ML15160A153

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NYS000486 - Stevens, Gary L., Presentation to ACRS on Technical Brief on Regulatory Guidance for Evaluating the Effects of Light Water Reactor Coolant Environments in Fatigue Analyses of Metal Components (December 2, 2014) (ML14351A368)
ML15160A153
Person / Time
Site: Indian Point  Entergy icon.png
Issue date: 12/02/2014
From:
State of NY, Office of the Attorney General
To:
Atomic Safety and Licensing Board Panel
SECY RAS
References
RAS 27898, ASLBP 07-858-03-LR-BD01, 50-247-LR, 50-286-LR
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NYS000486 Submitted: June 9, 2015 Advisory Committee on Reactor Safeguards Metallurgy and Reactor Fuels Subcommittee Meeting Technical Brief on Regulatory Guidance for Evaluating the Effects of Light Water Reactor Coolant Environments in Fatigue Analyses of Metal Components (Proposed Revision 1 to Regulatory Guide 1.207)

Gary L. Stevens, Sr. Materials Engineer Office of Nuclear Regulatory Research Component Integrity Branch Tuesday, December 2, 2014 NRC Headquarters Rockville, MD

Objective

  • At ACRSs request, the staff is providing this brief
  • NRC is revising the guidance for environmentally assisted fatigue (EAF)

- Regulatory Guide (RG)

  • Draft Regulatory Guide DG-1309, Guidelines for Evaluating the Effects of Light Water Reactor Coolant Environments in Fatigue Analyses of Metal Components

- Supporting technical basis NUREG

  • Draft NUREG/CR-6909, Revision 1 (ANL-12/60), Effect of LWR Coolant Environments on the Fatigue Life of Reactor Materials
  • Both draft documents were released for public comment

- The draft RG was published for 60-day public comment on 11/24/2014

- The draft NUREG was published for public comment during the time period of 4/17/2014 - 6/2/2014 2

Outline

  • Background

- What is cumulative usage factor (CUF)?

- What is EAF?

- Why is there NRC guidance on EAF?

- What is the NRC guidance on EAF?

- What is Reg. Guide 1.207 and NUREG/CR-6909?

- What is Fen?

  • Revisions to Fen Equations

- Review of updated fatigue data

- Review of air fatigue curves

- Review of changes to Fen expressions

  • Estimated Schedule for RG and NUREG Publication 3

BACKGROUND What is cumulative usage factor (CUF)?

What is EAF?

Why is there NRC guidance on EAF?

What is the NRC guidance on EAF?

What is Reg. Guide 1.207 and NUREG/CR-6909?

What is Fen? 4

What is cumulative usage factor (CUF)?

  • For nuclear plant design, cumulative fatigue damage due to applied cyclic loading is estimated using cumulative usage factor (CUF):

= = U1 + U2 + U3 + + UZ < 1.0

  • N is a function of the alternating stress, Sa, applied to a component, and is material dependent (i.e., it is a material property)
  • S-N curves (fatigue curves) are given in ASME Code,Section III, Mandatory Appendix I for different materials
  • Design fatigue curves are based on best fits of air test data with design factors applied S-N curves are usually defined in log-log form 5

What is EAF?

  • The fatigue curves in Section III of the ASME Code were developed from laboratory test data from small-scale, polished specimens tested in AIR
  • The AIR test data were used to develop design fatigue curves suitable for design:

o Develop best fit log-log curves for the AIR data for each material type o Adjust the best fit curves to account for worst-case mean stress effects using the Modified Goodman relationship o Apply factors* of 2 on strain amplitude (a) or 20 on cycles (N), whichever is more conservative, to develop AIR design curves for each material

  • More recent laboratory testing of specimens tested in WATER indicated that the AIR design curves may not adequately define fatigue life for materials exposed to WATER environments:

Note how some of the points for tests in WATER fall below the AIR design curve.

  • Factors to account for data scatter, size effects (i.e., small laboratory specimens vs. large 6 power plant components), surface finish, atmosphere, etc.

Why is there NRC guidance on EAF? (1/4)

Related Regulatory Requirements

  • Title 10 of the Code of Federal Regulations (10 CFR) Part 50, Domestic Licensing of Production and Utilization Facilities, Appendix A, General Design Criteria for Nuclear Power Plants

- General Design Criterion 1 Safety related SSCs must be designed, fabricated, erected, and tested to quality standards commensurate with the importance of the safety function performed

- General Design Criterion 30 Components included in the reactor pressure boundary must be designed, fabricated, erected, and tested to the highest practical quality standards

- 10 CFR 50.55a (c), endorses ASME Code for design of safety-related systems and components (Class 1)

Why is there NRC guidance on EAF? (2/4)

  • ASME Section III fatigue design curves developed in the late 1960s and early 1970s

- Air environments at ambient temperatures

- Margin of 2 on strain and a margin of 20 on cyclic life

- ASME Section III, NB-3121 identifies that the data used to develop the fatigue design curves did not include tests in environments that might accelerate fatigue failure

  • In the 1980s, the NRC initiated the Fatigue Action Plan (FAP) in response to findings primarily from early Plant Life Extension Studies
  • Research in Japan (Higuchi and Iida, 1991) and those at ANL (NUREG/CR-4667, 1990) identified potentially significant effects of light water reactor (LWR) coolant environment on fatigue lives of steels 8

Why is there NRC guidance on EAF? (3/4)

  • In 1995, closeout of the FAP* and resolution of Generic Safety Issue (GSI) 166, Adequacy of Fatigue Life of Metal Components, established that**:

- Risk to core damage from fatigue failure of RCS very small; no action required for current plant design life of 40 years

- NRC staff concluded that fatigue issues should be evaluated for extended period of operation for license renewal (under GSI 190)

  • In 1999, resolution of GSI 190, Fatigue Evaluation of Metal Components for 60-Year Plant Life ***

- 10 CFR 54.21, Aging Management Programs for license renewal should address component fatigue including addressing the effects of the LWR coolant environment

    • NUREG/CR-6674 (PNNL-13227), Fatigue Analysis of Components for 60-Year Plant Life, June 2000.
      • Thadani, Ashok C., Director of the Office of Nuclear Regulatory Research, U.S. Nuclear Regulatory Commission, memorandum to William D. Travers, Executive Director for Operations, U.S. Nuclear Regulatory Commission, Closeout of Generic Safety Issue 190, Fatigue Evaluation of Metal Components for 60 Year Plant Life, August 26, 9 1999, ADAMS Accession No. ML003673136

Why is there NRC guidance on EAF? (4/4)

  • On December 1, 1999, by letter to the Chairman of the ASME Board on Nuclear Codes and Standards (BNCS), the NRC requested that ASME revise the Code to include environmental effects in the fatigue design of components
  • ASME initiated the Pressure Vessel Research Council (PVRC)

Steering Committee on Cyclic Life and Environmental Effects

  • PVRC recommended revising the Code design fatigue curves (Welding Research Council (WRC) Bulletin 487)
  • ASME Code has struggled with this issue for more than 20 years; still no acceptable rules to address EAF in Section III

- Two Section III Code Cases have been published (N-761 and N-792),

but these have not been endorsed by NRC

  • Based on NRCs FAP efforts, guidance was developed for operating plants* to address EAF (1999) and new reactors to address EAF (2007) 10
  • License renewal applicants only (i.e., only applicable for operation beyond the 40-year design life of operating plants).

What is the NRC guidance on EAF? (1/3)

  • In the late 1990s, NRC published the results of their research efforts related to the impact of LWR coolant environments on the fatigue lives of steels:

- Chopra, O. K., and W. J. Shack, Effects of LWR Coolant Environments on Fatigue Design Curves of Carbon and Low-Alloy Steels, NUREG/CR-6583, ANL-97/18, 1998.

- Chopra, O. K., Effects of LWR Coolant Environments on Fatigue Design Curves of Austenitic Stainless Steels, NUREG/CR-5704, ANL-98/31, 1999.

  • Based on the direction of the FAP closeout, these NUREGs were adopted for use in guidance for license renewal applicants in the initial release of NUREG-1801, Generic Aging Lessons Learned (GALL) Report (2001)

- Chapter X.M1, Metal Fatigue of Reactor Coolant Pressure Boundary

What is the NRC guidance on EAF? (2/3)

GUIDANCE FOR NEW REACTORS

  • EAF guidance for new reactor design was issued in 2007:

- RG 1.207, Guidelines for Evaluating Fatigue Analyses Incorporating the Life Reduction of Metal Components Due to the Effects of the Light Water Reactor Environment for New Reactors March 2007.

  • The technical basis document for RG 1.207 is NUREG/CR-6909:

- NUREG/CR-6909, ANL-06/08, Chopra, O. K., and W. J. Shack, Effect of LWR Coolant Environments on the Fatigue Life of Reactor Materials - Final Report, February 2007.

12

What is the NRC guidance on EAF? (3/3)

GUIDANCE FOR OPERATING REACTORS

  • Currently, operating reactors that are not in the license renewal period have no guidance or requirements for considering EAF

- For carbon steel: May use either NUREG/CR-6583 OR NUREG/CR-6909 OR an NRC-approved alternative

- For stainless steel: May use either NUREG/CR-5704 OR NUREG/CR-6909 OR an NRC-approved alternative

- For Ni-Cr-Fe alloys: May use NUREG/CR-6909 OR an NRC-approved alternative.

13

What is Reg. Guide 1.207 and NUREG/CR-6909?

  • Defines fatigue multiplier, Fen, methodology
  • EAF guidance for new reactors
  • These documents provide the best vehicle for the NRC to consolidate and update EAF guidance 14

What is Fen? (1/2)

  • Initially, the NRC reviewed two methods for incorporating EAF effects; the second method was adopted:

- 1. Develop new environmental fatigue curves

- 2. Use of an environmental correction factor, Fen

  • Fen is defined as the ratio of fatigue life in air at room temperature to the fatigue life in water at the service temperature:

Fen = Nair/Nwater Fen is multiplicative to the calculated CUF in air:

CUFen = U1 Fen,1 + U2 Fen,2 ..... UZ Fen,Z 15

What is Fen? (2/2)

  • How is Fen computed?
  • For example, from Revision 0 of NUREG/CR-6909 for stainless steel materials:

Fen = exp [0.734 - T O R]

where:

T = transformed temperature:

T = 0 for temperature, T 150oC T = (T - 150)/175 for 150 < T < 325oC T = 1 for T 325oC O = transformed oxygen:

O = 0.281 for all fluid dissolved oxygen levels R = transformed strain rate:

R = 0 for strain rate, R 0.4%/s R = ln(R/0.4) for 0.001 R < 0.4%/s R = ln(0.001) for R < 0.001%/s 16

REASONS FOR REVISING REG. GUIDE 1.207 17

Reasons for Revising Reg. Guide 1.207

  • There are three reasons the NRC is revising the EAF guidance in RG 1.207:
1. To consolidate all EAF guidance
2. To update the guidance based on stakeholder feedback
3. To update the guidance based on all available research data
  • In 2010, the Office of New Reactors (NRO) and the Office of Nuclear Reactor Regulation (NRR) prepared a joint User Need Request (UNR)

- Requested the Office of Nuclear Regulatory Research (RES) to perform research activities to update EAF guidance and revise RG 1.207 and NUREG/CR-6909

- NRC also implemented an addendum to the NRC/EPRI Memorandum of Understanding (MOU) that authorized EPRI participation and co-funding of the NRCs EAF research activities 18

SUMMARY

OF REVISIONS TO REG. GUIDE 1.207 19

Summary of Revisions to Reg. Guide 1.207

  • The following revisions were made to RG 1.207:
1. The title was revised to remove New Reactors (i.e., the RG was made applicable to all LWRs)
2. The guidance was clarified to apply to all metal components exposed to LWR environments that have a CUF calculation required by a plants current licensing basis (CLB)
3. The background section was revised to incorporate the relevant content for operating reactors, license renewal, etc.
4. The Fen equations were revised based on stakeholder feedback and the updated research documented in NUREG/CR-6909, Rev. 1 20

REVISIONS TO FEN EQUATIONS Review of updated fatigue data Review of air fatigue curves Review of changes to Fen expressions Validation calculations Sample problem 21

Review of Updated Fatigue Data (1/3)

  • Initially, RES planned to gather and incorporate all publically available fatigue data published since the initial release of RG 1.207 (2007)
  • At the start of NRC research efforts, negotiations were undertaken with the Japan Nuclear Energy Safety Organization (JNES), now the Japan Nuclear Regulatory Authority (JNRA), to formally obtain all EAF data from Japanese research programs

- Pursued under the NRC/JNES Cooperative Materials Research Agreement

- Led to formal release of Japanese EAF data to NRC in October 2011*

  • RES gratefully acknowledges the release of the Japanese EAF research data, as documented in Report No.

JNES-SS-1005, Environmental Fatigue Evaluation Method for Nuclear Power Plants, Nuclear Energy System 22 Safety Division, Japan Nuclear Energy Safety Organization, March 2011, ADAMS Accession No. ML113010189.

Review of Updated Fatigue Data (2/3)

Summary of air fatigue data in Rev. 0/Rev. 1 of NUREG/CR-6909:

Material Data Available for Rev. 0 Data Available for Rev. 1 Increase*

Carbon Steels 153 points 254 points 66 %

(8 heats) (19 heats)

[Figure 7(a) of Rev. 0] [Figure 32(b) of Rev. 1]

Low-Alloy Steels 358 points 430 points 20 %

(19 heats) (22 heats)

[Figure 7(b) of Rev. 0] [Figure 32(d) of Rev. 1]

Austenitic Stainless 357 points 622 points 74 %

Steels (38 heats) (40 heats)

[Figure 35 of Rev. 0] [Figure 45(b) of Rev. 1]

Ni-Cr-Fe Alloys Not quantified 559 points N/A (45 heats)

[Figures 56 & 57 of Rev. 0] [Section 3.3 of Rev. 1]

23

  • The majority of the increase in data is attributed to the additional data reported in Report No. JNES-SS-1005.

Review of Updated Fatigue Data (3/3)

Summary of water fatigue data in Rev. 0/Rev. 1 of NUREG/CR-6909:

Material Data Available for Rev. 0 Data Available for Rev. 1 Increase*

Carbon Steels 318 points 638 points 100 %

(12 heats) (21 heats)

[Figure 27 of Rev. 0] [Figure 79 of Rev. 1]

Low-Alloy Steels 327 points 536 points 64 %

(13 heats) (20 heats)

[Figure 27 of Rev. 0] [Figure 79 of Rev. 1]

Austenitic Stainless 276 points 683 points 147 %

Steels (14 heats) (32 heats)

[Figure 52 of Rev. 0] [Figure 110 of Rev. 1]

Ni-Cr-Fe Alloys Not quantified 162 points N/A (13 heats)

[Figures 58 & 59 of Rev. 0] [Section 4.3 of Rev. 1]

24

  • The majority of the increase in data is attributed to the additional data reported in Report No. JNES-SS-1005.

Review of Air Fatigue Curves (1/12)

Best Fit AIR Curves for Carbon Steel From NUREG/CR-6909, Rev. 0: From NUREG/CR-6909, Rev. 1:

NOTE: The ANL best-fit air curves are identical in both of the above figures.

25

Review of Air Fatigue Curves (2/12)

Best Fit AIR Curves for Low Alloy Steel From NUREG/CR-6909, Rev. 0: From NUREG/CR-6909, Rev. 1:

NOTE: The ANL best-fit air curves are identical in both of the above figures.

26

Review of Air Fatigue Curves (3/12)

Distribution of Constant A for AIR Curves for Carbon Steel From NUREG/CR-6909, Rev. 0 From NUREG/CR-6909, Rev. 1 Curve fits are made using a Langer fit of the form:

ln(N) = A - B ln(a - C) where: A, B, C are constants a is the strain amplitude 27 N is the fatigue life (cycles)

Review of Air Fatigue Curves (4/12)

Distribution of Constant A for AIR Curves for Low Alloy Steel From NUREG/CR-6909, Rev. 0 From NUREG/CR-6909, Rev. 1 Curve fits are made using a Langer fit of the form:

ln(N) = A - B ln(a - C) where: A, B, C are constants a is the strain amplitude 28 N is the fatigue life (cycles)

Review of Air Fatigue Curves (5/12)

Design AIR Curve for Carbon Steel

  • Consistent with the ASME Code Section III Design Curve, adjustment factors must be applied to best-fit air curves to accommodate various material, loading, and environmental parameters
  • ASMEs factor of 2 on strain amplitude was maintained
  • To determine the most appropriate value for the adjustment factor on fatigue life, 25,000 Monte Carlo simulations were performed using the following factors:
  • Lognormal distributions were used, and the 5th and 95th percentile values were assumed as the minimum and maximum values for each factor
  • The 95th percentile value for the adjustment factor was calculated as 10.2 29

Review of Air Fatigue Curves (6/12)

Design AIR Curve for Carbon Steel

  • Although a factor of ~10 was supported by the Monte Carlo evaluation, adjustment factors of 2 and 12 were used to provide consistency with Rev. 0 work
  • NRC requested feedback on maintaining a factor of 12 vs.

changing to a factor of 10 when the draft of NUREG/CR-6909, Rev. 1 was released for public comment last spring NOTE: Existing ASME Code Section III design air curve is conservative compared to 30 NUREG/CR-6909, Rev. 1 (because of factor of 20 vs. 12)

Review of Air Fatigue Curves (7/12)

Design AIR Curve for Low Alloy Steel

  • A factor of 9.0 was obtained from the Monte Carlo simulations; again, adjustment factors of 2 and 12 were used to provide consistency with Rev. 0 work
  • NRC requested feedback on maintaining a factor of 12 vs.

changing to a factor of 10 when the draft of NUREG/CR-6909, Rev. 1 was released for public comment last spring NOTE: The existing ASME Code Section III design air curve is conservative compared to NUREG/CR-6909, Rev. 1 (because of factor of 20 vs. 12 and the combining of the 31 carbon steel and low alloy steel curves into one curve in Section III)

Review of Air Fatigue Curves (8/12)

Best Fit AIR Curves for Austenitic Stainless Steel From NUREG/CR-6909, Rev. 0: From NUREG/CR-6909, Rev. 1:

NOTE: Only Type 304 materials are shown; the ANL best-fit air curves are identical in both of the above figures.

32

Review of Air Fatigue Curves (9/12)

Distribution of Constant A for AIR Curves for Austenitic Stainless Steel From NUREG/CR-6909, Rev. 0 From NUREG/CR-6909, Rev. 1 Curve fits are made using a Langer fit of the form:

ln(N) = A - B ln(a - C) where: A, B, C are constants a is the strain amplitude 33 N is the fatigue life (cycles)

Review of Air Fatigue Curves (10/12)

Design AIR Curve for Austenitic Stainless Steel

  • A factor of 9.6 was obtained from the Monte Carlo simulations; again, adjustment factors of 2 and 12 were used to provide consistency with Rev. 0 work
  • Therefore, there is no change in the austenitic stainless steel design air curve between NUREG/CR-6909, Rev. 0 and NUREG/CR-6909, Rev. 1
  • NRC requested feedback on maintaining a factor of 12 vs.

changing to a factor of 10 when the draft of NUREG/CR-6909, Rev. 1 was released for public comment last spring NOTE: The existing ASME Code Section III design air curve is identical to the ANL design air curve shown. 34

Review of Air Fatigue Curves (11/12)

Best Fit AIR Curves for Ni-Cr-Fe Steel From NUREG/CR-6909, Rev. 0: From NUREG/CR-6909, Rev. 1:

NOTE: Only Ni-Cr-Fe weld metals are shown; the ANL best-fit air curves are identical in both of the above figures. 35

Review of Air Fatigue Curves (12/12)

Design AIR Curve for Ni-Cr-Fe Steel

  • Estimates of the cumulative distribution of Constant A in the fatigue -N curve for the various heats of Ni-Cr-Fe steels and their associated weld metals yielded a median value of 7.129
  • This value is slightly greater than the value of Constant A derived for austenitic SSs (6.891)
  • In other words, the fatigue lives of these Ni-Cr-Fe steels are approximately 25% greater than those for austenitic stainless steels
  • Based on these findings, the design air curve for austenitic stainless steel is used for Ni-Cr-Fe steel NOTE: The existing ASME Code Section III design air curve for stainless steel is also used for Ni-Cr-Fe steel. 36

Review of Changes to Fen Equations (1/10)

Fen equations for Carbon Steel From NUREG/CR-6909, Rev. 0 From NUREG/CR-6909, Rev. 1 Fen = exp[0.632 - 0.101 S*T*O*R*] Fen = exp[(0.003 - 0.031R*) S*T*O*]

where: where:

Transformed sulfur, S*: Transformed sulfur, S*:

S* = 0.001 (S 0.001 wt.%) S* = 2.0 + 98 S (S 0.015 wt.%)

S* = S (S 0.015 wt.%) S* = 3.47 (S > 0.015 wt.%)

S* = 0.015 (S > 0.015 wt.%)

Transformed temperature, T*: Transformed temperature, T*:

T* = 0 (T < 150°C) T* = 0.395 (T < 150°C)

T* = (T - 150) (150 < T 350°C) T* = (T - 75)/190 (150 < T 325°C)

Transformed dissolved oxygen, O*: Transformed dissolved oxygen, O*:

O* = 0 (DO 0.04 ppm) O* = 1.49 (DO < 0.04 ppm)

O* = ln(DO/0.04) (0.04 < DO 0.5 ppm) O* = ln(DO/0.009) (0.04 DO 0.5 ppm)

O* = ln(12.5) (DO > 0.5 ppm) O* = 4.02 (DO > 0.5 ppm)

Transformed strain rate, R*: Transformed strain rate, R*:

R* = 0 (R > 1%/s) R* = 0 (R > 2.2%/s)

R* = ln(R) (0.001 R 1%/s) R* = ln(R/2.2) (0.0004 R 2.2%/s)

R* = ln(0.001) (R < 0.001%/s) R* = ln(0.0004/2.2) (R < 0.0004%/s) 37 NOTE: For Rev. 0, Fen > 1.0 even when environmental effects do not apply.

Review of Changes to Fen Equations (2/10)

Fen equations for Low Alloy Steel From NUREG/CR-6909, Rev. 0 From NUREG/CR-6909, Rev. 1 Fen = same expression as for carbon steel Fen = exp[ - 0.101 S*T*O*R*]

where:

S*, T*, O*, R* are defined the same as for carbon steel NOTE: For Rev. 0, Fen > 1.0 even when environmental effects do not apply. 38

Review of Changes to Fen Equations (3/10)

Fen plots for Carbon and Low Alloy Steels Fen vs. strain rate, R: Fen vs. temperature, T:

30 60 Carbon & Low-Alloy Steels Carbon & Low-Alloy Steels S: 0.015 wt.%, Temp: 250 C S: 0.015 wt.%, Strain rate: 0.001%/s Env. Fatigue Correction Factor Fen Env. Fatigue Correction Factor Fen 25 Solid line: New expression 50 Solid line: New expression Dashed line: RG 1.207 (LAS) Dashed line: RG 1.207 (LAS)

Chain-dash line: JNES Chain-dash line: JNES 20 40 0.5 ppm DO 0.5 ppm DO 15 30 0.2 ppm DO 0.2 ppm DO 10 20 0.04 ppm DO 0.04 ppm DO 5 10 0 0 10-4 10-3 10-2 10-1 100 101 100 150 200 250 300 350 Strain Rate (%/s) Temperature ( C) 39

Review of Changes to Fen Equations (4/10)

Life predictions for Carbon and Low Alloy Steels The NRC and JNES predictions are in good agreement:

40

Review of Changes to Fen Equations (5/10)

Fen equations for Austenitic Stainless Steel From NUREG/CR-6909, Rev. 0 From NUREG/CR-6909, Rev. 1 Fen = exp[0.734 - T*O*R*] Fen = exp[-T*O*R*]

where: where:

Transformed temperature, T*: Transformed temperature, T*:

T* = 0 (T < 150°C) T* = 0 (T < 100°C)

T* = (T - 150)/175 (150 < T 325°C) T* = (T - 100)/250 (100 < T 325°C)

T* = 1 (T > 325°C)

Transformed dissolved oxygen, O*: Transformed dissolved oxygen, O*:

O* = 0.281 all DO levels O* = 1.49 (DO < 0.04 ppm)

O* = ln(DO/0.009) (0.04 DO 0.5 ppm)

O* = 4.02 (DO > 0.5 ppm)

Transformed strain rate, R*: Transformed strain rate, R*:

R* = 0 (R > 0.4%/s) R* = 0 (R > 10%/s)

R* = ln(R/0.4) (0.001 R 0.4%/s) R* = ln(R/10) (0.0004 R 10%/s)

R* = ln(0.001) (R < 0.001%/s) R* = ln(0.0004/10) (R < 0.0004%/s)

NOTE: For Rev. 0, Fen > 1.0 even when environmental effects do not apply. 41

Review of Changes to Fen Equations (6/10)

Fen plots for Austenitic Stainless Steel Fen vs. strain rate, R: Fen vs. temperature, T:

20 20 BWR NWC Austenitic Stainless Steels Austenitic Stainless Steels Solid line: New expression Strain rate: 0.0004%/s Env. Fatigue Correction Factor Fen Env. Fatigue Correction Factor Fen Dashed line: RG 1.207 (LAS) Solid line: New expression PWR PWR Chain-dash line: JNES dashed line: RG 1.207 (LAS) 15 15 All wrought & cast SSs BWR NWC in <0.1 ppm DO and Sensitized High-C & cast SS All wrought SS & CASS in >0.1 ppm DO in <0.1 ppm DO and 10 All wrought SSs except 10 Sensitized SS & CASS Sensitized High-C SS in >0.1 ppm DO Not sensitized in >0.1 ppmDO wrought SSs All wrought All wrought &

in >0.1 ppmDO

& cast SSs cast SSs 5 All DO levels 5 All DO levels Temp: 300 C 0 0 10-4 10-3 10-2 10-1 100 101 50 100 150 200 250 300 350 Strain Rate (%/s) Temperature ( C) 42

Review of Changes to Fen Equations (7/10)

Life predictions for Austenitic Stainless Steel The NRC and JNES predictions are in good agreement:

43

Review of Changes to Fen Equations (8/10)

Fen equations for Ni-Cr-Fe Steel From NUREG/CR-6909, Rev. 0 From NUREG/CR-6909, Rev. 1 Fen not specified Fen = exp[-T*O*R*]

It was noted that for Alloys 600 and 690 and where:

their welds, the updated ANL fatigue life Transformed temperature, T*:

model proposed for austenitic stainless steel was either consistent or conservative with T* = 0 (T < 50°C) respect to the fatigue -N data. T* = (T - 50)/250 (50 < T 325°C)

Transformed dissolved oxygen, O*:

Some licensees used a constant Fen of 1.49 O* = 0.06 (BWR NWC, DO 0.1 ppm) based on earlier recommendations made by O* = 0.14 (BWR HWC/PWR, DO < 0.1 ppm)

EPRI*; this value is not supported by the Transformed strain rate, R*:

available test data.

R* = 0 (R > 5.0%/s)

R* = ln(R/5.0) (0.0004 R 5.0%/s)

R* = ln(0.0004/5.0) (R < 0.0004%/s)

  • EPRI TR-105759, An Environmental Factor Approach to Account for Reactor Water Effects in Light Water Reactor Pressure Vessel and Piping Fatigue Evaluations, August 1996. 44

Review of Changes to Fen Equations (9/10)

Fen plots for Ni-Cr-Fe Steel Fen vs. strain rate, R: Fen vs. temperature, T:

45

Review of Changes to Fen Equations (10/10)

Life predictions for Ni-Cr-Fe Steel The NRC and JNES predictions are in good agreement:

106 106 Ni-Alloys and Weld Metals Ni-Alloys and Weld Metals NUREG/CR-6909 Expressions JNES Expressions High-DO Water High-DO Water Total Data: 78 105 105 Predicted Life (Cycles) Predicted Life (Cycles) 104 104 A600 Total Data: 78 A182 A600 103 103 A182 Total Data: 162 R-squared values Life: 0.85 Distance: 0.84 103 104 105 106 103 104 105 106 Experimental Life (Cycles) Experimental Life (Cycles) 46

Validation Calculations (1/2)

Several validation calculations were performed by estimating life using ASME Code methods (i.e., calculate CUF) and comparing the results to the experimental (i.e., measured) fatigue life Since the experimental data sets selected were tested to failure (i.e., CUF = 1.0+),

the goal of these evaluations was to benchmark the Fen methodology and make adjustments, if warranted The results of the following experimental data sets were compared with estimates of fatigue life based on the Fen methodology to validate the revised Fen expressions

1. Tests with changing strain rate within a strain cycle (Higuchi, Iida, and Asada, ASTM STP 1298, 1997; Higuchi, Iida, and Sakaguchi, ASME PVP-419, 2001; Higuchi, Sakaguchi, and Nomura, ASME PVP2007-26101, 2007)
2. Tests with changing strain rate and temperature within a strain cycle (Nomura, Higuchi, Asada, and Sakaguchi, ASME PVP-480, PVP2004-2679, 2004; Sakaguchi, Nomura, Suzuki, and Kanasaki, ASME PVP2006-ICPVT-11-93220, 2006)
3. Tests with spectrum loading (random strain amplitudes, Solin, ASME PVP2006-ICPVT-93833, 2006)
4. Tests with complex loading (actual PWR transient - cold and hot thermal shock, Le Duff, Lefrancois, and Vernot, ASME PVP2009-78129, 2009)
5. EPRI U-bend tests in inert and PWR environment (Hickling, Kilian, Spain, and Carey, ASME PVP2006-ICPVT-11-93318, 2006)
6. Thermal fatigue test of a stepped pipe (Jones, Holliday, Leax, and Gordon, ASME PVP-482, PVP2004-2748, 2004) 47

Validation Calculations (2/2)

Three Fen methods were used

1. Modified rate (strain-integrated) method
2. Simplified (average strain rate)
3. Multi-linear strain-based method The validation calculations for specimens agreed within the data scatter (i.e., factor of 2)

The validation calculations for components had mixed results For the EPRI U-bend tests, 5 out of 7 tests fell within the data scatter; the remaining 2 tests were conservatively predicted For the stepped pipe tests, results were mixed; however, NRC found issues with finite element analysis and did not pursue corrected analysis NRC recognizes that use of small-scale specimen fatigue test data to predict the fatigue lives of actual components may be conservative under certain conditions 48

Sample Problem Appendix C of NUREG/CR-6909, Rev. 1 contains a detailed sample problem

- Same as sample problem developed and solved by industry under EPRI guidance and funding

- Finite element based Intent was to demonstrate one example application of the Fen methodology A common but relatively simple problem Promote consistency in the application of EAF methods Not intended to be an exhaustive treatment for EAF evaluation Feedback from public stakeholders has been very positive 49

ESTIMATED SCHEDULE FOR RG AND NUREG PUBLICATION 50

Estimated Schedule

- All internal reviews completed; comments addressed

- Published for public comment on 11/24/2014 (79 FRN 69884)

- Public comment period closes on 01/23/2015

- All internal review completed; comments addressed

- Published for public comment 4/17/2014 - 6/2/2014

- More than 200 individual public comments were received from 10 commenters (see next slide)

- Responses are under development

  • Best-Estimate Publication Schedule

- Address all public comments on both documents - Summer 2015

- Reviews (including ACRS) - Fall 2015

- Publish final documents - December 2015 51

Public Comments on NUREG/CR-6909, Rev. 1 ADAMS Commenter No. Commenter Affiliation Accession No. Name 1 ML14157A322 Consultant, Japan Makoto Higuchi 2 ML14157A323 Consultant - CF Int. Engineering, France Claude Faidy 3 ML14157A324 AMEC, United Kingdom David Tice 4 ML14157A325 Westinghouse Electric Company, USA James Gresham 5 ML14157A326 Mitsubishi Heavy Industries, Japan Seiji Asada 6 ML14157A327 Rolls Royce PLC, United Kingdom Keith Wright 7 ML14157A328 Electricite de France, France Thomas Metais 8 ML14157A330 Hitachi, Japan Akihiko Hirano 9 ML14157A331 AREVA, Inc., USA Devin Kelley 10 ML14157A332 Kansai Electric Power Company, Republic of Korea June-soo Park 52

Questions or Comments?

53

BACKUP SLIDES 54

Method for Best Fit of Experimental Data Fatigue strain amplitude (a) vs.

life (N25) data are expressed as:

ln(N25) = A - B ln(a - C)

Constants determined from a best-fit of the fatigue a-N data NUREG/CR-6335 (1995) gives rigorous statistical analysis to estimate probability of initiating a fatigue crack Ideally, a best-fit of the experimental data should be determined for:

- low-cycle fatigue by minimizing the error in life

- high-cycle fatigue by minimizing the error in strain NRC used a best-fit of the experimental S-N data determined by minimizing the error in the distance between the data point and the curve However, both of these analyses may be biased depending on the heats of material used in obtaining the fatigue a-N data 55

Possible Mechanisms for Fatigue Crack Initiation Film Rupture/Slip Dissolution:

Incremental strain ruptures the protective surface oxide film Crack extension occurs by dissolution/oxidation of the freshly exposed surface Critical concentration of sulfide / hydrosulfide ions is required at the crack tip Hydrogen-Induced Cracking:

Hydrogen and vacancies produced by corrosion reaction enter the steel Hydrogen diffuses to strong trapping sites (manganese-sulfide inclusions) ahead of the crack tip, which act as initiation sites for local quasi-cleavage cracking as well as void formation Crack advances by linking of these microcracks with the main crack 56

Fatigue Crack Initiation -

Significant Results Fatigue data show very strong strain-rate dependence of life in LWR environments For low-alloy steels, fatigue data suggest that cracking occurs by hydrogen-induced cracking at high strain rates and by film rupture/slip dissolution at slow strain rates

- At high strain rates, surface cracks are inclined to the stress axis and grow in a tortuous manner; fracture surface exhibits the typical fan-like or quasi-cleavage cracking

- At slow strain rates, surface cracks are absolutely straight, perpendicular to stress axis; fracture surface is flat with evidence of crack arrest Fatigue crack initiation and crack growth may be enhanced in LWR environments by a combination of the two mechanisms

- Hydrogen produced by the oxidation reaction diffuses into the steel ahead of the crack tip, thereby changing the stacking fault energy, which results in more localized deformation

- Strain localization leads to increased film rupture frequency, and crack extension occurs by dissolution/oxidation of the freshly exposed surface Dynamic strain aging may play an important role in the cyclic deformation process

- Dynamic strain aging occurs in alloys containing solutes that segregate strongly to dislocations resulting in strong elastic interactions between the solute and dislocation stress-strain field

- Depends on temperature and strain rate 57

Effect of Dynamic Strain Aging In high-temp water, the synergistic interactions between environmentally assisted corrosion and dynamic strain aging in a fatigue environment may be rationalized as follows:

- Hydrogen and vacancies produced by the corrosion reaction at the crack tip enter the steel and hydrogen diffuses to strong trapping sites inside the crack tip maximum hydrostatic stress region (e.g.,

manganese-sulfide inclusion) ahead of the crack tip

- According to hydrogen-induced cracking, these sites act as initiation sites for local quasi-cleavage cracking and void formation, and these microcracks link with the main crack From Devrient et al. Env.

- According to an alternative mechanism, at a given macroscopic Degradation Conf., 2007 strain, the microscopic strain in a steel that is susceptible to dynamic strain aging is higher because of strain localization to small areas, which leads to higher rates and larger steps of oxide film rupture.

Therefore, the film rupture/slip dissolution process would enhance crack initiation or crack growth rates

- Such processes occur under certain conditions of temperature, strain rate, and DO level, and may enhance environmentally assisted corrosion and increase fatigue crack initiation and crack growth rates 58

Abbreviations and Symbols Used in this Presentation Abbreviation Definition Abbreviation Definition ANL Argonne National Laboratory PNNL Pacific Northwest Nuclear Laboratory ASME American Society of Mechanical Engineers PVRC Pressure Vessel Research Council BNCS Board on Nuclear Codes and Standards RES Office of Nuclear Regulatory Research CFR Code of Federal Regulations RG Regulatory Guide CLB Current Licensing Basis WRC Welding Research Council CUF Cumulative Usage Factor Symbol Definition DO Dissolved Oxygen Content A, B, C Constants for Langer Curve Fit EAF Environmentally Assisted Fatigue a Strain Amplitude (%)

FAP Fatigue Action Plan Fen Environmental Fatigue Multiplier GALL Generic Aging Lessons Learned O Fluid Dissolved Oxygen Content GSI Generic Safety Issue O* Transformed Oxygen Content JNES Japan Nuclear Energy Safety Organization R Strain Rate (%/s)

JNRA Japan Nuclear Regulatory Authority R* Transformed Strain Rate LWR Light Water Reactor S Metal Sulfur Content (wt. %)

S* Transformed Sulfur Content MOU Memorandum of Understanding T Temperature (°F or °C)

NRO Office of New Reactors T* Transformed Temperature NRR Office of Nuclear Reactor Regulation 59

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