LR-N970667, Requests Approval of Encl Repair Plan for Nozzle to Safe End Weld Associated W/Plant a Core Spray Loop.Action Necessary to Allow Repair of Through Wall Leak Discovered on Weld N5B on 970919

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Requests Approval of Encl Repair Plan for Nozzle to Safe End Weld Associated W/Plant a Core Spray Loop.Action Necessary to Allow Repair of Through Wall Leak Discovered on Weld N5B on 970919
ML20211N473
Person / Time
Site: Hope Creek PSEG icon.png
Issue date: 10/09/1997
From: Storz L
Public Service Enterprise Group
To:
NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LR-N970667, NUDOCS 9710160157
Download: ML20211N473 (18)
v • d • e


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e .c as Company Ltuis F. Stor F%Iic SoNce Electne and Gas Company P o Box 236. Hancocks Dndge. NJ OK138 (0 1 339-5700 se m .n - o.m.."*

OCT 9 1997 LR N970667 United States Nuclear Regulatory Commission Document Control Desk Washington, DC 20555 CORE SPRAY NOZZLE WELD REPAIR PLAN HOPE CREEK GENERATING STATION FACILITY OPERATING LICENSE NPF 57 DOCKET NO. 50 354

References:

1) Letter, Vermont Yankee Nuclear Power Corporation to NRC, FVY 87-07, dated 5/5/86
2) Letter, NRC to Vermont Yankee Power Corporation, dated 6/16/86 Gentlemen:

Pursuant to 10 CFR 50.55a(a)(3), Public Service Electric and Gas Company (PSE&G) requests approval of the attached repair plan for the nozzle to safe end weld associated with the Hope Creek "A" Core Spray loop (Weld NSB). This action is necessary to allow repair of a through wall leak that was discovered on the subject weld on September 19, 1997. Additional detail concerning the discovery of the through wall leak is provided in Attachment 1 to this letter.

The proposed plan for repairing the weld is included in Attachment 2 to this letter. The proposed repair is an engineered structural weld overlay. The structural reinforced weld overlay is designed in accordance with NUREG-0313 " Technical Report on Material /

j Selection and Processing Guidelines for BWR Coolant Pressure Boundary Piping" and /

IWB 3600 of Section XI of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel (B&PV) Code. The design of the weld overlay is consistent with the design of the weld overlay approved and implemented on the Vermont Yankee Core \

Spray system nozzle welds in 1986 (see References 1 and 2) with the exception that inconel 52 will be used as the filler material rather than inconel 82. Although PSE&G is prepared to perform the repair using either Inconel 52 or inconel 82, PSE&G's attached repair plan designates the use of inconel 52. The NRC safety evaluation report (SER) for the Vermont Yankee overlay concluded that the overlay met the ASME Code and 9710160157 9710o9 PDR ADOCK 0500o354 P PDR

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OCT 9 1997 Docum6nt Control Desk 2 LR N970667 NRC staff requirements (see Reference 2). In addition to utilizing the same design, PSE&G plans to implement the same post weld testing requirements that were implemented by Vermont Yankee and to re inspect the weld during the next refueling outage. The PSE&G proposed repair plan describes: 1) the criteria for the design,2) the repair methodology,3) the qualification requirements for procedures and welders, and 4) the examination and testing requirements associated with the repair. The plan also provides the basis for acceptability of the design for Hope Creek. The repair plan is in accordance with Section XI of the ASME Code and Generic Letter 88-01, 'NRC Position on IGSCC in BWR Austenitic Stainless Steel Piping."

PSE&G is also ' submitting information regarding the root cause of the cracking which has been determined to be integranular stress corrosion cracking (IGSCC). The information that supports this conclusion is contained in Attachment 3 to this letter.

Attachment 4 includes information regarding sample expansion and PSE&G's plans regarding inspection of additional welds.

PSE&G currently intends to begin the repair activities on October 17,1997 and requests NRC review and approval of this request by that date.

Should you have any questions regarding this request, we will be pleased to discuss them with you.

Sincerely, gu$ - da.

Attachments (4)

% 4933 a

. OCT 9 1997 Document Control Desk 3 i LR N970667 .

C Mr. H. Miller, Administrator - Region I U. S. Nuclear Regulatory Commission 475 Allendale Road King of Prussia, PA 19406 Mr. D. Jaffe, Licensing Project Manager - HC U. S. Nuclear Regulatory Commission One White Flint North 11555 Rockville Pike Mail Stop 14E21 Rockville, MD 20852 Mr. S. Morris (X24)

USNRC Resident inspector - HC-Mr. K. Tosch, Manager IV Bureau of Nuclear Engineering 33 Arctic Parkway Trenton, NJ 08625

^ ATTACHMENT 1 HOPE CREEK GENERATING STATION 4

FACILITY OPERATING LICENSE NFF 57 i

DOCKET NO. 50 354 DESCRIPTION OF CONDITION  !

i On 19 September 1997, Hope Creek personnel were conducting a routine tour of the j drywell during the seventh refueling outage. During this tour, the personnel noticed i

water dripping and observed that the water was coming from an area near the NSB

, core spray nozzle associated with the "A" Core Spray loop. Radiochemical analyses performed on samples of water taken from the drywellindicated that the fluid was 4

reactor coolant. Further investigation revealed the presence of through wallleaks at the top of the core spray nozzle-to-safe end weld. This placed the operability of the "A" l Core Spray loop in question, and the unit entered Limiting Conditions for Operation i 3,5.2, "ECCS - Shutdown" and 3.4.8, " Structural Integrity." The unit was in Operational Condition 5 at the time of discoverv.

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ATTACHMENT 2 HOPE CREEK GENERATING STATION FACILITY OPERATING LICENSE NPF 57 DOCKET NO. 50 354 CORE SPRAY NOZZLE WELD REPAIR PLAN 1 SCOPE The purpose'of this document is to provide the repair plan for the PSE&G Hope Creek NSB core spray nozzle to safe and weld repair.

2 BACKGROUND During routine inservice inspection at the Hope Creek Nuclear Generating Station in Refueling Outage 7, a through wallleak was identified in the vicinity of the NSB core spray nozzle. Upon further investigation, it was discovered that the leak was a result of three pin holes in the safe end to nozzle weld. The root cause investigation has concluded the defects are due to intergranular stress corrosion cracking (IOSCC) Flaws, although not through wall, were identified at similar locations in the past at several plants (Varmont Yankee, Pilgrim, and Brunswick) and were attributed to IGSCC. Of the various options tb3t were considered to disposition the defects, Public Service Electric & Gas Company (PSE&G) elected to repair the defects using a weld overlay, A similar repair was performed on both core spray nozzles at Vermont Yankee in 1986, however, Alloy 82 filler was used for the repair overlay at Vermont Yankee, whereas Alloy 52 filler will be used at Hope Creek.

Subsequent ' ultrasonic examinations were performed which revealed a flaw extending circumferentially from top dead center approximately 4.1 inches,1.6 inches in one direction and 2.5 inches in the opposite direction, on the ID near the fusion line between the safe end replacement weld, ENiCrFe 3 Alloy 182, to original safe end weld, ERNiCr 3 (Alloy 82) root ENiCrFe 3 (Alloy 182) balance which was performed in 1982. Furthermore the flaw (s) is located greater than 1 inch outward from the core spray _ nozzle to buttering fusion line. The flaw extends partially to fully through wall (see Attachment A). The replacement in 1982 involved replacing the original TP 304 safe end with a NI-Cr Fe SB 166 (Alloy 600) safe end.

The reactor vesselis constructed in accordance with ASME Code Section Ill, Nuclear Vessels, 1968 Edition with Addenda to and including Summer 1970 Addenda and Paragraph NB-3338.2(d)(4) of the Winter 1971 Addenda shall supersede Paragraph l-613(d) of the 1968 Edition. The core spray nozzle is constructed of SA 508 Class 2 low alloy steel, The reactor vessel ISI Program is in accordance with ASME XI,1983 Edition including Summer 1983 Addendum, 3 REPAIR DESCRIPTION The flaws in the weld will not be removed. After vessel drain down, the leak openings will be seal welded using the SMAW process using UNS W86152 (Code Case 21'3) electrodes or manual GTAW using UNS N06052 Alloy 52 filler metal (Code Case 2142). A weld overlay, using UNS N06052 Alloy 52 wire (Code Case 2142), will then be deposited, which will extend from the shoulder of the nozzle outward from the reactor vessel beyond the centerline of the ENiCrFe 3 Alloy 182 replacement safe end attachment weld, on to the safe end (see Attachments B and C). The overlay will extend around the full circumference of the nozzle to safe end weld for the required design length. The repair on the low alloy steel portion of the nozzle will be performed with the temperbead technique using Machine GTAW and Alloy 52 filler metal.

Attachment 2 LR N970667 R:p:Ir Plan After the. seal welding has been performed and PT examination accepted, the area will be pr'eheated to 300*F prior to Machine GTAW of the overlay. Maximum interpass temperature will be 400*F. At least three (3) layers of weld will be deposited (1/8 inch minimum thickness),

which will extend 1/2 inch minimum outward beyond the flaw (s) toward the safe end (see Attachment C). This overlay will be subjected to postheat at 450*F to 550*F and held for 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> minimum. After the nozzle is flooded, the balance of the weld overlay will be deposited with 60*F minimum temperature and ambient plus 50*F maximum interpass temperature, to 0.545 inches minimum final thickness, including the temperbead layers.

The final weld will be PT and UT examined in accordance with ASME lit,1992 Edition, no Addenda (Code Case N 4161) and Code Case N 432, including preservice UT examination in accordance with ASME XI,1992 Edition, including Addenda through 1993 (including Appendices Vil and Vill) and Code Case N 5041, modified for examhation of Ni-Cr Fe overlays.

Prior to initiation of the overlay, the design length will be marked using low stress dies. A second set of marks will be applied approximately 1/2 to 1 inch outside either end of the design overlay length. Punch marks shall be placed at 4 azimuthal locations. The axial distance between each set of marks will be measured and recorded. Following weld overlay application these measurements will be repeated and dimensions recorded to determine the axial shrinkage which occurred during the overlay operation. The thienness after seal welding the flaw (s) and the final weld overlay thickness will be determined using ultrasonics, 4 REPAIR JUSTlFICATION The repair overlay has been designed in accordance with NUREG 0313, Rev 2 and Code Case N 5041 modified for use on the vessel nozzle and Ni Cr Fe safe end and attachment welds. The analytical bases for the design are in accordance with the ASME Code Section XI, 1989 Edition, no Addenda, lWB 3641 as specified in NUREG 0313 Revision 2. The design basis for the repair is a circumferentially oriented flaw which extends 360* around the component and through wall. In addition, potential concems about the toughness of the original safe end attachment weld material are not applicable since no credit is taken, in the design, for the load carrying capability of the remaining component wall ligament. The weld overlay thickness and length will restore the design margins inherent in IWB 3641, including consideration of the flaw. Furthermore, since it has been shown that the weld overlay arrests IGSCC crack growth, degradatic . of the repaired location design margins due to further crack growth into the weld overlay is not a concern. The repair is considered a permanent repair subject to the periodic inspection requirements specified in NUREG-0313 Revision 2.

5 APPLICABLE ASME BOILER AND PRESSURE VESSEL CODES AND CODE CASES FOR THE REPAIR The rules for Class 1 vessels shall apply in accordance with and as modified by the applicable documents listed in this section.

5.1 Section XI,1989 Edition, no Addenda shall be applicable for the repair.

5.2 Code Case N 3891 shall be applicable.

5.3 Code Case N-432 shall be applicable, with modifications as described herein.

5.3.1 Paragraph 2.1(a) - The POR test plate was constructed of SA 533 Grade B Class 1 plate and not SA 508 Class 2 forging. The POR weld filler was ERNiCr-

1 Att:chment 2 LR N970667 R: pair PI:n 4

, 3 Alloy 82 instead of Alloy 52. ASME XI,1992 Edition, no Addenda allows the use of the same P Number Group Number and F Number for Machine GTAW Temperbead Welding Procedure Qualification (POR), rather than the same material specification, grade and class.

5.3.2 Paragraph 2,1 (g) welding consumables will be in accordance with NB 2000, ASME lil,1989 Edition, no Addenda and Code Case 2142.

5.3.3 Paragraph 2.1(h) . Dropweight and impact tests of the weld deposit v ire not performed since the weld deposit is F Number 43. NB 2000 does not require

, impact testing of the nickel alloy weld deposits.

5.3.4 Paragraph 3.0(a) . F.e'. eat will be maintained for the first three (3) layers or 1/8 inch temperbead depo. it thicktiess, whichever is greater, rather than completion of welding. Three (3) hyers of temperbead welding will provide the grain refinement and tempering to reduce the possibility of hydrogen embrittlement in the low alloy steel heat affected zone (HAZ). The POR was performed with preheat until six (6) layers of weld was deposited, 5.3.5 Paragraph 3.0(d)(4) The postheat will be performed after three (3) layers or 1/8 inch temperbead deposit thickness, whichever is greater, has been deposited rather than after completion of the final welr' iverlay. The postheat will provide for hydrogen migration from the temperbe, layers. The POR was performed with preheat until six (6) layers of weld was deposited and then postheat was performed. The balance of welding, for this repair, over the low alloy steel nozzle area, will be performed in accordance with the POR except without preheat or postheat.

5.4 The balance of welding over the balance of the safe end and safe end attachment welds will be performed using machine GTAW in accordance with P Number 43 to P Number 43 base materials welding procedure requirements in accordance with Section Ill,1989 Edition, no Addenda.

5.5 The manual welders and welding procedures shall be qualified in accordance with ASME ll1,1989 Edition, no Addenda, where temperbead welding is not applicable.

SMAW repairs in the temperbead portion of the weld, if required, may be performed in accordance with ASME XI,1989 Edition, no Addenda, using the half bead welding process for dissimilar welding. Other repairs, if required, may be performed using manual GTAW or SMM using procedures qualified in accordance with ASME lil, 1989 Edition, no Addenda.

5.6 Section 111,1989 Edition, rc Addenda shell be applicable for the welding materials, as modified by Code Cases 2142 and 2143.

5.7 Section 111, 1992 Edition, no Addenda, shall be applicable for NDE (Code Case N.

416-1) for the repair overlay, except ultrasonic examination instead of radiographic examination will be performed. PT and UT examination shall be over the areas specified by Code Case N 432 as well as the full weld overlay over the Ni-Cr Fe portions of the safe end and welds. ASME XI,1992 Edition, including Addenda through 1993, including Appendices Vil and Vill, shall be applicable for the preservice UT examination.

Attachment 2 LR.N970667 R:p:Ir Pl:n 5.8 Section XI,1992 Edition shall be applicable for the visual examination (VT 2) (Code Case N 4161) for the post repair leakage testing.

5.9 Code Case N 5041, as mc.dified by Code Case N 432 for use of UNS N06052 Alloy 52 weld filler being deposited on the vessel nozzle and Ni Cr Fe safe end and attachment welds shall be applicable.

6 SPECIFIC REQUIREMENTS 6.1 Seal welding shall be performed using the manual GTAW process using UNS N06052 Alloy 52 (Code Case 2142) filler metal or SMAW using UNS W86152 Alloy 152 electrode (Code Case 2143). The welders and welding procedures shall be in accordance with ASME lit,1989 Edition, no Addenda.

6.2 The seal weld (s) shall be PT examined in accordance with NB 5000, ASME lit,1992 Edition, no Addenda, as required by Code Case N 4161.

6.3 The welding consumables shall be in accordance with NB 2400 and NB 2600, ASME Ill,1989 Edition, no Addenda as modified by Code Cases 2142 and 2143..

6.4 The overlay shall be in accordance with Attachments B and C.

0.5 The overlay weld surfaces and contours shall be prepared suitable for liquid penetrant examination (PT), ultrasonic examination (UT), including preservice ultrasonic examination.

6.6 The temperbead overlay welding operators and welding procedures shall be qualified in accordance with Code Case N-432 (see 5.3). The manual welders and welding procedures shall be qualified in accordance with ASME 111,1989 Edition, no Addenda, where temperbead welding is not applicable.

6.7 For the purposes of repair, when the overlay thickness is within 1/8 inch of the low alloy steel nozzle, Machine GTAW temperbead or SMAW half bead welding shall be performed. SMAW repairs in the temperbead portion of the weld, if required, may be performed in accordance with ASME XI,1989 Edition, no Addenda, using the half bead welding process for dissimilar welding. Other repairs, outside the temperbead area,.if required, may be performed using manual GTAW or SMAW using procedures qualified in accordance with ASME Ill,1989 Edition, no Addenda.

6.8 - The weld overlay shall be PT examined in accordance with NB 5000, ASME lil, 1992 Edition, no Addenda.

6.9 The weld overlay shall be UT examined in accordance with NB 5000, ASME Ill,1992 Edition, no Addenda per Code Case N 4161. The preservice UT examination shall be performed using personnel and procedures qualified in accordance with Appendices Vil and Vill, ASME XI,1992 Edition including 1993 Addenda and Code Case N 5041, modified for UT examination of Ni Cr Fe weld overlays to the extent practical.

Att:chment 2 -

LR.N970667 R:p:Ir Plcn 6.,10 A. system leakage test at operating pressure and temperature shall be performed prior to or immediately after going into service in accordance with ASME XI,1992 Edition, no Addenda, per Code Case N-416-1.

6.11 The repair will be performed in accordance with a Traveler Core Spray Nozzle Repair Package. The Traveler will specify each operation by sequence with sign off required when each sequence is completed. FTl QC, PSE&G and ANil review and witness points will be included therein also. All repair procedures used will be included in the final upgraded Traveler package.

6.12 Repair activities by FTl shall be in accordance with FTl ASME XI QA Program.

Design activities will be performed by Structural Integrity Associates (SIA) in accordance with their QA program.

4 6.13 An NR.1 form shall be completed for the repair in lieu of the ASME XI NIS 2 form.

NR stamping shall not be required.

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. ATTACHMENT 3 HOPE L' 9EK GENERATING STATION FACILITY OPERATING LICENSE NPF 57 DOCKET NO. 50 354 DETERMINATION OF CAUSE OF THROUGH. WALL LEAKAGE

\ 1 J Based upon material susceptibility, ultrasonic test (UT) data, a demonstrated crack l propagation rate, industry experiences, and the absence of conflicting indications, PSE&G has concluded that the cause of the through wallleakage at the NSB Core Spray nozzle-to safe-end weldment is Intergranular Stress Corrosion Cracking (lGSCC) in Alloy 182 weld filler metal. Further details regarding the basis for the root cause j conclusions are provided below.

1. There are three conditions that are required for the occurrence of IGSCC. These i conditions include material susceptibility, an aggressive environment, and stress. >
Each condition is present at the NSB core spray nozzle-to safe end weld.

. The leak has been confirmed to exist in the Alloy 182 weld material, which is a j material that was identified and documented in the early 1980's as being highly  ;

j susceptible to IGSCC. A number of issues surrounding the use of Alloy 182 (and I other weld materials) were addressed in EPRI NP-4443," Evaluation of Safe End l Weld Materials and Safe-End Replacement Experience". This document was issued in 1986. When the Hope Creek safe-ends were replaced in 1982, the use of Alloy 182 weld metal was a standard industry practice by all vessel manufacturers.

. The NSB Core Spray nozzle and safe end experience normal boiling water reactcr water chemistry. This has been demonstrated to be an environment conducive to the initiation and propagation of IGSCC.

. The stresses present in the NSB nozzle are service induced stresses from

, operational activities and residual stresses from welding activities.

2. The defect has been characterized as lGSCC through the use of UT data taken and evaluated during the seventh refueling outage (RFO7). This evaluation supports the conclusion in two different ways: crack characteristics and crack growth rate. Further information concerning the RFO7 UT data is provided below.

. In accordance with PSE&G's Inservice inspection Program, the NSB nozzle was not scheduled for inspection during RFO7. However, upon discovery of the Page 1 of 4

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Attachm:nt 3 LR N970667

. Determinati:n cf Cau;o

,through wallleak and in accordance with the requirements of ASME XI, a UT inspection was peiformed. This examination was performed using techniques noted in General Electric Service Information Letter 455 Rev 1 Supplement 1, *lSi of Additional Alloy 182 Weldments", and NRC Iniormation Notice 90 30,

  • Ultrasonic Inspection Techniques for Dissimilar Metal Joints." The evaluation of this data, as well as a re evaluation of the sixth refueling outage UT data, by General Electric (PSE&G's NDE services supplier) revealed an indication characteristic of IGSCC. Data obtained using a 60 degree refracted longitudinal wave revealed a circumferential indication measuring 3.3 inches in length in the RFO6 data and 4.1 inches in length in the current data. The response signels had the characteristics of a crack in that the signals fluctuated with time as the transducer was moved parallel to the crack. This was the expected response from an IGSCC crack. The data also indicated a broad multiple faceted pattern of IGSCC and the echo dynamic travel of a through wall direction flaw.

This data was also reviewed by EPRI NDE Center personnel and by PSE&G ISI personnel. While these evaluations noted additional characteristics (i.e., axial indications and upstream / downstream indications), both were in full agreement concerning the characterization of the indication.

The data from the last scheduled UT (RF06 in 1995) was evaluated by personnel from the EPRI NDE Center. The evaluation of this data revealed an indicailon in the same location and with approximately 40% through wall penetration (0.56 inches). With a nominal thickness of 1.25 inches at the centerline of the weld, this would indicate a crack propagation of 0.69 inches during the past operating cycle. The upper bound IGSCC crack propagation rate is SE 05 inch /hr (BWR Owners Group Letter BWROG 92090 to NRC dated 6 October 1992). Taking account of the actual operating history of Hope Creek during the previous cycle, the expected crack propagation would be 0.63 inches. The actual crack propagation is consistent with this value.

3. IGSCC has been observed on multiple occasions in the Nuclear Indus ry, an:1 the life cycle characteristics of Hope Creek are consistent with those of ch'y r boiling water reactors exhibiting this phenomenon. The following examples include occurrences of IGSCC in both stainless steel and Alloy 182.

Page 2 of 4

Attachm:nt 3 LR N970667 Determinatl*n cf Crus) i i e ,Through wallIGSCC in the recirculation piping safe-ends at Duane Arnold in j 1978. This unit is a 538 MWe BWR-4 that was four years into its licensed li'etime l at the time of discovery (NUREG 0531).

e Pin hole leaks at the recirculation piping safe ends at Nine Mile Point Unit 1 in 1982. This unit is a 610 MWe BWR-5 that was 12 years into its licensed lifetime at the time of discovery (IE Information Notice 82-39).

j e Reportable indications in the heat affected zones of piping welds at Monticello and at Hatch Unit 1 in 1982. Monticello is a 536 MWe BWR 3 that was 11 years ,

1 into its licensed lifetime at the time of discovery, and Hatch Unit 1 a a 786 MWe l l BWR-4 that was eight years into its licensed lifetime at the time of discovery l (INPO SER 69 82). l

e Discovery of IGSCC in the inconel 162 weld butter of the recirculat!on piping safe ends at Pilgrim in 1984. This unit is a 679 MWe BWR-3 that was 12 years into its licensed lifetime at the time of discovery (IE Information Notice 84-41).  ;

e i Discovery of two pin-hole leaks in the safe-end to reducer weld at Browns Ferry  !

L Unit 3 in 1984. This unit is a 1065 MWe BWR-4 that was seven years into its j licensed lifetime at the time of discovery (IE Information Notice W-41).

i e Discovery of IGSCC in the core spray nozzle to safe end we'd et Vermont Yankee in 1986. The failure was detected in the Alloy 182 weid butter. This unit i is a 514 MWe BWR-4 that was 13 years into its licensed lifetime at the time of l discovery (Vermont Yankee Nuclear Power Corporation Letter FVY 86-3S to j USNRC---Core Spray Nozzle Weld Overlay --dated 5 May 1986).

4 e Discovery of lGSCC in the recirculation nozzle safe-end welds at Chinshan Unit 2 in 1987. The crack initiated in the Alloy 182 weld butter. This unit is a 604 MWe

BWR-4 that was 9 years into its licensed lifetime at the time of discovery (General Electric Proprietary keport PMWG G-537---Update of Nozzle / Alloy 182 Butter Cracking).

. Discovery of three pin-hole leaks in the core spray nozzle to safe end weld at j Hope Creek in 1997. The failure initiated in the Alloy 182 weld butter. This unit is a 1067 MWe BWR-4 that was 11 years into its licensed lifetime at the time of discovery, Page 3 of 4

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l Attachm:nt 3 LR N970667 Det:rminati:n cf Cau 3 1

4. , In addition to the evidence obtained from sources noted in items 13, a materials failure analysis was performed by PSE&G metallurgists. Three possible failure origins were considered: safe end failure, nozzle failure, and weld failure.

Possible failure modes were considered for each of these possibilities, and the likelihood of each failure mode was also considered. The possible failure modes for safe-end and nozzle failure were considered to have a low probability. This eliminated both safe end and nozzle failure, and these conclusions were confirmed by the current UT data showing the failure to be in the weld material.

Of the several possible failure modes for the weld,90% were assessed as having a low probability and 7% were assessed as having a medium probability.

Only a single failure mode, IGSCC, was assessed as having a high probability.

5. The evidence presented in items 1 through 4 to support PSE&G's analysis concerning the cause of the through wall cracking is substantial and without conflictir.g indications. Various metallographic techniques including boat samples, core samples, or replicas were also considered, and PSE&G's position is that there is a significant increase in costs and risks associated with these techniques without a corresponding increase in benefits. As a result, no additional metallographic techniques were employed.

Page 4 of 4

. ATTACHMENT 4 i

' HOPE CREEK GENERATING STATION

, FACILITY OPERATING LICENSE NPF 57 DOCKET NO. 50 354 ADDITIONAL EXAMINATIONS Hope Creek has identified 20 welds classified as Category D welds in accordance with Generic Letter 88 01. The PSE&G augmented inspection program requires examination of these 20 Category D welds on an every other refueling outage basis.

Accordingly, these uelds were examined during the sixth refueling outage (RFO6), and as a result, there were no examinations scheduled during the current refueling outage.

Following the discovery of a through-wallleak on the NSB core spray nozzle to-safe-end weld, PSE&G requested that a full Code ultrasonic (UT) detection examination of the weld be perforrned to assist in the determination of the extent of the defect. Sizing techniques were invoked to characterize the defect.

PSE&G also requested the NDE services supplier to re-evaluate the UT data from RFO6 for the Category D welds. A review of the construction radiographs for those Category D welds replaced on site during the 1982 safe-end replacement modifications was also performed. These reviews did not identify any flaws or suspect indications.

PSE&G has requested a third party review of the sixth refueling outage mechanized UT data. EPRI NDE Center personnelwere selected and are re evaluating this data.

A review of the sample expansion criteria found in NUREG 0313 Rev 2, Generic Letter 88-01, and Section XI of the ASME Code (1983 Editio1 including Addenda through Summer 1983) was performed. No specific requirements for sample expansion for Category D welds was found in NUREG 0313, Rev 2. As there were no scheduled examinations for the current refueling outage, the " Additional Examinations" requirements of Paragraph IWB-2430(a) of ASME Section XI (1983 Edition through the Summer 1983 Addenda) do not clearly apply.

However, due to the significance of a through-wall reactor coolant system leak, PSE&G's position is that additional welds of a similar nature will be examined during the current refueling outage. Using the guidance from ASME Section XI, and given that one exannnation was performed during this refueling outage for this categoy, one additional weld would be required to be examined. -

Using the guidance from NUREG-0313, Rev. 2, considerable effort was given toward the determination of a technicaljustification for selection of a specific inspection sample distribution.

Page 1 of 2

Attachm:nt 4 LR N970667 Additi:nsl Examinatiens Reviews were performed on safe end replacement modification records (for example:

weld process, filler materials, repair areas, NDE results, etc.); operating history of the Unit for cold water injections, and effects of Reactor Coolant chemistry control efforts and transients.

Based on the above, two welds were selected for examination. These examinations will be performed in accordance with a procedure and personnel qualified in accordance with the requirements of ASME Section XI, Appendix Vlli,1992 Edition with 1993 Addenda as modified by the Performance Demonstration initiative (PDI) document 'PDI Program Description'; currently Revision 1, Change 1. These requirements are being incorporated as an alternate (IWA 2240) to those requirements of the current ISI Program which complies with the 1983 F.dition, including Summer 1983 Addenda of Section XI. The additional welds are:

  • The NSA core spray to safe end nozzle weld was selected because its operational environment is similar to that of the NSB nozzle.

The N2D recirculation outlet to safe-end nozzle weld was selected because its -

technical characteristics are quite similar to those of the NSB nozzle weld.

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