1CAN059901, Application for Amend to License DPR-51,revising TS SRs & Applicable Bases Relevant to ISI Requirements for Portions of once-through SG Tubes Encompassed by Upper Tube Sheet. Proprietary Rept Encl.Rept Withheld,Per 10CFR2.790(b)(4)
| ML20206T234 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 05/14/1999 |
| From: | Hutchinson C ENTERGY OPERATIONS, INC. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML20137P387 | List: |
| References | |
| 1CAN059901, 1CAN59901, NUDOCS 9905240099 | |
| Download: ML20206T234 (16) | |
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1 Ent:rgy operations,Inc.
1448 SR 333 AusseMe, AR 72801 Tel501858 4888 C. Randy Hutchinson We Preson Operators AND May 14,1999 1CAN059901 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 Proposed Technical Speci6 cation Changes Revising Steam Generator Tubing Surveillance Requirements Gentlemen-Attached for your review and approval are proposed Technical Specification (TS) changes revising the requirements associated with Arkansas Nuclear One - Unit 1 (ANO-1) provisions for steam generator tubing inspection and repair. The proposed changes affect ANO-1 TS Surveillance Requirements and applicable bases relevant to inservice inspection requirements for the portions of the once-through steam generator (OTSG) tubes encompassed by the upper tube sheet.
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The proposed changes are desired to allow continued operation of ANO-1 beyond future
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OTSG iamaaation outages while preventing undue financial hardship, significantly increased radiological exposures, and unnecessary increases in outage duration due to repairs of f{0$
volumetric outer diameter intergranular attack (ODIGA) flawed tubes within the upper tubesheet. Current TSs, as revised by Amendment 191, allow ANO-1 to operate through its 15' core cycle by allowing degradation due to ODIGA beyond the defined plugging limit.
This current allowance is.being revised for ANO-1 operation beyond the end of cycle 15.
These revised requirements affect the surveillance criteria for that portion of the OTSG tube regarded as a primary-to-secondary pressure boundary located within the upper tube sheet and impacted by ODIGA. Analysis of this tube region for this degradat';n mechanism has indicated a negligible failure response compared to the remaining tube length during accident conditions.
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s ANO-1, in working with Psamatome Technologies, Inc. (FTI), has determined that it is aceaa*=hle to operate with specific ODIGA OTSG tube indications. The proposed changes are largely consistent with current TS criteria for which a OTSG tube may be removed from service or allowed to remain in service based on the ANO-1 TS Amendment 191, dated April 10,1998. These changes do not result in a substantial change in the potential for OTSG tube leakage or failure.
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1 U. S. NRC May 14,1999 1CAN059901 Page 2 The information provided in this submittal is based on topical repon BAW-10235P, Management Program for Volumetric Outer Diameter Intergranular Attack in the Tubesheets of Once-Through Steam Generators, Revision 0, prepared by FTI. This report is proprietary to FTI. Included with the submittal of Attachment 1 is a copy of topical report BAW-10235P, Revision 0. An affidavit from FTI is included in Attachment 3. The affidavit sets forth the basis on which the information may be withheld from public disclosure by the NRC and addresses the considerations listed in 10 CFR 2.790(b)(4).
Accordingly, Entergy Operations requests that the topical repon contained in Attachment 2 be withheld from public disclosure. A non-proprietary version of the topical report will be prepared and submitted under separate cover.
This proposed change has been evaluated in accordance with 10 CFR 50.91(a)(1) using criteria in 10 CFR 50.92(c) and it has been determined that this change involves no significant hazards considerations. The bases for these determinations are included in the attached submittal.
The proposed change is intended to allow continued operation of ANO-1 beyond the upcoming IRIS outage while leaving OTSG tubes with upper tubesheet ODIGA indications in service he to the high degree of confidence that this degradation will not cause leakage or 4
stmetural failure of the tubes during normal or accident conditions. Since the next ANO-1 OTSG outage is scheduled to commence on September 10, 1999, Entergy Operations requests NRC approval by September 1,1999, with implementation to occur prior to startup from IRIS.
i Very truly y 4[
dbb Attachments To the best of my knowledge and belief, the statements contained in this submittal are true.
SUBSCRIBED AND SWORN TO before me, a Notary Public in and for Am County and the State of Arkansas, this /3 day of
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U. S. NRC May 14,1999 1CANO$9901 Page 3 cc:
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. Nick Hilton NRR Project Manager Region IV/ANO-1 U. S. Nuclear Regulatory Commission NRR Mail Stop 13-D-18 One White Flint North 11555 Rockville Pike Rockville, MD 20852 Mr. David D. Snellings Director, Division ofRsdistion Control and Emergency Management Arkansas Department ofHealth 4815 West Markham Street-Li* Rock, AR 72205 9
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ATTACHMENT _1 IQ ICAN059901 PROPOSED TECHNICAL SPECIFICATION AND RESPECTIVE SAFETY ANALYSES IN THE MATTER OF AMENDING LICENSE NO. DPR-51 ENTERGY OPERATIONS. INC.
ARKANSAS NUCLEAR ONE. UNIT ONE DOCKET NO. 50-313 l
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Attachment I to 1CAN059901 Page 1 of12 DESCRIPTION OF PROPOSED CHANGES The proposed changes to the Arkansas Nuclear One, Unit 1 (ANO-1) Technical Specifications (TS) provide for the application of the volumetric outer diameter intergranular attack (ODIGA) alternate repair criteria (ARC). Amendment 191, dated April 10,1998, provided j
alternate repair criteria that applied only to the ANO-1 operating Cycle 15. The proposed change contained herein justifies continued operation beyond Cycle 15 for ANO-1 while leaving once-through steam generator (OTSG) tubes having ODIGA indications that are located in a defmed area of the upper tube sheet in service.
Additions, revisions, and deletions are proposed as indicated below to provide for the implementation of the ODIGA ARC applicable to future operating cycles at ANO 1.
An addition is made to specification 4.18.3.a.4, to address required testing of tubes and tube sections associated with the application of the ODIGA ARC. Requirements are added for 100% bobbin coil examination of the defined region of the upper tubesheet. In addition, the results of these examinations are being excluded from consideration in the first random sample.
Two sentences were added to the end of the first paragraph of 4.18.5.a.7 to specifically differentiate between current plugging limit criteria and that associated with the sections of tube contained within the defined region of the upper tubesheet when applying the ODIGA ARC. Because this section discusses acceptance criteria, specific reference is given to the location of such criteria associated with the ARC. This change also incorporates the specifications of the defined region.
The wording of the original specification is also modified to enhance readability.
The portions of 4.18.5.b that apply to the ANO-1 Cycle 15 ODIGA under Amendment 191 have been deleted in favor of the proposed changes of this submittal.
The current requirement to submit the ISI report to the NRC within 45 days as stated in the first paragraph of 4.18.6 is exter.ded to 90 days.
New item 4.18.6.e is added to require summary data associated with ODIGA to be included in the in-service inspection (ISI) report required to be submitted to the NRC.
The wording to the second paragraph of the bases was revised and additions made as applicable to support the application of the ODIGA ARC. Included in this change is reference to the Framatome Technologies, Inc. (FTI) topical report where specific criteria may be studied.
Attachment I to ICAN059901 Page 2 of12 Review of the current TS Section 4.18 indicated improvements could be made to enhance human factors. This involved moving current paragraphs from page to page to both allow for additions usociated with this submittal and at the same time enhance subject flow. The movement of specific paragraphs and other similar changes are discussed briefly below and, because they are administrative in nature, are not mentioned again in this submittal.
The last paragraph of 4.18.3.a.2, all of 4.18.3.a.3,4.18.3.b, and 4.18.3.c are moved from page 100k to page 110jl.
Notes 1,2, and 3 of 4.18.3 are moved from the top of page 1101 to page 100k.
The remainder of 4.18.4, currently at the top of page 110m, is moved forward to page 1101, allowing all of 4.18.4 to appear on a single page.
4.18.5.a.8, 4.18.5.a.9, and 4.18.5.b are moved from page 110ml to 110m, placing the acceptance criteria of 4.18.5 on a single page.
The remainder of 4.18.6, currently at the top of page 110n, is moved to 110ml, allowing the bases to be located on a single page.
In the first sentence of Specification 4.18.4.c.1, closure was added to the parenthesis.
A typographical error is corrected in Specification 4.18.5.a.4 such that the "s" sign is changed to the "2:" sign.
The following background provided in support of these changes is largely based on topical report BAW-10235P, Management Program for Volumetric Outer Diameter Intergranular Attack in the Tubesheets of Once-Through Steam Generators, Revision 0. Information of greater detail may be found by referencing this topical report.
BACKGROUND The inservice inspection of the ANO-1 OTSGs is conducted in accordance with ANO-1 TS 4.18. Specification 4.18.2 states: " Inservice inspection of steam generator tubin;j shall include non-destructive examination by eddy-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 generator shall be determined operable after completing the corresponding actions (plug, reroll, or sleeve all tubes exceeding the plugging limit and all tubes containing through-wall cracks) required by Table 4.18-2."
Table 4.18-2 specifies the expansion criteria for sampling of the steam generator tubes and requires " defective" tubes to be plugged or sleeved. Specification 4.18.5 defines Defect as:
"an imperfection of such severity that it exceeds the plugging limit except where the imperfection has been spanned by the installation of a sleeve. A tube containing a defect in its
Attachment I to 1CAN059901 Page 3 of12 pressure boundary is defective." Phoein. Iimit is defined in the same specification as: "the imperfection depth at or beyond which the tube shall be restored to serviceability by the installation of a sleeve, rerolled, or removed from service because it may become unserviceable prior to the next inspection; 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 stmetural integrity of this portion of the RCS will be maintained."
ANO-1 utihzes two model 177FA OTSGs. The OTSG is a strnight-tube, venical, counter-flow, once-through heat exchanger with shell-side boiling. Primary fluid from the reactor enters through an inlet nozzle in the top head, flows down through the tubes, is collected in the bottom head, and exits through two primary outlet nozzles. The feedwater enters through a series of spray nozzles near the top of the annular feedwater-heating chamber. Here the feedwater is heated to saturation temperature by direct contact with high-quality or slightly superheated bleed steam. The resulting saturated feedwater enters the tube bundle through ports near the bottom of the tube bundle. Nucleate boiling starts immediately upon contact with the hot tubes. Steam quality increases as the==ahey fluid flows upward between the tubes in counter-flow to,the primary fluid inside the tubes. The depanure from nucleate boiling occurs at about the 25-foot level at design conditions. The mode of heat transfer then changes from nucleate to film boiling. Steam quality continues to increase, but at a slower rate. After 100% quality is reached, the steam becomes superheated, leaves the tube bundle at the upper tubesheet, flows down the steam annulus, and exits through two steam outlet nozzles.
The more than 15,000 alloy 600 tubes employed in each OTSG are 5/8 inch OD x 0.037 inch nominal wall x 52 feet long. All are partially roll expanded and attached to the upper and lower tubesheets by fillet welds. The use of straight tubes results in almost pure counter-flow properties. This design along with the fact that alloy 600 tubes have a thermal coefficient of expansion slightly greater than that of the carbon steel shell, provide for compressive loading 4
of the tubes during normal operating conditions. Compressive loading tends to inhibit the initiation and propagation of stress related damage mechanisms. As a result of being both sensitized and stress relieved during manufacturing, the tubes illustrate an improved resistance to stress corrosion cracking, but a susceptibility to intergranular attack.
Examination of a tube removed from the A OTSG in 1978 revealed deposits and a corrosion film containing elevated levels of sulfur and silicon, with trace amounts of chlorine and other contaminants Such contamination was believed to have caused intergranular attack of the tubes secondary-side surface. This was further confirmed in 1982 during the examination of two OTSG B tubes. Sulfur and chlorine contaminants were again disclosed during the examination, and evidence of ODIGA was noted. One of these tubes indicated an ODIGA induced degradation pm ning approximately 50% through-wall (TW).
f Attachment I to ICAN059901 Page 4 of12 AAer further study, changes to the secondary system chemical controls at ANO-1 were implemented to minimize the ingress of sulfur and chlorides to the OTSGs. Results of tube examinations aAer 1984 indicated sulfur, chloride, and silicon contaminate levels were no longer elevated. Based on all available results to date, the damage mechanism appears to be dormant.
Through 1R13, ODIGA indications were sized and leR in service if measured bobbin coil extents were <40% TW, Testing performed on selected ANO-1 OTSG tubes removed during the IR13 outage, revealed that actual ODIGA through-wall (TW) depths were not consistent with the results of eddy current testing performed on the tubes during IR13. By this observation, it became apparent that ODIGA affected tubes having >40%TW depths may have been lea in service. Upon determination of non-compliance, ANO-1 promptly sought and was granted enforcement discretion. ANO-1 then began efforts to follow-up with an amendment to its TSs.-
Entergy Operations submitted an exigent TS change on April 11,1997 (ICAN049703), to allow a one time exception to the surveillance requirements of Specification 4.18.5.b. This e=captian allowed tubes with ODIGA 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. The April 11, 1997, submittal was supplemented on May 2,1997, by letter ICAN059702 which reduced the leakage limit through the OTSG tubes from 500 gallons per day (gpd) to 144 gpd for the remainder of Cycle 14. In response to this request, the NRC
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l issued A==d=aat No.189 to the ANO-1 license dated May 7,1997. This amendment allowed the unit to continue operation through the remainder of Cycle 14 with tubes that had potential through-wall defects in exceu of the 40% plugging limit.
The Babcock and Wilcox Owners Group (B&WOG) had previously been developing alternate repair criteria for freespan and tubesheet volumetdc ODIGA flaws. Because of the number of ODIGA indications detected in the upper tubesheet (UTS) regions of the ANO-1 OTSGs and due to inconsistencies in sizing ODIGA depths within the UTS, it was decided to focus efforts solely on the UTS region. Without verification of speci6c TW depth, each indication is conservatively considered to be above the current plugging criteria of 40%TW. Therefore, the B&WOG began immediate evaluation of an alternate repair criteda for ODIGA indications located in the UTS region only. Although topical report BAW-10226P was prepared and submitted prior to IR14, insufficient time prevented resolution of all outstanding issues.
Therefore, based on the information available, ANO-1 submitted a second amendment request to allow continued operation through Cycle 15.
In letter ICAN049803, dated April 1,1998, ANO-1 proposed an amendment provided discussion and technical bases supporting the treatment of ODIGA affected OTSG tubes within the UTS as unique in comparison to other tube defects. The proposed amendment was approved by the NRC on April 10,1998, allowing ODIGA affected tubes in the UTS region to remain in service during ANO-l's Cycle 15. As part of Amendment No.191 to the ANO-1 TS, Sve requirements were included: 100% bobbin coil inspection of the upper tubesheet region would be performed in IR14, a rotating pancake co'd would be used to confirm
Attachment I ts ICAN059901 Page 5 of12 ODIGA indications, IR14 voltages would be compared with data from 1R13, an upper limit was placed on flaw extents and allowed growth, and 1R14 in-situ tests would verify that potential leakage from ODIGA affected tubes in the UTS region would remain s; 50% of the primary-to-secondary leak rate limits assumed in the accident analysis for the associated cycle.
These requirements are fundamentally maintained and expounded upon in the proposed changes of this submittal. This proposed change will allow ODIGA affected tubes within the defined region of the UTS to remain in service beyond Cycle 15 while establishing a continued monitoring program to ensure the structural integrity and leakage rates of these tubes are j
maintained.
To determine effects ofvolumetric ODIGA on the tube integrity within the UTS, both normal operating conditions and limiting accident conditions were considered. Acceptance criteria for separate analyses were also taken into account. For example, acceptance criteria for structural evaluations differ from that criteria used in leakage evaluations and so forth. In addition, the evaluations are limited to the length of tube between the tube roll in the UTS and one inch above the secondary face of the UTS. Evaluations do not consider indications found in the tube roll length, the roll transition area, or beyond the UTS secondary face. The one inch buffer zone ensures that edge effects observed do not inhibit the proper characterization ofindications detected by bobbin coil examination.
Several laboratory tests were performed to verify both the structural integrity and the leakage rates of tubes with ODIGA indications of various TW depths and lengths would be acceptable. Among these are destructive examinations where a differential pressure is applied to the tube until failure or bursting is achieved. It is important to note that volumetric ODIGA does not_ involve a loss of wall thickness, but is limited to the degradation of the grain boundaries within the tube wall. Therefore, this damage mechanism has very little effect on the structural integrity of the tubing.
Experiments discussed in EPRI Report 6864-L indicated burst pressures of the portion of OTSG tubes located within an enclosure are not impected by flaws, provided the clearance between the outer tube wall and the enclosure is less than approximately 0.030 inches. The diametral gap in the UTS of ANO-1 OTSG tubes is 0.021 inches. All tests performed where defective tubes were confined within a tubesheet illustrated failure pressures consistent with that of tubes containing no flaws and all failures occurred outside the tubestat, typically 1.5 inches or more away from the tubesheet face.
4 Tensile stresses are by nature associated with certain cooldown transients. Values provided in topical report BAW-10235P, Revision 0, indicate the limiting tensile load for ANO-1 is 2097 lbs, based on a postulated SBLOCA event. A safety factor of 1/0.7 was considered with a resulting load of 2996 lbs used in the evaluation. The same report provides test results indicating tube structural integrity to be maintained by tubes with ODIGA flaws of 100% TW and a circumferential range of 140' The typical" thumbnail" shaped cross-section of ANO-1 ODIGA indications have previously shown maximum circumferential extents of
~80'.
Therefore, tensile stresses are not expected to have an apprec'able effect on UTS ODIGA indications at ANO-1.
E Attachment I to 1CAN059901 Page 6 of12 Fatigue loading may be high-cycle or low-cycle. High-cycle fatigue is believed to develop from flaws initiated at sites oflocalized corrosion or wear that propagates into fatigue cracks by flow induced vibration associated with high cross flow. This phenomenon is generally associated with the open tube lane area of the ANO-1 OTSGs. High cycle fatigue has been
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successfully addressed in the ANO-1 OTSGs by preventatively sleeving susceptible tubes through the UTS and top span of the OTSGs. Low-cycle fatigue results primarily from mechanical, thermal, and pressure cycling during normal plant operation. Such indications would be evidenced during eddy current inspections of the OTSG tubes and, if necessary, the tubes would be removed from service at that time. In the case of either type of fatigue loading, any resulting effects are not adversely impacted by the ODIGA alternate repair criteria proposal.
During the IR14 outage,36 ODIGA patches of various depths and lengths were in-situ tested at normal operating differential pressure of 1500 psi and the accident pressure of 2900 psi (safety valve liA including 3% tolerance and thermal uncertainty factors) while applying an axial load of 1402 lbs. No leakage was evidenced from any of the tubes tested. In addition, three ODIGA flawed tubes with four indications were pressurized to 4400 psi and 6500 psi and again indicated no leakage. Similar hot leak tests were performed in the laboratory under near-normal operating temperatures and accident pressure, with like results of no leakage.
For the purpose of postulating leakage, then, it is therefore assumed that the ODIGA must form a crack in order to develop a potential for leakage. At this point, however, the degradation is in a mixed-mode form and is not bound by the evaluations performed solely on ODIGAindications of the UTS.
In addition to the above discussions on various tube integrity issues, it should be noted that all of the tubes in the B OTSG experienced sigrdacent differential pressure (~2100 psi) and thermal loads for several hours in May of 1996 due to a plant transient on ANO-1. No leakage resulted from ODIGA indications as a result of this transient. Furthermore, ODIGA flaws have not contributed to primary-to-secondary leakage at ANO-1, though operation with in-service ODIGA flaws has existed for many years.
In order to effectively implement the proposed changes, not only is an evaluation of tube '
integrity required, but a method of evaluating the growth of ODIGA indications is also necessary. As mentioned previously, the improved chemistry control at ANO-1 has had the effect of removing the mechanism that is beheved to have caused the existing defects associated with ODIGA to grow or for new defects to form. This is supported by available eddy current information. The mean population voltage for bobbin testing performed over the period of 1993-1998 on more than 100 indications i'bstrated no appreciable increase in overall size of the ODIGA defects. In addition, OTSG bubble tests, in-situ pressure tests, tube pulls, and in-service leakage monitoring have not identified any 100%TW ODIGA indications or primary-to-secondary leakage attributed to ODIGA indications. Nevertheless, monitoring for growth is conservative and is discussed in length later in this submittal.
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i-Attachment I ts 1CAN059901 Page 7 of12
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The evaluations of topical report BAW-10235P, Revision 0, show that the volumetric ODIGA, due to its limited size, has very little effect on the structural performance or leakage potential of the tubing. That portion of the tube within the defined region of the UT3 are constrained by the presence of the tubesheet, thus preventing the tube burst due to the existence of ODIGA flaws. Tensile rupture of tubes with ODIGA is highly improbable based on the results of tensile testing OTSG tubes with uniform thinning and 100%TW holes. The potential consequences of fatigue are mitigated by preventative sleeving and evaluating ODIGA for growth. Evaluations have also illustrated that this type of damage mechanism, along with its typically small size, make it a very unlikely candidate for primary-to-secondary leakage. Lastly, any potential effect of cross-flow loads during a MSLB condition have been addressed and are considered negligible within the UTS.
DISCUSSION OF CHANGE Several changes to ANO-1 TS 4.18 are proposed to ensure the proper indentification, monitoring, assessments, and resulting actions, if any, are performed for ODIGA indications in the defined region of the UTS. Technical data, calculations, and exact testing methods and results are discussed in topical report BAW-10235P, Revision 0.
Chaneae to 4.18.3 "Selmian and Ta=*ina" An additional requirement to specification 4.18.3.a.4, ensures that both a bobbin and rotating coil examination are performed on all previously identified ODIGA indications as part of the first sample 6 :-*ian required by 4.18.3.a. The bobbin examination spans the length of the defined region of the UTS and is performed on all in-service tubes. This examination will assist in determining if any new indications are evident. The rotating coil inspections will include examining each indication with both the rotating pancake coil and the plus-point coil.
The results of these examinations are necessary to determine overall population and any growth ofODIGAindications.
In addition, the new 4.18.3.a.4 instructions exempt the results of the 100% bobbin coil examination from the first random sample since the sample size cannot be increased above i
100%. No value would therefore be added by such inclusion. Data collected under the performance of the two new requirements mentioned above are evaluated under the ODIGA ARC condition monitoring and operational assessment program, containing ' structions of m
how the data is to be used and actions required as a result of the data use. The overall assessment process includes four phases. The first phase will define the population of ODIGA indications in each OTSG. This is necessary when considering potential primary-to-secondary leakage during a MSLB. The second phase will determine the number of tubes that will
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undergo in-situ testing as a result of phase one findings. In-situ testing will then be performed in the third phase. The final phase documents the results of the previous phases as part of the ISI report. A detailed discussion may be found in topical report BAW-10235P, Revision 0.
F Attachment I ts ICAN059901 Page 8 of12 Chaaaan to 4.18.5 " Ace *atmace Criteria" An addition has been made to the end of the first paragraph under 4.18.5.a.7 to specifically differentiate UTS ODIGA tubes from the current plugging limit.
Corrective actions associated with ODIGA tubes will be performed in recordance with topical report BAW-10235P, Revision 0. In-situ testing will be performed as required, and any tubes found to leak will be removed from service. Other corrective actions will be addressed through the operational assessment. The original wording of this specification is also changed to enhance readability.
The portions of Spanha* ion 4.18.5.b that were added under TS Amandment 191 have been
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deleted. Where applicable, these Cycle 15 requirements have been revised and incorporated into the proposed changes of this submittal. The revisions are justified based on funher analyses that has been performed, discussed in topical report BAW-10235, since the submittal ofTS h===he 191.
Chanaan to 4.18.6 "Raanets" In addition, ANO-1 requests the allowed period fc submittal be extended from 45 days to 90 days. This is indicated in the change to the first pangraph of 4.18.6. Although gathered ODIGA data from the inspection would normally be avadable within 45 days, such a period is rigorous when considering the operational assessment portion of the ODIGA ARC. The assessment projects the conditions of ODIGA' tubes during the length of the following operating cycle and requires some time to accurately complete.
An additional specification is added, 4.18.6.e, requiring ODIGA condition monitoring and operational assessment data to be submitted to the NRC as part of the ISI report. The information submitted will include the number of detected ODIGA indications in each OTSG, the number of ODIGA indications left in service, and the total MSLB leakage predicted for the limiting OTSG.
Changes to Bases The wording of the second paragraph of the bases was revised and additions made as applicable to support the application of the ODIGA ARC. Reference is also given to the topical report BAW-10235P, Revision 0, in order to provide the user a success path for program detail The " defined region" referred io in the aforementioned proposed changes is also clarified in the bases In summation, the studies and evaluations performed indicate that ODIGA affected tubes within the defined area of the UTS do not pose an appreciable threat to safe plant operation or to the health and safety of the public. The proposed changes to the ANO ~ TS are consistent with the principles set forth by the NRC for risk informed decision making.
Current regulation is met based w the maintenance of structural integrity and leak rate limits assessed in this program Because the structural integrity and leak rate limits are maintained, no
- ts ICAN059901 Page 9 of12 chang to the defense-in-depth philosophy is evident. Safety margins consistent with the 4
design bases for ANO-1 are maintained considering the tubes have been shown to not burst I
within the defined region and leak rates are again maintained within limits. Based on these same criteria, no effect on core damage frequency, the consequences of a severe accident, or large early release frequencies is evident for ANO-1. Finally, a satisfactory performance monitoring program is established that both assesses current conditions and projects future conditions of tubes associated with ODIGA. Therefore, because identification, testing, monitoring, and reportability associated with ODIGA affected tubes within the defined region of the UTS have been adequately addressed, ANO-1 requests that the aforementioned changes to its technical specifications be approved.
3 Severe Accident Consideration The proposed TS change will be applied only to ODIGA flaws within the defined region of the UTS at ANO-1. Based on structural testing described above and in topical report BAW-10235P, Revision 0, it was concluded that burst within the tubesheet is not possible due to the tight diametral clearance between the tube and tubesheet. Conditions associated with a postulated severe accident do not affect this conclusion. Therefore, the probability of tube rupture does not increase. Because burst will not occur within this defined region of the UTS, thermal challenges e= mew with a severe accident cannot increase the probability of tube burst within this location. Furthermore, application of the ODIGA alternate repair criteria has no effect on the rema'isng containment structures, or on any plant process or procedure that would increase the likelihood or consequences of any accident.
In regard to core damage la4M steam generator tube ruptures, the conclusions made by the NRC in NUREG-1570, Risk Assessment of Severe Accident-Induced Steam Generator Tube Rupture, are that severe accident thermal challenges to steam generator tubes are not a concern for the B&W design. In addition to the above, preliminary results from an EPRI study indicate that B&W plants are not susceptible to the hot leg counter-current natural circulation phenomenon that presents a challenge to the steam generator tubes in other PWR designs. The B&W OTSG design is inherently protected against this natural circulation process hennan of the vertical orientation of the hot legs.
Therefore, the proposed changes to the ANO-1 TSs are not expected to increase the SG thermal challenge frequency or have an adverse risk impact on ANO-1.
DETERMINATION OF NO SIGNIFICANT HAZARDS CONSIDERATION Entergy Operations, Inc. is proposing that the Arkansas Nuclear One, Unit 1 (ANO-1)
Operating %- be amended to revise the requirements associated with the inspection, testing, and reporting of once-through steam generator (OTSG) tubes affected specifically by volumetric outer diameter intergranular sttack (ODIGA) within the defined regions of the upper tubesheet. Current standards do not consider tube burst probability for ODIGA indications within the defined region of the upper tubesheet (UTS), or the improbability for
Attachment I ts ICAN059901 Page 10 of12 leakage to occur from an ODIGA affected tube in this region. The proposed change is rwaaaary to prevent removing OTSG tubes from service that are functionally evaluated to provide a protective barrier for radiation release to the public without increasing the likelihood of an accident or inhibiting the ability to mitigate accidents. The proposed changes are consistent with the recommendations of topical report BAW-10235P, Management Program for Volumetric Outer Diameter Intergranular Attack in the Tubesheets of Once-Through Steam Generators, Revision 0, prepared by Framatome Technologies, Inc.
An evaluation of the proposed change has been performed in accordance with 10CFR50.91(a)(1) regarding no significant hazards considerations using the standards in 10CFR50.92(c). A discussion of these standards as they relate to this amendment request follows:
Criterion 1 -
Does Not Involve a Significant Increase in the Probability or Consequences of an Accident Previously Evaluated.
The once-through steam generators OTSG are used to remove heat from the reactor coolant system during normal operation and during accident conditions. The OTSG tubing forms a substantial portion of the reactor coolant pressure boundary. An OTSG tube failure is a breach of the reactor coolant pressure boundary and is a speci6c accident analyzed in the ANO-1 Safety Analysis Report.
The purpose of the periodic surveillance performed on the OTSGs in accordance with ANO-1 Technical Specification (TS) 4.18 is to ensure that the structural integrity of this portion of the reactor coolant system will be maintained. The TS plugging limit of 40% of the nominal tube wall thickness requires tubes to be repaired or removed from service because the tube may become unserviceable prior to the next inspection.
Unserviceable is defined in the TS 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 accident, or a steam line or feedwater line break. The proposed TS change allows OTSG tubes with ODIGA indications contained within a defined area of the UTS to remain in service with existing degradation exceeding the existing 40% through-wall (TW) plugging limit.
Extensive testing and plant experience has illustrated that ODIGA flaws confined to this area within the OTSG will not result in tube burst or tube leakage. Therefore, allowing ODIGA flaws in this specific region to remain in service will not alter the l
cor.ditions assumed in the cuaent ANO-1 accident analysis for OTSG tube failures under poahdatad accident conditions. In addition, the condition of the OTSG tubes in this region are monitored during regular inspection intervals to assess for evidence of growth. Any growth noted will be addressed through testing and the operational assessment.
Therefore, ANO-1 has determined that the identification, testing, monitoring, assessment, and corrective action programs provided in topical report BAW-10235P, Revision 0, sufficiently supports this change request.
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I Attachment I to ICAN059901 Page 11 of12 Application of the ODIGA alternate repair criteria will allow leaving tubes with ODIGA indications found in the defined area of the UTS in service while ensuring safe operation by monitoring and assessing the present and future conditions of the tubes.
ANO-1 has operated since 1984 with ODIGA affected tubes in service with no appreciable effect on structural integrity or indications of tube leakage from ODIGA sources within the UTS. Through the inspection, testing, monitoring, and assessment program previously mentioned, and the on-line leak detection capabilities available during plant operation, continued safe operation of ANO-1 is reasonably assured.
Therefore, the application of the ODIGA alternate repair criteria provided by topical report BAW-10235P, Revision 0, does not involve a signi6 cant increase in the probability or consequences of any acciden* previously evaluated.
Criterion 2 -
Does Not Create the Possibuity of a New or Different Kind of Accident from any Pmviously Evaluated.
The implementation of the ODIGA alternate repair criteria will not result ha any failure mode not previously analyzed. The OTSGs are passive components. The intent of the TS surveillance requirements are being met by these proposed changes in that adequate structural and leak integrity will be maintained. Additionally, the proposed i
change does not introduce any new modes of plant operation.
Therefore, this change does not 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 application of an alternate repair criteria Sr ODIGA provides adequate assurance with margin that ANO-1 steam generator tubes will retain their integrity under normal and accident conditions. The structural requirements of ODIGA affected tubes have been evaluated satisfactorily and meet or exceed regulatory requirements. Leakage rates for these tubes within the defined region of the upper tubesheet are essentially zero and are reasonably assured to remain within the assumptions of the accident analysis by proper application of the ODIGA alternate repair criteria program.
Because no appreciable impact is evidenced on the tubes structural integrity or its resulting leak rate, the margin to safety remains effectively unaltered.
Therefore, this change does not involve a significant reduction in the margin of safety.
Therefore, based upon the reasoning presented above and the previous discussion of the I
amendment request, Entergy Operations has determined that the requested change does not involve a significant hazards consideration.
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Attachment I ts ICAN059901 Page 12 of12 ENVIRONMENTALIMPACT EVALUATION 10 CFR St.22(c) provides criteria for and identification of licensing and regulatory actions eligible for categorical exclusion from performing an environmental assessment. A proposed amendment to an operating license for a facility requires no environmental assessment if operation of the facility in accordance with the proposed amendment would not: (1) involve a significant hazards consideration, (2) result in a significant change in the types or significant increase in the amounts of any effluents that may be released off-site, or (3) result in a signi6 cant increase in individual or cumulative occupational radiation exposure. Entergy Operations, Inc. has reviewed this license amendment and has determined that it meets the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9). Pursuant to 10 CFR 51.22(b), no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the proposed license amendment. The bases for this determination is as follows:
1.
The proposed license amendment does not involve a significant hazards consideration as described previously in the evaluction.
2.
As discussed in the no significant hazards evaluation, this change does not result in a significant change or significant increase in the radiological doses for any Design Based Accident. The proposed license amendment does not result in a significant change in the types or a significant increase in the amounts of any effluents that may be released off-site.
3.
The proposed license amendment does not result in a significant increase to the individual or cumulative occupational radiation exposure because this does not modify the method of operation of systems and components necessary to prevent a radioactive release.