ML17312A536

Submits APS Response to NRC Request for Addl Info Re 960102 Ltr,Gl 95-03, Circumferential Cracking of SG Tubes.

ML17312A536
Person / Time
Site:	Palo Verde
Issue date:	02/08/1996
From:	Stewart W ARIZONA PUBLIC SERVICE CO. (FORMERLY ARIZONA NUCLEAR
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
102-03601-WLS-S, 102-3601-WLS-S, NUDOCS 9602210186
Download: ML17312A536 (23)

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CATEGORY j.

A RFGULATOkINFORMATION DISTRIBUTION TEM (RIDE)

ACCESSION NBR:9602210186 DOC.DATE: 96/02/08 NOTARIZED: NO DOCKET ¹ 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 STEWART,W.L. Arizona Public Service Co. (formerly Arizona Nuclear Power RECIP.NAME RECIPIENT AFFILIATION Document Control Branch (Document Control Desk)

SUBJECT:

Submits APS response to NRC request for addi info 're 960102 ltr,GL 95-03, "Circumferential Cracking of SG Tubes."

DISTRIBUTION CODE: A001D COP1ES RECEIVED:LTR I ENCL I SIZE:

TITLE: OR Submittal: General Distribution E

NOTES:STANDARDIZED PLANT 05000528 Standardized plant. 05000529 6 Standardized plant. 05000530 0

RECIPIENT COPIES RECIP'IENT COPIES ID CODE/NAME LTTR ENCL ID CODE/NAME LTTR ENCL PD4-2 LA 1 1 PD4-2 PD 1 1 HOLIAN, B 1 1 THOMAS,C 1 1 INTERNAL: ACRS 6 6 c@BMAGEN~RAEMNM0 1 1 NRR/DE/EMCB 1 1 NRR/DRCH/HICB 1 1 NRR/DSSA/SPLB 1 1 NRR/DSSA/SRXB 1 1 NUDOCS-ABSTRACT 1 1 OGC/HDS2 1 .0 D

EXTERNAL: NOAC 1 1 NRC PDR 1 1 U

E NOTE TO ALL "RIDS" HELP US 70 REDUCE WASTE! CONTACT THE DOCUMENT CONTROL DESK, RECIPIENTS'LEASE ROOM OWFN SD-5(EXT. 415-2083) TO ELIMINATE YOUR NAME FROM DISTRIBUTION LISTS FOR DOCUMENTS YOU DON'T NEED!

TOTAL NUMBER OF COPIES REQUIRED: LTTR 19 ENCL - 18

Arizona Public Service PALO VERDE NUCLEAR GENERATING STATION'.O.

BOX 52034 PHOENIX, ARIZONA 85072-2034 102-03601-WLS/SAB/NLT WILLIAML. STEWART February 8, 1996 EXECUTIVE VICE PRESIDENT NUCLEAR U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Mail Station P1-37 Washington, DC 20555-0001

References:

1) Letter dated January 2, 1996, from Charles R. Thomas, Project Manager - Palo Verde, USNRC/NRR, to W. L. Stewart, Executive Vice President, Nuclear, APS

2) Letter No. 102-03401, dated June 27, 1995, from W. L. Stewart, Executive Vice President, Nuclear, APS, to USNRC

Subject:

Palo Verde Nuclear Generating Station (PVNGS)

Units 1, 2, and 3 Docket Nos. STN 50-528/529/530 Response to the Request for Additional Information Regarding Generic Letter 95-03 By letter dated January 2, 1996 (Reference 1), the NRC requested that Arizona Public Service Company (APS) submit additional information regarding Generic Letter (GL) 95-03, "Circumferential Cracking of Steam Generator Tubes." Enclosed with this letter is the requested information to supplement that which was previously provided by letter dated June 27, 1995 (Reference 2), in response to GL 95-03.

Should you have any questions, please contact Scott A. Bauer at (602) 393-5978.

Sincerely, 96022iOi86 960208 PDR ADOCK 05000528 P PDR WLS/SAB/NLT/AI Enclosure cc: L. J. Callan K. E. Perkins B. E. Holian K. E.,Johnston 2j.0073

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ENCLOSURE RESPONSE TO THE REQUEST FOR ADDITIONALINFORMATION REGARDING GENERIC LETTER 95-03

Response to the Request for Additional Information Regarding Generic Letter 96-03

1. CLARIFICATIONOF INSPECTIONS TO BE PERFORMED AT THE EXPANSION TRANSITION DURING NEXT OUTAGE AT UNITS 1 2 AND 3 NRC REQUIRED INFORMATION ITEM 1 There appear to be some discrepancies in your Generic Letter 95-03 response regarding the examinations to be performed during the next outage at Units 1, 2, and 3 at the expansion transition region.

In Section IX, for example, you state that a 100 percent plus-point motorized rotating pancake coil (MRPC) exam will be performed in U3R5: This is consistent with Table 3. However, in Section X, you state that a 20 percent initial sample will be performed and the sample will be expanded to 100 percent if a circumferential indication is found and 12 months have passed since the last 100 percent inspection.

Furthermore, in Section X you state that 1000 tubes (approximately 10 percent)

'ill be examined in the cold leg at the'xpansion transition during U3R5; however, this program may be discontinued for U1R6 and U2R6 pending the Unit 3 results.

Table 3, however, indicates that 10 percent of the cold-leg expansion transitions will be examined during U2R6.

As you noted in your Generic Letter 95-03 response, these discrepancies may be a result of the uncertainties associated with the allowable run times for Units 1, 2, and 3. However, please clarify the inspections to be performed at the expansion transition during the next outage at Unit 1, 2, and 3.

APS RESPONSE TO ITEM 1

=Section X of APS'esponse to Generic Letter 95-03 (Reference 2) defined a minimum standard MRPC inspection program for the assessment 'of circumferential cracking in the PVNGS steam generators. Table 3 of Reference 2 provided a projected inspection plan for the following three inspections at PVNGS (U3R5, U2R6 and U1R6). Since the projected inspections listed in Table 3 exceed the minimum MRPC program defined in Section X, APS does not regard the information to be in conflict.

The Staff requested additional clariTication of eddy current inspections to be performed at the expansion transition location. Since the submittal of Reference 2, the U3R5 steam generator inspections have been conducted. As'indicated in

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Table 3 of our response, a 100% Hot Leg MRPC inspection and a 10% Cold Leg MRPC inspection was conducted at the expansion transition region.

Based on the U3R5 results, the approved eddy current scope for U2R6 has been established and is provided as Attachment 1 of this response. As indicated in the attached Table, the inspection includes a 100% Plus Point MRPC inspection of expansion transitions in the Hot Leg and a 500 tube MRPC sample in the Cold Leg. The inspection scope also identifies the applicable Cold Leg inspection expansion criteria.

The U1R6 inspection program has not been finalized at this time, however APS intends to conduct a 100% Hot Leg MRPC of the expansion transition region as indicated in'Table 3 of Reference 2.

2; CLARIFICATION OF INSPECTIONS AT THE U-BEND AND SQUARE BEND REGION NRC REQUIRED INFORMATION ITEM 2 In your response, you indicated that U-bend (Row 1 and 2) and square bend inspections were performed and that no indications of circumferential cracking were reported. Please clarify the extent of these examinations (e.g., 3 percent of the tubes in Row 1 and 2). If this region is susceptible to circumferential cracking, please provide the future inspections plans for this region.

APS RESPONSE TO ITEM 2 APS has conducted a 100% MRPC inspection of Row 1 and 2 U-bends in all three PVNGS units. As indicated in Reference 2, no circumferential defects have been identified. As indicated in Attachment 1, continuation of this program is planned for U2R6.

Since 1993, APS has conducted over 32,000 square bend MRPC inspections at PVNGS. These inspections were conducted to determine the extent of axial cracking in the upper bundle region of the steam generators. No circumferential cracks have been identified in these inspections. APS therefore concludes that these areas are not susceptible to circumferential cracking. APS will continue to perform inspections in this area for axially oriented defects.

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3. CLARIFICATION OF ',.'SEVERE" DENTING NRC REQUIRED INFORMATION ITEM 3 In your response, you stated that there has been no evidence of "severe" denting of the Palo Verde steam generators. Please clarify what is meant by severe denting. If a voltage threshold is used for determining the severity of dented locations, provide the calibration procedure used (e.g., 2.75 volts peak-to-peak on 4-20 percent through-wall ASME holes at 550/130 mix). In addition, provide the past inspection scope and your future inspection plans for dented locations if these areas are susceptible to circumferential cracking.

APS RESPONSE TO ITEM 3 In Reference 2, APS highlighted the cfesign features of the System80 steam generators which preclude denting. The use of the term "severe" was to emphasize the relationship between industry identified circumferential cracking and dented support locations. As stated previously, the horizontal supports at PVNGS are of eggcrate design, while the bend and horizontal regions are supported by batwing and vertical lattice supports respectively. The supports are manufactured from Type 409 ferritic stainless steel.. The large flow area in the System80 support design provides better irrigation and reduces the potential for steam blanketing, and is therefore less likely to be blocked by crud, boiler water deposits, and corrosion products. Since the support material is Type 409 ferritic stainless steel, it is not susceptible to magnetite corrosion which has resulted in denting and lockup at plants with carbon steel supports. Furthermore, APS has incorporated boric acid secondary water treatment for corrosion mitigation. Boric acid addition has proven to be effective in eliminating denting (EPRI Steam Generator Reference Book, EPRI TR-103824s-V1 R1, December 1994). APS stated, in Reference 2, that the expected impact of these design and operational measures have been substantiated via eddy current in all three units and tube pull activities in Unit 2.

Since 1993 APS has conducted 100% full length bobbin coil inspections during PVNGS refueling outages. PVNGS has recorded/measured dents with a variety of techniques during past outages. These measurements have been influenced by changes in eddy current probe design, acquisition equipment, analysis set-up and calibration, and procedural requirements. The current practice at PVNGS, as shown in the Bobbin Coil Technique Sheet provided as Attachment 2, is to set voltage on the 50% AVB/BWwear in the P2 (500/100 absolute mix) channel to 5 volts (Vmax) and save to all channels. This yields a voltage of approximately 4.5 volts in the P1 (500/100 differential mix) channel. In earlier outages, APS required the setup to be 4 volts on the 4-20% ASME holes and stored to all channels. This is consistent with 2.75 volts on the 4-20% ASME holes with the P1 channel.

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This setup value has not been considered essential since eddy current inspections have not detected corrosion product type denting for the reasons stated above.

APS does require, by procedure, the trending of recordable dent signals. New dents or changes in dent signals (> 20 volts) require an MRPC exam. It should also be noted, that the square bend MRPC examinations described in Item 2, include inspection of two horizontal eggcrates (08H, 09H) and three vertical lattice supports (VS1, VS2 and VS3), and no evidence of circumferential cracking has been identified. Consequently, the statements provided in Reference 2 regarding the susceptibility to circumferential cracking at support or dented locations are valid. No programmatic or scope changes are planned as a result of our previous inspections.

DISCUSSION OF THE. USE OF TERRAIN PLOTS NRC REQUIRED INFORMATION ITEM 4 During the Maine Yankee outage in July and August 1994, several weaknesses were identified in their eddy current program. The staff discussed these deficiencies in NRC Information Notice 94-88, "Inservice Inspection Deficiencies Resulting in Severely Degraded Steam Generator Tubes," and observed that several circumferential indications could be traced back to earlier inspections when the data was reanalyzed using terrain plots. These terrain plots had not been generated as part of the original field analysis for these tubes. For the rotating pancake coil (RPC) examinations performed at your plant at locations susceptible to circumferential cracking during the previous inspection (i.e., the previous inspection per your Generic Letter 95-03 response), discuss the extent to which terrain plots were used to analyze the eddy current data. If terrain plots were not routinely used at locations susceptible to circumferential cracking, discuss whether the RPC eddy current data has been reanalyzed using terrain mapping of the data.

If terrain plots were not routinely used during the outage and your'data has not been reanalyzed with terrain mapping of the data, discuss your basis for- not reanalyzing your previous RPC data in light of the findings at Maine Yankee.

Discuss whether terrain plots will be used to analyze the RPC eddy current data at. locations susceptible to circumferential cracking during your next steam generator tube inspection (i.e., the next inspection per your Generic Letter 95-03 response).

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APS RESPONSE TO ITEM 4 As stated on page 6 of 14 in Reference 2, APS submitted a description of the MRPC techniques used at PVNGS for circumferential cracking as a result of issues identified in the 1994 Maine Yankee inspections. In that submittal APS stated that PVNGS eddy current procedures require analyst review of both the terrain plot (C-scan) and the lissajous presentation for tubesheet transition locations. The letter further states that this requirement has been in place since 1993. This requirement has not changed and will remain unchanged for the U2R6 and U1R6 steam generator inspections.

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ATTACHMENT1 0

1~

Steam Generator Eddy Current Outage Scope Outage U2R6 Table 1: Eddy Current Scope

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'.!;~,'- - Inspection -'<'xtent "": - SG'2-Il '

'SG 2-2 'Purpose Method 100% Full Length Bobbin Full Length -10,700 -10,000 Standard Refueling Outage Bobbin Bobbin Program Program (Ref memo 323-00258-DFG/ECS 1/25/93)

MRPC ARC MRPC 07H-2nd VS -2700 -2700 Area of Interest for ARC Region axial defects.

Upper Bundle ARC MRPC 07H-2ndVS -200 -200 Sample of Areas between Columns Sample 40-150 and Rows90-110 based on ATHOS Model Results Hot Leg MRPC TSH 10,700 -10,000 Circumferential Indications 100% Top ofTubesheet Generic Letter 95-03 Program Row 1 and 2 MRPC 07H-07C -110 -110 Short Radius U-bend cracking MRPC > 20% bobbin- MRPC Support 125+ 250+ Bounds results of Unit 2RS support from U2RS Locations cracking Cold Leg MRPC MRPC -500 -500 Program to match U2RS MMI Program locations/ Generic Letter 95-03 Note: Thc plus point MRPC Probe will be utilized in U2R6 Expansion Criteria Axial ARC Region Indications:

Five (5) tube buffer zone (all directions)

MRPC of any Bobbin indications that exceed PVNGS Plugging Criteria MRPC of all I codes and bobbin indications pcr 73TI-9RC01 Circumfcrntial Cracks Expand to 100% of Cold Lcg Tubcshcet if(1) SCI/MCI is detected in cold lcg sample Expand to 20% of Cold Lcg Tubcshcet ifSCI/MCI >50 tubes in affcctcd SG T/te followiag eqaipntent sltoalrl be available or rearly to <leploy based oa Tabeslteet exanls UT Probes In-Sita Pressare I:qaiinneal Silasti e MolrVIDPT Test I."qaiplneat

j I ATTACHMENT2 P

PALO VERDE NUCLEAR GENERATING STATION NUMBER REV AlVALFSIS TECHNIQUE SHEET APPLICABILITY:

BOBBIN COIL EXAMINATIONSOI" STEAM GENERATOR TUBING APPLICABLE ATS NUMBERS: SG10 EQUIPMENT SOFPiVARE NO: EDDYNET 95 p 1.4 MODEL: 700 MANUF: ZETEC DIFFERENTIAL PI (1-5) P3 (1-5) P4(1-3-5)

SPAN 509o 50% 50% 50% EC 50% R-TRASH 50%

PHASE 40 DEG 40 DEG 40 DEG 40 DEG PM-HORZ PM-HORZ PM-HORZ CAL STD ASME ASME ASME ASME ASME ASME ASME CURVE DEGREE NA DEGREE NA DEGREE NA SUPPRESS NA NA NA NA SUFI'-R SUFl'-R SUFI'-R/R-'IR BSOLUTE P2 ( 2-6)

SPAN 30% 30% 10% 50% EC 30% (50% wear)

PHASE UP/PM-H UP/PM-H UP/PM-H UP/90 DEG UP/PM-H CAL STD ASME ASME ASME EGGCRATE NA NA NA NA VOLT SUPPRESS NA NA ~ NA NA SUPT-R VOLTS: SET the 50% WEAR in P2 TOSV (VMAX)AND SAVE(STORE TO ALLCHANNELS NOTES: 1. THE ABOVE SPANS ARE A MINIMUM

2. THE ABOVE PHASE SHOULD BE WH~+ 5 DEGREES

3. UNLESS NOTED, THE ABOVE SPANS AND PHASE ARE OF THE.100% HOLE

4. COLORS UIILIZEDFOR SCREEN PRESENTATION SHALL BE THOSE USED FOR CALIBRATION RECORDING REQUIREMENTS CHANNEL INDICATION INDICATION P1 ALLDEGRADATION P1 TSH & OIH CRACKING P1,5,6 UPPER HOTLEG CRACKING PRIMARY ANALYSISONLY P4 EXP TRANS CRACKING Pl DNT p20V P2 BW, EC, & VS WEAR Pl p5V P1 p5V RESOLUTION ONLY GRAPHICS: D4 FOR ALL'" CODES, CRACKING, PLP's, PLI's, ALOD ALL ~

EFFECTIVE DATE:

PREPARER'PS l0-23-u5 APPROYhLt PAGE I OF2

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