NDLI: Constraint Based Assessment of Postulated Nozzle Corner Cracks

Content Provider	The American Society of Mechanical Engineers (ASME) Digital Collection
Author	Siegele, Dieter Varfolomeyev, Igor Nagel, Gerhard
Copyright Year	2002
Abstract	Brittle failure for reactor pressure vessels (RPV) under loss of coolant accidents (LOCA) considering strip and plume cooling show the nozzle corner as leading region in load level (e.g. Siegele et al., 1999). For such transients postulated nozzle corner cracks are also leading in crack driving force compared to the fracture toughness of the material. On the other hand, the crack tip constraint and consequently the failure probability is reduced by yielding caused by high thermal stresses and in addition by the crack size being small relative to the bulk of the flange material. Under these conditions, the flaw assessment in the nozzle corner using fracture toughness data obtained on standard specimens with high constraint level is over-conservative. In this situation it is suitable to introduce the loss of crack tip constraint into the brittle failure analysis of the nozzle corner. This investigation focuses on the assessment of surface cracks in the nozzle corner of an RPV. Using the finite element method temperature and stress calculations are carried out for a postulated LOCA event. For crack postulates in the nozzle corner of various size and geometry in the nozzle corner, crack driving parameters (such as the J-integral and the stress intensity factor) are determined as functions of the crack tip temperature. To account for the crack tip constraint, the T-stress is then evaluated and used along with the master curve approach as suggested by Wallin (2001). Significant loss of constraint is found for the nozzle corner resulting in a large shift of the fracture toughness curve to lower temperatures, thus excluding initiation of the crack postulates.
Sponsorship	Pressure Vessels and Piping Division
Starting Page	73
Ending Page	77
Page Count	5
File Format	PDF
ISBN	0791846547
DOI	10.1115/PVP2002-1352
Volume Number	Fatigue, Fracture and Damage Analysis, Volume 2
Conference Proceedings	ASME 2002 Pressure Vessels and Piping Conference
Language	English
Publisher Date	2002-08-05
Publisher Place	Vancouver, BC, Canada
Access Restriction	Subscribed
Subject Keyword	Strips Temperature Cooling Reactor vessels Plumes (fluid dynamics) Flanges Probability Fracture (materials) Brittleness Finite element methods Stress Fracture toughness Transients (dynamics) Geometry Failure analysis Nozzles Coolants Corners (structural elements) Surface cracks Failure Thermal stresses Accidents
Content Type	Text
Resource Type	Article

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