International Atomic Energy Agency
Ageing, Life Limiting Factors
Presented by:
Tibor Szikszai
Ri-man Consulting, Hungary
[email protected]
Joint ICTP-IAEA Essential Knowledge Workshop on Deterministic Safety
Analysis and Engineering Aspects Important to Safety, Trieste, Italy 12 – 23
October 2015 (week 1)
Contents of the presentation
!  Introduction
!  Design lifetime considerations
!  Cycle management
!  Ageing mechanisms
!  Ageing evaluation tasks
!  Ageing management
!  Management of obsolescence
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Introduction
81% of
operational
reactors have
more than 20
years of
operation
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Introduction
"  The time related or time dependent changes affecting
the safety of the NPP shall be followed and evaluated,
and the necessary follow-up actions shall be taken to
keep the safety on an acceptable level.
"  Structures, systems, and components (SSCs) of a
nuclear power plant experience two kinds of timedependent changes:
!  physical ageing and wear of SSCs causing
degradation of their performance characteristics over
time or with use
!  obsolescence, where SSCs become out of date in
comparison with current knowledge, technology,
standards, and regulations
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Introduction
"  Ageing management is the engineering, operational,
inspection, and maintenance actions that control, within
acceptable limits, the effects of physical ageing and
obsolescence of SSCs occurring over time or with use.
"  An ageing management program (AMP) is a set of
policies, processes, procedures, arrangements, and
activities for managing the ageing of the SSCs for an
NPP.
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Design lifetime considerations
"  The design lifetime of the plant is dependent on the
non-replaceable plant component with the shortest
designed lifetime
"  The designed progress of the ageing effects of the nonreplaceable components predetermines the lifetime of
the plant
"  Also the allowed by the design maximum number of the
cycle of specific events may be a lifetime limiting factor
It is essential to observe and follow the development of
the limiting factors, and demonstrate the safety during the
residual lifetime.
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Design lifetime considerations
"  The design should specify the number of allowed load
cycles of different types:
!  Number of specific operational events, like power
changes in different ranges
!  Number of reactor scrams
!  Number of other initiating events with equipment
damages
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Cycle management
"  Control of the cycles:
!  The occurring operational events and incidents
should be analyzed in order to determine, if they
“consume” from one or more allowed cycles, and the
residual allowed number of cycles should be kept in
operational records and likely in licensing
documentation
!  If the number of events of a kind reaches the
maximum allowed cycles, the plant operator should
implement special technical measures to allow
continued operation, otherwise this would mean the
end of the lifetime of the plant...
!  Difficulty is the interpretation of the maximum
number, if it is 1.
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Ageing effects
"  “Ageing effects are net changes in
the characteristics of an SSC that
occur with time or use and which
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Ageing effects
"  Ageing effects may be positive or negative.
!  Examples of positive effects are increase in concrete
strength from curing and reduced vibration from
wear-in of rotating machinery.
!  Examples of negative effects are reduction in
diameter from wear of a rotating shaft, cracking,
thinning or loss in material strength from fatigue or
thermal ageing, and loss of dielectric strength or
cracking of cable insulation.
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Ageing mechanisms
"  An ageing mechanism represents an increased
likelihood of failure / degradation of the SSCs. The
following elements should be evaluated to identify and
characterize an ageing mechanism:
!  Type of ageing mechanism and its impact on the
reliability parameters in time;
!  Stressors and environment;
!  Maintenance programs;
!  Inspection programs (detection of degradation);
!  Replaceable components, etc.
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Ageing mechanisms
"  An ageing mechanism also can map into one of the
three categories:
!  It induces an initiator (typically: fails or degrades an
operating system or its boundary);
!  It fails or degrades mitigation system, but does not
induce an initiator (e.g. fails or degrades a standby
safety system);
!  It, at the same time, induces an initiator and fails or
degrades a mitigation system.
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Ageing evaluation tasks
"  Screening of SSCs and related ageing mechanisms for
incorporation into the an AMP
!  Divide the SSCs of each generic type (e.g. motor
driven pumps, motor operated valves, piping, !) into
sub-groups by considering selected attributes
including:
" System / function;
" Safety class
" Location and environment;
" Operating stressors
" Applicable ageing mechanisms, etc.
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Ageing evaluation tasks
"  Screening of SSCs and related ageing mechanisms for
incorporation into an AMP
!  Each SSC group / ageing mechanism from the
Preliminary List is first classified into one of the
several risk categories, based on the consideration
of:
" Increased likelihood of failure, and
" Consequences of failure
Increased Likelihood of Failure
Consequences
of Failure
Low
High
Low
Risk Category:
Low
Risk Category:
Medium
High
Risk Category:
Medium
Risk Category:
High
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Ageing evaluation tasks
"  Screening of SSCs and related ageing mechanisms for
incorporation into an AMP
!  Evaluate each sub-group from the perspective of
increased failure likelihood due to ageing by
considering attributes such as:
" Type of applicable ageing mechanism and associated time
dependent reliability model;
" Testing and maintenance programs;
" Replacing / renewing;
" In-service inspection programs;
" Ageing management strategies, etc.
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Ageing managament
Concept of ageing
management
PLAN
2. Development and optimization of
activities for ageing management of a
structure/component
Preparing, coordinating, maintaining and
improving activities for ageing management:
"  PLAN
"  DO
Improve effectiveness
of ageing management
programmes
"  CHECK
"  ACT
• Document regulatory requirements and
safety criteria
• Document relevant activities
• Describe coordination mechanisms
• Improve effectiveness of ageing
management based on current
understanding, self-assessment and
peer review
Minimize
expected
degradation
1. Understanding ageing of a
structure/component
Key to effective ageing management based
on the following information:
ACT
5. Maintenance of a
structure/component
Managing ageing effects:
• Preventive maintenance
• Corrective maintenance
• Spare parts management
• Replacement
• Maintenance history
Mitigate
degradation
• Materials and material properties,
fabrication methods
• Stressors and operating conditions
• Ageing mechanisms
• Sites of degradation
• Consequence of ageing degradation
and failures
• R&D results
• Operational experience
• Inspection/monitoring/maintenance history
• Mitigation methods
• Current status, condition indicators
CHECK
4. Inspection, monitoring and
assessment of a structure/component
DO
3. Operation/use of a
structure/component
Managing ageing mechanisms:
• Operation according to
procedures and technical
specifications
• Chemistry control
• Environmental control
• Operating history, including
transient records
Check
for
degradation
Detecting and assessing ageing effects:
• Testing and calibration
• Pre-service and in-service inspection
• Surveillance
• Leak detection, vibration monitoring, etc.
• Assessment of functional capability/fitness
for service
• Record keeping
FIG. 1. Systematic approach to managing ageing of a structure or component.
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of ageing management
programmes
Ageing
"  Understanding the
ageing of a structure
or component is the
keyACT
to its effective
5. Maintenance
of a
ageing
management.
structure/component
Managing ageing effects:
• Preventive maintenance
• Corrective maintenance
• Spare parts management
• Replacement
• Maintenance history
Mitigate
degradation
understanding, self-assessment and
peer review
managament
1. Understanding ageing of a
structure/component
Key to effective ageing management based
on the following information:
• Materials and material properties,
fabrication methods
• Stressors and operating conditions
• Ageing mechanisms
• Sites of degradation
• Consequence of ageing degradation
and failures
• R&D results
• Operational experience
• Inspection/monitoring/maintenance history
• Mitigation methods
• Current status, condition indicators
CHECK
4. Inspection, monitoring and
assessment of a structure/component
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Ageing managament
PLAN
The PLAN activity means
coordinating, integrating
and modifying existing
programmes and
activities that relate to
managing the ageing of a
structure or component
and developing new
programmes, if
necessary.
Improve effectiveness
of ageing management
programmes
2. Development and optimization of
activities for ageing management of a
structure/component
Preparing, coordinating, maintaining and
improving activities for ageing management:
• Document regulatory requirements and
safety criteria
• Document relevant activities
• Describe coordination mechanisms
• Improve effectiveness of ageing
management based on current
understanding, self-assessment and
peer review
1. Understanding ageing of a
structure/component
ACT
18
Key to effective International
ageing management
based
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on the following information:
ructure/component
Ageing managament
to effective ageing management based
he following information:
The DO activity means
terials
and materialexpected
properties,
minimizing
rication methods
degradation of a structure
essors and operating conditions
component through its
eingor
mechanisms
‘careful’
operation or use in
es of
degradation
accordance
with
operating
nsequence
of ageing
degradation
d failures
procedures and technical
D results
specifications.
erational experience
pection/monitoring/maintenance history
igation methods
rrent status, condition indicators
CK
spection, monitoring and
ssessment of a structure/component
ecting
and assessing ageing effects:
19
DO
3. Operation/use of a
structure/component
Managing ageing mechanisms:
• Operation according to
procedures and technical
specifications
• Chemistry control
• Environmental control
• Operating history, including
transient records
Check
for
degradation
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• Current status, condition indicators
Ageing managament
Mitigate
degradation
CHECK
activity
CHECK
The
means
4. Inspection, monitoring and
assessment of a structure/component
the timely detection and
characterization of
Detecting and assessing ageing effects:
significant degradation
• Testing and calibration
• Pre-service and in-service inspection
through inspection and
• Surveillance
monitoring of a structure or
• Leak detection, vibration monitoring, etc.
• Assessment of functional capability/fitness
component, and the
for service
assessment of observed
• Record keeping
degradation to determine the
type and timing
FIG.of1.any
Systematic approach to managing ageing of a str
corrective actions required.
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2.8. The PLAN activity in Fig. 1 means coordin
modifying existing programmes and activities that r
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ageing of a structure or component
and developin
Ageing managament
ACT
The ACT activity means
the timely mitigation and
correction of component
degradation through
appropriate maintenance
and design modifications,
including component
repair and replacement of
a structure or component.
5. Maintenance of a
structure/component
Managing ageing effects:
• Preventive maintenance
• Corrective maintenance
• Spare parts management
• Replacement
• Maintenance history
Mitigate
degradation
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Ageing managament
The closed loop indicates the continuous improvement of
the ageing management programme for a particular
structure or component, on the basis of
!  feedback of relevant operating experience
!  and results from research and development,
!  and results of self-assessment and peer reviews,
to help ensure that emerging ageing issues will be
addressed.
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Ageing managament
"  Systematic approach to managing ageing in the
operation of nuclear power plants
!  Organizational arrangements;
!  Data collection and record keeping;
!  Screening of SSCs for the purposes of ageing
management;
!  Review of the management of ageing;
!  Condition assessment;
!  Development of ageing management programmes;
!  Implementation of ageing management programmes;
!  Improvement of ageing management programmes.
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Ageing managament
"  Systematic approach to managing ageing in the
operation of nuclear power plants
!  Organizational arrangements;
!  Data collection and record keeping;
!  Screening of SSCs for the purposes of ageing
management;
!  Review of the management of ageing;
!  Condition assessment;
!  Development of ageing management programmes;
!  Implementation of ageing management programmes;
!  Improvement of ageing management programmes.
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Proactive strategy for ageing managament
"  Ageing management of SSCs important to safety should
be implemented proactively (with foresight and
anticipation) throughout the plant’s lifetime, i.e. in
design, fabrication and construction, commissioning,
operation (including long term operation and extended
shutdown) and decommissioning.
"  Regulatory requirements for ageing management
should be established and updated and guidance
should be developed to ensure that the operating
organization of a nuclear power plant implements an
effective ageing management programme.
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Proactive strategy for ageing managament
"  The operating organization should be responsible for
demonstrating that the relevant issues of ageing that
are specific to the plant are clearly identified and
documented in the safety analysis report throughout
the plant’s lifetime.
"  Issues of ageing arising from other plants should be
considered by the operating organization in evaluating
the ageing management measures proposed by
suppliers.
"  The ageing management activities of suppliers and the
operating organization should be overseen by the
regulatory body throughout the plant’s lifetime.
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Managament of obsolescence
"  Nuclear power plant safety can be impaired if
obsolescence of SSCs is not identified in advance and
corrective actions are not taken before associated
declines occur in the reliability or availability of SSCs.
"  Management of obsolescence is a part of the general
approach for enhancing nuclear power plant safety
through ongoing improvements of both performance of
SSCs and safety management.
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Managament of obsolescence
"  Types of obsolescence
!  Knowledge
" Manifestation
• 
Knowledge of current standards, regulations and technology relevant
to SSCs not updated
" Consequences
• 
Opportunities to enhance plant safety missed; Reduced capability for
long term operation
" Management
• 
Continuous updating of knowledge and improvement of its application
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Managament of obsolescence
"  Types of obsolescence
!  Standards and regulations
" Manifestation
• 
• 
Deviations from current regulations and standards, both hardware and
software;
Design weaknesses (e.g. in equipment qualification, separation,
diversity or severe accident management capabilities)
" Consequences
• 
• 
Plant safety level below current standards and regulations (e.g.
weaknesses in defence in depth, or higher core damage frequency);
Reduced capability for long term operation
" Management
• 
Systematic reassessment of plant against current standards (e.g.
periodic safety review) and appropriate upgrading, backfitting or
modernization
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Managament of obsolescence
"  Types of obsolescence
!  Technology
" Manifestation
• 
• 
Lack of spare parts and/or technical support;
Lack of suppliers and/or industrial capabilities
" Consequences
• 
• 
Declining plant performance and safety owing to increasing failure
rates and decreasing reliability;
Reduced capability for long term operation
" Management
• 
• 
• 
Systematic identification of useful service life and anticipated
obsolescence of SSCs; Provision of spare parts for planned service
life and timely replacement of parts;
Long term agreements with suppliers;
Development of equivalent structures or components
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