ANP-10326Q1NP, Rev. 0, 'Response to First Request for ...

AAREVA

Response to First Request forAdditional Information

ANP-10326Q1 NPRevision 0

ANP-10326P,Environmentally Assisted Fatigue: ModifiedEffective Correction Factor for AusteniticStainless Steels

October 2013

AREVA NP Inc.

(c) 2013 AREVA NP Inc.

AREVA NP Inc. ANP-10326Q1NPRevision 0

Response to First Request for Additional InformationANP-10326P Page i

Contents

Paqe

Q U E S T IO N 1 .................................................................................................................. 1

Response 1 ......................................................I............................................... 2

QUESTION 2 ......................................................................................................... 5Response 2 ...................................................................................................... 6

QUESTION 3 ......................................................................................................... 7Response 3 ...................................................................................................... 8

QUESTION 4 ................................................................................................................ 12

Response 4 .................................................................................................... 13

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ANP-10326Q1NPRevision 0

Page ii

List of Tables

Table 1-1 Comparison of Fen Factors ........................................................................ 3

Table 1-2 Comparison of RFs ................................................................................. 4

Table 3-1 Adjusting factors for in-air fatigue design curve ....................................... 10

AREVA NP Inc.



Page iii

List of Figures

Figure 3-1 NUREG/ CR-6909 Methodology .......................................................... 11

Figure 4-1 Applicability of AREVA's Method .......................................................... 15


Response to First Request for Additional InformationANP-10326P Pagqe iv

Nomenclature

Acronym DefinitionANL Argonne National LaboratoryASME American Society of Mechanical EngineersDO Dissolved Oxygen

LCF Low Cycle FatiguePWR Pressurized Water ReactorRF Correction Factor that Reduces the Fen Factor (Reduction Factor)

RG Regulatory Guide N,Rt Measure of RoughnessSS Stainless SteelTR Topical Report

AREVA NP Inc. ANP-10326QINPRevision 0

Response to First Request for Additional InformationANP-1 0326P Page 1

QUESTION 1

The NRC staff has previously endorsed the EAF methodology in NUREG/CR-6909,

Revision 0, in Regulatory Guide 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." As mentioned above, NUREG/CR-

6909 is under revision; Revision 1 will include the results of all of NRC/Argonne National

Laboratory (ANL) research efforts to date, including the evaluation of significant

additional fatigue data available since the original publication of the report in 2007. The

draft of NUREG/CR-6909, Revision 1, is anticipated to be distributed for public

comment at the end of 2013, and is expected to be endorsed in a revision to Regulatory

Guide 1.207 thereafter. In advance of this publication, NRC staff has discussed the

results of this research at public interactions including committee meetings for the

American Society of Mechanical Engineers Boiler and Pressure Vessel Code. The

comprehensive presentation from May 2012, as well as all public comments and

responses and a revised presentation, are available in the NRC ADAMS at Accession

No. ML1 3008A005. Given that the proposal in the TR would result in less conservative

decisions than the methodology described in either revision of NUREG/CR-6909, the

TR should provide justification of its proposed methodology with respect to those

endorsed by the NRC staff.


Response to First Request for Additional InformationANP-10326P Paqe 2

Response 1

The AREVA NP Inc. (AREVA) Topical Report (TR) ANP-10326P, Revision 0 uses

NUREG/CR-6909, Revision 0 to demonstrate the Fen method. Regulatory Guide (RG)

1.207 refers to NUREG/CR-6909 Revision 0, issued in February 2007.

AREVA reviewed the revised comprehensive presentation from May 2012, as well as

the public comments and responses available in the NRC ADAMS at Accession No.

ML13008A005, (Reference 1). A comparison was performed to determine the

difference between Fen calculated in accordance with NUREG/CR-6909, Revision 0,

and Fen calculated using the equations provided in Reference 1, as well as the impact of

the equations provided in Reference 1 on the reduction factor (RF), calculated in

accordance with TR ANP-10326P . As shown in Table 1-1, the revised Fen formulation

of Reference 1 yields values that are reduced by a maximum of 3.1 percent, and, as

shown in Table 1-2, RFs that are reduced by [

I and that the AREVA methodology is

applicable for the material and testing conditions under consideration.

Justification of the proposed RFs, applicable to the Fen factor for Type 304L stainless

steel (SS) and the simulated PWR environment considered (Dissolved Oxygen (DO)

less than 0.1), is based on AREVA's experimental work, presented in TR ANP-10326P.

I

AREVA NP Inc.

Response to First Request for Additional InformationANP-1 0326P


Paae 3

AREVA's experimental work supplements NUREG/CR-6909, [

References for Response 1:

1. O.K. Chopra, Y. Garud, and G. Stevens, 2012, "Update of NUREG/CR-6909

Methodology for Environmentally Assisted Fatigue (EAF) - Revised Fen

Expressions," revised presentation, NRC ADAMS at Accession No.

ML13008A005, December 2012

Table 1-1 Comparison of Fen Factors

Loading Fen Fen DifferenceANP-10326P Reference I (%)

Revision 0 (Note)

Triangular signal with strain rate 2.08 2.11 +1.440.4%/s

Triangular with strain rate 0.01%/s 5.07 4.97 -1.97

Triangular with strain rate 0.1%/s 2.91 2.91 0Short complex signal A Ea=0.6 5.97 5.80 -2.85

Long complex signal A Ea=0.6 5.88 5.70 -3.06Short complex signal A Ea=0.3 5.88 5.70 -3.06

Short complex signal B Ea=0.6 5.98 5.80 -3.01

Short complex signal B Fa,=0.3 6.01 5.83 - 3.00

Short complex signal C Fa=0.6 6.37 6.17 -3.14

Short complex signal D Ea=0.6 6.02 5.84 -2.99

Short complex signal D Ea=0.3 6.02 5.84 -2.99

Note to Table 1-1:

1. Used NUREG/CR-6909, Revision 0

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ANP-10326Q1 NPRevision 0

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Table 1-2 Comparison of RFs



QUESTION 2

ANP-1 0326P discusses a modified correction factor for EAF evaluation that is

applicable to all austenitic stainless steels. However, Section 3.1 of ANP-10326P notes

that AREVA's test results to establish the modified correction factor were based on

three sources of Type 304L stainless steel (a rolled plate, a forged slab, and a cold

forged branch). Table 3-3 of Section 3.2 of ANP-10326P indicates that a total of 37

specimens were tested, which included 22 polished and 15 ground specimens. Section

4.0 summarizes available surface finish tests from ANL. The applicability of AREVA's

test results to all types of austenitic stainless steels was not provided in

ANP-1 0326P. Therefore, use of the results from testing of 37 specimens of three forms

of Type 304L stainless steel to develop a modified correction factor that is applicable to

all forms and types of austenitic stainless steels is not justified.



Response 2

Through experimental work, AREVA identified that there is margin in the methodology

proposed in NUREG/CR-6909 for the type 304L austenitic SS that can partially account

for environmental effects on the life of components. As a result, a Reduction Factor

(RF) was developed to account for the identified margin, which can be used to modify

the Fen factor developed in NUREG/CR-6909, Revision 0 for the water environment

considered.

As mentioned in Section 3.1 of the TR ANP-10326P, three sources of SS were used,

with the majority representing 304L rolled plate with a thickness of approximately four

inches for the tests in a PWR- simulated environment. The material exhibits a mean in-

air fatigue life similar to that predicted by the Argonne National Laboratory (ANL) mean

curve in NUREG/CR-6909, Revision 0 and also in Reference 1, as shown in Figure 3-7

of the TR ANP-10326P. The material has representative chemical composition and

mechanical properties of materials currently used in the nuclear industry.

The American Society of Mechanical Engineers (ASME) design in-air fatigue curve

includes an adjustment factor of 2.0 to account for material variability and data scatter.

NUREG/CR-6909 does not consider specific adjustment factors in the development of

its design in-air fatigue curve but suggests that a range of 2.1 to 2.8 is an inherent factor

in the data intended to account for material variability and data scatter. AREVA

recognizes that the testing of a single material type does not allow for bounding of

material variability concerns. Therefore, ANP-10236P, Revision 1 clarifies that

application of the method is limited to Type 304L austenitic SS and PWR environmental

conditions.


Response to First Request for Additional InformationANP-10326P Page 7

QUESTION 3

As identified in Table 12 of NUREG/CR-6909 and summarized in Table 2-1 of

ANP-1 0326P, the NRC considered a factor for surface finish effects in the range of 2.0

to 3.5 based on limited available data, as part of the overall factor of 12 on life applied to

the best fit mean air curve to develop the design fatigue curve for austenitic stainless

steels. The factor of 12 was arrived at based on a Monte Carlo statistical evaluation to

develop an overall factor that bounded 95 percent of all available data. The effective

environmental fatigue correction factor (Fen) for austenitic stainless steels (Equation 38

of NUREG/CR-6909) was then applied to the design fatigue curve, and is a function of

three important variables: transformed temperature, strain rate, and dissolved

oxygen. However, AREVA's proposed modified correction factor, per Equation 16 of

ANP-1 0326P, is applied to adjust the Fen factor. The application of the modified

correction factor to the Fen value without the need for consistently developing a surface

finish factor in the Fen relationship or modifying the overall factor of 12 on life and the

associated design fatigue curve was not justified, nor was the modified correction factor

developed consistently with the Monte Carlo statistical approach described in Chapter 7

of NUREG/CR-6909 for the type of austenitic stainless steel material that was tested.


Response to First Request for Additional InformationANP-10326P Paqe 8

Response 3

Experimental work was performed for Type 304L austenitic SS, which AREVA uses in

its applications, [

] Through the testing, AREVA identified and quantified an

experimental margin that can account for environmental effects. Given the Fen

Equations in NUREG/CR-6909, AREVA proposes that correction factors be applied to

the Fen for the conditions and material tested.

AREVA recognizes that for the evaluation of the overall factor of 12 on life, statistical

Monte Carlo simulations were performed, according to the procedure described in

Section 7.0 of NUREG/CR-6909, assuring a 95 percent bound of the population. The

procedure is demonstrated in Figure 3-1. [

I

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Response to First Request for Additional InformationANP-1 0326P


Paae 9

Table 2-1 of TR ANP-10236P, Revision 1 is updated according to the information

presented in Table 3-1.


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Table 3-1 Adjusting factors for in-air fatigue design curve

Parameter 5 th percentile 9 5 th Mean ANP-10326Ppercentile Revision 0

Material Variability 2.1 2.8 2.5 [ JSize Effect 1.2 1.4 1.3 [

Surface Finish, 2.0 3.5 2.8etc.

Loading History 1.2 2.0 1.6 [ JTotal Adjustment 6.0 27.4 14.6 n/al

Note to Table 3-1:

1. AREVA did not intend to produce a new design curve, but to examine the available

experimental margin identified in the methodology proposed in NUREG/CR-6909 for

Type 304L SS.

AREVA NP Inc.



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Figure 3-1 NUREG/ CR-6909 Methodology

£.ANL Design Curve

(inAir)

Fen " Overall factor= 12

ANIL Methodology......e.inWe .....

ANL Methodology (Curve in Water)ANL Mean Air

Curve

Fen = exp(O.734 - 0.281 . T'. E)

2.08 < Fen < 11; at 300°C I

N25 N



QUESTION 4

Section 2.3, Page 2-9 of ANP-1 0326P identifies that the impact of the Modified

Goodman correction for mean stress effects was not considered in the experimental

margin term, d, because the correction for mean stress effects is not applicable in the

low cycle fatigue regime for austenitic stainless steel. This statement is not sufficiently

justified, nor is the application of the experimental margin term, d, limited only to low

cycle fatigue results in the proposed methodology.


Response to First Request for Additional InformationANP-10326P Paae 13

Response 4

The experimental margin d and the AREVA methodology are limited to

] This

terminology is in accordance with literature and NUREG/CR-6909 (LCF considered less

than 100,000 cycles).

In Figure 4-1, the best-fit mean data (mean curve), Equation 32 of NUREG/CR-6909, is

in blue color and the design curve in light blue color. The mean curve is adjusted for the

Goodman mean effect (applicable only when the stress amplitude is less than the yield

strength) and then a factor of 12 on cycles, or 2 on stress is applied, whichever is worse

in order to obtain the design curve. These operations are shown in Figure 4-1, [

] This evaluation procedure is in accordance with Section

5.1.8 of NUREG/CR-6909.



AREVA performed testing with controlled strain amplitude, as Section 3.2.2.2 of the TR

explains. Mean stress was not applied. [

ANP-10326P, Revision 1 provides additional clarification for the area of applicability for

the proposed method.

AREVA NP Inc.



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Figure 4-1 Applicability of AREVA's Method

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