Transactions of the Korean Society of Pressure Vessels and Piping (한국압력기기공학회 논문집)

Korean Society of Pressure Vessels and Piping (한국압력기기공학회)
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Evaluation of Fracture Toughness considering Constraint Effect of Reactor Pressure Vessel Nozzle

원자로압력용기 노즐부 구속효과를 고려한 파괴인성 평가

  • 권형도 (한국수력원자력(주) 중앙연구원) ;
  • 이연주 (한국전력기술(주) 원자로설계개발단) ;
  • 김동학 (한국수력원자력(주) 중앙연구원) ;
  • 이도환 (한국수력원자력(주) 중앙연구원)
  • Received : 2019.05.24
  • Accepted : 2019.06.11
  • Published : 2019.06.30
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Abstract

Actual stress distributions in the nozzle of a pressure vessel may not be in plane strain condition, implying that the crack-tip constraint condition may be relaxed in the nozzle. In this paper, a methodology for evaluating the fracture toughness of the ASME Code is presented considering the relaxation of the constraint effect in the nozzle of the reactor pressure vessel. The crack-tip constraint effect is quantified by the T-stress. The equation, which represent the relation between the fracture toughness in the lower constraint condition and the plane strain fracture toughness, is derived using the T-stress. This equation is similar to the method for evaluating the fracture toughness of the Master Curve for low constraint conditions. As a result of evaluating the fracture toughness considering the constraint effect in the reactor inlet, outlet and direct injection nozzles using the proposed equation, it was confirmed that the fracture toughness in the nozzles is higher than the plane strain fracture toughness. Applying the proposed evaluation methodology, it is possible to reflect the relaxation of the constraint effect in the nozzles of the reactor pressure vessel, therefore, the safe operation area on the pressure-temperature limit curve can be prevented from being excessively limited.

Keywords

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Fig. 1 Postulated nozzle corner defect (From ASME Code, Section XI, Appendix G)

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Fig. 2 Finite element model and circumferential position for T-stress calculation of the inlet nozzle of the reactor pressure vessel

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Fig. 3 Input pressure and temperature for the finite element analysis

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Fig. 4 T-stress of the inlet nozzle of the reactor pressure vessel

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Fig. 5 Fracture toughness of the nozzles of the reactor pressure vessel

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