Fatigue Monitoring

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Fatigue Monitoring

• Zoran Bertalanic, M.Sc.E.E.

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Who are we?

• Energy Institute Ltd., Zagreb, Croatia
• founded in 1953.
• scientific research organisation in field of
  electrical power engineering
• Year 2008 58 employees, 44 with university
  degree (76)

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Historical View - Croatia

• 1895 HPP Jaruga near Sibenik, 2 2.7 MW, 36 GWh
• Wilhelm Roentgen of Germany invents the x-ray
  photograph
• The Lumière Brothers debut the cinématographe,
  showing the first projected moving pictures to an
  audience in Paris.
• J. Edgar Hoover was born
• Mark Twain visited Teslas laboratory
• 1906 HPP Miljacka, 24 MW
• 1907 TPP Zagreb, 0.8 MW
• 1908 HPP Ozalj, 3.2 MW
• 2008... still no NPP

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NPP Krko

• South-eastern part of Slovenia, on the Sava river
• 1974 construction start
• May 1981 first fuel loading
• October 1981 first synchronisation
• February 1984 Commercial operation

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What do we do?
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Thermal Stratification Fatigue Stress
Monitoring of RCS Line

• (Fatigue Monitoring)

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Fatigue Monitoring

• Krko Class 1 components ? according to ASME
  Code, Section III, Class 1
• Fatigue analysis based on set of cyclic
  operations (conservative at design time)
• Tech. Spec. ? limited number of transients
• During operation ? unanalyzed events discovered ?
  most important for fatigue is Thermal
  Stratification, Cycling and Striping (TASCS)

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Stratification?
Stress stratification in horizontal piping system
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Stratification?
Unisolable piping where stratification is possible
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Stratification?
Periodic turbulence penetration stratification
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FATIQUE MONITORING

• Tracing conformance of actual plant operation to
  the design basis and keep appropriate records of
  such conformance
• alternative to cycle counting (Tech. Spec.), can
  be used to fulfil licence requirements

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First phase of Fatigue Monitoring (2002)

• acquire operating data from stratification
  (fatigue) sensitive locations
• locations where thermal stratification mostly
  appear
• unisolated parts of auxiliary class 1 piping
  (including surge line)
• pressurizer

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Monitoring Equipment

• Requirements
• only surveillance, not needed for shutdown, no
  seismic or safety related requirements
• Method
• external mounted temperature detectors
• Detectors
• RTDs

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Monitoring Equipment

• Why RTDs and not T/C?
• Better accuracy
• Stable output within broad temp. ranges
• Stable over long time
• Provide accurate reading over narrow temperature
  spans
• Good on-site experience
• Follow more linear curve
• Total price with extension wire is lower

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RTD Locations

• leak-off lines with 2 sensors (redundancy)
• horizontal lines with 2 to 5 temperatures

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Locations?

• normal charging lines
• alternate charging lines
• pressurizer auxiliary spray line
• residual heat removal suction lines
• pressurizer surge line
• pressurizer

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RTD locations

• Normal charging

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RTD locations

• Alternate charging

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RTD locations

• PressurizerAuxiliary Spray

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RTD locations

• Residual Heat Removal

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RTD locations

• Pressurizer Surge Line

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RTD locations

• Pressurizer
• total 6 RTDs (0-400C)
• T1 (2 pcs)
• T3 (2 pcs)
• T10 (2 pcs)

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RTD locations
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Sum of all RTD sensors
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First problems

• installation during outage 2002
• first problems
• influence of environment temperature (bad thermal
  insulation)
• poor RTD-surface contact (big difference in
  measured temperature)
• influence of metallic parts/supports (heat is
  carried away, lower temperature is measured)

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First problems (2)

• Damage of sensors during installation of thermal
  insulation
• Design change request

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First analysis (Dec 2002)

• Primary side works very stable, no significant
  stratification
• Transients noticeable during power decrease for
  test purposes
• Additional data needed (3start-up, 3shut-down)

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Conclusion

• Modification
• very simple
• high achieved/cost factor
• Fatigue
• most important aging factor of critical
  components
• Analysis
• must record several start-up and shut-down events
  (or other events) to collect necessary data

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Conclusion

• Benefits
• Monitor fatigue to confirm basic design
• Reduce fatigue of key components
• change procedures (start-up and shut-down)
• involve operators to follow the procedures, show
  them temperature on mimics
• Better in-side view on critical components during
  work or transient conditions
• Extend life-time