Analysis of ageing related events : a summary report from the European clearinghouse.
Date: 2020-03-18
Institutions: Joint Research Centre
Subjects: maintenance, nuclear energy, nuclear power station, nuclear reactor, nuclear safety, nuclear technology, research report

ANALYSIS OF AGEING RELATED EVENTS 

A summary report from the 
European Clearinghouse 

Ballesteros Avila A. 

2020 

EUR 30128 EN 

 
 
 
 
This publication is a Technical report by the Joint Research Centre (JRC), the European Commission’s science 
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Contact information  
Name: Antonio BALLESTEROS AVILA 
Address: Westerduinweg 3, PO Box, 1755 ZG Petten – The Netherlands 
Email: Antonio.BALLESTEROS-AVILA@ec.europa.eu 
Tel.: +31 (0)224 56 5241 

EU Science Hub 
https://ec.europa.eu/jrc 

JRC119754 

EUR 30128 EN 

PDF 

ISBN 978-92-76-17299-4 

ISSN 1831-9424 

doi: 10.2760/239397 

Luxembourg: Publications Office of the European Union, 2020 

© European Atomic Energy Community, 2020  

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How to cite this report: A. Ballesteros, Analysis of Ageing related Events. A summary report from European 
Clearinghouse, EUR 30128 EN, Publications Office of the European Union, Luxembourg, 2020, ISBN 978-92-76-
17299-4, doi:10.2760/239397, JRC119754. 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Contents 

Abstract ................................................................................................................................................................................................................................... 1 

Acknowledgements .......................................................................................................................................................................................................... 2 

1.  INTRODUCTION ........................................................................................................................................................................................................... 3 

2.  AGEING AND LONG TERM OPERATION ......................................................................................................................................................... 4 

3.  AGEING OF THE EUROPEAN FLEET ................................................................................................................................................................. 5 

4.  THE EUROPEAN CLEARINGHOUSE ................................................................................................................................................................... 6 

5.  LESSONS LEARNED FROM AGEING EVENTS ............................................................................................................................................. 7 

5.1  Events screening in the IRS database .............................................................................................................................................. 7 

5.2  Reference age .................................................................................................................................................................................................. 7 

5.3  Analysis of events ......................................................................................................................................................................................... 7 

5.4  High level lessons learned ....................................................................................................................................................................... 9 

6.  CONCLUSIONS .......................................................................................................................................................................................................... 11 

References .......................................................................................................................................................................................................................... 12 

List of abbreviations and definitions ................................................................................................................................................................. 13 

List of figures………………………………………………………………………………………………………………………………………………………… 14 

i 

Abstract 

This  report  presents  a  summary  of  the  results  of  a  review  of  available  recent  international 
operating  experience  on  ageing  events  reported  by  nuclear  power  plants.  Event  reports  retrieved 
from IAEA  IRS database are  characterised and used to derive insights and lessons learned. These 
lessons learned cover issues such as hidden deficiencies in design visible in aged components only 
after  many  years  of  plant  operation,  deficiencies  in  ageing  and  maintenance  programmes, 
accelerated  ageing  or  the  adequacy  and  effectiveness  of  the  inspection  and  monitoring  methods. 
The  findings  of  this  study  aim  to  support  the  licensees  to  improve  the  safe  operation  of  nuclear 
power plants and the regulatory authorities to exercise their oversight role. 

1 

Acknowledgements 

This  summary  report  has  been  prepared  by  the  European  Clearinghouse  on  NPP  Operating 
Experience Feedback at the Joint Research Centre (JRC), Petten, The Netherlands. The IRS database 
of NPP events managed by the IAEA was used for this study. 

The author would like to thank Miguel Peinador for his feedback and contribution to this report. 

2 

1. 

INTRODUCTION 

Nuclear  safety  of  the  operating  nuclear  power  plants  (NPP)  has  to  be  in  the  core  of  their  life 
management. NPPs have to be operated safely and reliably. European Countries involved in nuclear 
energy  are  spending  their  efforts  in  improving  safety  of  the  operating  plants  and  of  those  under 
construction, which is in accordance with the Euratom Treaty obligations. To this respect, the IAEA 
requirements  for  the  safe  operation  of  nuclear  power  plants  identify,  among  others  priorities, 
Maintenance, Testing, Surveillance and Inspection programmes and Ageing Management of safety 
related components.  

Recognising  the  importance  of  peer  review  mechanisms  in  delivering  continuous  improvement  to 
nuclear safety, the amended Nuclear Safety Directive [1] introduced a European system of topical 
peer reviews (TPR). The subject 'Ageing Management' was chosen in 2017 as the first TPR exercise 
on  the  basis  of  the  age  profile  and  the  potential  long  term  operation  of  European  NPPs.  The 
national  assessment  reports  [2]  prepared  under  this  first  TPR  gave  numerous  examples  where 
operating experience (OPEX) has been used to inform ageing management. There are many existing 
fora for sharing OPEX. For example, the IRS and IGALL managed by the IAEA , the CNRA and CSNI 
under  the  OECD-NEA,  and  the  European  Clearinghouse    on  Operating  Experience  Feedback  of  the 
JRC of the European Commission. 

3 

2. 

AGEING AND LONG TERM OPERATION 

The original design life of structural, mechanical and electrical components, particularly those that 
technically  limit  the  power  plant  operation  (e.g.  reactor  pressure  vessel,  containment,  etc.),  was 
originally  estimated to  be  around  30-40  years,  considering  anticipated  operational  conditions  and 
ambient environment under which they are operated. In reality, the plant operational conditions and 
ambient  environment  parameters  are  below  the  limits  established  during  the  initial  design.  While 
economical feasibility falls into operating organization competence, a decision regarding the plant 
safety  level  depends  on  country's  regulatory  requirements.  Generally,  a  thorough  technical 
assessment  of  the plant physical  condition is  needed,  so that  to  identify  safety  enhancements  or 
modifications,  and  the  impact  of  changes  to  NPP  programmes  and  procedures  necessary  for 
continued safe operation.  

Long  term  operation  (LTO)  of  nuclear  power  plants  offers  numerous  benefits.  For  instance,  it  is 
economically  advantageous  compared  to  other  power  sources.  This is  because  it  requires  a  much 
lower capital investment cost, leading to low investment risks for investors and capital markets, and 
lower  consumer  costs.  Furthermore,  it  reduces  the  EU’s  energy  import  dependency  on,  primarily, 
fossil fuels and provides reliability to the grid. 

As mentioned in the communication from the European Commission COM(2017) 237 on the Nuclear 
Illustrative Programme (PINC) [3], many operators in Europe have expressed the intention to operate 
their nuclear power plants for longer than envisaged by their original design. From a nuclear safety 
point of view, continuing to operate a nuclear power plant requires two things: demonstrating and 
maintaining plant conformity to the applicable regulatory requirements; and enhancing plant safety 
as  far  as  reasonably  practicable.  Depending  on  the  model  and  age  of  the  reactor,  national 
regulators  assume  that  granting  long-term  operation  programmes  will  mean  extending  their 
lifetime by 10 to 20 years on average. 

4 

3. 

AGEING OF THE EUROPEAN FLEET 

The lack of new build over the last 25 years or so has resulted in a switch within the industry. It has 
moved  from  design,  construction  and  the  development  of  new  systems  to  the  strengthening  of 
safety  systems,  both  through  engineered  safeguards  and  the  implementation  of  rigorous  safety 
assessment  and  the  life  extension  of  existing  reactors,  where  ageing  management  of  structures, 
systems and components plays a central role. 

There are 125 nuclear power reactors  in operation in the European Union. The age distribution of 
current nuclear power plants is showed in Figure 1. Major part of the EU reactors are between 30 to 
43 years old. Hence, from both the safety and security of supply viewpoints, ageing of these power 
plants  is  of  increasing  concern  to  European  policy  makers,  citizens  and  utilities.  The  possibility  of 
extending  the  life  of  the  existing  plants  is  very  attractive  to  utilities,  especially  given  the  public 
opposition in several European countries to construct new NPPs. 

Figure 1: Age distribution of the EU operating nuclear power reactors 

5 

 
 
 
4. 

THE EUROPEAN CLEARINGHOUSE 

The  European  Network  on  Operating  Experience  Feedback  (OEF)  for  Nuclear  Power  Plants  [4],  or 
European Clearinghouse, was established in 2008 by European nuclear safety regulators. The aim 
was to promote the regional sharing of operating experience, the dissemination of lessons learned 
from  NPP  operation,  and  the  understanding  of  the  role  of  OEF  systems  in  the  safe  and  reliable 
operation of existing and new build NPPs. The centralised office of the European Clearinghouse is 
operated by the Joint Research Centre (JRC) of the European Commission at Petten (NL) site. Figure 
2 shows the main tasks carried out and deliverables issued in support of the Clearinghouse network 
members. 

        Figure 2: Participants and deliverables of the European Clearinghouse 

The European Clearinghouse regularly carries out in-depth analyses of events related to a particular 
topic (the so-called "topical studies") in order to identify and disseminate the lessons learned aiming 
at reducing the recurrence of similar events in the future. The  Clearinghouse Steering Committee 
requested  in  2017  to  update  the  topical  study  on  Ageing  (previously  issued  in  2011)  with  the 
objective to draw generic and case-specific lessons making them available to the members of the 
European  Clearinghouse.  A  summary  of  methodology  used  and  the  results  obtained  in  the  new 
study on Ageing [5] is presented in the following sections. The lessons are derived from the analysis 
of ageing related events occurred in NPPs in the last 10 years, reported between 01/01/2008 and 
30/06/2018 in the IAEA IRS database.  

6 

 
 
 
 
5. 

LESSONS LEARNED FROM AGEING EVENTS 

5.1 

Events screening in the IRS database 

The International Reporting System for Operating Experience (IRS) is an international system jointly 
operated by  the International Atomic  Energy  Agency (IAEA)  and  the  Nuclear Energy  Agency of the 
Organisation for Economic Cooperation and Development (OECD/NEA). The IRS was established as a 
simple  and  efficient  system  to  exchange  important  lessons  learned  from  operating  experience 
gained  in  nuclear  power  plants  of  the  IAEA  and  NEA  Member  States.  The  IRS  database  contains 
about 4000 event reports with detailed descriptions and analyses of the event’s causes that may 
be relevant to other plants. 

The screening of ageing related events was carried out in two steps: 

•  Step  1:  The  query  capabilities  of  the  IRS  database  are  used  to  retrieve  an  initial  list  of 

potentially relevant events. 

•  Step  2:  The  reports  obtained  from  the  previous  step  are  briefly  reviewed  to  confirm  their 
relevance. Even if apparently relevant, a  report could be  screened out if it  is insufficiently 
detailed or if its quality is too low to be useful for the purposes of the study. 

The  query  result  in  the  IRS  database  for  the  period  01/01/2008  -  30/06/2018  was  a  list  of  173 
ageing  event  reports  (step  1),  which  were  reviewed  to  confirm  their  relevance.  After  detailed 
analysis of the 173 event reports (step 2), only 113 reports were considered as relevant. 

5.2 

Reference age 

It was possible in this work to calculate the average age of the nuclear power plant when the event 
occurred. This can be expressed by: 

where, 

Reference Age = 

event

start op.

𝑛𝑛
1
∑ (𝑡𝑡

− 𝑡𝑡

)/𝑛𝑛

n = final number of selected ageing events 

tevent = time when the event happened 

tstart op. = time when the plant started operation 

The analysis provides a Reference Age of 28 years (331 months) with a standard deviation of 10 
years (123 months).  In other words, on average, ageing related events occur after 28 years from 
the start of reactor operation. 

5.3 

Analysis of events 

The event reports were characterised according to the following defined criteria: plant status when 
the event happened, detection means of the event, affected systems, affected components, direct 
cause, root causes, ageing mechanisms, consequences and corrective actions. This section highlights 
several relevant findings. 

7 

 
 
 
 
The distribution of root causes is given in Figure 3. A maximum of three different root causes was 
attributed  to  each  event.  Deficiencies  in  maintenance  or  surveillance  is  the  most  important  root 
cause,  followed  by  deficiencies  in  design  and  in  ageing  management  programmes  (AMP).  To  this 
respect, we infer that the establishment of an effective AMP, as early as possible in the lifetime of 
the plant, will significantly contribute to preventing events and the resulting consequences. 

Figure 3: Distribution of root causes 

Figure  4  shows  that  corrosion  (38  times)  is  the  main  cause  of  failure,  followed  by  fatigue  (28 
times). Other important contributions are coming from thermal ageing, wear and electrical ageing. 
Many events only appear after a long period of operation of a component or material, and the main 
cause was a deficiency in the consideration of ageing effects in the life design. Figure 5 sheds some 
light  on  this  issue  and  illustrates  that  fatigue  is  the  main  degradation  mechanism  in  relation  to 
hidden deficiencies in design. 

 Figure 4: Ageing mechanisms present in the events    

8 

 
 
   
 
Figure 5: Deficiencies in design vs. ageing mechanism 

The  analysis  performed  allows  us  to  correlate  deficiencies  (or  absent)  in  ageing  management 
programme  with  the  ageing  mechanism.  In  this  case,  electrical  ageing  is  the  most  relevant 
contributor  to  failure.  This  indicates  the  need  for  improvement  of  the  ageing  management 
programmes of electrical and I&C components. 

Figure 6 illustrates the corrective actions. A maximum of three corrective actions were allocated to 
a single event. As expected, the main corrective action was the replacement or repair of equipment. 
Changes in maintenance programme was the second most usual corrective action followed, in this 
order,  by  monitoring  or  inspection  improvement,  design  modification  and  changes  in  ageing 
management programme. 

Figure 6: Distribution of corrective actions 

5.4 

High level lessons learned 

The  extraction  of  the  lessons  learned  from  the  operating  experience  was  completed  in  two  steps. 
First (step 1), low level lessons learned (LL-LL) were retrieved from the IRS database, or developed 
in  some  cases,  for  a  large  number  of  the  113  analysed  events.  A  total  of  110  low  level  lessons 
learned were obtained. They are given, together with a short summary of the events in [5]. Several 
lessons were allocated to the same event in many cases. These low level lessons learned are very 

9 

 
 
 
 
 
specific,  so  that  they  would  have  a  too  limited  applicability.  To  address  this  issue,  the  low  level 
lessons  learned  were  grouped  under  similar  topic  or  underlying  key  message  to  get  a  high  level 
lesson learned (step 2). A total of 10 high level lesson learned (HL-LL) were developed [5]. In order 
to restrict the length of this report and just give a flavour of the work performed, only several high 
level lessons learned are presented in Figure 7.  

Low level 
lessons 
learned

IRS 
events

Grouping 
lessons 
learned

Examples of High level lessons learned

 HLLL-1: Appropriate measures should be taken and design features should be 
introduced  in  the  design  stage  to  facilitate  effective  ageing  management 
throughout the life of the plant. 

 HLLL2:  Ageing  Management  Programmes  as  well  as  maintenance  programmes 
should  be  reviewed  and  updated  to  take  into  account  modifications  in  the 
current licensing bases. 

 HLLL-3:  The  adequacy  and  effectiveness  of  the  inspection  and  monitoring 
methods  should  be  periodically  reviewed  to  maintain  plant  safety  and  to 
ensure  feedback  and  continuous  improvements  of  ageing  management.  The 
evaluation of technology and methods should consider the need for detection 
of unexpected degradation, depending on how critical the structure, system or 
component is to safety. 

 HLLL-4: Adequate oversight by the licensee is recommended during all phases 
of  design,  procurement,  testing,  receipt  inspection  and  installation  to  avoid 
events  where  wrong  material  is  used.  When  a  wrong  or  low  performance 
material  is  already  installed,  the  rate  of  material  degradation  can  often  be 
reduced by optimizing operating practices and system parameters. 

 HLLL-5:  The  operating  organization  should  ensure  that  Ageing  Management 
Programmes (AMP) are reviewed on a regular basis and, if needed, modified to 
ensure  that  they  will  be  effective  for  managing  ageing.    Where  necessary, 
frequently as a result of reviewing operating experience, new AMPs have to be 
developed. 

Figure 7: Some representative high level lessons learned 

10 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
6. 

CONCLUSIONS 

Ageing  is  a  concern  for  the  safe  long-term  operation  of  NPPs.  In  particular  for  the  EU  nuclear 
reactors, which are many of them between 30 – 43 years old. To this respect, operating experience 
from ageing events can contribute significantly to enhance nuclear safety. 

The IRS database was screened to select relevant events related to ageing, which took place in the 
period 01.01.2008 – 30.06.2018. In total 113 events were analysed. The statistical analysis showed 
that the Reference Age of a nuclear power plant is 28 years. This amount represents the average 
age of a nuclear power plant when the event occurred. Deficiencies in maintenance or surveillance 
is  the  most  important  root  cause,  followed  by  deficiencies  in  design  and  in  ageing  management 
programmes.  Corrosion is  the  main  degradation mechanism,  followed  by  fatigue.  Other important 
contributions are coming from thermal ageing, wear and electrical ageing. Many events only appear 
after long-term operation of an aged component or material, and the main cause was a deficiency 
in design that was hidden. 

110 low level lessons learned (specific for the events) and 10 high level lessons learned (generic) 
have been obtained in this study. They cover different areas, such as hidden deficiencies in design, 
the  impact  of  ageing  on  maintenance  and  inspection,  deficiencies  or  lack  of  ageing  management 
programmes, use of wrong material, etc.  

This  study  highlights  that  the  continuous  analysis  of  ageing  related  events  and  the  efficient 
utilization of operational experience provides important insights for improving the quality of ageing 
management programmes and for preventing the occurrence of unusual events. 

11 

References 

[1] Council Directive 2014/87/Euratom of 8 July 2014 amending Directive 2009/71/Euratom.  

https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=uriserv%3AOJ.L_.2014.219.01.0042.01.ENG 

[2] Topical Peer Review exercise on Ageing Management http://www.ensreg.eu/country-specific-
reports 

[3] Communication on a Nuclear Illustrative Programme (PINC). 
https://ec.europa.eu/energy/sites/ener/files/documents/nuclear_illustrative_programme_pinc_-
_may_2017_en.pdf 

[4] European Clearinghouse on Operating Experience Feedback.  

https://clearinghouse-oef.jrc.ec.europa.eu/ 

[5] Antonio Ballesteros Avila, Analysis of ageing related events occurred in nuclear power plants, 
2019, JRC119082. 

12 

 
 
List of abbreviations and definitions 

AMP 

Ageing Management Programme 

CNRA    

Committee on Nuclear Regulatory Activities of the OECD-NEA 

CSNI    

Committee on the Safety of Nuclear Installations of the OECD-NEA 

HL-LL   

High Level Lesson Learned 

IAEA 

International Atomic Energy Agency 

IGALL   

International Generic Ageing Lessons Learned 

IRS 

I&C 

JRC 

International  Reporting  System  for  Operating  Experience  jointly  operated  by 
the IAEA and OECD/NEA 

Instrumentation and Control 

Joint Research Centre of the European Commission 

LL-LL   

Low Level Lesson Learned 

LTO 

NPP 

Long Term Operation 

Nuclear Power Plant 

OECD/NEA  Nuclear Energy Agency 

OEF 

Operating Experience Feedback 

OPEX   

Operating Experience 

PINC 

TPR 

Communication on a Nuclear Illustrative Programme 

Topical Peer Review 

13 

 
  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
List of figures 

Figure1. Age distribution of the EU operating nuclear power reactors………………………………………………….5 

Figure 2. Participants and deliverables of the European Clearinghouse……………………………………………….6 

Figure 3. Distribution of root causes………………………………………………………………………………………………………..8 

Figure 4. Ageing mechanisms present in the events………………………………………………………………………………8    

Figure 5. Deficiencies in design vs. ageing mechanism………………………………………………………………………….9 

Figure 6. Distribution of corrective actions……………………………………………………………………………………………...9 

Figure 7. Some representative high level lessons learned…………………………………………………………………...10 

14 

 
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doi: 10.2760/239397 

ISBN 978-92-76-17299-4