInvestigationv

Fig. 5. German ‘‘Basis Safety Concept’’.

Environmentally AssistedCracking (EAC)

- Stress CorrosionCracking (SCC)- Strain Induced Corrosion Cracking (SICC)- Corrosion Fatigue (CF)

STRESSES

Plastic Deformation

Fatigue

- Defornmation- Ratcheting

- Matrerial no resistant- Electro-chem. attack

ENVIRONMENTMATERIAL

Surface corrosionPittingSelective corrosionErosion-corrosion

- Mechanical and thermal loads- Change of material caused by operation

- Unfavourable state of material- Local stresses- Unfavourable (local) environment

Fig. 4. Causes and consequences of damage mechanisms for mechanical components.

E. Roos et al. / International Journal of Pressure Vessels and Piping 83 (2006) 756–766 759

J in-service monitoring as well as periodic examina-tions (discontinuous measures) of the consequencesof possible in-service damage mechanisms and

J follow-up of the state of present knowledge (review-ing the state of knowledge, consideration of researchresults and follow-up investigations of failure cases).

SSC are to be assigned to group 2 if they are of safety-related importance, but may fail in single cases. In doing soit shall be ensured that measures have to be taken duringoperation to maintain the present quality and to exclude‘‘common-mode’’ failure. Subsequent failures are of no

effect from the safety-related point of view. To maintainthe quality requires preventive maintenance (time-orientedor state-oriented), Fig. 7.SSC are to be assigned to group 3 if failure cannot be

definitely excluded and subsequent failures are considerednegligible from the safety-related point of view. There areno defined demands on the quality in service. It is sufficientto maintain measures against failures.The safety-related important SSC shall be included in

group 1 as defined in Chapter 1 ‘‘application range’’ ofKTA Safety Standard 3201.2 [4] as well as in the GeneralSpecification ‘‘Basis Safety of Pressurized Components’’ [3].

ARTICLE IN PRESS

Operation

Bas

is S

afet

y

• D

esig

n•

Mat

eria

l•

Man

ufac

ture

Component Integrity

FailureMechanisms

Inde

pend

ent R

edun

danc

ies

Consideration of

Mul

tiple

Par

ties

Tes

ting

Wor

stca

seP

rinci

ple

Pla

nt M

onito

ring

and

Doc

umen

tatio

nP

rinci

ple

Val

idat

ion

Prin

cipl

e

Change of

Causes

-MaterialBehaviour

- Loading

- Environ-ment

Conse-quences- Wall Thinning- Grooves- Crack Formation- Crack Growth- Leckage- Failur / Break- Malfunction

Knowledgeby-Experience-Research-Development-Technical Codes

Methods-In-service Monitoring-Non-

DestructiveExamination

-FractureMechanics

Quality-andSafety Analyses

Fig. 6. Concept to prove the integrity of components.

Group 2

Group 3

Group 1

AGEINGConceptual Technological

Qualityafter

Design

Quality afterManufacture

(As-built)

As-bulit Qualityafter some time of

operation

Componentfailure

Subse-quent

damage

Req

uire

men

ts a

ccor

ding

tosp

ecifi

catio

ns;

spec

ific

desi

gn(m

ater

ial,

mau

fact

ure,

shap

e, d

imen

sion

s,lo

adin

g, p

ostu

late

d fla

ws)

Mat

eria

l sel

ecte

d,as

-bui

lt sh

ape

and

dim

ensi

ons,

dete

cted

find

ings

Leak

age

Bre

akW

ear

Fric

tion

... Sub

sequ

ent f

aliu

re o

fre

dund

ant c

ompo

nent

s;da

mag

e of

adj

oini

ngsy

stem

e;flo

odin

g;...

Physical Ageing

Load

ing,

Env

irnm

ent,

Cha

nge

of m

ate-

rial c

hara

cter

istic

Fat

igue

,C

rack

initi

atio

n,C

rack

gro

wth

,Le

akag

e,in

crea

sed

fric

tion,

...

Causes Consequences

PROOF OF INTEGRITY

PREVENTIVE MAINTENANCE

FAILURE ORIENTATED MAINTENANCE

Fig. 7. Correlation between the state of quality as well as ageing and related to the groups 1–3.

E. Roos et al. / International Journal of Pressure Vessels and Piping 83 (2006) 756–766760

3. Quality of components after design and manufacture

Requirements on material, design, calculation, construc-tion and fabrication are included in guidelines, codes andstandards and in the General Specification ‘‘Basis Safety

of Pressurized Components’’ [3] as well as in specifi-cations. It is the responsibility of the plant operatorto prevent damage resulting from construction andoperation of the plant in accordance with the state-of-the-art [1,2].

ARTICLE IN PRESS

Table 1

Causes, consequences and proof of damage mechanisms

Damage mechanisms Causes Consequences Analysis/proof

Plastic deformation Overload (excess load) (unspecified or

unknown loading conditions)

Plastic deformation,

collapse

Stress analysis, limitation of primary

stresses sactualosallowable, operationalin-service monitoring

Corrosion SCC Type and level of loading,

environmental conditions, state of

material

Crack formation, crack

growth

Stress analysis, operational in-service

monitoring (load, medium), choice of

material, limited crack growth (da/dN

or da/dt neglectable), ISI and

periodical inspection

SICC

CF

Erosion–corrosion Environmental conditions, state of

material, geometrical conditions,

piping layout, mode of operation

Plane wall thinning

(surface corrosion, local)

Wall thickness measuring, operational

in-service monitoring

Fatigue High mechanical and/or thermal loads

and corresponding number of load

cycles

Crack formation Fatigue analysis, usage factor Do1,

operational in-service monitoring, ISI

and recurrent inspection

Wear Type and level of loading, state of

material

Influence on functioning Wall thickness measuring, operational

in-service monitoring

E. Roos et al. / International Journal of Pressure Vessels and Piping 83 (2006) 756–766 761

The assessment of the actual design and construction isbased on requirements included in the KTA safetystandards [4] and in the RSK-guidelines [3] as well as thespecifications to be considered which show the state ofquality obtained within the scope of design and fabrication.The following items are of concern

�

Materials:J As-built status corresponds to the requirements

stated in the specifications.J The materials selected correspond to their applic-

ability (the mechanical and thermal loads have to beconsidered; sufficiently resistant against the environ-mental conditions).

J Mechanical-technological and fracture-mechanicsproperties (base material and weld metal).

J Product form, low sensitivity against all manufactur-ing processes especially welding.

J Type and extent of testing, test certificates (accep-tance certificates).

�

Construction and layout:J As-built status corresponds to the requirements

stated in the specifications (dimensions, shape/struc-turing, welds and weld shapes, supports, repairmeasures, etc.).

J The construction shall be in conformity withsuitability for the intended function, with suitabilityfor strength, intended material, intended manufac-ture (suitability for testing/fabrication) and easymaintenance and inspection.

J A clear piping layout including supports anddampers.

�

Strength behaviour:Determination of the relevant stresses on the basis ofspecified loads by stress analysis, fatigue analysis andfracture-mechanics analyses. � Inspections performed (state of findings):

Results of inspections, e.g. non-destructive testing(NDT), within the scope of manufacturing and specialtests.

The SSC quality assessed after design and manufacturerepresents the state prior to commissioning. Consequently,the results cannot be transferred to the actual as-built stateof the SSC. Deviations have to be balanced out dependingon the requirements such as detailed proofs, extended in-service monitoring, recurrent tests and optimised mode ofoperation.

4. Change of component quality during operation by possible

damage mechanisms

Damage occurring in SSC may be caused by unfavour-able interaction of the parameters in Fig. 4:

�

Changes of the material characteristics during opera-tion. � Changes of the applied loads (e.g. mechanical, thermal

stresses).

� Changes of the environmental conditions.

These mechanisms are able to damage the SSC due tooperation and shall be controlled by measures, which resultin

�

no inadmissible change of the material characteristicsand � no inadmissible loading conditions (operational loads

are recorded and well-controlled, no inadmissibledynamic loads).

The loads are mainly recorded using in-service monitor-ing. On the one hand, this is by standard instrumentation(recording of global and local parameters) such as

ARTICLE IN PRESSE. Roos et al. / International Journal of Pressure Vessels and Piping 83 (2006) 756–766762

monitoring of important operational parameters and datato record global loads. On the other hand, it is bymeasuring the chemical water composition, e.g. [15] andlocal strains. It has to be ensured that for the determinationof the position to be instrumented, the measured variable,the extent of measuring and the measuring equipment, theoperational parameters, the mode of operation and the functioning of active components (e.g. snubbers, valves) areconsidered in the abovementioned sense. Because of theseaspects, measures to monitor the causes of possible operational in-service damage mechanisms, which meanschecking the influencing parameters, is of the highest priority and is indispensable for the SCC assigned to group 1.

Monitoring of the conseqoperational damage mechanism

(e.g. non destructive testing, monidestructive testin

I

ar st

no

yes

Assessment ofthe present

design

Redunda(e.g. detailadditional

Requirementsof the „Basis Safety“

are fullfilled?

Evaluation of the a

Identification and monipossible operational da

mechanical and thermalloads

Evaluation of the loae.g. stress analysis,

fracture mechan

Determination of measuconsequences of operation

areas ofrelevance

temet

Evaluation of thgeneral concep

Additional measu

Determination ofoperational damage

mechanisms

no

yes

Fig. 8. Component integrity ac

Concerning SSC assigned to group 2 the consequences ofdamage shall be monitored or checked using periodicaltesting and in-service monitoring to control operation [4].The consequences of damage can affect the quality and/orthe functionality of an SSC and may lead to failure. Suchconsequences are, for example, wall thinning, notchformation and crack initiation, crack growth, leakage,fracture, etc. Methods are implemented depending on thepossible in-service damage mechanisms, e.g. [16]. For SSCof group 1 this requires redundancy in representative areas.The procedure concerning the monitoring of the causes

and consequences of in-service damage mechanisms in SSCis established in KTA 3201.4 [4], Fig. 8.

uences ofs to be assumed

toring of loose parts,g)

ti

no

Determination ofthe relevant

loading conditions

nt measuresled analyses, monitoring)

Specifiedloads are

kept?

ctual state of quality

toring of the causes ofmage mechanisms

water chemistry

ds and strength fatigue analysis,ics analysis

res to monitor the al damage mechanismssthod

testinterval

et Closed concept

res

no

yes

positive

Pre

sen

t Q

ual

ity

Gu

aran

tee

Op

erat

ion

Ch

ang

es o

f th

e st

ate

of

the

art

cording to KTA 3201.4 [4].

ARTICLE IN PRESSE. Roos et al. / International Journal of Pressure Vessels and Piping 83 (2006) 756–766 763

5. Procedure for application to mechanical SSC

5.1. Proof of integrity for group 1 SSC

The integrity shall be proved within the scope of thelifetime or ageing management only for mechanical SSCassigned to group 1, Figs. 3 and 6–8. The following pointshave to be dealt with [11]:

�

Documentation and assessment of the actual (as-built)state of quality according to the respective requirements.Documentation and assessment of the actual design isaccording to the requirements on the material and theconstruction (design and calculation, layout) includingmanufacture. These requirements are laid out in theKTA safety standards and the RSK-guidelines includingthe general specification basis safety and specificationsto be considered.The relevant loads shall be determined and must bechecked within the scope of thJ Stress analysis (relevant stresses on the basis of

recorded data for operational loads and specifiedloads for accidental conditions taking into accountthe actual design).

J Fatigue analysis (equivalent stress range resultingfrom the relevant loads and limitation of the fatigueusage factor based on the number of load cycles; thisis of importance for the determination of therecurrent non-destructive inspection intervals).

J Fracture-mechanics analyses shall be performed forthe minimum flaw sizes detectable by recurrent non-destructive testing, for postulated flaw sizes and, ifneeded, for flaws caused by possible in-servicedamage mechanisms. Postulated flaw sizes have tobe assessed in relation to their critical size under in-service loads including the specified accidental loads.In determining the crack growth for the time of theinspection intervals the relevant in-service loadsshould be assumed. In case of determining oper-ationally related flaws the critical size under in-service loads, e.g. relevant loads from in-servicemonitoring, including the specified accidental loadsare to be assessed and as a function of the damagemechanism crack initiation and crack growth are tobe determined.Determination of possible in-service damage mechan-

isms: It needs to be clarified whether in-servicerelated damage mechanisms may occur. Therefore,possible damage mechanisms shall be excluded orshall be identified in view of operational experienceand the NDT results, as well as the present state ofknowledge. The parameters that cause corrosion aswell as the state after manufacturing are to becompiled according to the present state of knowledgefor austenitic and ferritic materials.

�

The required state of quality shall be guaranteed forsubsequent operation.

Identification and monitoring of the causes of possible

operational damage mechanisms: The proven quality ofan SSC after manufacture or a certain time in operationshall be maintained during subsequent operation. Thein-service monitoring of the plant is of greatestimportance with the first priority to monitor the causes(influencing parameters) of possible in-service damagemechanisms (see Table 1). Monitoring of the mode ofoperation (corresponding to the specified values or not;pressure, temperature, displacements, water chemistry)includes leakages occurring in the valves. The mechan-ical, thermal and corrosive loads have to be kept withinspecified limits. Knowledge about the actual loads isimportant because they are the basis for the stressanalysis, fatigue analysis and fracture-mechanics ana-lyses.Defining the influencing parameters for the causes of the

damage mechanisms and their recording: The extent of in-service monitoring is to be defined on the basis of theassessment of the actual state of quality. The purpose ofthe standard instrumentation is to monitor the variablesof state and data necessary for the integrity of the SSC.The purpose of the in-service monitoring and therecurrent inspection is to guarantee the basic SSC designassumptions, especially loads (mechanical, thermal, cor-rosive) remain constant during operation and recordprobable changes. Furthermore, the in-service monitoringshall demonstrate that dynamic loads can be excluded andquasi-static global and local loads which are relevant tothe integrity of the SSC can be recorded completely.Monitoring of the consequences of in-service damage

mechanisms: The procedure is based on the requirementsof the nuclear safety standard KTA 3201.4. The extent ofthe in-service monitoring is to be defined relative to thepossible damage mechanisms. This concerns the para-meters important to integrity and data to guaranteesubsequent operation (global and local measuring, leakagemonitoring) as well as the extent of the periodicinspections (NDT and destructive testing). These inspec-tions shall be applied to representative areas which resultfrom assessment of the most critical stressed areas andshall monitor the consequences of possible damagemechanisms. The inspection methods and definition ofthe intervals is component-related depending on thecomponent quality in relation to the damage mechanismsto be expected. The results of fracture-mechanics assess-ments for critical crack sizes and crack growth rates shallbe considered. The investigation of removed parts is alsopart of the in-service monitoring. When changes, repairsand maintenance measures take place, consideration hasto be made about the type of investigation performed onremoved parts to extend knowledge and to optimise theassessment concept. When selecting the test method, theareas monitored and the test intervals, the followingaspects have to be considered:

J

Knowledge about the causes of operation-relateddamage mechanisms.

ARTICLE IN PRESSE. Roos et al. / International Journal of Pressure Vessels and Piping 83 (2006) 756–766764

J

Actual knowledge about the state of the plant andoperational loads.

J

Knowledge from failure analyses and destructiveinvestigations performed on removed parts.

J

Knowledge from fracture mechanics assessment ofminimum detectable flaw sizes or postulated flaw sizes.

5.2. Preventive maintenance for group 2 SSC

Preventive maintenance of the state of quality forsubsequent operation is to be kept and guaranteed forSSC assigned to group 2. Relevant failures have to bechecked (monitoring of consequences of operationaldamage mechanisms). Consequential failures have no effectin view of the safety relevance. This means that the actual(as-built) state of quality has to be maintained forsubsequent operation. This takes place by preventive (time-or condition-oriented) maintenance

�

Demonstration and assessment of the state of qualityaccording to particular requirements.J Demonstration and assessment of the actual design

according to the requirements of the KTA safetystandards, the RSK-guidelines including the generalspecification basis safety as well as specifications andstandards. This concerns the requirements on thematerial and construction (design and calculation)including manufacture.

J Results of tests performed (state of findings ofmanufacture, NDT, etc.).

J Operational experience (mode of operation, datarecords and results of operational in-service monitor-

DATA BA

Improve AMP

effectiveness

Correct

unacceptable

degradation

PLAN

Coordinati

(ageing manageme

Group 1 S

Group 2 S

Group 3 S

CHECK

monitoring, ana

evaluatio

(detecting and a

ageing of the

ACT

correction measures

(managing ageing

effects)

Fig. 9. Ageing management procedu

ing, failure investigations, NDT, maintenance mea-sures, etc.).

J Determination of the damage mechanisms.

SIS

on

nt p

SC

SC

SC

lys

n

ss

effe

re

�

Operational in-service monitoring and maintenancemeasures (time or condition oriented).The preventive maintenance can be organised in thefollowing areasJ Maintenance (measures to keep the nominal condi-

tion).J Inspection and measurement (measures and actions

to determine and asses the actual as-built status).J Repair work (measures to restore the required state

of quality).

5.3. Failure-oriented maintenance for group 3 SSC

Mechanical SSC assigned to group 3 are allocated tofailure-oriented maintenance and are not to be consideredwithin the scope of ageing management.

6. Technical and organisational measures

The engineering and organisational measures requiredwithin the scope of the ageing management of mechanicalSSC are oriented essentially on the recommendations byRSK and the criteria compiled by the BMU projectSR2319 [17]. A database embedded in a Deming-process(PDCA-cycle) [18,19] is the essential element containing allinformation relevant to ageing management, Fig. 9.Running through the PDCA cycle the appropriateorganisational units have access to information in thedatabase which can be updated and if need be completed

DODODO

Minimize

expected

degradation

Check for

degradation

rogram)

preventive measures

(managing ageing

mechanism)

is and

essing

cts)

(PDCA-cycle) [18,19].

ARTICLE IN PRESSE. Roos et al. / International Journal of Pressure Vessels and Piping 83 (2006) 756–766 765

by necessary measures. This guarantees the availability ofcomplete and updated information for all participants inthe ageing management process (AMP). Additional in-formation concerning operational damage mechanisms isincluded e.g. in [20,21].

The results obtained from research, technical publica-tions, as well as circular letters and notifiable events and ifneeded findings from other accessible databases have to beconsidered. The data are to be integrated into the powerplant organisation according to a PDAC-cycle, Fig. 9. Thisincludes in particular the following aspects:

�

‘‘Plan’’ (coordination)—co-ordinating ageing manage-ment activities.J Documents the regulatory and the expert require-

ments and safety criteria.J Considers the development of the nuclear codes and

standards, of the safety criteria and of guidelines aswell as relevant activities.

J Describes and up-dates the organisational and co-ordination mechanism.

J Optimises, if necessary, the ageing managementprogramme based on current state-of-the-art.

�

‘‘Do’’ (preventive measures)—managing ageing mechan-ism.J Operation according to the procedures and technical

specifications.J In-service monitoring of the water chemistry and the

environmental influences.J Documentation of the mode of operation (history)

including transient records.

� ‘‘Check’’ (monitoring, analysis, assessment)—detecting

and assessing ageing effects.J Recording of the causes and consequences of damage

mechanisms by online in-service monitoring andrecurrent tests as well as data recording.

J The as-built status is to be compared with thenominal condition and the changes to be expecteddue to ageing are to be assessed.

�

‘‘Act’’ (correction measures)—managing ageing effects.J Preventive and corrective maintenance.J Replacement and maintenance history.

7. Concluding remarks

Guidelines, codes and standards contain regulations andrequirements with respect to the quality of mechanical SSCof nuclear power plants. This concerns safe operationduring the total lifetime (lifetime management), safetyagainst ageing phenomena (ageing management) and proofof integrity (e.g. break exclusion). Within this, ageingmanagement is a key element. Depending on thesafety-relevance of the SSC under observation, includingpreventive maintenance, various engineering measuresare required. In particular to be considered in thisconnection are the mechanisms which contribute system-

specifically to the damage of the mechanical SSC anddefine their controlling parameters which have to bemonitored and supervised by appropriate continuous ordiscontinuous measures. The approach to assure the highstandard of quality in operation and the processing of thetechnical and organisational aspects are demonstrated andexplained.

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