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Progress in Nuclear Energy 53 (2011) 668e672
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Progress in Nuclear Energy
journal homepage: www.elsevier .com/locate/pnucene
Nuclear power plant commissioning experience
Benoît Zerger*, Marc NoëlEuropean Clearinghouse on Operational Experience Feedback for Nuclear Power Plants, Institute for Energy, Joint Research Centre, European Commission, P.O Box 2, 1755 ZG Petten,The Netherlands
a r t i c l e i n f o
Article history:Received 21 December 2010Received in revised form21 December 2010Accepted 26 April 2011
Keywords:ExperienceFeedbackCommissioningTestConstructionEvent
* Corresponding author. Tel.: þ 31 224 56 51 88; faE-mail address: [email protected] (B. Ze
0149-1970/$ e see front matter � 2011 Elsevier Ltd.doi:10.1016/j.pnucene.2011.04.010
a b s t r a c t
In this paper, we present the results of the analysis of the events related to the commissioning of newnuclear power plants and reported to the IAEA International Reporting System database. These resultsare extracted from a study performed by the European Clearinghouse on Nuclear Power Plant Opera-tional Feedback about the events related to the construction, the manufacturing and the commissioningof new nuclear power plants.
After the initial screening of the database, we have analysed in detail 34 events in order to highlightthe lessons learned specific to different components and to raise the general recommendations related tothe commissioning.
This paper summarizes the main lessons learned and the main recommendations concerning thecommissioning-related events. These recommendations concern mainly the time of the testing, thescope of the tests, the documentation of the tests, the test acceptance criteria, the systems reconfigu-ration after commissioning tests and the management of the temporary devices.
� 2011 Elsevier Ltd. All rights reserved.
1. Introduction
The results are extracted from a study (European Commission,2010) which has been done by the centralised office of the Euro-pean Clearinghouse on Nuclear Power Plant (NPP) OperationalFeedback (OEF) in the frame of technical work e preparation oftechnical report on preselected subject; in this case on experiencefrom events related to construction, manufacturing and commis-sioning of Nuclear Power Plants.
In the European Union, in order to support the Community activi-ties on evaluation of NPP operational events, a centralized regional“Clearinghouse” on NPP OEF was established in 2008 at the JointResearch Centre e Institute for Energy (JRC-IE), on request of NuclearSafety Authorities of several Member States, in order to improve thecommunication and information sharing on OEF, to promote regionalcollaborationonanalyses of operational experience anddisseminationof the lessons learned (Noël, 2010).Oneof the tasksperformedconsistsin performing in-depth analysis of event families (topical studies)(Bruynooghe and Noël, 2010), (Martin Ramos et al., 2010).
Interest in constructing new nuclear power plants is increasingworldwide. Some countries are embarking in a nuclear program forthe first time, others decided to re-start the construction of nuclearpower plants after a hiatus of decades. According to the PowerReactor Information System (PRIS) of the International Atomic
x: þ31 224 56 56 37.rger).
All rights reserved.
Energy Agency (IAEA), 55 construction projects are currentlylaunched or under consideration worldwide.
Starting new build is very demanding since much of the earlierexperience and resources have progressively been lost from thenuclear industry. Circumstances are quite different from 1970’swhen most of the currently operating plants were constructed.Vendors had large experienced organizations ready to go ahead,and had less need to rely on subcontractors. In addition, there wasno shortage of skilled manufacturing capacity, and designs wereoften based onwork done in similar ongoing or completed projects.
Consequently, lessons learned from the past constructionperiods or from the ongoing construction projects are veryimportant for the increased number of utilities and regulatorsinvolved in the construction of new NPPs in order to reduce theprobability that construction or commissioning problems whichalready occurred happen again.
Efforts to collect lessons learned form construction experiencehave already been done in the past, for example the United StatesNuclear Regulatory Commission (US NRC) report to the Congress,dated 1984 (United States Nuclear Regulatory Commission (US-NRC), 1984). More recently, the Nuclear Energy Agency (NEA) ofthe OECD created the Working Group on the Regulation of NewReactors (WGRNR) which examines the regulatory issues of siting,licensing and supervision of the new NPPs.
However, there is no recent comprehensive study publishedon lessons learned from events related to pre-operational phases.As a result, the Member States Safety Authorities participating to
B. Zerger, M. Noël / Progress in Nuclear Energy 53 (2011) 668e672 669
the European Clearinghouse on OEF agreed that it was necessary toperform an up-to-date analysis of both ancient and recentconstruction experience.
The study covers construction, commissioning andmanufacturing events, of which origin is prior to the start of thecommercial operation, in order to raise lessons learned andrecommendations for current and future construction programmes.
This paper focuses on the events related to the commissioningstage, which is defined by the IAEA glossary (IAEA, 2007) asfollows: “the process by means of which systems and componentsof facilities and activities, having been constructed, are madeoperational and verified to be in accordance with the design and tohave met the required performance criteria.” It gives complemen-tary results to the IAEA safety guide (IAEA, 2003).
2. Methodology
The Incident Reporting System (IRS) is an international systemjointly operated by the IAEA and the Nuclear Energy Agency of theOrganisation for Economic Cooperation and Development (OECD/NEA). It contains about 3600 event reports that provide detaileddescriptions and preliminary analyses of the event’s causes thatmay be relevant to other plants.
The IRS establishes a detailed framework inwhich the plant andthe characteristics of the incident can be classified according toa systematic set of codes which is later on very useful to retrieve theinformation.
Table 1Results of the IRS queries.
Query Number of registeredevents
2.4. Pre-operational 82.4.2 Commissioning 675.4.4. Equipment start-up 205.4.13. Commissioning
(of new equipment)12
Text searches 120Date searches 331TOTAL 558
2.1. Screening of the database
In the first stage, the commissioning-related events among theevents reported to the IRS from the start-up of this system until 30November 2009 are identified. The list of events is screened todistinguish the relevant events.
The web-based IRS has an advanced search tool to query theevents database by setting a combination of criteria on the fields:
- Guidewords- Countries- Plant names- Reactor type- Reactor supplier- Plant capacity- Incident date- Report submission date- IRS number- Start of commercial operation
Additionally, a word or phrase can be searched in all or in part ofthe reports.
For this study, the IRS database was searched by codes, by textstring searches and by date.
A systematic list of codes can be found in Appendix C Dictionaryof Codes of the IRS Guidelines (IAEA, 2009). This list has beenreviewed in detail to select the combination of codes to retrieve theevents of interest. The selected code are indicated in the tablebelow.
Moreover the results of text string searches of the word‘commissioning’ in the fields ‘title’, ’abstract’, ‘root causes’ and‘lessons learned’ are added to the code-driven query.
Finally, the events whose date preceded the date of start ofoperation were selected, as well as the events that occurred duringthe year following the start of operation. Indeed, even thoughconstruction or commissioning events can be detected years after
the start of operation, it was assumed that their occurrence wouldbe higher at the beginning of commercial operation.
The initial search with the combination of codes selected in thepreceding section, the text searches and the date searches yielded558 events (see Table 1 below).
After removing the overlaps, there are 409 events remaining forthe final short list.
The first step of the screening consists in selecting the relevantevents and in eliminating the others.
Events were rejected because they were related to plant modi-fications, because they are not relevant or because the IRS report isnot detailed or complete enough to be used for this report.
After this step, there were 34 remaining relevant IRS reports.
2.2. Analysis of the selected events
In the second stage, the selected events are analyzed to identifyand group the lessons learned from the incidents in differentcategories. For each category, a brief description is given of thenature of the root and direct cause or both, the consequences andthe lessons learned.
Each of these categories is further classified according to thetype of concerned component: pipes, pumps, valves, electricalcomponents, Instrumentation & Control, pumps, fire protection,ventilation and emergency diesel generators.
This structure enables to raise recommendations applicable foreach type of components. Moreover, it enables to identify moregeneric recommendations than a classification in systems whichare dependant on the reactor design.
3. Discussion
Fig. 1 shows the distribution of the commissioning events pertype of component. Almost half of the events relate to I&C defi-ciencies, 24% are related to mechanical components (pipes, valves,pumps) and the remaining events are related to fire protection,electrical components and emergency diesel generator.
3.1. Instrumentation and control
Fifteen IRS commissioning events related to I&C deficiencies.The following events should be noted:
- Three events describe deviations caused by commissioningactivities such as the disconnection of control room alarms toreduce the interference with normal activities, impropermodification of logic on containment hatch doors, or completeloss of the reactor protection system due to inadequate prep-aration of commissioning tests.
- Two events report undetected deviations during commis-sioning tests: a mistake in the I&C of a radioactive release
Fig. 1. Distribution of IRS commissioning events.
B. Zerger, M. Noël / Progress in Nuclear Energy 53 (2011) 668e672670
systemwhichwas not detected because the sump sensors werenot tested, and failure of a pressuriser safety relief valve to closebecause the control signal from the reserve control panel wasnot verified.
- During a load rejection test, a ‘fast trend update program’ wasturned on to collect data, which caused an unexpectedbehaviour of the reactor. A fault had been detected in thissoftware at commissioning stage but had not been correctedbecause it had been analysed as without any consequences onother programmes.
- Discrepancies between vessel level swell sensors were due tosnubbers found in three of the sensing lines. The presence ofthese snubbers was not documented and it was assumed thatthey were installed during the commissioning period beforeinitial start-up for sensor testing purposes.
The main lessons learned are:
- The need for safety and impact analysis prior to commissioningactivities
- Software with known or suspected faults should not be used incontrol circuits as it may have an unexpected influence onother programs.
3.2. Mechanical components
Two commissioning events related to pumps. The first eventreports the failure of the three seals of a Reactor Coolant Systempump which could be explained by the pressure or temperaturetransients during the commissioning tests. The second eventreports insufficient performance of the containment spray pumpsdue to excessive pressure loss in the heat exchangers, whichremained undetected for a long time because the entire contain-ment spray system was never tested.
Thiseventemphasized theneed tocarryout complex testsof safetysystems in condition representative of full accident configuration toverify that they comply with their design characteristics (partial testsof the recirculation by-pass lines may not be enough).
One commissioning event was reported involving pipes:a temporary valve needed for commissioning was left on aninstrumentation pipe, which led to a high frequency vibration cycleand subsequently to the fatigue fracture of the pipe.
Two commissioning events related to valves. In one case,temporary bolts which clamped a valve for transportation andhydrotests purposeswere left after commissioningandblocked reliefvalves in the closed position, which led the licensee to improve themonitoring of these temporary bolts. In the other case, a feedwatercheck valve failed partially because the commissioning tests allowedthe feedwater system to be operated in violation of procedures.
These events show the needs to manage properly the temporarydevices and that the commissioning tests can also be a cause offailure and should be performed with proper quality assurance andquality control procedures.
3.3. Electrical components
For electrical components, three IRS events related to theinsufficient scope of commissioning, which left deficienciesundetected:
- High voltage cables had not been adequately tested during thecommissioning stage. As a result, hidden defects in the insu-lation of the supply cables for the protection sensors in thesecond safety system train were not discovered in time.
- Ineffective verification of the backup batteries for fire alarmcontrol panels due to insufficient functional checks duringcommissioning, maintenance and testing.
- Breaker logic was not fully tested because the breakers weremistakenly assumed to be the same as those installed andalready tested in another plant unit.
A fourth event related to the commissioning activities them-selves, when a grid disruption occurred during battery testing andled to a loss of power supply. Afterwards, the testing ranges for thebatteries were modified to ensure that they remained connected tothe electrical switchboards and consumers during unloading tests.
The lessons learned are:
- To define a sufficient scope for commissioning activities.- To take into account the loss of external power during thetesting of batteries.
3.4. Fire protection
Four IRS events are relevant for this section:
- Fire detection did not actuate because too many detectors werefitted in the same loop and because the commissioning testsdid not cover the situation where a lot of detectors are chal-lenged simultaneously.
- Undetected flaws in functioning of dampers because the damperswere not tested as a whole, but each component was testedseparately (thermal actuation, electrical remote actuation)
- A CO2 fire protection system was kept in manual mode toprevent its actuation on sensing welding fumes but wasnevertheless actuated by welding works because of a wiringerror dating from initial construction that had not beendetected during commissioning.
- A fire protection valve remained partially open after commis-sioning tests
- A fire propagated quickly during commissioning because thefire protection was not complete at that time.
B. Zerger, M. Noël / Progress in Nuclear Energy 53 (2011) 668e672 671
The lessons learned are:
- To ensure comprehensive scope of the commissioningactivities.
- 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 standbysafety systems are in the right configuration after commis-sioning tests.
3.5. Emergency diesel generators
One event report mentions that information about the range ofa potentiometer was not properly communicated from the TestingTeam to the Operating Team and, as a result, the output voltage ofthe EDG was lower than expected.
Another event reports that several failures of a EDG protectionsystem remain undetected during the commissioning tests becausethe components of this protection system were tested individuallybut not the protection system as a whole.
A last event relates to improper implementation of EDG testprocedures which caused an improper coupling of the EDG to themains, out of synchronism, and therefore led to damages.
4. Recommendations
This section presents the main recommendations raised fromthe study, based on concrete examples.
4.1. Time of testing
One event reports the build-up of a coating on a switch overalmost two years of non-operability, after a functional test at thepre-operational stage and before start of plant operation.
This event shows the need to assess the period between thecommissioning tests of a component or system and the time whenthe component or system must be available.
The functionality of any standby component which is normally notin operation must be regularly tested, as a long period of inactivity andthe construction of other equipment during this period could alter thetest results.
4.2. Scope of the tests
Many events report deficiencies which remain undetectedbecause of the insufficient scope of the commissioning tests, forvarious reasons.
4.2.1. Test conditionsSome events report the following:
- A gap between the building structure and sump strainers dueto lack of quality assurance during construction. This gap wasnot identified at the commissioning stage because the systemcould not be tested under real accident conditions.
- Incorrect installation of an orifice plate in the containmentdecompression system, not detected at the constructionstage because it would have required a full test of the entirecontainment decompression system immediately afterinstallation and therefore an additional containment pressuretest.
- Inadequate performance of the containment spray pumps dueto excessive pressure loss in the heat exchangers, which
remained undetected for a long time because the entirecontainment spray system was never tested with waterdelivery to the spray nozzles.
The safety systems should be tested in conditions representative ofreal accident conditions, and if that is not possible, specific arrange-ments should be made for the systems concerned in terms of accep-tance tests, quality assurance, etc.
4.2.2. Comprehensiveness of testsThe following events are highlighted too:
- A non-return valve was found fitted in the wrong direction inthe RCS pump fire extinguishing system. The incorrectmounting was not detected during commissioning because thesystem was tested from downstream of the non-return valve.
- A leftover blank flange was found downstream of tank safetyvalve, in an untested line.
- High voltage cables had not been adequately tested. As a result,hidden defects in the insulation of the supply cables for theprotection sensors in the second safety system train were notdiscovered in time.
- Ineffective checking of the backup batteries for fire alarmcontrol panels.
- Fire detection did not actuate because toomany detectors werefitted in the same loop and because the commissioning testsdid not cover the situation were a lot of detectors arechallenged.
- A mistake in the I&C of a radioactive release system was notdetected because the sump sensors were not tested
- Failure of a pressuriser safety relief valve to close was notdetected because the control from the reserve control panelwas not verified.
- Improper location of probes during construction that remainedundetected for years, because the scope of commissioning andsurveillance tests was not broad enough and/or because thesensing lines were not equipped to be tested at their connec-tion points.
The scope of the tests should include all the components anddevices that are used during normal operation and those which couldbe used under accident conditions, including passive components suchas pipes, as they may be clogged, and including manufacturedcomponents, with correct documentation, as the quality control at themanufacturing plant may be deficient.
The automatic start-up of systems after a power disruptionshould be tested during commissioning.
4.2.3. Fragmented testsThe following should be noted:
- Multiple electrical and I&C deficiencies in an emergency dieselgenerator (missing components, incorrect logic), whichremained undetected because the components were tested,but not the system as a whole.
- Undetected malfunctioning of dampers because the damperswere not tested as a whole, but each component was testedseparately (thermal actuation, electrical remote actuation)
Both these events show that sometimes a deficiency of a systemcannot be detected because the system is not tested as a whole.Instead, some components are tested separately, and sometimes bydifferent entities.
Safety systems should be submitted to overall functional tests as faras possible, to ensure not only the performance of each single
B. Zerger, M. Noël / Progress in Nuclear Energy 53 (2011) 668e672672
component but the performance of the whole system, including theinteractions between different components.
4.2.4. Non-actuation tests
- A CO2 fire protection system was kept in manual mode toprevent actuation on sensing welding fumes, but was never-theless actuated by welding work.
- Incorrect wiring led to the degradation of a reactor protectionvoting logic from ‘2 out of 30 to a logic ‘1 out of 20, which wasnot detected during the commissioning tests because themeasuring channel was not tested in a ‘1 out of 30 voting logic.
The tests should be designed to detect an unexpected (spurious)actuation of a safety system.
4.2.5. Commissioning of different unitsA breaker logic was not fully tested because the breakers were
mistakenly assumed to be the same as those installed and alreadytested in the other plant’s unit.
The commissioning tests should be repeated with the same scope atall units, because each unit is unique at least from the installationpoint of view.
4.2.6. Conducting simultaneous testsOne event reports that a hole was discovered in a duct, creating
a pathway through the containment integrity, but had not beendetected for a long time because the ventilation test proceduresentailed operating several ventilation systems at the same time,which actually masked some degradations of the containmentintegrity.
The commissioning tests should be designed to take account of thefact that simultaneous tests may have an influence on each other’sresults.
4.3. Documentation of tests
The following event should be noted: the polarity of a trans-former was inverted in accordance with an incorrect wiringdiagram. The error was not detected during the polarity checksbecause they were performed following the wiring diagram andnot following the design diagram.
The acceptance or commissioning tests should not be designed tocheck the installation drawings, which may be wrong, but should referto the original design drawings.
4.4. Test acceptance criteria
One event report indicates that valve motors failed to pull in at80% of rated voltage as specified in the procurement documents.Commissioning tests showed that the contactors closed at highervoltage than expected, but the test was considered successfulbecause there was no acceptance criterion about the contactorclosure voltage.
The test acceptance criteria should allow testers to verify not onlythe functionality of a system or component but also its level ofperformance.
4.5. Systems reconfiguration after commissioning tests
One event report describes a fire protection valve whichremained partially open after commissioning tests.
The proper reconfiguration of the systems after the commissioningtests should be checked.
4.6. Use of temporary devices
Several event reports describe deficiencies or failures due totemporary devices used for commissioning. Some of thesetemporary devices led to the safety systems being inoperable foryears.
The following can be highlighted:
- temporary bolts which clamped a valve for transportation andhydrotests purposes were left after commissioning and blockedrelief valves in the closed position
- temporary valve needed for commissioning was left on aninstrumentation pipe, which led to a high frequency stresscycle and subsequently to the fatigue fracture of the pipe.
Temporary devices used at the commissioning stage should beproperly documented in order to ensure that all the temporary devicesare removed after their use.
5. Conclusions
This paper presents an extract of the study about the experiencefeedback of construction, manufacturing, and commissioning ofnew NPP. It is based on the analysis of 34 IRS event reports whichhave been identified after the screening of the whole IRS database,which corresponds to the smallest group of events analyzed in thisstudy (13% of the analyzed IRS events). Beyond the lessons learntwhich can be raised for specific components, the paper shows thatspecial attention should be paid to the scope of the tests: thecommissioning tests should be performed in representativeconditions, they should enable to test every device or component ofa system but the performance of the whole system as well, and thecommissioning tests programme should consider the potentialinterference between different simultaneous tests.
As the commissioning tests should not cause a degradation ofthe safety, special attention should also be paid to the managementof the temporary devices needed for the tests and to the properreconfiguration of the systems following the tests.
Acknowledgements
The work was carried out within the European Commission (EC)research and development programme.
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