ML20086D991
| ML20086D991 | |
| Person / Time | |
|---|---|
| Site: | Byron, Braidwood  |
| Issue date: | 07/07/1995 |
| From: | Pontious H COMMONWEALTH EDISON CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML20086D995 | List: |
| References | |
| NUDOCS 9507110103 | |
| Download: ML20086D991 (39) | |
Text
. _ _ _ _ .
. t i' pl i Commonwealth IWimn Company 14(W) Opus Piace Downers Grove, 11.60515 w
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f July 7, 1995 4 l 1 . U.S. Nuclear Regulatory Commission
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Document Control Desk Washington, D.C. 20555
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Subject:
Supplement to Application for Amendment to
- ph Facility Operating Licenses- F Q
Byron Nuclear Power Station, Units 1 and 2
% NPF-37/66; NRC Docket Nos. 50-454/455 Braidwood Nuclear Power Station, Units 1 and 2 NPF-72/77; NRC Docket Nos. 50-456/457
References:
- 1. D. Saccomando letter to the Nuclear :
Regulatory Commission dated February 13,
- 1995, transmitting Proposed Technical Specification Amendment Regarding g Increase in IPC Crit la =
T
- 2. D. Saccomando lette; _o the Nuclear Regulatory Commission dated June 20, n 1995, transmitting Latest Final Results j for the Leak Test Program for Indications Restricted from Burst 1
Reference 1 transmitted Commonwealth Edison Company's
~
(Comed's) proposal to amend Appendix A, Technical Specifications of Facility Operating Licenses NPF-37, NPF-66, NPF-72 and NPF-77. The proposed amendment request )N addresses Technical Specification changes necessary to @
increase the Interim Plugging Criteria (IPC) value for Byron and Braidwood Stations Unit 1 Steam Generators (SGs).
. Information contained in this amendment request justifies an
- increase in the IPC for the hot-leg tube intersections with outside diameter stress corrosion cracking (ODSCC) from 1.0 volt to 3.0 volts. f 1
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NRC Document Control Desk July 7, 1995 Subsequent to that amendment request Comed and the NRC met on February 23, 1995, to discuss the submittal. During that meeting Comed presented a model which addressed leakage from indication restricted from burst (IRB). After discussions, Comed pursued the development of an alternate leak rate model along with a test program to support the alternate leak rate model. Reference 2 submitted the latest final results of the leak rate test program along with our conclusion that the free span leak rate calculation methodology approved for ODSCC at the tube support plate (TSP) provides sufficient conservatism for use with a calculate leak rates with 3.0 volts IPC. Comed believes that the use of this methodology is acceptable, but to help '
expedite the review, Comed is requesting the Staff's review
- and approval of the leak rate methodology contained in Attachment F.
The attached package supersedes that which was previously submitted via Reference 1. The following describes how this supplement differs from the previously submitted amendment request.
To expedite review and approval of this proposed amendment, Comed will use the Generic Letter POD value of 0.6 for all voltage amplitude ranges. The February 13, 1995, submittal discussed the use of a voltage dependent POD and submitted the EPRI Project 6424/RP-3580, " Probability of Detection by Bobbin Inspection for the NRC review and approval. This report is being modified to account for the possible initiation of new ODSCC indications between scheduled SG inspections.
When complete, this report will be used as the basis for a future request for an alternate POD.
In this supplement, Comed submits a Leak Rate Methodology for Indications Restricted from Burst in Attachment F. This methodology replaces the one previously submitted in Sections 9.7 and 9.8 of WCAP-14273.
NRC Document Control Desk July 7, 1995 As a conservative measure, both Byron and Braidwood nave reduced their Unit 1 reactor coolant system Dose Equivalent Iodine-131 from 1.0 microcuries/ gram to 0.35 microCuries/ gram until the steam generators are replaced.
Byron and Braidwood intend on repairing / plugging all indications greater than 3 volts and has eliminated the request to implement a 10 volt limit for unconfirmed indications.
The Technical Specification pages submitted in this supplement reflect the model technical specifications included in the May 30, 1995, Frank J. Miraglia memorandum to Edward L. Jordan requesting CRGR review of Generic Letter 95-XX, " Voltage-Based Repair Criteria for Westinghouse Steam Generator Tubes Affected by Outside Diameter Stress Corrosion Cracking." Byron and Braidwood followed the memorandum as closely as possible when making the required changes to their current specifications. However, since Byron and Braidwood are proposing essentially two repair limits; a 3.0 volt repair limit for the hot-legs and a 1.0 volt repair limit for the cold-legs, some minor changes from the model technical specifications were required. This change was discussed with the Staff on June 29th and it appeared to be acceptable.
This package consists of the following:
Attachment A: Description and Safety Analysis of Proposed Changes to Appendix A Attachment B: Byron /Braidwood Unit 1 Steam Generator Alternate Plugging Criteria Methodology i
Attachment C-1: Proposed Changes to the Technical Specification Pages for Braidwood Station Attachment C-2: Proposed Changes to the Technical Specification Pages for Byron Station l
L .. -- - _ _ _ _ _ _ _ _ _ _ _ _ . _ _ _ . _ _ _ _ _
NRC Document Control Desk July 7, 1995 Attachment D: Evaluation of Significant Hazards Consideration Attachment E: Environmental Assessment Attachment F: Leak Rate Methodology
.This amendment request is considered a cost beneficial licensing action. Application of a 3.0 volt alternate plugging criteria (APC) for ODSCC indications at the hot-leg TSPs would reduce the projected maximum number of tubes needing plugging or repair due to ODSCC to 80 for Byron, 62 for Braidwood. This represents a " savings" of 920 tubes at Byron and 913 tubes at Braidwood that would have had to be plugged or repaired using the previous 1.0 volt IPC. This represents a dollar savings of $1.8 Million apiece at Byron and Braidwood assuming all these tubes were plugged.
However, since plugging levels this high approach currently analyzed maximums, sleeving these tubes could add as much as
$6.1 Million apiece at Byron and Braidwood in outage inspection and repair costs. This dollar savings is based only upon repair costs and does not include additional costs associated with plant output derating, extension of outage time and person-rem. Comed requests approval of this proposed amendment by August 15, 1995. Approval by this date will help minimize the cost associated with the mobilization of equipment prior to the steam generator tube inspections.
Please note that the application of the APC is applicable to only Byron Unit 1 and Braidwood Unit 1. It is however being submitted for all four operating licenses because the Technical Specification pages are common to both units.
I To the best of my knowledge and belief, the statements contained in this document are true and correct. In some respects these statements are not based on my personal knowledge, but on information furnished by other Comed employees, contractor employees, and/or consultants. Such information has been reviewed in accordance with company practice, and I believe it to be reliable.
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l NRC Document Control Desk July 7, 1995 Please address any further comments or questions regarding this matter to this office.
g=z . :: ~ = z =:==:=4ll Sincerely, OFFICIAL SEAL i
j< MARY JO YACK ll '
ll feOT ARY PUBlic ST ATE OF ILifN
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Attachments cc: D. Lynch, Senior Project Manager-NRR R. Assa, Braidwood Project Manager-NRR G. Dick, Byron Project Manager-NRR E. Duncan, Acting Senior Resident Inspector-Braidwood H. Peterson, Senior Resident Inspector-Byron H. Miller, Regional Administrator-RIII Office of Nuclear Safety-IDNS
ATTACHMENT A DESCRIPTION AND SAFETY ANALYSIS OF PROPOSED CHANGES TO APPENDIX A TECHNICAL SPECIFICATIONS OF FACILITY OPERATING LICENSES NPF-37, NPF-66, NPF-72, AND NPF-77 A. DESCRIPTION OF THE PROPOSED CHANGE Commonwealth Edison (Comed) proposes to amend Byron and Braidwood Technical Specification (TS) 3.4.5, " Steam Generators," the Bases for TS 3.4.5, and TS 3.4.8, " Specific Activity". This proposal supersedes the previous Comed request of February 13, 1995.
The changes proposed to TS 3.4.5 will implement a 3.0 volt bobbin coil probe, voltage based, Steam Generator (SG) Tube Support Plate (TSP) Alternate Plugging Criteria (APC) limit for Outside Diameter Stress Corrosion Cracking (ODSCC) indications at the hot-leg TSP intersections.
The changes proposed to TS 3.4.8.a involve reducing Reactor Coolant System (RCS) dose equivalent Iodine-131 (I-131) for both Byron and Braidwood.
For Byron and Braidwood, additional changes are proposed to make Byron and Braidwood TS consistent with the Model TS contained in the May 30, 1995 Frank J. Miraglia memorandum to Edward L. Jordan requesting CRGR review of Generic Letter 95-XX, " Voltage-Based Repair Criteria For Westinghouse Steam Generator Tubes Affected by Outside Diameter Stress Corrosion Cracking" (May 30 Memorandum).
Specific changes are discussed in detail in Section E of this attachment. Affected TS pages showing the actual changes are included in Attachments C-1 and C-2.
B. DESCRIPTION OF THE CURRENT REQUIREMENT For Byron and Braidwood, the Technical Specification Surveillance Requirements (TSSR) for TS 3.4.5 require, in part, that axial flaws indicative of ODSCC confined within the thickness of the TSP may remain in service provided that the following requirements are met:
If the flaw-like bobbin coil signal amplitude is less than or equal to 1.0 volt, or 1
i i
If the flaw-like bobbin coil signal amplitude is greater than 1.0 volt but less than or equal to 2.7
. volts and the signal is not confirmed with Rotating Pancake Coil (RPC) examination, and The flaw-like signal is not in a location that is susceptible to collapse or deformation during a postulated Loss Of Coolant Accident (LOCA) + Safe Shutdown Earthquake (SSE) event.
Tubes containing flaw-like bobbin coil signal amplitudes greater than 2.7 volts must be plugged or repaired, regardless of RPC confirmation.
For Byron only, if as a result of leakage due to a mechanism other than ODSCC at the TSP intersection, or some other cause, an unscheduled inspection is performed, bobbin coil voltage limits are determined in accordance with an equation that takes into account the time remaining in the cycle, the structural limit voltage, and the bobbin voltage at the Beginning Of Cycle (BOC).
For Braidwood only, the TSSRs discuss eddy current inspection guidelines and contain a requirement that the projected End of Cycle (EOC) distribution of crack indications must result in a total primary to secondary leakage of less than 9.1 gallons per minute (gpm).
For Byron and Braidwood, TS 3.4.8.a requires that the specific activity of the RCS be limited to 1.0 microCuries per gram (pci/gm) dose equivalent I-131. For Braidwood only, TS 3.4.8.a references a footnote which requires that for Unit 1 Cycle 5, RCS dose equivalent I-131 will be limited to 0.35 pci/gm.
C. BASES FOR THE CURRENT REQUIREMENT The surveillance requirements for inspection of SG tubes ensure that the structural integrity of this portion of the RCS will be maintained. For tubes left in service due to application of Interim Plugging Criteria (IPC), analyses are performed to demonstrate acceptable probability of tube burst, and that Main Steam Line Break (MSLB) leakage is within site specific limits. Inservice inspection of SG tubing is essential in order to maintain surveillance of the conditions of the tubes in the event that there is evidence of mechanical damage or progressive degradation due to f design, manufacturing errors, or inservice conditions that i
l lead to corrosion. Inservice inspection of SG tubing also provides a means of characterizing the nature and cause of any tube degradation so that corrective measures can be j taken.
2 l
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For Byron only, the unplanned inspection voltr.ge equation takes into account indication growth that occ urs during the cycle. It conservatively establishes a voltage limit for each previously identified indication above which the tube must be plugged.
The inspection guidelines identified in the Braidwood Specifications ensure that the maximum number of indications are detected and ensure reliable, consistent acquisition and analysis of data.
With respect to TS 3.4.8, the limitations on the specific activity of the reactor coolant ensure that the resulting 2-hour doses at the Site Boundary will not exceed an appropriately small fraction of Title 10 Code of Federal Regulations Part 100 (10 CFR 100) dose guideline values following a SG tube rupture accident in conjunction with an assumed steady state reactor-to-secondary SG leakage rate of 1 gpm.
The current Braidwood Unit 1 Cycle 5 limit of 0.35 pci/gm referenced in the footnote to TS 3.4.8.a is based on ensuring the resulting 2 hour2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> doses at the Site Boundary will not exceed an appropriately small fraction of 10 CFR 100 dose guideline values in conjunction with the predicted MSLB leakage calculated as part of Braidwood Station's April 30, 1994, D. Saccomando to W. Russell letter.
For Braidwood, the leakage limits specified in the TS ensure that current offsite dose limits are maintained.
D. NEED FOR REVISION OF THE REQUIRE 3MNT At Byron and Braidwood, Unit 1 has four Westinghouse Model D-4 SGs and Unit 2 has four Westinghouse Model D-5 SGs.
These models differ-significantly in tube and TSP materials and design. The D-4 SGs have 0.75 inch thick carbon steel TSPs with drilled hole tube supports. The D-5 SGs have 1.125 inch thick stainless steel TSPs with Quatrefoil tube supports. The D-4 SG tubes are mill annealed Inconel 600 which were hard rolled into.the tubesheet during initial assembly. Subsequently, the D-4 tubes were shot peened in the tubesheet area and thermally stress relieved in the U-bend area. The D-5 tubes are heat treated Inconel 600 which were hydraulically expanded into the tube sheet during initial assembly. Over the past several refueling outages, the number of Unit 1 SG tubes plugged per outage has been increasing. Unit 1 has had more defective tubes than Unit 2 primarily due to the design differences between the D-4 and D-5 SGs as described above.
3 I .__ _ _ - _ _ _ - - -
Current repair projections for the Braidwood Unit 1 Cycle 5 Refueling Outage indicate that, using the current 1.0 volt IPC, as many as 975 SG tubes may need to be plugged or repaired by sleeving due to ODSCC. If all these tubes were plugged, this would result in a total of 2653 plugged tubes in the Braidwood Unit 1 SGs. Projections for Byron
+
Station's Unit 1 Mid-Cycle outage indicate that, using the current 1.0 volt IPC, as many as 1000 SG tubes may need to be plugged or repaired by sleeving due to ODSCC. If all these tubes were plugged, this would result in a total of
, 2752 plugged tubes in the Byron Unit 1 SGs. Plugging levels this high approach currently analyzed maximum levels and could result in significantly reduced RCS flow rates, plant output deratings, excessive outage repair costs and severely restricted SG life. Sleeving a sufficient number of tubes to reduce plugging to acceptable levels would result in a significant increase in outage cost, outage length, and radiation exposure.
Application of a 3.0 volt APC for ODSCC indications at the hot-leg TSPs would reduce the projected maximum number of tubes needing plugging or repair due to ODSCC to 80 for Byron, 62 for Braidwood. This represents a " savings" of 920 tubes at Byron and 913 tubes at Braidwood that would have had to be plugged or repaired using the previous 1.0 volt IPC. This represents a dollar savings of $1.8 Million apiece at Byron and Braidwood assuming all these tubes were plugged. However, since plugging levels this high approach currently analyzed maximums, sleeving these tubes could add as much as $6.1 Million apiece at Byron and Braidwood in outage inspection and repair costs.
Calculations conducted for Braidwood and Byron have shown that the resulting 2 hour2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> doses at the Byron and Braidwood site boundaries will not currently exceed an appropriately small fraction of 10 CFR 100 dose guideline values in conjunction with the predicted MSLB leakage calculated in accordance with this submittal and a dose equivalent I-131 level of 1.0 pci/gm. The site allowable leakage calculated using a dose equivalent I-131 level of 1.0 pci/gm is 9.4 gallons per minute (gpm) for Braidwood, and 12.8 gpm for Byron. This leakage includes accident leakage and the allowed 0.1 gpm primary-to-secondary leakage of the 3 unfaulted SGs per TS 3.4.6.2.c. However, in order to provide a defense in depth approach to application of this requested APC and to envelope any future increases in MSLB leakage due to tube degradation, both Byron and Braidwood are lowering their RCS dose equivalent I-131 levels to 0.35 pci/gm for all future cycles until SG replacement. Site allowable leak rates calculated using 0.35 pci/gm dose equivalent I-131 are 26.8 gpm for Braidwood and 36.5 gpm for Byron. This leakage also includes accident leakage and the 4
l allowed 0.1 gpm primary-to-secondary leakage of the 3 unf aulted SG:, per TS -3. 4. 6. 2.c.
Bases changes are being made to Braidwood and Byron'TS in order to accurately reflect the changes made to the individual specifications.
Finally, additional changes-are being made to make Byron and ,
Braidwood TS consistent with.the model TS contained in the )
May 30 Memorandum. !
E. DESCRIPTION OF THE REVISED REQUIREMENT !
For both Byron Unit-1 and Braidwood Unit 1, Comed is !
requesting an APC of 3.0 volts for ODSCC indications at hot-leg TSP intersections and an APC of 1.0 volt for ODSCC indications'at cold-leg TSP intersections.
'For Byron, the equation for determining cold-leg voltage :
acceptance criteria for an unplanned outage is revised for {
conformance to the May 30 Memorandum. For Braidwood, the ,
equation 1for'mid-cycle unplanned outage cold-leg voltage !
acceptance criteria is added to the specification for l conformance with the May 30 Memorandum. The hot-leg voltage plugging or repair limit remains at 3.0 volts for unplanned j outages for both Byron and Braidwood.
Braidwood's probability of tube burst limit is decreased from 2.5x104 to 1.0x104 consistent with the May 30 Memorandum. TS 3.4.8 is being revised for both Byron and Braidwood to reduce the Unit 1 RCS dose equivalent I-131 limit from 1.0 pci/gm to 0.35 pci/gm. Other changes are 1 being made to Byron and Braidwood TS to make them more '
consistent with the requirements of the May 30 Memorandum.
The specific TS modifications necessary to accomplish the t changes discussed above are described below. .
TSSR 4.4.5.2. Steam Generator Tube Samole Selection and Insoection
.These changes to the surveillance' requirements will specify ;
that all' tubes remaining in service due to application of l APC be included among the tubes to be inspected as part of, i or in addition to, the sample selection made in accordance i with the criteria of Table 4.4-2 of TSSR 4.4.5.2. The surveillance requirements will specify the minimum tube length inspection scope necessary to implement APC. These changes are consistent.with the direction given in the May 30 Memorandum. l 5
For consistency, Item 5 of TSSR 4.4.5.2.b for Braidwood will be renumbered as Item 6. A new Item 5 will be added to TSSR !
4.4.5.2.b for Braidwood, and revised for Byron. This item reads as follows:
i
} "5) For Unit 1, indications left in service as a result of application of the tube support plate voltage-based
, repair criteria shall be inspected by bobbin coil probe during all future refueling outages."
For Byron, this item was previously incorporated. However,
- it will be revised by adding the word refueling to the
- existing specification.
TSSR 4.4.5.2.d will be revised to read as follows:
"d. For Unit 1, implementation of the steam generator tube / tube support plate repair criteria requires a 100-2 percent bobbin coil inspection for hot-leg and cold-leg tube support plate intersections down to the lowest
- cold-leg tube support plate with known outside diameter i stress corrosion cracking (ODSCC) indications. The l determination of the lowest cold-leg tube support plate intersections having ODSCC indications shall be based l
on the performance of at least a 20 percent random j sampling of tubes inspected over their full length."
l TSSR 4.4.5.4. Acceptance Criteria l
TSSR 4.4.5.4.a.6 will be changed to be consistent with the guidance provided in the May 30 Memorandum. The modified section of TSSR 4.4.5.4.a.6 will read: l
" ...For Unit 1, this definition does not apply to tube ;
support plate intersections for which the voltage-based )
( repair criteria are being applied. Refer to 4.4.5.4.a.11 for I the repair limit applicable to these intersections."
( l TSSR 4.4.5.4.a.11 will be replaced with the plant specific Insert D identified in Attachments C-1 and C-2. Insert D defines the repair limit requirements for APC implementation l and incorporates the 3.0 volt hot-leg APC limits and the 1.0 l volt cold-leg APC limits.
1 1
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L Insert D reads as follows:
I L
- 11. For Unit 1, the Tube Suonort Plate Pluacina Limit is used'for the disposition of an alloy 600 steam generator tube for continued service-that is experiencing predominantly axially oriented outside diameter stress corrosion cracking confined within the ~
thickness of the tube support plates. At tube support plate intersections, the plugging (repair) limit is based on maintaining steam generator tube serviceability as described below:
i I a. Steam generator. tubes, with' degradation attributed to outside diameter stress corrosion cracking within the bounds of the cold-leg tube support plate with bobbin voltages less than or equal to the lower voltage repair limit-[ Note 1] will be allowed to remain in service. Steam generator tubes, with degradation attributed to outside diameter stress corrosion cracking within the bounds of the hot-leg tube support plate with bobbin voltages less than or equal to 3.0 volts will be allowed to remain in service.
- b. Steam generator tubes with degradation attributed to outside diameter stress corrosion cracking within the bounds of the cold-leg tube support plate with a bobbin voltage greater than the lower voltage repair limit [ Note 1], will be repaired or plugged, except as noted in 4.4.5.4.ll.d below,
- c. Steam generator tubes with degradation attributed to outside diameter stress corrosion cracking within the bounds of the ;
hot-leg tube support ~ plate with a bobbin voltage greater than 3.0 volts will be repaired or plugged.
- d. Steam generator tubes, with indications of potential degradation attributed to outside diameter stress corrosion cracking within the bounds of the cold-leg tube support plate with a bobbin voltage greater than the lower voltage repair limit [ Note 1] but less than or equal to the upper voltage repair limit
[ Note 2], may remain in service if a rotating pancake coil inspection does not detect degradation. Steam generator tubes, with ,
indication of outside diameter stress corrosion cracking degradation within the 7
I bounds of the cold-leg tube support plate with a bobbin voltage greater than the upper voltage repair limit [ Note 2] will'be plugged or repaired.
- e. Certain' intersections as identified in WCAP-14046, Section 4.7, will be excluded from application of the voltage-based repair criteria as it is determined that these intersections may collapse or deform following a postulated LOCA + SSE event. ;
- f. If~an unscheduled mid-cycle inspection is performed, the following mid-cycle repair limits apply instead of the limits identified in 4.4.5.4.11.a, 4.4.5.4.11.b and 4.4.5.4.11.d for outside diameter stress corrosion cracking indications occurring in :
the steam generator cold-legs. For outside l diameter stress corrosion cracking +
indications occurring in the steam generator hot-legs, the limits in 4.4.5.4.11.a and 4.4.5.4.11.c apply. The mid-cycle repair limits are determined from the following j equations:
V" V"= i
- 1. 0 +NDE+Gr ( CL-A c )
CL Va= Vm (Vm -Vm)(CL-At)
~
g i
Where:
Vma = upper voltage repair limit Vua = lower voltage repair limit Vmmt = mid-cycle upper voltage repair limit based on time into cycle Vmm. = mid-cycle lower voltage repair limit based on Vun, and time into cycle At = length of time since last i
scheduled inspection l
during which V we and Vum l were implemented i
8
..- - . - - - ,. _ _ _.- . _. - _ . _ _ , , - ------ - . , _ _ _ _ . . , . . _ , - . , . - , . _ ,. ,,,... _ - . .. .____,-..i
CL = cycle length (the time.
between two scheduled ,
steam generator l inspections) l l
Vst = . structural limit voltage Gr = : average growth rate per cycle length NDE = 95-percent cumulative probability allowance for nondestructive examination uncertainty (i.e., a value of 20 percent has been approved: ;
by NRC)
Implementation of these mid-cycle repair limits '
should follow the same approach as in TS 4.4.5.4.11.a, 4.4.5.4.11.b, 4.4.5.4.11.c and ;
4.4.5.4.11.d. .
Note 1: The lower voltage repair limit is 1.0 volt for indications of outside diameter stress corrosion :
cracking occurring at cold-leg tube support plate '
intersections.
Note 2: The upper voltage repair limit for indications of outside diameter stress corrosion cracking occurring at cold-leg tube support plate intersections is calculated according to the methodology in the May 30, 1995 Frank J. Miraglia memorandum to Edward L. Jordan requesting CRGR i review of Generic Letter 95-XX, " Voltage Based Repair Criteria for Westinghouse Steam Generator Tubes Affected by Outside Diameter Stress ;
- Corrosion Cracking" i TSSR 4.4.5.5, Reoorts k TSSR 4.4.5.5.d will be replaced with Insert E. Insert E 6
f.i reads as follows- !
1.
, "d. For implementation of the voltage based repair criteria ;
I to tube support plate intersections for Unit 1, notify .
l- the staff prior to returning the steam generators to service should any of the following conditions arise:
i' l
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- 1. If estimated leakage based on the projected end-of-cycle (or if not practical, using the actual measured end-of-cycle) voltage distribution exceeds the leak limit (determined from the licensing basis dose calculation for the postulated main steam line break) for the next operating cycle.
- 2. If circumferential crack-like indications are detected at the tube support plate intersections.
- 3. If indications are identified that extend beyond the confines of the tube support plate.
- 4. If indications are identified at the tube support plate elevations that are attributable to primary water stress corrosion cracking.
- 5. If the calculated conditional burst probability based on the projected end-of-cycle (or if not practical, using the actual measured end-of-cycle) voltage distribution exceeds 1 x 10-2, notify the NRC and provide an assessment of the safety significance of the occurrence."
This change removes from TS the requirement to report SG inspection results to the Nuclear Regulatory Commission within 90 days of completion of the inspection. This requirement is currently incorporated in Byron TS and was part of the proposed changes to Braidwood TS in the February 13, 1995 submittal. Byron and Braidwood will continue to report SG inspection results in accordance with the May 30 Memorandum.
TS 3.4.8 For Braidwood, the reference to Cycle 5 in the footnote to TS 3.4.8.a will be deleted. This footnote now reads:
"**For Unit 1, reactor coolant DOSE EQUIVALENT I-131 will be limited to 0.35 microCuries per gram."
For Braidwood, a footnote with wording identical to that described above has also been added to TS 3.4.8 actions a and b and the notations for Table 4.4-4.
t-For Byron, a footnote to TS 3.4.8.a, TS 3.4.8 actions a and b and Table 4.4-4 will be added. This footnote will read:
"**For Unit 1, reactor coolant DOSE EQUIVALENT I-131 will be limited to 0.35 microcuries per gram."
10
i .For Byron and Braidwood, Figure 3.4-1 of TS 3.4.8 is being revised-to include a new transient Iodine limit curve-for B Unit ~1 based on the new Unit 1 dose equivalent Iodine level i of 0.35 pei/gm. A footnote is added to identify Unit l-l curve applicability when RCS Specific Activity is greater 1 than 0.35 pci/gm Dose Equivalent I-131 )
BASES 3/4.4.5, Steam Generators The discussion in the Bases Section of TS dealing with the dispositioning of SG tubes experiencing ODSCC cracking within the thickness of the TSPs will be revised. ,
The revised discussion reads as follows for ,
-Byron [Braidwood]:
I "The voltage-based repair limits for Unit 1.in Surveillance Requirement (SR) 4.4.5 implement the guidance in the NRC's i May 30 Memorandum on voltage based repair criteria for i Westinghouse steam generators (SG) with the exception of the i specific voltage limit. The May 30 Memorandum discusses a ;
l 1.0 volt Alternate Plugging Criteria (APC).
L Byron [Braidwood] SR 4.4.5 implements a 3.0 volt APC for Unit 1 SGs per WCAP-14273, " Technical Support for Alternative Plugging Criteria with Tube Expansion at Tube Support Plate j Intersections for Braidwood-1 and Byron-1 Model D-4 Steam )
i Generators."
j The voltage based repair limits of SR 4.4.5 are L
applicable only to Westinghouse-designed SGs with outside i diameter stress corrosion cracking (ODSCC) located at the 1 tube-to-TSP intersections. The voltage-based repair limits o are not applicable to other forms of SG tube degradation nor are they applicable to ODSCC that occurs at other locations ;
within the SG. Additionally, the repair criteria apply only to indications where the degradation mechanism is dominantly axial ODSCC with no significant cracks extending outside the !
l thickness of the support plate. Refer to the NRC's May 30 ;
Memorandum on voltage based repair criteria for Westinghouse i SG for additional description of the degradation morphology. ,
l Implementation of SR 4.4.5 requires a derivation of the i voltage structural limit from the burst versus voltage empirical correlation and then the subsequent derivation of the voltage repair limit from the structural limit (which is then implemented by this surveillance).
The voltage structural limit is the voltage from the L burst pressure / bobbin voltage correlation, at the 95-percent i prediction interval curve reduced to account for the lower 95/95- ercent tolerance bound for tubing material properties at 650 F (i.e., the 95-percent LTL curve). The voltage o 11 l'
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. . .-.L.~._..-_--.---~.-,...-, , , . . . . . . - - - . _ . . . . , ~ _ . . _ . - _ . .--.- .--_. ....-.. - .,. ;. . ~. .. -
1 l
1 structural limit must be adjusted downward to account-for potential flaw growth during an operating interval and to account for NDE uncertainty.
The upper voltage repair limit for cold-leg indications at the tube support plate; V6t, is determined from the structural voltage limit by applying following equation:
Vuxt=Vst-Vor-Ves where Vca represents the allowance for flaw growth between inspections and Ves represents the allowance for potential i sources of error in the measurement of the bobbin coil voltage. Further discussion of the assumptions necessary to determine the voltage repair limit is contained in the NRC's ,
May 30 Memorandum on voltage based repair criteria for Westinghouse SGs.
The mid-cycle equation in SR 4.4.5.4.ll.f should only be used during unplanned inspections in which eddy current data is acquired for indications at the cold-leg tube support plates. The voltage repair limit for indications at I the hot-leg tube support plate remains 3.0 volts during i unplanned inspections. ;
l SR 4.4.5.5 implements several reporting requirements recommended by the NRC's May 30 Memorandum for situations I which the NRC wants to be notified prior to returning the SGs to service. For the purposes of this reporting requirement, leakage and conditional burst probability can be calculated based on the as-found voltage distribution rather than the projected end-of-cycle voltage distribution (refer to the May 30 Memorandum for more information) when it is not practical to complete these calculations using the projected end-of-cycle voltage distributions prior to returning the SGs to service. Note that if leakage and conditional burst probability were calculated using the measured end-of-cycle voltage distribution for the purposes of addressing the May 30 Memorandum generic letter sections 6.a.1 and 6.a.3 reporting criteria, then the results of the projected end-of-cycle voltage distribution should be provided per the May 30 Memorandum generic letter section 6.b(c) criteria."
The discussion of inputs to the maximum site allowable primary-to-secondary leakage for EOC MSLB conditions is ,
revised to reference APC rather than IPC. The specific l value of the limit is removed.
12
.. = . . . - _- - _- - . . . . . . . . - - - ..
L F. BASES FOR THE' REVISED REQUIREMENT The technical bases for'the changes proposed in this amendment request are contained in the following documents: )
WCAP 14273,_" Technical Support for Alternate Plugging Criteria.with Tube Expansion at Tube Support Plate '
Intersections for Braidwood 1 and Byron 1 Model D-4
' Steam Generators." January 1995.
WCAP 14046, "Braidwood Unit 1 Technical Support for
. Cycle 5' Steam Generator Interim Plugging Criteria," ;
L Revision 3, March 1995, l
- Electric Power Research Institute (EPRI) Report NP-7480- -
- L, " Steam Generator Tubing Outside Diameter Stress l Corrosion Cracking at Tube Support Plates - Database ,
for Alternate Repair Criteria, 3/4 Inch Tubing." Volume ;
- 2, October 1993, l
- Westinghouse Document SG-95-01-003, " Byron Unit 1 End-of-Cycle 6 Interim Plugging Criteria Report." January i 17, 1995.
- WCAP 14277, "SLB Leak Rate and Tube Burst Probability !
Analysis Methods for ODSCC at TSP Intersections." j January 1995 l
\
May 30, 1995 Frank J. Miraglia memorandum to Edward L. l Jordan requesting CRGR review of Generic Letter 95-XX,
" Voltage Based Repair Criteria for Westinghouse Steam Generator Tubes Affected by Outside Diameter Stress ;
Corrosion Cracking." ,
I A comparison of the May 30 Memorandum with currently approved IPCs at Byron and Braidwood identified a number of ,
TS differences. These specification differences are identified in Section E of this document. These changes are l primarily editorial in nature and provide clarification and !
conformance to the May 30 Memorandum.
In addition to updating Byron and Braidwood Station's TS for conformance with the May 30 Memorandum, this amendment request proposes to implement a 3.0 volt APC repair limit for hot-leg tube intersections with ODSCC for both Byron and Braidwood. While the current 1.0 volt IPC criteria is based on a structural limit derived from freespan tube burst conditions, the 3.0 volt APC criteria is based on the constraining effects of the TSP to reduce burst probability to negligible levels. Selected hot-leg tubes will be hydraulically expanded to serve as anchors to limit tube support plate motion during a postulated steam line break 13 ,
l
__ _ _ . _ _ .. . _ . _ . _ . _ _ . . - - . ~ _ - _ . . _ . _ _ _ .. . _., _ . _ . _ _ _
l
event. With TSP motion limited, the length of a crack confined within the TSP that would be subjected to freespan
' conditions due to TSP movement would be greatly reduced, thus reducing tube burst probabilities during accident conditions.
Acoroach The approach applied to developing the 3.0 volt APC methodology for hot-leg tube support plate intersections is based on developing the minimum requirements, establishing-design objectives more limiting than the minimum requirements, and evaluating the overall performance based on supporting analyses for the tube expansion process. The general approach can be described as follows:
Define acceptable TSP displacements to reduce the tube burst probability to negligible levels based on the conservative assumption that all hot-leg TSP intersections have throughwall indications equal to the
-limited TSP displacement resulting from tube expansion.
Identify the tubes and locations that require expansion i to limit TSP movement during MSLB events to j displacements that result in negligible tube burst probabilities.
Identify additional tubes and locations for expansion to provide sufficient redundancy in the unlikely event that one or two expansions fail due to degradation.
- Define tube expansion functional requirements and process qualifications to ensure that design requirements are met.
- Calculate a tube structural voltage limit based on limited TSP displacement due to tube expansion. 1
- Demonstrate that MSLB leakage with limited TSP displacement due to tube expansion can be adequately determined by the proposed leakage predictions as described in Attachment F.
Maintain current leakage limits and operational measures to monitor, trend, and respond to SG tube leakage as specified in the original IPC submittal.
Maintain current eddy current inspection guidelines to increase detectability and reduce voltage variability.
14
i l
l Attachment B provides a detailed description of the methodology used for evaluation of the increased APC limit for hot-leg intersections and a discussion of the l operational measures in place at both Byron and Braidwood i l
relative to APC implementation.
Braidwood will be deleting the reference to Cycle 5 in the footnote referenced in Braidwood TS 3.4.8.a, adding footnotes limiting Unit 1 dose equivalent I-131 to TS 3.4.8 actions a and b and Table 4.4-4 and revising Figure 3.4-1 to l accommodate the Unit 1 Iodine limit. Byron will be adding a l footnote to TS 3.4.8.a, TS 3.4.8 actions a and b and Table l 4.4-4 to require that Unit 1 RCS dose equivalent I-131 be limited to 0.35 pci/gm. Byron Figure 3.4-1 will also be revised to accommodate the new Unit 1 Iodine limit.
Calculations conducted for Braidwood and Byron have shown that the resulting 2 hour2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> doses at the Byron and Braidwood site boundaries will not currently exceed an appropriately small fraction of 10 CFR 100 dose guideline values in ,
conjunction with the predicted MSLB leakage calculated in i accordance with this submittal and a dose equivalent I-131 l level of 1.0 pei/gm. The site allowable leakage calculated ;
using a dose equivalent I-131 level of 1.0 pci/gm is 9.4 gpm i for Braidwood, and 12.8 gpm for Byron. This leakage includes accident leakage and the allowed 0.1 gpm primary-to-secondary leakage of the 3 unfaulted SGs per TS !
3.4.6.2.c. However, in order to provide a defense in depth approach to application of this requested APC and to envelope any future increases in MSLB leakage due to tube )
degradation, both Byron and Braidwood are lowering their RCS '
dose equivalent I-131 levels to 0.35 pci/gm for all future cycles until SG replacement. Site allowable leak rates calculated using 0.35 pci/gm dose equivalent I-131 are 26.8 gpm for Braidwood and 36.5 gpm for Byron. This leakage also includes accident leakage and the allowed 0.1 gpm primary- l to-secondary leakage of the 3 unfaulted SGs per TS 3.4.6.2.c.
1 G. IMPACT OF THE PROPOSED CHANGE With the implementation of this license amendment request, the Braidwood and Byron Unit 1 SGs will continue to satisfy the requirements of RG 1.121. For the hot-leg TSP intersections, the use of tube expansion and stabilization limits the tube / TSP relative displacements that occur during a postulated MSLB such that the tube burst margins for Braidwood Unit 1, and Byron Unit 1 are reduced to negligible levels.
15
Lowering the Unit 1 RCS dose equivalent I-131 limit from 1.0 pci/gm to 0.35 pci/gm is conservative, provides a defense in depth approach to implementation of this APC and ensures that the resulting 2 hour2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> dose rates at the Braidwood and Byron site boundaries will not exceed an appropriately small fraction of 10 CFR 100 dose guideline values with the predicted MSLB leakage calculated in accordance with this submittal until SGs are replaced at both sites.
Implementation of this amendment request could "save" as many as 920 tubes at Byron and 913 tubes at Braidwood Ll.at would have had to be plugged or repaired using the previous 1.0 volt IPC. This represents a dollar savings of $1.8 Million apiece at Byron and Braidwood assuming all these tubes were plugged. However, since plugging levels this high approach currently analyzed maximums, sleeving these tubes could add as much as $6.1 Million apiece at Byron and Braidwood in outage inspection and repair costs. This will also minimize the RCS loop flow asymmetries and thermal power derates.
H. SCHEDULE REQUIREMENTS Comed requests that this amendment request be approved prior to August 15, 1995 to allow application of the provisions of this amendment request in Byron Station's Unit 1 Mid-Cycle Outage, and Braidwood Station's Unit 1 Refuel Outage.
l I
i l
l 16
1 I
I 1
i !
L '
L ATTACHMENT B BYRON /BRAIDWOOD UNIT 1 STEAM GENERATOR g ALTERNATE PLUGGING CRITERIA METHODOLOGY I:
i-l Introduction This amendment request proposes to implement a 3.0 volts bobbin coil probe, voltage based,. Steam Generator (SG) Tube Support Plate (TSP) Alternate Plugging Criteria (APC) limit for Outside Diameter Stress Corrosion Cracking i (ODSCC) indications at the hot-leg TSP intersections for both l l
the Byron and Braidwood Unit 1 steam generators (SG). While l the 1.0 volt Interim Plugging Criteria (IPC) criteria is l
! based on a structural limit derived from freespan tube burst. '
l conditions, the 3.0 volt APC criteria is based on the
! constraining effects of the TSP to reduce burst probability
! to negligible levels. Selected hot-leg tubes will be l hydraulically expanded to serve as anchors to limit tube support plate motion during transient conditions. These tubes essentially become additional stayrods that restrict potential displacements. With TSP motion limited, the length of a crack confined within the TSP that would be subjected to freespan conditions due to TSP movement would be greatly reduced, thus reducing tube burst probabilities during accident conditions. i 1
The general approach for supporting a 3.0 volt APC at the hot-leg TSP intersections can be described as follows:
Define acceptable TSP displacements to reduce the tube j burst probability to negligible levels based on the conservative assumption that all hot-leg TSP intersections have throughwall indications equal to the limited TSP displacement resulting from tube expansion.
Identify the tubes and locations that require expansion to limit TSP movement during Main Steam Line Break (MSLB) events that result in negligible tube burst probabilities.
Identify additional tubes and locations for expansion to provide sufficient redundancy in the unlikely event that one or more expansions fail due to degradation.
Define tube expansion functional requirements and process qualifications to ensure that design requirements are met.
1
L l'
l Calculate a tube structural voltage limit based on i
limited TSP displacement due to tube expansion. l Demonstrate that MSLB leakage with limited TSP displacement-due to tube expansion can be adequately determined by the proposed leakage predictions as described in Attachment F.
Maintain current leakage limits and. operational measures.to monitor, trend, and respond to SG tube leakage as specified in the original IPC submittal.
Maintain existing eddy current inspection guidelines to increase detectability and reduce voltage variability.
The cold-leg APC repair limit will remain at 1.0. volt as approved in the current Technical Specifications (TS). The structural voltage limit for cold-leg intersections based on ;
l freespan considerations is increased from 4.54 volts to 4.75 i volts, due to the inclusion of the latest Byron and Braidwood tube pull results into the industry database.
Discussed below is a summary of the analyses and methodologies used to support and apply a 3.0 volt APC at the hot-leg. intersections and a 1.0 volt APC at the cold-leg intersections. These analyses are contained in WCAP 14273,
" Technical' Support for Alternate Plugging Criteria with Tube Expansion at Tube Support Plate Intersections for Braidwood 1 and Byron 1 Model D-4 Steam Generators," and WCAP 14277, "SLB Leak Rate and Tube Burst Probability Analysis Methods i for'ODSCC at TSP Intersections." Braidwood and Byron will satisfy all requirements of the May 30, 1995 Frank J.
Miraglia memorandum to Edward L. Jordan requesting CRGR '
review of Generic Letter 95-XX, " Voltage-Based Repair Criteria for Westinghouse Steam Generator Tubes Affected by Outside Diameter Stress Corrosion Cracking" (May 30 t Memorandum).
TSP Disolacement and Tube Burst Considerations 3 During a postulated MSLB event, rapid depressurization of the secondary side results in fluid blowdown, water flashing, and hydraulic loading on the TSPs. This hydraulic loading can cause TSP' deflections and relative tube to TSP displacements. For application of the Byron and Braidwood Unit 1 APC, as proposed in this amendment, the relative tube to TSP displacements during postulated MSLB events are evaluated and limited through tube expansion to result in negligible tube burst probabilities.
2 l I
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1
( Several modeling techniques are employed to determine i hydraulic loading on the TSPs and to determine i displacements. A thermal hydraulic model was developed to l predict critical SG parameters during a postulated MSLB such
! as mass flowrate, pressure drop, fluid temperature, steam quality and void fraction.
l The model was run for several different plant operating conditions to determine the most conservative loads l resulting from a MSLB. The hot standby condition with a l MSLB at the SG nozzle yields the more limiting hydraulic loads and was used in evaluation for limiting tube displacements. A safety factor of 2 was applied to the hydraulic loads for additional conservatism.
- A structural model was developed to determine relative tube i to TSP motions under MSLB loads that were determined with
! the thermal hydraulic model discussed above. The structural l model utilizes a general purpose finite element code that l accounts for the physical SG structures and materials, as well as MSLB hydraulic loading. Locations of tube expansions that restrict TSP motion can also be evaluated with the model.
The analyses contained in these models also evaluated acoustic pressure waves caused by the steam line break, and found acoustic effects to have negligible impact on TSP i hydraulic loads. 1 To support a 3.0 volt APC the TSP motion is limited during MSLB events to displacements that result in negligible tube burst probabilities. The modeling techniques described above are used to determine relative tube to TSP motions.
These techniques determine the length of a crack within a TSP that could be uncovered due to the relative tube to TSP displacement. From this freespan exposed crack length, a tube burst probability is derived from a correlation that relates crack length to tube burst pressure. i The evaluation conservatively assumes that every hot-leg tube intersection (32,046 intersections) contains a through-wall crack with length equal to the TSP displacement and which is located at the edge of the TSP. Alternatively, it is assumed that every hot-leg tube intersection contains a through-wall crack length approximately equal to the thickness of a TSP. For all the postulated 32,046 through-wall cracked intersections a total tube burst probability of 1x104 was selected as the target for negligible burst probability. This is a factor of 1000 lower than the May 30 Memorandum limit of 1x10-2 The 1x10 4 tube burst probability corresponds to a maximum through-wall crack freespan length of 0.31" for the postulated 32,046 indications. Therefore, 3
l
I a maximum displacement of 0.31" is the tube expansion design I criteria used for limiting TSP motion. However, a 0.1" )
maximum displacement was selected to be the functional l design goal for tube expansion. This provides added l conservatism and ability to perform in situ pressure testing of indications for increasing the leak rate database for constrained tubes. With a 0.1" displacement for all hot-leg intersections, the total burst probability for through wall indications at all hot-leg intersections is reduced from ,
lx104 to 1x10-2 .
A number of tubes were selected for tube expansion to limit the displacement to less than 0.1". Additional tubes were l selected to be expanded to serve as redundant or back-up l tubes in the unlikely event that a tube expansion fails due to degradation. The redundant tubes ensure that a maximum i displacement of 0.31" and a burst probability of 1x104 is I achieved when one or more expansions fail. An additional two tubes are required to be expanded to limit a bending stress in the top support plate.
Tube Exoansion As previously discussed, tube expansion will be used on selected tubes to limit relative tube to TSP motion during postulated MSLB events to result in negligible tube burst probabilities. The tube expansion process will essentially convert the selected tubes into stayrods to restrict potential TSP displacements. This is accomplished by hydraulically expanding the tube into the TSP and also 1 creating a bulge larger than the TSP drill hole above and below the TSP to lock the tube into the TSP to limit motion in both directions. The expanded tubes will be stabilized and removed from service.
The tube expansion process and stabilization is accomplished with a sleeve stabilizer. A sleeve is hydraulically expanded into the parent tube to create the necessary expansion and bulge for tube to TSP locking. The sleeve serves two purposes, 1) provides stabilization if the tube fails at the expansion, and 2) provides additional stiffness to the expanded joint. The sleeve stabilizer is designed to prevent damage to adjacent tubes in the unlikely event that the parent tube is severed at the expansion joint. The added stiffness of the expanded joint due to the sleeve provides additional resistance to TSP displacement. The expansion process is a qualified process to ensure that the expansion design functional requirements are met for each application. The expanded tubes will be inspected following the expansion process to ensure that the desired expansion parameters have been achieved.
4
. - - . _ . - - .- .- - . _ - - --- . . - - . . - - - - - = . -
1 Degradation of the parent tube expansion or sleeve is not an expected phenomenon. Tube degradation is affected by temperature and stresses in the tube. The operating temperature of the expanded tube is greatly reduced since the tube is removed from service. The temperature of the expanded tube will be the temperature of the secondary side of the SG, which typically ranges from about 520 F to 544 F, as compared to an inservice tube that experiences temperatures of about 610 F. Laboratory tests have indicated that reducing the temperature from an inservice tube to that-of a plugged tube results in a reduction in the stress corrosion cracking initiation by a factor of 16 for similarly stressed tubing.
Corrosion tests have been performed for varying expansion diameters up to and above those required for TSP locking. >
These tests have concluded that for the expansion process described the stress corrosion cracking potential is not expected to exceed that for hydrau?ic or hardroll tubesheet expansions. An inspection of three expanded tubes will be performed at a frequency of every three fuel cycles to ensure that degradation of the expansions is not occurring.
To perform these inspections, each tube must be de-plugged, inspected, and re-plugged. If circumferential degradation is detected at an expansion, then the inspection will be expanded to other expansions in the SG based on the severity of the indications found in the base inspection.
Industry experience has shown that in severely dented SGs, tube support plates have been observed to be cracked.
Evaluations were performed to assess this concern pertaining particularly to the application of tube expansion to support the 3.0 volt APC.
A finite element analysis was performed and established that the dent size necessary to cause a stress intensity that exceeds the yield strength of the TSP was a 65 mil diametral dent. Therefore, dents of a smaller size are not expected to produce stress levels that would be a cracking concern.
Byron and Braidwood Unit 1 SGs have not experienced corrosion assisted denting at the TSP to date. To establish that denting does not produce a TSP cracking concern in the future at Byron and Braidwood, the bobbin coil probe will be used as a go/no-go gauge to assess dent sizes. The criteria used to ensure that dents are below the size necessary to cause excessive TSP stress levels is the passage of a 0.570" i diameter bobbin probe through the tube. If the tube does ;
not allow passage of a 0.570" probe due to a dent at a TSP, then a tube exclusion zone is to be established to prevent a 3.0 volt APC from being applied to those areas that contain stressed TSPs.
5
, __ _ _. _ ____.___ _ _ _.~.__._ ____.____ _ ._,_._._
1 Structural Voltace Limit and Leakaae Considerations The purpose of the TS repair limit is to ensure that tubes accepted for continued service will retain adequate structural and leakage integrity during normal, transient, and postulated accident conditions, consistent with General '
Design Criteria (GDC) 14, 15, 31, and 32 of Title 10 Code of Federal Regulations Part 50 (10 CFR 50), Appendix A. i Structural integrity is defined as maintaining adequate ;
margins against gross failure, rupture, and collapse of the 1 SG tubing. Regulatory Guide (RG) 1.121, " Basis for Plugging Degraded PWR Steam Generator Tubes," requires a structural j safety margin of 1.43 against tube failure under postulated 1 accident conditions and a safety margin of 3.0 against burst :
during normal operation. ,
The proposed APC meets the requirements of RG 1.121 and l demonstrates that tube leakage is acceptably low and that l tube burst is a highly improbable event during normal ;
operation and postulated MSLB events. Implementation of this APC results in offsite doses that are a small fraction of 10 CFR 100 limits.
For axial ODSCC located at cold-leg intersections, the current 1.0 volt IPC criteria are still applicable. These criteria are derived from freespan burst considerations and are consistent with May 30 Memorandum requirements. The structural voltage limit is based on the log-linear relationship between tube burst and bobbin coil voltage.
The database used for the calculation of the Byron and Braidwood structural limit is consistent with that described in the May 30 Memorandum, with the inclusion of the recent Byron and Braidwood tube pull results. Since tube burst is precluded during normal operating conditions due to the l constraining effects of the TSP, a safety margin of 1.43 is l used to derive the lower 95% confidence level voltage under MSLB conditions. This structural voltage limit is 4.75 volts. The voltage limit for allowing non-confirmed RPC indications to remain in service will be calculated by the methodology described in the May 30 Memorandum.
For axial ODSCC located at hot-leg intersections, tube burst probabilities are reduced to negligible levels during normal, transient, and postulated MSLB conditions due to limited TSP displacements from tube expansion. Therefore, MSLB leakage criteria dictates the structural and repair ,
limits. Since axial ODSCC does not significantly impact the axial tensile loading of the tube, the more limiting degradation modes are cellular corrosion and Inter-Granular Attack (IGA). Significant IGA depths have not been 6
+ --.v.r wn , e , --en---e,.a-m.,--,p+ .-n -, -..er-,<,v,.vm. _ep.,79..----w,--rum e ,,, yem er+ e, w n w , , ,- m - *e r
4 experienced at the Byron or Braidwood units or in the l industry. Thus, cellular corrosion is the expected crack
] morphology at TSPs to affect tensile load limits.
From available data (refer to Section 9.0 of WCAP-14273),
- the pressure that would be required to cause axial separation of a tube with cellular corrosion is well above the 3 times normal operating pressure differential at a bobbin voltage of 37' volts, with a lower bound 95%
l confidence level applied. Due to the limited size of the i database, an additional safety factor is applied to i conservatively establish a lower bound structural limit of 20 volts. Accounting for voltage growth and NDE
- uncertainty, the full APC limit exceeds 10 volts. However, l for added conservatism a single voltage repair limit for hot-leg indications is specified in this request. All hot-
- leg indications with bobbin coil probe voltages greater than 3.0 volts will be plugged or repaired, regardless of RPC inspection results.
. Although the probability of burst is greatly reduced at hot-
- leg tube intersections due to the constraining effects of 2
the TSP, the probability of higher MSLB leak rate values has been evaluated. A finite probability exists that a crack I may open to the limits of the tube to TSP gap and cause
'j increased leakage. This probability is equivalent to the probability of free span burst. Leakage from these Indications Restricted From Burst (IRB) will be accounted for by methods described in Attachment F. These analyses are discussed in the June 20, 1995 D. Saccomando letter to
! Office of Nuclear Reactor Regulation subject: Additional l Information Pertaining to the Application for Amendment to ;
Facility Operating Licenses: Byron Nuclear Power Station, Units 1 and 2 NPF 37/66; NRC Docket Nos. 50-454/455, ,
Braidwood Nuclear Power Station, Units 1 and 2 NPF-72/77, l l NRC Docket Nos 50-456/457, " Steam Generators" (June 20 1995 l I
letter).
The total primary-to-secondary tube leakage at MSLB conditions due to APC application and any other approved alternate repair criteria is not to exceed the site i allowable leak rate as calculated in accordance with previously approved IPCs. The site allowable leakage calculated using a dose equivalent I-131 level of 1.0 pei/gm is 9.4 gallons per minute (gpm) for Braidwood, and 12.8 gpm for Byron. Site allowable leak rates calculated using 0.35 pci/gm dose equivalent I-131 are 26.8 gpm for Braidwood and l 36.5 gpm for Byron. This leakage also includes accident i leakage and the allowed 0.1 gpm primary-to-secondary leakage of the 3 unfaulted SGs per TS 3.4.6.2.c.
2 7
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, .-_ ._ _ _ , , . - - - . . _ _ y_., - , _ . - , _ . . . . _ _ . , .
Probability of Detection Probability of Detection (POD) of eddy current indications is an important consideration in the development and implementation of APC. The POD is used to adjust the Beginning Of Cycle (BOC) voltage distribution to account for indications not detected during the inspection. The voltage distribution of detected indications is scaled up by a factor of 1/ POD and tubes repaired are then subtracted to form the assumed population and voltage distribution for the next operating cycle. The adjusted BOC voltage distribution is used in tube leak and burst assessments in support of the APC.
To expedite review and approval of this proposed amendment, Comed will use the May 30 Memorandum POD value of 0.6 for all voltage amplitude ranges. The February 13, 1995, submitral discussed the use of a voltage dependent POD.
This discussion was supported by an Electric Power Research Institute (EPRI) report. This report is being modified to account for the possible initiation of new ODSCC indications between scheduled SG inspections. When complete, this report will be used as the basis for a future request for an alternate POD.
MSLB Leakace and Burst Probability Analysis Methods The analysis methodologies to support the current 1.0 volt IPC and proposed 3.0 volts APC are consistent with the requirements of the May 30 Memorandum, the analysis methods described in the October 24, 1994, Byron Unit 1 Safety Evaiuation Report (SER) and WCAP 14277. For the proposed 3.0 volts APC at hot-leg intersections, the effects of limited TSP displacement are incorporated into the analyses, however the analysis methodologies remain the same.
Consistent with the May 30 Memorandum, MSLB leakage analyses continue to be based on the EPRI Probability of Leakage (POL) model and the conditional leak rate correlation with the addition of a contribution for IRBs. The leakage assessment consists of predicting a freespan leak rate as a function of bobbin coil voltage, assuming that a leak l occurs. The POL model uses the Nuclear Regulatory Commission (NRC) accepted single log-logistic function form.
The conditional leak rate correlation (leak rate to bobbin voltage correlation) is a linear regression fit of the logarithms with an upper bound 95% confidence level. This correlation is deemed to be valid when a p-value test result of less than 5% is demonstrated.
8
I l
A Monte Carlo simulation is applied to the POD adjusted BOC .
voltage distribution to estimate the MSLB leak rate and l burst probabilities at the End Of Cycle (EOC) condition.
This approach applies considerations for NDE uncertainty and voltage growth. A full Monte Carlo technique is used to account for regression parameter uncertainty.
l The database for the leak and burst correlations is consistent with the database used to support the Byron Unit 1 Cycle 7 IPC as described in the October 24, 1994, SER and the Byron Unit 1 90 day IPC report for Cycle 7 dated January 30, 1995, with the inclusion of Byron Cycle 6 tube pull results. The results of the Braidwood Unit 1 and Byron Unit 1 tube pull results were added to the industry database.
For the cold-leg indications, the MSLB leak rate value is
! calculated as described above. MSLB tube burst analyses !
continue to be based on EPRI tube burst correlations that demonstrate a log-linear relationship between tube burst pressure and bobbin coil voltage. The correlation used to define the structural voltage limit uses a lower 95%
confidence level reduced to account for the lower 95/95-percent tolerance bound for tubing material properties at 650 F (i.e. the 95% LTL curve) to correlate burst pressure to bobbin voltage. The tube burst analysis calculates the total probability of burst for a given voltage distribution.
This total burst probability includes the summation of the i probabilities of burst due to 1 tube bursting, 2 tubes !
bursting, etc.
Those tubes which will be excluded from application of APC as a result of the possibility of collapse during a Loss Of Coolant Accident (LOCA) with Safe Shutdown Earthquake (SSE) event have been identified in the revision to WCAP 14046 which was submitted to the NRC on June 19, 1995.
Insoection Recuirements Technical Specification Surveillance Requirement (TSSR) 4.4.5.2 requires bobbin coil inspections to be performed on 1 100% of the hot-leg tubes down to the lowest cold-leg TSP I elevation having ODSCC. A minimum of a 20% random sample is also to be inspected over the full length of the tube.
Rotating Pancake Coil (RPC) inspections are to be performed on the following indications:
All hot-leg TSP indications greater than 3.0 volts.
All cold-leg TSP indications greater than 1.0 volt.
9 1
,_ _ . _ _ . . . _ . . , , . . . , . . ~ , . _. . . , , . .
All TSP intersections that contain dents greater than 5.0 volts and a 20% sample of dents between 2.5 volts and 5.0 volts. If Primary Water Stress Corrosion Cracking (PWSCC) or circumferential cracking is detected, 100% of the dents between 2.5 volts and 5.0 volts will be inspected.
L -
All intersections with large mixed residuals that l could cause a 3.0 volt signal in a hot-leg tube or I a 1.0 volt signal in a cold-leg tube to be missed or misread. -
All intersections'with interfering signals from copper deposits. Neither Braidwood nor Byron has i
significant copper deposits in the SGs. Guidance
! on. conducting RPC inspections for interference ,
signals due to copper has been included in both station's inspection guidelines.
Any flaw-like indication confirmed by RPC at intersections .:
with dent signals greater than 2.5 volts, large mixed residuals and copper deposits will result in the tube being i repaired by sleeving or plugged. In addition, APC will not i be applied to any crack-like indication in a wedge area or the Flow Distribution Baffle.
Also, the following data acquisition and analysis -
requirements will be met: ,
- The bobbin coil will be calibrated against a reference standard in tN 1.aboratory by direct testing or by use of . s'fer standard.
The voltage response ut new bobbin coil probes for ,
the 40% to 100% American Society of Mechanical .
Engineers (ASME) through-wall holes will not !
differ from the nominal voltage by more than i 10%.
- Probe wear will be controlled by either an in-line measurement device or through the use of a periodic wear measurement. When utilizing the ;
periodic wear measurement approach, if a probe is >
. found to be out of specification (15%), all tubes ,
inspected since the last successful calibration will be reinspected with a new calibrated probe.
10
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Data analysts will be trained in the use of the Comed Byron and Braidwood Stations Units 1 and 2 Eddy current Analysis Guidelines and qualified through site specific testing. Data analyst performance will be consistent with the assumptions for analyst measurement variability utilized in the tube integrity evaluations.
Quantitative noise criteria (resulting from e electrical noise, tube noise, calibration standard 4
noise) will be included in the data analysis procedures. Data failing to meet these criteria
- will be rejected, and the tube will be reinspected.
Data analysts will review the mixed residuals on the standard itself and take action as necessary to minimize the residuals.
- A 0.610 inch diameter bobbin coil probe will be utilized for the inspection. If a 0.610 inch diameter probe will not pass through a portion of a tube, APC will not be applied to the portion of the tube that is inspected by a smaller probe.
f Data analysts will be trained on the potential for PWSCC cracking to occur at TSP intersections. The i data analysts will be sensitized to identify indications attributed to PWSCC.
The bobbin and RPC examinations will be performed using enhanced inspection guidelines that are intended to increase detectability and reduce voltage variability in support of 4 APC implementation. The APC guidelines that will be used in the Braidwood Unit 1 and Byron Unit 1 Fall 1995 inspections are the same guidelines used to support the Byron Unit 1 Fall 1994 IPC inspection.
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Ooerational Measures Braidwood Station's April 25, 1994, and Byron Station's August 1, 1994, request for a 1.0 volt IPC contained a description of enhanced operational and procedural measures e that Braidwood and Byron Station had taken to ensure a
! defense-in-depth approach against SG tube failures and detection of flaws that would exceed steam line break
- leakage limits. The measures remain in place at both Braidwood and Byron and are summarized below.
Actions have been taken to mitigate the corrosive environment in the TSP crevices and to increase the i
likelihood that future growth rates and crack
- morphologies will be within expected bounds.
The alert and alarm setpoints on the main steam line i and steam jet air ejector radiation monitors have been
- lowered to ensure early positive indication of primary
! to secondary leakage.
I Chemistry procedures have been revised to facilitate l " quick counts" of chemistry samples to give rapid confirmation of SG leakage.
SG chemistry sampling frequencies have been increased to hourly when primary-to-secondary leakage is detected, and then reduced to not less frequently than once per day once leakage stabilizes.
In order to quickly determine if SG leakage is increasing during a tube leak event, Braidwood Operating Abnormal Procedure (BwOA SEC-8)and Byron Operating Abnormal Procedure (BOA SEC-8), have been revised to require that radiation monitors be checked I at an increased frequency when SG leakage is detected.
Tube rupture, tube leakage, and main steam line break scenarios are conducted frequently in the simulator.
These scenarios include varying radiation monitor responses as appropriate.
Byron and Braidwood Emergency Procedures require continuous monitoring for SG tube leakage. Bw0A SEC-8, and BOA SEC-8 require continued monitoring of leakage during a shutdown to ensure detection of increasing leakage.
Control Room daily surveillances have been revised to
, require that hourly trend readings of steam jet air I ejector radiation monitor activity levels be reviewed on a daily basis.
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i For both Braidwood and Byron, TS 3.4.6.2.c has been changed to limit primary-to-secondary leakage to 600
- gallons per day total reactor-to-secondary leakage through all SGs not isolated from the Reactor Coolant System, and 150 gallons per day through any one SG.
May 30 Memorandum Review Comed will implement all the requirements contained in the May 30 Memorandum. Below is a list which summarizes some of the key requirements contained in this memorandum.
Exclusion of Intersections APC will not be applied to the following intersections:
LOCA + SSE tubes (Wedge area).
Dents greater than 5.0 volts.
Dents 2.5 volts to 5.0 volts with crack-like indications.
Large mixed residuals that could cause a 3.0 volt indication in a hot leg tube or a 1.0 volt indication in a cold leg tube to be i missed or misread. ;
Intersections with interfering copper signals.
Flow distribution baffles.
PWSCC or Circumferential crack-like indications at TSP.
I Recair Criteria j The following indications / tubes will be repaired:
All hot leg TSP indications greater than 3.0 volts, regardless of RPC confirmation.
All cold leg intersections greater than the upper voltage limit.
All cold leg intersections between the lower voltage limit and the upper voltage limit that are confirmed by RPC.
Tubes with known leakage.
RPC confirmed flaws indicative of ODSCC/PWSCC at locations that are excluded from APC as described above. ;
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APC Voltace Limit Determination A single voltage limit of 3.0 volts for hot leg TSPs.
A lower voltage limit of 1.0 volt for cold leg TSPs.
For cold leg TSPs, an upper voltage limit is determined by reducing the structural voltage limit by voltage growth and NDE uncertainty.
Determined prior to each outage.
Use the larger of the site specific growth rate or 30%/EFPY.
NDE uncertainty of 20% of the BOC voltage.
Voltaae Growth Distribution
- Growth rates determined by indications identified at two successive inspections, except that indications that grow from no detectable degradation (NDD) to a relatively large voltage will be included (e.g.; 2.0 volts).
Current cycle growth rates will be used if the current inspection or the current and previous inspections used IPC guidelines. i The most limiting growth rates will be used from the last two inspection cycles.
Negative growth rates will be included as zero growth.
Re-evaluation of previous cycle data will be compensated for changes made in data acquisition guidelines.
- Effects of chemical cleaning will be evaluated, if performed.
1 Tube Pulls A minimum of two tubes and 4 TSP intersections have been removed. A minimum I of one additional tube (minimum 2 TSP I intersections) will be removed following 34 i effective full power months or 3 refueling i cycles, whichever is shorter.
Alternatively, Comed will participate in a NRC approved industry sponsored tube pull program.
Leak / burst tests will be performed under MSLB conditions to confirm failure mode is axial and to add to the industry correlation database.
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l Destructive testing will also be performed to confirm degradation morphology.
Tube selection will be consistent with the May 30 Memorandum.
l Ooerational Leakace i
Implemented 150 gpd leakage limit.
Implemented a primary-to-secondary leakage j monitoring program.
Effectiveness of leakage monitoring procedures and operator actions have been
, assessed and appropriate procedure changes l made.
Leakage instrumentation alarm setpoints have been reviewed and revised as appropriate.
MSLB Leakace and Burst Probability Assessments BOC voltage distribution determined by scaling upwards the as-found voltage distribution by 1/(POD = 0.6) and then subtracting the indications repaired.
EOC voltage distributions determined by Monte Carlo simulations that account for voltage growth, eddy current variability, and parameter uncertainty.
MSLB leakage based on EPRI Probability of leakage model and conditional leak rate model and reflects an upper 95/95% confidence level.
The database used for leak and burst correlations will be the industry database as approved by the NRC.
Calculated MSLB leakage will not exceed offsite or control room dose limits.
POB limit under postulated MSLB conditions will not exceed lx10-2, 15
Reoortina Recuirements NRC notification prior to returning the SG to service (Mode 4) should any of the following arise:
Projected EOC or as-found MSLB leakage i exceeds site allowable limit.
l Projected EOC or as-found probability of l
burst exceeds 1x10-2, j
If circumferential crack-like indications are found at TSP l intersections.
l If indications are identified that l extend beyond the confines of the TSP.
If PWSCC indications are found at TSPs.
l A safety assessment is to be provided to the Staff should the MSLB leakage or probability of burst values exceed their respective limits.
The complete results of the inspection, structural assessments, the Upper Voltage Repair limit used, and tube pull results, if applicable, are to be submitted to the Staff within 90 days of plant restart (Mode 2).
Insoection Recuirements 100% bobbin coil probe of hot leg tubes down to the lowest cold leg indication.
Minimum 20% bobbin coil probe of cold leg tubes.
RPC Insoection Recuirements All hot leg TSP indications greater than 3.0 volts.
All cold leg TSP indications greater than 1.0 volts.
All TSP intersections that contain dents ,
I greater than 5.0 volts and a 20% sample of dents between 2.5 volts and 5.0 volts. If ;
Primary Water Stress Corrosion Cracking
]
(PWSCC) or Circumferential Cracking is detected, 100% of the dents between 2.5 volts and 5.0 volts will be inspected.
All intersections with large mixed residuals that could cause a 3.0 volt signals in a hot leg tube or a 1.0 volt signal in a cold leg tube to be missed or misread.
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All intersections with interfering signals from copper deposits. Neither Braidwood nor Byron has significant copper deposits in the SGs. Guidance on conducting RPC inspections for interference signals due to copper has i
been included in both stations inspection guidelines.
Data Acauisition and Analysis
- The bobbin coil will be calibrated against a l
reference standard in the laboratory by
- direct testing or through use of a transfer standard.
The voltage response of new bobbin coil probes for the 40% to 100% American Society of Mechanical Engineers (ASME) through-wall holes will not differ from the nominal voltage by more than 10%.
- Probe wear will be controlled by either an in-line measurement device or through the use of a periodic wear measurement. When utilizing the periodic wear measurement approach, if a probe is found to be out of specification (15%), all tubes inspected since the last successful calibration will be reinspected with a new calibrated probe.
Data analysts will be trained in the use of the Comed Byron and Braidwood Stations Units 1 and 2 Eddy Current Analysis Guidelines and qualified through site specific testing.
Data analyst performance will be consistent with the assumptions for analyst measurement variability utilized in the tube integrity evaluations.
Quantitative noise criteria (resulting from electrical noise, tube noise, calibrations standard noise) will be included in the data analysis procedures. Data failing to meet these criteria will be rejected, and the tube will be reinspected.
Data analysts will review the mixed residuals on the standard itself and take action as necessary to minimize the residuals.
A 0.610 inch diameter bobbin coil probe will be utilized for the inspection. If a 0.610 inch diameter probe will not pass through a portion of a tube, APC will not be applied to the portion of the tube that is inspected by a smaller probe.
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l Data analysts will be trained on the potential for primary water stress corrosion cracking to occur at TSP intersections. The l
data analysts will be sensitized to identify l indications attributed to primary water l stress corrosion cracking.
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