2008 INTERNATIONAL CONFERENCE ON PROGNOSTICS AND HEALTH MANAGEMENT

Proactive Management of Materials Degradationfor Nuclear Power Plant Systems

Leonard J. Bond, Senior Member IEEE, Tom T. Taylor, Steven R. Doctor, Senior Member IEEE, AmyB. Hull, and Shah N. Malik

Abstract- There are approximately 440 operating reactors inthe global nuclear power plant (NPP) fleet that have an averageage greater than 20 years and design lives of 30 or 40 years. TheUnited States is currently implementing license extensions of 20years on many plants, and consideration is now being given to theconcept of "life-beyond-60," a further period of license extensionfrom 60 to 80 years and potentially longer. In almost all countrieswith NPPs, authorities are looking at some form of licenserenewal program. There is a growing urgency as a number ofplants face either approvals for license renewal or shut down,which will require deployment of new power plants. In supportof NPP license renewal over the past decade, various nationaland international programs have been initiated.

This paper reports part of the work performed in support ofthe U.S. Nuclear Regulatory Commission's (NRC's) ProactiveManagement of Materials Degradation (PMMD) program. Thepaper concisely explains the basic principles of PMMD and itsrelationship to advanced diagnostics and prognostics andprovides an assessment of some the technical gaps in PMMD andprognostics that need to be addressed.

Index Terms- materials damage prognostics, materialsdegradation, NPP license renewal, proactive management

I. INTRODUCTION

THERE are approximately 440 operating nuclear powerreactors in the current global fleet located in 30 countries

that fall into six basic design types. The two most commondesign types are pressurized water reactors (PWR) and boilingwater reactors (BWR), which account for 265 and 94 of theoperating reactors, respectively. All of the 104 commercialpower reactors operating in the United States are either of thePWR or BWR design types. The average age for this fleet ofreactors is more than 20 years, and the initial design liveswere either 30 or 40 years. The existing nuclear power plants

Manuscript received May 18, 2008. This work was supported in part by theU.S. Nuclear Regulatory Commission (NRC), Office of Nuclear RegulatoryResearch under contract N6019.

L. 1. Bond is with Pacific Northwest National Laboratory, Richland, WA99352 USA (corresponding author 509-372-4172, fax: 509-375-6497; e-mail:leonard.bond@pnl.gov ).

T. T. Taylor and S. R. Doctor are with Pacific Northwest NationalLaboratory, Richland, WA 99352 USA.

A. B. Hull and S. N. Malik are with the U.S. Nuclear RegulatoryCommission, Washington DC 20555 USA.

are considered too valuable to discard at the end of their initialdesign lives. The cost of building replacement generatingcapacity, and at the same time providing new plants that meetthe growth in demand for electricity, would test the availabletechnical, regulatory, and economic infrastructures. It istherefore important to see where technology can help tomanage existing power plants more effectively, enable licenseextension for the existing fleet, and contribute to both newadvanced light-water reactors (LWRs) and other advancednew designs with initial design lives of 60 years, all within thelimits set by demanding materials and operationalrequirements.

In a number of countries, there are programs designed toenable operating license extension beyond 30 years and inothers extend the operating license from 40 to 60 years. TheUnited States has already established a process for plantassessment and license renewal from 40 to 60 years, and it isexpected that more than 90 percent of current plants will seekNPP license renewal. Consideration is being given todetermine if it is feasible to extend operating lives further with"licensing beyond 60," extending operation to 80 years andpotentially longer. Long-term NPP operation requires that thetechnical challenges related to detecting, characterizing,monitoring, and managing materials degradation andremaining life prediction (prognostics) need to be identifiedand addressed.

All parts of an NPP are subject to the continuousdegradation of materials due to normal service conditions,which include normal operation and transient conditions;postulated and post-accident conditions are excluded. Thesetime-dependent degradation phenomena can potentially causeall parts of a nuclear power plant system to lose their designfunction partially or totally. If not managed, degradationbecomes a problem for all nuclear components because theirsafety margin in terms of material properties can potentiallybe reduced. The generic aging lessons that have been learnedin the United States for legacy nuclear plants are discussed indetail in two extensive reports [1], [2]. License renewal(following NRC Regulations, Title 10, Code of FederalRegulations Part 54: 10 CFR 54.21) addresses passivesystems, structures, and components that perform an intendedfunction without moving parts or a change in configuration orproperties. These insights from license renewal aresupplemented by a report prepared by an expert panel that

2008 INTERNATIONAL CONFERENCE ON PROGNOSTICS ANII

assessed proactive materials degradation applied to legacyplants and tabulated data on materials and specificcomponents susceptibility to known or expected degradation[3]. The information in this report has now been put into theform of an Information Tool which can be accessed and usedon the web [see website http://pmmd.pnl.gov ]

In order to ensure safe long-term NPP operation, it isincreasingly necessary to adopt new approaches and modifycurrent operation and maintenance practices. At the heart ofthe new approaches is proactive management of materialdegradation (PMMD), which moves degradation assessment(at the time of measurement and prediction of future state ­prognosis) and its management from a reactive mode to aproactive one through understanding, monitoring, andmanaging materials degradation/aging processes and plantoperational parameters to optimize life-cycle economics whilemaintaining the highest levels of safety.

II. DIAGNOSTICS AND PROGNOSTICS: STATE OF THE ART AND

POTENTIAL

The past decade has seen significant development withinboth the nuclear and wider engineering communities from theuse of periodic nondestructive testing (NDT) to condition­based maintenance (CBM) and advanced life management.These activities have been called by various names, includingstructural health monitoring, material damage prognostics, andPMMD. Where these approaches have been applied, they havebeen implemented, in most cases, with on-line methodsdeveloped for advanced monitoring and diagnostics. As theeconomic value of CBM and other advanced monitoringapproaches is demonstrated, there is increasing interest inprognostics, the prediction of the remaining safe or service lifefor both active components such as pumps as well as passivecomponents that do not need any external input, such as basicstructural materials, to operate.

A. Diagnostics

It was recognized in the mid-1970s that NDT needed tobecome a quantitative, science-based technology. Quantitativeresearch was initiated in the 1980s [4]. Many of themeasurement capabilities for nondestructive testing andevaluation (NDT/NDE) were identified as set by fundamentalphysics [5] . It was also recognized that there are differentlevels of performance that can be achieved in the laboratory,on production parts, and in-service.

Recent years have seen development of betterunderstanding of the NDT/NDE measurement processes andquantification of performance in terms of a probability ofdetection (POD) rather than a size for an ultimate detectionlimit. The operator or inspector is also recognized as a keyelement in the inspection system, and not all operatorsperform to the same level. The top 10% of inspectors havebeen found to perform at exceptional levels [6]. The medianinspector does not achieve similar reliability or sensitivity. Inpart to address performance reliability for in-service

inspection (lSI), there has been a move to automation. Thebest automated system can give repeatability, although itusually does not reach the ultimate sensitivity/detection limitsachieved by the best inspectors.

Advances in monitoring technologies from other industriescan potentially benefit both legacy and new nuclear powerplants, particularly when using advanced on-line monitoringand diagnostics for condition-based maintenance and, in thefuture, prognostics. Digital instrumentation/controls andadvanced diagnostics/prognostics are being developed inhigh-technology industry communities and are now beingconsidered for NPP deployment in the USA. There is aconvergence between materials damage prognostics [7]; thecivil engineering damage and damage evolution models undermultiple stressors; the traditional "vibration" monitoringcommunity looking towards new challenges in systems usedby the defense community [8]; technology to achieve totalstructural health management [9]; and the NDE communitylooking at aging due to thermal embrittlement, fatigue, andneutron degradation [10].

There have also been new approaches to the management oflife in mechanical systems [11 ] and research intocharacterization of materials in aging systems, particularlyearly-degradation phenomena that occur before the"traditional" defects (such as cracks) detected by conventionalNDT develop into flaws with sizes that are detectable [12].The trend of seeking to move from periodic NDE to on-linecondition-based maintenance started several years ago in otherindustries [6]. A review of the current paradigms and practicesin system health monitoring and prognostics has recently beenprovided [13].

There remain significant measurement challengesassociated with characterization of aging in NPP materials,and in particular irradiated reactor components [10], [14]. Anexample of one major series of activities moving from NDE tocharacterization of aging and degradation is found in the workof Dobmann and colleagues. In early papers, they reportedusing ultrasonic and micromagnetic techniques to measurestrength and toughness and detecting early damage [15]. Thisevolved into work that addresses the demand for describingdamage and service-related aging [16], which evolved into asignificant European project involving round-robin samplecharacterization [17] and bringing together condition­dependent NDT and fracture mechanics [18]. An increasinglydiverse range ofNDT/NDE tools are being considered in bothlaboratory and field studies [10], [12] for aging phenomenacharacterization, as shown with new applications of magneticmethods [10]. Techniques such as ultrasonic backscatter andacoustic birefringence are being investigated as possible toolsfor in-service monitoring. The development of concepts foradvanced on-line structural health monitoring for next­generation reactor designs such as the International ReactorInnovative & Secure (IRIS) has been initiated [19].

As this article is being written, 42 U.S. operatingcommercial NPPs have completed the license extensionprocess [see the NRC website http://www.nrc.gov/reactors/

operating/licensing/renewal!applications.html for detailedinformation on the license extension process in the U.S.].Every plant granted license extension has committed todeveloping the tools to manage degradation processes such asvoid swelling where no accepted or reliable detection ormeasurement technology presently exists. Therefore, theworking details of these degradation management programshave yet to be defined, and the regulator has to review oraccept these future programs.

To address these challenges, a convergence is developingthat is bringing together capabilities in the materials scienceand NDE communities.

B. Prognostics

Prognostics (for machinery) is the prediction of a remainingsafe or service life based on an analysis of system or materialcondition, stressors, and degradation phenomena. Based onobserved data and predicted behavior, moving fromdiagnostics to prediction of life and technologies for structuralhealth monitoring/management requires the development ofnew approaches. The range of developing approaches isillustrated in schematic form in Fig. 1. The various empiricalmethods for process and equipment prognostics have beenreviewed by Hines [20]. An extensive review of machinerydiagnostics and prognostics for condition-based maintenanceis provided by Jardine et al [21] but again, it does not considernuclear power systems.

An assessment of the state of diagnostics and prognosticstechnology maturity was recently provided [22]. The currentstatus for various system elements, including both active andpassive structures, is shown in Table I.Technologies are being developed for non-nuclearapplications (including instrumentation and system healthmonitoring for electronics) in what is being called "electronicsprognostics" [23]. There are also various life consumptionmonitoring (LCM) methods that are indirect, rather thandirect, for performing prognostics and health managementwhere environmental stress histories are collected by sensorsand damage is inferred from these. An example of theapplication of such an approach applied to electronic system isprovided by Ramakrishan and Pecht [24]. There are alsointegrated technologies being developed for advanced fighteraircraft and unmanned aerial vehicle system healthmonitoring, which include both electrical/electronic andmechanical systems. Within advanceddiagnostics/prognostics, systems have been deployed forindividual elements, but fully integrated systems are still beingdeveloped.

For the existing nuclear power plants, particularly when lifeextension is being developed, there are opportunities to deployon-line monitoring/prognostics, assuming it can be demon­strated that there is still remaining useful life in the plant. Keyto developing advanced prognostic schemes (in active systemssuch as pumps and valves) that give maximum warning ofdegradation focuses on monitoring the stressor rather than

Evolutionary orTrending Models(Data Driven, Feature­

Based Correlation),Expericnce-based

Prognostics(Failure PDFs. Fewsensors or model)

Range of System Applicability

Fig. 1. Range of prognostic approaches.TABLE I

ASSESSMENT OF STATE OF MATURITY FOR DIAGNOSTIC (D) AND PROGNOSTIC

(P) TECHNOLOGIES [23]

Diagnostic/Prognostic Technology for: AP(a) A(b) I(C) NO(d)

Basic Machinery (motors, pumps, D Pgenerators, etc.)Complex Machinery (helicopter D Pgearboxes, etc.)Metal Structures (passive and active) D PComposite Structures (passive and active) D&PElectronic Power Supplies (low power) D PAvionics and Controls Electronics D PMedium Power Electronics (radar, etc.) D PHigh Power Electronics (electric D&Ppropulsion, etc.)

(a) AP = Technology currently available and proven effective.(b) A = Technology currently available, but V&V not completed.(c) I = Technology in process, but not completely ready for V&V.(d) NO = No significant technology development in place.

V&V = Verification and Validation: is the process of checking that aproduct or system meets specifications and fulfils its intended purpose.

solely the subsequent effects of aging and degradation. Aschematic showing system operational performance andstressor magnitude is given as Fig. 2 [25], [26]. Themonitoring of the stressor (e.g., a temperature, cavitation,vibration, or a pressure) combined with active system controlparameter management across several precursors enables useof the "warning time" (~T in Fig. 2) to adjust operationalparameters and limit or at least control rates of degradation fora path to failure. In order for this type of strategy to besuccessful, physics-based models relating the stressors to therate of aging or degradation must be developed in theprognostic scheme.

To move from periodic inspection to on-line monitoring forcondition-based maintenance (and eventually prognostics)will require advances in sensors; better understanding of whatand how to measure within the plant; enhanced datainterrogation, communication, and integration; new predictivemodels for damage/aging evolution; system integration forreal-world deployments; quantification of uncertainties in

what are inherently ill-posed problems; and integration ofenhanced, condition-based maintenance/prognosticsphilosophies into new plant designs, operation, and operatingand maintenance approaches.

Stressor Amplitude Approach Prj \,. I P Pmat) or 'lrtua arameter

~--V~----'-""J~~' . NOBALERT

Reduced Cone/ of t Jnccrtainl)'

TIME

Fig. 2. Stressor Measurement Giving Time for Intervention Prior to Failure[24], [25].

III. PROACTIVE MANAGEMENT OF MATERIALS DEGRADATION

PMMD has the objective to identify materials andcomponents where future degradation may occur. In somecases, the degradation may involve phenomena not yetexperienced in the operating fleet but where there islaboratory data and/or a mechanistic understanding thatindicates that they may be pertinent to future reactoroperations.

PMMD includes the methodology and actions needed tomanage both active and passive elements in the nuclear powerplant systems throughout their existence to minimize theimpact of degradation, maintain safety, and potentially enableextensions to system operating life.

A. Relationship between PMMD and Prognostics

PMMD is the emerging technical and methodological basisneeded to support enhanced system management throughoutits life, including life-extension for legacy NPPs. Theseapproaches involve "sensing" material property changes andparameter trends that are precursors to traditionally monitoreddegradation mechanisms and phenomena (e.g., crack growth)that are detected by conventional NDT technologies such aseddy current or ultrasound. To be effective, PMMD needs tounderstand the phenomena of stressor-material interactionsand sense early precursor material property changes. Anexample of a possible degradation phenomenon could beradiation-induced void swelling. PMMD also includes theassessment of the impact of material degradation on thesystem or unit life-cycle.

Prognostics can be defined as being a "forecast of futureperformance and/or condition." Prognostics (for active andpassive components) is the prediction of a remaining safe orservice life based on an analysis of the system or materialscondition, stressors, degradation phenomena, and operatingconditions.

In the context of materials degradation assessment,prognostics is the science, enabling technology andmethodologies needed to predict the remaining safe (serviceor licensable) life and ensure operational reliability for asystem or sub-system. Prognostic methodologies can beimplemented in several ways but in all cases includedegradation phenomena, the driving stressors, and (in mostcases) models to predict the degradation rate and therebyextrapolate remaining life (or time at which intervention isrequired).

Such methods can therefore form a key element within aPMMD program by adding a "predictive" element to theproactive activities through the understanding andquantification of the rate of material degradation and resultantimpact on system safety/life. Prognostic methods also providea positive impact on Probabilistic Risk Assessment (PRA)through the ability to manage and schedule outages andmaintenance activities [26].

In understanding the relationship between PMMD andprognostics, it is helpful to understand some definitions withthe prognostics lexicon in this context:

Prognostics - The ability to predict reliably the remaininguseful life of mechanical components within an actionabletime period with acceptable confidence limits [27].

Prognostic Accuracy or Confidence Level - The accuracy interms of difference between the future forecast ofperformance or condition and the actual future valueachieved expressed as ± an amount or as a percentage of theforecast. It may also be applied to the accuracy of thepredicted time to failure, time to a given performancedegradation point or percentage, or the remaining usefullife.

Prognostic Horizon - The maximum time or relatedparameter (such as number of cycles) for which a givenPrognostic Technique will achieve a set accuracy orconfidence level. For example, technique "A" may achievea 90% prognostic accuracy with a horizon of 200 operatinghours, or Prognostic Technique "B" may achieve a 75%prognostic accuracy with a prognostic horizon of threecycles/missions.

Prognostic Metrics - Those measures of performance of aprognostic technique or system that characterize theperformance and predictive reliability of that technique orsystem for a specific application. These metrics mayinclude:- Demonstrated versus design prognostic accuracy­

confidence level.- Demonstrated versus design prognostic horizon.- Demonstrated reliability of the prognostic system versus

the system it monitors.- Applicability or robustness of the prognostic technique or

system - how many other applications can the techniquebe applied to with commensurate accuracy, reliability,and horizon attributes.

The reliability of prediction, in terms of both false positives

"Now" Time

Structural Integrity Limit

NDE Resolution Limit

Fig. 3. Schematic Diagram Illustrating Degradation, or Damage, Developmentwith Time, and the Differentiation between Reactive and Proactive Actions.Note that the degradation process vs. time is rarely linear, as is often assumed.

------- _--_ _--- _- ----_ _----_ _ _---------- _ ---------

-- __ .. _---p-----_.- .. _------

for these statements are outlined in detail in NUREG/CR6923 [3].

2) The proactive management of materials degradationincreases the available time for mitigation, which is afunction of the incubation time before significant damagestarts and the subsequent kinetics of accumulating damage.

3) Considering license renewal, power uprates, and thepotential for "life beyond 60" years, addressingdegradation in a reactive fashion has the potential to resultin an unacceptable loss of safety margin. Current reactivemanagement of materials degradation limits the timewindow following the damage observation during whichmitigation actions can be developed before anunacceptable degree or level of damage is reached. Thisconstraint may lead to the deployment of incompletemitigation strategies.

4) Extended operation of a nuclear power plant requires theplant owner to address two major issues concerningdegradation.a. Developing effective aging management programs for

known degradation as currently addressed in licenserenewal [1], [2].

b. Developing a technically based program to understandthe impact of stressors that can drive "damage" ormaterial life utilization and then detect and mitigateboth potential stressors and degradation that has not yethappened but has the potential to occur.

5) PMMD programs should include degradation mode­component combinations with applied stressors wherethere was a high susceptibility to degradation based inlarge part on multiple observations in operating plantsregardless of the knowledge level concerning degradation.

6) PMMD programs should include degradation mode­component combinations where there was little or noevidence to date of degradation in the plants but wherethere was sufficient evidence from laboratoryinvestigations to indicate that degradation in the plantsmight be expected in the future. Reference [3] hasidentified specific degradation mode-componentcombinations where the knowledge level of the systeminterdependencies is low and additional proactive actions

and unpredicted events, have potential for significanteconomic impacts. It is therefore important to boundreliability for predictions which causes quantification of theuncertainty within prognostic capabilities to be central to theimplementation of PMMD methodologies, particularlyconcerning its integration with and impact on PRA.

B. Basic Principles ofProactive Management ofMaterialsDegradation

The difference between reactive and proactive approachesto the management of materials degradation is illustrated inFig. 3. In the reactive management scenario, there is limitedtime following the damage observation during whichmitigation actions can be developed before an unacceptabledegree of damage occurs. This constraint may lead to thedeployment of incomplete mitigation strategies. The timeconstraint is considerably reduced in the proactivemanagement scenario, with the increase in available time formitigation development being a function of the incubationtime before damage starts and the subsequent kinetics ofdamage accumulation.

In order to meet the objective of a proactive materialdegradation assessment and management program, it isnecessary to understand stressors and assess various damageand damage accumulation rate/severity relationships forexisting and potential degradation modes, materials,environments, and operating states for the different LWRcomponents. This assessment may be based on formulationsfor the various stressor and damage-time relationships or moregenerally on the basis of operating and laboratory experienceand engineering judgment.

The six principles of proactive management of materialsdegradation were deduced from [3] and are highlighted toemphasize their importance.

1) Materials degradation has occurred in LWRs and willcontinue as long as LWRs are in operation. The trendwithin the nuclear power industry is to operate plants forlonger periods of time and at increased power levels. Thenumbers of power plants requesting power uprates I andsuccessfully applying for licensee renewal are examples ofthe trend. Material degradation (especially potential newmodes of degradation) will likely increase as NPPs areoperated for longer periods of time and at increased powerlevels. The use of alternate materials or modified operatingconditions may potentially counteract these factors but ingeneral are not fully qualified and can address only afraction of the degradation modes. The technical reasons

IThe NRC regulates the maximum power level at which a commercialnuclear power plant may operate. With other data, this power level is used inmany of the licensing analyses that demonstrate plant safety. This power levelis also included in the license and technical specifications for the plant. TheNRC controls any change to a license or technical specification, and thelicensee may alter these documents only after NRC approves the licensee'sapplication for change. The definition of power uprate is the process ofincreasing the maximum power level at which a commercial nuclear powerplant may operate.

(such as research) may be warranted if PMMD bymitigation is desired.

The overall approach to developing a proactivemanagement program for materials degradation involves twosteps. The first is to identify the components of interest thatmight undergo future degradation as completed in [3] (alsosometimes referred to as proactive materials degradationassessment, PMDA). The second step is to identify thetechnical gaps in plant programs that detect, characterize, andmonitor stressors resulting degradation in all LWRcomponents susceptible to future degradation. The technicalgaps may require dedicated research projects to address theidentified technical deficiency (e.g., develop effectivemitigation strategies, inservice inspection and on-linemonitoring techniques, and repair procedures).

IV. TECHNICAL GAPS THAT NEED TO BEADDRESSED FOR PMMD

In understanding the nature of the challenge faced withinthe nuclear power community in moving towards PMMD, it ishelpful to first briefly provide an assessment of currentpractice and understand some of the current on-goingevolution of technologies. NDT has moved from being a"workmanship" standard to becoming part of a "fitness-for­service" assessment - combing inspection and evaluation ofindication significance using engineering mechanics methods.

There are already known to be significant opportunities todeploy new technologies when upgrades, includingmodernization of instrumentation and control systems, areimplemented at existing facilities. The economic benefit froma predictive maintenance program can be demonstrated from acost/benefit analysis. An example is the program for the PaloVerde Nuclear Generating Station [28]. An analysis of the 104U.S. legacy systems has indicated that the deployment of on­line monitoring and diagnostics has the potential for savings atover $IB per year when applied to all key equipment [29].On-line monitoring is now being deployed as part of new lightwater reactor plants; e.g., by AREVA in the new reactor atOlkiluoto in Finland [30]. New designs for advanced nuclearpower plants, such as those within the Gen IV program, willrequire longer intervals (potentially 4 years) betweenscheduled outages, and also shorter outages. To achieve suchperformance, enhanced on-line monitoring and diagnosticsbecome essential and these methods are those needed to applyPMMD to legacy systems.

There is now a trend in the United States, which is firmlyrooted in current methods, to move from periodic lSI tocondition-based maintenance. There is recognized to be anacute need to optimize maintenance to improve both reliabilityand competitiveness ofNPP within the energy sector. A recentIAEA report collects and analyses proven condition-basedmaintenance strategies and techniques in IAEA MemberStates [31] and this provides a useful benchmark regardingcurrent practice. In addition there has also been IAEA activity

to provide assessments for the state-of-the-art in on-linemonitoring, particularly in the context of the potential forimproving performance in NPP. The first of the two reportslooks at instrument channel monitoring [32] and the secondlooks at process and component condition monitoring,together with diagnostics [33]. As discussed earlier there arealso various research activities that are looking at the needsand potential for on-line structural health monitoring foradvanced reactors [18].

The move from advanced monitoring, lSI and condition­based maintenance (CBM), which is seeing increasingdeployment in legacy NPP, to PMMD involves a fundamentalphilosophical change: the move from being reactive tobecoming proactive. The current most advanced monitoring isbeing deployed, together with digital I&C systems, in newNPP outside the U.S. For example, the current CBM methodsand strategies are focused on active components (e.g., pumps,motors, valves) and PMMD includes and is central to theassessment of passive components (e.g., pressure vessel, coreinternals, concrete, and cables), ensuring reliability andprediction of remaining safe and service life.

Clearly, implementation of PMMD programs will requiresignificant basic and applied research. To date, discussion hasdivided the identified technical gaps into categories: thetechnical gaps that need to be addressed by basic science,those technical gaps in engineering, and those that need to beaddressed from a regulatory/codes and standards point ofview. The full scope of these needs is still being defined [34].

Examples of some gap areas are given below.

A. Gaps in Basic Science for PMMD

In order to move from a reactive mode to a proactive modewhen dealing with degradation, there are fundamentalmaterials science gaps that need to be addressed. The ElectricPower Research Institute (EPRI) has developed a detaileddescription of several gaps that require basic science todevelop reasonable solutions.

- Limited mechanistic understanding of environmentallyassisted cracking of reactor coolant system componentsin light water reactors: Material degradation problemsdue to environmentally assisted cracking have cost theU.S. nuclear industry at least $10 billion in the last 30years because of forced and extended outages, increasedinspection requirements, component repairs and replace­ments, and increased scrutiny by the regulator. A bettermechanistic understanding of crack initiation and earlycrack propagation processes that cause stress corrosioncracking and irradiation-assisted stress corrosioncracking is required to develop reliable predictive modelsand cost-effective mitigation technologies. The PrimarySystem Corrosion Research Program has the lead forovercoming this barrier [34].

- Incomplete understanding of the effects of some LWRwater-chemistry variables: Detailed understanding ofwater chemistry variables is essential in the design andimplementation of chemistry programs that limit

operational and maintenance impacts. Improvedunderstanding would enable plant owners and operatorsto define optimized chemistry programs on a plant­specific basis to reduce corrosion damage, minimize therelease of corrosion products into coolant systems, andmitigate the impact of chemistry-related problems onplant safety, operation, and profitability. The WaterChemistry Control Program has the lead for overcomingthis barrier [34].

B. Gaps in Engineeringfor PMMn

In order to move from a reactive mode to a proactive modewhen dealing with degradation, there are gaps in engineeringthat need to be addressed and require the basic science thatsupports the engineering solution. EPRI has developed adescription of several gaps that require engineering to developreasonable solutions.

- Lack ofan integrated, proactive approach for managingdegradation of reactor coolant system components inpressurized water reactors, including the steamgenerator: The lack of a comprehensive and integratedapproach for addressing materials degradation issues inPWR reactor coolant systems can result in ineffectivediagnosis and maintenance of nuclear equipment andcomponents. Refined approaches are needed to providethe technical bases for resolving four pressing issues:cracking of nickel-alloy components and welds inprimary piping and penetrations; reactor vessel internalscracking; reactor pressure vessel integrity; and pipingfatigue damage. The Materials Reliability Program hasthe lead for overcoming this barrier [31].

- Lack ofan integrated, proactive approach for managingdegradation of reactor coolant system components inboiling water reactors: The lack of a comprehensive andintegrated approach for addressing materials degradationissues in BWR reactor coolant systems can result inineffective diagnosis and maintenance of nuclearequipment and components. Refined approaches areneeded to develop strategies and technology that enableplant operators to inspect, assess, mitigate, and repairstress corrosion cracking in core shrouds, other majorreactor vessel internals components, and primarypressure-boundary piping. The Boiling Water ReactorVessel and Internals Program has the lead forovercoming this barrier [34].

C. Technical Gaps that Need to be Addressed within theFramework ofCodes and Standards Regulation

Currently, Section XI of the ASME Boiler and PressureVessel Code only specifies criteria for periodic inspectionsthat must be conducted for active and passive components.There is no specific guidance or criteria for PMMD programs.

V. CONCLUSION

The move from periodic inspections to condition-basedmaintenance and now consideration of prognostics has the

potential to significantly impact the operation of legacy andnew nuclear power plants. It has been demonstrated that theapplication of stressor-based prognostics to active LWRcomponents (e.g., pumps, valves, motors, etc.) has thepotential to reduce operations and maintenance costssignificantly. The proactive management of materialsdegradation program being investigated by the NRC extendsconsideration to include major passive systems (e.g. pipingand pressure vessels). It builds on advanced diagnostic andprognostic methods developed in the wider engineeringcommunity and addresses key needs as the nuclear powercommunity looks at extended operation, which in the UnitedStates is licensing beyond 60 years. To achieve the goals ofextended operation, various forms of on-line monitoring andpredictive remaining-life methodologies will need to bedeveloped and deployed.

ACKNOWLEDGEMENT

The work described in this paper was performed at thePacific Northwest National Laboratory, a multi-programnational laboratory operated by Battelle for the U.S.Department of Energy.

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[34] L. 1. Bond, S. R. Doctor, and T. T. Taylor, Proactive Management ofMaterials Degradation - A Review ofPrinciples and Programs. PacificNorthwest National Laboratory, PNNL-XXXX (in preparation).

Leonard J. Bond (S'76-A'77-M'92-SM'05)received his B.S. degree in applied physics in 1974and a Ph.D. degree in physics in 1978, both from theCity University, London, England. He is currently aLaboratory Fellow at the Pacific Northwest NationalLaboratory (PNNL) in Richland, Washington. Hebegan his career with British Gas and was then aresearch Fellow (Ministry of Defense) at the CityUniversity, London. Beginning in 1979, he heldvarious faculty positions at University College

London. In 1986, he spent the summer working as a guest scientist at the IowaState University Center for Nondestructive Evaluation, Ames. He waspromoted to Reader in Ultrasonics, University College London in 1990.

He took a sabbatical and worked at the National Institute of Standards andTechnology, Boulder, Colorado, starting in 1990, where he developed a high­pressure, gas-coupled transmission acoustic microscope. He remained in theUnited States and held posts as a research professor at the University ofColorado, Boulder and at the University of Denver, where he also was chiefscientist for the Denver Research Institute. He moved to PNNL in Richland,Washington, in 1998. His current research interests focus on diagnostics andprognostics, applied to energy, defense and process systems and the use ofultrasound for novel measurements. He has authored or co-authored more than230 papers, and holds nine patents.

Dr. Bond is a Fellow of the Institute of Physics (UK), a Senior Member ofIEEE, a Member of lEE/lET (UK), and a Chartered Electrical Engineer. He iscurrently Director-elect (2008) for IEEE Region 6.

Amy B. Hull received her B.S. degree inbiochemistry (chemistry) in 1980 from Iowa StateUniversity, Ames, Iowa and a Ph.D. degree ingeochemistry in 1987, from NorthwesternUniversity, Evanston, Illinois, focusing ondissolution kinetics. She began her career in 1980with the Nalco Chemical Company. She is currentlya Senior Materials Engineer in the Division ofEngineering, Office of Nuclear Regulatory Research,at the U.S. Nuclear Regulatory Commission (NRC).Beginning in 1987, she was a materials scientist inthe Corrosion Section at Argonne National

Laboratory (ANL), Argonne, Illinois. Over her 20-yr ANL career, she mainlyworked on projects for DOE (fusion reactor materials; radioactive materialspackaging, transportation, and disposal; international technology evaluation;

and NNSA initiatives for proliferation prevention), and NRC (NPP agingdegradation issues and license renewal). Following a two-year appointment asan Intergovernmental Personnel Act (IPA) detailee from ANL to NRC, shejoined NRC in 2006. Her current research interests include the proactivemanagement of materials degradation and evaluation of candidate structuralmaterials for new and advanced reactors. She has authored or co-authoredmore than 200 publications or reports and holds one patent. Dr. Hull is anactive member of ASME and ANS.

Shah N. Malik received his B.E. (mechanicalengineering) degree with Honors from University ofAllahabad, India in 1971; M.Tech. (mechanicalengineering) degree from Indian Institute ofTechnology, Kanpur, India in 1974; and a Ph.D.degree in engineering mechanics from the Ohio StateUniversity, Columbus, Ohio, in 1979. He is currentlya Senior Materials Engineer in the Division ofEngineering, Office of Nuclear Regulatory Research,at the U.S. Nuclear Regulatory Commission (NRC).During 1980-1984, he worked as a research

engineer at Babcock & Wilcox Company (Alliance, Ohio) and WestinghouseAdvanced Reactors Division (Madison, Pennsylvania). From 1984-1991, heworked as a Materials Engineer at General Electric Aircraft Engines(Cincinnati, Ohio). Since 1991, he has been working as a Senior MaterialsEngineer at the NRC in the Office of Nuclear Regulatory Research. Hiscurrent research interests include the proactive management of materialsdegradation, modular probabilistic fracture mechanics computer codedevelopment, structural integrity evaluation, and evaluation of candidatestructural materials for high temperature advanced reactors. He has authoredor co-authored numerous publications and reports. Dr. Malik is an activemember of ASME and ASTM.

Steven R. Doctor (S'63-M73-SM93-LSM'08)received his B.S. degree in electrical engineering in1966 from Purdue University, W. Lafayette, Indiana;a M.S. in 1969; and a Ph.D. in 1973 both in electricalengineering from Iowa State University, Ames,Iowa. He began his career by participating in theCooperative Education Program at Purdue Universityat White Sands Missile Range 1963-1965 and thenworked at White Sands Missile Range in 1966. Hewas an Assistant Professor at Iowa State Universityfrom 1973-1976 in the electrical engineering

department. He started his career in nondestructive testing at the PacificNorthwest National Laboratory, Richland, Washington, in 1976 as a ResearchEngineer, held several positions, and lastly was promoted to a LaboratoryFellow position in 1991. His research interests have been focused for morethan 30 years on the quantification of NDE reliability for nuclear power plantcomponents, assessing the impact of the NDE unreliability on componentintegrity, and identifying how to improve NDE performance. He has been theauthor or co-author on more than 180 papers and reports and holds 3 patents.Dr. Doctor is a Fellow of ASNT, a Life Senior Member of IEEE, and amember of several committees of the ASME Boiler and Pressure Vessel CodeSection XI.

Tom Taylor received his B.S. degree from Miami University, Oxford,Ohio in 1971. He began his career with Nuclear Services Corporation inCampbell, California, where he performed ultrasonic in-service examinations

in several U.S. nuclear power plants. He startedworking at Pacific Northwest National Laboratory(PNNL) in 1978 as a research engineer.

Since his employment at PNNL, he has 27 yearsof experience in the commercial nuclear powerindustry, involving a broad spectrum of activitiesincluding the following.

- Line management responsibility for 35Professional Engineers, Scientists and Technicians

- Development and management ofcollaborative programs, both nationally andinternationally, that address issues in the commercial

nuclear power industry- Development of national codes and standards for the commercial

nuclear industry- Acting on behalf of the Department of Energy and coordinating work

among four National Laboratories for a Department of Energy program thatdeveloped technology used in chemical weapons treaty verification.

Mr. Taylor is recognized for helping establish the first performancedemonstration rules specified by Section XI of the American Society ofMechanical Engineers Boiler and Pressure Vessel Code, establishing theNondestructive Training and Certification Center in Ukraine, and hisleadership role in several International Atomic Energy Agency programs. Hisarea of expertise includes program management, nuclear reactor safety and in­service inspection, and nondestructive materials characterization.