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Nuclear Engineering and Design 241 (2011) 2916– 2926

Contents lists available at ScienceDirect

Nuclear Engineering and Design

jo u r n al hom epage : www.elsev ier .com/ locate /nucengdes

uclear power plant construction: What can be learned from past and on-goingrojects?

enoît Zerger ∗, Marc Noëluropean Clearinghouse on Operational Experience Feedback for Nuclear Power Plants, Institute for Energy, Joint Research Centre, European Commission, P.O. Box 2,755 ZG Petten, The Netherlands

r t i c l e i n f o

rticle history:eceived 7 March 2011eceived in revised form 27 May 2011ccepted 28 May 2011

a b s t r a c t

This paper presents a study performed by the European Clearinghouse on Operational Experience forNPPs and covering events related to construction, commissioning and manufacturing of nuclear powerplants (i.e. events prior to the start of commercial operation). The events considered are both issuesdetected during the pre-operational stages, and events detected during further operation of the plant.

This study summarises the analysis of 582 construction, commissioning and manufacturing relatedevents reported to different databases. To help identify generic lessons learned, the events were clas-sified into three main categories: construction, manufacturing and commissioning, and secondly, intosub-categories related to components: civil engineering, electrical components and Instrumentation &Control,. . .

This paper presents the concrete lessons learned for the different components.

. Introduction

.1. Background

Nuclear Power Plant (NPP) operational experience has beensed for many years to improve the safety of nuclear facilitieshroughout the world.

In the European Union, to support EU activities on evaluationf NPP operational events, a centralised regional ‘Clearinghouse’n NPP operational experience feedback (OEF) was established in008 at the JRC-IE, at the request of the nuclear safety authorities ofeveral Member States. Its purpose is to improve communicationnd information sharing on OEF, and to promote regional collabo-ation on analyses of operational experience and dissemination ofhe lessons learned (Noël, 2010).

One of the technical tasks of the European Clearinghouse iso perform in-depth analysis of families of events (‘topical stud-es’) (Bruynooghe and Noel, 2010; Martin Ramos et al., 2010), inrder to identify the main recurring causes, contributing factors andessons learned, and to disseminate and promote recommendationso reduce the recurrence of similar events in the future.

In this framework, the European Clearinghouse on OEFerformed a study on experience from events related to con-

∗ Corresponding author. Tel.: +31 224 56 51 88; fax: +31 224 56 56 37.E-mail address: benoit.zerger@ec.europa.eu (B. Zerger).

029-5493/$ – see front matter © 2011 Elsevier B.V. All rights reserved.oi:10.1016/j.nucengdes.2011.05.037

© 2011 Elsevier B.V. All rights reserved.

struction and commissioning of Nuclear Power Plants (EuropeanCommission, 2010).

1.2. Objectives and scope

Interest in constructing new nuclear power plants is increasingworldwide. Some countries are embarking on a nuclear programmefor the first time, while others have decided to re-start constructionof nuclear power plants after a hiatus of decades. According to thePower Reactor Information System (PRIS) of the IAEA, currently 55construction projects have been launched or are being consideredworldwide.

Starting new build is very demanding, as much of the earlierexperience and resources have progressively been lost from thenuclear industry. Circumstances are quite different from 1970swhen most of the plants currently operating were constructed.Vendors had large experienced organisations ready to go ahead,and had less need to rely on subcontractors. In addition, there wasno shortage of skilled manufacturing capacity in the market, anddesigns were often based on work done in similar ongoing or com-pleted projects.

Consequently, lessons learned from the past construction peri-ods or from the ongoing construction projects are very importantfor the increased number of utilities and regulators involved in

building new NPPs. They will help to reduce the recurrence of pastconstruction or commissioning problems.

Efforts to collect lessons learned from construction experiencehave already been made in the past, for example the United States

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uclear Regulatory Commission (US NRC) report to Congress, dated984. More recently, the Nuclear Energy Agency (NEA) of the OECDreated the Working Group on the Regulation of New ReactorsWGRNR) which examines the regulatory issues of siting, licensingnd supervision of the new NPPs.

However, there is no recent comprehensive published study onessons learned from events related to the pre-operational phases.he Member States’ Safety Authorities participating in the Euro-ean Clearinghouse on OEF therefore agreed that it was necessaryo conduct an up-to-date analysis of both past and current con-truction experience.

This study covers construction, commissioning and manufac-uring events originating prior to the start of the commercialperation, in order to highlight lessons learned and recommenda-ions for current and future construction programmes.

The construction stage includes the construction of the buildingsnd the initial installation of components, the manufacturing stagencludes both on-site and off-site manufacturing.

However, it must be stressed that operating plant modificationsnd design deficiencies are beyond the scope of the study. Indeed,he amount of events including design deficiencies is very high andt was decided to address this issue in a separate study for clarityeasons.

The study of the European Clearinghouse contains some trendnalyses of the events, technical lessons learned and cross-cuttingndings. The aim of this paper is to focus on the technical lessons

earned which can be reviewed by NPP utilities and by Regulatoryodies to ensure they are considered in the current constructionrocesses.

. Methodology

The Clearinghouse study has been based on various sources ofnformation (STUK, 2006, 2008) and mainly on the screening ofatabases, as described below.

.1. Screening of databases

The relevant events have been collected by screening threenformation sources: the IRS database, the US Licensee Eventeports and the WGRNR database. Those information sources haveeen screening from the beginning of their operation until Decem-er 2009.

.1.1. IRS databaseThe Incident Reporting System (IRS) is an international system

ointly operated by the IAEA and the OECD/NEA. It contains about600 event reports that provide detailed descriptions and prelimi-ary analyses of the causes that may be relevant to other plants.

Each IRS report becomes part of the web-based IRS, which wasreated to facilitate data input and report availability and speedsp access to information. The IRS provides a detailed framework

n which the plant and the characteristics of the incident can belassified according to a systematic set of codes (IAEA, 2010) whichs later on very useful for retrieving the information.

For this study, 1090 events were screened and 247 were applicable.

.1.2. WGRNR databaseThe WGRNR has developed a new database for construction

xperience feedback to allow WGRNR members to share world-ide construction inspection findings. The reports are available in

he work area of the WGRNR website. In December 2009, 100 eventeports were stored in the WGRNR database.

These reports relate to past and recent design, construction andanufacturing experience in various countries. Some are regis-

nd Design 241 (2011) 2916– 2926 2917

tered in the IRS database, others are only in national databases orhave been presented at meetings or workshops.

After screening these reports, 26 events were identified as appli-cable for this report, of which 7 overlap with the IRS database orwith other WGRNR reports.

2.1.3. US NRC databaseUS commercial nuclear reactor licensees are required to report

certain events under US NRC regulation 10CFR50.73. These reports,called ‘Licensee event reports’ (LER), are available to the pub-lic on the NRC’s website https://nrcoe.inel.gov/secure/lersearch/index.cfm.

The NRC website does not allow querying by guide words, so arough text search was performed on the word ‘construction’ in thetitles and abstracts of the reports.

The text search yielded 857 LERs. Most of them showed norelevance to construction or commissioning but were related tomaintenance or modification works which were reported as ‘con-struction’ works in the reports. After screening the NRC website,which contains LERs from 1980 onwards, there were 309 relevantLERs left.

The purpose of this search was not to obtain an exhaustiveview of construction-related events in the USA but to supplementthe study with event typologies which are not tackled in the IRSdatabase or in the WGRNR reports.

2.2. Analysis of events

The events identified were classified in three categories for thepurpose of the study with definitions based on the IAEA glossary(IAEA, 2007):

- Construction. ‘The process of (. . .) assembling the components ofa facility, the carrying out of civil works, the installation of com-ponents and equipment (. . .)’, prior to the start of commercialoperation.

- Commissioning. ‘The process by means of which systems and com-ponents of facilities and activities, having been constructed, aremade operational and verified to be in accordance with the designand to have met the required performance criteria’.

- Manufacturing of components and equipment which wereinstalled in the plant prior to the start of commercial operation.

Each of these categories is further classified according to the typeof component concerned: pipe, valve, weld, civil work, electricalcomponents, I&C, etc.

This structure enables us to make recommendations bothfor each different pre-operational stages and for each type ofcomponent. Moreover, it enables us to identify more generic rec-ommendations than a classification into systems depending on thereactor design.

After this classification, each category and sub-category wasscreened to show the lessons learned for a given component at agiven stage of construction. In addition, general recommendationswere identified. The overall process is described in Fig. 1.

The events screened were either rejected or placed in one ormore of the relevant categories on the basis of a review of eachevent. The events were selected if they had a connection with con-

struction, whether this connection is a direct cause, root cause orcontributing factor. An event which occurred during the construc-tion of the plant but which had no relation with the constructionwas rejected.

2918 B. Zerger, M. Noël / Nuclear Engineering and Design 241 (2011) 2916– 2926

Construction Manufacturing Commissioning

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. Overview Of the screening results

.1. Introduction

The figures below show the results of the screening process.By way of an introduction to this section, readers should note

he following limitations:

1) As this report is based on different sources of information (IRSdatabase, WGRNR reports, LERs), the content and the structureof the reports covered are not homogeneous, nor are the criteriafor reporting.

2) Countries report events to the IRS on a voluntary basis.

For reason (1), the results below are shown only for the IRSeports which have a homogeneous structure and are represen-ative of worldwide events.

For reason (2), the results below should be considered as an indi-ator providing a pointer to further analysis but not as a scientificesult.

.2. Results

Fig. 2 shows the distribution of the 247 IRS event reports in the categories mentioned above. Almost half of the selected eventsre related to the construction phase whereas only a few have beenound relevant to the commissioning stage.

It should be noted that several of these categories may coinciden a single reported event, and that one report may describe severalvents.

Moreover, manufacturing events are supposed to relate to the

anufacturing of components which were installed in the plant

efore initial start-up, but sometimes the event reports did notllow us to distinguish these events from those connected to theanufacturing of components installed during operation.

Fig. 2. Distribution of the selected events.

It may introduce some inaccuracy into the statistics, but thelessons learned are relevant in both types of event.

Fig. 3 shows the distribution of the 247 IRS reports into groupsof components.

As this figure shows, almost half of the applicable events arerelated to mechanical components: pipes, pumps, steam genera-tors, valves, welds and others (corresponding to six events relatingto fuel channels, the vessel, handling devices or waste facilities).The other main sub-categories are related to electrical components,instrumentation and control and civil works.

It has to be mentioned that some events involve different typesof component, which means that a IRS report can be consideredseveral times in different categories.

4. Overview of the lessons learned

This section aims to present some of the lessons learned whichhave been raised in the Clearinghouse study.

B. Zerger, M. Noël / Nuclear Engineering a

Civil Work8%

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Fig. 3. Distribution of IRS reports into groups of components.

.1. Electrical components

.1.1. Electrical connectionsMany events relate to electrical connections and are due to

nsufficient quality assurance and quality control during instal-ation, leading to the use of the incorrect type of connection,nadequate fixing or damage to the connections.

Some examples can be given:

deviation from Environmental Qualification (EQ) requirementsdue to instrument racks supplied with unqualified splices. Thesesplices were not indicated on the drawings and the cable con-nections were not inspected, to avoid compromising the EQrequirements,

non-watertight cable connectors which allowed moisture toenter the plug socket of a control rod drive,

break of a hinged electrical connection, cracking of termination lugs, incorrect wire stripping that resulted in insulation under the ter-mination lugs,

motor leads separated from the lugs.

oreover, another event shows that there were no openings allow-ng the equipment to vent and to drain accumulated water on 156unction boxes containing terminal blocks, as required by the instal-ation specification. Lack of these openings resulted in breachesf EQ requirements and had a potential impact on safety-relatedquipment. The cause of this deviation was that information abouthe draining openings got lost somewhere between the designernd the contractor’s staff carrying out the installation.

The following lessons learned can be raised form those events:

The installation procedures should be written, and the qualitycontrols should be performed, so as to ensure the right type ofconnection, proper fastening and avoidance of damage during theconnection activities. For that reason, the connections should notbe covered by insulation until checked.Attention should be paid to connections between two different

types of cables and conductors.

Special attention should be paid to the crimping of the conductorsduring manufacture and installation of the electrical panels toensure the connection quality, and to the quality of the connection

nd Design 241 (2011) 2916– 2926 2919

lugs. Stamping, in particular, should not impair the mechanicalproperties of the lugs.

- During installation, the size of the connection lugs should be mon-itored in order to ensure a good connection with the conductors.

- Special attention should be paid to the Environmental Qualifica-tion of supplied conduits or junction boxes, and more especiallyto the electrical splices. In addition to document review, inspec-tion should be performed at the manufacturing stage when theinspection itself does not test the EQ.

- Specific attention should be paid to the openings of the junctionboxes which allow drainage of the accumulated water inside theboxes during some accidents.

4.1.2. Electrical cablesConcerning the electrical components, the main deficiency

reported deals with electrical cables (nine out of 23 IRS construc-tion events related to electrical components) and more especiallyinsulation defects that led to the actual or the potential malfunctionof safety components, violations of the Environmental Qualificationdesign, short circuits and fires. Six of these nine events are identifiedas leading to potential common cause failure.

The causes of those events are:

- damage to the cables when they were pulled through penetra-tions,

- poor quality of the cable sheathing,- damage to the cable sheathing due to excessive bend of the cable,- cable which is not fire-resistant as designed,- cable route that does not allow the separation of trains and units,- wiring errors,- damaged sheathing due to lack of Quality Assurance (QA) and

Quality Control (QC) during connection of the cables.

Event reports describe also the following: non-homogeneous PVCinsulation which resulted in lowering of the insulation, an electricarc between the earth wire and a power wire, which were installedtoo close together, and incorrect alignment of the conductor withthe sheathing, leading to damage to the conductor.

The lessons learned are:

- A comprehensive cable condition monitoring programme shouldbe implemented in the construction stage. The cable sheathing ofthe safety-significant systems should be checked after installationwhere it is accessible, more especially at the bends and at theelectrical connection. During construction, inspection should beperformed in the cable trays before there are closed.

- The cable fire rating should be checked and the cable route shouldbe verified to ensure the separation of trains and units.

- An individual and specific procedure should be written for instal-lation of multiple cables in a single penetration, in order to avoiddamage during installation. The installation of designed separa-tions in the penetrations should be checked.

- During manufacturing, special attention should be paid to thefollowing points: homogenous blending of additives in the PVCsheathing and eccentric positioning of the conductor in relationto the protective sheath.

4.1.3. BreakersThe other main reported deficiency in electrical components

concerns the breakers (eight out of the 23 applicable IRS events).The malfunctions of breakers led to actual or potential loss of power

faults:

- misalignment of the linkage of the trip devices,

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wrong material (magnetic material), fouling of the mechanical parts.

oreover, another event report describes a loss of power partiallyaused by incorrect adjustment of a breaker’s draw-out unit.

Finally, an event report relates that circuit breakers werenstalled in the plant without seismic positioners, or with the seis-

ic positioner oriented upside down relative to the position inhich the breaker was originally qualified for a Safe Shutdown

arthquake. These deficiencies would endanger the functioning ofhe breaker during an earthquake. The root causes of these eventsere a lack of documentation and lack of adequate acceptance

esting during initial construction.The lessons learned are:

The manufacturer’s documentation should specify the adjust-ment of the breaker’s draw-out unit and this adjustment shouldbe checked.

Special attention should be paid to the following items:- The alignment of the linkage of the trip devices.- The use of proper material.- The removal of the temporary latches.- The cleanliness of the parts.

Special attention should be paid to the proper installation of theseismic positioners of the breakers.

.1.4. TransformersSome events involve the failure of transformers and led to the

ailure of the main transformer, the loss of external power supplyr to shutdown of the reactor. These events arose from:

non-existent support for windings, allowing them to becomedeformed during a short-circuit,

malfunction of the high-voltage bushings, believed to be due tothe handling and storage conditions.

ther event reports describe deficiencies of transformer insulators:issing insulator elements, poor quality of the supporting insula-

ors and insufficient consideration of the insulators’ shelf life.The lessons learned are:

The presence of the transformer winding supports should bechecked in order to avoid winding deformation in the event ofhigh current.

The condition of stored bushings should be checked periodicallyand the power factor of stored bushings should be checked beforeputting them in service.

Attention should be paid to the shelf life of the insulators prior toinstallation.

.1.5. Electrical switchesSome events relate to the failure of electrical switches, on the

ne hand due to the build-up of a coating over a long period ofon-operability at the pre-operational stage, and on the other, toissing stop screws.The lessons learned are that the installation instructions for

witches should specify if stop screws have to be installed and theechanical stops of the switches should be checked during start-up

ests.

.1.6. Batteries

Events relate to degradation of batteries due to incorrect prepa-

ation of epoxy resin and to impurities introduced into the platesuring the welding process.

The lessons learned are:

nd Design 241 (2011) 2916– 2926

- Batteries should be checked for damage before installing them onsite.

- During manufacturing, special attention should be paid to theabsence of impurities during welding of the plates and to thepreparation of the resin used for sealing.

4.2. Instrumentation and control

Many event reports relate to I&C deficiencies that led to actualor potential malfunction of safety systems or to reactor shutdown.Some report wiring errors, cable damage, clogging of instrumen-tation air pipes, soldering defects or incorrect sealing of electricalconnections.

Some specific events were:

- Two events report the improper location of probes during con-struction that remained undetected for years, even though in onecase the probe signal was negative instead of positive, becausethe scope of commissioning and surveillance tests was not broadenough and/or because the sensing lines were not equipped tobe tested at the connection points. The causes of these errorswere the imprecision of the initial construction documents andshortcomings in quality control before operation.

- Incorrect calibration of pressure transmitters (incorrect assess-ment of static pressure) due to inappropriate review of vendordocumentation.

- Deviations from the original design in the installation of analoguetransformer modules. These deviations were due to the use ofsix different kinds of modules on the plant without proper iden-tification and resulted in the lack of overvoltage protection insome modules. Moreover those errors were not detected becauseovervoltage protections were not tested on site.

- Improper wiring of the reactor protection logic which remaineduncorrected for years despite detection during commissioningbecause, on the vendor’s advice, operating documents were mod-ified to fit the installed wiring without any safety analysis.

- Incorrect setting of the delay time due to a lack of safety analysiswhen this setting was modified from the manufacturer’s recom-mendations.

One event report describes that temperature sensors were con-nected to the wrong indicators during plant construction. Anotherdescribes incorrect routing of impulse lines which meant that tworedundant SG level impulse lines were located too close to eachother, thus affecting the functional redundancy of the instrumentlines.

Moreover, there are also manufacturing events involving I&Cdeficiencies which led to malfunction of safety systems or reactorshutdown. These events report for instance manufacturing defectsof capacitors, operational amplifiers or contactors.

Some specific events were:

- Valve motors failed to pull in at 80% of rated voltage as specified inthe procurement documents. Commissioning tests showed thatthe contactors close at higher value than expected but the test wasconsidered successful because there was no acceptance criterionabout the contactors’ closure voltage.

- Incorrect wiring led to the degradation of a reactor protectionvoting logic ‘2 out of 3’ to a logic ‘1 out of 2’.

- Failure of a pump’s oil level detector because the contacts of thereed switch of ‘high level’ alarm were adhering, due to manufac-turing deficiencies. The clearance of the contacts was afterwards

checked during manufacturing.

Concerning commissioning, the following event should be noted:during a load rejection test, a ‘fast trend update program’ was

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urned on to collect data, which caused an unexpected behaviourf the reactor. A fault had been detected in this software at com-issioning stage but had not been corrected because it had been

nalysed as without any consequences on other programmes.The main lessons learned are:

The need for safety analysis and appropriate documentation if thewiring is modified from the original design.

The need for safety analysis if manufacturer’s recommended set-tings are changed.

Need to test both the ‘2 out of 3’ and ‘1 out of 3’ voting logicsto identify a potential malfunction of one of the three measuringchannels.

The I&C modules’ overvoltage protection should be tested. The probe installation should be closely monitored duringconstruction and appropriate commissioning tests should beprepared and carried out to detect any defect in every singlecomponent of a measuring channel.

The initial calibration of measurement transmitters should bechecked against vendor documentation.

Closure of the valve motor contactors at the minimum expectedvoltage for design basis conditions should be tested.

Control software with known or suspected faults should not beused as this may have unexpected influences on other software.

The clearance of the reed switch contacts should be checked dur-ing manufacturing.

The minimum distance allowing functional redundancy shouldbe ensured between redundant impulse lines.

.3. Weld

There are several event reports related to welding during theonstruction stage, the majority of which mention faults in pipeelding leading to real or potential coolant leakage, or to damage

o safety equipment pipes. Some events involve defects of spentuel pool or metallic liner welds.

Although these deficiencies occurred during the constructiontage, 15 out of the 18 defects were not revealed until years laterthe detection time is on average 11 years after the start of oper-tion) because of a component failure (8 events) or thanks to themprovement of the inspection technology or even by chance dur-ng maintenance or inspection of a nearby zone.

For the pool liner, the lesson learned is that the liner weldshould be accessible for inspection during welding and the weldead length should be reduced.

One event reports the lack of weld identification and docu-entation and another missing structural welds in a boiling water

eactor (BWR) torus.Finally, two other events are related to poor welding quality of

he metallic liner due to lack of quality control by the utility and itsontractor, to the welding environment, and to a misunderstand-ng of the safety significance of welding operations. The followingon-conformances were observed: non-exhaustive welding data,ystematic manual welding although automatic welding is givenriority by the construction code, lack of documentation of param-ters, high number of repairs, weld buckles due to incompatibilitiesf the bottom and upper ring modules (upper part circumferenceonger than the circumference of the bottom module), incorrect

anagement of welding material. As a result, the licensee wasequested to perform additional inspections for manual welding,o develop protections for the welding areas and to carry out 100%on destructive testing (NDT) until the repair rate decreases, as well

s to improve the QC of its sub-contractors’ activities.

The manufacturing events are related to welding deficiencieshich affect mostly pipes but also tanks, exchangers, canopy seals,

essel head nozzles and control rod guide tubes.

nd Design 241 (2011) 2916– 2926 2921

As with construction, the causes of the deficiencies are not fullydetailed. The reported events refer to lamellar tearing, cold crack-ing, cracking due to low ferrite level of the filler metal, initial stressconcentration, incorrect heat treatment, incorrect weld seam, lackof fusion, degradation of the buttering in bi-metallic welding, brit-tle layer due to excessive fusion of the filler metal with the basemelt, or chloride pollution at the manufacturing shop.

Some of these deficiencies caused the welds to fail some yearslater (for 11 events out of 18).

Some events include:

- Crack indications in a bi-metallic weld remained undetectedbecause of a misinterpretation of the inspection results. One les-son learned from this event is that extra attention should be paidto these welds, and more specifically to the border between but-tering and base material.

- Some defects remained undetected until the failure of a pipe inthe refuelling machine coupling module, because the welds werenot included in the ISI programme due to the lack of recommen-dations from the manufacturer and from the ISI company aboutthe refuelling machine.

- Failure of control rod thermal sleeve guide due to poor weldingconditions. The defect was not detected earlier because there wasno acceptance inspection after the assembly of the vessel head.

The lessons learned are:

- All welds should be inspectable at the construction stage.- The original welding documents and inspection results should be

carefully kept as they are needed for further in-service inspec-tions.

- Extra attention should be paid to bi-metallic welding, and morespecifically to the border between buttering and base material.

- Care should be taken that the welding environment (on the con-struction site) allows compliance with the construction code.

- Events related to welds show the very high importance of appro-priate weld QA, QC & inspection programmes.

4.4. Valves

Some event reports describe construction deficiencies related tovalves that led to malfunctioning of or damage to safety systems.They report that:

- A check valve was found fitted in the wrong direction in the RCSpump fire extinguishing system. The wrong mounting remainedundetected during commissioning because the system was testeddownstream of the check valve.

- A valve failed to close because a contactor spring was uninten-tionally displaced during cleaning activities prior to start-up.

Moreover, one event reports that several motor compartmentdrains of safety valve actuators were found missing or clogged bypainting, affecting the actuators’ EQ.

These deficiencies were partially due to a lack of communicationabout the function and significance of the drains, resulting in theinadvertent painting of the drains.

Other events report valve manufacturing deficiencies which ledin most of the cases to the failure of the valves (malfunction, leak-age) and as a result to malfunction of safety systems or reactor

shutdown.

The main deficiencies are:

- incorrect dimensions of stems,

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malfunction of the pilot valve of a safety relief valve partially dueto loss of the pre-stroke cone due to removal of the transportationprotection,

manufacturing of valve outlet bodies with wrong angles, althoughall the certificates were correct,

stem bending and stem damage during manufacturing. As a cor-rective, the QC of manufacturing operations has been improvedand the measurement of stem linearity has been added to theprocedures.

The lessons learned are:

Need for comprehensive commissioning tests of the RCS pumpfire extinguishing system. Some components are not easily acces-sible for visual inspection. The event report proposes injectingcompressed air upstream of the valves.Need to check that the contactor springs are in the correct positionafter cleaning activities.The importance of acceptance checks when the componentsarrive on site.The need for proper valve transportation conditions.

The as-built situation may be incorrect in spite of properdocumentation. As a result, a capacity test is necessary for safety-related systems.

Special attention should be paid to the proper installation ofdrains in the safety valves’ actuator boxes.

.5. Pipes

Concerning construction, the events mostly report actual orotential pipe leakages, pipe clogging or incorrectly installed com-onents (strainers, orifice plates, supports, etc.). Two of thesevents are reported as a potential Common Cause Failure (CCF) withotentially high safety significance, as they could lead to leakagerom the Reactor Cooling System (RCS).

The main reported deficiencies in connection with damagedipes are:

installation of a pipe at the wrong time because the pipe to beinstalled was found to be too long at the time of construction,

damaged pipe bend during installation due to the use of leversto align the pipes. NB in this case, the quality control was carriedout by a company connected to the installation company,

crack due to chloride stress corrosion cracking caused by leftovervinyl tapes from the construction stage,

crack partially due to excessive stress caused by installation, insufficient wall thickness due to slight eccentricity between thepipe and the thinning machine,

leakage from a plastic effluent pipe due to incorrect pipe material.

he main reported deficiencies relating to improper installation ofiping components are:

Some event reports mention that HELB (High Energy Line Break)or seismic restraints are missing or not properly installed. Manysupport deficiencies are reported too (supports not properlywelded, supports attached to cable trays, incorrect installationof the supports’ embedded plates, supports attached to shoringplates instead of embedded plates, etc.).

Remaining blank flange found downstream of tank safety valve,

in untested lines.Temporary strainers left in pump suction piping of safety injec-tion and reactor spray systems and remained undetected becausethey were assumed to be permanent.

nd Design 241 (2011) 2916– 2926

One event report relates that some differences were found atthe construction stage between as-built pipe insulation and thedesigned insulation. These differences related to the weight of theinsulation, which affects the design of the pipe supports, and couldhave compromised the seismic behaviour of the pipe supports inthe event of an earthquake.

The main reported deficiencies concerning clogged pipes are:

- Two out of four ECCS (Emergency Core Cooling System) linespartially blocked by debris from construction stage. The lack ofsurveillance of the sumps during construction allowed workersto throw debris into the sumps. This underlines the lack of trainingand safety culture as well.

- A piece of wood blocked the cooling pipe of a main generatorphase.

- Foreign matter (screws, welding dam) partially blocked fuel chan-nels on several occasions, or was found in a safety injection pipe(pipe plug remaining from the welding operations).

Other event reports concern pipe manufacturing. They arerelated to:

- reheat cracking in the heat-affected zone of welding due to thecoarse structure of the outer surface. The coarse grains were prob-ably due to the bending process of the pipe (heating from outside,slow bending process and high niobium to carbon ratio in thematerial),

- another grain size issue is reported from a current constructionprogramme. This issue deals with the grain size which exceedsthe criteria, probably because of the large size of the forgings,combined with the cycle of forgings and heat treatments, whichwas not optimised,

The lessons learned are:

- The pipes should be exhaustively inspected during construction.- The grain size should be specified for hot-formed austenitic tube

bends.- Special attention should be paid to the proper installation of pipe

supports and restraints intended to mitigate the consequences ofearthquakes or HELB.

- The installed pipe insulation weight should be verified to complywith the seismic specifications for pipe supports.

- Measures should be taken to avoid clogging pipes with con-struction debris and other foreign materials. A Foreign MaterialExclusion (FME) + cleanliness/housekeeping policy should beimplemented from the very beginning of the project.

- Rigorous management of temporary devices should be imple-mented, to avoid leaving temporary blind flanges, orifices, etc.inside the pipes after commissioning of the plant.

4.6. Civil work

4.6.1. AnchoringMany event reports involve anchoring deficiencies and all of

them are identified in the IRS database as a potential CCF, as theanchored material may become displaced in accident situationsand during earthquakes. The affected components are pipes, powersupply and control cabinets or battery chargers.

The causes of the deficiencies are:

- deficient fixing of the pipes’ anchor plates,- deficiencies in pipes’ anchor bolt fastenings due the failure to

drive the anchor wedge deep enough into concrete. A contribut-ing factor may have been that the holes were too small,

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lack of quality assurance during installation (independent inspec-tion, written instructions, check lists, etc.),

insufficient training of the installation personal using work sam-ples,

incorrect final checks of installed anchors (before mounting theanchor plate),

inadequate coordination and unclear division of responsibilitiesbetween the department in charge of systems and that in chargeof buildings,

use of incorrect tools (for example, drills).

The lessons learned are:

Every step of installation should be checked and documented andthe requisite checks must be carried out by competent personnel.

Before the installation of safety-related anchors, the function ofthe anchoring devices should be explained to the personnel indetail. The personnel must be trained and the installation instruc-tions must be available and understood.

It must be ensured that the specified tools are used (for example,drill bits and drilling machine).

As the anchoring devices are at the interface between systemsand structures, there must be sufficient cooperation between thedepartments for systems and the construction departments in theplanning and control phase. This applies to the licensee as well asthe technical supervisor organisation and the authority.

.6.2. Penetrations and building sealsThis section deals with deficiencies in building seals, penetra-

ions and hydrostatic barriers which compromise the sealing ofhe buildings and could therefore allow a potential release of con-amination or ingress of water, which could lead to flooding orquipment corrosion.

Four events were identified as potential CCF, mainly becausef the ingress of water or humidity which could damage differentnd/or redundant safety systems.

The causes of the deficiencies are:

seal construction faults (sealing band not adherent to the con-crete, damage to the seal, from objects such as metal plates lyingaround during construction, cracks in the concrete allowing waterto seep around the seal). More specifically, one event reportsthe late detection of defective flood seals because the seals werealso fire barriers, and only this latter function was considered forinstallation, acceptance testing and subsequent maintenance,

absence of leak testing at the acceptance stage, deficient leak-tightness of pipe penetrations which remainedundetected because the penetrations were not included in theplant documentation.

The lessons learned are:

Every single penetration and building seal should be properlydocumented (location, role, design) to ensure proper follow-upduring further plant operation.The initial design of inter-building seals should take into consid-eration the need to be able to conduct checks on the quality ofinstallation at the construction stage and subsequently. To do so,the seals should be accessible over their entire length and closeto a floor for ease of repair.

When a penetration seal functions as both a fire barrier and a

flood barrier, it is important for licensees to consider both func-tions in the design, installation, inspection, and maintenance. Thisincludes accounting for static head pressure to ensure watertightseals do not get dislodged.

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4.6.3. Metallic linerTwo events relating to the metallic liner were reported: both

involve construction faults leading to the damage to the liner.One of the reported deficiencies concerns the improper concrete

construction, which led to a large bulge in the liner.As a lesson learned, it is also proposed that maximum allowed

sizes of containment liner bulge should be determined through arisk-informed approach, to help decide when corrective action isneeded.

4.6.4. Building structureThis section deals with deficiencies related to concreting, steel

rebar and pre-stressed cables. This group contains eight events, fourof which were detected during current construction programmes.

The event reports refer to the following:

- A lack of reinforcement steelwork of the basemat, associated withlarge volume of concrete, leading to the appearance of cracks inthe basemat concrete of the reactor building. The operator treatedthe cracks by filing with epoxy resin under pressure to protectthe exposed steelwork and close ground water paths, and hadto evaluate the leak-tightness and mechanical resistance of thebasemat.

- Failure of pre-stressing cables in VVER containment structurecaused by exceeding the plastic deformation limit and by cor-rosion due to humidity and lack of lubricant inside the cablechannelling device.

Some event reports related also to construction deficienciesof concrete blocks or masonry walls (lack of grout, of rein-forcement, insufficient anchoring), which could have led to thedamage of safety-related systems in the vicinity in case ofearthquake.

One event report shows that a small void was discovered in theconcrete below the reactor building equipment hatch during a SGreplacement. This void might have been caused by the horizontalwall construction joint which is near the bottom of the hatch sleeve,making it difficult to prevent the formation of air pockets duringconcrete pouring. Also, this area contained reinforcing steel, tendonsheathing, and strain gauge material, making it difficult to accessfor concrete consolidation.

The proposed lessons learned are:

- The humidity and the lubricant inside the channelling device ofthe pre-stressing cables should be monitored during construc-tion.

- The minimum thickness of lubricant on the external wire lay-ers following manufacture of containment pre-stressing systemcables should be precisely specified.

- A procedure should be developed to restore the lubricant onexternal wire layers after assembly of containment pre-stressingsystem cables at NPP units, in order to prevent metal corrosion inthe cable wires during operation of the containment pre-stressingsystem.

- The size of concrete sections of the basemat could have an influ-ence on the appearance of cracks.

- Special attention should be paid that concrete block wallsand masonry walls are constructed with regard to the seismicresponse of the walls and potential damage to any safety-related

equipment in the vicinity.

- Concrete pouring should be validated by mock-up for locationswhere access may be difficult for concrete consolidation (highdensity of steel reinforcement, etc.).

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.7. Pumps

Concerning construction, the event reports concern:

damage to a reactor coolant pump due to loose parts from con-struction stage,

malfunction of the containment spray pumps due to a screen leftin the pump suction after cleaning operations in the constructionstage.

The manufacturing events report mainly:

damage to a RHR (Reactor Heat Removal) pump due to insufficientlubrification, caused by a faulty gauging of the visual ‘minimum’and ‘maximum’ markings on the inspection glass,leak in a RCS pump casing seal due to insufficiently tightenedstuds and inadequate seal quality,failure of a RCS pump due to an inadequate mechanical preloadon the cap screws which attach the pump impeller to the pumpshaft end plate,

deficient automatic start of boron injection pumps after powerdisruption, due to missing wires and defective control card,

leak in an auxiliary feedwater (AFW) pump due to low manufac-ture quality of the butt-end seal,

failure of high pressure safety injection (HPSI) pumps due toincorrect welding of stop pins in the rotor and to a piece of metalinside the diffuser,

potential inoperability of RHR pump motors due to overheating ordisengagement of the power cables because of incorrect electricalconnections of the motors (wrong size of the lugs).

The lessons learned form these events are:

Need for monitoring of loose parts and temporary equipment. Check the markings on pumps’ oil inspection glass. Test the pumps’ automatic start-up after a power disruption dur-ing commissioning.

Improve the acceptance procedures for safety-critical compo-nents. It is proposed for instance to disassemble motors foracceptance tests in order to check the internal parts and themounting dimensions.

.8. Steam generators

As for steam generators (SG), two events report damage ofG tubes due to loose parts, despite the cleanliness inspectionerformed prior to operation. This may have been caused by accu-ulation of loose parts in the upper part of the SG, which were thenashed down after pre-service inspections.

Several manufacturing events are related to steam generators.hey mainly report SG tube leakages or cracks in the tubes or innother part of the SG.

For the SG tubes, the main reported cause of failure is stressorrosion cracking due to the tube expansion process and a metaluild-up on the tube plate caused by insufficient cleaning duringanufacture and assembly.Another cause of tube leakage is reported to be the handling con-

itions. For example, the tube packing crate used screws and somef them came into contact with the tube. This event underlines theeed to monitor the fabrication process, including the packaging.ube acceptance inspections should also be performed at the SGanufacturing site and any quality deviation should be noted by

he pre-service inspection staff on the NPP site, in order to facilitatehe review of inspection data.

A deviation from the original tube support design was alsoeported: such deviations can result in increased tube vibration and

nd Design 241 (2011) 2916– 2926

therefore in increased tube wear and fatigue. The lesson learned isthe importance of verifying the location of the tube supports, inorder to detect any deviation from design, but also to detect theoperation-induced movements of these supports and to identifythe high-stress locations, if the SG is already in operation.

One event report describes that five SG tubes were incorrectlypositioned inside the steam generator, in such a way that a tube inthe upper tube sheet did not exit through the corresponding holein the lower tube sheet. This deficiency led to the plugging of thewrong tubes and to extra tube loading. The event report explainsthat the deficiency remained undetected for years because therewere no requirements for the tube to be verified in the same holein each tube sheet. As a corrective, the utility plugged the tube andintroduced a free path test with an Eddy Current Test (ECT) probe.

The lessons learned from those events are:

- Pre-service inspections of the SG should be carried out after theflushing of the SG.

- Special attention should be paid to the tube expansion processand to cleanliness during manufacturing and assembly of the SGin order to avoid stress corrosion cracking.

- Tube acceptance inspections should also be performed at the SGmanufacturing site and any quality deviation should be knownby the pre-service inspection staff on the NPP site, in order tofacilitate reviewing of inspection data.

- The location of the SG tube supports should be checked.- The path of the SG tubes through the corresponding holes in the

tube sheets should be checked.

4.9. Emergency diesel generators

Construction events relate to the inoperability of the emergencydiesel generators. The causes of these events are:

- missing supports for small diameter tubing, allowing vibrationsand leading to a tubing failure,

- misalignment of the off-gas compensators which led to cracks inthe compensators,

- insufficiently tightened bolt on a big-end bearing cap which cameloose and damaged the lubrication spray nozzle.

Other events describe the following manufacturing deficiencies:

- forging deficiency of a rocker arm in the exhaust valves mecha-nism which led to crack, then break,

- multiple electrical and I&C deficiencies (missing components,incorrect logic), which remained hidden because the componentswere tested but not the system as a whole,

- manufacturing fault in the exciter regulator, defective drilled holein the air supply system, manufacturing faults in the fuel con-troller, connecting rod damaged by a cutting tool.

The lessons learned from these events are:

- Commissioning tests should allow to verify the proper operationof a whole system.

- The manufacturer must implement quality assurance provisionsfor handling, transport, storage, assembly and disassembly andfor all kinds of components (exciter regulator, air supply system,fuel controller. . .).

4.10. Fire protection

Concerning construction, the event reports relate to fire barriers,to the extinguishing system and to dampers.

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On fire barriers, the events report improper installation of bar-iers, which could have allowed fire propagation into different fireectors. In one case, a subcontractor removed part of a vendor-rovided fire barrier and the acceptance inspection was performednly randomly by sampling. In the other case there was, incorrectpacing of mechanical fasteners due to wrong installation proce-ures, inadequate thickness of silicone foam, remaining temporaryeals, use of mineral wool in bridge cable boxes, etc.

As for the extinguishing systems, a spurious injection of CO2 wasue to a wiring error in the fire protection control panel, anotherpurious activation was due to an improper cable connection in aumid environment and a leak from a fire protection system wasue to several mechanical deficiencies during the installation of theipes.

Finally, two events report a missing damper, the improper fireating of numerous dampers due to inappropriate procurementocuments and wrong connection of dampers to the thermal actu-tion device.

The causes of the events are directly connected to the lack ofuality assurance and quality control by the company in charge ofhe installation and by the licensee.

Other event reports relate commissioning deficiencies:

Fire detection did not actuate because too many detectors werefitted in the same loop and because the commissioning tests didnot cover the situation where a lot of detectors are challenged.

Undetected flaws in functioning of dampers because the damperswere not tested as a whole, but each component was tested sep-arately (thermal actuation, electrical remote, etc.).

A CO2 fire protection system was kept in manual mode to pre-vent its actuation on sensing welding fumes but was neverthelessactuated by welding works because of a wiring error dating frominitial construction that had not been detected during commis-sioning.

A fire protection valve remained partially open after commission-ing tests.

A fire propagated quickly during commissioning because the fireprotection was not complete at that time.

The lessons learned for the latest are:

To ensure comprehensive scope of the commissioning activities. To ensure that the scope of commissioning includes checking ofpreventive interlocks such as non-actuation of a fire protectionsystem if it is in lockout.

To reinforce surveillance in order to ensure that the standby safetysystems are in the right configuration after commissioning tests.

.11. Ventilation

Concerning construction, the events reports concern severaleficiencies of the emergency ventilation of the control roomincorrect damper position, drains connected to external atmo-phere, malfunction of a fan). Many of these problems were notiscovered until flow balance and differential pressure measure-ents were carried out on the control room ventilation systems.Some event reports also describe incorrect installation of blow-

ut panels (oversized bolts or incorrect panel size) or missing blow-ut panels in the turbine building, which, in the event of HELB, couldave led to a pressure inside the building exceeding the structuralapability of the building.

Another event report relates to missing or encumbered tor-

ado venting panels which could have compromised the building’structural behaviour in a tornado. One of the main causes of theseeficiencies was the lack of design information about the ventinganels.

nd Design 241 (2011) 2916– 2926 2925

The lessons learned from those events are:

- Flow balance and differential pressure measurements should beconducted on the control room ventilation systems in order todetect potential deficiencies.

- Special attention should be paid to the proper installation of thebuildings’ overpressure protection devices (blow-out panels ortornado venting panels).

4.12. Crane

One event reports early wear of a heavy load crane due to theincorrect installation of two right-hand wound cables. The lessonlearned from this event is that cranes should be included in thecommissioning programmes and the tests and verifications shouldbe done prior to the main load lift.

5. Conclusions

As there was no recent comprehensive published study onlessons learned from events related to the pre-operational phases,it was decided to perform this analysis of past and current con-struction experience in order to provide both the utilities and theregulatory bodies with up-to-date lessons learned.

Based on various sources of information (mainly IRS database,US LERs and WGRNR reports), this study addressed the eventslinked with the construction of new nuclear reactors, includingcomponent manufacturing and commissioning.

About 247 IRS reports, 26 WGRNR reports and 309 US LERs werereviewed and distributed into categories related to technical itemsor components: civil structures, electrical components, mechanicalcomponents, etc.

This study showed that the most affected items by construc-tion, manufacturing or commissioning deviations are I&C (19%),electrical components (17%), welds (14%), valves (10%) and pipes(9%) and allowed to raise more than 50 technical lessons learnedwhich can complement usefully the existing IAEA documents(IAEA, 2001, 2009) which bring interesting recommendations con-cerning quality assurance, organisation and management systemsfor construction projects.

Most of the findings presented in this paper could be found inlarge construction sites but may not have consequences as crit-ical as in the nuclear industry. Therefore the deficiencies whichoccurred during construction, manufacturing and commissioningof a new reactor and which can remain major latent failures for along time after the reactor starts to operate need to be minimizedas much as possible.

This study shows also that it is possible to extract lessons learnedand recommendations for construction from operational experi-ence. However, it must be stressed that many more lessons learnedcould have been raised if more detailed information about con-struction had been available. Indeed, the event reports do notalways include information about non-conformances detected andcorrected prior to plant operation, as they have no impact on thesafety of the operating plant during the reported event.

Moreover, in most of the event reports resulting from con-struction deficiencies, the lessons learned for current and futureconstruction projects were often not fully considered; instead theyfocused more on the corrective action required for the operatingplant in question.

Therefore, it could be very valuable to share construction expe-rience in a systematic and timely manner at international level,especially as more than 50 new reactors are currently being con-structed or considered worldwide.

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cknowledgment

The work was carried out within the European Commission (EC)esearch and development programme.

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