ML18017A376
| ML18017A376 | |
| Person / Time | |
|---|---|
| Site: | Limerick  |
| Issue date: | 01/17/2018 |
| From: | Jim Barstow Exelon Generation Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| Download: ML18017A376 (10) | |
Text
Exelon Generation January 17, 2018 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001 Limerick Generating Station, Units 1 and 2 200 Exelon Way Kennett Square. PA 19348 www.exeloncorp.com 10 CFR 50.55a Renewed Facility Operating License Nos. NPF-39 and NPF-85 NRC Docket Nos. 50-352 and 50-353
Subject:
End of Interval Relief Request Associated with the Third Ten-Year lnservice Inspection (ISi) Interval
References:
- 1) Letter from J. Barstow (Exelon Generation Company, LLC) to U.S. Nuclear Regulatory Commission, "End of Interval Relief Request Associated with the Third Ten-Year lnservice Inspection (ISi) Interval," dated September 29,2017
- 2) Email from V. Sreenivas (U.S. Nuclear Regulatory Commission) to T.
Loomis (Exelon Generation Company, LLC), "Limerick Units 1 and 2:
Request for Additional Information (RAI): Relief Request 13R-23 Regarding Limited Examination Coverage (EPID: L-2017-LLR-0098)," dated December 19, 2017 In the Reference 1 letter, in accordance with 1 O CFR 50.55a, "Codes and standards,"
paragraph (g)(5)(iii), Exelon Generation Company, LLC (Exelon), requested relief from the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel (B&PV)
Code,Section XI, "Rules for lnservice Inspection of Nuclear Power Plant Components." This relief request applies to the third ten-year lnservice Inspection (ISi) interval, which concluded on January 31, 2017, for the Limerick Generating Station, Units 1 and 2. The third ten-year ISi interval complied with the ASME Boiler and Pressure Vessel Code,Section XI, 2001 Edition with 2003 Addenda.
In the Reference 2 letter, the U.S. Nuclear Regulatory Commission requested additional information. Attached is our response.
There are no regulatory commitments in this response.
End of Interval Relief Requests January 17, 2018 Page 2 If you have any questions concerning this response, please contact Tom Loomis at (610) 765-5510.
Respectfully, James Barstow Director - Licensing & Regulatory Affairs Exelon Generation Company, LLC
Attachment:
End of Interval Relief Request Associated with the Third Ten-Year lnservice Inspection Interval - Response to Request for Additional Information cc: USNRC Region I, Regional Administrator USNRC Senior Resident Inspector, LGS USNRC Project Manager, LGS R. R. Janati, Pennsylvania Bureau of Radiation Protection
Attachment End of Interval Relief Request Associated with the Third Ten-Year lnservice Inspection Interval - Response to Request for Additional Information
Response to Request for Additional Information Page 1 By letter dated September 29, 2017 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML17275A202), Exelon Generation Company, LLC (the licensee) submitted Relief Request l3R-23 to the U.S. Nuclear Regulatory Commission (NRG or the Commission) for the third 10-year inservice inspection interval of Limerick Generating Station (Limerick), Units 1 and 2. In its submittal of Relief Request 13R-23, the licensee requested relief from the examination coverage requirements of Section XI, "Rules for lnservice Inspection of Nuclear Power Plant Components," of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code), applicable to certain ASME Code Class 1 and 2 vessel welds and nozzle inner radii. Specifically, pursuant to Title 10 of the Code of Federal Regulations (1 O CFR) 50.55a(g)(5)(iii), the licensee requested relief on the basis that achieving the ASME Code-required examination coverage for the subject components in Relief Request l3R-23 is impractical. Section 50.55a(g)(6)(i) of 1 O CFR states that the Commission may grant such relief and may impose such alternative requirements as it determines are authorized by law; will not endanger life or property or the common defense and security; and are otherwise in the public interest, giving due consideration to the burden upon the licensee that could result if the requirements were imposed on the facility. In order to make a determination that there is reasonable assurance of structural integrity and leaktightness (and thus the request will not endanger life and property), the NRG staff requires responses to the following requests for additional information (RAls) to complete the review of Relief Request 13R-23.
RAI 1
Table 13R-23.1, "Limerick Generating Station, Unit 1 - List of Components with Limited Examination Coverage," of Attachment 1 of the submittal states that four indications were found during the examination of the weld BF (600290), "Shell Ring No. 2 Vertical Seam Weld (RPV},"
which is an ASME Code Examination Category B-A, Item No. 81.12 weld. The licensee determined the four indications to be acceptable per ASME Section XI.
The NRG staff requests the following regarding the four indications:
(a) Clarify that the four indications meet the acceptance standards of IWB-3510.1, "Allowable Planar Flaws," of Section XI of the ASME Code.
(b) To ensure that the four indications are not new indications that could present a challenge to the structural integrity of the subject weld, the NRG staff requests the licensee to state whether the four indications were recorded in previous inservice inspection intervals. If they were not recorded, please explain why they were not recorded. Also, state whether there has been any other plant-specific degradation of the subject weld.
Response
(a) All four indications identified in 1 R14 (2012) were determined to be embedded indications with no discernable through-wall dimensions, and therefore, meet the acceptance standards of ASME Section XI, Table IWB-3510-1.
(b) Weld BF (600290) was previously examined during the second lnservice Inspection (ISi) interval in 1 R09 (2002) with two indications identified. The two indications were evaluated and determined to meet the acceptance standards of ASME Section XI, Table IWB-3510-1.
The two indications identified in 1 R09 were also identified in 1 R 14 (2012) and remain unchanged.
Response to Request for Additional Information Page2 The two additional indications identified in 1R14 (2012) are attributed to enhancements in NOE technology since the 1 R09 (2002) exam. These two indications were found within the "near field" which is an area in the examination beam where it is difficult to predict the signal amplitude from a reflector due to the constructive and destructive interference of the multiple waves which originate from the transducer face. However, with a better discernable sectoral scan display, the indications could be confirmed and characterized during 1 R14 (2012).
Both indications were evaluated and determined to meet the acceptance standards of ASME Section XI, Table IWB-3510-1.
No additional indications or plant-specific degradation were identified in weld BF during the third ISi interval.
RAl2:
Under the "Applicable Code Requirements" section of Relief Request l3-R23, the licensee states that the extent of examination requirement for Examination Category B-D, Item Number 83.90, per Table IWB-2500-1, requires a volumetric examination of all nozzle-to-vessel welds. The licensee further states that during the third interval, Limerick, Units 1 and 2, was approved to use ASME Code Case N-702 in a safety evaluation report dated September 9, 201 O (ADAMS Accession No. ML102390467) for Relief Request 13R-14. The licensee additionally stated that, as allowed by ASME Code Case N-613-1, Limerick, Units 1 and 2, performed a volumetric examination using a reduced examination volume (A-B-C-D-E-F-G-H) of Figures 1, 2, and 3 of the code case in lieu of the previous examination volumes of ASME Section XI, Figures IWB-2500-7(a), (b), and (c).
Code Case N-613-1 allows a modification to the examination volume to 1/2 inch on either side of the weld for reactor pressure vessel nozzle-to-vessel welds as shown in Figure IWB-2500-7, (a),
(b), and (c). Code Case N-702 allows a reduction in the sample size for BWR RPV nozzle-to-vessel welds from 100 percent of the welds to 25 percent of the welds of a given type of nozzle. The technical basis of Code Case N-702 does not mention a reduced examination volume for the RPV nozzle-to-vessel welds. Therefore, the NRC staff is concerned that use of both Code Cases N-702 and N-613-1 for the same nozzles may not be consistent with the technical basis of Code Case N-702.
However, the examination coverage diagrams for several of the RPV nozzle-to-vessel welds appear to show that the licensee attempted to examine the full volume specified in Figure IWB-2500-7, rather than the reduced examination volume allowed by Code Case N-613-1.
Therefore, the staff requests that the licensee clarify:
- 1. For which RPV nozzle-to-vessel welds is the reduced examination volume of Code Case N-613-1 being applied?
- 2. Is Code Case N-613-1 being applied to the same nozzle-to-vessel welds for which Code Case N-702 is being applied?
- 3. If so, justify applying Code Case N-613-1 to welds for which Code Case N-702 is also being applied.
Response
Response to Request for Additional Information Page 3
- 1. The reduced volume of Code Case N-613-1 was applied to nozzle-to-vessel welds beginning with the 1R13 (2010) and 2R11 (2011) refuel outages for the Limerick Generating Station, Units 1 and 2. Prior to 2010, examinations were performed in accordance with Figure IWB-2500-7(b). Table RAl-2-1 below identifies the nozzle-to-vessel welds that were examined in the third interval and the resultant coverage obtained after applying the reduced examination volume of Code Case N-613-1. None were limited except for the N4D nozzle-to-vessel weld on both Units, which was included in this relief request.
Table RAl-2-1: Nozzle-to-vessel welds that utilize Code Case N-613-1 Unit Nozzle Description Outage Coverage Results Comments Examined Obtained 1
N1A Recirculation 1R14 91.4%
RI 9 recordable indications Suction acceptable per Table IWB-3510-1.
1 N1B Recirculation 1R16 99.3%
NRI Suction 1
N2C Recirculation 1R15 98.9%
NRI Discharae 1
N4A Feedwater Inlet 1R14 95.6%
RI 1 recordable indications acceptable per Table IWB-3510-1.
1 N4B Feedwater Inlet 1R15 98.2%
NRI 1
N4C Feedwater Inlet 1R15 98.2%
NRI 1
N4D Feedwater Inlet 1R15 87.3%
NRI 1
N4E Feedwater Inlet 1R14 95.6%
RI 1 recordable indications acceptable per Table IWB-3510-1.
1 N4F Feedwater Inlet 1R14 95.6%
NRI 1
N7 Head Vent 1R16 97.1%
NRI 1
N8B Jet Pump Instrument 1R15 97.5%
NRI 2
N1B Recirculation 2R11 97.2%
NRI Suction 2
N2B Recirculation 2R12 95.8%
NRI Discharqe 2
N2F Recirculation 2R12 95.8%
NRI Discharqe 2
N3B Main Steam 2R11 98.6%
NRI 2
N4A Feedwater Inlet 2R12 95.6%
RI 2 recordable indications acceptable per Table IWB-3510-1.
2 N4C Feedwater Inlet 2R12 95.6%
NRI 2
N4D Feedwater Inlet 2R12 84.2%
NRI 2
N7 Head Vent 2R13 92.0%
NRI 2
N9 CRD Return 2R11 98.5%
NRI RI - Recordable Indication NRI - Non-Recordable Indication
Response to Request for Additional Information Page4
- 2. Code Case N-702 is not applicable to the Feedwater nozzles {N4), the CAD return nozzle
{N9), and the Recirculation Suction Nozzles {N1). Code Case N-702 is applicable to the Recirculation Discharge Nozzles {N2), Main Steam Nozzles {N3), Core Spray Nozzles {NS),
Head Vent and Spare Nozzles {N6 and N7), Jet Pump Instrument Nozzles {NB), and Low Pressure Coolant Injection Nozzles {N17). Table RAl-2-2 identifies the nozzle-to-vessel welds that utilize both Code Case N-613-1 and N-702.
Table RAl-2-2: Nozzle-to-vessel welds that utilize both Code Case N-613-1 and N-702 Unit Nozzle Description Outage Coverage Results Comments Examined Obtained 1
N2C Recirculation 1R15 98.9%
NRI Discharqe 1
N7 Head Vent 1R16 97.1%
NRI 1
N88 Jet Pump Instrument 1R15 97.5%
NRI 2
N28 Recirculation 2R12 95.8%
NRI Discharqe 2
N2F Recirculation 2R12 95.8%
NRI Discharqe 2
N3B Main Steam 2R11 98.6%
NRI 2
N7 Head Vent 2R13 92.0%
NRI 2
N9 CAD Return 2R11 98.5%
NRI RI - Recordable Indication NRI - Non-Recordable Indication
- 3. The technical basis for Code Case N-702 is provided in EPRI Technical Report 1016123, "BWRVIP-108NP: BWR Vessel and Internals Project Technical Basis for the Reduction of Inspection Requirements for the Boiling Water Reactor Nozzle-to-Vessel Shell Welds and Nozzle Blend Radii." At the nozzle-to-vessel shell weld, the BWRVIP-108NP report concluded that the conditional probability of failure is very small {<1x10-s for 40 years) with or without any inservice inspection, and therefore, was technically justified.
Additionally, the BWRVIP-108NP report assumed fabrication and stress corrosion flaws were present in the nozzle-to-vessel weld and not the heat-affected zone or in the base material. The weld itself is examined whether applying Section XI, Figure IWB-2500-7{b) or Code Case N-613-1. The difference is in the amount of base material examined on either side of the weld. Code Case N-613-1 requires examination of the base material for a distance of 1/2" on either side of the weld.Section XI, Figure IWB-2500-7{b) requires examination of base material for a distance of half the shell thickness {ts/2) on both sides of the weld. This reduction in base material examination identified in Code Case N-613-1 was approved for use without condition in Revision 14 of Regulatory Guide 1.147 in August 2005.
Therefore, the technical basis of Code Case N-702 remains applicable even when applying Code Case N-613-1 during inservice inspections because: (1) the conditional probability of failure is very small with or without any inservice inspection, and (2) the nozzle-to-shell weld volume that is examined is the same volume where assumed flaws were evaluated in the BWAVIP-108NP report.
RAI 3
Response to Request for Additional Information Page 5 For the components in ASME Code,Section XI, Examination Categories 8-D, listed in Table 13R-23.1 and Table 13R-23.2, "Limerick Generating Station, Unit 2 - List of Components with Limited Examination Coverage," in Attachment 1 of the submittal, and for the Examination Category C-8, Item No. C2.22 in Table 13R-23.1, the NRC staff requests the licensee to confirm that (1) no recordable indications were found in the components and (2) there has been no plant-specific operating experience regarding degradation of the components.
Response
(1) During the third ISi interval, no recordable indications were identified during examination of the Examination Category 8-D components listed in Table 13R-23.1 or Table 13R-23.2.
During the third ISi interval, no recordable indications were identified during examination of the Examination Category C-8, Item No. C2.22 component listed in Table 13R-23.1.
(2) During the third ISi interval, there has been no plant-specific operating experience related to degradation of the Examination Category 8-D components listed in Table 13R-23.1 or Table l3R-23.2. During the third ISi interval, there has been no plant-specific operating experience related to degradation of the Examination Category C-8, Item No. C2.22 component listed in Table 13R-23.1.
RAl4:
The licensee included an examination coverage plot for nozzle inner radius RHR-HXAR-N41R (244801) of Limerick, Unit 1, on page 17 of Enclosure 1 of the submittal. To gain a better understanding of the examination coverage, the NRC staff requests an examination coverage diagram similar to the other scan diagrams included in the submittal that clearly shows scan lines to the inner radius volume defined in Figures IWC-2500-4(a) or (b) "Nozzle-to-Vessel Welds" of Section XI of the ASME Code.
Response
The examination coverage plot provided on page 17 of Enclosure 1 for the nozzle inner radius RHR-HXAR-N41R (244801) is the only figure included in the examination datasheet. The examination datasheet also included a Nozzle Inner Radius Coverage Calculation Sheet which is contained in Enclosure 1.
Nozzle Inner Radius Coverage Calculation Sheet
- I HITACHI Nozzle Inner Radius Coverage Calculation Sheet Limerick Unit-1, LiR15, 2014 RHR-H><AR-N41R IRHR Heat Exchanger Inner Radius)
CODE CROSS-SECTIONAL AREA TOTAL CODE COVERAGE Required Exam Percent Weld Length =
360 Area sq. in.
Area Scanned of Area Weld length Exam Volume =
3.5 Zone 1-60" A
3.5 2.1 60.0%
180 Zone 1-80" 8
3.5 1.4 40.0%
360
% Total Compasite Coverage=
CODE CROSS-SECTIONAL AREA TOTAL CODE COVERAGE Required Exam Percent Weld Length,.
Area sq. in.
Area Scanned of Area Weld Length Exam Volume=
I
% Total Composite Coverage=
Jl'wade F. Miller GEHltachl Laval Ill-RT, UT, MT, PT and VT*1,2,S
'113/JtJ Comments A -Manual UT was limited due to nozzle to vessel mismatch.
8-Manual UT was limited due to nozzle configuration.
Note - Rounding methods may affect calculated values. Weld length in degrees.
Percent 30.0%
40.0%
70.0%
Percent 0.0%
ReY D 9/llle>