Nuclear Safety
NEA/CSNI/R(2015)7
April 2015
www.oecd-nea.org

First-term Status Report for

the Component Operational
Experience Degradation andAgeing Programme (CODAP)
2011-2014

Unclassified

NEA/CSNI/R(2015)7

Organisation de Coopération et de Développement Économiques
Organisation for Economic Co-operation and Development

04-May-2015___________________________________________________________________________________________English text only
NUCLEAR ENERGY AGENCYCOMMITTEE ON THE SAFETY OF NUCLEAR INSTALLATIONSNEA/CSNI/R(2015)7
Unclassified
First-term Status Report on Component Operational Experience Degradation and Ageing Programme
CODAP (2011-2014)

JT03375563

English text only

Complete document available on OLIS in its original format
This document and any map included herein are without prejudice to the status of or sovereignty over any territory, to the delimitation ofinternational frontiers and boundaries and to the name of any territory, city or area.

NEA/CSNI/R(2015)7

ORGANISATION FOR ECONOMIC CO-OPERATION AND DEVELOPMENTThe OECD is a unique forum where the governments of 34 democracies work together to address the economic, socialand environmental challenges of globalisation. The OECD is also at the forefront of efforts to understand and to help
governments respond to new developments and concerns, such as corporate governance, the information economy and thechallenges of an ageing population. The Organisation provides a setting where governments can compare policy experiences,
seek answers to common problems, identify good practice and work to co-ordinate domestic and international policies.
The OECD member countries are: Australia, Austria, Belgium, Canada, Chile, the Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Israel, Italy, Japan, Luxembourg, Mexico, the Netherlands, New
Zealand, Norway, Poland, Portugal, the Republic of Korea, the Slovak Republic, Slovenia, Spain, Sweden, Switzerland,
Turkey, the United Kingdom and the United States. The European Commission takes part in the work of the OECD.
OECD Publishing disseminates widely the results of the Organisation’s statistics gathering and research on economic,
social and environmental issues, as well as the conventions, guidelines and standards agreed by its members.

NUCLEAR ENERGY AGENCYThe OECD Nuclear Energy Agency (NEA) was established on 1 February 1958. Current NEA membership consists of
31 countries: Australia, Austria, Belgium, Canada, the Czech Republic, Denmark, Finland, France, Germany, Greece, Hungary,
Iceland, Ireland, Italy, Japan, Luxembourg, Mexico, the Netherlands, Norway, Poland, Portugal, the Republic of Korea, theRussian Federation, the Slovak Republic, Slovenia, Spain, Sweden, Switzerland, Turkey, the United Kingdom and the UnitedStates. The European Commission also takes part in the work of the Agency.
The mission of the NEA is:– to assist its member countries in maintaining and further developing, through international co-operation, the scientific,
technological and legal bases required for a safe, environmentally friendly and economical use of nuclear energy forpeaceful purposes;– to provide authoritative assessments and to forge common understandings on key issues, as input to government
decisions on nuclear energy policy and to broader OECD policy analyses in areas such as energy and sustainable
development.
Specific areas of competence of the NEA include the safety and regulation of nuclear activities, radioactive waste
management, radiological protection, nuclear science, economic and technical analyses of the nuclear fuel cycle, nuclear law
and liability, and public information.
The NEA Data Bank provides nuclear data and computer program services for participating countries. In these and related
tasks, the NEA works in close collaboration with the International Atomic Energy Agency in Vienna, with which it has a Cooperation Agreement, as well as with other international organisations in the nuclear field.

This document and any map included herein are without prejudice to the status of or sovereignty over any territory, to the delimitation of international
frontiers and boundaries and to the name of any territory, city or area.
Corrigenda to OECD publications may be found online at: www.oecd.org/publishing/corrigenda.
© OECD 2015
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THE COMMITTEE ON THE SAFETY OF NUCLEAR INSTALLATIONSThe NEA Committee on the Safety of Nuclear Installations (CSNI) is an international committee
made up of senior scientists and engineers with broad responsibilities for safety technology and research
programmes, as well as representatives from regulatory authorities. It was created in 1973 to develop andco-ordinate the activities of the NEA concerning the technical aspects of the design, construction andoperation of nuclear installations insofar as they affect the safety of such installations.
The committee’s purpose is to foster international co-operation in nuclear safety among NEA member
countries. The main tasks of the CSNI are to exchange technical information and to promote collaboration
between research, development, engineering and regulatory organisations; to review operating experienceand the state of knowledge on selected topics of nuclear safety technology and safety assessment; toinitiate and conduct programmes to overcome discrepancies, develop improvements and reach consensus
on technical issues; and to promote the co-ordination of work that serves to maintain competence innuclear safety matters, including the establishment of joint undertakings.
The priority of the committee is on the safety of nuclear installations and the design and constructionof new reactors and installations. For advanced reactor designs, the committee provides a forum for
improving safety-related knowledge and a vehicle for joint research.
In implementing its programme, the CSNI establishes co-operative mechanisms with the NEA’s
Committee on Nuclear Regulatory Activities (CNRA), which is responsible for the Agency’s programme
concerning the regulation, licensing and inspection of nuclear installations with regard to safety. It also cooperates with the other NEA Standing Technical Committees as well as with key internationalorganisations such as the International Atomic Energy Agency (IAEA) on matters of common interest.

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EXECUTIVE SUMMARY

Structural integrity of piping systems is important for plant safety and operability. In recognition ofthis, information on degradation and failure of piping components and systems is collected and evaluatedby regulatory agencies, international organisations (e.g., OECD/NEA and IAEA) and industry
organisations worldwide to provide systematic feedback to reactor regulation and research anddevelopment programmes associated with non-destructive examination (NDE) technology, in-service
inspection (ISI) programmes, leak-before-break evaluations, risk-informed ISI, and probabilistic safetyassessment (PSA) applications involving passive component reliability.
Several OECD Member Countries have agreed to establish the OECD/NEA "Component Operational
Experience, Degradation & Ageing Programme" (CODAP) to encourage multilateral co-operation in thecollection and analysis of data relating to degradation and failure of metallic piping and non-piping
metallic passive components in commercial nuclear power plants. The scope of the data collection includes
service-induced wall thinning, part through-wall cracks, through-wall cracks with and without active
leakage, and instances of significant degradation of metallic passive components, including piping pressure
boundary integrity. The Project is organised under the OECD/NEA Committee on the Safety of Nuclear
Installations (CSNI).
CODAP is the continuation of the 2002–2011 "OECD/NEA Pipe Failure Data Exchange Project"(OPDE) and the Stress Corrosion Cracking Working Group of the 2006–2010 “OECD/NEA SCC and
Cable Ageing project” (SCAP). OPDE was formally launched in May 2002. Upon completion of the 3rd
Term (May 2011), the OPDE project was officially closed to be succeeded by CODAP. SCAP was enabled
by a voluntary contribution from Japan. It was formally launched in June 2006 and officially closed withan international workshop held in Tokyo in May 2010. Majority of the member organizations of the two
projects were the same, often being represented by the same person. In May 2011, thirteen countries signed
the CODAP 1st Term agreement (Canada, Chinese Taipei, Czech Republic, Finland, France, Germany,
Korea (Republic of), Japan, Slovak Republic, Spain, Sweden, Switzerland and United States of America).
A key accomplishment of CODAP is the establishment of a framework for the systematic collectionand evaluation of service-induced degradation and failure of passive metallic components. The Online
Event Database facilitates data entry as well as database interrogation. The Online Knowledge Base allows
for the capturing, sharing, transferring, storing and utilizing technical information on environmental
degradation mechanisms, structural integrity evaluations, relevant R&D results, and national codes andstandards for design and construction and in-service inspection.
The Online Event Database includes almost 4700 event records from 324 commercial nuclear power
plants. The Online Knowledgebase includes country specific collections of documents and supporting
information sorted by degradation mechanisms based on the events in the Online Event Database.
This project report describes the status of the First Term (2011-2014) of the CODAP event databaseand knowledge base. A review of the operating experience as documented in the event database addresses
trends-and-patterns, the effectiveness of various strategies to mitigate environmental degradation, and theexperience with non-destructive examination.
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TABLE OF CONTENTSEXECUTIVE SUMMARY .............................................................................................................................5
LIST OF FIGURES .........................................................................................................................................9
LIST OF ABBREVIATIONS AND ACRONYMS ......................................................................................10
1.

INTRODUCTION ..................................................................................................................................11
1.1
1.2
1.3

2.

CODAP OBJECTIVE AND SCOPE .....................................................................................................15
2.1
2.2

3.

Scope of Event Database.................................................................................................................25
Working with the Event Database...................................................................................................27
High-Level Database Summary ......................................................................................................28

CODAP KNOWLEDGE BASE .............................................................................................................33
6.1
6.2

7.

Principles of Data Quality ...............................................................................................................21
QAP Scope ......................................................................................................................................22
Confidentiality ................................................................................................................................23
Coding Guideline ............................................................................................................................23

CODAP EVENT DATABASE ..............................................................................................................24
5.1
5.2
5.3

6.

Responsibilities of Project Participants...........................................................................................17
The NEA Secretariat .......................................................................................................................17
CSNI ...............................................................................................................................................17
CODAP Project Review Group ......................................................................................................18
The Operating Agent .......................................................................................................................18
The Knowledge Base Coordinator ..................................................................................................19QUALITY ASSURANCE PROGRAM .................................................................................................21
4.1
4.2
4.3
4.4

5.

Data Collection Methodology .........................................................................................................15
CODAP Knowledge Base ...............................................................................................................16

PROJECT ORGANISATION ................................................................................................................17
3.1
3.2
3.3
3.4
3.5
3.6

4.

Project History ................................................................................................................................11
Transition from OPDE to CODAP .................................................................................................13
Report Structure ..............................................................................................................................13

Knowledge Management ................................................................................................................33
Structure of CODAP-KB ................................................................................................................33

OPERATING EXPERIENCE INSIGHTS .............................................................................................37
7.1 RCPB Crack and Leak Events ........................................................................................................37
7.2 Primary Water Stress Corrosion Cracking ......................................................................................40
7.4 Service Water Piping Failures.........................................................................................................42
7.5 Socket Weld Failures ......................................................................................................................44
7.5.1 Socket Weld Failure Data ..........................................................................................................45
7.5.2 Socket Weld Reliability and Integrity Management .................................................................46
7.6 NDE Failures...................................................................................................................................47

8.

DATABASE ACCESSIBILITY ............................................................................................................50

9.

CONCLUSIONS AND FUTURE PLANS ............................................................................................53
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9.1
9.2
10.

Conclusions and Recommendations ...............................................................................................53
Planned Activities Beyond 2014 .....................................................................................................53
REFERENCES ...................................................................................................................................55

APPENDIX A CODAP PRG ACTIVITY REPORT ...................................................................................57
A.1
A.2
A.3
A.4

PRG Meetings .................................................................................................................................58
CODAP Topical Reports ................................................................................................................58
CSNI WGRISK Project on “Use of OECD Data Project Products in PSA” ..................................58
Conference Participation .................................................................................................................58

APPENDIX B GLOSSARY OF TECHNICAL TERMS.............................................................................61

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LIST OF FIGURES

Figure 1: CODAP Database Opening Screen ............................................................................................... 27
Figure 2: CODAP Main Menu ..................................................................................................................... 28
Figure 3: Database Content by Geographic Region ..................................................................................... 30
Figure 4: Cumulative Number of Failure Records ....................................................................................... 30
Figure 5: Damage / Degradation Mechanisms in CODAP Event Database ................................................. 31
Figure 6: CODAP-KB Structure .................................................................................................................. 34
Figure 7: CODAP-KB Work Area ............................................................................................................... 35
Figure 8: CODAP-KB Advanced Search Area ............................................................................................ 35
Figure 9: An Example of a CODAP-KB Search .......................................................................................... 36
Figure 10: RCPB Piping Crack & Leak Events ........................................................................................... 38
Figure 11: RCPB Crack & Leak Events Involving Non-Piping Passive Components................................. 39
Figure 12: RCPB Piping @ Power Leak Events .......................................................................................... 39
Figure 13: Summary of PWSCC Incidents in PWR Primary Circuits 1986-2014 ....................................... 40
Figure 14: PWSCC Incidents Involving Reactor Coolant Cold Leg & Hot Leg Piping .............................. 42
Figure 15: SW Piping & Non-Piping Passive Component Failures ............................................................. 43
Figure 16: Selected Socket Weld Failure Data (1990-2014) ........................................................................ 46
Figure 17: NDE Failure Population in CODAP Event Database ................................................................. 49

LIST OF TABLES

Table 1: CODAP Completeness Index (CI) Definitions .............................................................................. 22
Table 2: Scope of CODAP Event Database ................................................................................................. 26
Table 3: Database Content by Participating Country ................................................................................... 29
Table 4: Database Content by Plant Type & Passive Component Category ................................................ 29
Table 5: An Example of Code Class 1 Socket Weld Populations ................................................................ 45

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LIST OF ABBREVIATIONS AND ACRONYMS

OD
OECD

Outside Diameter
Organisation for Economic CoOperation and DevelopmentOPDE OECD Pipe Failure Data Exchange
Project
PCSG Pipe Cracking Study Group
PDA
Performance Demonstration
Administrator
PDI
Performance Demonstration Initiative
PMDA Proactive Materials Degradation
Assessment
PRG
Project Review Group
PSA
Probabilistic Safety Assessment
RC
Reactor Coolant
RCPB Reactor Coolant Pressure Boundary
RF
Refuelling Cycle
RHR
Residual Heat Removal
RI-ISI Risk Informed In-Service Inspection
RIM
Reliability and Integrity Management
RT
Radiographic Testing
RV
Relief Valve
RPVIS Reactor Pressure Vessel Internals
SCAP Stress Corrosion Cracking and Cable
Ageing Project
SW
Service Water
TRM
Technical Requirements Manual
UHS
Ultimate Heat Sink
UT
Ultrasonic Testing
VHP
Vessel Head Penetration
VT
Visual Inspection TechniqueXML
Extensible Mark-up Language

AFCN
AMP
ASME

Agence Fédérale de Contrôle Nucléaire
Ageing Management Program
American Society of MechanicalEngineers
ASN
L'Autorité de sûreté nucléaire
BMI
Bottom Mounted Instrument
CL
PWR Reactor Coolant System ColdLeg
CSNI
Committee on the Safety of Nuclear
Installations
CSV
Character Separated Values
DEGB Double-Ended Guillotine Break
DN
Nominal Diameter [mm]E/C
Erosion-Corrosion
E-C
Erosion-Cavitation
EDF
Electricité de France
EMDA Expanded
Material
Degradation
Assessment
FAC
Flow Accelerated Corrosion
GALL Generic Aging Lessons Learned
HL
PWR Reactor Coolant System Hot LegHTHeat Transport
IAEA International Atomic Energy Agency
IAGE CSNI Working Group on Integrity andAgeing of Components and Structures
ID
Inside Diameter
IGALL International Generic Aging Lessons
Learned
ISI
In-Service Inspection
KB
Knowledge Base
LOCA Loss-of-Coolant Accident
NEA
Nuclear Energy Agency
NDE
Non-Destructive Examination

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1.

INTRODUCTION

Structural integrity of piping components and systems and non-piping passive components such as thereactor pressure vessel and internals is important for plant safety and operability. In recognition of this,information on degradation and failure of metallic piping and non-piping passive components is collected
and evaluated by regulatory agencies, international organisations (e.g., OECD/NEA and IAEA) andindustry organisations worldwide to provide systematic feedback for example to reactor regulation andresearch and development programmes associated with ageing phenomena, non-destructive examination(NDE) technology, in-service inspection (ISI) programmes, leak-before-break evaluations, risk-informed
ISI, and probabilistic safety assessment (PSA) applications involving passive component reliability.
Since 2002, the OECD/NEA has operated an event database project that collects information on
passive metallic component degradation and failures of the primary system, reactor pressure vesselinternals, main process and standby safety systems, and support systems (i.e., ASME Code Class 1, 2 and
3, or equivalent), as well as non-safety-related (non-code) components with significant operational impact.
With an initial focus on piping systems and components (the OPDE Project), the scope of the project in2011 was expanded to also address the rector pressure vessel and internals as well as certain other metallic
passive components that are susceptible to environmental degradation. In recognition of the expanded
scope, the Project Review Group approved the transition of OPDE to a new, expanded “Component
Operational Experience, Degradation & Ageing Programme” (CODAP).
1.1

Project History

Reviews of service experience with safety-related and non-safety-related piping systems have beenongoing ever since the first commercial nuclear power plants came on line in the 1960’s. In 1975 the U.S.
Nuclear Regulatory Commission established a Pipe Crack Study Group (PCSG) charged with the task ofevaluating the significance of stress corrosion cracking in boiling water reactors (BWRs) [1] andpressurised water reactors (PWRs) [2]. Service experience review was a key aspect of the work by the
PCSG. Major condensate and feedwater piping failures (e.g., Trojan and Surry-2 in the U.S.) due to flow
accelerated corrosion (FAC) resulted in similar national and international initiatives to learn from service
experience and to develop mitigation strategies to prevent recurrence of pipe failures [3][4][5]. Early
indications of the significance of thermal fatigue phenomena evolved in the 1970s, and, again, systematic
reviews of the service experience enabled the introduction of improved piping design solutions, NDE
methods, and operating practices [6].
The team of analysts responsible for the seminal Reactor Safety Study (WASH-1400) [7] performed alimited evaluation of nuclear and non-nuclear power plant piping reliability based on field experience dataon pipe failures. This evaluation was aimed at estimation of loss-of-coolant-accident (LOCA) frequencies
for input to the two PSA models of WASH-1400. After the publication of WASH-1400 in 1975 manyother R&D projects have explored the roles of structural reliability models and statistical evaluation
models in providing acceptable input to PSA. Furthermore, during the past 20 years efforts have been
directed towards establishment of comprehensive pipe failure event databases as a foundation for
exploratory research to better understand the capabilities and limitations of today’s piping reliability
analysis frameworks. Risk-informed piping reliability analysis relies on statistical evaluations of validated
operating experience data, complemented with structural reliability modeling insights.
Assessment of passive component service experience data has been an integral element of regulatory
and industry programs to address long term operation and nuclear plant license renewal. Examples of such
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programs include the Proactive Materials Degradation Assessment (PMDA), Expanded Materials
Degradation Assessment (EMDA), Generic Aging Lessons Learned (GALL) and International Generic
Aging Lessons Learned (IGALL).1 A common feature of these four programs is the acknowledgement ofsystematic reviews of the accumulated service experience data as one-of-several inputs to the developmentof a technical basis for practical ageing management of metallic passive components.
In parallel with these focused efforts to evaluate service experience data and to correlate theoccurrence of material degradation with piping design and operational parameters, initiatives have beenpresented to establish an international forum for the systematic collection and exchange of service
experience data on piping. An obstacle to the use of the database by other countries of national qualitativeand quantitative pipe failure information is that criteria and interpretations applied in the collection andanalysis of events and data differ among the various countries. A further impediment is that thedescriptions of reported events and their root causes and underlying contributing factors, which areimportant to the assessment of the events, are usually written in the native language of the countries where
the events were observed.
To overcome these obstacles, the preparation for the OECD Pipe Failure Data Exchange (OPDE)
Project was initiated in 1994 by the Swedish Nuclear Power Inspectorate (SKI)2. In 1994 SKI launched a
5-year R&D project to explore the viability of creating an international pipe failure database. During thisperiod SKI hosted meetings to present results of the R&D and to discuss the principles of databasedevelopment and maintenance.3 Since May 2002, the OECD/NEA has formally operated the project under
the coordination of the Committee on the Safety of Nuclear Installations (CSNI). The first term of the
Project covered the years 2002-2005, the second term covered the period 2005-2008, and the final term
covered the period 2008-2011 [8].
In May 2011 the Project Review Group (PRG) approved the transition of OPDE to a new, expanded
OECD-NEA Component Operational Experience, Degradation & Ageing Programme (CODAP). A first
CODAP National Coordinators Meeting was held at NEA Headquarters in November 2011. The CODAP
PRG Membership corresponds to that of the OPDE, with two additional member countries (Slovak
Republic and Chinese Taipei). The CODAP project builds on the success of OPDE and a related OECDNEA data project, the SCAP-SCC Working Group.
In 2006 the SCC and Cable Ageing Project (SCAP) was established under the auspices of the
OECD/NEA to assess, due to their implication on nuclear safety and their relevance for plant ageing
management, two subjects: stress corrosion cracking (SCC) and degradation of cable insulation. The
project ran successfully from June 2006 to June 2010 [9]. SCAP was financed through a Japanesevoluntary contribution to the NEA.
Fourteen NEA member countries joined the SCAP project in 2006 to share knowledge and by 2010seventeen countries had joined the project. The International Atomic Energy Agency (IAEA) and theEuropean Commission, through its Joint Research Centre in Petten, also participated as observers.
The objective of the SCAP coordinated project was to share the corporate knowledge and operating
experience, to understand the failure mechanisms, and to identify effective techniques and technologies to1

Detailed information on PMDA, EMDA and GALL are available at www.nrc.gov. The IGALL is summarized in IAEATECDOC-1736 (April 2014), which is available at www.iaea.org.
2
Swedish Radiation Safety Authority (SSM) as of July 1, 2008
3
In September 1996 SKI organised the “Initial Meeting of the International Cooperative Group on Piping Performance” withparticipants from thirteen countries. Again, in September 1997 SKI organized the “Seminar on Piping Reliability” (SKI Report
97:32); this time with participants from eleven countries.

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effectively manage and mitigate active degradation in nuclear power plants. The specific objectives of the
project were to:•Establish a complete database with regard to major ageing phenomena for SCC and degradationof cable insulation through collective efforts by OECD/NEA members.

•

Establish a knowledge base in these areas by compiling and evaluating the collected data andinformation systematically.

•

Perform an assessment of the data and identify the basis for commendable practices which will
help regulators and operators to enhance ageing management.

The scope of the SCAP SCC Working Group activities covered class 1 and 2 pressure boundary
components, reactor pressure vessel internals and other components with significant operational impact,excluding steam generator tubing. The entire SCC database consisted of an event database and general
information.
The
generalinformationconsistedofregulations/codes&
standards,
inspection/monitoring/qualification, preventative maintenance/mitigation, repair/replacement, safetyassessment, and R&D. Together these information categories comprised the Knowledge Base.
1.2

Transition from OPDE to CODAP

Following the completion of the SCAP project, SCC Working Group participants were interested insome form of continuation and discussions were initiated to explore possible alternatives. It was recognisedthat there were many aspects very similar to those existing in OPDE and the concept of a new project wasenvisaged to combine the two projects into the “Component Operational Experience, Degradation &Ageing Programme” (CODAP). The objective of CODAP is to collect information on passive metallic
component degradation and failures of the primary system, reactor pressure vessel internals, main process
and standby safety systems, and support systems (i.e., ASME Code Class 1, 2 and 3, or equivalent). It also
covers non safety-related (non-Code) components with significant operational impact.
During the three OPDE Project Terms (2002-2011), the event database was maintained anddistributed as a Microsoft® Access database. This database was distributed on a CD to the National
Coordinators twice per calendar year. Towards the end of the first Project Term, a web-based databaseformat was developed to facilitate data exchange. The web-based OPDE resided on a secure server at the
NEA Headquarters. With the 2011 transition from OPDE to CODAP, a new and enhanced web-based
database format was implemented. As of mid-2012, the entire CODAP event database resides on a secure
server at NEA Headquarters. Provisions exist for online database interrogation (e.g., event review, QA,
queries) as well as downloading queries (in CSV- or XML-file format) and selected event records or entire
database (in XML-file format) to a local computer or computer network. In addition to the event database,
CODAP includes a web-based Knowledge Base (KB) that contains relevant national and internationalreference material on passive metallic component damage and degradation mechanisms. Included in the
KB are codes and standards, R&D results, regulatory frameworks, and country-specific aging management
programs. As for the event database, the KB resides on a secure server at NEA Headquarters.
1.3

Report Structure

Section 2 describes the CODAP objective and scope. The CODAP organization and quality assurance
program are described in Sections 3 and 4, respectively. The event database and knowledge base aredescribed in Section 5 and 6, respectively. A selective and high-level review of the operating experience
with piping and non-piping passive components is documented in Section 7. It addresses trends-andpatterns, the effectiveness of various strategies to mitigate environmental degradation, and the experience
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with non-destructive examination. Database accessibility is addressed in Section 8. Conclusions and futureplans are addressed in Section 9. Finally, a list of references is included in Section 10. Appendix A
includes a CODAP-PRG activity report, and Appendix B is a glossary of terms.

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2.

CODAP OBJECTIVE AND SCOPE

CODAP is the continuation of the 2002-2011 “OECD/NEA Pipe Failure Data Exchange Project”(OPDE) and the work by the Stress Corrosion Cracking Working Group of the 2006 – 2010 “OECD/NEA
SCC and Cable Ageing Project” (SCAP). OPDE was formally launched in May 2002. Upon completion of
the 3rd Term in May 2011 the OPDE project was officially closed. SCAP was enabled by a voluntary
contribution from Japan. It was formally launched in June 2006 and officially closed with an international
workshop held in Tokyo in May 2010. Most of the members of the two projects were the same, often being
represented by the same person. The scope of the CODAP is based on a combination of the concepts fromthe two projects. Thus it encompasses service experience data on metallic piping and non-piping passive
components and well as a Knowledge base as in SCAP but addressing the full range of failure mechanisms
as in OPDE.
2.1

Data Collection Methodology

The CODAP Project exchanges data on passive component degradation and failure, including serviceinduced wall thinning, non-through wall crack, leaking through-wall crack, pinhole leak, leak, rupture andseverance (pipe break caused by external impact). For non-through wall cracks the CODAP scope
encompasses degradation exceeding design code allowable for wall thickness or crack depth as well assuch degradation that could have generic implications regarding the reliability of in-service inspection (ISI)
techniques. The following failure modes are considered4:•

Non-through wall defects (e.g., cracks, wall thinning) interpreted as structurally significant
and/or exceeding design code allowable;•

Loss of fracture toughness of cast austenitic stainless steel piping. The loss of fracture toughness
is attributed to thermal ageing embrittlement.

•

Through-wall defects without active leakage (leakage may be detected following a plant
operational mode change involving depressurization and cool-down, or as part of preparations fornon-destructive examination, NDE);•

Small leaks (e.g., pinhole leak, drop leakage) resulting in piping repair or replacement;•

Leaks (e.g., leak rates within Technical Specification limits);•

Large leaks (e.g., flow rates in excess of Technical Specification limits);•

Major structural failure (pressure boundary "breach" or "rupture").

In other words, the CODAP Event Database collects data on the full range of degraded conditions,from "precursors" to major structural failures. The structural integrity of a pressure boundary is determined
4

Appendix E of the CODAP “Coding Guideline” documents the different national reporting thresholds.

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by multiple and interrelated reliability attributes and influence factors. Depending on the conjoint
requirements for damage and degradation, certain combinations of material, operating environment,loading conditions together with applicable design codes and standard, certain passive components aresubstantially more resistant to damage and degradation than others. As an example, for stabilized austenitic
stainless steel pressure boundary components, there are no recorded events involving active, through-wallleakage. By contrast, for unstabilized austenitic stainless steel, multiple events involving through-wallleakage have been recorded, albeit with relative minor leak rates. Flow-accelerated corrosion (FAC), if
unmonitored, is a relatively aggressive degradation mechanism that has produced major structural failures,
including double-ended guillotine breaks (DEGB). The types of pipe failure included in the CODAP Event
Database are:•Event-based failures that are attributed to damage mechanisms and local pipe stresses. Examples
include high-cycle vibration fatigue due to failed pipe support, and hydraulic transient (e.g.,
steam or water hammer) acting on a weld flaw (e.g., slag inclusion).

•

Failures caused by environmental degradation such as stress corrosion cracking due to combined
effects of material properties, operating environment (e.g., corrosion potential, irradiation) andloading conditions.

The CODAP Event Database is a web based, relational database consisting of ca. 100 uniquely
defined data fields. It is a blend of free-format fields for detailed narrative information and fields definedby drop-down menus with key words (or data filters) or related tables. A basic premise of the use ofnarrative information is to preserve original event information as recorded in root cause evaluation reports
and reportable occurrence reports. The "related tables" include information on material, location of damage
or degradation, type of damage or degradation, system name, safety class, etc. The event databasestructure, database field definitions and data input requirements are defined in a coding guideline, which iscentral to the project, including database maintenance, data validation and quality control. The database
design has benefitted from a multidisciplinary approach involving chemistry, metallurgy, non-destructive
examination, structural integrity and PSA. Each event record relates to a uniquely defined component
boundary.
2.2

CODAP Knowledge Base

The CODAP Knowledge Base (KB) has been established to systematically compile basic
international technical information of relevance to the project. The KB is password protected and resides
on a secure server at NEA Headquarters in Paris, France. The KB is intended to provide a source of
information on technical issues related to all the failure mechanisms covered by the Event Database. The
type of information collected includes regulations, codes and standards with respect toinspection/monitoring/ non-destructive examination qualification, preventive maintenance/mitigation,
repair/replacement, operability determination, safety assessment/risk characterization, and R&D. The
information is both of a general nature and also more specific for the different degradation mechanisms.
The KB is intended to provide a source of systematically organised information for the project members, aswell as input to the topical reports that are prepared by the PRG members. There is a search function tofacilitate retrieval of information.
The KB is a web-based area of the CODAP project domain. It is organised as a hierarchical system offolders for general information, degradation specific information and a country folder for each project
member. The country folders have two purposes: 1) to upload files for inclusion in the common KB, and 2)
to provide a means of organising documents of national interest and relevance. In the latter casedocumentation can be in the language of the country, with a title in English. In the other folders all
documents are in English.
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3.

PROJECT ORGANISATIONThis section describes the CODAP project organization. The Operating Procedures, a controlled
document, describes the project organization, infrastructure and additional guidelines for the project toachieve the objectives as stated in the CODAP Terms and Conditions for project operation.
3.1

Responsibilities of Project Participants

All power for the CODAP resides with the signatory countries bound by a legal agreement “Terms &Conditions.” The Project Review Group (PRG), formed by the representatives of the signatories (normally
the National Coordinator) and an OECD/NEA representative holds all the power to make decisions on
running the project. Signatories may involve other bodies in their countries by separate operational
agreements.
3.2

The NEA Secretariat

OECD/NEA is responsible for administering the project according to OECD rules. This means
secretarial and administrative services in connection with the funding of the Project such as calling forcontributions, paying expenses incurred in connection with the Operating Agent and Knowledge Base
(KB) Coordinator, and keeping the financial accounts of the Project. NEA appoints the Project Secretariat.
3.3

CSNI

The OECD/NEA Committee for Safety of Nuclear Installations (CSNI) acts as an umbrella committeeof CODAP. Prior to publication of project-related results, all public domain reports prepared by the
CODAP Project Review Group undergo independent review by the CSNI.
The CSNI is an international committee made up of senior scientists and engineers, with broad
responsibilities for safety technology and research programmes, and representatives from regulatory
authorities. It was set up in 1973 to develop and co-ordinate the activities of the NEA concerning thetechnical aspects of the design, construction and operation of nuclear installations insofar as they affect thesafety of such installations.
The committee’s purpose is to foster international co-operation in nuclear safety amongst the OECDmember countries. The main tasks of the CSNI are to exchange technical information and to promotecollaboration between research, development, engineering and regulatory organisations; to review
operating experience and the state of knowledge on selected topics of nuclear safety technology and safetyassessment; to initiate and conduct programmes to overcome discrepancies, develop improvements andresearch consensus on technical issues; to promote the coordination of work that serves to maintaincompetence in the nuclear safety matters, including the establishment of joint undertakings. While theprimary focus of the committee is on existing power reactors and other nuclear installations; it also
considers the safety implications of scientific and technical developments of new reactor designs.

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The CSNI Working Group on Integrity and Ageing of Components and Structures (IAGE) has as
general mandate to advance the current understanding of those aspects relevant to ensuring the integrity ofstructures, systems and components, to provide for guidance in choosing the optimal ways of dealing withchallenges related to the integrity of operating, as well as new nuclear power plants, and to practice anintegrated approach to design, safety and plant life management. In this context, CODAP is improving thequality of data obtained relating to piping and non-piping passive component degradation experience, and,in turn, rendering such data more useful in predicting structural component degradation and failure.
3.4

CODAP Project Review GroupThe CODAP Project Review Group (PRG) runs the Project, with assistance from the NEA Project
Secretary, the Operating Agent and KB Coordinator. The PRG meets at least once per year. The PRG
responsibilities include but are not limited to the following types of decisions:

3.5•

Secure the financial and technical resources necessary to carry out the Project•Nominate the CODAP project chairperson•

Define the information flow (public information and confidential information)•

Approve the admittance of new members•

Nominate project task leaders (lead countries) and key persons for the PRG tasks•

Define the priority of the task activities•

Monitor the progress of the project and task activities•

Approve and monitor the work of the Operating Agent and quality assurance•

Approve and monitor the work of the Knowledge Base Coordinator.
The Operating Agent

To assure consistency of the event database data contributed by the National Coordinators the Project
operates through an Operating Agent. The Operating Agent verifies whether the event information
provided by the National Coordinators complies with the CODAP Coding Guidelines (CG); CODAP-PR01[10]. It also verifies the completeness and accuracy of the data and assigns the quality index jointly withrespective National Coordinator who has provided such data.

The CODAP Applications Handbook (CODAP-AH) [11] includes guidelines for extracting insightsfrom the event database about material degradation, including failure trends and event population data for
input to statistical parameter estimation tasks. It includes descriptions of the data processing steps that areneeded to facilitate statistical evaluations of operating experience with metallic piping components andnon-piping passive components. Whereas the CODAP Coding Guideline (CODAP-CG) defines databasestructure and data submission requirements, the CODAP-AH includes guidelines for creating databasequeries and associated data processing steps. CODAP-AH is a companion document to CODAP-CG.

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3.6

The Knowledge Base Coordinator

To assure consistency of the KB material and information contributed by the National Coordinators
the Project operates through a KB Coordinator. The KB Coordinator verifies whether the material andinformation provided by the National Coordinators complies with the KB Structure; CODAP-PR04.

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4.

QUALITY ASSURANCE PROGRAM

The objective of the Quality Assurance Programme (QAP) is to establish organizational and technicalprinciples and measures for quality assurance (QA) and monitoring of the work during operation of the
CODAP Project to ensure high quality of the final product (CODAP Event Database, CODAP Knowledge
Base, and companion reports). The QAP applies to all activities in the project and is to be followed by all
project participants.
4.1

Principles of Data Quality

To achieve the objectives established for the CODAP event database a coding format has beendeveloped. This Coding Format is reflected in the Coding Guideline. The Coding Guideline builds on
established pipe failure data analysis practices and routines that acknowledge the unique aspects of passive
component reliability in heavy water reactor and light water reactor operating environments (e.g.,
influences by material and water chemistry).
For an event to be considered for inclusion in the event database it must undergo an initial screening
for eligibility.5 An objective of this initial screening is to go beyond the abstracts of event reports to ensurethat only pipe degradation and failures according to the work scope definition are included in the database.
Data quality is affected from the moment the field experience data is recorded at a nuclear power
plant, interpreted, and finally entered into a database system. The field experience data is recorded indifferent types of information systems ranging from action requests, work order systems, via ISI databases
and outage summary reports, to licensee event reports or reportable occurrence reports. Consequently thedetails of a degradation event or failure tend to be documented to various levels of technical detail in thesedifferent information systems. Building a CODAP event database record containing the full event history
often entails extracting information from multiple sources.
The term “data quality” is an attribute of the processes that have been implemented to ensure that any
given database record (including all of its constituent elements, or database fields) can be traced to thesource information. The term also encompasses “fitness-for-use”, that is, the database records should
contain sufficient technical detail to support database applications.
In CODAP, a “Completeness Index” (CI) is used for database management purposes. It distinguishes
between records for which more information must be sought and those considered to be complete (Table1). Each record in the database is assigned a CI, which relates to the completeness and comprehensivenessof the information in the database relative to the requirements of the Coding Guideline.
The “Completeness Index” is also intended as a database filter for determination of the‘fitness-for-application.’ The range of possible database applications covers advanced applications (e.g.,
the study of the effect of different water chemistries on specific degradation susceptibilities), risk-informed
applications (e.g., technical basis for degradation mechanism assessment in risk-informed ISI programme
development, or statistical parameter estimation in support of internal flooding PSA), and high-level
5

Section 5 covers database scope.

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summaries of service experience trends and patterns. Advanced database applications would normally relyon queries that are address specific subsets of the overall database content. By contrast, high-level databaseapplications would draw on information from the entire database content.
Table 1: CODAP Completeness Index (CI) Definitions
Completeness
Index
1

Description
Validated – all source data have been reviewed – no further action is expected

2

Validated – source data may be missing some non-essential information – no further
action anticipated. The term “non-essential” implies that information about piping
layout (including location of a flaw) may not be known exactly but can be inferred
based on other, similar events (at same or similar plant)3

Not validated – validation pending

Completeness also relates to the completeness of the event population in the database. The Operating
Agent periodically monitors the completeness of CODAP by comparing how other data sources capture
noteworthy events.
4.2

QAP Scope
The QA Programme covers all aspects of the CODAP Project, including:•Confidentiality (see below for additional details);•

Coding Guidelines (see below for additional information);•

Event Database development and maintenance. Any updating of database structure or content,
including database scope issues, can be performed only by the Operating Agent with technicalsupport from NEA-IT and must first be approved by the PRG;•

Knowledge Base development and maintenance. Any updating of KB structure or content can be
performed only by the KB Coordinator with technical support from NEA-IT and must first be
approved by the PRG;•

Data collection and data exchange. Data collection and coding of national data is performed by
National Coordinators or persons/organizations to whom/which the NC delegates this
responsibility. The data submitted to Operating Agent should be approved by the national
authorities/utilities and ready for data exchange.;•

Data submittal. The National Coordinators are responsible for data submissions;•

Distribution of information. Official distribution of project documentation takes place via
publication on the password protected Project website;•

External review. In certain cases the CODAP PRG may submit a document containing general
information for review by the CSNI or a CSNI Working Group (e.g., the “Integrity ofComponents and Structures”, or “Operating Experience”). After completion of a review andsubsequent comment approval by the CODAP PRG, a document containing general information
is published as a CSNI report.
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4.3

Confidentiality

The CODAP Project differentiates between public domain information and confidential information.
There are three levels of confidential information:

4.4

1.

Level 1. Applies to all documentation developed by the Project Review Group. It is published on
the password protected Project website. Selected Level 1 documents may become available tointerested parties via external reporting by OECD/NEA. Such documents must undergo review
and approval by the CSNI.

2.

Level 2. Applies to the Online CODAP event database, national data and data analysis results.
This material is kept on the NEA Secure Server, is password protected, and can be accessed only
by authorized users. It is distributed only among active PRG members under the Terms &Conditions, is never published on the Project Web Site or distributed outside of the PRG.

3.

Level 3. Applies to proprietary raw data and associated reference material used in creating
database records. This material is kept on the NEA Secure Server. PRG members who areinterested in this material shall contact the appropriate National Coordinator. In the web-based
event database, any attachment containing proprietary information is clearly marked as a “Level3” document.
Coding Guideline

To achieve the objectives of the CODAP Project, a Coding Format is developed. This Coding Format
is reflected in the Coding Guideline (CODAP-PR01) which is a controlled document. The Coding
Guideline builds on established passive component failure data analysis practices and routines that
acknowledge the unique aspect of passive component reliability (e.g., influence by material and waterchemistry). All database development and data coding activities are to be based on the Coding Guideline.

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5.

CODAP EVENT DATABASEThe CODAP Event Database is a web based, relational database consisting of ca. 100 uniquely
defined data fields. It is a mixture of free-format fields for detailed narrative information, fields defined bydrop-down menus with key words (or data filters) or related tables, and hyperlinks to additional
background information (e.g., photographs, root cause evaluation reports). The "related tables" include
information on material, location of damage or degradation, type of damage or degradation, system name,safety class, etc. At the end of the First Term the CODAP Event Database included ca. 4,700 records on
degraded and failed metallic piping and non-piping passive components. Section 5 presents the scope ofthe event database and summarizes the database structure and main features of the Online Event Database.
5.1

Scope of Event Database

The event database scope and structure, database field definitions and data input requirements aredefined in the Coding Guideline, which is central to the project, including database maintenance, data
validation and quality control. The database design has benefitted from a multidisciplinary approach
involving chemistry, metallurgy, structural integrity and PSA expertise.
The CODAP Event Database collects service experience data on the full range of degradedconditions, from "precursors" to major structural failures involving metallic piping components and nonpiping metallic passive components. According to the IAEA Safety Glossary [12], a passive component isdefined in the following way:•

A passive component is “component whose functioning does not depend on an external input
such as actuation, mechanical movement or supply of power.
− A passive component has no moving part, and, for example, only experiences a change inpressure, in temperature or in fluid flow in performing its functions. In addition, certain
components that function with very high reliability based on irreversible action or change
may be assigned to this category.
− Examples of passive components are heat exchangers, pipes, vessels, electrical cables andstructures. It is emphasized that this definition is necessarily general in nature, as is thecorresponding definition of active component.
− Certain components, such as rupture discs, check valves, safety valves, injectors and somesolid state electronic devices, have characteristics which require special consideration before
designation as an active or passive component.”

With the above definition as a basis and building on the OPDE and SCAP-SCC project experience,
recent operating experience and associated regulatory actions, the Project Review Group made further
refinements and specializations to arrive at a scope definition as summarized in Table 2. Consistent with
the Operating Procedures, the scope definition is revisited and periodically updated. In Table 2, the column“Metallic, Non-Piping Passive Components” captures the BWR and PWR internals as documented andevaluated in IAEA-TECDOC-1471 [13] and IAEA-TECDOC-1119 [14], respectively.
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NEA/CSNI/R(2015)7

Passive Component Types

Passive Component
Category

Table 2: Scope of CODAP Event Database
Metallic Piping Components
Safety-related piping
Non-safety related piping
Fire water system piping
Small-, medium- and large-diameter piping
Above-ground piping
Below-ground (buried) piping
Pressure Tubes - PHWR

Metallic, Non-Piping Passive Components
Reactor pressure vessel (RPV)
RPV internals
Heat Exchanger (H/X)
Steam Generator (S/G)
Pump casing
Pressurizer
Valve body
Bolting
Calandria Vessel - PHWR
Tank
BMI - Bottom Mounted Instrument Nozzle (PWR)
Bracket / Console
Canopy Weld
Collector assembly (WWER)
Control Rod Guide Tube Support Pin
Core Plate
Core Shroud
Core Shroud Head Bolt
Core Shroud Weld
Core Spray Sparger (BWR)
Core Spray Sparger Weld (BWR)
Core Support
CRDM Housing
CRDM Nozzle
CST - Condensate Storage Tank
Diffuser Plate
Heater Sleeve (Pressurizer)
H/X Shell
ICI Tube
In-Core Instrument Guide Tube Nozzle
In-Core Monitoring Housing
J-Groove Weld
Jet Pump Hold-Down Beam (BWR)
Jet Pump Riser (BWR)
Lower Fuel Element Alignment Pin
PHB Diaphragm Plate
RPV Head
RPV Bottom Head
RWST - Refueling Water Storage Tank
S/G Partition Plate
S/G Shell
S/G Tube (restricted to tubing of Alloy 690 or
Alloy 800 material)
SBLC Tank (BWR)
Steam Dryer
Upper Fuel Element Alignment Pin
VHP - RPV Vessel Head Penetration

Bend
Bend – Long Radius
Bend – Short RadiusBranch connection
Branch connection - butt welded
Branch connection - socket welded
Elbow
Elbow – 90-Degree
Elbow – 45-Degree
FlangeExpanderExpansion joint
FlangeMixing tee
Pipe
Pipe - BONNA
Pipe - buried / below ground
Pipe - cement lined
Pipe - epoxy / PVC lined
Pipe - rubber lined
Reducer
Reducing elbow
Reducing tee
Tee
Weld – butt
Weld – socket

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NEA/CSNI/R(2015)7
In CODAP the term “failure” covers the full spectrum of degraded conditions, from rejectable flaws
requiring repair or replacement to major structural failures. As an example, ASME Section XI, Article
IWA-3000 [15] defines acceptance standards for flaws that are discovered during non-destructive
examinations (NDEs). Flaws determined to be rejectable (i.e., not fit for continued operation) according torelevant NDE code are required to be repaired or replaced.
5.2

Working with the Event Database

CODAP is a relational database. The data entry is managed via input forms, tables, roll down menus
and database relationships. Figure 1 shows the Online opening screen and Figure 2 shows the Online main
work area. The Online Version is accessible via a secure server at the Nuclear Energy Agency
Headquarters. User names and passwords are provided by NEA IT-Department upon written request by
National Coordinator. The Online Version includes help menus. The project members’ work area includes
a FAQ area as wells as tutorials on how to input data and perform searches and queries.

Figure 1: CODAP Database Opening Screen
The Main Menu page is displayed in Figure 2. There are a total of seven (7) sub-meus: 1) Records, 2)Create, 3) Search, 4) Statistics, 5) Delete, 6) Export, and 7) Help. The online user-interface supports thefull suite of database operations, from initial data submission and QA through applications:•

Records. This menu provides an overview of th entire database content and provides basic
information such as plant name, event date, when records was first created, when a record waslast updated as well as QA status (i.e., draft, validation pending, validation completed. This menu
supports database mangement.

•

Create. The data input format is equivalent to that presented in Section 5. Each record added tothe database is assigned a unique “EID/Key” number”. “Create new record” opens the data input
form. A partially filled in form can be saved and retrieved and the information modified asneeded. Use the “Tab Key” to move from form one field to another. The user may append
attachments (e.g., drawings, photographs, PDF files) to a data record.
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NEA/CSNI/R(2015)7•

Search. This tab includes two areas: 1) Search Criteria, and 2) Result Column. The entire
database can be searched and filtered by a very large number of attributes.

•

Statistics. This tab supports basic database queries. The query results can be exported to a local
computer as a CSV (Character-Separated Value) file or XML (Extensible Markup Language)
file. Selecting "CSV" automatically generates an Excel-file with the tabular query results.
Additional post-processing of data may be performed on a local computer/computer network.

•

Delete. This tab enables deletion of individual records or a set of records. Only NEA-IT and the
Operating Agent can execute this function and upon pre-approval by respective National
Coordinator.

•

Export. Downloading records from the Online Version is straightforward. Pressing the "Export"
button returns a listing of all records. Selected records or the entire database can be exported to a
local computer. The Online Version creates a zip-file ("Export" file") that can be opened or saved
to a local disc. The data records are converted to a XML file format that is compatible with
Microsoft® Office programs (e.g., Access, Excel, Word).

•

Help. This tab provides user support. It includes abbreviated versions of the Coding Guidelines
and Applications Handbook.

Figure 2: CODAP Main Menu
5.3

High-Level Database Summary6

The CODAP event database content is summarized in Tables 3 and 4 and Figures 3 through 5.
Operating experience insights are covered in Section 7. Table 3 summarizes database content by Project
Member Country. In Table 4 the database content is summarized by plant type (BWR, PHWR, or PWR),
failure mode and passive component category, that is, piping versus non-piping passive component. The
latter category includes Reactor Pressure Vessel Internals (RPVIS). The CODAP “Terms and Conditions”

6

This summary of the database content is current as of 30-November-2014

28

NEA/CSNI/R(2015)7
and “Operating Procedures” define the expectations regarding data submissions. Respective National
Coordinator has overall responsibility for data submissions.
Figure 3 is a graphical representation of the database content by geographical region (European
Union, incl. Switzerland, and Pacific Basin Region7). Included in this chart is the number of operating
reactor units that produced the operating experience. Figure 4 shows the cumulative number of failure
records over the time period covered by CODAP (1970 to 2014). Figure 5 is a summary of damage &degradation mechanisms. A more detailed presentation of the passive component operating experience
insights is documented in Section 7.
Table 3: Database Content by Participating Country
Project Members
Country
StatusBE
Member of OPDE Term 1 & 2 (2002-2008)
CA
Member since 2002
CH
Member since 2002
CZ
Member since 2002
DE
Member since 2002
ES
Member since 2002
FI
Member since 2002
FR
Member since 2002
JP
Member since 2002
KR
Member since 2002
MX
Member of SCAP-SCC Project (2006-2010)
SE
Member since 2002
SK
Member since 2011
TW
Member since 2011
US
Member since 2002
CODAP Event Database Content - No. of Records:

Number of Data
Submissions
8
187
95
25
350
50
56
148
287
69
3
365
5
15
3035
4698

Table 4: Database Content by Plant Type & Passive Component Category
OPDE (2002-2011) 8
Plant
Type

CODAP (2011-2014)

Piping

BWR

Part
ThroughWall
816

PHWR

Piping

Non-Piping incl. RPVIS
Part
ThroughThroughWall
Wall
85
37

946

Part
ThroughWall
1033

55

99

67

111

5

10

PWR

296

1581

340

1660

184

182

Totals:

1167

2626

1440

2755

274

229

ThroughWall

ThroughWall
984

7

With respect to CODAP, the Pacific Basin Region includes the following project member countries: Canada, Chinese-Taipei,
Japan, Korea (Republic of), and USA.
8

The OPDE database was based on an in-kind contribution by the Swedish regulatory authority. This in-kind contribution
consisted of an Access database on pipe failure events in commercial nuclear power plants (1970-1998). The event populationconsisted of 2290 event records.

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NEA/CSNI/R(2015)7

2442

Through-Wall Defects
541

Pacific Basin - 202 Reactor Units
EU + CH - 122 Reactor Units

1154

Non-Through-Wall Defects
561

0

500

1000

1500

2000

2500

3000

No. Database Records

Figure 3: Database Content by Geographic Region
3000

2000

1500

1000

500

0

1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014

Cumulative No. of Failure Records

2500

Crack-Full (No Active @ Power Leakage)

Part Through-Wall

Through-Wall Leaks

Figure 4: Cumulative Number of Failure Records

30NEA/CSNI/R(2015)7

Fatigue

Corrosion Fatigue
Thermal Fatigue
Low-Cycle Fatigue
High-Cycle Fatigue

Corrosion

General Corrosion
Galvanic Corrosion
Crevice / Pitting Corrosion
Dealloying - Selective Leaching

Flow-Assisted
Degradation

MIC - Microbiologically Influenced Corrosion
Steam Jet Impingement Erosion (SS Material)
Erosion-Corrosion
Erosion-Cavitation
FAC - Flow Accelerated Corrosion (FAC)ECSCC (OD)TGSCCPWSCC - Ni-Base Metals

SCC

SICC - Strain Induced Corrosion Cracking
NI-SCC (CS Material)
IGSCC - Stabilized Austenitic Stainless SteelIGSCC-PWR - Unstabilized Austenitic Stainless SteelIGSCC-BWR - Unstabilized Austenitic Stainless SteelCISCC - Chloride Ion SCC (ID)
0.0%

5.0%

10.0%

15.0%

20.0%

Percentage of Total Event Population)

Figure 5: Damage / Degradation Mechanisms in CODAP Event Database

31

25.0%

NEA/CSNI/R(2015)7

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NEA/CSNI/R(2015)7

6.

CODAP KNOWLEDGE BASE

The CODAP Knowledge Base (KB) has been established to reflect basic international technicalinformation of relevance to the project in a systematic manner. The KB is password protected and resides
on a secure server at NEA Headquarters in Paris, France. The KB is intended to provide a source of
information on technical issues related to all the failure mechanisms covered by the Event Database. The
type of information collected includes regulations/codes and standards, inspection/
monitoring/qualification, preventive maintenance/mitigation, repair/replacement, safety assessment, andR&D. The information is both of a general nature and also more specific for the different damage anddegradation mechanisms. The KB is intended to provide a source of systematically organized information
for members, as well as input to the topical reports that the project is preparing. There is a search function
to facilitate retrieval of information.
6.1

Knowledge Management

In principle, the objective of knowledge management (KM) involves preserving institutional or
corporate knowledge about a specific subject matter [16]. In the context of CODAP, KM involves
preserving the discipline-specific analysis methods and techniques, phenomenology associated withenvironmental degradation mechanisms, research and development, operating experience, codes-andstandards, design and construction, safety analysis, licensing, flaw tolerance evaluations, long term
operation, and aging management. In CODAP the approach to KM is through implementation of a webbased Knowledge Base. The CODAP KB builds on the experience gained from the SCAP-SCC Project,which undertook to develop a KB on stress corrosion cracking [9].
6.2Structure of CODAP-KB

The CODAP Knowledge Base consists of a collection of documents and supporting information
arranged in a manner such that it is easily retrievable by participants. Documentation is in English (or theoriginal language together with an English translation). The information is sorted according to the different
degradation mechanisms in the Event Database.
The structure of the Knowledge Base is hierarchical such that generic information which is applicable
to all, or many, of the degradation mechanisms lies highest and then the specific degradation mechanisms
lie below. This information is common and accessible to all participants. The information at each level willcomprise, but not be limited to:•Regulations, Codes and Standards;•

Inspection, monitoring, qualification;•

Damage and degradation mechanism information;•

References, e.g., technical reports, archival journal articles, conference proceedings;•

Important events (Reference events from the Event database) will be included in the mechanism
specific areas.
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NEA/CSNI/R(2015)7
Participating countries can collect national information in their country folders. Material in country
folders need not be translated except for the title. This ensures that the Knowledge Base Coordinator canassess the relevance of material for inclusion in the common area.
The content of the Knowledge Base is defined and agreed by the PRG together with the Knowledge
Base Coordinator and the Operating Agent. The structure of the KB is illustrated in Figure 6 and the webbased KB Work Area is illustrated in Figure 7. The web-based KB includes an advanced search capability(Figure 8), and an example of a KB search results is illustrated in Figure 9.
CODAP-KB

Regulation/ code and standard

General information

Inspection/ Monitoring/ Qualification
Preventive Maintenance/ Mitigation
Repair/ Replacement
Safety Assessment
Research and Development
Regulation/ code and standard

IGSCC

Inspection/ Monitoring/ Qualification
Preventive Maintenance/ Mitigation
Repair/ Replacement
Safety Assessment
Research & Development
IGSCC in Ni base alloys
PWSCC
IASCC
TGSCC
ECSCC
FAC
Thermal Fatigue
CODAP Topical Reports
Country reports: basically same structure
Figure 6: CODAP-KB Structure

34

NEA/CSNI/R(2015)7

Figure 7: CODAP-KB Work Area

Figure 8: CODAP-KB Advanced Search Area

35

NEA/CSNI/R(2015)7

Figure 9: An Example of a CODAP-KB Search

36

NEA/CSNI/R(2015)7

7.

OPERATING EXPERIENCE INSIGHTSThe CODAP First Term Version of the Event Database includes approximately 4,700 records on
metallic piping and non-piping metallic passive component failures from 356 reactor units representing ca.
10,500 commercial reactor-operating-years. Of the database content, 50% of the records relate to PWRs,
46% to BWRs, and 4% to PHWRs.9 Chapter 7 addresses selected operating experience insights involving
reactor coolant pressure boundary (RCPB) crack and leak events, primary water stress corrosion cracking(PWSCC) of PWR passive components, service water piping failures, socket weld failures, and NDE
reliability.10
7.1

RCPB Crack and Leak Events

This section summarizes the field experience with BWR, PHWR and PWR primary water system (orreactor coolant pressure boundary, RCPB) cracks and leaks. The latter involves leak events that haveoccurred during operating modes other than cold shutdown; i.e., full power, low power, hot standby or hot
shutdown. All at-power leak events have been detected early and resulted in early, controlled reactor
shutdown. The leakages have been detected by leak detection systems Leakages during hot standby or hot
shutdown have resulted in orderly cooldown to the cold shutdown state. In some cases these leaks havebeen discovered fortuitously when drywell (BWR) or containment (PWR) entry was made for some otherpurpose.
For the time period 2002-2014, Figure 10 summarizes the RCPB piping crack and leak event
population. Figure 11 summarizes the RCPB non-piping passive component crack and leak event
population. In Figure 10, an outlier (calendar years 2002 and 2003) refers to intergranular stress corrosion
cracking (IGSCC) of Reactor Recirculation (RR) piping welds in Japanese BWR plants. This 2002-2003
Japanese experience involved relatively shallow (< 20% through-wall) cracks in cold worked austenitic
stainless steel piping of Type AISI 316L All cracks were discovered during scheduled non-destructive
examination. In Figure 11, an important sub-population relates to PWSCC of PWR reactor pressure vessel
head penetrations (VHPs).
Figure 12 summarizes the operating experience involving RCPB piping leak events that occurred withthe reactor in operating modes other than cold shutdown; i.e., full-/low-power, hot standby or hot
shutdown. The operating experience is organized by cumulative number of events versus through-wall leakor flow rate threshold values for the period 1970 to 2014 and 1990-2014, respectively. The majority ofevents have involved very small (or perceptible) through-wall leaks. For the entire period covered by the
CODAP event database (1970-2014), about 90% of primary water leak events have been below or well
below 6×10-2 kg/s, which corresponds to the Technical Specification limit for manual shutdown. Only a
few events have produced significant RCPB through-wall flow rates above 1 kg/s (> 10 gpm), examples
include the following events:

9

The PWR event population includes events at WWER reactors in Czech Republic, Finland and Slovak Republic. The PHWR
event population includes events in Canadian and Korean (Republic of) plants.

10

The operating experience review is current as of 30-November-2014.

37

NEA/CSNI/R(2015)7•

In December 1994, a small LOCA occurred due to a reactor coolant relief valve (RV) failure andresulting complications. The sequence of events leading up to the pressure boundary breachbegan with the RV opening due to a failed instrument air (IA) supply line. As a consequence of
this initial IA line failure and the opening of the RC-RV, relief valves on the primary heattransport system bleed condenser lifted. After the initial opening, one of these RVs shut andbegan to chatter. The valve chattering caused stress in the RV inlet pipe and eventually led to thedevelopment and propagation of cracks in the lower elbow of the inlet pipe which caused theprimary pressure boundary breach. This event occurred at a PHWR plant.

•

In January 1993, with the reactor in hot shutdown, a failure of a vent line on the Residual Heat
Removal (RHR) suction line off of the Reactor Coolant hot leg released water into theContainment Building in addition to a RHR relief valve that was opening prematurely.
Investigation of the vent line determined a weld had been damaged by vibration during previous
water hammer events. The mass flow rate through the broken pipe was estimated at ca. 10 kg/s.

•

In November 1991, a reactor coolant leak at an instrument line fitting failed causing a forced
reactor shutdown. The failed instrument line connected to the top of steam generator ‘A’ hot leg.
The mass flow rate through the broken instrument line was estimated at ca. 6 kg/s. The root cause
evaluation determined that the failed instrument line (part of the Reactor Vessel Level Indication
System) was caused by an improperly installed compression fitting.

•

In July 1998, a primary water leak resulted in manual reactor shutdown. The leak was on a DN25
line at a tee near a valve and resulted in the loss of heat transport (HT) inventory at the rate of
approximately 3 kg/s. The fractured pipe section was cut out and submitted for immediate failure
analysis. The line break was attributed to a high cycle fatigue failure caused by a positive
displacement pump producing a constant source of flow-induced vibrations.
90

80

No. RCPB Piping Crack & Leak Events

70

60

50
BWR - 180 Event Records
PHWR - 17 Event Records
PWR - 112 Event Records

40

30

20

10

0
2002

2003

2004

2005

2006

2007

2008

2009

2010

2011

2012

2013

2014

Figure 10: RCPB Piping Crack & Leak Events38

NEA/CSNI/R(2015)7
16

No. RCPB Non-Piping Passive Component Crack & Leak Events

14

12

10

BWR - 5 Event Records

8

PHWR - 5 Event Records
PWR - 54 Event Records

6

4

2

0
2002

2003

2004

2005

2006

2007

2008

2009

2010

2011

2012

2013

2014

Figure 11: RCPB Crack & Leak Events Involving Non-Piping Passive Components
700

Cumulative No. @Power RCPB Leak Events

600

500

400

300

200

100

0
1.0E-04

1.0E-03

1.0E-02

1.0E-01

1.0E+00

1.0E+01

Observed RCPB Through-Wall Leak/Flow Rate (Threshold Values) [kg/s]
No. RCPB Leak Events - 1990-2014 - 296 Records

No. RCPB Leak Events - 1970-2014 - 604 Records

Figure 12: RCPB Piping @ Power Leak Events
39

1.0E+02

NEA/CSNI/R(2015)7
7.2

Primary Water Stress Corrosion Cracking

Nickel-base alloys, particularly Alloy 600, and weld metals Alloy 82, 132 and 182, have proved to besusceptible to IGSCC in normal specification PWR primary water systems. This is commonly known as
PWSCC. The history of the Alloy 600 IGSCC discovery is documented in Reference [17]. Available
operating experience shows that temperature and fabrication induced residual stresses have a large
influence on PWSCC in Alloy 600 weld metal. Examples of components affected include pressurizer, hotleg, cold leg, drain, and reactor coolant pump nozzle-to-safe end dissimilar metal welds (ASME XI
Category B-F welds), penetrations welded to the reactor vessel and reactor vessel head and steam
generator. Figure 13 is a summary of PWSCC records in the CODAP event database. The database
contains over 300 records pertaining to PWSCC incidents in PWR primary circuits since the mid-1980s.

VHP

145

BMI-Nozzle

4

RCS-HL-INSTR-PEN

29

RCS-HL/SG-Inlet

20

RCS-HL11

RCS-CL1

PRZ-SURGE

4

PRZ-RELIEF/SAFETY/SPRAY8

PRZ-INSTR

33

PRZ-HTR

67
0

20

40

60

80

100

120

140

160

No. Failure Records in CODAP

Figure 13: Summary of PWSCC Incidents in PWR Primary Circuits 1986-2014
Detection of PWSCC can be challenging because this form of cracking exhibits tight and complex
branching in the nickel-base weld metal and forgings. With reference to Figure 13, examples of recent(2002-2014) PWSCC incidents include non-through-wall and through-wall flaws involving bottommounted instrument (BMI) nozzles and steam generator inlet nozzles at Japanese, French and U.S. plants.
In all cases, these flaws have been identified during in-service inspection activities and they have resulted
in expanded or unplanned outage work, including extensive root cause evaluations and operability
evaluations. In the CODAP event database, four (4) PWSCC incidents involving BMI nozzles are:•Japanese PWR Unit, January 2003: A possible indication of PWSCC (< 1 mm) in the base metalof BMI No. 48 was detected through eddy current testing (ET) from the nozzle inner diameter40

NEA/CSNI/R(2015)7(ID). The ET was performed prior to planned water jet peening of the nozzle ID. There have beenno subsequent reports of detected indications in BMIs at the affected unit or any other Japaneseplant.
•US PWR Unit, April 2003: Leakage from BMIs No. 1 and 46 was identified during walkdowns
to support the utility's Boric Acid Corrosion Control Program. Non-destructive examination(NDE) did not reveal any other indications of PWSCC beyond the cracking in BMI nozzles No. 1
and 46.

•

French PWR Unit, October 2011. Indications that were interpreted as PWSCC were detected via
UT from the inside of the nozzles as part of the third 10-year ISI. There was no evidence of boric
acid deposits on the bottom head during the second and third ISI interval. Electricité de France(EDF) expanded the requirement for internal UT inspection of BMIs to all reactor vessels in the
French fleet.

•

US PWR Unit, October 2013. The cause of the pressure boundary leakage was axial cracking in a
sub-surface BMI nozzle J-groove weld flaw that extended into the nozzle to a length exceeding
the J-groove weld leg thickness. The laboratory analysis of the boat sample suggests the weld
flaw became wetted at some point during service which enabled concentration of environmental
constituents that promoted PWSCC in the weld and nozzle materials. Leakage occurred once theaxial cracking extended below the J-groove weld root.

In some Japanese and U.S. PWR plants the reactor coolant hot leg and cold leg are connected to thesteam generator inlet/outlet nozzle, respectively, via dissimilar (Category B-F) welds of Alloy 82/132/182
weld material. Summarized in Figure 14 are PWSCC incidents (2007-2012) involving the steam generator(S/G) inlet nozzle dissimilar metal welds. This figure shows the measured crack depth of each individual
cracking incident. Of the 20 incidents recorded in the CODAP event database, 19 incidents involved
Japanese PWR plants and one event involved a U.S. reactor unit. The latter PWSCC incident occurred in2012 and is of interest because of the extent of cracking and an apparent NDE deficiency:•

During the performance of work activities to support Alloy 600 dissimilar metal weld overlay
work on the 'B' Reactor Coolant loop hot leg to the 'B' Steam Generator nozzle weld, twothrough-wall defects were identified. The workers noted a small amount of water seeping fromthe indications in the nozzle weld area. The indications were in the area of excavation that was
being performed for the weld overlay project. Approximately 25 mm of weld material had been
removed prior to the seepage being identified. The root cause evaluation determined the leakage
developed due to PWSCC in a susceptible material (i.e. Alloy 82/182). After review of thefabrication records, it was further determined that the primary water stress corrosion cracks werecaused by extensive ID weld repairs performed only on the 'B' Hot Leg nozzle. Of special
noteworthyness, during the initial UT-examination, several axially oriented flaws went
undetected by the manual conventional ultrasonic testing (UT) technique. The flaws were
subsequently detected as a result of outside-diameter (OD) surface machining in preparation for a
full structural weld overlay. A detailed assessment of the failure of the applied UT technique isdocumented in Reference [17]. According this reference, a number of critical factors may havecombined in the failure to detect the axial flaws. The intent of the site-specific performance
demonstration was to apply a modified version of a generic procedure for this examinationorginally qualified by the US industry’s Performance Demonstration Initiative (PDI). The North
Anna qualification approach played a substantial role in this event.

41

NEA/CSNI/R(2015)7

Through-Wall
Crack Depth [%]

100%

10%

1%
1 ® 2 ® 3 ® 4 ® 5 ® 6 ® 7 ® 8 ® 9 ® 10 11 12 13 14 15 16 17 18 19 20 1 2 3 ® 4 5 6 ® 7 8 ® 9 ® 10 1 ® 2 ® 3 4® ® ® ® ® ® ® ® ® ® ®
®
RCS Hot Leg - RPV Outlet Nozzle RCS Cold Leg RPV Inlet
NozzleRCS Hot Leg - S/G Inlet

Figure 14: PWSCC Incidents Involving Reactor Coolant Cold Leg & Hot Leg Piping11
7.4

Service Water Piping Failures

The field experience with Service Water (SW) piping is abundant and includes non-through-wallflaws and through-wall flaws that have resulted in repair or replacement of affected pipe sections. The highsafety significance associated with SW piping degradation and failures has warranted corrective actions to
reduce both the frequency and potential consequences of operating events involving such degradation andfailures. Limited to the German and US operating experience with SW piping, Figure 15 summarizes thefailure data contained in the CODAP event database for the period 2002-2014. A detailed overview of theGerman experience with SW system piping and non-piping passive components is documented in
Reference [18].
Service water piping systems carry cooling water to various heat exchangers throughout a power
plant. It removes the heat from such auxiliary systems as component cooling heat exchangers, emergency
diesel generators, containment coolers, lubrication oil coolers, room coolers, and chiller condensers. It
consists of an intake structure for the cooling water, a distribution system within the plant and an outlet
structure. Suction is taken from the ultimate heat sink (e.g., ocean, river, lake, or reservoir), heat isremoved via various heat exchangers, and the water is discharged back to the ultimate heat sink (UHS) or
self-contained UHS (e.g., spray cooling pond or cooling tower). With an infinite supply of water, the SW
systems represent an important potential flood source. Relative to the in-plant SW piping design androuting, there are four basic types of SW system designs: 1) open loop system, 3) open recirculating
system with a self-contained ultimate heat sink such as spray cooling pond or a cooling tower, 3) closed
11

Superscript “®” indicates a “repair weld,” refer to the Glossary of Terms for a definition.

42

NEA/CSNI/R(2015)7
loop system, and 4) closed loop system with a self-contained UHS. Each of the four system designs has
advantages and disadvantages relative to SW pipe aging characteristics.
25

No. Failure Records

20

15

DE - 43 Records
US - 119 Records
10

5

0
2002

2003

2004

2005

2006

2007

2008

2009

2010

2011

2012

2013

2014

Figure 15: SW Piping & Non-Piping Passive Component Failures
The SW piping system operates under corrosive and erosive service conditions. The system is prone
to degradation involving localized pitting and wall thinning and through-wall leaks. The rate of material
degradation differs significantly across the plant population, however. Factors influencing the rate ofdegradation include:•

System Design. The service conditions tend to be somewhat more aggressive in open or straightthrough systems than the closed systems. The latter type is more amenable to chemical treatment
programs.

•

Piping Material Selection. Compared to other in-plant process and standby safety systems, theoperating environment in SW piping is aggressive. However, the rate of degradation is strongly
correlated with the chosen type of piping material. Some plants in Chinese-Taipei, Sweden andthe US have made extensive piping replacements using high-performance stainless steel tomitigate or even eliminate corrosion susceptibilities. Relative to austenitic stainless steels ofType 304 or 316, the high-performance stainless steels are defined as those with substantiallyhigher chromium, molybdenum and nitrogen content. Listed below are typical SW piping
materials:− Carbon steel (e.g., A-106 Gr. B).

43

NEA/CSNI/R(2015)7− Stainless steel (Type 304 or 316); mainly used for small- to medium-diameter (≤ NPS8)
piping. As susceptible to microbiologically influenced corrosion (MIC) as carbon steel,
however.
− “High performance stainless steels” developed specifically for salt water systems.
− Nickel-copper alloys.
− Lined carbon steel piping; many plants use cement-, rubber- or epoxy/PVC-lined carbon steel
piping where the service environment is erosive. Lining failure due to thermal cycling andimproper welding frequently causes localized pitting and pinhole leaks, however.
In the U.S., Generic Letter 90-05 [19] develops the Nuclear Regulatory Commission position on
temporary non-Code repairs of moderate-energy piping systems. Such repairs are applicable until the nextscheduled outage exceeding 30 days, but no later than the next scheduled refueling outage. The guidance in
the Generic Letter applies when a flaw is detected during plant operation. If a flaw is detected during ascheduled shutdown, a code repair is required before plant restart. Non-Code approaches must be
submitted for review and evaluation to the NRC on a case-by-case basis for consideration before a relief
request is granted. The principles of Generic Letter 90-05 have been adopted by the regulatory authorities
of Chinese-Taipei [20] and Spain. The Generic Letter 90-05 includes an evaluation guideline on temporary
repairs. This guideline consists of four parts:

7.5

1.

Flaw detection during plant operation and impracticality determination. “Impractical” means that
affected section of piping cannot be isolated for completing a Code repair within the Technical
Specification Limiting Condition for Operation (LCO) without a plant shutdown. For example an
LCO may prescribe that an affected SW train must be restored to operable status within 72 hours
or be in at least hot standby within the next 6 hours.

2.

Root cause determination and flaw characterization. This determination should include a positive
identification of root cause and an identification of the most susceptible locations in the piping
system.

3.

Flaw evaluation. The flawed piping should satisfy the criteria of one of two approaches, the“through-wall flaw” approach or the “wall thinning” approach for non-through wall flaws.

4.

Augmented inspection. If the flaw is evaluated and found acceptable, the plant operator should
perform an augmented inspection via UT or RT to assess the overall degradation of the system.
The augmented inspection, performed within 15 days of detection of the flaw, which results in a
temporary non-Code repair, is part of the relief acceptance criteria of the repair. The inspection
should be performed for at least the 5 most susceptible (and accessible) locations.
Socket Weld Failures

A socket weld is a pipe attachment detail in which a pipe is inserted into a recessed area of a valve,
fitting (e.g., elbow or tee), or flange. In contrast to butt welds, socket welds are mainly used for smalldiameter piping of nominal size 50 mm or less. Fatigue resistance is lower than that in butt-welded
construction due to the use of fillet welds and fitting geometry. The CODAP event database includes
ample information on socket weld failures. Socket welds are used extensively in safety-related piping
systems. Table 5 includes a sample of socket weld populations in primary system piping. The information
has been obtained through reviews of fabrication isometric drawings.
44

NEA/CSNI/R(2015)7
Socket weld design requirements are defined in the “ASME Code for Pressure Piping” [21]. This
Code specifies minimum welding dimensions for socket welds. An important dimensional parameter is thegap between pipe and fitting prior to welding. The failure data includes numerous instances where
insufficient gap (or “pull-back”) has contributed to weld failure. National “technical requirements
manuals” (TRMs) typically include additional details on socket weld dimensional requirements. As one
example, the Swedish Nuclear Power Companies have jointly developed a TRM entitled “TechnicalRegulations for Mechanical Equipment” [22] which is an “implementation document” that interprets therelevant national regulatory requirements. Sections 3.3.8 and 4.1.3.2 of this particular TRM identifies the
specific requirements that apply to the installation of socket welds in safety-related piping systems.
Table 5: An Example of Code Class 1 Socket Weld Populations
ASME III Class 1 Small-Bore Piping Systems

Plant / Plant Type
Plant A / WH 4-LoopPlant B / WH 4-LoopPlant C / WH 4-LoopPlant D / WH 4-LoopPlant E / WH 4-LoopPlant F / WH 2-LoopPlant G / WH 4-LoopPlant H / WH 4-LoopPlant I / WH 4-LoopPlant J / WH 4-LoopPlant K / WH 4-Loop

7.5.1

Date ofCommercial
Operation
Sep-85
Aug-87
Jul-88Oct-88Dec-84
Jun-74
Aug-74
Aug-76
Aug-90Aug-88Jun-89Socket Welds

Weld Population
Butt Welds

Total

Pipe Size

872
828
933
962
77
345
433
333
150
49
59

175
181
136
129
Not Determined
Not Determined
195
96
300
182
190

1047
1009
1069
1091
--628
429
450
231
249

≤ DN25≤ DN25≤ DN25≤ DN2525 ≤ DN < 100≤ DN50≤ DN50≤ DN50≤ DN50≤ DN50≤ DN50

Socket Weld Failure Data

There have been frequent occurrences of high-cycle fatigue failures of socket welded connections insafety related piping systems. Limited to the French (Reference [23]) and US operating experience(CODAP), respectively, Figure 16 summarizes socket weld failure data for the period 1990-2014.

45

NEA/CSNI/R(2015)7
60

50

No. Socket Weld Failures

40

30

20

10

0
1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014
CODAP - Class 1

CODAP - Class 2

CODAP - Class 3

CODAP - All

EDF - PVP2011-57893 - Safety Related Piping

Figure 16: Selected Socket Weld Failure Data (1990-2014)
7.5.2

Socket Weld Reliability and Integrity Management

This section compares and contrasts certain aspects of the French and U.S. industry practices withrespect to socket weld reliability and integrity management (RIM). In 2002 the French regulatory
authority, Autorité de sûreté nucléarie (ASN) issued a directive concerning socket weld integrity (DGSNRBCCN/OT/VF No. 020406 [24]). According to this directive, socket welds not meeting the requirements
for weld dimensions and/or weld integrity as specified by the RCC-M Code [25] “…shall be replaced withbutt welds.” In response to the directive by ASN, EDF implemented a systematic socket weld integrity
program for all of its Class 900 MWe PWR plants [23].
In the US, NUREG-1801 [25] provides a technical basis for determining the adequacy of aging
management programs (AMPs) for license renewal. Section XI.M35 of this reference augments therequirements in ASME Section XI, 2004 Edition (Rules for In-service Inspection of Nuclear Power Plant
Components). According to Table IWB-2500-1 of the ASME Code, an external surface examination ofsmall-bore Class 1 piping should be included for piping less than DN100. Other ASME Code provisions
exempt from examination piping of size DN25 and smaller. This program is augmented to include pipingfrom DN25 to less than DN100. Also, Examination Category B-P requires system leakage of all Class 1
piping.
According to the NRC, for a one-time inspection to detect cracking resulting from thermal andmechanical loading or intergranular stress corrosion of full-penetration welds, the inspection should be avolumetric examination. For a one-time inspection to detect cracking in socket welds, the inspection
should be either a volumetric or opportunistic destructive examination. Opportunistic destructive
examination is performed when a weld is removed from service for other considerations, such as plant46

NEA/CSNI/R(2015)7
modifications. A sampling basis is used if more than 1 weld is removed. These examinations provide
additional assurance that either aging of small-bore ASME Code Class 1 piping is not occurring or the
aging is insignificant, such that a plant-specific aging management program (AMP) is not warranted. The
one-time inspection is applicable to small-bore ASME Code Class 1 piping and systems less than DN100
and greater than or equal to DN25. The program includes pipes, fittings, branch connections, and all fulland partial penetration (socket) welds.
This program is applicable to systems that have not experienced cracking of ASME Code Class 1
small-bore piping. This program can also be used for systems that experienced cracking but have
implemented design changes to effectively mitigate cracking. (Measure of effectiveness includes (1) the
one-time inspection sampling is statistically significant;(2) samples will be selected as described in
Element 5, Monitoring and Trending below; and (3) no repeated failures over an extended period of time.)
For systems that have experienced cracking and operating experience indicates that design changes havenot been implemented to effectively mitigate cracking, periodic inspection is proposed, as managed by aplant-specific AMP. Should evidence of cracking be revealed by a one-time inspection, periodic inspection
is implemented using a plant-specific AMP. If small bore piping in a particular plant system has
experienced cracking, small bore piping in all plant systems are evaluated to determine whether the cause
for the cracking affects other systems.
7.6

NDE Failures

The ASME Boiler and Pressure Vessel Code Section XI, “Rules for Inservice Inspection of Nuclear
Power Plant Components” [15] provides requirements for examination, testing, and inspection ofcomponents and systems, and repair/replacement activities in a nuclear power plant. The mandatory
Appendix VIII of ASME Section XI provides requirements for performance demonstration (PD) for
ultrasonic examination procedures, equipment, and personnel used to detect and size flaws. When ASME
Section XI was first issued in 1971, the ultrasonic inspection techniques specified were adapted frommanufacturing practices and were based on previous experience with fatigue cracking. The ultrasonicexamination rules were prescriptive and had not been evaluated on nuclear reactor service-induced
degradation mechanisms. The reliability of the nondestructive examinations (NDE) that were specified by
Section XI was not quantified via testing. Instead, the initial premise of Section XI was that reliableultrasonic testing (UT) could be ensured through detailed rules [27].
Based on early field experience, the failure of ISI to detect leaking cracks raised concerns regarding
the effectiveness of ultrasonic testing being conducted at nuclear power plants and showed that
improvements in inspection requirements were needed. In response, the NRC sponsored R&D to assess
nondestructive examination (NDE) reliability. This research showed that prescriptive requirements could
not be written to sufficiently accommodate the diversity of power plant materials, field conditions, andflaw degradation processes typically encountered. It was subsequently decided that a performance-based
testing approach would be the most effective means for achieving the needed improvements in NDE
reliability.
In 1991 the US utilities formed the Performance Demonstration Initiative (PDI) to implement the thencurrent performance demonstration requirements of the ASME Code, Section XI, Appendix VIII
“Performance Demonstration for Ultrasonic Examination Systems.” The PDI designated the ElectricPower Research Institute (EPRI) Nondestructive Examination Center to be the Performance Demonstration
Administrator (PDA).
The CODAP event database captures NDE failures in detecting pre-existing flaws before exceeding
acceptance criteria. In the database passive component failure information is recorded in a tiered manner.
First, basic failure information is recorded to address the most fundamental information about an event and47

NEA/CSNI/R(2015)7
this includes a free-format event narrative that describes the sequence of events, including plant response,
consequence, in-plant location of failed component, dimensional data, and component type. This isfollowed by recording the known ISI history, including date when the failed component was last inspected,
method of NDE qualification if a qualified method had been used, and any NDE performance deficiencies
or failures. Finally, details about the service environment (e.g., water chemistry, stresses, pressure andtemperature) are recorded as a lead-in to details from root cause evaluations (flaw data, chemicalcomposition of material, results of metallographic examinations, apparent and underlying causes ofmaterial degradation). When NDE fails to detect leaking cracks one or more of the following factors arepresent:•

A rejectable flaw indication is determined to be acceptable for continued operation. This could be
due to misinterpretation of NDE results.

•

Use of improperly qualified NDE technique.

•

Poor implementation of ASME Appendix VIII.

•

A qualified Appendix VIII procedure misses a flaw.

Summarized in Figure 17 is the NDE failure population in the CODAP event database. Examples ofrecent (2002-2014) NDE failures include the previously addressed occurrence at a U.S. plant (Section 7.2)
and the following selected events:•

US PWR Unit, April 2014. While performing planned inspections of Reactor Coolant Systempiping welds, two flaw indications were identified on a 1.5 inch High Pressure Safety Injection
Line connection to the Reactor Coolant System piping (cold leg). After confirmatory inspections
and evaluation, one of the two flaw indications was determined to not meet the acceptancecriteria specified in ASME Section XI. This flaw was missed during the previous refuelingoutage as a result of a probable skill-based human performance error. The flaw was detectedduring normal inspections required by the NDE Augmented Examination program, which isdriven by EPR MRP-146 ("Thermal Fatigue in Normally Stagnant Non-Isolable Reactor Coolant
System Branch Lines") [28]. Non-isolable branch lines connected to the NC system aresusceptible to high cycle thermal fatigue if exposed to specific operational conditions andconfigurations. Examples of susceptible locations are horizontal lines where in-leakage past avalve is present and lines see turbulent swirl penetration from adjacent piping flow. Initial MRP146 inspections were performed in 2008 and did not include the area where the flaw was
discovered.

•US PWR Unit, November 2013. Following a controlled shutdown in response to a RCPB leak,visual inspection confirmed that the leak was located on a High Pressure Injection Line. The root
cause evaluation determined that a crack-like indication in the failed location had existed since2011. Furthermore, the root cause evaluation concluded that inadequate procedural guidanceexisted for the conduct of Augmented Examinations and appropriate disposition of UT
examination results where conditions limited the weld volume that could be examined. A UTlimitation is defined as any obstruction or condition that limits the extent of angle beam scanningor limits the extent of required coverage using straight beam scanning. When adequate weld
volumes could not be examined on the nozzle safe end-to-pipe butt weld, no procedural guidance
provided weld volume acceptance criteria or directed these limitations to be entered into thecorrective action program for evaluation. During the root cause investigation, metallurgicalanalysis documented that the crack propagated over several operating cycles. Historical NDE
data revealed that the crack was visible in existing radiographs. Had the failed weld volume been48

NEA/CSNI/R(2015)7
adequately interrogated, the crack would have been identified before propagating through wall.
The licensee reviewed the results of the previous UT examination performed in 2012 using a
NDE procedure and found no reportable indications. However, in 2011, the licensee performed aradiographic examination specifically to check the condition and position of a thermal sleeve.
The focus of the review was limited to that area; however, the safe end area containing cracked
weld was incidentally visible on the film. Following the current event, the licensee re-reviewed
the 2011 radiographic film and a crack-like indication was identified in the side wall image of theweld at approximately the same location as corresponding to the current crack location. From there-review of the film, this crack-like indication appeared to be approximately 50% through-wall.
35

30

20

15

10

5

BWR - 119 Records

PHWR - 6 Records

PWR - 156 Records

Figure 17: NDE Failure Population in CODAP Event Database

49

2014

2012

2013

2011

2010

2009

2008

2007

2006

2005

2004

2003

2002

2001

2000

1999

1998

1997

1996

1995

1994

1992

1993

1991

1990

1989

1988

1987

1986

1985

1984

1983

1982

1981

1980

1979

1975

0

1974

No. NDE Failures

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8.

DATABASE ACCESSIBILITYThe CODAP Terms and Conditions contain statements on the use of data within or outside CODAP
and on the handling of proprietary information. The Event Database is a restricted database and its accessis limited to participating organisations that provide input data. The database is available on the Internet
via a secure server located at the OECD-NEA Headquarters.
It has been recognised by the Project Review Group that many member organisations will want topass on the CODAP database to their consultants for use in specific projects, and suchlike. For this purpose
a non-confidential version of the CODAP database will be made available for use by consultants for alimited period of time. Before supplying a non-confidential version the member organisation making therequest must provide the National Coordinator with written proof that the intended recipient of the nonconfidential version of the database has agreed to comply with the confidentiality terms and conditions of
the project.

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9.

CONCLUSIONS & FUTURE PLANS

CODAP is the continuation of the 2002–2011 "OECD/NEA Pipe Failure Data Exchange Project"(OPDE) and the Stress Corrosion Cracking (SCC) Working Group of the 2006–2010 “OECD/NEA SCC
and Cable Ageing project” (SCAP). OPDE was formally launched in May 2002. Upon completion of the
3rd Term (May 2011), the OPDE project was officially closed to be succeeded by CODAP. SCAP wasformally launched in June 2006 and officially closed with an international workshop held in Tokyo in May
2010. Following the completion of the SCAP project, its SCC Working Group participants were interested
in some form of continuation and a new project was formed in 2011 by combining OPDE and SCAP-SCC
into the “Component Operational Experience, Degradation & Ageing Programme” (CODAP).
9.1

Conclusions and Recommendations

During the first term the original objectives of the project were achieved and an operational webbased database was launched successfully. The PRG also implemented a web-based Knowledge Base (KB)
intended to provide a source of information on technical issues related to all the failure mechanisms
covered by the Event Database. The type of information collected includes regulations/codes andstandards, and relevant documents on national activities in the areas of inspection/monitoring/qualification,
preventive maintenance/mitigation, repair/replacement, safety assessment, and R&D. The information isboth of a general nature and also more specific for the different degradation mechanisms. The KB is
intended to provide a source of systematically organized information for the project members. In addition
to the web-based event database and the KB, the PRG produced two topical reports intended fordissemination to interested parties within the international nuclear safety community.
The key objectives of CODAP are to encourage and support the multilateral exchange of operating
experience data on metallic piping components and non-piping passive components. As indicated in
Sections 5 (CODAP Event Database) and 7 (Operating Experience Insights), the current content of thedatabase has a strong U.S. bias. A recommendation for the second term (2015-2017) of the project is to put
in place operating procedures and processes whereby future national data submissions are commensuratewith the number of operating reactors. Furthermore, in-depth database applications will be pursued toinvestigate the correlations between reported degradation and failure events versus piping system designmodifications, degradation mitigation practices and NDE qualification.
It is equally important to put in place a process to capture legacy information concerning significant
events. In the context of CODAP, the term “significant” implies both significant unexpected structuraldegradation or failure and events that have prompted significant regulatory action. Database completenessstrongly affects the possibilities to perform advanced database applications.
9.2

Planned Activities Beyond 2014

The PRG recognizes that there are a multitude of future challenges concerning the response toenvironmental degradation of passive components in heavy water and light water reactor operating
environments. It is important to ensure that the almost five decades of operating experience insights bepreserved and made readily available to future generations of material scientists, structural engineers and53

NEA/CSNI/R(2015)7
PSA engineers. In planning for activities beyond 2014 questions concerning the effectiveness ofdegradation mitigation processes and NDE reliability needs to be addressed, One way of doing so is toactively monitor any perceived or actual trends and patterns in the worldwide operating experience datathat is fed back to the CODAP event database.
The PRG has prepared Terms & Conditions for the 2nd Term (2015-2017) of CODAP. The second term of
the project places an emphasis on two aspects of operating experience data exchange and analysis. First, toencourage active data submissions by the PRG membership, an improved web-based database structure
will be implemented. A detailed database improvement plan was presented at the CODAP08 PRG meetingin December 2014. Second, continued database applications will be pursued through an expanded program
to develop topical report.

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10.

REFERENCES[1]

U.S. Nuclear Regulatory Commission, Investigation and Evaluation of Cracking in Austenitic
Stainless Steel Piping of Boiling Water Reactor Plants, NUREG-75/067, Washington, DC, 1975.

[2]

U.S. Nuclear Regulatory Commission, Investigation and Evaluation of Cracking Incidents in
Piping in Pressurized Water Reactors, NUREG-0691, Washington, DC, 1980.

[3]

Brown, E.J., Erosion in Nuclear Power Plants, AEOD/E4-16, Office for Analysis and Evaluationof Operational Data, U.S. Nuclear Regulatory Commission, Washington, DC, 1984.

[4]

Cragnolino, G., Czajkowski, C., and Shack, W.J., Review of Erosion-Corrosion in Single-Phase
Flows, NUREG/CR-5156, U.S. Nuclear Regulatory Commission, Washington, DC, 1988.

[5]

IAEA, Corrosion and Erosion Aspects in Pressure Boundary Components of Light Water Reactors,
Proc. Specialist Meeting Organized by the IAEA, IWG-RRPC-88-1, Vienna, Austria, 1990.

[6]

OECD Nuclear Energy Agency, Experience with Thermal Fatigue in LWR Piping Caused by
Mixing and Stratification, Specialist Meeting Proceedings, NEA/CSNI/R(98)8, Issy-lesMoulineaux, France, 1998.

[7]

U.S. Nuclear Regulatory Commission, Reactor Safety Study. An Assessment of Accident Risks in
U.S. Commercial Nuclear Power Plants, WASH-1400 (NUREG-75/014), Washington, DC, 1975.

[8]

OECD Nuclear Energy Agency, OECD/NEA Piping Failure Data Exchange Project (OECD/NEA
OPDE), Final Report, NEA/CSNI/R(2012)16, Issy-les-Moulineaux, France, 2012.

[9]OECD Nuclear Energy Agency, Technical Basis for Commendable Practices on Ageing
Management – SCC and Cable Ageing Project (SCAP), Final Report, NEA/CSNI/R(2010)5, Issyles-Moulineaux, France, 2010.

[10]

OECD Nuclear Energy Agency, OECD/NEA Component Operational Experience, Degradation &Ageing Programme, Database Coding Guideline & User Manual, Revision 1, CODAP-PR01, Issyles-Moulineaux, France, 2013.

[11]

OECD Nuclear Energy Agency, OECD/NEA Component Operational Experience, Degradation &Ageing Programme, Database Applications Handbook, CODAP-PR05, Issy-les-Moulineaux,France, 2013.

[12]

IAEA, Safety Glossary. Terminology Used in Nuclear Safety and Radiation Protection,
STI/PUB/1290, Vienna, Austria, 2007.

[13]

IAEA, Assessment and Management of Ageing of Major Nuclear Power Plant Components
Important to Safety: BWR Pressure Vessel Internals, IAEA-TECDOC-1471, Vienna, Austria,
2005.

[14]

IAEA, Assessment and Management of Ageing of Major Nuclear Power Plant Components
Important to Safety: PWR Pressure Vessel Internals, IAEA-TECDOC-1119, Vienna, Austria,
1999.

55

NEA/CSNI/R(2015)7[15]

American Society of Mechanical Engineers, 2007 ASME Boiler and Pressure Vessel Code,
Section XI: Rules for Inservice Inspection of Nuclear Power Plant Components, 2008a Addenda,
New York, NY, July 2008.

[16]

OECD Nuclear Energy Agency, Knowledge Transfer and Management of Operating Experience,
NEA/CNRA/R(2012)1, Issy-les-Moulineaux, France, 2012.

[17]

Combrade, P., Ford, P. and Nordmann, F., Key Results from Recent Conferences on Structural
Materials Degradation in Water Cooled Reactors, A.N.T. International, Mölnlycke, Sweden,
December 2010.12[18]

Anderson M.T. et al, Final Assessment of Manual Ultrasonic Examinations Applied to Detect
Flaws in Primary System Dissimilar Metal Welds at North Anna Power Station, PNNL-22553,
Pacific Northwest National Laboratory, Richland, WA, March 2014.

[19]

Elmas, M., Reck, H. and von der Cron, D., Betriebserfahrung mit Komponenten dersicherheitstechnisch wichtigen Nebenkühlwassersysteme in deutschen Analgen mit DWR und
SWR, GRS-A-3634, Gesellschaft für Analgen- und Reaktorsicherheit, Cologne, Germany,
February 2012.

[20]

U.S. Nuclear Regulatory Commission, Guidance for Performing Temporary Non-Code Repairs of
ASME Code Class 1, 2 and 3 Piping, Generic Letter 90-05, Washington, DC, 1990.

[21]

Ting, K. And You, J.S., “The Experiences of Non-Code Repairs for Nuclear Safety-Related Piping
in Taiwan,” Nuclear Engineering and Design, 214:83-89, 2002.

[22]

American Society of Mechanical Engineers, Process Piping. ASME Code for Pressure Piping,
B31, ASME B31.3-2002, New York, NY, 2002.

[23]

Swedish Nuclear Power Companies, TBM: Technical Requirements for Mechanical Equipment,
Revision 6, Stockholm, Sweden, 2012.13[24]

Economou, J., Thebault, Y. and Costes, P-E., “Small-Bore Branch Connection Fatigue,”
PVP2011-57983, Proc. ASME 2011 Pressure Vessels and Piping Division Conference, American
Society of Mechanical Engineers, New York, NY, 2011.

[25]

Direction Générale de la Sûreté Nucléaire et de la Radioprotection, Assemblages “Socket
Welding” du Circuit Primaire Principal des REP, Décision DGSNR-BCCN/OT/VF No. 020406,
Paris, France, October 10, 2002.

[26]

AFCN, Design and Construction Rules for Mechanical Components of the PWR Nuclear Islands,
RRC-M, Paris La Defense, France, 2012.

[27]

U.S. Nuclear Regulatory Commission, Generic Aging Lessons Learned (GALL) Report, NUREG1801, Revision 2, Washington, DC, December 2010.

[28]

Doctor, S.R et al, The Technical Basis Supporting ASME Code, Section XI, Appendix VIII:
Performance Demonstration for Ultrasonic Examination, NUREG/CR-7165, U.S. Nuclear
Regulatory Commission, Washington, DC, May 2013.

[29]

Electric Power Research Institute, Materials Reliability Program: Management of Thermal Fatigue
in Normally Stagnant Non-Isolable Reactor Coolant System Branch Lines (MRP-146, Revision 1),
Report ID 1022564, Palo Alto, CA, June 2011.

12

Available at www.antinternational.com.

13

Available at http://corporate.vattenfall.se/om-oss/var-verksamhet/var-elproduktion/forsmark/entreprenor-och-konsult/pakt/

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APPENDIX A
CODAP PRG ACTIVITY REPORT57

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A.1

PRG Meetings

During the 3-½ years (2011-2014) of the First Term of the CODAP Project, the Project Review
Group met on eight (8) occasions (Table A-1). With the exception for CODAP02 and CODAP08, allmeetings were held at the OECD Conference Centre, Paris, France. The CODAP02 and CODAP08
meetings were held at NEA Headquarters in Issy-les-Moulineaux, France.
Table A-1: Project Review Group Meetings 2011-2014
Meeting
CODAP01, Project Kick-off Meeting
CODAP02, National Coordinators Meeting
CODAP03, National Coordinators Meeting
CODAP04, National Coordinators Meeting
CODAO05, National Coordinators Meeting
CODAP06, National Coordinators Meeting
CODAP07, National Coordinators Meeting
CODAP08, National Coordinators Meeting
CODAP Phase 2 Kick-off Meeting

A.2

Date(s)May 18-19, 2011
November 8-9, 2011
May 29-30, 2012
December 11-12, 2012
May 30-31, 2013
November 6-7, 2013
May 14-15, 2014
December 9-10, 2014
December 11, 2014

CODAP Topical Reports

During the First Term of CODAP the PRG produced two Topical Reports. These reports
constitute CODAP Event Database and Knowledge Base insights reports and are intended as “portals”
for future database application projects and in-depth studies of selected degradation mechanisms.
Prepared in 2013, a first Topical Report addressed flow-accelerated corrosion (FAC) of carbon steel
and low alloy steel piping (NEA/CSNI/R(2014)6). A second Topical Report addressed operating
experience with electro-hydraulic control (EHC) and instrument air (IA) system piping(NEA/CSNI/R(2015)6). Both reports are in the public domain and available as PDFs on the Internet at
http://www.oecd-nea.org/nsd/docs/indexcsni.html.
A.3

CSNI WGRISK Project on “Use of OECD Data Project Products in PSA”

During 2012 the PRG supported the subject Working Group on Risk (WGRISK) project byattending meetings, sharing of information and responding to a survey on database applications in thecontext of PSA. On October 15-16, 2012, the PRG presented its perspectives on the use of the
OPDE/CODAP data project products in PSA. The results of the survey on database applications are
documented in NEA/CSNI/R(2014)2: Use of OECD/NEA Data Project Products in Probabilistic
Safety Assessment (June 2014).
A.4

Conference Participation

During the first term of CODAP, the project was represented at the following international
conferences:•

ICONE-20, 20th International Conference on Nuclear Engineering, Anaheim, CA, USA, July
30 – August 3, 2012. On July 30, 2012, project team members delivered a tutorial on“Analytical Framework for the Derivation of Piping Reliability Parameters from Service
Experience Data.”•

American Nuclear Society, International Topical Meeting on Probabilistic Safety
Assessment and Analysis, Columbia, SC, September 22-26, 2013.

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Paper #84, OECD/NEA CODAP Event Data Project on Passive Component Degradation &Failures in Commercial Nuclear Power Plants•

Pacific Basin Nuclear Conference, Vancouver, BC, Canada, August 25-28, 2014.
Paper PBNC2014-025, OECD/NEA Multilateral Cooperation in the Area of Structural
Integrity & Aging Management•

Fontevraud 8, International Conference on the Contribution of Materials Investigations andOperating Experience to LWR’s Safety, Performance and Reliability, Avignon, France,
September 15-18, 2014.
Paper O-T05-163, OECD/NEA Component Operational Experience, Degradation & Ageing
Project•

2014 International Mechanical Engineering Congress & Exposition IMECE-2014, Montreal,
QC, Canada, November 14-20, 2014.
Paper IMECE2014-40106 (Plenary Presentation), CODAP Project on International
Cooperation in the Area of Structural Integrity of NPP

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APPENDIX BGLOSSARY OF TECHNICAL TERMS

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Boat Sample. The Boat Sampling Technique (BST) has been developed for obtaining samples fromthe surface of a pressure boundary component. The technique is a nondestructive surface samplingtechnique as it does not cause any plastic deformation or thermal degradation of the operating component.
BST can be used, remotely and in water-submerged condition, with the help of a handling mechanism. The
samples are boat-shaped, having 3 mm maximum thickness and require 180 minutes for getting scooped
from a location. The samples are used for metallurgical analysis to confirm the integrity of the component.
BST incorporates mainly sampling module, handling mechanism and electric and pneumatic sub-systems.
Bonna Pipe. Piping intended for raw water service. It is fabricated from rolled and seam welded steel
plates. It has an internal concrete liner and an external reinforced concrete liner.
Cavitation. Cavitation damage may occur when there is a flowing liquid stream that experiences adrop in pressure followed by a pressure recovery. Such a pressure drop (i.e., the difference between the
upstream pressure and the downstream pressure) can occur in valve internals where the flow has toaccelerate through a small area. As the fluid moves through the restricted area, the fluid velocity increases
and the pressure decreases as shown by the momentum equation (i.e., Bernoulli’s theorem). If the local
pressure passes below the vapour pressure at the liquid temperature, then small bubbles are formed. Whenthe downstream pressure rises above the vapour pressure, these bubbles collapse. The collapse of the
bubbles causes high local pressures and very high local water jet velocities. If the collapsing bubbles areclose enough to a solid surface, damage to that surface will occur. The collapse of the numerous bubbles
generates noise and vibration. Most often, cavitation causes most of its damage by vibration (e.g., cracked
welds, broken instrument lines, loosened flanges). The erosion caused by cavitation also generates particles
that contaminate the process fluid.
Component Boundary. Defines the physical boundary of a component required for system operation.
A component boundary definition should be consistent with the parameter database supporting PSA model
quantification. Isometric drawings (fabrication isometrics and ISI isometrics) uniquely defines the piping
component boundaries.
Damage Mechanism. Excessive internal or external loading conditions that cause physical damage to
a component pressure boundary. Examples include, high-cycle vibration fatigue and thermal stratification,
as well as pressure shocks from steam/water hammer.
Degradation Mechanism. Phenomena or processes that attack (crack, erode, wear, etc) a pressureretaining material over time and might result in a reduction of pressure boundary integrity. Also, includes
phenomena that cause changes in material properties (e.g., reduction in fracture toughness).
Erosion Cavitation (E-C). This phenomenon occurs downstream of a directional change or in thepresence of an eddy. Evidence can be seen by round pits in the base metal and is often wrongly diagnosed
as FAC (see below). Like erosion, E-C involves fluids accelerating over the surface of a material; however,unlike erosion, the actual fluid is not doing the damage. Rather, cavitation results from small bubbles in aliquid striking a surface. Such bubbles form when the pressure of a fluid drops below the vapour pressure,the pressure at which a liquid becomes a gas. When these bubbles strike the surface, they collapse, or
implode. Although a single bubble imploding does not carry much force, over time, the small damage
caused by each bubble accumulates. The repeated impact of these implosions results in the formation ofpits. Also, like erosion, the presence of chemical corrosion enhances the damage and rate of material
removal. E-C has been observed in PWR stainless steel decay heat removal and charging system piping.
Erosion/Corrosion (E/C). “Erosion” is the destruction of metals by the abrasive action of moving
fluids, usually accelerated by the presence of solid particles or matter in suspension. When corrosion

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occurs simultaneously, the term erosion-corrosion is used. In the CODAP Event Database, the term
“erosion/corrosion” applies only to moderate energy carbon steel piping (e.g., raw water piping).
Fatigue. “Fatigue” refers to an aging degradation mechanism where components undergo cyclic
stress. This mechanism involves either low-load, high frequency stresses or high-load, low frequency
stresses generated by thermal cycling, vibration, seismic events, or loading transients. Environmental
factors may accelerate fatigue and eventually may result in a component failure.
Fillet Weld. Fillet welding refers to the process of joining two pieces of metal together whether they
be perpendicular or at an angle. The weld is triangular in shape and may have a concave, flat or convex
surface depending on the welder’s techniqueFlashing. Flashing occurs when a high-pressure liquid flows through a valve or an orifice to a regionof greatly reduced pressure. If the pressure drops below the vapour pressure, some of the liquid will be
spontaneously converted to steam. The downstream velocity will be greatly increased due to a much lower
average density of the two-phase mixture. The impact of the high velocity liquid on piping or components
creates flashing damage.
Flow Accelerated (or Assisted) Corrosion (FAC). FAC is “a process whereby the normally protectiveoxide layer on carbon or low-alloy steel dissolves into a stream of flowing water or water-steam mixture.”
It can occur in both single phase and two phase regions. The cause of FAC is a specific set of waterchemistry conditions (e.g., pH, level of dissolved oxygen), and there is no mechanical contribution to thedissolution of the normally protective iron oxide (magnetite) layer on the inside pipe wall.
Liquid Droplet Impingement (LDI). Liquid droplet impingement is caused by the impact of highvelocity droplets or liquid jets. Normally, LDI occurs when a two-phase stream experiences a highpressure drop (e.g., across an orifice on a line to the condenser). When this occurs, there is an accelerationof both phases with the liquid velocity increasing to the point that, if the liquid strikes a metallic surface,damage to the surface will occur. The main distinction between flashing and LDI is that in flashing thefluid is of lower quality (mostly liquid with some steam), and with LDI, the fluid is of higher quality(mostly steam with some liquid).
Repair Weld (or Welding). Any welding performed after original construction, but prior tocommissioning (e.g., hot functional testing).
Solid Particle Erosion (SPE). SPE is damage caused by particles transported by the fluid stream
rather than by liquid water or collapsing bubbles. If hard, large particles are present at sufficiently highvelocities, damage will occur. In contrast to LDI, the necessary velocities for SPE are quite low. Surfaces
damaged by SPE have a very variable morphology. Manifestations of SPE in service usually include
thinning of components, a macroscopic scooping appearance following the gas/particle flow field, surface
roughening (ranging from polishing to severe roughening, depending on particle size and velocity), lack of
the directional grooving characteristics of abrasion, and in some but not all cases, the formation of ripple
patterns on metals.
Thermal Aging. Possible effects of elevated temperature service include phase transformations that
can adversely affect mechanical properties. Extended time at elevated temperature may permit even very
slow phase transformations to occur. This is of particular concern for cast stainless steel components where
the formation of a brittle alpha-phase can result in a loss of fracture toughness and lead to brittle failure.
Thermal Stratification. Hot water can flow above cold water in horizontal runs of piping when theflow (hot water into a cold pipe or cold water into a hot pipe) does not have enough velocity to flush the63

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fluid in the pipe. The temperature profiles in the pipe where the top of the pipe is hotter than the bottomcauses the pipe to bow along with the normal expansion at the average temperature.
Water Hammer. If the velocity of water or other liquid flowing in a pipe is suddenly reduced, apressure wave results, which travels up and down the pipe system at the speed of sound in the liquid. Water
hammer occurs in systems that are subject to rapid changes in fluid flow rate, including systems with
rapidly actuated valves, fast-starting pumps, and check valves.

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