IR 05000528/1993035
| ML20058K691 | |
| Person / Time | |
|---|---|
| Site: | Palo Verde  |
| Issue date: | 11/18/1993 |
| From: | Vandenburgh C NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V) |
| To: | Conway W ARIZONA PUBLIC SERVICE CO. (FORMERLY ARIZONA NUCLEAR |
| References | |
| NUDOCS 9312160005 | |
| Download: ML20058K691 (3) | |
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Docket Nos. 50-528
50-529
50-530
Arizona Public Service Company P.O. Box 53999, Station 9082 Phoenix, Arizona 85072-3999 Attention:
Mr. W. D. Conway i
Executive Vice President, Nuclear
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Gentlemen:
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Thank you for your letter of October 25, 1993, in response to our Notice of
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Violation and Inspection Report No. 50-528/93-35, 50-529/93-35, and
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50-530/93-35, dated September 16, 1993, informing us of the steps you have
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taken to correct the items which we brought to your attention.
Your
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corrective actions will be verified during a future inspection.
Your cooperation with us is appreciated.
Sincerely,
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C. A. VanDenburgh, Chief
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Reactor Projec'
Branch cc:
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Mr. Steve Olea, Arizona Corporation Commission
James A. Beoletto, Esq., Southern California Edison Company Mr. Charles B. Brinkman, Manager, Washington Nuclear Operations l
Mr. Aubrey Godwin, Director, Arizona Radiation Regulatory Agency i
Chairman, Maricopa County Board of Supervisors
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Jack R. Newman, Esq., Newman & Holtzinger, P.C.
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Mr. Curtis Hoskins, Executive Vice President and Chief Operating Officer, i
Palo Verde Services Roy P. Lessey, Jr., Esq., Akin, Gump, Strauss, Hauer and Feld Bradley W. Jones, Esq., Akin, Gump, Strauss, Hauer and Feld i
Mr. Ronald J. Stevens, Director, Nuclear Regulatory Affairs, APS bec w/ copy of letter dated October 25, 1993:
l Docket File
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Resident inspector Project inspector G. Cook
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R. Huey i
Dottie Clevenger bec w/o copy of letter dated October 25, 1993:
M. Smith
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NUCLEAR REGULATORY COMMISSION
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UNrrED STATES
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REGION V
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1450 MARIA t.ANE
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WALNUT CREEK, CAUFORNIA 9459S-5368
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NOV 18 1923
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r Docket Nos. 50-528 50-529
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50-530
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Arizona Public Service Company
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P.O. Box 53999, Station 9082
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Phoenix, Arizona 85072-3999 Attention:
Mr. W. D. Conway
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Executive Vice President, Nuclear l
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Gentlemen:
Thank you for your letter of October 25, 1993, in, response to our Notice of j
Violation and Inspection Report No. 50-528/93-35, 50-529/93-35, and 50-530/93-35, dated September 16, 1993, informing us of the steps you have taken to correct the items which we brought to your attention.
Your
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corrective actions will be verified during a future inspection.
Your cooperation with us is appreciated.
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Sincerely, j
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C. A. VanDenburgh, C i.e f Reactor Projects Br n h
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cc:
Mr. Steve Olea, Arizona Corporation Commission
James A. Beoletto, Esq., Southern California Edison Company
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Mr. Charles B. Brinkman, Manager, Washington Nuclear operations
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Mr. Aubrey Godwin, Director, Arizona Radiation Regulatcry Agency Chairman, Maricopa County Board of Supervisors Jack R. Newman, Esq., Newman & Holtzinger, P.C.
Mr. Curtis Hoskins, Executive Vice President and Chief Operating Officer, Palo Verde Services Roy P. Lessey, Jr., Esq., Akin, Gump, Strauss, Hauer and Feld Bradley W. Jones, Esq., Akin, Gump, Strauss, Hauer and Feld Mr. Ronald J. Stevens, Director, Nuclear Regulatory Affairs, APS
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RECEIVED
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P O BOX $3999. * PHOEN!X ARCONA L507?O999
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i 102-D2702-WFC/ BAG /PJC wwAM F CONWAY October 25,1993
& KtCUTivt vitt FPESCENT NUCL E AR U. S. Nuclear Regulatory commission ATTN: Document Control Desk Mail Station P1-37 Washington, D. C. 20555 Reference:
Letter dated September 16, 1993, from C. A. VanDenburgh, Chief, Reactor Projects Branch, NRC, to W. F. Conway, Executive Vice President, Nuclear, APS
Dear Sirs:
,
Subject:
Palo Verde Nuclear Generating Station (PVNGS)
Units 1,2, and 3
Docket Nos. STN 50-528/529/530
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Reply to Notice of Violation 50-529/93-35-02 File: 93-070-026 j
Arizona Public Service Company (APS) has reviewed NRC inspection Report 50-528/529/530/93-35 and the Notice of Violation dated September 16,1993. Enclosure 1 to this letter is a restatement of the Notice of Violation. APS' response is provided in
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Enclosure 2. An extension to October 25,1993, for this response was granted in a telephone conversation on October 13,1993, between Howard J. Wong, NRC, and Burton A. Grabo, APS.
Should you have any questions, please call Burton A. Grabo at (602) 393-6492.
Sincerely, hr
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WFC/ BAG /PJC/rv Enclosures:
1.
Restatement of Notice of Violation 2.
Reply to Notice of Violation cc:
B. H. Faulkenberry J. A. Sloan
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ENCLOSURE 1
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RESTATEMENT ~OF t
NOTICE OF VIOLATION NO. 50-529/93-35-02
NRC INSPECTION
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CONDUCTED JULY 13 THROUGH AUGUST 16,1993-
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RESTATEMENT OF NOTICE OF VIOLATION 50-529/93-35-02
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During an NRC inspection conducted on July 13, thro 0gh August 16,1993, two violations j
of NRC requirements were identified. In accordance with the General Statement of Policy i
and Procedure for NRC Enforcement Actions," 10 CFR Part 2. Appendix C, the violations
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are listed below:
A.
Unit 2 Technical Specification 6.5.3.4.f requires that the Offsite. Safety Review i
Committee (formerly the Nuclear Safety Group) revievi significant operating abnormalities or deviations from normal and expected performance of unit.
equipment that affect nuclear safety.
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Contrary to the above, as of March 14, 1993, the Offsite Safety Review Committee / Nuclear Safety Group had not reviewed abnormal crack growth rates
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in cedain tubes in Unit 2 Steam Generator 22 and the identification of a mid-span
crack in another tube also in Steam Generator 22 (location R117/C54), which were significant abnormalities from normal and expected performance. The cracks had
been identified in the third refueling outage (1991) up to 80% through-wall which had not been detected in the previous refueling outage. In addition, one axial
i crack was found to be in the free span area between a horizontal support and a
diagonal support and had grown from being undetectable to 75% through-wall in one operating cycle.
i This is a Severity Level IV violation (Supplement I) applicable to Unit..
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ENCLOSURE 2
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REPLY TO NOTICE
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NOTICE OF VIOLATION 50-529/93-35-02 l
I NRC INSPECTION
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CONDUCTED JULY 13 THROUGH AUGUST 16,1993
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REPLY TO NOTICE OF VIOLATION 50-529/93-35-02
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Admission Or Denial Of The Alleaed Violation
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APS admits the violation with comment.
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Reason For The Violation
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In light of the subsequent 1993 Unit 2 steam generator tube rupture, Arizona Public l
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Service Company (APS) agrees that the initial occurrence of mid-span axial cracking, i
i which was found during the unit's 1991 refueling outage (U2R3), represented a significant
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operating abnormality. APS contends, however, that the six axial indications found at the
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first tube support were common in the industry and did not represent significant
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i operating abnormalities. APS Engineering's root cause analysis concluded that the axial cracking was Intergranular Attack /intergranular Stress Corrosion Cracking (lGAllGSCC).
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IGA /lGSCC was not a new failure mechanism, but the occurrence of IGA /lGSCC in the free span area was new to the industry.
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APS Engineering initiated Engineering Evaluation Request (EER) No. 91-RC-134
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to evaluate inspection and repair options. The disposition of~the EER required the a
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following short term actions:
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1)
ECT inspection scope was increased to 100 percent of the 01H intersection l
with bobbin coil ECT. The inspection was performed from both the hot and
cold leg sides; therefore, the tubes inspected from the cold leg side were l
actually full-length inspections.
A minimum of 500 full-length tube
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inspections were specified to address the 09H indication. Expansion criteria were set such that identification of any additional axial crack indications l
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would have required an increase in the ECT scope to a 100 percent, full-length inspection.
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The extent of tube degradation was identified and quantified by bobbin coil
.l eddy current technique and verification of potential crack areas was done j
with rotating pancake coilinspections.
3)
A detailed review of all data including previous ECT testing records was
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performed, and a data base of axial crack indications was developed.
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The industry data base was consulted, and third party reviews were used to determine the adequacy of the actions taken and proposed by APS.
Eddy current data for the cracked tubes was submitted to the EPRI NDE i
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Center for further evaluation.
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An engineering disposition of the degraded tubes and an evaluation of continued service were performed.
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A recommendation regarding tube pulling and a cost and schedule analysis l
for the actual tube pulling process were provided.
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Upon completion of these actions, APS plugged the affected tubes and returned the steam generators to service.
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The Notice of Violation states that the depth of the defects identified during U2R3
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were significant based upon an apparent rapid rate of crack growth. The Augmented
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Inspection Team's (AIT) report (50-529/93-14) refers to Reg Guide 1121, " Bases for
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Plugging Degraded PWR Steam Generator Tubes," as providing the basis for steam generator structural criteria and further states that an analysis was not performed on the
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pressure retaining capability of the free span indicaBon.
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Reg Guide 1.121 was issued "for comment" in August 1976 and has not been l
I finalized. However, the draft Reg Guide is accepted by PVNGS in the " Updated Final
i Safety Analysis Report," Section 1.8, "Conformance to NRC Regulatory Guides."
Reg Guide 1.121 is specific as to the methods E
' table to the NRC for establishing the l
limiting safe conditions for steam generator tub
'jradation beyond which defective tubes, as established by inservice inspection, should be removed from service. It is the
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AIT's position that a supplemental safety evaluation should have been performed in 1991
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to determine if the defective tubes found by the PVNGS Steam Generator Inspection Program during U2R3 met the criteria in Section C.3 of Reg Guide 1.121. Since ECT j
j detectability for crack indications is suspect below the plugging limits specified in the l
i PVNGS Technical Specifications, the results of such a Reg Guide 1.121 analysis would J
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not have been applied to reducing the Technical Specification plugging limits. Instead,
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l the results would have been applied to increasing inspection frequencies in order to i
account for Aowable degradation during the operating cycle. There is no guidance for this application of the Reg Guide 1.121 recommendations.
Following the March 1993 Unit 2 steam generator tube rupture and in response
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J to AIT concerns, APS engineering contracted with APTECH Engineering Services for a
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structural evaluation to determine if the defect found in tube Fi117C54 would meet the
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structural criteria set forth in Reg Guide 1.121. The results of the APTECH analysis-
demonstrated the margins of safety as defined by the Reg Guide could not be met for
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either normal operation (three times normal operating pressure) or accident conditions
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(1.4 times main steam line break pressures). However, sufficient margin did exist so that j
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J the tube would not have failed under normal operating conditions or main steam line break pressures. In addition, the defect as sized independently by EPRI woiJtd have met regulatory guide safety margins, which further demonstrates the difficulty in substantiating.
tube structural adequacy by ECT techniques alone. APTECH also performed a bounding
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calculation for evaluating crack defects in the Unit 2 steam generators. The results
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I include critical flaw diagrams for assessing axial defects. The critical flaw diagrams used l
Reg Guide 1.121 limits, as-built material properties, and burst criteria which have baen t
compared to actual PVNGS burst tests.
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Although the results of the subsequent APTECH evaluation of tube R117C54 in
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accordance with Reg Guide 1.121 indicated that the defect would not meet the margins
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of safety as prescribed, it is not evident that changes in the length of the unit's operating l
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cycle would have been statistically supported with respect to crack growth rate, l
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probability of detection, and anticipated initiation rate when the defects were originally
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identified in U2R3. Further, the PVNGS Technical Specification basis for defining a
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seriously degraded steam generator is the number of defective tubes, not necessarily the j
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condition of a single tube or tubes.
Reg Guide 1.121 implies that the basis for
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operational degradation may account for a maximum number of tubes allowed to fail and j
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still remain within the original safety analysis margigs. Therefore, a single freespan indication or tubes with defects that are structurally reinforced by tube support plates l
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would not be indicative of a seriously degraded safety barrier.
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l Corrective Steps That Have Been Taken And Results Achieved I
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Following the Unit 2 steam generator tube rupture, APS established a task force
'I to evaluate the conditions which led to the tube failure. 'The task force was staffed with j
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senior APS personnel and technical staff, as well as industry consultants to develop l
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recovery efforts and to ensure that the necessary corrective actions were implemented j
in a thorough and adequate manner. The task force documented its findings in the l
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" Unit 2 Steam Generator Tube Rupture Analysis Report" which was reviewed by the
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OSRC and submitted to the NRC.
In addition, APS Engineering had a structural evaluation of the initial U2R3 axialindications performed by APTECH Engineering Services with further evaluation by the EPRI NDE Center. These evaluations were described l
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During the course of the steam generator tube rupture analysis and recovery, APS i
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determined that for the foreseeable future steam generator issues and performance would
require strategic management. To meet that need, the Steam Generator Project Group
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has been established under a full-time manager. The group's mission is to' identify and Page 5 of 7 J
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- - predict failure modes that could potentially impact steam generator tube integrity and to
develop and coordinate the implementation of strategies to minimize the adverse effects
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of identified failure mechanisms. These activities $11 minimize the potential for a tube
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rupture or for a release of radioactivity, thereby, heightening nuclear safety.
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Corrective Steps Taken To Avoid Further Violations An enhanced process has been developed to evaluate ECT indicatioris that exceed
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the existing PVNGS, Reg Guide 1.121, structurallimits as defined by analysis or testing.
The following evaluation steps will be used:
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A Condition Report / Disposition Request (CRDR) will be initiated for ECT
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indications that meet the criterion described above.
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2.
A CRDR will be initiated for ECT-identified defect mechanisms that are not
covered by existing analyses.
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A statistical evaluation of crack growth rate, probability of detection, and
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anticipated initiation rate will be performed, as required, to determine if the identified defect (s) support full-cycle operation.
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A safety analysis in accordance with 10 CFR 50.59 will be performed to
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determine if the condition increases the probability or consequences of an accident or reduces margins of safety as defined in the Technical Specifications.
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A presentation to the OSRC will be made when (a) the evaluation indicates a significant deviation or abnormality; (b) the evaluation indicates reduced l
cycle operation, and/or (c) sufficient information is available to permit a
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return to power for an interim period until the evaluation can be finalized.
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This methodology has been implemented based upon lessons learned during U2R4.
These steps will provide increased attention to the evaluation / resolution of steam I
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~ ' generator tube defects and will also provide a mechanism for presenting the evaluations j
to the OSRC when required. The actions described,will also aid in maintaining PVNGS'
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strong steam generator assessment program and ittfproactive involvement with evolving
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industry experience and practices.
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Date When Full Compliance Will Be Achieved At a joint meeting of the Plant Review Board and the OSRC on July 7,1993, the OSRC reviewed the draft " Unit 2 Steam Generator Tube Rupture Analysis Report." Draft
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and final reports were sent to all OSRC members for review and comment.
Full
compliance was achieved when the OSRC completed its review prior to submission of f
the report to the NRC on July 18,1993.
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On August 11, 1993, the OSRC conducted a formal meeting at which the j
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Committee approved the following statement:.
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Based on extensive ECT examination, visual inspection, plugging of defective tubes, crack growth analysis per Regulatory Guide 1.121, administrative limits for
DEO l-131, enhanced leakage detection process, revised EOPs, improved
chemistry controls, and operator training, the OSRC has concluded that PVNGS i
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Unit 2 can be restarted without undue risk to the health and safety of the public.
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In addition, based upon the multiple tube rupture analysis, continued operation of Units 1 and 3 is acceptable, with the administrative limits on DEO l-131 and the
enhanced leakage monitoring process / action limits.
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