ML20117K314
| ML20117K314 | |
| Person / Time | |
|---|---|
| Site: | Braidwood  |
| Issue date: | 08/30/1996 |
| From: | Stanley H COMMONWEALTH EDISON CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML20117K317 | List: |
| References | |
| NUDOCS 9609110231 | |
| Download: ML20117K314 (7) | |
Text
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, Commonw ealth 1:dnon (:ompany liraidu ood Generating Mation Route *I, llox Hi
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August 30,1996 l Office of Nuclear Reactor Regulation i
U.S. Nuclear Regulatory Commission Washington, D.C 20555 Attention: Document Control Desk l
Subject:
Braidwood Station Units I and 2 Request to Amend Facility Operating License NPF-72 and NPF-77 Technical Specification " Steam Generators" NRC Docket Numbers: 50-456 and 50-457
References:
- 1. G. Stanley letter to the Nuclear Regulatory Commission dated August 2,1996, transmitting," Operating Interval B, tween Eddy Current inspections for Circumferential l Indications in the Braidwood Unit i Steam Generators" I
- 2. G. Stanley letter to the Nuclear Regulatory Commission dated August 20,1996, transmitting Additional Information pertaining to the Operating Interval for Braidwood Unit i Steam Generators l 3. D. Lynch letter to D. Farrar dated May 22,1996, transmitting Extension of the Operating l Interval Between Eddy Current inspections for Circumferential Indications in the Braidwood Unit i Steam Generators 1
l l Pursuant to 10CFR50.90, Commonwealth Edison Company (Comed) proposes to amend Appendix A, l l Technical Specifications of Facility Operating Licenses NPF-72 and NPF-77 and requests that the Nuclear
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Regulatory Commission (NRC) grant an amendment to Technical Specification 3.4.5 " Steam Generators."
The current Technical Specification 3/4.4.5 describes the necessary surveillance requirements and acceptance criteria to determine steam generator operability. The proposed amendment modifies the Technical Specification to add a footnote which specifies a repair criteria for top of tube sheet indications if found as part of reviewing previous Unit 1 October 1995 eddy current steam generator data.
This proposed amendment would require the repair of top of tube sheet indication if the distribution of indications exceed
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- the conditional probability of burst of 10 2, or 1
- a predicted main steam line breat leakage rate greater than the site l allowable limits.
The proposed footnote would only be in effect for Braidwood Unit I Cycle 6. I In Reference 3, the NRC accepted Comed's proposal to operate Braidwood Unit I to October 15, 1996, prior to initiating a mid-cycle steam generator tube inspection outage. Subsequent to this submittal, Comed performed additional look backs and analysis of the steam generator tube eddy current data and
, believes that sufficient technicaljustification exists which supports full cycle operation of Braidwood Unit
- 1. This information has been submitted to the Staff via References 1 and 2 and has been discussed in
- meetings with the Staff on August 15th and 26th. We understand that the Staff has questions concerning this justification and Comed is in the process of addressing all of the outstanding issues. Of particular interest is the use of an appropriate beginning of cycle distribution for Braidwood Unit 1 Cycle 6.
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NRC Dodument Control Desk August 30,1996 ,
1 To best determine this distribution, Comed intends to re-examine the eddy current data for the limiting steam generator using Eddynet-95 analysis software and increased analyst awareness. The results of this review will be factored into our evaluation to determine if full cycle operation is justified. This Technical Specification amendment request will define the criteria to determine the appropriate cycle length for Braidwood Unit 1.
Enclosed for your review are:
Attachment A: Description and Safety Analysis of the Proposed Changes Attachment B Marked Up Pages of the Proposed Changes Attachment C: Evaluation of Significant Hazards Considerations for the Proposed Changes Attachment D: Environmental Assessment of the Proposed Changes Comed is requesting that the Staff review and approve this amendment request as soon as possible. Braidwood i Unit 1 is currently scheduled to shut down for the inspection of the steam generators on October 11,1996. Comed l requests that the amendment request be approved by October 4th to allow sufficient time for the reexamination and evaluation of the data. ,
This Technical Specification amendment request is applicable to Braidwood Unit I only, although it'is being docketed for Braidwood Units I and 2 due to the Technical Specifications being common to both units.
This amendment request for the Technical Specification amendment has been reviewed and approved by onsite and off-site review in accordance with Braidwood Procedures.
To the best of my knowledge and belief, the statements contained in '.his document are true and correct.
If you have any questions concerning this amendment request please contact Denise Saccomando, Senior PWR I Licensing Administrator at(630)663-7283. l f A rrr#rnex ^x Sincerely, 1 ^- ,
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TINA M TAMAY .SANTOUN j Gene Stanley norAny Pusuc. ST AT E OF ILLINOl ,k Vice President MY CoMMitmON EXPIMES:04/19/06 -
'braidwood Station ^"^^^^^" " ^" # # ^" " " ^" J Attachments cc: M. D. Lynch, Senior Project Manager-NRR R. R. Assa, Braidwood Project Manager-NRR A. B. Beach, Regional Administrator-Rill C. Phillips, Senior Resident inspector-Braidwood Office of Nuclear Safety-IDNS a
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1 ATTACHMENT A DESCRIPTION AND SAFETY ANALYSIS OF PROPOSED CHANGES TO APPENDIX A TECHNICAL SPECIFICATIONS OF l FACILITY OPERATING LICENSES l NPF-72, AND NPF-77 l l I A. DESCRIPTION OF TIIE PROPOSED CIIANGE l Commonwealth Edison (Comed) proposes to revise Technical Specification Surveillance Require. ment (TSSR) 4.4.5.4.a 6) " Plugging or Repair Limit," of TS 3.4.5," Steam Generators,"
, This revision will provide guidance on actions to be taken based upon the results of a review of l previous Braidwood Steam Generator (SG) Non-Destructive Examination (NDE) data for top of l tube sheet indications.
l These changes are discussed in detail in Section E of this attachment. The affected TS pages showing the proposed changes are included in Attachment B of this request.
l l B. DESCRIPTION OF TIIE CURRENT REQUIREMENT TSSR 4.4.5.4.a 6) defmes the Plugging or Repair Limit as the imperfection depth at or beyond l which the tube shall be removed from service by plugging or repaired by sleeving of the affected l area. The plugging or repair limit imperfection depth for the tubing and laser welded sleeves is l equal to 40% of the nominal wall thickness. The plugging limit imperfection depth for TIG ,
l welded sleeves is equal to 32% of the nominal wall thickness. For Unit 1, this defmition does not
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l apply to defects in the tubesheet that meet the criteria for an F* tube. For Unit 1, Cycle 6, this i defmition does not apply to the tube support plate intersections for which the voltage-based repair criteria are being applied. Refer to 4.4.5.4.a.11 for the voltage based repair limit applicable to tube support plate intersections.
C. BASES FOR TIIE CURRENT REQUIREMENT The surveillance requirements for inspection of SG tubes ensure that the structural integrity of this portion of the Reactor Coolant System (RCS) will be maintained.
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 design, manufacturing errors, or inservice conditions that lead to corrosion. Inservice o tfsyps6040 doc
inspection of SG tubing also provides a means of characterizing the nature and cause of any tube degradation so that corrective measures can be taken.
D. NEED FOR REVISION OF TIIE REQUIREMENT Braidwood conducted NDE inspections of the Unit 1 SGs for top of tube sheet cracking in February of 1995 and October of 1995. All circumferential indications identified during these inspections were stabilized and the tube was plugged.
l Since these inspections were conducted, technologies and techniques have improved. In light of these improvements, Braidwood will re-analyze previous NDE data to determine the most accurate Beginning of Cycle (BOC) distribution of circumferential ODSCC indications in the Top l of Tube Sheet (TTS) roll transition. This re-analysis will be done while Braidwood Unit 1 is I
operating.
Currently, no criteria exist in the TSSR for TS 3.4.5 specifically for the disposition of top of tube sheet indications. Braidwood has, in the past, conservatively plugged all top of tube sheet indications identified during the NDE inspection. However, since the re-analysis of previous inspection data will occur while Braidwood Unit 1 is on-line, this practice could result in a shutdown of Unit 1. This could represent an unnecessary transient for Unit 1. Thus, to prevent an unnecessary transient for Braidwood Unit 1, it is necessary to revise the TSSR for TS 3.4.5 to include criteria for the dispositioning of outside diameter stress corrosion crack (ODSCC) indications found in the TSS roll transition. This will be a one time change to TS 3.4.5, for Unit 1, Cycle 6, to accommodate this re-analysis.
E. DESCRIPTION OF TIIE REVISED REQUIREMENT l
TSSR 4.4.5.4.a 6) will be revised to include criteria for the dispositioning ofindications found in the TTS roll transition that may be revealed by Braidwood's re-analysis of previous NDE data.
This is a one time only change to TSSR 4.4.5.4.a 6).
A footnote will be added to TSSR 4.4.5.4.a 6) This footnote will read:
l For Unit 1, Cycle 6, operation may continue provided that the projected distribution of indications found in the top of tube sheet roll transition resulting from the re-analysis of previous NDE data results in a probability of burst ofless than 1 x 10 2 and predicted leakage is less than the site allowable leak limit. Otherwise, Unit 1 will shutdown and top of tube sheet indications will be plugged or repaired."
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F. BASES FOR TIIE REVISED REQUIREMENT Braidwood Unit I performed a 100% inspection of all four steam generators during inspections j i performed in February and October of 1995. These inspections used the 0.080" rotating pancake '
l coil (RPC) probe. The 0.080" pancake coil was used because it is sensitive to circumferential degradation, and experience has shown it can detect indications that are important to maintain.ing adequate leakage and burst margins. The total number of circumferential indications detected i during the 1995 inspections were 16 and 23. All tubes with circumferentialindications were stabilized and the tube plugged prior to Braidwood Unit I returning to service.
Experience with Byron Unit 1 indicates that the use of 0.080" RPC probe results in a reduction in the size of the largest potentialindications detected at the end of subsequent operating intervals.
Experience also shows that the detection capability of the 0.080" RPC decreases with decreasing l indication size, and that relatively small indications may go undetected. The ability to detect relatively small indications depends in part on analyst training and data analysis capabilities. In ;
order to determine the most accurate BOC distribution of circumferential TTS indications, l Braidwood will be performing a re-analysis of the October 1995 NDE data.
l Re-evaluation of the October 1995 inspection data will use enhanced analyst training and data ;
analysis software for detection of and of sizing circumferential ODSCC indications. This ;
enhanced training and analysis software is comparable to that used in 1996 at Byron Unit 1. The enhanced analysis methods can be expected to increase the probability of detection (POD),
! especially for smaller indications, and the look-back evaluation likely will identify indications present in October 1995, but not identified in October 1995. l The purpose of this Technical Specification change is to provide guidance for disposition of TTS l roll transition ODSCC indications found during this re-analysis and to ensure that tubes accepted for continued service will retain adequate structural and leakage integrity during normal operation, and postulated transient accident conditions. The proposed re-evaluation of the Braidwood Unit 1 inspection data will provide information to ensure the requirements of RG 1.121 are met by demonstrating the tube leakage and probability of burst is acceptably low. I Performing the look-back evaluation with the enhanced techniques provides confirmation and i l
additional assurance that adequate margin against leak and burst will be maintained during Cycle l 6 at Braidwood Unit 1.
The methodology for assessing structural and leakage margins for Braidwood Unit 1 for this l request were submitted to the NRC August 2,1996 and are outlined below.
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- 1. Calculate the allowable primary to secondary leakage during a MSLB event based on a small fraction of the 10 CFR 100 limits at the site boundary.
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l 2 Develop an in-service voltage distribution of TTS ODSCC indications based on an enhanced review of the 1995 inspection data at Braidwood, Unit 1 l 3. Define growth rates during the 1995 operating period 1
- 4. Predict EOC-6 voltage distribution
- 5. Evaluate the EOC-6 voltage distribution for tube burst and leakage during a MSLB event.
- 6. Apply Comed and industry data to define the conditions corresponding to acceptable burst l and leak margins.
- 7. Calculate the anticipated leak rate during MSLB.
- 8. Compare the calculated leak rate with the site allowable limit, including consideration of leakage from other identified mechanisms, to ensure the leakage is less than the site allowable limit.
- 9. Calculate the conditional probability of burst for the End-Of-Cycle 6 voltage distribution to 2
determine ifit is less than 1 x 10 i
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- 10. Declare the SG operable if the anticipated EOC leak rate is less than the site allowable limit and there is an acceptable probability of burst at the End of Cycle 6.
l An important element in the Braidwood, Unit I analysis is the use of a Comed and industry data l base to assess the probability of burst and the potential primary to secondary leakage through degraded steam generator tubes at MSLB differential pressures. This data base includes pulled tubes and in-situ tests.
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G. IMPACT OF THE PROPOSED CIIANGE i This proposed change requires that the projected EOC distribution ofindications resulting from the re-analysis NDE data must maintain adequate margin to probability of burst and leak limits.
l Otherwise the Unit must be shutdown and all top of tube sheet indications plugged or repaired.
l Thus this amendment will not adversely affect off site doses during normal or accident conditions. l This amendment will not result in any changes to existing systems or equipment, nor will it result in the installation of any new systems or equipment. The change is administrative in nature in that it provides criteria for assessing the results of the re-analysis of Braidwood's Unit 1 SG NDE data.
l Therefore, this amendment request has no significant negative impact on any system or operating i mode.
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II. SCIIEDULE REQUIREMENTS In order to prevent an unnecessary shutdown for Unit 1, Comed requests that this proposed change be approved as soon as possible, and not later than October 4,1996.
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