The assessment of reactor pressure vessel defects allowing for crack tip constraint and its effect on the calculation of the onset of the upper shelf

T-stress is used as an indicator of the condition of crack tip constraint. In current fracture mechanics engineering applications in the U.S. nuclear industry, T-stress generally has been ignored during the calculation of applied stress intensity factors (SIF). Consideration of this crack tip constraint component could affect the evaluation of material fracture behavior, under either plane strain or plane stress or plane strain and plane stress combination. When the T-stress shows that the condition of crack front constraint is not plane strain, incorporation of T-stress may allow reduction of unnecessary conservatisms in such calculations. Under this condition, the allowable stress intensity factor is modified by increasing it above the KIc value, and it potentially increases the predicted allowable flaw sizes. In this paper, T-stress has been calculated using 3-D finite element analyses (FEA) with a typical semi-elliptical crack in a reactor pressure vessel (RPV) nozzle blend radius. Both thermal and internal pressure load cases are considered. To verify this finite element analysis approach, this method is applied to comparable literature models. The FEA results are consistent with closed-form solutions for T-stress calculation.

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Investigation on Constraint Effect of a Reactor Pressure Vessel Subjected to Pressurized Thermal Shocks

Journal of Pressure Vessel Technology ◽

10.1115/1.4028017 ◽

2014 ◽

Vol 137 (1) ◽

Cited By ~ 2

Author(s):

Guian Qian ◽

Markus Niffenegger

Keyword(s):

Fracture Mechanics ◽

Pressure Vessel ◽

Plastic Material ◽

Crack Tip ◽

Constraint Effect ◽

Elastic Plastic ◽

Elastic Plastic Material ◽

Crack Tip Constraint ◽

Reactor Pressure ◽

Thermal Shocks

The integrity of a reactor pressure vessel (RPV) related to pressurized thermal shocks (PTSs) has been extensively studied. This paper introduces the method of using fracture mechanics for the integrity analysis of a RPV subjected to PTS transients. A 3-D finite element (FE) model is used to perform thermal and fracture mechanics analyses by considering both elastic and elastic–plastic material models. The results show that the linear elastic analysis leads to a more conservative result than the elastic–plastic analysis. The variation of the T-stress and Q-stress (crack tip constraint loss) of a surface crack in a RPV subjected to PTSs is studied. A shallow crack is assumed in the RPV and the corresponding constraint effect on fracture toughness of the material is quantified by the K–T method. The safety margin of the RPV is larger based on the K–T approach than based only on the K approach. The J–Q method with the modified boundary layer formulation (MBL) is used for the crack tip constraint analysis by considering elastic–plastic material properties. For all transient times, the real stress is lower than that calculated from small scale yielding (SSY) due to the loss of crack tip constraint.

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Effect of Plastic Constraint and Cladding on Semi-Elliptical Shaped Crack in Fracture Toughness Evaluation for a Reactor Pressure Vessel Steel

10.1115/pvp2021-61725 ◽

2021 ◽

Author(s):

Masaki Shimodaira ◽

Tohru Tobita ◽

Yasuto Nagoshi ◽

Kai Lu ◽

Jinya Katsuyama

Keyword(s):

Fracture Toughness ◽

Pressure Vessel ◽

Crack Tip ◽

Reactor Pressure Vessel ◽

Pressure Vessel Steel ◽

Fracture Toughness Test ◽

Integrity Assessment ◽

Plastic Constraint ◽

Shaped Crack ◽

Reactor Pressure

Abstract In the structural integrity assessment of a reactor pressure vessel (RPV), the fracture toughness (KJc) should be higher than the stress intensity factor at the crack tip of a semi-elliptical shaped under-clad crack (UCC), which is prescribed in JEAC4206-2016. However, differences in crack depth and existence of cladding between the postulated crack and fracture toughness test specimens would be affected to the plastic constraint state and KJc evaluation. In this study, we performed fracture toughness tests and finite element analyses to investigate the effect of plastic constraint and cladding on the semi-elliptical shaped crack in KJc evaluation. The apparent KJc value evaluated at the deepest point of the crack exceeded 5% fracture probability based on the Master Curve method estimated from C(T) specimens, and the conservativeness of the current integrity assessment method was confirmed. Few initiation sites were observed along the tip of semi-elliptical shaped crack other than the deepest point. The plastic constraint state was also analyzed along the crack tip, and it was found that the plastic constraint at the crack tip near the surface was lower than that for the deepest point. Moreover, it was quantitatively showed that the UCC decreased the plastic constraint. The local approach suggested higher KJc value for the UCC than that for the surface crack, reflecting the low constraint effect for the UCC.

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Evaluation on Constraint Effect of Reactor Pressure Vessel Under Pressurized Thermal Shock

Volume 1B: Codes and Standards ◽

10.1115/pvp2013-97566 ◽

2013 ◽

Cited By ~ 1

Author(s):

Naoki Ogawa ◽

Kentaro Yoshimoto ◽

Takatoshi Hirota ◽

Shohei Sakaguchi ◽

Toru Oumaya

Keyword(s):

Fracture Toughness ◽

Thermal Shock ◽

Surface Crack ◽

Pressure Vessel ◽

Crack Tip ◽

Reactor Pressure Vessel ◽

Constraint Effect ◽

Elastic Plastic ◽

Pressurized Thermal Shock ◽

Reactor Pressure

In recent years, the integrity of reactor pressure vessel (RPV) under pressurized thermal shock (PTS) accident has become controversial issue since the larger shift of RTNDT in some higher fluence surveillance data raised a concern on RPV integrity. Under PTS condition, the combination of thermal stress due to a temperature gradient and mechanical stress due to internal pressure causes considerable tensile stress inside the wall of RPV. Currently, RPV integrity is assessed by comparing stress intensity factor on a crack tip under PTS condition and a reference toughness curve based on the fracture toughness data of irradiated compact specimens. Since PTS loading is large enough to cause plastic deformation, a crack tip behavior on the inner surface of RPV can be explained by elastic-plastic fracture mechanics using the J-integral. In this study, 3D elastic plastic finite element analyses were performed to assess the crack tip behavior on surface of a RPV under Loss of coolant Accident, which causes one of the most severe PTS condition. In order to quantify the constraint effect on a surface crack, J-Q approach was applied. The constraint effect of a surface crack was compared with a compact specimen and its influence on the fracture toughness was assessed. As a result, the difference of constraint effect was clearly obtained. And it is recommended to consider constraint effects in the evaluation of structural integrity of RPV under PTS.

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Constraint Effect on Fracture Mechanics Evaluation for an Under-Clad Crack in a Reactor Pressure Vessel Steel

Volume 1: Codes and Standards ◽

10.1115/pvp2020-21441 ◽

2020 ◽

Author(s):

Masaki Shimodaira ◽

Tohru Tobita ◽

Hisashi Takamizawa ◽

Jinya Katsuyama ◽

Satoshi Hanawa

Keyword(s):

Fracture Toughness ◽

Surface Crack ◽

Pressure Vessel ◽

Crack Tip ◽

Reactor Pressure Vessel ◽

Pressure Vessel Steel ◽

Constraint Effect ◽

Rpv Steel ◽

Low Constraint ◽

Reactor Pressure

Abstract For structural integrity assessment of the reactor pressure vessel (RPV) in JEAC 4206-2016, it is required that the fracture toughness (KJc) be higher than the stress intensity factor at the crack tip of a postulated under-clad crack (UCC) near the inner surface of RPV steel under the pressurized thermal shock event. Previous analytical studies showed a low constraint effect at the crack tip of an UCC, compared with that of a normal surface crack. Such a low constraint effect may increase the apparent KJc. In this study, we performed three-point bending (3PB) fracture toughness tests and finite element analysis (FEA) for RPV steel containing an UCC or a surface crack to quantitatively investigate the effect of cladding on the KJc. The FEAs considering the anisotropic property of the cladding successfully reproduced the load vs. load-line displacement curves obtained from the tests. We found that the apparent KJc for the UCC was considerably higher than that for the surface crack. FEA also showed that the constraint effect for the 3PB test specimen with the UCC was lower than that for the specimen with the surface crack owing to the cladding. Thus, a low constraint effect from an UCC may increase the apparent KJc.

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Investigation on Constraint Effect of a Reactor Pressure Vessel Subjected to Pressurized Thermal Shocks

Volume 1B: Codes and Standards ◽

10.1115/pvp2013-98161 ◽

2013 ◽

Cited By ~ 2

Author(s):

Guian Qian ◽

Markus Niffenegger

Keyword(s):

Fracture Mechanics ◽

Pressure Vessel ◽

Plastic Material ◽

Crack Tip ◽

Constraint Effect ◽

Elastic Plastic ◽

Elastic Plastic Material ◽

Crack Tip Constraint ◽

Reactor Pressure ◽

Thermal Shocks

The integrity of a reactor pressure vessel (RPV) related to pressurized thermal shocks (PTSs) has been extensively studied. This paper introduces the method of using fracture mechanics for the integrity analysis of a RPV subjected to PTS transients. A 3-D finite element (FE) model is used to perform thermal and fracture mechanics analyses by considering both elastic and elastic-plastic material models. The results show that the linear elastic analysis leads to a more conservative result than the elastic-plastic analysis. The variation of the T-stress and Q-stress (crack tip constraint loss) of a surface crack in a RPV subjected to PTSs is studied. A shallow crack is assumed in the RPV and the corresponding constraint effect on fracture toughness of the material is quantified by the K-T method. The safety margin of the RPV is larger based on the K-T approach than only based on the K approach. The J-Q method with the modified boundary layer formulation (MBL) is used for the crack tip constraint analysis by considering elastic-plastic material properties. For all transient times, the real stress is lower than that calculated from small scale yielding (SSY) due to the loss of crack tip constraint.

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Reactor Surveillance Test and Fracture Mechanics Evaluation of Irradiation Embrittlement in Reactor Pressure Vessel Steels

Journal of Engineering Materials and Technology ◽

10.1115/1.3224818 ◽

1980 ◽

Vol 102 (4) ◽

pp. 317-326

Author(s):

Hideaki Takahashi ◽

Kiyoshi Saito ◽

Tetsuo Shoji ◽

Kazuhiro Date ◽

Masahiko Suzuki

Keyword(s):

Fracture Toughness ◽

Pressure Vessel ◽

Crack Tip ◽

Reactor Pressure Vessel ◽

Evaluation Procedure ◽

Pressure Vessel Steel ◽

Irradiation Embrittlement ◽

Tip Resistance ◽

Controlled Fracture ◽

Reactor Pressure

With special reference to a nuclear reactor surveillance test, a new evaluation procedure for the fracture toughness from Charpy Vee-notch data is developed. This procedure utilizes a recrystallization-etch technique to determine the crack tip energy dissipation (Wp) within an intense strain region or the dissipation rate (dWp/da). These two parameters serve to characterize the crack tip resistance to cleavage-controlled fracture initiation. The effects of specimen geometry, strain rate, temperature and notch acuity on the cleavage-controlled fracture toughness transition are explained using a critical value of Wp or dWp/da and a modified rate parameter. A feasibility of the new surveillance test procedure for evaluating the irradiation embrittlement of reactor pressure vessel steel, such as SA533B-1, is here verified experimentally, utilizing the Charpy or small compact tension specimen irradiated in a test reactor.

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Elastic-Plastic Fracture Analysis of a Reactor Pressure Vessel Subjected to Pressurized Thermal Shock

Volume 6A: Materials and Fabrication ◽

10.1115/pvp2017-66221 ◽

2017 ◽

Author(s):

Huajing Guo ◽

Zhongxian Wang ◽

Poh-Sang Lam

Keyword(s):

Thermal Shock ◽

Pressure Vessel ◽

Three Dimensional ◽

Reactor Pressure Vessel ◽

Pressurized Thermal Shock ◽

Dimensional Finite Element ◽

Fracture Theory ◽

Crack Tip Constraint ◽

Three Dimensional Finite Element ◽

Reactor Pressure

Three-dimensional finite element models are used to analyze a reactor pressure vessel with an axial semi-elliptical surface crack subjected to pressurized thermal shock. During the thermal shock event, the J-A2 two-parameter fracture theory is used to investigate the temperature-dependent constraint effect at the deepest point and the surface point of the crack. Using the R6 methodology, a series of constraint-based crack failure assessment curves during the thermal shock can be obtained. It was found that the crack tip constraint should be considered for developing a more realistic failure criterion.

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