NOC-AE-12002837, Response to Request for Additional Information: Application of an Alternative to Requirements for Examination of Class 1 and Class 2 Piping Welds (Relief Request RR-ENG-3-04)

Response to Request for Additional Information: Application of an Alternative to Requirements for Examination of Class 1 and Class 2 Piping Welds (Relief Request RR-ENG-3-04)

ML12138A009
Person / Time
Site:	South Texas
Issue date:	05/09/2012
From:	Ruvalcaba M South Texas
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
NOC-AE-12002837, TAC ME7055, TAC ME7056, G25, RR-ENG-3-04, STI: 33452169
Download: ML12138A009 (10)

Text

Nuclear Operating Company South Texas Pro/ect Electric Generatlin Station PO. Bom 28,9 Wadswtorth. Tesas 77483 -

May 9, 2012 NOC-AE-12002837 File No.: G25 10 CFR 50.55a U. S. Nuclear Regulatory Commission Attention: Document Control Desk One White Flint North 11555 Rockville Pike Rockville, MD 20852-2738 South Texas Project Units 1 and 2 Docket Nos. STN 50-498, 50-499 Response to Request for Additional Information:

Application of an Alternative to Requirements for Examination of Class 1 and Class 2 Piping Welds (Relief Request RR-ENG-3-04) (TAC Nos. ME7055/ME7056)

Reference:

Marco Ruvalcaba, STP Nuclear Operating Company, to NRC Document Control Desk, "Request for Relief to Apply an Alternative to the ASME Section Xl Code Requirements for Examination of Class 1 and Class 2 Piping Welds (Relief Request RR-ENG-3-04)," dated September 1, 2011 (NOC-AE-1 1002705) (ML11250A170)

In accordance with the provisions of 10 CFR 50.55a(a)(3)(i), the STP Nuclear Operating Company (STPNOC) submitted the referenced request for relief from the ASME Section Xl code requirements for inservice inspection of Class 1 and Class 2 piping welds. Attached are responses to NRC requests for additional information provided February 2, 2012.

There are no commitments in this letter.

Approval of this relief request will allow risk-informed selection of Class 1 and Class 2 piping welds for examination during for the third 10-year inspection interval, effective until September 24, 2020 (Unit 1) and October 18, 2020 (Unit 2).

If there are any questions, please contact either Mr. Philip L. Walker at (361) 972-8392 or me at (361) 972-7904.

Marco Ruv Icaba Manager, Testing and Programs Engineering PLW

Attachment:

Response to Request for Additional Information: Application of an Alternative to Requirements for Examination of Class 1 and Class 2 Piping Welds (Relief Request RR-ENG-3-04)

STI: 33452169 Ac17.

NOC-AE-1 2002837 Page 2 of 2 cc: (paper copy) (electronic copy)

Regional Administrator, Region IV John Ragan U. S. Nuclear Regulatory Commission Chris O'Hara 1600 East Lamar Blvd. Jim von Suskil Arlington, TX 76011-4611 NRG South Texas LP Balwant K. Singal A. H. Gutterman, Esquire Senior Project Manager Kathryn M. Sutton, Esquire U.S. Nuclear Regulatory Commission Morgan, Lewis & Bockius LLP One White Flint North (MS 8 B1) 11555 Rockville Pike Balwant K. Singal Rockville, MD 20852 U. S. Nuclear Regulatory Commission Senior Resident Inspector Richard Pena U. S. Nuclear Regulatory Commission Kevin Polio P. 0. Box 289, Mail Code: MN1 16 City Public Service Wadsworth, TX 77483 C. M. Canady C. Mele City of Austin City of Austin Electric Utility Department 721 Barton Springs Road Peter Nemeth Austin, TX 78704 Crain Caton & James, P.C.

Richard A. Ratliff Alice Rogers Texas Department of State Health Services

Attachment NOC-AE-12002837 Page 1 of 8 SOUTH TEXAS PROJECT UNITS I AND 2 RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION:

APPLICATION OF AN ALTERNATIVE TO REQUIREMENTS FOR EXAMINATION OF CLASS 1 AND CLASS 2 PIPING WELDS (RELIEF REQUEST RR-ENG-3-04)

1. Please state if the augmented inspection program for high energy break exclusion zone piping remain unaffected by the 3 rd Interval risk-informed inservice inspection (RI-ISI) program

Response

The augmented inspection program for the high energy break exclusion zone piping is not affected by the RI-ISI program to be applied during the third interval.

2. The NRC issued rulemaking on June 21, 2011 which requires licensees to follow an augmented inservice inspection program in accordance with American Society of Mechanical Engineers (ASME) Code Case N-770-1, "Alternative Examination Requirements and Acceptance Standards for Class 1 PWR [Pressurized Water Reactors] Piping and Vessel Nozzle Butt Welds Fabricated With UNS N06082 or UNS W86182 Weld Filler Material With or Without Application of Listed Mitigation Activities," and limitations listed in Title 10 of Code of Federal Regulations (10 CFR),

Paragraph 50.55a(g)(6)(ii)(F). In addition, the NRC held a public meeting to discuss the June rulemaking and the implementation of Code Case N-770-1 on July 12, 2011. Agencywide Document Access and Management System (ADAMS)

Accession No. ML112240818 documents the NRC summary of that meeting. Please state how will STP Nuclear Operating Company (STPNOC) address the requirements of the June 2011 rulemaking and ASME Code Case N-770-1 in implementing RR RR-ENG-3-04?

Response

Prior to the approved rulemaking, the STP Inservice Inspection Program was in compliance with MRP-139, "Primary System Piping Butt Weld Inspection and Evaluation Guidelines." The STP Inservice Inspection Program has been augmented by incorporating Code Case N-770-1 consistent with the requirements of the 10 CFR 50.55a(g)(6)(ll)(f)(1) rulemaking. No programmatic changes were required. Only editorial changes were needed to update the STP program to the new standard.

3. The original RI-ISI program required inclusion of 10% of the ASME Class 1 piping non-socket welds. Is this requirement met by the 3 rd interval RI-ISI program? Tables 3 and 4 do not identify any piping classes or ASME Section Xl code categories making it impossible for the NRC staff to determine if this requirement was retained.

Please provide details to facilitate NRC staff review.

Response

STP Unit 1 has a Class 1 population of 593 welds: 13 socket welds and 580 butt welds. Of 68 Class 1 welds selected for examination, four are socket welds and 64

Attachment NOC-AE-12002837 Page 2 of 8 are Class 1 butt welds. The 64 Class 1 butt welds are approximately 11% (10.99%)

of the total Class 1 butt weld population of 580.

STP Unit 2 has a Class 1 population of 589 welds: 20 socket welds and 569 butt welds. Of 69 Class 1 welds selected for examination, four are socket welds and 65 are Class 1 butt welds. The 65 Class 1 butt welds are approximately 11 % (11.03%)

of the total Class 1 butt weld population of 569.

Tables 3 and 4 of the September 1, 2011, application provide comparisons between the original and the proposed programs showing changes in weld selection for Units 1 and 2, respectively. The ASME Code classes for the various systems listed are provided in Table 1 (Unit 1) and Table 2 (Unit 2) of the September application.

Tables 1 and 2 are reproduced here as an attachment for clarity.

4. Starting on the bottom of Page 1 of the attachment to your September 1, 2011 submittal, there is a discussion of how review of the program led to the following changes and discusses 1) a change in the exemption size for auxiliary feedwater piping from the 1989 code to the 2004 code, 2) revised Probabilistic Risk Assessment Licensing Branch (PRA) model and 3) repair/replacement activities which modified the piping arrangements. In reviewing Tables 3 and 4, the NRC staff noted a significant change in the number of welds from the original program to the 3 rd interval RI-ISI program. Please modify Tables 3 and 4 to indicate the reason for the change in the number of welds (e.g. code change, revised PRA, repair/replacement, etc.) to facilitate NRC review of the 3 rd interval RI-ISI program.

Response

The original program consisted of two separate programs, one per Code Case N-560, and one per Code Case N-578. New Tables were developed showing this breakdown compared to the revised Interval 3 program and are attached as replacement Tables 3 and 4. Where there has been a significant change in the weld population during the Third Interval, the change is in response to one of the following as noted in the revised tables:

" During the intervening years between ASME Section Xl, 1989 Edition, applicable during the second interval, and the 2004 Edition, the exemption size of Class 2 auxiliary feedwater piping changed. Per IWC-1222, the exemption size for Class 2 auxiliary feedwater piping decreased from 4 NPS to 1-1/2 NPS. Lines are now included in the RI-ISI program that were previously exempt.

• Welds were added to the ISI program due to replacement of Unit 1 Steam Generators at the end of the first interval and the Unit 2 Steam Generators at the start of the second interval.

• The new consequence rankings for consequence segments 1(2)-CVCS-6, 1(2)-RCS-27, 1(2)-SIS-01a and 1(2)-SIS-01c are incorporated into the Risk Ranking, Element Selection, and Risk Impact Analysis.

" The re-analysis for Interval 3, determined an additional reactor coolant system (RCS) weld is susceptible to thermal stratification, cycling, and striping (TASCS).

Attachment NOC-AE-12002837 Page 3 of 8

5. STP Nuclear Operating Company provided justification for probabilistic risk assessment (PRA) quality by referencing a previous NRC approved risk informed application. Since PRA quality is determined sufficient commensurate with each application, please provide the NRC staff validation that those supporting requirements important to this application are addressed in the PRA. Additional information can be found in NRC safety evaluation (Adams Accession No. ML 1262A206) which references Electric Power Research Institute Technical Report 1021467.

RESPONSE

The STP risk-informed inservice inspection (RI-ISI) program is written in compliance with EPRI 1021467, "Nondestructive Evaluation: Probabilistic Risk Assessment Technical Adequacy Guidance for Risk-Informed In-Service Inspection Programs."

The STP PRA was determined by the NRC to be Category 2 for internal events and in compliance with the high level requirements for fires and external events. The NRC staff has reviewed EPRI TR 1021467 and concluded that the TR provides reasonable assurance that the PRA meets supporting requirements necessary for development of an RI-ISI program.

Table 2-1 of EPRI 1021467 provides a summary of supporting requirements by capability category. Supporting requirements are identified for the following elements:

IE - Initiating Event Analysis AS - Accident Sequence Development Analysis SC - Success Criteria SY - Systems Analysis HR - Human Reliability Analysis DA - Data Analysis IF - Internal Flood QU - Quantification LE - LERF Analysis Potential quantitative insights from analysis of other hazard groups would not impact conclusions with respect to acceptance criteria. This approach is consistent with risk-informed decision-making as described in NRC Regulatory Guide 1.174, "An Approach for Using Probabilistic Risk Assessment in Risk-Informed Decisions on Plant-Specific Changes to the Licensing Basis." Because of this and the guidance in EPRI 1021467, the STP PRA is of sufficient quality for this application.

Attachment NOC-AE-12002837 Page 4 of 8 TABLE I (No Change)

UNIT I - SYSTEM SELECTION AND SEGMENT I ELEMENT DEFINITION System ASME Code Class Number of Segments Number of Elements RCS - Reactor Coolant System Class 1 13 21 SIS - Safety Injection System Class 2 56 736 RHRS - Residual Heat Removal System Class 2 29 364 CSS - Containment Spray System Class 2 9 126 AFW- Auxiliary Feedwater System Class 2 23 167 FWS - Feedwater System Class 2 20 144 MSS - Main Steam System Class 2 40 197 SLS - Sludge Lancing System Class 2 1 12 CVCS - Chemical and Volume Control System Class 2 0 0 Total: 191 Total: 1767 TABLE 2 (No Change)

UNIT 2 - SYSTEM SELECTION AND SEGMENT I ELEMENT DEFINITION System ASME Code Class Number of Segments Number of Elements RCS - Reactor Coolant System Class 1 11 30 SIS - Safety Injection System Class 2 55 693 RHRS - Residual Heat Removal System Class 2 28 361 CSS - Containment Spray System Class 2 9 118 AFW-Auxiliary Feedwater System Class 2 24 162 FWS - Feedwater System Class 2 20 120 MSS - Main Steam System Class 2 40 201 SLS - Sludge Lancing System Class 2 1 8 CVCS - Chemical and Volume Control System Class 2 0 0 Total: 188 Total: 1693

Attachment NOC-AE-12002837 Page 5 of 8 TABLE 3 (Modified)

COMPARISON BETWEEN ORIGINAL AND UPDATED RI-ISI PROGRAMS BY RISK CATEGORY - STP UNIT I Risk Failure Potential Original Interval 3 CC N-560 CC N-578 Total Reason for Change in System(1 ) Consequence Weld Count Category Rank Rank Degradation Category Weld Weld Weld Weld RI-ISI Mechanism Caegt Count RI-ISI Weld Count RI-ISI Weld Count RI-ISI Count RCS 2 High High TASCS Medium RCS 2 High High TASCS, TT Medium RCS 2 High High TASCS, TT Medium PRA Conseq Change (+2)

(2) (High) (PWSCC) (Medium) 140 46 140 46 143 36 TASCS Determination (+1)

RCS 2 High High TT Medium 2 High TT Medium (2) (High) (PWSCC) (Medium)

RCS 4 Medium High None Low None Low 202 11 202 11 209 21 SG Repement (+8) 4 Medium (2) (High) High (PWSCC) (Medium) SG Rpaent(8 RCS 5a Medium Medium TASCS Medium RCS 5a Medium Medium TASCS, TT Medium 7 1 1 0 8 1 8 1 No Change RCS 5a Medium Medium TT Medium RCS 6a Low Medium None Low 6 0 12 0 18 0 18 0 No Change RCS 6b Low Low TT Medium 2 0 0 0 2 0 0 0 PRA Conseq Change (-2)

RCS 7a Low Low None Low 8 0 8 0 8 0 No Change SIS 5a Medium Medium TT, IGSCC Medium 3 1 3 1 3 1 No Change SIS 6a Low Medium None Low 23 0 678 0 701 0 447 0 PRA Conseq Change (-254)

SIS 6b Low Low TT, IGSCC Medium 3 0 3 0 3 0 3 0 No Change SIS 7a Low Low None Low 33 0 55 0 88 0 345 0 PRA Conseq Change (+257)

RHRS 5a Medium Medium TT Medium 12 2 12 2 12 2 No Change RHRS 6 Low Medium None Low 81 0 332 0 413 0 413 0No Change Low Medium None Low RHRS 6a RHRS 7 Low____ _____26 Low None Low 6 0 20 0 0 26 0 No Change RHRS 7a Low Low None Low I I IIII_ I CSS 6a Low Medium None Low 126 0 126 0 106 0 PRA Conseq Change (-20)

Attachment NOC-AE-12002837 Page 6 of 8 TABLE 3 (continued) (Modified)

COMPARISON BETWEEN ORIGINAL AND UPDATED RI-ISI PROGRAMS BY RISK CATEGORY - STP UNIT I Risk Failure Potential Original Interval 3 System(1 ) Consequence CC N-560 CC N-578 Total Reason for Change in Category Rank Rank Degradation Category Weld RI-ISI Weld Count Mechanism CaegrRI-ISI Weld RI-ISI Weld RI-ISI Count Count Count Count CSS 7a Low Low None Low 0 0 20 0 PRA Conseq Change (+20) 5a Medium TASCS Medium (3) (High) (FAC) (High)

AFV 5a Medium Medium TASCS, TT Medium 26 3 26 3 38 Revised Exemption Size (3) (High) (FAC) (High) (+12) 5a Medium TT Medium (3) (High) (FAC) (High)

AFW 6a Low Medium None Low 141 0 141 0 335 Revised Exemption Size (3) (High) (FAC) (High) (+194) 6FS 5a Medium Medium TASS Medium 16 2 16 2 18 2 SG Replacement (+2)

(3) (High) (FAC) (High) 6FWS 6a Low Medium None Low 128 0 128 0 128 0 No Change (3) (High) (FAC) (High) I I MSS 6a Low Medium None Low 197 0 197 0 197 0 No Change SLS 7d Low None None Low 12 0 12 0 12 0 No Change CVCS 5a Medium Medium TT Medium 0 0 2 1 PRA Conseq Change (+2)

CVCS 6a Medium Low TT Medium 11 0 11 0 9 0 PRA Conseq Change (-2)

CVCS 6b Low Low TT Medium 0 0 0 0 No Change CVCS 7a Low Low None Low 47 0 47 0 47 0 No Change Total 2331 66 2547 68 Note 1: Systems are defined in Table 1 Change from original 216 2 PWSCC pressurized water stress corrosion cracking TASCS thermal stratification, cycling, and striping TT thermal transient FAC flow-accelerated corrosion

Attachment NOC-AE-12002837 Page 7 of 8 TABLE 4 (Modified)

COMPARISON BETWEEN ORIGINAL AND UPDATED RI-ISI PROGRAMS BY RISK CATEGORY - STP UNIT 2 Risk Failure Potential Original Interval 3 Consequence CC N-560 CC N-578 Total Reason for Change in Category Rank Rank Degradation Category WldWWelRI-It WeldWeld Mechanism Weld RI-I SI Weld I Weld RI-ISI Count Count Count Count RCS 2 High High TASCS Medium RCS 2 High High TASCS, TT Medium 2 High TASCS, TT Medium RCS (2) (High) High (PWSCC) (Medium) 135 46 135 46 137 35 PRA Conseq Change (+2)

RCS 2 High High TT Medium 2 High TT Medium (2) (High) (PWSCC) (Medium)

RCS 4 Medium High None Low 4 Medium None Low 206 11 206 11 214 22 SG Replacement (+8)

(2) (High) (PWSCC) (Medium)

RCS 5a Medium Medium TASCS Medium RCS 5a Medium Medium TASCS, TT Medium 12 1 12 1 12 2 No Change RCS 5a Medium Medium TT Medium RCS 6a Low Medium None Low 35 0 35 0 35 0 No Change RCS 6b Low Low "T Medium 2 0 2 0 0 0 PRA Conseq Change (-2)

RCS 7a Low Low None Low 10 0 10 0 10 0 No Change SIS 5a Medium Medium TT, IGSCC Medium 3 0 3 0 3 1 No Change SIS 6a Low Medium None Low 23 0 553 0 576 0 348 0 PRA Conseq Change (-228)

SIS 6b Low Low "T, IGSCC Medium 3 0 3 0 3 0 No Change SIS 7a Low Low None Low 33 0 140 0 173 0 401 0 PRA Conseq Change (+228)

RHRS 5a Medium Medium TT Medium 12 2 12 2 12 2 No Change RHRS 6 Low Medium None Low 65 0 393 0 393 0 No Change RHRS 6a Low Medium None Low 328 0 RHRS 7 Low Low None Low 5 0 26 0 26 0 No Change RHRS 7a Low Low None Low 21 0 ________________

CSS 6a Low Medium None Low 118 0 118 0 97 0 PRA Conseq Change (-21)

Attachment NOC-AE-1 2002837 Page 8 of 8 TABLE 4 (continued) (Modified)

COMPARISON BETWEEN ORIGINAL AND UPDATED RI-ISI PROGRAMS BY RISK CATEGORY - STP UNIT 2 Risk Failure Potential Original Interval 3 System(I) Consequence CC N-560 CC N-578 Total Weld RI-ISI ReasonWeld forCount Change in Rank Rank Degradation Category Weld Weld Weld Reld Count W Category Mechanism RI-ISI RI-ISI RI-ISICon Count Count Count CSS 7a Low Low None Low 0 0 21 0 PRA Conseq Change (+21)

AFW 5a 5 Medium Meim Medium TASCS (A) Medium (ih (3) (High) (FAC) (High)

Medium TASCS, TT Medium 29 3 29 3 40 4 Revised Exemption Size (+7)

AFW 5a Medium (3) (High) (FAC) (High) SG Replacement (+4) 5a Medium TT Medium (3) (High) (FAC) (High)

AFW 6a Low Medium None Low 133 0 133 0 337 0Revised Exemption Size (3) (High) (FAC) (High) (+204) 6FWS 5a Medium Medium TASOS Medium 13 2 13 2 18 2 SG Replacement (+5)

(3) (High) (FAC) (High) 6FWS 6a Low Medium None Low 107 0 107 0 133 0 SG Replacement (+26)

(3) (High) (FAC) (High)

MSS 6a Low Medium None Low 201 0 201 0 201 0 No Change SLS 7d Low None None Low 8 0 8 0 8 0 No Change CVCS 5a Medium Medium TT Medium 0 0 2 1 PRA Conseq Change (+2)

CVCS 6a Medium Low TV Medium 4 0 4 0 2 0 PRA Conseq Change (-2)

CVCS 6b Low Low TT Medium 8 0 8 0 8 0 No Change CVCS 7a Low Low None Low 36 0 36 0 36 0 No Change Total 2243 65 2497 69 Note 1: Systems are defined in Table 2 Change from original 254 4 PWSCC pressurized water stress corrosion cracking TASCS thermal stratification, cycling, and striping

-1 thermal transient FAC flow-accelerated corrosion