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Probabilistic leak-before-break assessment of a main coolant line

: Varfolomeev, I.; Ivanov, D.; Siegele, D.; Nagel, G.

Bajwa, C.S. ; American Society of Mechanical Engineers -ASME-, Pressure Vessels and Piping Division:
ASME Pressure Vessels and Piping Conference 2010. Proceedings. Vol.7: Operations, applications and components : Presented at ASME 2010 Pressure Vessels and Piping Division/K-PVP conference; July 18 - 22, 2010, Bellevue, Washington, USA
New York/NY.: ASME, 2010
ISBN: 978-0-7918-4926-2
Pressure Vessels and Piping Conference <2010, Bellevue/Wash.>
Conference Paper
Fraunhofer IWM ()

The paper presents results of a probabilistic leak-before-break (LBB) assessment of a ferritic main coolant line of a pressurized water reactor representative for German nuclear power plants. The analysis approach is based on the elastic-plastic fracture mechanics methodology, incorporating the failure assessment diagram to calculate the critical through-thickness crack size, as well as fatigue crack growth calculations to determine the flaw length at wall penetration. An essential part of this study is the collation and statistical treatment of material data, such as strength properties, crack resistance and fatigue crack growth curves, and their incorporation in the probabilistic assessment. The analysis yields negligible break probabilities, thus demonstrating the LBB behavior of the piping. This conclusion is validated by results of a sensitivity study with additional conservative assumptions and simplifications with respect to the initial crack size and material st ate. For the sake of simplicity, the blocking effect of the intact austenitic cladding on the crack extension, as well as the conditional probability of crack penetration through the wall during the service life are neglected in this investigation. Through an additional treatment of these issues a more realistic assessment is achieved, resulting in even smaller failure probabilities.