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System Analysis, Part I

Training Course on PSAIslamabad, Pakistan, May 2-6, 2005. Principal Objective of System analysis Task in a PSA for a NPP. To develop system models for safety functions intervening in the accident sequence headers.Fault tree Analysis is the technique most broadly used for system modelling.Event

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System Analysis, Part I

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    1. 1 System Analysis, Part I Javier Yllera, j.yllera@iaea.org IAEA (SAS/NSNI)

    2. Training Course on PSA Islamabad, Pakistan, May 2-6, 2005

    3. Training Course on PSA Islamabad, Pakistan, May 2-6, 2005

    4. Training Course on PSA Islamabad, Pakistan, May 2-6, 2005 Example of Event Tree - Very Small LOCA The training event we are about to begin will provide you with the …. Instructions The training event we are about to begin will provide you with the …. Instructions

    5. Training Course on PSA Islamabad, Pakistan, May 2-6, 2005 Event Tree /Fault Tree Link Fault tree (FT) is a graphical representation and analytical method whereby an undesired event (e.g. state of a system) is specified through the ET heading, and the system is then analyzed to find out all potential ways how the undesired event can occur FT is a systematic deductive way to determine all failure combinations of the system leading to the undesired “TOP” event. It implicitly considers however knowledge that may have been gained through inductive methods, e.g. FMEA In PSA, FT is used to model the failure of events in the accident sequence event trees and some initiating events as well The so called functional trees are small fault trees that link the event tree headers with several safety systems or human actions required to perform the function modelled in the header. The training event we are about to begin will provide you with the …. Instructions The training event we are about to begin will provide you with the …. Instructions

    6. Training Course on PSA Islamabad, Pakistan, May 2-6, 2005

    7. Training Course on PSA Islamabad, Pakistan, May 2-6, 2005

    8. Training Course on PSA Islamabad, Pakistan, May 2-6, 2005

    9. Training Course on PSA Islamabad, Pakistan, May 2-6, 2005 Model (System) Boundaries: External and Internal

    10. Training Course on PSA Islamabad, Pakistan, May 2-6, 2005 Internal boundaries: Model resolution

    11. Training Course on PSA Islamabad, Pakistan, May 2-6, 2005 Examples of component boundaries

    12. Training Course on PSA Islamabad, Pakistan, May 2-6, 2005 Example of the considered components & failure modes list

    13. Training Course on PSA Islamabad, Pakistan, May 2-6, 2005 Examples of System Boundaries Definition Hydraulic and pneumatic systems for pipe headers – Connection to pipeline or vessel of another system; for pipelines connected to support systems : connection with head pipelines of the support system.

    14. Training Course on PSA Islamabad, Pakistan, May 2-6, 2005 Examples of System Boundaries Definition Heat Exchangers (including the internal ones ) are included in the cooled system if they are exclusive

    15. Training Course on PSA Islamabad, Pakistan, May 2-6, 2005 Examples of System Boundaries Definition Electrical supplies to main consumers, e.g pumps.

    16. Training Course on PSA Islamabad, Pakistan, May 2-6, 2005 Examples of System Boundaries Definition Electrical systems: The models start from the bus bars to avoid postulating a different Top event for each consumer

    17. Training Course on PSA Islamabad, Pakistan, May 2-6, 2005 Basic Event Naming Scheme A systematic naming scheme for the basic events is needed for automated linking of the events with the reliability data base, receiving the adequate data and understanding the meaning of the basic events from its code. The possibilities depend upon the quantification software. Example:

    18. Training Course on PSA Islamabad, Pakistan, May 2-6, 2005 Human error types considered in analysis Pre-accident human errors , e.g. misalignment after test or maintenance, calibration errors, etc. Post-accident human errors, foreseen in the emergency procedures: Failures to perform required manual actions Failures to back up automatic actuation failures Sometimes, recovery actions

    19. Training Course on PSA Islamabad, Pakistan, May 2-6, 2005 Typical system dependencies

    20. Training Course on PSA Islamabad, Pakistan, May 2-6, 2005 Documentation of dependencies

    21. Training Course on PSA Islamabad, Pakistan, May 2-6, 2005 Test and maintenance activities Corrective maintenance: Time point and duration unpredictable. Required component realignments to be analyzed with plant personnel. Activities having a similar impact on the system can be group together. probabilities of maintenance outages to be obtained preferably from plant records. Special attention to maintenance work affecting other systems through interfaces. Results can be documented in a “Maintenance Matrix”. Test: Performed periodically according to surveillance procedures. Realignments according to procedures. List of directly and indirectly tested components should be determined. If the test affects system unavailability, it should be postulated. Test duration normally estimated through test records or expert judgements. Analysis of human actions and automatic actuations for consideration of potential pre accident human errors. Results to be documented in a test matrix. The test matrix is used for the human reliability analysis and for inputting test intervals as parameters to the component data base Preventive maintenance: Periodically performed. Normally not acceptable as a direct equipment test, but in may help to test indirectly minor components and if conducted at power operation may affect system availability and be the origin of human errors

    22. Training Course on PSA Islamabad, Pakistan, May 2-6, 2005 Boundary conditions and modeling assumptions It is essential to define and justify boundary conditions and the modeling assumptions. Examples: Pre-accident system conditions, e.g. any assumption on which train is running and which one is in stand by if so modeled success criteria modeled, automatic actions that will or will not credited or taken into consideration The same with human actions Flow diversion through other pipes (depending on relative size) Consideration or not of passive failures, etc. Combination of values that will be assigned to house events,etc. Considerations about common cause failures

    23. Training Course on PSA Islamabad, Pakistan, May 2-6, 2005 Division into subsystems

    24. Training Course on PSA Islamabad, Pakistan, May 2-6, 2005 Division into subsystems

    25. Training Course on PSA Islamabad, Pakistan, May 2-6, 2005 Fault tree development Fault tree handbook (NUREG-)492)

    26. Training Course on PSA Islamabad, Pakistan, May 2-6, 2005 Fult Tree Elements

    27. Training Course on PSA Islamabad, Pakistan, May 2-6, 2005 Fault Tree Elements (cont.)

    28. Training Course on PSA Islamabad, Pakistan, May 2-6, 2005 Boolean operators: Fault tree gates

    29. Training Course on PSA Islamabad, Pakistan, May 2-6, 2005 Gate types and symbols

    30. Training Course on PSA Islamabad, Pakistan, May 2-6, 2005 “AND” Gate

    31. Training Course on PSA Islamabad, Pakistan, May 2-6, 2005 “OR” Gate

    32. Training Course on PSA Islamabad, Pakistan, May 2-6, 2005 “K of N” Gate

    33. Training Course on PSA Islamabad, Pakistan, May 2-6, 2005 Basic events Basic event – event not further analyzed. Basic events are considered statistically independent from each other.

    34. Training Course on PSA Islamabad, Pakistan, May 2-6, 2005 Basic events symbols

    35. Training Course on PSA Islamabad, Pakistan, May 2-6, 2005 Simple fault tree example

    36. Training Course on PSA Islamabad, Pakistan, May 2-6, 2005 Simple fault tree example

    37. Training Course on PSA Islamabad, Pakistan, May 2-6, 2005 Minimal cut set identification

    38. Training Course on PSA Islamabad, Pakistan, May 2-6, 2005 House events (logical flags)

    39. Training Course on PSA Islamabad, Pakistan, May 2-6, 2005 House events (logical flags)

    40. Training Course on PSA Islamabad, Pakistan, May 2-6, 2005 House events (logical flags)

    41. Training Course on PSA Islamabad, Pakistan, May 2-6, 2005 House events (logical flags)

    42. Training Course on PSA Islamabad, Pakistan, May 2-6, 2005 House events (logical flags)

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