ML17305B656

Requests Approval to Use ASME Code Case N-474-1 to Replace Unit 2 RCS Hot Leg Nozzles,Currently Alloy 600,w/Alloy 690 Matl Which Is More Resistant to Primary Water Stress Corrosion Cracking

ML17305B656
Person / Time
Site:	Palo Verde
Issue date:	07/18/1991
From:	Conway W ARIZONA PUBLIC SERVICE CO. (FORMERLY ARIZONA NUCLEAR
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
161-04062-WFC-R, 161-4062-WFC-R, NUDOCS 9107230366
Download: ML17305B656 (24)

Text

ACCELERATED DIS UTION DEMONST TION SYSTEM REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)

ACCESSION NBR:9107230366 DOC.DATE: 91/07/18 NOTARIZED: NO DOCKET FACIL:STN-50-528 Palo Verde Nuclear Station, Unit 1, Arizona Publi 05000528 STN-50-529 Palo Verde Nuclear Station, Unit 2, Arizona Publi 05000529 STN-50-530 Palo Verde Nuclear Station, Unit 3, Arizona Publi 05000530 AUTH. NAME AUTHOR AFFILIATION CONWAY,W.F. Arizona Public Service Co. (formerly Arizona Nuclear Power RECIP.NAME RECIPIENT AFFILIATION Document Control Branch (Document Control Desk)

SUBJECT:

Requests approval to use ASME Code Case N-474-1 to replace Unxt 2 RCS hot leg nozzles,currently Alloy 600,w/Alloy 690 D matl which is more resistant to primary water stress corrosion cracking.

DISTRIBUTION CODE: A001D TITLE: OR COPIES RECEIVED:LTR Submittal: General Distribution

( ENCL 4 SIZE:

A NOTES:STANDARDIZED PLANT 05000528 Standardized plant. 05000529 Standardized plant. 05000530 D

RECIPIENT COPIES RECIPIENT COPIES ID CODE/NAME LTTR ENCL ID CODE/NAME LTTR ENCL PD5 LA 1 1 PD5 PD 1 1 TRAMMELL,C 2 2 THOMPSON I M 2 2 INTERNAL: ACRS 6 NRR/DET/ECMB 7D 1 1 NRR/DET/ESGB 1 NRR/DOEA/OTSBl1 1 1 NRR/DST 8E2 1 NRR/DST/SELB 7E 1 1 NRR/DST/SICB8H7 1 NRR/DST/SRXB 8E 1 1 NUDOCS-ABSTRACT OGC/HDS1 RES/DSIR/EIB 0

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NOTE TO ALL "RIDS" RECIPIENTS:

PLEASE HELP US TO REDUCE WASTE! CONTACT THE DOCUMENT CONTROL DESK, ROOM P 1-37 (EXT. 20079) TO ELIMINATEYOUR NAME FROM DISI'RIBUTION LISTS FOR DOCUMENTS YOU DON'T NEED!

TOTAL NUMBER OF COPIES REQUIRED: LTTR 27 ENCL 25

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Arizona Public Service Company P.O. BOX 53999 ~ PHOENIX, ARIZONA85072-3999 WILLIAMF. CONWAY 161-04062-WFC/RAB EXECUTIVEVICEPRESIDENT NUCLEAR July 18, 1991 Docket Nos. STN 50-528/529/530 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Mail Station Pl-37 Washington, D. C. 20555

Subject:

Palo Verde Nuclear Generating Station (PVNGS)

Units 1, 2, and 3 Request to Use ASME Code Case N-474-1 File: 91-008-010; 91-056-026 Arizona Public Service Company (APS) requests NRC Staff approval in accordance with 10 CFR 50.55a(a)(3) to use ASME Code Case N-474-1. The Code Case, approved March 5, 1990 by the ASME, allows the use of Alloy 690 (UNS 06690, minimum yield strength, 35 ksi) in ASME Class 1 components. APS is planning to replace PVNGS Unit 2 Reactor Coolant System (RCS) hot leg nozzles, currently Alloy 600, with Alloy 690 material which is more resistant to Primary Water Stress Corrosion Cracking (PWSCC). The Alloy 600 nozzles to be replaced are considered susceptible to PWSCC due to their high yield strength, specific heat treatment, fabrication procedures, and a high temperature location.

Cracking of Alloy 600 nozzles has not occurred at PVNGS; however, APS intends to replace seven nozzles used to monitor steam generator differential pressure and a sampling nozzle in order to preclude potential cracking. The replacement work will take place during the refueling outage for Unit 2, scheduled to start on October 17, 1991.

Alloy 690 has been installed at various facilities including Calvert Cliffs, Unit

2. ASME Code Case N-20-3, which was accepted for use by NRC Regulatory Guide 1.85 approves use of Alloy 690, meeting specification SB-163, when separate Alloy 690 welding procedures and performance qualifications are established. ASME Code Case N-474-1 applies to SB-163, SB-166, SB-167, and SB-168. APS will use Alloy 690 per SB-166, "Nickel-Chromium-Iron-Alloy Rod, Bar and Wire" for hot leg nozzle material. The applicable welding requirements in Code Cases N-20-3 and N-474-1 will be used. In addition, procurement of material will be in conformance with ASME Quality Assurance requirements.

The use of Alloy 690, per the technical requirements stipulated above, will provide improved PWSCC resistant material and an acceptable level of quality and increased safety. APS is requesting NRC authorization to use Alloy 690 in Code Case N-474-1 prior to the start of the PVNGS Unit 2 refueling on October 17, 1991. The NRC approved a similar request for Baltimore Gas and Electric Company in a letter dated April 5, 1990.

9107230366 91071S PDR ADOCK 05000528 'I P PDR Ijo

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161-04062-MRC/RAB July 18 , 1 99 1 U. S . Nuclear Regulatory Commission Attn: Document Control t to Use ASME Code Case N- 474 - 1 Desk'eques Page 2 A summary descrip tion of the ho t leg nozzle replacement process is attached for your information (Attachment 1 ) . In addition, a copy of ASME Code Case N- 474 - 1 is provided as Attachment 2 .

'lease call h

h'h Michael E. Pow'ell at (602) 340-4981 if you have any questions.

Sincerely, h

h WFC/RAB/pmm Attachments cc: J. B. Martin D. H. Coe A. C. Gehr A. H. Gutterman

1 161-04062-NFC/RAB July 18 , 199 1 ATTACHMENT

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161-04062-AtFC/RAB July 18 , 1 991 BACKGROUND Primary Water Stress Corrosion Cracking (PWSCC) of Alloy 600 material used as Reactor Coolant System penetrations has been experienced at BG&E's Calvert Cliffs-2 and was documented by Combustion Engineering (CE) Infobulletin 89-06 and NRC Information Notice 90-10. As part of APS'nvestigation of applicability of PWSCC in Alloy 600 penetrations at PVNGS, the material and manufacturing record of the RCS penetrations fabricated from Alloy 600 were reviewed. Based on criteria developed in conjunction with the Combustion Engineering Owners Group, the penetrations were grouped into categories relating to the material's susceptibility to PWSCC. Eight nozzles in Unit 2 were determined to have high susceptibility to PWSCC and the decision was made to remove and replace these nozzles. The remaining penetrations in Unit 2 and all of the penetrations in Units 1 and 3 were classified as either having low or moderate susceptibility to PWSCC. As more information about Alloy 600 and PWSCC becomes available, the penetrations in the low or moderate categories will be further evaluated.

The improved corrosion resistance of Alloy 690 over Alloy 600 is well documented in industry studies. Studies performed by Babcock

& Wilcox (EPRI NP-5761, Stress Corrosion Cracking of Alloys 600 and 690 in AVT Water at Elevated Temperatures), and CE, Westinghouse, and EDF (EPRI NP-4665S-SR, Proceedings: Workshop on Thermally Treated Alloy 690 Tubes for Nuclear Steam Generators) have shown Alloy 690 to be more resistant to stress corrosion cracking in a variety of PWR water environments which have produced cracking in Alloy 600 material. These include primary water, with boric acid and lithium hydroxide additions representing the start, middle and end of typical fuel cycles, lead contaminated, cold worked, creviced conditions and a variety of secondary side environments in which the nominal AVT chemistry is faulted with aggressive contaminants.

The attached figures show the location, existing configuration and replacement design of the seven instrument nozzles and one sampling nozzle in Unit 2 that will be replaced in the next refueling outage.

Four of the nozzles are located in each hot leg and provide connection for Reactor Coolant Pump and Steam Generator differential pressure instruments and a hot leg sampling nozzle.

t 161-04062-MFC/RAB July 18, 1991 Description of Modification:

The existing Alloy 600 nozzle will be trimmed to a length of approximately three inches. The machining fixtures will then be installed. After the fixture is installed, the integral flow restrictor in the nozzle will be machined out to allow access for Non-Destructive Examination (NDE) of the existing nozzle. An eddy current examination will be performed to determine if cracking has initiated in the nozzle lD. Upon completion of the NDE, the remainder of the nozzle will be removed and the hole enlarged to accept.'the corrosion resistant sl'eeve. " The new weld prep is then machined "into the'uter wall of the hot leg piping. The corrosion resistant sleeve is then fitted up and rolled into place over its length to provide zero clearance. After verification of the sleeve position, the remote ID w'elder is installed and the inner end of the sleeve is welded to

'the,cladding'on the inside diameter of the pipe. A visual inspection of the 'eld is performed. The replacement Alloy 690 nozzle is then installed. A~ preheat, of, the base metal is required to complete the pressure boundary weld. 'Other requirements 'include a post welding soak.

NDE requirements for the weld include a PT examination of the weld at the 1/2 T location and of the final layer.

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V ~ ~ h CASE N-474-5 CASES OP ASME BOILER AND PRESSURE VESSEL CODE Approvat Date: March 6, 1880 See Nunrerlo Index for oxplnr Von and any raaf/imraVon dates.

Case N-474-1 shall bc determined in accordance with NB-3133 us-Design Stress Intensities and Yield Strength Values ing Fig. VII-1102-1 in Appendix VII of Section III.

for UNS N06690 Vflth a Minimum Specified YIeld (c) rVelding Procedures and Performance Quali-I Strength of 35 ksi, Class Components fication shaH bc in accordance with Section IX and Section III, DMsion 1 this Section. The material shall be considcrcd to be P-No. 43.

E Inquiry; Is it permissible in thc construction of (d) This Case number shall be listed on the Data Class 1 components conforming to the requirements Rcport Form for the component.

of Section III, Division 1, to use nickel chromium-iron UNS N06690 with a minimum yield strength of 35 ksi as speciQed in material SpcciQcation SB-163, TABLE 1 SB-166, SB-167> and SB-1687 I Otstgn Stress Yield Stnngth, l Tent pcrature InutLINy, S~ kst ksl Reply: It is the opinion of the Comrnittcc that the 100 23D 55.0 material speciQed in the Inquiry may be used in the 3L6 200 258 construction of Class I components under the rules 300 233 29.8 of Section III, Division I, provided the foHowing ad- COO 25 5 28.7 ditional requirements arc met. 500 238 27.8 (a) The stress intensity and minimuns yield 600 27.6 700 238 27.6 strength values shaH be as shown in Table I. 27.6 800 23.3 (b) For external pressure thc required thickness

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