*Westinghouse

FaxTo: NRC Rulemaking & Directives Branch

Office of Adminiitration

Fax: 301-492-3446

fl ':531

Date: June 12. 2009

From:Direct faxDirect Tel,

e-mail:

Jim Gresham

412-374-3846

412-374-4643

grshaja@wesTinghouse, com

-101-7

Pages 9 including cover page

Your ref

Our ref LTR-NRC-09-30

Subject LTR-NRC-09-30Comments on Draft Regulatory Guide DG-1211, "Comments on DraftRegulatory Guide DG-1211, Materials and Inspections for ReactorVessel Closure Studs"

60 A)S 22~Ck'/, 52-

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A BNFL Group company

* Westinghouse Westinghouse Electric CompanyNuclear ServicesP.O. Box 355Pittsburgh. Pennsylvania 15230-0355USA

U.S. Nuclear Regulatory CommissionOffce of AdministrationRulemaking and Directives Branch

Mail Stop: TWB-05-B01MWashington, DC 20555-0001

Direct tel,Direct fax:

e-mail:

412-374-4643412-374-3846greshaja@wostinghouse.com

Our ret LTR-NRC-09-30

12 June 2009

Subject- Comments on Draft Regulatory Guide DG-121 1, Materials and Inspections for Reactor VesselClosure Studs

Dear Sir or Madam:

Westinghouse Electric Company LLC appreciates this opportunity to comment on the proposed updatesto U.S. Nuclear Regulatory Commission Regulatory Guide 1.65, Rev. 0. Comments on the DG-1211 areprovided in the attachunent.

If you have any questions, please contact me at 412-374-4643.

Very truly yours,

J.A. Gresham, ManagerRegulatory Compliance and Plant Licensing

Attachment

cc: G. C. Bacuta, Jr. (NRC)M. Melton (NEI)W. E. Norris (NRC)J. H. Riley (NEI)

Attachment to LTR-NRC-09-30Page I of'6

Westinghouse Electric Company Review of U.S. NRC Draft Regulatory Guide DG-1211

Materials and Inspections for Reactor Vessel Closure Studs

(Proposed Revision 1 of Regulatory Guide 1.65, dated October 1973)

This document provides Westinghouse Electric Company comments on the proposed revision toU.S. Nuclear Regulatory Guide (NRC) Regulatory Guide (RG) DG-1211, "Materials andInspections for Reactor Vessel Closure Studs."

C. Regulatory Position - Section 1. Bolting Materials

Comment 1:

The wording of the 4 th paragraph of the "Discussion" section is confusing with regard to therestriction on material strength. It first states that the stud materials with maximum ultimatetensile strength less than 170 ksi are relatively immune to stress corrosion cracking (SCC). Thenext sentence states that the stud sizing should be performed so that the maximum measuredyield strength will not result in a maximum ultimate tensile strength that exceeds 150 ksi.Referenced NUREG-1801 indicates that stud materials with yield strength that exceeds 150 ksiare susceptible to SCC. This part of the discussion seems to be mixing up the guideline in Rev.0 and the proposed guideline in Rev. 1 and needs editorial clarification. The current revision ofNUREG-0800 still references Regulatory Guide 1.65 Revision 0 and the 170 ksi maximumtensile strength guideline. Based on the first statement, ultimate tensile strength is the keyproperty for resistance to SCC. However, the NUREG indicates that yield strength is the keyproperty. The discussion should be reworded to indicate whether both ultimate tensile strengthand yield strength should be limited, or whether just a yield strength of less than 150 ksi is thekey property based upon the NUREG.

Comment 2:

Westinghouse understands that Rev. 1 of Regulatory Guide 1.65 will not apply to the DesignCertification for AP1 000. The Design Certification was granted based on conformance to theguidelines in the Regulatory Position of Rev. 0. Therefore, this proposed requirement is notcurrently reflected in the AP1 000 reactor vessel design specification. The maximum ultimatetensile strength is instead specified to be 170 ksi, based on RG 1.65, Rev. 0. The first bulletedrequirement in the proposed revision to the "Regulatory Position" section restricts the measuredyield strength to 150 ksi maximum. The AP1000 closure bolting material supplier has indicatedthat the limitation on yield strength would be a hardship on the supply of this material.Furthermore, the discussion in the draft regulatory guide makes it unclear as to whether both theyield strength and ultimate tensile strength should be limited, as discussed in Comment 1,although the proposed revision to the Regulatory Position only includes the limitation on yieldstrength.

Comment 3:

Westinghouse recommends that the Regulatory Guide maintains its existing limitation onmaterial tensile strength. Data for SA-540 bars used for reactor pressure vessel (RPV) studs,nuts, and washers was compiled from six utilities for twelve reactor vessels (discussion and dataevaluation follows). Review of this data confirms that it would be difficult for material suppliers

Attachment to LTR-NRC-09-30Page 2 of 6

to comply with the proposed yield strength restriction. While the tensile data rarely exceededthe 170 ksi guideline, yield strength values greater than 150 ksi were observed in approximately10% of the test cases. A complicating factor from these test results is that the materialspecification requires tensile specimens taken from both ends of each bar. In many caseswhere the yield strength result from one end of a bar exceeded 150 ksi, the test result from theother end was less than 150 ksi. Such results could lead to increased rejection rates and highercosts with no significant benefit to structural integrity or safety.

Combining this observation with the fact that RPV studs are tensioned not torqued, so as tominimize potential overloads, and that use of deleterious lubricants, particularly those containingmolybdenum disulfide compounds, has been eliminated, the proposed Regulatory Guideposition to limit maximum yield strength to 150 ksi has limited or no benefit. Based on thesupplier input Westinghouse has received and reviewed, Westinghouse suggests that thelimitation be on the ultimate strength value (170 ksi).

Attachment to LTR-NRC-09-30Page 3 of 6

Supplement to Comment 3

SA-540 Grades 23 & 24, Class 3 RPV Stud Material Properties

Yield and tensile strength properties were compiled for SA-540 Grades 23 and 24, Class 3reactor pressure vessel (RPV) stud materials. The data represent tensile test results from eachend of bars to be used for RPV studs, nuts and washers from six different utilities and a total oftwelve operating RPVs. The data are those originally reported for each RPV and do not reflectall replacement stud material that may have been procured over the operating life of the plant.

Table 1 presents simple summary statistics for the assembled yield and tensile strength data.The total number of tensile strength values was higher (254 vs. 240) than the yield strengthvalues because only tensile strength was reported for some lots of bar material.

Table 1Tensile Strength (ksi) Yield Strength (ksi)

Minimum Spec. 145.0 Minimum Spec. Requirement 130.0RequirementR.G. 1.65 Maximum Limit 170.0 Proposed R.G. 1.65 Rev. 1 150.0

LimitMean (ksi) 159.01 Mean (ksi) 143.09Standard Error 0.3188 Standard Error 0.3838Median (ksi) 159.0 Median (ksi) 143.6Mode 160.0 Mode 145Standard Deviation (ksi) 5.0809 Standard Deviation (ksi) 5.6940Sample Variance 25.8164 Sample Variance 32.4217Kurtosis -0.1371 Kurtosis -0.2967Skewness 0.0600 Skewness -0.2576Range 26 Range 27.1Minimum 147.0 Minimum 130Maximum 173.0 Maximum 157.1Count 254 Count 220Confidence Level (95.0%) 0.6278 Confidence Level (95.0%) 0.7565

The mean tensile strength value of 159 ksi is approximately two standard deviations from theexisting Regulatory Guide 1.65 limit of 170 ksi on tensile strength. The mean yield strengthvalue of 143 ksi is only slightly less than one standard deviation below the proposed limit onyield strength of 150 ksi in the draft revision of Regulatory Guide 1.65. These distributionsindicate that there is a higher likelihood of yield strength results exceeding the newly proposedlimit than there was for tensile strength based on the existing limit.

Plots of the tensile and yield strength data in Figures 1 and 2 illustrate this behavior. The tensileand yield strength data are plotted for all heats/lots of bar material reported by plant site or unit.The reported test values are compared to the minimum specified requirements of the materialspecification and the maximum limits, recommended and proposed, from Regulatory Guide1.65. Histograms of the tensile and yield strength distributions are provided in Figures 3 and 4for information.

Attachment to LTR-NRC-09-30Page 4 of 6

As shown in Figure 1, only a few (6 out of 254) tensile strength values exceed the 170 ksi limit,even though some of the heats or lots of material represented were not procured with themaximum 170 ksi limit imposed on tensile strength. In comparison, Figure 2 shows that

FIGURE 1

175

17"

I R.G. 1.65 Limit on Measured Tensile Strength 170 ksi I

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I SA-540 B23 or B24 Cl. 3 Min. Specified Tensile Strength 145 ksi I

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considerably more (27 out of 220) yield strength test values exceed the maximum 150 ksi limit.This result is further complicated by the SA-540 requirement that tensile tests be performed on aspecimen from each end of each bar. In many cases, where one of the tests results in a yieldstrength value >150 ksi, the second specimen from the same bar results in a value less than150 ksi. The newly proposed limitation in the draft Regulatory Guide is not clear on how suchtest results should be addressed. If any tensile test result >150 ksi must be consideredrejectable, a significant increase in rejection of bar material would be imposed. The increasedrejection rate would have an adverse effect on material availability, cost and delivery schedulewith no benefit to integrity of the RPV closure or safety.

Attachment to LTR-NRC-09-30Page 5 of 6

FIGURE 2

160

155

150

Proposed R.G. 1.65 Rev. I Limit on Measured Yield Strength 150 ksi

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SA-540 B23 or B24 Cl. 3 Min. Specified Yield Strength 130 ksi I

0 50 100 150 200 250SA-540 Gr 23 or Gr 24 Class 3

Attachment to LTR-NRC-09-30Page 6 of 6

FIGURE 3

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