vgbe energy journal 5 (2022) - International Journal for Generation and Storage of Electricity and Heat

Operating experience from ageing events occurred at nuclear power plants
Unknown
Other
Chemical ageing
Creep
Electrical ageing
Erosion
Wear
Corrosion
Irradiation damage
Thermal ageing
Fatigue
Relaxation
Swelling
1
1
Lessons learned
1
The extraction of the lessons learned from
the operating experience has been completed
in two steps. First (step 1), low level lessons
learned 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 Annex 2 of
reference [ Ballesteros Avila A., 2019]. Several
lessons are allocated to the same event
in many cases. These low level lessons
learned are very specific, so that they would
2
Fig. 7. Ageing mechanisms present in the events.
Other
Creep
Wear
Corrosion
Thermal ageing
Fatigue
Relaxation
1
1
1
1
3
3
4
Ageing Mechanism - Number of times
13
13
Deficiencies in Design versus Ageing Mechanism
Fig. 8. Deficiencies in design versus ageing mechanism.
Other
Wear
Thermal ageing
Swelling
Erosion
Fatigue
Electrical ageing
Corrosion
3
Absent or Deficiencies in AMP versus Ageing Mechanism
1
1
2
Fig. 9. Deficiencies in ageing management programmes versus ageing mechanism.
15
15
5
5
6
6
7
28
38
10
12
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). In the following paragraphs
the high level lessons learned are
presented:
Lesson learned #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.
Lesson learned #2 – Ageing Management
Programmes as well as maintenance programmes
should be reviewed and updated
to take into account modifications in the
current licensing bases.
Lesson learned #3 – The monitoring of the
environmental conditions, as information
source for ageing management, is of high
importance. In particular, a review of possible
changes in environmental conditions
(e.g. temperature, radiation, etc.) that could
affect ageing should be performed in case of
operational changes or structures, systems
and components (SSC) modifications.
Lesson learned #4 – The maintenance and
inspection programmes should be evaluated
and, if considered necessary, updated (frequency,
testing methods, procedures, etc.)
on the basis of the findings of the ageing
management programme.
Lesson learned #5 – Ageing management
programmes for specific degradation mechanisms
should be developed to avoid or
mitigate accelerated ageing (e.g., flow accelerated
corrosion, fretting, stress corrosion
cracking, thermal ageing). It is important
also to identify and justify possible associated
changes in process conditions (e.g., flow
pattern, velocity, vibration) that could cause
premature ageing and failure.
Lesson learned #6 – 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 SSC is to
safety.
Lesson learned #7 – 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.
Lesson learned #8 – Data on operating experience
can be collected and retained for
use as input for the management of plant
ageing. Reviews of operating experience can
identify areas where ageing management
programmes can be enhanced or new programmes
developed.
Lesson learned #9 – Earlier detection of
degradation is necessary to ensure timely
application of mitigation strategies. There is
the possibility that such early physical damage
(e.g., change of locally averaged material
properties) can be detected with appropriate
sensors.
Lesson learned #10 – The operating organization
should ensure that ageing management
programmes are reviewed on a
regular basis and, if needed, modified to ensure
that they will be effective for managing
44 | vgbe energy journal 5 · 2022