Effect of initial flaw and load assumptions on risk estimate changes

    Research output: Chapter in Book/Report/Conference proceedingConference article in proceedingsScientificpeer-review

    Abstract

    This study concerns the effect of initial flaw and load assumptions on nuclear power plant (NPP) piping component failure probability and risk estimate changes. As the main criterion for the acceptance of a risk informed in-service inspection (RI-ISI) program is that the overall risk shall not increase when moving from the earlier ISI program to the risk informed one, means for robust quantification of the change in risk are needed. Worldwide, several assumptions and recommendations have been published both for NPP pipe weld initial flaw distributions and welding process induced residual stresses (WRSs), the latter being often the dominant load component for welds. Failure potential and risk analyses were performed with probabilistic fracture mechanics code VTTBESIT and Markov process application for three representative NPP piping welds, covering a wide range of initial flaw and load assumptions. The considered degradation mechanism is stress corrosion cracking (SCC). In the light of the analysis results, it can be concluded that both the size distributions of the initial cracks and WRSs have a remarkable impact on the risk values. The larger the initial cracks and higher on the tensile side the WRSs, the higher the resulting risk values, and vice versa.
    Original languageEnglish
    Title of host publicationBaltica IX. International Conference on Life Management and Maintenance for Power Plants
    EditorsPertti Auerkari, Juha Veivo
    Place of PublicationEspoo
    PublisherVTT Technical Research Centre of Finland
    Pages103-124
    ISBN (Print)978-951-38-8025-5, 978-951-38-8026-2
    Publication statusPublished - 2013
    MoE publication typeA4 Article in a conference publication
    EventBALTICA IX - International Conference on Life Management and Maintenance for Power Plants - Helsinki-Stockholm, Finland
    Duration: 11 Jun 201313 Jun 2013

    Publication series

    SeriesVTT Technology
    Number106
    ISSN2242-1211

    Conference

    ConferenceBALTICA IX - International Conference on Life Management and Maintenance for Power Plants
    CountryFinland
    CityHelsinki-Stockholm
    Period11/06/1313/06/13

    Fingerprint

    Defects
    Nuclear power plants
    Residual stresses
    Welding
    Welds
    Cracks
    Stress corrosion cracking
    Fracture mechanics
    Markov processes
    Inspection
    Pipe
    Degradation

    Cite this

    Cronvall, O. (2013). Effect of initial flaw and load assumptions on risk estimate changes. In P. Auerkari, & J. Veivo (Eds.), Baltica IX. International Conference on Life Management and Maintenance for Power Plants (pp. 103-124). Espoo: VTT Technical Research Centre of Finland. VTT Technology, No. 106
    Cronvall, Otso. / Effect of initial flaw and load assumptions on risk estimate changes. Baltica IX. International Conference on Life Management and Maintenance for Power Plants. editor / Pertti Auerkari ; Juha Veivo. Espoo : VTT Technical Research Centre of Finland, 2013. pp. 103-124 (VTT Technology; No. 106).
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    title = "Effect of initial flaw and load assumptions on risk estimate changes",
    abstract = "This study concerns the effect of initial flaw and load assumptions on nuclear power plant (NPP) piping component failure probability and risk estimate changes. As the main criterion for the acceptance of a risk informed in-service inspection (RI-ISI) program is that the overall risk shall not increase when moving from the earlier ISI program to the risk informed one, means for robust quantification of the change in risk are needed. Worldwide, several assumptions and recommendations have been published both for NPP pipe weld initial flaw distributions and welding process induced residual stresses (WRSs), the latter being often the dominant load component for welds. Failure potential and risk analyses were performed with probabilistic fracture mechanics code VTTBESIT and Markov process application for three representative NPP piping welds, covering a wide range of initial flaw and load assumptions. The considered degradation mechanism is stress corrosion cracking (SCC). In the light of the analysis results, it can be concluded that both the size distributions of the initial cracks and WRSs have a remarkable impact on the risk values. The larger the initial cracks and higher on the tensile side the WRSs, the higher the resulting risk values, and vice versa.",
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    Cronvall, O 2013, Effect of initial flaw and load assumptions on risk estimate changes. in P Auerkari & J Veivo (eds), Baltica IX. International Conference on Life Management and Maintenance for Power Plants. VTT Technical Research Centre of Finland, Espoo, VTT Technology, no. 106, pp. 103-124, BALTICA IX - International Conference on Life Management and Maintenance for Power Plants, Helsinki-Stockholm, Finland, 11/06/13.

    Effect of initial flaw and load assumptions on risk estimate changes. / Cronvall, Otso.

    Baltica IX. International Conference on Life Management and Maintenance for Power Plants. ed. / Pertti Auerkari; Juha Veivo. Espoo : VTT Technical Research Centre of Finland, 2013. p. 103-124 (VTT Technology; No. 106).

    Research output: Chapter in Book/Report/Conference proceedingConference article in proceedingsScientificpeer-review

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    N2 - This study concerns the effect of initial flaw and load assumptions on nuclear power plant (NPP) piping component failure probability and risk estimate changes. As the main criterion for the acceptance of a risk informed in-service inspection (RI-ISI) program is that the overall risk shall not increase when moving from the earlier ISI program to the risk informed one, means for robust quantification of the change in risk are needed. Worldwide, several assumptions and recommendations have been published both for NPP pipe weld initial flaw distributions and welding process induced residual stresses (WRSs), the latter being often the dominant load component for welds. Failure potential and risk analyses were performed with probabilistic fracture mechanics code VTTBESIT and Markov process application for three representative NPP piping welds, covering a wide range of initial flaw and load assumptions. The considered degradation mechanism is stress corrosion cracking (SCC). In the light of the analysis results, it can be concluded that both the size distributions of the initial cracks and WRSs have a remarkable impact on the risk values. The larger the initial cracks and higher on the tensile side the WRSs, the higher the resulting risk values, and vice versa.

    AB - This study concerns the effect of initial flaw and load assumptions on nuclear power plant (NPP) piping component failure probability and risk estimate changes. As the main criterion for the acceptance of a risk informed in-service inspection (RI-ISI) program is that the overall risk shall not increase when moving from the earlier ISI program to the risk informed one, means for robust quantification of the change in risk are needed. Worldwide, several assumptions and recommendations have been published both for NPP pipe weld initial flaw distributions and welding process induced residual stresses (WRSs), the latter being often the dominant load component for welds. Failure potential and risk analyses were performed with probabilistic fracture mechanics code VTTBESIT and Markov process application for three representative NPP piping welds, covering a wide range of initial flaw and load assumptions. The considered degradation mechanism is stress corrosion cracking (SCC). In the light of the analysis results, it can be concluded that both the size distributions of the initial cracks and WRSs have a remarkable impact on the risk values. The larger the initial cracks and higher on the tensile side the WRSs, the higher the resulting risk values, and vice versa.

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    SN - 978-951-38-8026-2

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    BT - Baltica IX. International Conference on Life Management and Maintenance for Power Plants

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    Cronvall O. Effect of initial flaw and load assumptions on risk estimate changes. In Auerkari P, Veivo J, editors, Baltica IX. International Conference on Life Management and Maintenance for Power Plants. Espoo: VTT Technical Research Centre of Finland. 2013. p. 103-124. (VTT Technology; No. 106).