1CAN129702, Application for Amend to License DPR-51,establishing Alternate Repair Criteria for Upper Tubesheet Region of ANO-1 Sgs.Proprietary Topical Rept BAW-10226P Encl.Rept Withheld (Ref 10CFR2.790(b)(4))
| ML20197A837 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 12/12/1997 |
| From: | Huchinson C ENTERGY OPERATIONS, INC. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML19317C807 | List: |
| References | |
| 1CAN129702, GL-95-05, GL-95-5, NUDOCS 9712230211 | |
| Download: ML20197A837 (17) | |
Text
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I Eni.rsy oper.none,Inc.
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1448 LR 333 I
RwAR AR 72801
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Tel531-BW4S88 ~
C. Randy Hutchin.on Vu PresrM ae w o ;
December 12,1997 - _
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- U. S. Nuclear Regulatory Commission Document Control Desk
- Mail Station OPI-17 ;
Washington, DC 20555 :
Subject:
Arkansas Nuclear One - Unit 1 Docket No,50-313 License No. DPR-51 ;
Technical Specification Change Request Establishing Alternate ,
Repair Criteria For Outer Diameter Intugranular Attack In The Upper Tubcsheet Of The Unit 1 Steam Generators Gentlema:
Attached, for your review and approval, is a proposed amendment to Arkansas Nuclear One Unit 1 (ANO-1) Technical Specifications. The proposed amendment request establishes an
, alternate repair criteria (ARC) for the upper tubesheet region of the ANO-1 steam generators. s The basis for this change is a report prepared for the Babcock and Wilcox Owners Group (B&WOG) BAW-10226P, " Alternate Repair _ Criteria For Volumetric Outer Diameter Intergranular Attack In The Tubesheets Of Once Through Steam Generators."_ Entergy ,
4 Operations has chosen to provide the lead plant submittal for the B&WOG for the use of the ARC, f
'his is the second submittal in support of an ARC application for ANO-1. Entergy Operations' letter of August 13,1997 (ICAN089702), submitted the first in series of three submittals to the Nuclear Regulatory Commission (NRC) which would justify the use of an
- ARC for outer diameter intergranular attack (ODIGA) flaws in tubes within the tubesheet, r The third submittal was to include the proposed technical specification clumges and the no n significant hazards consideration. Since the final report was completed within weeks of the wg
- material that was planned for the second submittal, it was determined to be more efficient to
, f a- - make only one additional submittal transmitting the final topical report and the proposed ,
I technical specification change request with its nssociated no significance' hazards To consideration.
! -ac rThe attached technical specification change was developed utilizing the applicable guidance .
J 0 Iound in NRC Generic Letter 95-05, Voltage-Based Repair Criteria For Westinghouse Steam Generator Tubes 'Affected By_Outside Diameter Stress Corrosion Cracking." .The significant -
[, ? difference between the ARC proposed for the tubesheet volumetric IGA in the once through .
i steam generators and the support plate stress corrosion cracking ARC for the Westinghouse
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U. S. NRC -
December 12,1997.-
1CAN129702 Page 2 plarits is that the flaws within the tubesheet cannot burst and are not anticipated to leak under
' accident conditions. These conclusions were reached- based upon. deterministic testing perforw.ed by Framatome Technologies, Inc. (FTI) for the B&WOG in support of *his change -
request.- These factors and the unique aspects ofIGA within the tubesheet as compared to-stress corrosion cracking (SCC) at the support plates has resulted in deviations from the guidance in Generic Letter 95 05.
The attached report, BAW-10226P, contains info.t ation proprietary to FTI An af5 davit setting for th the basis on which the information may be withheld firom public disclosure by the NRC.and addressing the considerations listed in 10CFR2.790(bX4) was attached to the August 13,1997 submittal. As indicated in that letter, a non-proprietary version of the report was to be submitted at a later date. The non-proprietary version will be provided in January 1998.
The proposed change has been evaluated in accordance with 10CFR50.91(a)(1) using criteria--
in 10CFR50.92(c) and it has been determined that this change im>olves no significant hazards considerations. The bases for these determinations are included in the attached submittal.
Entergy Operations requests that the effective date for this change be within 30 days of F issuance. Although this request is neither exigent nor emergency, your prompt review is requested prior to the next ANO-1 refueling outage (1R14) which is currently scheduled to begin March 28,1998. If this amendment is not processed by the IR14 outage, over 400 tubes with volumetric IGA indications within the upper tubesheet will require repair or removal from service by plugging. As demonstrated (a the topical report supporting this change, these tubes do not represent a challenge to the future safe operation of ANO-1.
If you have any questions on the attached material, or the information which was previously submitted to you on bis subject, please contact my staff at 501-858-4619. To facilitate the NRC's review, Entergy Operations and the B&WOG are prepaced to meet with the NRC staff to discuss the technical consideration necessary to use the subject ARC.
U. S. NRC December 12,1997 1CAN129702 Page 3 l
- Very truly a s
, v.
CRH/dej Attachments To the best of my knowledge and belief, the statements contained in this submittal are true.
SUBSCRIBED AND SWORN TO before une a Notary Pu ic in d for b County and the State of Arkansas, this //4hhay of ,1997./'
Exbl&
Notary fublic-My Commission Empires f[//IV//, /M 4
U. S. NRC December 12,1997 1CAN129702 Page 4 cci - Mr. Ellis W Merschoff Regional Administrator U. S, Nuclear Regulatory Commission RegionIV 611 Ryan Plaza Drive, Suite 400 Arlington, TX 76011-8064 NRC Senior Resident Inspector Arkansas Nuclear One P.O. Box 310 London, AR 72847 Mr. George Kalman NRR Project Manager Region IV/ANO-1 & 2 U. S. Nuclear Regulatory Comndssion NRR Mail Stop 13-H 3 One White Flint North 11555 Rockville Pike Rockville, MD 20852 Mr. David D. Snellings Director, Division of Radiation Control and Emergency Management Arkansas Department of Health 4815 West Marklam Street Little Rock, AR 72205
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4 - .a _ . . -1..
6 ATTACHMENT IQ 1CAN129702' PROPOSED TECHNICAL SPECIFICATION -
Ab'R RESPECTIVE SAFETY ANALYSES IN THE MNITER OF AMENDING LICENSE NO. DPR-51 ENTEROY OPERATIONS. INC.
ARKANSAS NUCLEAR ONE. UNIT ONE DOCKET NO. 50 313
, , m-. - ., m ,m -r- t
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-1CAN129702 Page 2 of12 1
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!' DESCRIPTION OF PROPOSED CHANGES The Arkansas Nuclear One, Unit 1 (ANO-1) Technical Sp....fications (TS) have been revised utilizing the guidance provided in NRC Generic Letter 95-05. The following changes are ,
Proposed:
a 3.1.6.3.b This specification is revised to lower the leakage' limit through any one steam
, generator to less than 150 gallon per day (0.104 spm) firom the current limit of 500 gallons
- per day (0.347 spm). The 500 gallon per day limit has been reduced in the current technical i
speci6 cation to 144 gallons per day (0.1 spm) for the remainder of Cycle 14. This temporary reduction was assodsted with amendment 189 to the ANO-1 technical @**lons. The y reference to the Cycle 14 limit is deleted since this change request it 4t amicipated to be >
approved until aRer the completior of Cycle 14.-
4.18.3.a This specification is revised to add specification 4.18.3.a.4 which identifies new voltage-based 2 repair criteria and requires those indications leR in service as 'a result ofs ,
applying the new criteria to be inspected by bobbin and rotating coil probes during subsequent refueling outages.
J 4.18.3.b The existing specification 4.18.3.b is renumbered 4.18.3.c to facilitate the addition of a new speci6 cation.' The new 4.18.3.b ilequires a 100% bobbin coil 'mspection of the upper tubesheat when the tubesheet voltage-based repair criteria are_ utilized. The specification
- excludes the results of this 100% inspection from the first random samp'e results.
4.18.5.a The existing specification 4.18.5.a.7 Pluomino Limits. is modified by adding the following sentences: This ddinition does not apply to the upper tubesheet volumetric indications to which the voltage-base repair criteria are being applied. Refer to specification 4.18.5.a.10 for the repair limit applicable to these indications. A new specification 4.18.5.a.10 is added. This specification defines the repair limits for. upper tubesheet predominately -
volumetric outer diameter intergranular attack (ODIGA) indications located 2.75 inches from the secondary face of the tubeshow ta, but not including, the roll transition. The repair limit is based upon a bobbin indication of greater than l' 18 volts, minus an allowance for growth over the next operating cycle, and a determination that the indication is volumetric based upon J rotating coil examination.
4.18.5.b The reference to the Cycle 14 allowance to leave upper tubesheet ODIGA flaws in
-- service with potential through-wad depths in excess of the plugging limit is deleted since this
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change request is not anticipated to be approved until aRor the completion of Cycle 14. If this dumge request is acted upon prior to the end of Cycle 14 this provision should be ra*=laad 4.18.6' For implementation of the tsa=ha=* voittge-based repair criteria, new NRC r reporting criteria are added inclnding notification if leakage is detected during in-situ leak N
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Attachment to 1CAN129702
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testing of tubesheet volumetric indications, and if tubesheet indications.previously lea in service show signs of growth beyond that seen in the previous cycle.
, 4.18 Bases . The Bases' are revised to include discussions of the vokage-based repair criteria.
BACKGROUND The inservice inspection of the' ANO-1 steam generators is conducted in accordance with
' ANO-1 Technical Specification (TS) 4.18. Specification 4.18.2 states: " Inservice inspection :
of steam generator tubing shall include non-destructive examination by oddy-current testing or other equivalent techniques." Specification 4.18.3 requires that a minimum sample size be examined in accordance with specification 4.18.5. Specification 4.18.5.b. notes: "The steam i generator shall be determined operable aAer completing the ' corresponding actions (plug or' :
i sleeve all tubes exceeding the plugging limit and all tubes containing through-wall cracks) n required by Table 4.18-2." Table 4.18-2 specifies the expansion criteria for sampling of the steam generator tubes rnd requires " defective" tubes to be plugged or sleeved. Specification 3 4.18.5 defines Defect as: "an imperfection of such severity that it exceeds the plugging lirnit except where the imperfection has been spanned by the installation of a riceve. _ A tube 4
containing a defect in its pressure boundary is defective." Plunaina Limit is deGned in the same specification as: "the imperfection depth at or beyond which the tube shall be restored i- to serviceability by the installation of a sleeve or removed from service because it may become unserviceable prior to the next iam-*laa; it is equal to 40% of the nominal tube wall thickness "
The bases for specification 4.18 states: "The surveillance requirements for inspection of the steam generator tubes ensure that the structural integrity of this portion of the RCS will be mamtained."
l l Intergranular attack (IGA) is known to be present above the 15th tube support plate (TSP) within the ANO 1 once through steam generators (OTSGs) as verified by destructive j ~' examination from previous tube pulls. IGA is a damage mechanism caused by corrosion of
- the material grain boundaries. The corrosion resulted from contaminants introduced on the tubing dudng the early years cf plant operation. The contaminant causing IGA of the ANO-1 l tubing is sulfur as a result of thermal decomposition ofion exchange resins. The ANO-1 IGA
_can be categorized as volumetric or " patch-like," with no specific orientation. Since L
discovery, there has been no evidence ofleakage from IGA flaws at ANO-1.
During the IR13 refueling outage, an eddy current technique was employed to depth-size the IGA._ This technique was qualified per Appendix H of the EPRI "PWR Steam Generator n Tube Examination Guidelines." Compliance with the EPRI guideline was considered an acceptable method to qualify non-destructive examination (NDE) techniques for the detection and sizing of damage mechanisms. This technique was used to depth-size all IGA flaws within the upper tubesheet (UTS). During this inspection, greater than 25% of all indications
, . detected-within the UTS region by the bobbin coil examination technique were examined
( using the rotating pancake coil (RPC) technique to characterize these flaws. All UTS IGA
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- 1CAN129702 Page.4 of 12-1
- indications with a depth size of >40% through-wall (TW), es determined by the qualified sizing technique, were removed firom service by plugging during this inspection.
During IR13, three tubes with bobbin indications within the UTS were removed from the steam generator. Two e the three tubes contained flaws that would have required repairc The ti.ird tube was ne6. J repair limit and may have been preventively repaired, The tubes were selected because they contained multiple indications with depes sepresentative of the average indication depths as sized by eddy current. The tubes were burst in the laboratory without the presence of a tubesheet. All three tubes burst at approximately 10,000 pai, only l
! slightly below virgin tube burst pressure. - ARer bursting the tubes the flaws were examined and sized.- If a flaw was not opened by the burst of the tube, it was bent open for destructive <
I examination (DEL The DE results were not consistent with the previous qualification data of the bobbin coil for sizing IGA flaws in the UTSi The reason for the inconsistency in sizing IGA in the UTS is indeterminate. As a result of this condition, it is possible that tubes were i L left in service with through-wall defects greater than the technical specification plugging limit.
$ When non-compliance was determined at 2012 CDT on April 8,'1997, the time clock for TS 4.0.3 was entered alhwing 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> to seek regulatory relief. ANO verbally requested L notification of enfercement discretion at 1400 CDT on April 9,1997. Verbal approval of this ,
enforcement discretion request was received at 1535 CDT on April 9,1997. This discretion
_was in effect until May 7,1997, or until the Staff acted on a proposed technical specification
- change reqmt to be submitted by Entergy Operations, whichever occurred first.
l Entergy Operetions submitted an exigent TS change on April 11,1997 (1CAN049703), to allow a one time exception to the surveillance requirements of Section 4.18.5.b. This exception allowed tubes with IGA indications within the upper tube sheet with potential through-wall depths greater than the plugging limit to remain in service for the remainder of Cycle 14 (spring 1998). The Apnl 11,1997, submittal was supplemented on May 2,1997, by letter ICAN059702 which reduced the leakage limit through the steam generator tubes from 500 gallons per day (gpd) to 144 gpd for the temainder of Cycle 14. In response to this request, the NRC issued Amendment No.189 to the ANO-1 license dated May 7,1997. This amendment allowed the unit to continue operation thmugh the remainder of Cycle 14 with
- tubes that had potential through-wall defects in exceu of the 40% plugging limit.
Prior to IR13 the B&WOG was working on the development of an ARC for volumetric
-ODIGA flaws anywhere in the OTSG.' In response to the events at ANO, the B&WOG expedited its schedule and focused its initial work on volumetric ODIGA indications within the tubesheet. The B&WOG plans were discussed with the NRC in a meeting at the NRC offices in Rockville, Maryland on June 16, 1997. During this meeting, it was noted that -
- ANO-1 would serve as the lead plant for NRC review of proposed technical specification changes associated with the implementation of the ARC. It was agreed that submittal of the ARC information as it was developed would facilitate a more timely NRC staff resiew. A l series of three submittals were proposc4 ith the last submittal containing the final topical report and the application for a tcclinica specification change including the no significance
. hazards considera: ion.- TN first submittal was transmitted on August 13, 1997, via letter 4
Attesir.w.; to ;
Page 5 of12' ;
- ICAN089702. This initial version ~of the report included a general OTSG description and-discussion of plant chemistry, flaw morphology of pulled tubes, non-destructive examination -
(NDE) of pulled tubes and a demonstration- that laboratory devdoped ODIGA is fully -l representative of Geld ODIOA. This initial information was critical to the Anal document in . j that the leakage testing'would be performed primarily on laboratory samples since the field l data was limited and none of the volume *ric ODIGA flaws removed to date firem OTSGs has leaked under accident loads
. Since the Anal report was completed within weeks of the material that was planned for the -
' second suumittal, it was determined to be more efficient to only make one additional submittal ,
i transmitting the Anal topical report and the proposed technical specification change request with its associated no significance bzards considerat i on. The final topical report, BAW.
10226P, " Alternate Repair Criteria For Volumetric Outer Diameter Intergranular Attack In :
The Tubesheet Of Once Through Steam Generators," in support of this technical specification -- i f change is attached.
The attached technical specification change was developed utilizing the applicable guidance !
found in NRC Generic Letter 95-05," Voltage-Dased Repair Criteria For Westinghouse Steam Generator Tubes Affected By Outside Diameter Stress Corrosion Cracking." The signi6 cant difference between the ARC nroposed for the tubesheet volumetric ODIGA in the OTSGs and the support plate stress corto. ion cracking ARC for the Westinghouse plants is that flaws '
within the tubesheet cannot burst and, based upon the voltage-based repair criteria, are not anticipated to leak under accident conditions. These factors and the unique aspects ofIGA within the tubenheet, as compared to SCC at the support plates, has resulted in some deviations from the guidance in Generic Letter 95-05.
4 JUSTIFICATION OF CHANGE The surveillance requirements for inspection of the steam generator tubes ensure that the stmetural integrity of this portion of the RCS will be maintained The voltage-based repair limit proposed to be added to SR 4.18 implements the criteria derived from BAW-10226P,
" Alternate -Repair Criteria for Volumetric Outer Dbmeter Intergranular Attack in _ the -
Tubesheets of Once Through Steam Generators." The voltage-based repair limits are not -
_ applicable to other forms of OTSG tube degradation nor are they applicable to ODIGA that d
occurs at other locations within the OTSGs. Additionally, the repair criteria applies only to indications where the degradation mechanism is dominantly volumetric.
BAW-10226P evaluated the potential fu; tube burst and accident induced leakage as a result of applying the voltage-based repair criteria to volumetric ODIGA _within the tubesheet. To
- assess the potential for burst and leakage, numerous tasks were performed. The flaw morphology and eddy current charac: eristics of volumetric ODIGA were defmed based on tube pull- data from several B&W plants. Based upon laboratory _ examination, the characteristics of the volumetric ODIGA morphology are essentially the same for all the plants 1
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.1CAN129702 Page 6 of12 iniwhich tubes were pulled. The characteristic " thumbnail" profile, lack of significant corrosion of the base material, and minimal pitting in the affected area were present regardless of location or elevation within the OTSG. It was concluded from these evaluations that i volumetric IGA can be treated generically for those plants which had tubes evaluated as part ,
- of the study. . It was concluded firom a review of oddy current data firom the pulled tubes that : 1
' the oddy current response of ODIGA firom different plants and locations within the OTSG are very similar. The oddy current data from the tubes examined had low bobbin voltage signals :
and similar lisasjous shapes. They were also distinguishable as volumetric by utilizing the axial-ar.d circumferential channels of an RPC probe, and typically show an irregular cone formation on the pancake coil strip chart prcfile.
4
'to supplement the pulled tube data base, laboratory grown ODIGA flaws were utilized. The ,
ability oflaboratory ODIGA to simulate in-generator ODIGA was evaluated comparing the l laboratory'ODIGA to similarly sized field flaws.--This was accomplished by destructively examining laboratory ODIGA specimens and comparing their morphology to the sign.fice.nt- ,
featuret of field ODIGA patches. The eddy current response was evaluated by compar'mg critical parameters of the laboratory ODIGA to the same parameters for field ODIGA from pulled tubes.- The results indicated that the laboratory ODIGA is the same morphology and exhibits similar eddy current response. As a result of these findings, it was concluded that the
-laboratory ODIGA is fully representative of service-induced volumetric ODIGA. Therefore, the laboratory flaws could be used to suppbnent the pulled tube ODIGA database for the af ternate repair criteria development.
To evaluate the structural integrity of volumetric ODIGA in the tubesheet region of the OTSG, burst rupture, tensile rupture, and fhtigue failure modes were evaluated. Because of the constraint of the OTSG tube radial displacement within the tubesheet, burst pressures l- below that of an unflawed tube is precluded. Testing of axial loads up to 1.7 times main l steam line break (MSLB) load during leak testing showed no indication of any tensile rupture concerns. Fstigue is addressed through previous preventive sleeving campaigns, the application of an exclusion zone of 2.75 inches from the secondary face of the tubesheet, and examination of all indications left in service as a result of applying the voltage-bued repair criteria at each scheduled inspection. Therefore, the volumetric ODIGA does not pose a structural threat to burst or tensile rupture under postulated MSLB conditions or a fatigue failure.
Hot leak testing was performed at the bounding _MSLB temperature, pn:ssure, and load.
Testing was performed on 29 samples with volumetric ODIGA with bobbin indications
' ranging from 0.04 to 1,62 volts. None of these flaws showed signs ofleakage under these loads. An additional 8 laboratory samples and 1I tube pull indications were included on the
. basis of bounding electrodischarge machining (EDM) testing. The EDM patches were fabricated in the same heat of material used to manufacture the laboratory ODIGA specimens.
The EDM patches were mac%d to depths ranging from approximately 84 to 95% through-wall, with patch diameters of 0.30 and 0.50 inches. The severity of the EDM patches bound the potential effects of having a real ODIGA pa ch in a tube that is of similar depth and diameter. These EDM patches bound the extents (length, width and depth) of all pulled tube
? Attachment to 1CAN129702 Page 7 of 12 --
volumetric ODIGA flaws and thus provide the basis for including these Aaws and smad laboratory IGA' patches into the leak rate database, without actually leak testing the patches. ;
- None of the EDM patches showed signs ofleakage as a result of applying acci< lent loads.
Therefore, it was concluded that volumetric ODIGA flaws with oddy current indiccicos up to - .
l.62 volts will not leak under accident conditions, and that this is en acceptable threshold value to use to assume zero accident leakage.
To establish a repair limit the threshold value is further reduced, as appropriate, to account for eddy current measurement uncertainty and growth over one fuel cycle to determine a voltage-based: repair limi:. Repair of all indications greater than the repair limit precludes the ;
. possibility of structural failure or primary to secondary leakage during the next planned operating cycle.
, This adjustment can be expressed by the following equation:
Vai, = Vn,,6,u - Vu - Va, where ,
- Vat, = Repair limit (volts)
Vn,,6,u = Threshold voltage (volts)
Va= EC measurement uncensinty (volts)
Vo, = Growth over one fuel cycle (volts)
I' The leak test results discussed above support a threshold voltage of 1.62 volts.
L Eddy current uncertainty consists of three constituents. The first component is an allowance l
for probe wear. During implementation of the voltage-based repair criteria, probe wear will l be monitored by use of a wear standard. Variations in signal amplitude up to 15% wih be l accepted, but variations beyond 15% will cause the probe to be replaced. The remaining component.1 of eddy current uncertainty are the effects of varying signal noise .mplitude and analysis variability. The effects of these variables were studied and quantified for a combined o uncertainty due to these two components equal to 0.20 volts. Thus the combined eddy current measurement uncertainty is (1.62 0.15) + 0.20 = 0.44 volts.
To assure consistency with the eddy current measurement uncertainty assumptions derivd in BAW-10226P, the inspections of the upper tubesheet will be performed consistent with that specified in Appendix A to the topical.
An extensive growth rate study was performed on ANO-1 previous oddy current bobbin data.
The change in bobbin voltage from 1993 1996 was determined for 120 uppcr tubesheet indications. - The reruits show that the average vohage change per effective full power year (EFPY) is "zero" and the variability about this average is attributed to eddy current
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Attachment to 1CAN129702 -
Page 8 of 12
uncertainty.: This study indicates that the voluinetric ODiGA in tne ANO-1 upper tubesheet is not growing. To account for potential growth in the future, growth rate studies will be.
conducted each outage. For senservatism the 95%' upper tolerance limit of the data.will be used in the establishment of the cycle speci6c voltage base repair limit. For example, based upon the review of 1993 1996 data the upper tolerance limit allows fo; a potential growth rate of 0.07 volts /EFPY. Assuming a two year cycle length, the allowance for growth is 0.14
- volts.
i Therefore, assuming growth rate remains the same, for ANO-1 the repair limit for a two year cycle length would be:
j Vn = 1.62 - 0.44 - 0.14 Vn = 1.04 volts Tubes containing volumetric ODIGA indications within the upper tubesheet have been removed from the ANO-1 OTSGs on four separate occasions in the past; 1978, 1982, 1984, j and 1996. A total of six tubes with 17 indications have been removed and destruuively e examined. The results of these examinations showed the flaws to exhibit the same basic morphology. However, flaws removed prior to 1996 were larger. The data froen the five 4 tubes removed in 1982 and 1996 were used in the development of the ARC From this data and the growth rate study, the damage mechanism appears stable and consistent with that first detected in the late 1970s Since there have been no tubes with ODIGA indications removed from the lower tubesheet, Entergy Operations is restricting the application of the ARC to the ,
upper tubesheet only.
i l In lieu of future tube pulls in support of the ARC, as recommended by Generic Letter 95-05, Entergy Operations plans to conduct in-situ leak tests to further supplement the leakage data l' '
base and to demonstrate the conservatism of the voltage-based repair criteria. During each l
outage the voltage-based repair criteria is applied, four of the largest accessible tubesheet l
volumc.aic ODIGA indications with bobbin voltage measurements of >l.0 volt will be in-situ leak tested. It is envisioned that as additional data is gained, either through in-situ tests or
[
leak tests of additional laboratory samples, that a higher voltage threshold will be justified.
The decision to pull tubes in the future will be based on the detection of unusual conditions which could call into question aspects of the voltage-based repair limit.
[
In addition to the testing documented in BAW-10226P, which shows no anticipated leakage from the volumetric ODIGA flaws wLhin the tubesheet, historical ANO-1 plant data also
- supports this conclusion There have been no known primary-to-secondary leaks in the history of ANO-1 attributed to an volumetric ODIGA indication despite tim fact that many ODIGA indications have remained in service for years.
Additionally, during May 1996, the "B" OTSG tubing was subjected to a differential pressure of approximately 2100 psid for several hours as a result of a feedwater transient. No immediate increase in primary-to-secondary leak rate was noted during the event or following
Attachment to j 1CAN129702 l
Page 9 of12 st .rtup. The primary-to-secondary leak rate did increase by approxima.r.y 18 gpd three days following startup; however, none of the leakage detected during the subsequent refueling outage was attributed to a volumetric IGA flaw. It is concluded from ANO-l's history that leakage through IGA flaws in the upper tubesheet is highly unlikely even under accident conditione The limiting licensing basis accident with respect to dose consequences from assumed tube leakage is the MSLB accident. This accident assumes a total leakage of I gpm with 1% failed fuel in the core. The proposed technical specification change limits primary to secondary leakage to 150 gr.llons per day through either steam generator for a combined total leakage through both steam generators of 300 gallons per day or 0.208 gallon per minute. Since there is no additional leakage anticipated as a result of applying the voltage-based repair criteria to the upper tubesheet, the existing accident dose calculations remain bounding.
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Attachment t'o - ]
Page 10 of12 ' j DETERMINATION OF NO SIGNIFICANT liAZARDS CONSIDERATION i An u evaluation of ft he proposed change has _ been pecformed in accordance with 10 CFR 50.91(a)(1) regarding no significant hazards considerations using the standards in 10 CFR 50.92(c). A discussion of these standards as they relate to this amendment request follows:
Criterios 1 - Does Not involve a Sigalficant Increase in the Probability or Consequences of an Accident Previously Evaluated.
The steam generators are used to remove heat from the reactor coolant system during normal 1 operation and during accident conditions. The steam generator tubing forms a substantial j portion of the reactor coolant pressure boundary, A steam generator tube failure is a violation ,
of the reactor coolant pressure boundary and is a specific accident analyzed in the ANO-1
. Safety Analysis Report.
The purpose of the periodic surveillance performed.on the steam genc dors in accordance .
- with ANO-1 Technical Specification 4.18 is to ensure that the structural integrity of this portion of the reactor coolant system (RCS) will be maintained. The technical specification i
plugging limit of 40% of the nominal tube wall thickness requires tubes to be :epaired or
, removed from service bec.use the tube may become unnrviceable prior to the next inspection. Unserviceable is defined in the Tb as the condition of a tube ifit leaks or contains a defect large enough to affect its structural integrity in the event of an operating basis carthquake, a loss-of-coolant raccident, or a steam line break. The proposed techniccl specification specifies an alternate plugging limit for upper tubesheet solumetric outer alameter intergranular attack (ODIGA) indications. Based upon extensive testing and plant experience, it has been determined that upper tubecheet volumetric ODIGA flaws with a I bobbin voltage indication less than that specified by the proposed technical specification can l remain in service while maintaining the serviceability of the tube.
l From testing performed on simulated flaws within the tubesheet, it has been shown tlut the l patch IGA indications within the upper tubesheet, with depths up to 100% through-wall, do not represent structurally significant flaws which would 'mcrease the probability of a tube failure beyond that currently assumed in the ANO-1 Safety Analysis Report.
The dose consequences of a MSLB accident are analyzed in the ANO-1 accident analysis.
This analysis assumes the unit is operating with a 1 gpm steam generator tube leak and that the unit has been operating with 1% defective fuel.
Increased leakage during a postu'ated MSLB accident resulting from applying the voltage-base repair criteria to upper tubesheet volumetric ODIGA is not expected. ODIGA has been present in the ANO-1 stean generators for many years with no known leakage attributed to this damage mechanism. Because ofits localized nature and morphology, the flaw does not open under accident conditions. To further support this conclusion, hot leak. testing at the bounding MSLB temperature, pressure, and load was performed on tubing with representative
Attachment to 1CAN129702 l Page11of12 l laboratory generated flaws. The leak testing was performed or. 29 samples with volumetric ODIGA with bobbin indications of 0.04 to 1.62 volts. None of these flaws showed signs of leakage as a result of these loads. Additionally, four specim as created by electrodischarge machining (EDM) with depths up to approximately 95% through-wall were tested with no leakage detected. It was, therefore, concluded that volumetric ODIGA flaws with an eddy current indication up to 1.62 volts will not leak under accident conditions, and that this is an acceptable threshold value to use to assume zero accident leakage.
This change allows volumetric ODIGA flaws within the tubesheet, which are not projected to meet or exceed the 1.62 volt threshold when considering eddy wrrent uncertainty and an allowance for growth, to remain in service. Continued operation with these flaws present does not result in a significant increase in the probability or consequences of an accident previously evaluated for ANO-1.
TL:refore, this change does g involve a significant increase in the probability or consequences of any accident previously evaluated.
Criterion 2 - Does Not Create the Possibility of a New or Different Kind of Accident from any Previously Evaluated.
The steam generators are passive components. The intent of the technical specification surveillance requirements are being met by this change in that adequate structural and leakage integrity will be maintained. Additionally, the proposed change does not introduce any new modes of plant operation.
Therefore, this change does g create the possibility of a new or different kind of accident from any previously evaluated.
Criterion 3 - Does Not Involve a Significant Reduction in the Margin of Safety.
The margin of safety is not reduced by the implemeritation of the proposed technical specification change allowing volumetric ODIGA flaws within the upper tubesheet which meet the proposed acceptance criteria to remain in service.
Testing of upper tubesheet volumetric ODIGA flaws removed from the ANO-1 OTSGs during IR13, showed the flawed tubes to be capable of withstanding differential pressures of 10,000 psid without the presence of the tubesheet. Testing of simulated through-wall flaws of up to 0.5 inch in diame:er within a tubesheet showed that the tubes siways failed outside of the tubesheet. Thus the structural requirements listed in the - bases of the technical specification are satisfied considering this change.
Tubes with volumetric ODIGA indications within the tubesheet which satisfy the acceptance criteria specified in the proposed technical specification change are not anticipated to leak
Attachment to 1CAN129702 Page 12 of 12-under accident conditions. This is due to the small size of the flaws and their morphology.
This premise has been demonstrated through years of actual plant operation with no known.
leakage attributable to these flaws, even considering a plant transient in 1996 which exposed the ?B" steam generator to a primary-to-secondary pressure differential of 2l00 paid.' The sotential for leakage under accident conditions was'the focus of testing performed on representative samples of flawed OTSG tubing. These tests confirmed for tubenheet flaws, within the bounds of thc proposed technical speci6 cation change, that leakage is not expected l under accident conditions With no increased accident leakage anticipated as a resuh of the j proposed technical specification change, the offsite dose consequences from a MSLB accident i remain unchanged from that currently analyzed in the ANO-1 Safety Analysis Report.
Therefore, this change does DQL involve a significant reduction in the margin of safety.
In conclusion, based upon the reasoning presented above and the previous discussion of the amendraent request, Entergy Operations has detdned that the requested change does D91 I involve a significant lerds consideration.
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l PROPOSED TECHNICAL SPECIFICATION CHANGES
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