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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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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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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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).