RS-07-123, Additional Information Supporting Risk-Informed Inservice Inspection Relief Request
| ML072530024 | |
| Person / Time | |
|---|---|
| Site: | Byron  |
| Issue date: | 09/07/2007 |
| From: | Simpson P Exelon Nuclear |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| RS-07-123 | |
| Download: ML072530024 (10) | |
Text
Exelon Generation www.exeloncorp.com 4 300 Winfield Road Warrenville, IL 60555 RS-07-123 September 7, 2007 U. S. Nuclear Regulatory Commission ATTN : Document Control Desk Washington, DC 20555-0001 Byron Station, Units 1 and 2 Facility Operating License Nos. NPF-37 and NPF-66 NRC Docket Nos. STN 50-454 and STN 50-455
- Exelom, Nuclear Subject :
Additional Information Supporting Risk-Informed Inservice Inspection Relief Request
References:
1. Letter from D. M. Hoots (Exelon Generation Company, LLC) to U. S. NRC, "Byron Station, Units 1 and 2, Transmittal of Inservice Inspection Program Plan for the Third Ten year Inspection Interval," dated February 14, 2006
- 2.
Letter from R. F. Kuntz (U. S. NRC) to C. M. Crane (Exelon Generation Company, LLC), "Byron Station, Unit Nos. 1 and 2 - Request for Additional Information Related to Relief Request 13R-02 (TAC Nos. MD3855 and MD3856," dated August 8, 2007 In Reference 1, Exelon Generation Company, LLC (EGC) submitted the third ten-year inspection interval Inservice Inspection Program for Byron Station, Units 1 and 2. Section 8 of the Inservice Inspection Program plan contained alternatives to the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code,Section XI, "Rules for Inspection and Testing of Components of Light Water Cooled Plants." Relief Request 13R-02 requested NRC approval to continue implementation of alternative risk-informed selection and examination criteria for certain pressure retaining piping welds.
In Reference 2, the NRC requested additional information related to Relief Request 13R-02. In response to this request, EGC is providing the attached information.
September 7, 2007 U. S. Nuclear Regulatory Commission Page 2 There are no regulatory commitments contained in this letter. Should you have any questions related to this letter, please contact Mr. Kenneth M. Nicely at (630) 657-2803.
Respectfully,
, U-U
~Iatrick R. Simpson Manager, Licensing Attachment : Response to Request for Additional Information
NRC Request 1 It is not clear what is meant by a more refined methodology for implementing additional examinations. How do the alternative criteria for additional examinations contained in Code Case N-578-1 provide a more refined methodology?
Response
Additional examinations are discussed in Section 3.6.6.2 of Electric Power Research Institute (EPRI) TR-112657, "Revised Risk-Informed Inservice Inspection Evaluation Procedure,"
Revision B-A. This section discusses requirements for additional examinations at a high level, based on service conditions, degradation mechanisms, and the performance of evaluations to determine the scope of additional examinations.
A more specific discussion regarding the requirements for additional examinations is contained within paragraph -2430 of American Society of Mechanical Engineers (ASME) Code Case N-578-1, "Risk-Informed Requirements for Class 1, 2, or 3 Piping, Method B." Exelon Generation Company, LLC's (EGC's) statement that "the alternative criteria for additional examinations contained in Code Case N-578-1 provides a more refined methodology for implementing necessary additional examinations" refers to the additional specificity and clarity discussed within paragraph -2430 of ASME Code Case N-578-1, when compared to the high level discussion in EPRI TR-112657.
NRC Request 2 Please verify that any additional examinations required due to the identification of flaws or relevant conditions will be conducted during the current outage.
Response
ATTACHMENT Response to Request for Additional Information While not explicitly specified in paragraph -2430 of Code Case N-578-1, EGC intends to perform additional examinations required due to the identification of flaws or relevant conditions, which exceed the acceptance standards, during the current outage.
NRC. Request 3 Discuss how ultrasonic examinations will be performed for each degradation mechanism. What volumes will be examined and what techniques will be used?
Response
Section 4 of EPRI TR-112657 states "Application of RI-ISI uses NDE techniques that are designed to be effective for specific degradation mechanisms and examination locations."
Section 4 also identifies methods of examination for each degradation mechanism with the primary method being ultrasonic testing (UT) techniques. However, EPRI TR-112657 does not identify the examination volumes for components without a degradation mechanism. In addition, EPRI TR-112657 does not specify examination volumes and methods for socket welds.
EGC has requested to use the examination methods from Code Case N-578-1 instead of the methods from EPRI TR-112657, except that the volumetric method will be used to examine primary water stress corrosion cracking (PWSCC), as discussed in response to NRC Request 5 Page 1 of 8
ATTACHMENT Response to Request for Additional Information below. In addition, the VT-2 examination method will be used to examine socket welds in accordance with the provisions of Code Case N-578-1, Table 1.
The examination figures specified in Section 4 of EPRI TR-112657 will be used to determine the examination volume based on the degradation mechanism and component configuration.
Table 1 below provides a comparison of degradation mechanisms, examinations volumes, and examination methods.
Page 2 of 8 Table 1 : Applicable Degradation Mechanisms, Examination Volumes, and Examination Methods DEGRADATION MECHANISM (INITIALS) N-578-1 ITEM NUMBER TR-112657 SECTION XI EXAMINATION VOLUME TR-112657 N-578-1 EXAMINATION CONFIGURATION EXAM EXAM COMMENTS EXAM EXAM METHOD FIGURE FIGURE METHOD METHOD COMMENTS Thermal Fatigue (TF) R1.11 Butt-welds 4-1 IWB-2500-8(c) RI-ISI volume increased Volumetric Volumetric No difference in 4-2 IWC-2500-7(a) beyond counterbore, and is method.
applied to smaller piping diameters and thicknesses.
Sweep-o-Lets 4-3 IWB-2500-9 RI-ISI volume shifted to blend area of branch connection fitting.
IWC-2500-11 UT not required for Class 2.
Weld-o-Lets 4-4 IWB-2500-10 RI-ISI volume increased for thicker materials.
IWC-2500-10 UT not required for Class 2.
Primary Water Stress Corrosion Cracking (PWSCC) R1.15 Butt-welds 4-9 IWB-2500-8(c) RI-ISI includes all VT-2 or VT-2 Byron has susceptible base materials in Volumetric adopted visual volume requirements. IWB-and volumetric 2500-8(c) volume methods per determined by weld MRP-139 along dimensions.
with the RI-ISI Program.
Intergranular Stress Corrosion Cracking (IGSCC) R1.16 Butt-welds 4-10 IWB-2500-8(c) RI-ISI volume increased Volumetric Volumetric No difference in 4-11 IWC-2500-7(a) beyond counterbore, and is method.
applied to smaller piping diameters and thicknesses.
Sweep-o-Lets 4-12 IWB-2500-9 RI-ISI volume increased for thicker materials.
IWC-2500-11 UT not required for Class 2.
Weld-o-Lets 4-13 IWB-2500-10 RI-ISI volume increased for thicker materials.
IWC-2500-10 UT not required for Class 2.
Microbiologically-Induced Corrosion (MIC) R1.17 Butt-Welds 4-15 N/A Section XI does not address Volumetric Volumetric No difference in this examination type.
or Visual or Visual method.
Currently, all MIC susceptible components are within the station Service Water Program.
NRC Request 4 Please describe how volumetric examinations will be performed. Will volumetric examinations include the volume required for ASME Section XI examinations? Will ASME Section XI, Appendix Vill qualified examiners and procedures be used for all volumetric exams? Will the examination volume be scanned for both axial and transverse indications for all exams?
Response
ATTACHMENT Response to Request for Additional Information in general, EGC plans to use UT techniques for volumetric examinations.
For the components addressed by the Risk Informed Inservice Inspection (RI-ISI) program, ASME Section XI focuses primarily on weld examinations. Risk informed examination volumes also include portions of piping and fitting base materials that are susceptible to particular degradation mechanisms. The examination figures specified in Section 4 of EPRI TR-112657 differ from the examination figures in ASME Section XI for certain component configurations and evaluated degradations. The differences between the examination programs are summarized in Table 1 above. Table 1 is limited to the current degradation mechanisms and component configurations at Byron Station.
The ASME Section XI, Mandatory Appendix I, "Ultrasonic Examinations," specifies that UT examination procedures, equipment, and personnel used to detect and size flaws in piping welds shall be qualified by performance demonstration in accordance with ASME Section XI Appendix VIII, "Performance Demonstration for Ultrasonic Examination Systems." The RI-ISI program complies with Appendix VIII for weld examinations. In cases where the examination Page 3 of 8 Table 1 : Applicable Degradation Mechanisms, Examination Volumes, and Examination Methods DEGRADATION MECHANISM (INITIALS) N-578-1 ITEM NUMBER TR-112657 SECTION XI EXAMINATION VOLUME TR-112657 N-578-1 EXAMINATION CONFIGURATION EXAM EXAM COMMENTS EXAM EXAM METHOD FIGURE FIGURE METHOD METHOD COMMENTS Flow Accelerated Corrosion (FAC) R1.18 Piping Components 4-16 thru N/A Section XI does not address Volumetric Volumetric No difference in 4-22 this examination type.
per FAC method.
Currently, all FAC program susceptible components are within the station FAC Program.
No Damage Mechanism R1.20 Butt-welds N/A IWB-2500-8(c) Examination requirements N/A Volumetric Examination IWC-2500-7(a) are not identified in TR-requirements 112657. Examination are not identified figures are taken from N-in TR-112657.
Sweep-o-Lets IWB-2500-9 578-1 and include the expanded exam volume Weld-o-Lets IWB-2500-10 specified in Table 1 Note(1).
All Damage Mechanisms Socket Welds N/A N/A No volumetric examination N/A VT-2 Examination figure specified.
requirements are taken from N-578-1 Table 1 Note (12).
ATTACHMENT Response to Request for Additional Information requirements cannot be met, EGC will submit a request for relief in accordance with 10 CFR 50.55a, "Codes and standards."
The examination methods are designed to be effective for specific degradation mechanisms and examination locations. The potential directions for flaw propagation are in both the axial and transverse orientations. The volumetric scanning will be in both axial and circumferential directions to detect the flaws in these orientations.
NRC Request 5 How will dissimilar metal welds be addressed? Discuss in detail the technical basis for including alloy 600 pressure-retaining dissimilar metal welds in your risk-informed inservice inspection, rather than a separate augmented program to the RI-ISI program.
Response
All dissimilar metal (DM) welds, as characterized in ASME Section XI IWA-9000, have been evaluated for failure potential and consequence of failure along with the other non-exempt piping. The piping segments containing the DM welds were classified into the appropriate RI-ISI categories, and appropriate elements were selected per the category requirements for examination during the third inspection interval. The examination requirements of the RI-ISI program are applied to the selected components.
EGC intends to perform the mandatory visual and volumetric examinations from MRP-139 throughout the inspection interval as an augmented examination program in parallel with the RI-ISI program. Once during the inspection interval, the volumetric examination scheduled under MRP-139 will also be credited to the RI-ISI program where appropriate. This approach will satisfy the requirements of both the RI-ISI and the MRP-139 programs, and will ensure that the inspection program will address the industry issue regarding PWSCC in Alloy 600 components.
NRC Request 6 Provide information regarding : examinations/system/components/degradation mechanisms/class, etc. similar to that provided in Attachment 1 of the Callaway submittal dated March 28, 2006 (Agencywide Documents Access and Management System Accession No. ML061010704). The information should show a summary of the changes in inspections from the Section XI program and changes from the previous risk informed-inservice inspection (RI-ISI) program to the proposed RI-ISI program.
Response
The requested information is provided in Tables 2 and 3 below.
ATTACHMENT Response to Request for Additional Information Page 5 of 8 Table 2 : System/Selection Comparisons Between ASME Section XI and Risk Informed Programs for Unit 1 N
UNIT 1 : 2"° INTERVAL ASME XI (1989 EDITION)
UNIT 1 : 2"° INTERVAL RI-ISI (1989 EDITION)
I~
UNIT 1 : 3R° INTERVAL RI-ISI (2001 EDITION/2003 ADDENDA)
CAT.
WELD WELD RISK CONSEQ.
FAILURE POTENTIAL WELD RI-ISI RISK CONSEQ.
FAILURE POTENTIAL WELD RI-ISI i
COUNT SEL.
CAT.
RANK RANK DM(s)
RANK COUNT SEL.
CAT.
RANK RANK DM(s)
RANK COUNT SEL.
Note' 617 16 MS Note 3 C_F_2 181 14©© B-F 16 16 PWSCC i
176 58 RC None 400 66 B-J 577 133 RY
ATTACHMENT Response to Request for Additional Information Page 6 of 8 Table 3 : System/Selection Comparisons Between ASME Section XI and Risk Informed Programs for Unit 2 UNIT 2 : 2"° INTERVAL ASME XI (1989 EDITION)
UNIT 2 : 2 N° INTERVAL RI-ISI (1989 EDITION)
UNIT 2 : 3R° INTERVAL RI-ISI (2001 EDITION/2003 ADDENDA) m WELD WELD RISK CONSEQ.
FAILURE POTENTIAL WELD RI-ISI RISK CONSEQ.
FAILURE POTENTIAL WELD RI-ISI CAT.
COUNT SEL.
CAT.
RANK RANK DM(s)
RANK COUNT SEL.
CAT.
RANK RANK DM(S)
RANK COUNT SEL.
Note' i
CS CV FW Note3 Table 2: System/Selection Comparisons Between ASME Section XI and Risk Informed Programs for Unit 1 N
UNIT 1 : 2"° INTERVAL UNIT 1 : 2"° INTERVAL RI-ISI (1989 EDITION)
UNIT 1 : 3R° INTERVAL RI-ISI (2001 EDITIOW2003 ADDENDA)
ASME XI (1989 EDITION)
N m
WELD WELD RISK CONSEQ.
FAILURE POTENTIAL WELD RI-ISI RISK CONSEO.
FAILURE POTENTIAL WELD RI-ISI CAT.
COUNT SEL.
CAT.
RANK RANK DM(s)
RANK COUNT SEL.
CAT.
RANK RANK DM(s)
RANK COUNT SEL.
4 M
H None L
278 28 4
M H
None L
267 27 B-J 522 87 SI 5
M M
TF IGSCC M
146 17 5
M M
TF IGSCC M
254 27 C-F-1 422 34 6/7 L
520 0
6/7 L
423 0
SX C-F-2 282 22 2
H H
282 Note 2 2
H H
282 Note 2 C-F-1 4
0 60 24 0
6/7 24 0
VQ C-F-2 20 1
Abbreviations :
ATTACHMENT Response to Request for Additional Information SX - Essential Service Water VQ - Containment Purge CAT. - Category SEL. - Selection CONSEQ. - Consequence DM - Degradation Mechanism Page 7 of 8 Table 3 : System/Selectlon Comparisons Between ASME Section XI and Risk Informed Programs far Unit 2 w
UNIT 2: 2"° INTERVAL ASME XI (1989 EDITION)
UNIT 2 : 2" ° INTERVAL RI4SI (1989 EDITION)
UNIT 2 : 3R° INTERVAL RI-ISI (2001 EDITION/20D ADDENDA)
WELD WELD RISK CONSEO.
FAILURE POTENTIAL WELD RI4SI RISK CONSEO.
FAILURE POTENTIAL WELD RI-ISI 3
CAT.
COUNT SEL.
CAT.
RANK RANK DM(s)
RANK COUNT SEL.
CAT.
RANK RANK DM(s)
RANK COUNT SEL.
MS 3
H M
FAC H
8 Note 2 1
H H
FAC H
8 Note 2 Note 3 C-F-2 171 14 6/7 None 163 0
4 M
H None L
163 16 B-F 16 16 2
H H
165 42 2
H H
168 52 RC H
None L
41 4
M H
None L
377 41 4
M 367 5
M M
TF IGSCC M
2 0
B-J 529 125 6/7 L
13 0
6/7 L
8 0
RH B-J 70 18 4
M H
None L
215 22 4
M H
None L
215 22 C-F-1 245 18 6/7 100 0
6/7 100 0
RY B -F 6
6 2
H H
TF PWSCC M
37 10 2
H H
TF PWSCC M
34 13 B-J 112 30 4
M H
None L
81 9
4 M
H None L
84 12 B-J 519 126 4
M H
None L
262 26 4
M H
None L
243 25 SI 5
M M
TF IGSCC M
160 16 5
M M
TF IGSCC M
253 26 C-F-1 413 33 617 L
510 0
617 L
436 0
SX C-F-2 294 22 2
H H
294 Note 2 2
H H
294 Note VQ C-F-1 4
0 6/7 24 0
617 24 0
C-F-2 20 1
Systems :
AF - Auxiliary Feedwater FW - Main Feedwater RH - Residual Heat Removal CS - Containment Spray MS - Main Steam RY - Pressurizer Piping CV - Chemical and Volume Control RC - Reactor Coolant SI - Safety Injection
ATTACHMENT Response to Request for Additional Information Ranking :
L - Low M - Medium H - High Note : Low Risk Categories 6 and 7 do not require examinations. The tables do not show the six possible combinations of Failure Potential and Consequence rankings that result in a Low Risk ranking.
Degradation Mechanisms (Initials) (RI-ISI Item Number) (Name):
PWSCC R1.15 Primary Water Stress Corrosion Cracking FAC R1.18 Flow Accelerated Corrosion IGSCC R1.16 Intergranular Stress Corrosion Cracking PIT R1.17 Pitting MIC R1.17 Microbiologically-Induced Corrosion TF R1.11 Thermal Fatigue (includes TT and TASCS mechanisms)
None R1.20 No Damage Mechanism Note' : Auxiliary Feedwater piping nominal pipe size 4" and smaller was previously exempted from examination in the 2"d inspection interval (1989 Edition) by paragraph IWC-1222. In the 3`d inspection interval (2001 Edition through the 2003 Addenda), these piping segments are included in the RI-ISI program and are subject to examination per IWC-1222(b).
Note 2 : Systems or portions of systems that have a degradation mechanism addressed by a separate augmented program are examined under the augmented program for that particular degradation mechanism. If no other degradation mechanism is identified, the element is removed from the RI-ISI element selection population and retained in the appropriate augmented inspection program.
The augmented programs are the Flow Accelerated Corrosion program for FAC and the Service Water program for MIC and PIT. If another degradation mechanism is present, which is not addressed by the augmented program, the remaining degradation mechanism is examined as part of the RI-ISI program.
Note 3 : To assist in the comparison between programs, the inclusion of the High Energy Line Break (HELB) Augmented program is not shown. The tables are limited to the non-exempt Class 1 and 2 elements subject to examination under the ASME Section XI program and subsequently incorporated into the RI-ISI program. The merger of the RI-ISI and HELB programs occurred in the third inspection interval using the methods specified in EPRI TR-1006937. This merger involved the addition of welds beyond the Class 2 boundary within the break exclusion area.