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Journal Articles

Constraint effect on fracture mechanics evaluation for an under-clad crack in a reactor pressure vessel steel

Shimodaira, Masaki; Tobita, Toru; Takamizawa, Hisashi; Katsuyama, Jinya; Hanawa, Satoshi

Proceedings of ASME 2020 Pressure Vessels and Piping Conference (PVP 2020) (Internet), 7 Pages, 2020/08

In JEAC 4206 which prescribes the methodology for assessing the structural integrity of reactor pressure vessels (RPVs), an under-clad crack (UCC) at the inner surface of RPV is postulated, and it is required that the fracture toughness of RPV steels is higher than stress intensity factor for at the crack tip during the pressurized thermal shock event. In the present study, to investigate the effect of cladding on the fracture toughness, we performed three-point bending fracture toughness tests and finite element analyses (FEAs) for an RPV steel containing an UCC or a surface crack, and the constraint effect for UCC was also discussed. As the result, we found that the fracture toughness for UCC was considerably higher than that for surface crack. On the other hand, the FEAs showed that the cladding decreased the constraint effect for UCC.

Journal Articles

Probabilistic fracture mechanics benchmarking study involving the xLPR and PASCAL-SP codes; Analysis by PASCAL-SP

Mano, Akihiro; Katsuyama, Jinya; Li, Y.

Proceedings of ASME 2020 Pressure Vessels and Piping Conference (PVP 2020) (Internet), 7 Pages, 2020/08

A probabilistic fracture mechanics (PFM) analysis code PASCAL-SP has been developed by Japan Atomic Energy Agency (JAEA) for evaluating the failure probability of piping in nuclear power plant considering aged-related degradations such as primary water stress corrosion cracking (PWSCC) in pressurized water reactor environments and fatigue. To strengthen the confidence of analysis results, benchmarking study is being performed with PFM analysis code xLPR which has been developed by U.S.NRC in collaboration with EPRI. The benchmarking study consists of deterministic and probabilistic analyses on PWSCC under the common analysis conditions. In addition, deterministic sensitivity analysis on weld residual stress distributions is also included in the benchmarking study. These analyses are carried out by U.S.NRC and JAEA independently using their own codes. At current stage, the deterministic analyses by both xLPR and PASCAL-SP codes have been finished and probabilistic analyses are underway. This paper presents the details of conditions and comparisons of the results between the two codes in the deterministic analyses. In the deterministic analyses, both codes provided almost the same results including the values of stress intensity factor. In addition, probabilistic analysis conditions and results obtained from PASCAL-SP are presented.

Journal Articles

Extension of PASCAL4 code for probabilistic fracture mechanics analysis of reactor pressure vessel in boiling water reactor

Lu, K.; Katsuyama, Jinya; Li, Y.

Proceedings of ASME 2020 Pressure Vessels and Piping Conference (PVP 2020) (Internet), 10 Pages, 2020/08

Journal Articles

Improved Bayesian update method on flaw distributions reflecting non-destructive inspection result

Katsuyama, Jinya; Miyamoto, Yuhei*; Lu, K.; Mano, Akihiro; Li, Y.

Proceedings of ASME 2020 Pressure Vessels and Piping Conference (PVP 2020) (Internet), 8 Pages, 2020/08

We have developed a probabilistic fracture mechanics (PFM) analysis code PASCAL4 for evaluating failure frequency of reactor pressure vessels (RPVs). It is known that flaw distributions have an important role in failure frequency calculation in PFM analysis. Previously, we proposed likelihood function to obtain more realistic flaw distributions applicable for both case when flaws are detected and when there is no flaw indication as the inspection results based on Bayesian update methodology. Here, it can be applied to independently obtain posterior distributions of flaw depth and density. In this study, we improve the likelihood function to enable them to update flaw depth and density simultaneously. Based on the improved likelihood function, an example is presented in which flaw distributions are estimated by reflecting NDI results through Bayesian update and PFM analysis. The results indicate that the improved likelihood functions are useful for estimating flaw distributions.

Journal Articles

Bayesian uncertainty evaluation of Charpy ductile-to-brittle transition temperature for reactor pressure vessel steels

Takamizawa, Hisashi; Nishiyama, Yutaka; Hirano, Takashi*

Proceedings of ASME 2020 Pressure Vessels and Piping Conference (PVP 2020) (Internet), 7 Pages, 2020/08

no abstracts in English

Journal Articles

Allowable external flaws and acceptance standards for high toughness ductile pipes subjected to bending moment and internal pressure

Hasegawa, Kunio; Li, Y.; Lacroix, V.*; Mares, V.*

Proceedings of ASME 2020 Pressure Vessels and Piping Conference (PVP 2020) (Internet), 6 Pages, 2020/08

Authors have developed more precise equations using the Limit Load Criteria, which is called Modified Limit Load Criteria, hereafter. As the results of the Modified Limit Load Criteria, failure stresses for external flawed pipes are always smaller than the failure stresses obtained by the Limit Load Criteria provided by the ASME Code Section XI. It seems that the allowable flaw sizes of the Acceptance Standards provided by the ASME Code Section XI are less conservative for external flaws. The objective of this paper is to demonstrate difference of failure stresses by the Limit Load Criteria and Modified Limit Load Criteria for external flawed pipes. In addition, the allowable flaws of the Acceptance Standards are examined by large and small diameter pipes with external flaws using the Modified Limit Load Criteria.

Journal Articles

Development of the buckling evaluation method for large scale vessel by the testing of Gr.91 vessel subjected to vertical and horizontal loading

Okafuji, Takashi*; Miura, Kazuhiro*; Sago, Hiromi*; Murakami, Hisatomo*; Ando, Masanori; Miyazaki, Masashi

Proceedings of ASME 2020 Pressure Vessels and Piping Conference (PVP 2020) (Internet), 9 Pages, 2020/08

Buckling evaluation methods capable of evaluating elasto-plastic buckling under axial compression, bending, and shear loads are required for cylindrical vessels of fast reactors to cope with thinning due to increasing diameter and application to the seismic isolation design against huge seismic ground motion. In this study, in order to confirm the applicability of the proposal evaluation method, several buckling tests and FE analyses were carried out using the specimens made of Modified 9Cr-1Mo steel. The buckling modes and strength data in the load region where the interaction of axial compression, bending and shear buckling could occur were examined. As a result, it was confirmed that the proposal evaluation method estimated the buckling load in the tests conservatively. In addition, buckling strength evaluated by elasto-plastic buckling analysis had good accuracy compared to each test result by considering the stress-strain relationship and imperfection of test specimen.

Journal Articles

Proposal of simulation materials test technique and their constitutive equations for structural tests and analyses simulating severe accident conditions

Hashidate, Ryuta; Kato, Shoichi; Onizawa, Takashi; Wakai, Takashi; Kasahara, Naoto*

Proceedings of ASME 2020 Pressure Vessels and Piping Conference (PVP 2020) (Internet), 9 Pages, 2020/08

Although it is very essential to clarify how the structure collapses under the severe accident conditions, the failure mechanisms in excessive high temperatures are not clarified. However, it is very difficult and expensive to perform structural tests using actual structural materials. Therefore, we propose to use lead alloys instead of actual structural materials. For demonstration of analogy between the failure mechanisms of lead alloys structure at low temperature and those of the actual structures at high temperature, numerical analyses are required. Although the authors proposed inelastic constitutive equations for numerical analyses in 2019, the equations could not successfully express because of large variations observed in the material tests of the lead alloy. In this study, we propose the improved inelastic constitutive equations of the lead alloy on the basis of the material test results used by aged alloy which can stabilized the material characteristic.

Journal Articles

Assessment of flaw interaction under combined tensile and bending stresses; Suitability of ASME code case N877-1

Dulieu, P.*; Lacroix, V.*; Hasegawa, Kunio

Proceedings of ASME 2020 Pressure Vessels and Piping Conference (PVP 2020) (Internet), 7 Pages, 2020/08

When detected flaws are in close proximity, proximity rules given in the Fitness-foe Service codes require to combine the interacting flaws into a single flaw. ASME Code Case N877-1 provides alternative proximity rules for multiple radial oriented planar flaws. The calculations of flaw interaction have been performed under pure membrane stress. However, actual loading conditions induce non-uniform stresses in the component thickness direction. The objective of this paper is assess the suitability of ASME Code Case N877-1 with regards to the presence of a bending part in the applied stress distribution. For that purpose, various applied stress profiles and flaw configurations are covered. The effect on flaw interaction is assessed trough three-dimensional XFEM analyses.

Journal Articles

Treatment of the interaction with the free surface of the component for combined subsurface flaws; Technical basis for revision of IWA-3300 and Table IWB/IWC-3510-1

Lacroix, V.*; Dulieu, P.*; Hasegawa, Kunio; Mares, V.*

Proceedings of ASME 2020 Pressure Vessels and Piping Conference (PVP 2020) (Internet), 8 Pages, 2020/08

When flaws are detected in pressure retaining components, a flaw characterization has to be carried out in order to determine unequivocally the flaw geometry. This flaw characterization is done according to rules provided in the FFS codes. The first step of the flaw characterization addresses the interaction of the flaw and the free surface. The second step of the flaw characterization addresses the interaction of the flaw with the adjacent flaws. In the ASME Code Sec. XI, there is a lack on how to treat the interaction of a combined flaw and the free surface of the component. The ASME Code Sec. XI flaw characterization is not clear. Some typical examples of unrealistic flaw assessment rules are depicted in this paper. The paper is used as technical basis for improvement of the ASME Code in order to clarify the treatment of combined flaw in the flaw characterization (IWA-3300, IWB/IWC-3510-1)

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