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Research Papers: Materials and Fabrication

Simulation of Stress Corrosion Cracking in In-Core Monitor Housing of Nuclear Power Plant

[+] Author and Article Information
Yuichi Shintaku

Tokyo University of Science,
2641 Yamazaki, Noda,
Chiba 278-8510, Japan
e-mail: shin@me.noda.tus.ac.jp

Fuminori Iwamatsu

Hitachi Research Laboratory,
Hitachi, Ltd.,
11 Saiwai-cho 3-chome, Hitachi,
Ibaraki 317-8511Japan
e-mail: fuminori.iwamatsu.vt@hitachi.com

Kazuhiro Suga

Tokyo University of Science,
2641 Yamazaki, Noda,
Chiba 278-8510, Japan
e-mail: ksuga@rs.noda.tus.ac.jp

Yoshitaka Wada

Kinki University,
341, Kowakae,
Higashiosaka 577-8502, Japan
e-mail: wada@mech.kindai.ac.jp

Masanori Kikuchi

Tokyo University of Science,
2641 Yamazaki, Noda,
Chiba 278-8510, Japan
e-mail: kik@me.noda.tus.ac.jp

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received March 22, 2013; final manuscript received October 1, 2014; published online February 20, 2015. Assoc. Editor: Xian-Kui Zhu.

J. Pressure Vessel Technol 137(4), 041401 (Aug 01, 2015) (13 pages) Paper No: PVT-13-1054; doi: 10.1115/1.4028735 History: Received March 22, 2013; Revised October 01, 2014; Online February 20, 2015

In the in-core monitor (ICM) housing of a reactor pressure vessel (RPV), residual stress has been widely reported to cause stress corrosion cracking (SCC) damage in the weld heat-affected zone. For this reason, it is important to evaluate the crack growth conservatively, and with high confidence to demonstrate fitness for service. This paper presents crack growth simulations in an ICM housing, which is welded at two different angles to the RPV. One weld angle is at the bottom of the RPV, and the welding area of the ICM housing is axisymmetric. The other angle is at the curved position of the RPV, and the weld area of the ICM housing is asymmetric. In these weld areas, crack growth behavior is estimated by superposed-finite element method (S-FEM), which allows generation of a global finite model and a detailed local mesh representing the crack independently. In the axisymmetric weld area, axial, slant and circumferential surface cracks are assumed at two locations where the residual stress fields are different from each other: one is isotropic and the other is circumferential. It is shown that crack growth behaviors are different under different residual stress fields. The results of S-FEM are compared with those of the influence function method (IFM), which assumes that an elliptical crack shape exists in a plate. It is shown that the IFM result is conservative compared to that of S-FEM. Next, an axial surface crack is assumed at the uphill, downhill, and midhill asymmetric weld areas. The midhill crack growth behavior is different from the uphill and downhill behaviors. Finally, two surface cracks are simulated in the asymmetric weld area and two initial crack arrangements are assumed. These results show the differences of the crack interaction and the crack growth process.

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Figures

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Fig. 2

Crack growth direction

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Fig. 3

Geometry of Pressure Vessel Reactor Lower Head

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Fig. 4

Geometry of ICM housing (a) axisymmetric weld area (b) antisymmetric weld area

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Fig. 5

Global mesh representing ICM housing (a) axisymmetric weld area (b) antisymmetric weld area

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Fig. 6

Initial crack shape

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Fig. 7

Definition of crack shape (a) definition of crack length and depth (b) definition for eccentric angle

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Fig. 8

Initial crack in symmetric weld area of ICM housing and distribution of residual stress (a) hoop stress σθ (b) axial stress σz

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Fig. 9

Initial crack shape (a) axial crack (b) slant crack (c) circumferential crack

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Fig. 10

Stress intensity factor KI of axial crack in symmetric weld area (ψ = 0 deg, z = 15 mm) (a) a/t = 0.2 (b) a/t = 0.6

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Fig. 11

Axial crack growing process in symmetric weld area (ψ = 0 deg, z = 15 mm) and distribution of hoop stress

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Fig. 12

Stress intensity factor KI of slant crack in symmetric weld area (z = 15 mm)

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Fig. 13

Normalized stress intensity factor KII/KI of slant crack in symmetric weld area (ψ = 45 deg, z = 15 mm)

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Fig. 14

Normalized stress intensity factor KIII/KI of slant crack in symmetric weld area (ψ = 45 deg, z = 15 mm)

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Fig. 15

Slant crack growing process in symmetric weld area (ψ = 45 deg, z = 15 mm) (a) a/t = 0.2 (b) a/t = 0.3 (c) a/t = 0.6

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Fig. 16

Stress intensity factor KI of slant crack in symmetric weld area (ψ = 45 deg, z = 25 mm)

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Fig. 17

Slant crack growing process in symmetric weld area (ψ = 45 deg, z = 25 mm) (a) a/t = 0.2 (b) a/t = 0.4 (c) a/t = 0.6

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Fig. 18

Circumferential crack growing process in symmetric weld area (ψ = 90 deg, z = 25 mm) (a) a/t = 0.2 (b) a/t = 0.4 (c) a/t = 0.6

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Fig. 19

Relationship between crack speed and initial crack angle (a) comparison of crack depth (b) comparison of crack length

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Fig. 21

Comparison of S-FEM and IFM due to difference in crack growth behavior and geometry of ICM housing (a) comparison of crack depth (b) comparison of crack length

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Fig. 22

Initial crack in antisymmetric weld area of ICM housing and distribution of residual stress

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Fig. 23

Stress intensity factor KI in uphill of antisymmetric weld area

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Fig. 24

Crack growing process in uphill of antisymmetric weld area (a) a /t = 0.2 (b) a/t = 0.6

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Fig. 25

Slant crack growing process in middle hill of antisymmetric weld area (a) a /t = 0.2 (b) a/t = 0.6

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Fig. 26

Initial crack arrangement in symmetric weld area (a) parallel arrangement to weld line (b) vertical arrangement to weld line

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Fig. 27

Crack growing process of two vertical cracks to weld line (a) 0.0 [year] (b) 3.3 [year] (c) 6.8 [year]

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Fig. 28

Stress intensity factor KI of two vertical cracks to weld line (a) 0.0 [year] (b) 3.3 [year] (c) 6.8 [year]

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Fig. 29

Crack growing process of two parallel cracks to weld line (a) 0.0 [year] (b) 6.6 [year] (c) 19.8 [year]

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Fig. 30

Stress intensity factor KI of two parallel cracks to weld line (a) 0.0 [year] (b) 6.6 [year] (c) 19.8 [year]

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Fig. 31

Relationship between crack speed and difference of the initial arrangement of two cracks

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