NL-04-2265, Unit 1 Updated Analysis of Core Shroud Vertical Welds and Supplemental Information

Unit 1 Updated Analysis of Core Shroud Vertical Welds and Supplemental Information

ML043430471
Person / Time
Site:	Hatch
Issue date:	12/03/2004
From:	Sumner H Southern Nuclear Operating Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
NL-04-2265, TAC MC1322
Download: ML043430471 (12)

Text

H.L Sumner, Jr. Southern Nuclear Vice President Operating Company, Inc.

Hatch Project Post Office Box 1295 Birmingham, Alabama 35201 Tel 205.992.7279 SOUTHERNANA December 3, 2004 COMPANy Energy to Serve Your World' Docket No.: 50-321 NL-04-2265 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D. C. 20555-0001 Edwin 1. Hatch Nuclear Plant Unit I Updated Analysis of Core Shroud Vertical Welds and Supplemental Information Ladies and Gentlemen:

By letter dated November 14, 2003, Southern Nuclear Operating Company (SNC) provided to the NRC the calculation and a description of the methodology of the updated flaw analysis of the Edwin I. Hatch Nuclear Plant Unit 1 flawed Core Shroud Vertical welds. In a subsequent letter dated January 30, 2004, SNC provided to the NRC the related fluence calculation and methodology.

The two flawed shroud vertical welds were re-examined using ultrasonic examination techniques during the Spring 2004 refueling outage. SNC contracted Structural Integrity Associates, Inc. to perform an update to the flaw analysis using the most recent inspection results and the guidance provided by BWRVIP-76. Enclosure I provides responses to questions previously asked by the staff per the facsimile dated March 11, 2004 regarding the previous analysis, and Enclosure 2 provides the most recent analysis prepared by Structural Integrity Associates, Inc. The responses and analysis in the enclosures supercede the analysis submitted by the letter dated November 14, 2003.

This letter contains no NRC commitments. If you have any questions, please advise.

Sincerely, H. L. Sumner, Jr.

HLS/ifl/sdl

Enclosures:

1. Responses to NRC Questions Regarding Hatch Unit I Shroud EPFM Analysis

2. Elastic-Plastic Fracture Mechanics Evaluation of the Plant Hatch Unit I Core Shroud V5 andV6 Welds

.A(OI

U. S. Nuclear Regulatory Commission NL-04-2265 Page 2 cc: Southern Nuclear Operating Company Mr. J. T. Gasser, Executive Vice President Mr. G. R. Frederick, General Manager - Plant Hatch RTYPE: CHA02.004 U. S. Nuclear Regulators Commission Dr. W. D. Travers, Regional Administrator Mr. C. Gratton, NRR Project Manager - Hatch Mr. D. S. Simpkins, Senior Resident Inspector - Hatch

Edwin I. Hatch Nuclear Plant Enclosure I Responses to NRC Questions Regarding Hatch Unit 1 Shroud EPFM Analysis

StructuralIntegrityAssociates, Inc.

3315 Almaden Expressway Suite 24 San Jose, CA 95118-1557 Phone: 408-97848200 Fax: 408-978-8964 www.structntcom mhereffa@structintcom November 11, 2004 MLH-04-085 Mr. Denver Atwood MC B052 Sr. Engineer Southern Nuclear Operating Co.

40 Inverness Center Parkway Birmingham, AL 35242

Subject:

Transmittal of Structural Integrity Associates Responses to NRC Questions Regarding Hatch Unit 1 Shroud EPFN Analysis

Reference:

SIR-04-120, Rev. 0, October 2004

Dear Denver:

Structural Integrity Associates (SI) is pleased to transmit the enclosed responses to NRC questions regarding the referenced report.

Please contact me or Stan Tang if you have any questions.

Very truly yours, Marcos L. Herrera, P.E.

Senior Associate ii Enclosure cc: HTCH-07Q Project File Austln, TX Centennial, CO Charlotte, NC N Stonington, CT Silver Spring, MD Sunrise, FL Unlontown, OH Whittier, CA 512-533-9191 303-792-0077 704-597-5554 860-599-6050 301445-8200 954-572-2902 330-899-9753 562-944-8210

Responses to Request for Additional Information The Updated Analysis of Core Shroud Vertical Welds Edwin I. Hatch, Unit 1 Southern Nuclear Operating Company TAC No. MC 1322 1.1 On Page 1 of Attachment l it is stated that a constant crack growth rate (CGR) of 5x10-5 in/hr was assumed. As a result of the Nuclear Regulatory Commission (NRC) staff's review of the Boiling Water Reactor (BWR) Vessel and Internal Project (BWRVIP) reports, the staff has approved the used of different constant CGRs for applications to BWR internals under different water conditions using hydrogen water chemistry (HWC) and noble metal chemistry application (NMCA). The continued use of these CGRs has to be justified when new data become available. Provide the worst applied stress intensity factor (K) for flaws in the core shroud vertical welds to demonstrate that your constant CGR is still valid in light of the new data in BWRVIP-99, "BWR Vessel and Internals Project - Crack Growth Rates in Irradiated Stainless Steels in BWR internal Components," for high fluence applications. When you calculate the applied K for flaws in the core shroud vertical welds, you need to consider weld residual stresses

Response

The longest through-wall crack at the end of next 15 years re-inspection interval is about 37 inches, compared to the length of the vertical weld of about 98 inches, close to 40% of the total weld length. If included the remaining two cracks, Figure 4 of Attachment 1, the total crack length would be about 66 inches, at 67% of the total weld length. Since the weld residual is self equilibrium in nature, as the crack grows in length, the residual stress is relaxed and reduced to essentially non-existence when the through-wall crack extends to the entire length of the vertical weld. In the current evaluation, it is reasonable to assume the residual stress, if it exists, is very small and insignificant. Therefore, in the subsequent evaluation, the effect of residual stress on the applied stress intensity factor and crack growth rate is not significant and can be ignored.

A linear elastic fracture mechanics evaluation was performed for the longest axial through-wall crack in the V6 weld. Under only pressure loading, using a center crack panel, the stress intensity factor is calculated to be about 13 ksi4in for the longest through-wall crack in the V6 weld. Using the normal water chemistry disposition curve, the crack growth rate is about 5x10-5 in/hr. If the hydrogen water chemistry disposition curve is used, the crack growth rate is about 2x 10-5 in/hr. Therefore, the use of a constant 5x10-5 in/hr in the current evaluation is judged to be conservative.

Report SIR-03-115 by Structural Integrity Associates, Inc.

2-1 On Page 3-1 of Report SIR-03-115 it is stated that the J-Integral considers internal pressure only.

Not considering weld residual stresses in your previous evaluation of the core shroud weld flaws was justified because limit load analysis was used there. This is not generally true when elastic-plastic fracture mechanic (EPFM) or linear elastic fracture mechanics is the dominant fracture mechanism.

Justify that you could ignore weld residual stresses in the current EPFM application.

Response

It is referred to the response to Question 1.1 for the justification of not including the residual stress in the evaluation.

2.2 On Page 3-1 of Report SIR-03-115, it is stated that JappliedTapplied curves are based on J-Integral by incrementing the crack size. It is further stated on Page 4-1 of this report that the J-integral is calculated from the crack tip opening displacement (CTOD), as reported in EPRI Report NP-1735, "Methodology for Plastic Fracture." To validate this CTOD approach, provide a comparison of the J-integral determined from a numerical integration over a path encircling the crack tip and those from the CTOD approach.

Response

The original definition of J-integral is best suited for two dimensional models. This original form is not suited for three-dimensional problems in numerical analysis. It is necessary to convert the original equation into a volume integral before it could process the results from the three dimensional finite element crack models.

A verification of CTOD approach was performed using pc-CRACK, [1]. pc-CRACK has the capabilities of performing linear elastic and elastic-plastic fracture mechanics evaluation. The elastic-plastic fracture mechanics is based on the estimation scheme developed by C. F. Shih, under the sponsorship of the Electric Power Research Institute. This scheme is similar to the approach using integration over a path encircling the crack tip.

Two problems were used in the verification. The first problem is a part through circumferential crack in a cylinder under remote tension, Figure 1. The cylinder has a thickness of 9 inches with t/R = 0.1. Two different crack sizes and loading conditions were considered. The first case is with a crack depth ratio, a/t, of 0.25 and a remote tension stress at 40 ksi. Both plane strain and plane stress conditions were considered. The second case is a through wall circumferential crack in cylinder under remote tension, Figure 2. The cylinder has a wall thickness of 0.4 inches, with an outside diameter of 2.4 inches. The through crack length ratio, a/b (crack length to circumference), is 0.125, with a remote tension load of 200 kips.

The finite element models for the J-integral calculation using CTOD are shown in Figures 3 and 4. The part-through circumferential crack finite element model is shown in Figure 3. The through-wall circumferential crack finite element model is shown in Figure 4.

Table 1 presents the verification results between the J-integral calculated from CTOD approach and pc-CRACK. It shows a very reasonable comparison, indicating the validity of using the CTOD approach for estimating the J-T curve.

Reference:

1. pc-CRACK for Windows, Version 3.1-98348, Structural Integrity Associates, 1998.

Table 1 Comparison of J-Integral Results Model Stress, a/t, J-Integra1 (in-kip/in2 )

Load a/b Condition CTOD pc-CRACK Part through Circumferential 40 ksi 025 Plane strain 9.59 9.6 Crack, under remote tension Plane stress 7.18 9.97 Through wall Circumferential 200 0.12 Plane strain 3.93 3.40 crack under remote tension kips 5 Plane stress 2.94 3.46

Stress(c) orLoad(L) t a REQUIRED INPUTS:

I , L: stress Dr load a: cack depth 2R0 : outside diameter It: wall thickness la:- crack increment for Tearing Modulus Calculation.

Default: 0.005 Figure 1 Part-Through Circumferential Crack in Cylinder Under Remote Tension

2a stress()

or load(L)

REQUIRED INPUTS: I 2R%: outside diameter a: half cracklength 2b: Circumference IP t: vall thickness RL: stress orload Aa crack increment for Tearing Modulus Calculation default: 0.005 Figure 2 Through-Wall Circumferential Crack in Cylinder Under Remote Tension

Figure 3: Finite Element Model of Part Through Circumferential Crack for J-Integral Calculation using CTOD

Cylinder with through Figure 4: Finite Element Model of Circumferential Through Wall Crack for J-Integral Calculation using CTOD