ML17312B656
| ML17312B656 | |
| Person / Time | |
|---|---|
| Site: | Palo Verde  |
| Issue date: | 09/02/1997 |
| From: | Thomas K NRC (Affiliation Not Assigned) |
| To: | James M. Levine ARIZONA PUBLIC SERVICE CO. (FORMERLY ARIZONA NUCLEAR |
| References | |
| TAC-M98110, NUDOCS 9709100160 | |
| Download: ML17312B656 (8) | |
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UNITED STATES NUCLEAR REGULATORY COIVIMJSSION WASHINGTON, D.C. 20555-0001 September 2,
1997 Hr. James H. Levine Executive Vice President, Nuclear Arizona Public Service Company Post Office Box 53999 Phoenix. Arizona 85072-3999
SUBJECT:
ARIZONA PUBLIC SERVICE COMPANY -
PALO VERDE UNIT 2.
STEAN GENERATOR OPERATING INTERVAI (TAC NO. H98110)
Dear Hr. Levine:
By letters dated January 3,
- 1997, and Hay 9, 1997. Arizona Public Service Company (APS) provided information to support a full cycle of operation for the Palo Verde Nuclear Generating Station.
Unit 2 steam generators.
The information pertained to Cycle 7 operation of Unit 2 which began in Hay 1996.
Hid-cycle steam generator tube inspections have been performed for Unit 2 since the Unit 2 steam generator tube rupture event in 1993.
Since this event. the operating intervals between the Unit 2 inspections have been 4.5
- months, 6 months, 3.5 months.
and 12 months.
The information in the January and Hay 1997 submittals provide APS's basis for operating the Unit 2 steam generators for 16.5 months.
The January 3, 1997, submittal contained, in part. information per taining to past inspection results and an analysis of the structural and leakage integrity of the Unit 2 steam generator tubes following Cycle 7 operation.
APS concluded that the structural and leakage integrity of the Unit 2 steam generators will be maintained until the scheduled refueling at the end of Cycle'.
The analysis performed is similar to that used in justifying an approximately 15.5 month operating interval for Unit 3, which ended in the spring of 1997, and an approximately 12 month operating interval for Unit 2, which ended in the spring of 1996.
A public meeting was held between APS and the NRC staff'n February 20, 1997.
to discuss the results of the steam generator tube eddy current inspections articularly as it relates to the issue of an appropriate Cycle 7 operating ength for Palo Verde Unit 2 (NRC meeting summary dated March 25. 1997).
Structural and leakage integrity analysis were discussed during the meeting.
At the conclusion of the meeting, the staff indicated that they did not identify any significant concerns with APS's conclusion about the Unit 2 operating cycle length;
- however, since the staff did not review APS's probabilistic methodology in detail, the staff requested that the licensee submit the inspection results from the Unit 3 outage (which commenced in February 1997) to provide further assurance that the probabi listic methodology conservatively predicted the end-of-cycle conditions for Unit 3.
Since the O
methodology used for Unit 2 is similar to th'at used for Unit 3, conservative results from Unit 3 would provide added confidence that the prediction for Unit 2 would also be conservative.
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Mr. James M. Levine September 2,
1997 I
By letter dated April 18,
- 1997, APS submitted Palo Verde Unit 3 steam generator inspection results from the spring 1997 outage.
This letter also included a comparison of the actual Unit 2 steam generator tube inspection results to those which were predicted.
APS concluded that the Unit 3 end-of-cycle tube conditions were conservatively predicted based on the inspection results.
These projections are for tube indications in the region of the steam generator referred to as the ARC (i.e.. the region where free span outside diameter stress corr osion cracking (ODSCC) has been observed).
During the Palo Verde Unit 3 spring 1997 outage.
another issue was raised which had potential implications for Unit 2.
APS identified 17 tubes in the Unit 3 steam generator (SG). "3-2". that experienced greater than normal degradation rates in the batwing stay cylinder (BWSC) area.
APS attributed the increased wear rate to a modification performed in SG "3-2" during the previous outage which was designed to reduce recirculating loop flow resistance (thereby reducing the progression of'DSCC in the ARC region).
Consequently, APS determined that an increase in central cavity vertical flow rates occurred which negatively affected degradation rates in the BWSC area.
A similar, but more extensive.
modification was completed in Unit 2.
SG "2-2."
It was postulated that the more extensive modification could increase central cavity vertical flow rates in SG "2-2" even higher than those experienced in SG "3-2." and therefore BMSC wear rates in SG "2-2" could be even higher than those experienced in SG "3-2."
This means that the condition idi ntified at Unit 3 does not bound the potential Unit 2 wear rate.
Consequently, APS conducted a supplementary cycle length assessment to take into consideration the impact of potentially higher wear rates for Unit 2.
This assessment was submitted to the NRC by letter dated May 9.
- 1997, APS performed both a probabilistic and deterministic assessment to develop predictions for end-of-cycle (EOC) conditions for BMSC area wear.
The pr obabilistic model approach was similar to that previously used by APS for ARC region steam generator degradation.
The probabilistic model was benchmarked by performing a Unit 2 simulation, and comparing projected EOC 6 severity of'ear indications to actual EOC 6 wear (as identified in the spring 1997 outage).
The deterministic assessment was developed based on historical plant data and laboratory testing.
Both models support a full cycle of operation for Cycle 7.
Although the NRC did not review the methodologies in detail. the staff concluded that (1) the deterministic assessment appears reasonable; (2) the probabilistic methodology has previously been used by APS for other degradation mechanisms and has provided a conservative prediction of actual end-of-cycle conditions, and (3) the probabilistic and deterministic model (independent models) support a full cycle of operation f'r Cycle 7.
The staff will monitor the Unit 2 inspection results during the fall 1997 outage.
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Mr. James M. Levine September 2,
1997 In summary, the staff tound that APS's tube integrity assessment, benchmarking of the tube integrity model, and defense-in-depth
- measures, including improvements in water chemistry, leakage monitoring, and emergency operating procedures, provide reasonable assurance that Unit 2 can be safely operated until the end of Cycle 7 (approximately 16.5 months of operation) before performing the next steam generator eddy current inspection.
If you have any questions regarding this matter, please contact me at (301) 415-1362.
Sincerely, Original Signed By Kristine M. Thomas, Project Manager Project Directorate IV-2 Division of Reactor Projects III/IV Office of Nuclear Reactor Regulation Docket No.
STN 50-529 cc:
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- OGC, 015818 EAdensam(e-mail)
WBateman KThomas EPeyton JStrosnider, EMCB
- KPerkins, WCFO
- PGwynn, RIV
- DKirsch, WCFO TSullivan, EMCB DOCUMENT NAME: PV98110. LTR OFC PDIV-2/PM PDIV-2/LA EMCB/BC NAME KTh mas:ye DATE 8/R /97 ey 8&(997 AL tros 8
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Mr. James M. Levine I
lI CC:
Hr. Steve Olea Arizona Corporation Commission 1200 W. Washington Street Phoenix. Arizona 85007 Douglas Kent Porter Senior Counsel Southern California Edison Company Law Department.
Generation Resources P.O.
Box 800
- Rosemead, California 91770 Senior Resident Inspector USNRC P. 0.
Box 40
- Buckeye, Arizona 85326 Regional Administrator, Region IV U. S. Nuclear Regulatory Commission Harris Tower 8 Payi llion 611 Ryan Plaza Drive. Suite 400 Arlington, Texas 76011-8064 Chairman.
Board of Supervisors ATTN:
Chairman 301 W. Jefferson, 10th Floor
- Phoenix, Arizona 85003 Mr. Aubrey V. Godwin. Director Arizona Radiation Regulatory Agency 4814 South 40 Street Phoenix.
Arizona 85040 Ms. Angela K. Krainik, Manager Nuclear Licensing Arizona Public Service Company P.O.
Box 52034
- Phoenix, Arizona 85072-2034 Hr. John C. Horne. Vice President Power Supply Palo Verde Services 2025 N. Third Street.
Suite 220 Phoenix, Arizona 85004 September 2,
1997 Mr. David Summers Public Service Company of New Mexico 414 Silver SW, f0604 Albuquerque.
New Mexico 87102 Mr. Robert D. Bledsoe Southern California Edison Company 14300 Mesa Road.
Drop D41-SONGS San Clemente, California 92672 Mr.. Robert Henry'alt River Project 6504 East Thomas Road
,Scottsdale.
Arizona 85251 Terry Bassham, Esq.
General Counsel El Paso Electric Company 123 W. Mills El Paso.
Texas 79901 Mr. Robert Burt Los Angeles Department of Water 8 Power Southern California Public Power Authority ill North Hope Street, Room 1255-B Los Angeles, California 90051
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