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Fracture Mechanics Analyses of Embedded Cracks Under PTS and Effects of Residual Stresses

[+] Author Affiliations
Guian Qian, Markus Niffenegger

Paul Scherrer Institute, Villigen PSI, Switzerland

V. F. González-Albuixech

CIIM Universitat Politècnica de València, Valencia, Spain

Paper No. PVP2017-66202, pp. V06AT06A050; 7 pages
doi:10.1115/PVP2017-66202
From:
  • ASME 2017 Pressure Vessels and Piping Conference
  • Volume 6A: Materials and Fabrication
  • Waikoloa, Hawaii, USA, July 16–20, 2017
  • Conference Sponsors: Pressure Vessels and Piping Division
  • ISBN: 978-0-7918-5799-1
  • Copyright © 2017 by ASME

abstract

One potential challenge to the integrity of a reactor pressure vessel (RPV) of a pressurized water reactor is posed by a pressurized thermal shock (PTS), which is associated with severe cooling of the RPV followed by its repressurization. PTS transients lead to high tensile circumferential and axial stresses in the RPV wall. If the stress intensity factor (SIF) is large enough, a critical crack may grow. Thus, the RPV has to be assessed against cleavage fracture.

In this paper, two kinds of embedded cracks, i.e. semielliptical and elliptical crack with depth of 17 mm and length of 102 mm are considered. The extended finite element method (XFEM) is used to model such postulated cracks. The embedded crack with tip in the cladding/base interface causes a high KI. This is due to the stress discontinuities at the interface between the materials. In the FAVOR (probabilistic fracture mechanics code) calculation, for such cracks the closest point to the inner surface is calculated in order to be conservative. However, due to the highly ductile cladding material, it is unlikely for the embedded crack to propagate through the cladding. Thus, it is more appropriate to consider the outer surface point of the crack front.

The effect of welding residual stress and cladding/base interface residual stress on the crack driving force is studied. Surface cracks are assumed in the study of residual stresses. Results show that considering realistic welding residual stresses may increase KI by about 5 MPa·m0.5, while the cladding/base interface residual stress has a negligible effect on KI. The reason is that the cladding residual stress is only localized to the interface and it decreases significantly through the vessel wall.

Copyright © 2017 by ASME

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