ML20134J662
| ML20134J662 | |
| Person / Time | |
|---|---|
| Site: | Byron, Braidwood  |
| Issue date: | 02/05/1997 |
| From: | Hosmer J COMMONWEALTH EDISON CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9702120242 | |
| Download: ML20134J662 (9) | |
Text
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Q>mm' nwecith litiwn Company
,- 1400 Opus Place
' Downers 45 rove;11Rd)515-5701 February 5,1997 U.S. Nuclear Regulatory Commission Washington, D.C. 20555 l
Attn: Document Control Desk
Subject:
Response to Request for Additional Information Related to the Proposed Extension of the Byron 1 and Braidwood 13.0 Voh License Amendment for ODSCC Byron Nuclear Power Station Unit 1 NRC Docket Number: 50-454 i
Braidwood Nuclear Power Station Unit I NRC Docket Number: 50-456 j
References:
1.
H. Stanley letter to the Nuclear Regulatory Commission dated i
August 19,1996, transmitting Request for Technical Specification Amendment Pctaining to the 3 Volt Renewal 2.
M. Lynch letter to I. Johnson dated January 27,1997, transmitting Request for Additional Information Related to the Proposed Extension of the Byron 1 and Braidwood 13.0 Volt License Amendment for ODSCC Reference 1 transmitted the Commonwealth Edison Company (Comed)'s request to renew the 3.0 Volt Interim Plugging Criteria for the Byron Unit I and Braidwood Unit 1
[f steam generators. Based upon that submittal, the Nuclear Regulatory Commission (NRC) l issued a Request for Additional Information (RAI) which was transmitted via Reference 2.
The Attachment contains Comed's response to Questions 1 through 11. The response to Question 12 will be transmitted to the Staff at a later date.
9702120242 970205 DR ADOCK 05000454 l
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U.S. Nuclear Regulatory Commission February 5,1997 Comed would like to bring to the Staff's attention an error in the August 19,1996, submittal. In Attachment B, pages B-15 and B-21, Comed included the requirement to inspect fifly tubes adjacent to each anti-rotation device in all four SGs along with twenty tubes along the patch plate seam in one SG, under the section of the submittal listing the Rotating Pancake Coil (RPC) scope. This is incorrect in that these tubes will be initially screened using the bobbin coil technique as developed under the EPRI Tube Support Plate Inspection Program. Ifindications are identified by bobbin, additional RPC inspections will be performed. This inspection approach is the same scope and technique used in support of the initial 3.0 volt IPC implementation at Braidwood I and Byron 1 in the Fall of1995.
If you have any questions concerning this correspondence, please contact Denise M.
Saccomando, Senior PWR Licensing Administrator at (630) 663-7283.
I Sincerely, t
-N j d W l(/
John B. Hosmer Engineering Vice President Attachment cc:
D. Lynch, Senior Project Manager-NRR G. Dick, Byron /Braidwood Project Manager-NRR C. Phillips, Senior Resident Inspector-Braidwood S. Burgess, Senior Resident inspector-Byron A. B. Beach, Regional Administrator-RIII Oflice of Nuclear Safety-IDNS K:nla\\bybwd\\stgen\\3vrrai
ATTACHMENT REQUEST FOR ADDITIONAL INFORMATION RELATED TO THE EXTENSION OF THE 3.0 VOLT LOWER VOLTAGE REPAIR LIMIT FOR ODSCC BYRON UNIT 1 AND BRAIDWOOD UNIT 1 DOCKET NOS. STN 50-454 AND STN 50-456 1.
Provide a summary of the results from the inspection of the steam generator (SG) internal structures conducted in the Byron 1 outage in October 1995, similar to the summaries provided in the two reports cited in the references below.
Response
A summag of the results from the inspectic' of the steam generator (SG) internal structures conducted in the mid-cycle outage at Byron 1 in October 1995 were provided to the NRC in Byron letter BYRON-96-0074 to the Office of Nuclear Reactor Regulation, dated March 19,1996," Byron Unit 1 Steam Generator Interim l
Plugging Criteria 90 Day Report." Attachment A of this letter, " Tube Support Plate Stmetural Integrity Verifications," contains a summary of the results. No indications of degradation of the internal structures were found.
2.
The licensee stated in Reference 1 that it visually inspected 89 vertical support bars and 157 vertical support bar welds in the four SGs and found no indication of structural degradation in the welds which would prevent the support bars from performing their function. State whether any types ofindications were found. If so, describe the natu. of these indications, including the number of such indications and their location and an evaluation of their potential effect on their structural capability of the vertical support bar welds.
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Response
1 No indications of any type were found.
I 3.
In Reference 1, the licensee stated that it inspected 50 tubes around each of the three l
antirotation devices and did not find any operationally-induced degradation of the tube support plates (TSPs). State whether any type of degradation was found. If so, describe the nature of the degradation, including the extent, the location, the probable cause and an evaluation of the effect on the structural capability of the TSPs.
Response
No type of degradation was found.
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4.
In its letter dated August 19,1996, the licensee stated that it will use a modified eddy current inspection (ECI) technique to inspect 50 tubes adjacent to each antirotation device in all four SGs and to inspect 20 tubes along the patch plate seam in one SG.
State when and where this inspection will be performed (e.g., during the upcoming refueling outages at Braidwood 1 and Byron 1).
Response
The inspection of the fifly tubes adjacent to each antirotation device and the twenty tubes along the patch plate seam will be performed during the upcoming refueling outage (AIR 06) at Braidwood I and during the next refueling outage (BIR08) at Byron 1, unless SG replacement occurs during that outage.
5.
State whether the presence of the TSP intersections will continue to be verified during SG ECIs.
Response
The presence of the Tube Support Plate (TSP) intersections will continue to be verified during all Interim Plugging Criteria (IPC) inspections at Braidwood I and Byron i until SG replacement. A voltage-based repair criteria for axialindications at the TSPs will not be applied to the replacement SGs.
6.
In its letter dated August 19,1996, the licensee stated that it will verify the integrity of the SG tube expansions at the TSP intersections for the 21 SG tubes used to stabilize the TSPs by inspecting 20 percent.of these expansions. Additionally, this sample of SG tubes will also be inspected at the top of the tubesheet in the roll transition zone. State when and where this SG tube inspection will be performed (e.g., during the upcoming refueling outages at Braidwood I and Byron 1). Describe the criteria for selecting the initial inspection sample of SG tubes.
Response
The inspection to verify the integrity of the SG tube expansions and the top-of-the tubesheet for each of these expanded tubes will be performed during the upcoming A1R06 refueling outage at Braidwood I and during the upcoming BIR08 refueling outage at Byron 1, unless SG replacement occurs during that outage. Twenty percent of the total expansions will be inspected. Each tube selected for inspection will have all TSP expansions and the hot-leg top-of-tubesheet roll transition regions inspected by Plus Point as described below. Considering the similarity of the tubes j
selected for the expansion process between the SGs, the similarity of the operation between the SGs, and the need to remove the SG tube plug to inspect the expansions, the following selection criteria has been established:
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j SGs representative of the total population of Outside Diameter Stress Corrosion e
Cracking (ODSCC) at TSPs and top of tubesheet indications Tubes from each of the fourteen bundle regions where TSP expansions were performed.
Tubes containing both the minimum and maximum number of expansions per tube.
The current program for Braidwood 1 consists of inspecting the steam generators in loops A and D for the initial 20% sampling. These generators represent approximately 50% of the ODSCC at the TSPs and approximately 40% of the top-of-tubesheet indications to date. Ifinspections at Byron 1 are required prior to SG replacement, a similar selection process will be performed. The selection process will include a tube from each of the fourteen tube bundle regions where expansions were performed. This will provide a representative sampling of all variations on location l
and number of expansions per tube. If tooling limitations do not allow removal of a particular plug without personnel entry into the steam generator channel head, another tube will be selected.
The expansions will be examined by a method equivalent to or better than that used during the previous outages. This method will include the use of the EddyNet 95 software. The method used at Byron 1 and Braidwood 1 during the installation of the expansions used the ANSER software. The sleeve expansions at the TSPs will be examined using a Gimbated Plus Point coil. The expansions at the top-of-tubesheet will be examined using the Plus Point probe. These inspection techniques are sensitive to axial and circumferential indications. If a circumferential crsck like indication is identified at the TSP expansion or if a circumferential crack like indication is detected at the top of the tubesheet of a locked tube, the inspection program will be enlarged to include 100% of the locked tubes in each SG.
7.
In its submittal dated August 19,1996, the licensee also stated that the staff will not be notified if axial indications are detected at the sleeved and expanded joint intersections of the 21 SG tubes with the TSPs or at the TTS. Since these SG tubes were inspected before plugging and no indications were found, the staff requests that it be promptly notified if any type ofindication is found in subsequent inspections of these locations.
Response
Comed will notify the StafTprior to unit restart if either axial or circumferential indications are detected at the sleeve expanded joint or at the top-of-tubesheet. This is a requirement listed in Section 4.5.3 of the Safety Evaluation approving the original 3.0 Volt IPC dated November 9,1995.
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The August 19,1996, submittal stated that axial indications at the top-of-tubesheet or at the TSP expansion will not result in a displacement of the TSP by more than 0.1 inches. Therefore, finding axial indications at the TSP expansion or at the top-of-tubesheet region will not require expansion of the inspection scope.
f If circumferential indications are detected at either the sleeve expanded joint or top-of-tubesheet, an analysis will be done to determine the effect of these indications on TSP displacement. Repairs will be implemented to maintain TSP displacement less than or equal to 0.1 inch. Detection of circumferential indications will result in j
expanding the inspection to 100% of the tubes containing TSP expansions.
Selection of the original tubes for TSP locking required the tubes to be free of axial or circumferential indications at the top-of-tubesheet. Tubes containing axial i
ODSCC at the tube-to-TSP intersections were allowed to be se.ected for TSP locking candidates. Braidwood 1 contains three tube-to-TSP intersections with indications that were dispositioned as axial indications confined within the TSP intersection. At Byron 1, none of the tube-to-TSP intersections contained indications. The baseline inspection of the top-of-tubesheet region and sleeve expansion joints did not reveal i
any axial or circumferential indications other than the original, axial ODSCC at the tube-to-TSP intersections discussed above.
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8.
The licensee stated in its August 19,1996 submittal, that it will continue to implement the criteria for eddy current probe wear recommended by the Nuclear Energy Institute (NEI). This approach requires that all indications greater than 75 percent of l
the lower voltage repair limit which were inspected with a worn probe, be re-i inspected with a new probe. State whether Braidwood I and Byron 1 will continue j
to reinspect with a new probe after determining that significant probe wear exists, indications greater than 75 percent of 1.0 volt, even hot-leg intersections at which the 4
3.0 volt alternate repair criteria (ARC) is applied.
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Response
i Braidwood I and Byron 1 will use the alternate probe wear criteria (NEI criteria) which was submitted to the NRC in a letter on March 19,1996, and implemented 3'
during the Byron 1, March 1996, inspection. Byron 1 and Braidwood I will reinspect all indications greater than 75 percent of the lower Voltage Repair limit (1.0 volt) 4 including hot leg indications, for tubes inspected with probes which do not meet the
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probe wear criteria.
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9.
In its submittal dated August 19,1996, the licensee stated that the probability of axial tensile failure will be calculated in accordance with the guidance in Generic Letter (GL) 95-05 and will combine this probability with the conditional probability of axial burst failure if any indications with a voltage greater than or equal to 15 volts are identified or if a large number ofindications between ten and fifleen volts are identified. State the basis for specifying a limit of 15 volts. Indicate why there is an upper limit on this range. Define what constitutes a large number ofindications, including the basis for this criterion.
Response
As stated in our August 19,1996 submittal, the number ofindications predicted at the end of cycle 7 between ten and fifteen volts for Braidwood I is 0.3 indications, and 4.59 indications at the end of cycle 9 for Byron 1. The maximum voltage predicted at the end of cycle 7 is 10.5 volts for Braidwood 1 and 13.5 volts at the end of cycle 9 for Byron 1. Comed conservatively selected a limit of fifteen volts to require a probability of axial tensile burst failure calculation based on the following:
The structural limit for axial tensile tearing is approximately 35 volts. Comed has conservatively chosen a value less than half of this limit before requiring the calculation of the probability of burst contribution from axial tensile failure.
The probability of axial tensile burst for a fifteen volt indication is extremely 4
small, approximately 4x10 An indication less than fifteen volts would add a negligible contribution to the total burst probability.
Fifteen volts is higher than the maximum indication voltage predicted for the end of the next cycle of operation at both sites.
A small fraction of the lx10-2 burst probability limit was selected as a goal for the contribution ofindications greater than ten volts. A goal of lx10-3 was selected.
4 Given the probability of tensile rupture associated with a ten volt signal being 3x10,
it would take approximately 325 indications near ten volts before a probability of lx10'3 is reached. Given the probability of tensile mpture associated with a fifteen 4
volt signal being 4x10, it would take approximately 250 indications near fifteen volts before a probability of lx10 is reached.
Therefore, Comed will not calculate the contribution due to the probability of axial tensile burst unless greater than 250 indications in the range of ten to fifteen volts are detected or unless an indication greater than fifteen volts is detected.
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9.
In its submittal dated August 19,1996, the licensee stated that the probability of axial tensile failure will be calculated in accordance with the guidance in Generic Letter (GL) 95-05 and will combine this probability with the conditional probability of axial burst failure if any indications with a voltage greater than or equal to 15 volts are identified or if a large number ofindications between ten and fifleen volts are identified. State the basis for specifying a limit of 15 volts. Indicate why there is an upper limit on this range. Define what constitutes a large number ofindications, including the basis for this criterion.
Response
As stated in our August 19,1996 submittal, the number ofindications predicted at the end of cycle 7 between ten and fifleen volts for Braidwood 1 is 0.3 indications, and 4.59 indications at the end ofcycle 9 for Byron 1. The maximum voltage predicted at the end of cycle 7 is 10.5 volts for Braidwood 1 and 13.5 volts at the end of cycle 9 for Byron 1. Comed conservatively selected a limit of fifteen volts to require a probability of axial tensile burst failure calculation based on the following:
The structural limit for axial tensile tearing is approximately 35 volts. Comed has conservatively chosen a value less than half of this limit before requiring the calculation of the probability of burst contribution from axial tensile failure.
The probability of axial tensile burst for a fifleen volt indication is extremely 4
small, approximately 4x10 An indication less than fifleen volts would add a negligible contribution to the total burst probability.
Fifleen volts is higher than the maximum indication voltage predicted for the end of the next cycle ofoperation at both sites.
j A small fraction of the lx10-2 burst probability limit was selected as a goal for the contribution ofindications greater than ten volts. A goal of lx10-' was selected.
4 Given the probability of tensile rupture associated with a ten volt signal being 3x10,
it would take approximately 325 indications near ten volts before a probability of 1x10 is reached. Given the probability of tensile rupture associated with a fifleen 4
volt signal being 4x10, it would take approximately 250 indications near fifleen volts before a probability of lx10~' is reached.
Therefore, Comed will not calculate the contribution due to the probability of axial tensile burst unless greater than 250 indications in the range of ten to fifleen volts are detected or unless an indication greater than filleen volts is detected.
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- 10. The licensee proposed to add definitions of both the Locked TSP Model and the Freespan Mode into the Byron 1 and Braidwood 1 TSs. However, the staff review of the definitions proposed to be added to the TS Section 4.4.5.4.a indicate that 1
intersections containing a corrosion-induced dent greater than 0.065 inches are not excluded. Provide a basis for this approach.
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Response
Intersections containing a corrosion-induced dent greater than 0.065 inches are i
excluded from application ofIPC based on the proposed Technical Specification.
Proposed Technical Specification Sections 4.4.5.4.a.]1 and 4.4.5.4.a.12 list areas 4
excluded from application of both the Locked Tube Model and the Free Span Model a
IPC. These Technical Specification sections exclude IPC from being applied to "All tube-to-tube support plate intersections where IPC cannot be applied per Generic Letter 95-05." The Generic Letter requires the use of a 0.610 inch diameter bobbin coil piobe for the inspection of 3/4 inch tubing. If a dent greater than 0.065 inches is present, passage of a 0.610 inch diameter bobbin coil probe is not possible; therefore, j
application oflPC at that intersection is not allowed per the Generic Letter and proposed Technical Specification definitions.
I1. Provide the scheduled date for the start of the Braidwood 1 Cycle 6 refueling outage and the Byron 1 Cycle 8 refueling outage.
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Response
The Braidwood 1 Cycle 6 refueling outage (AIR 06) is scheduled to start March 29, 1997. The Byron 1 Cycle 8 refueling and steam generator replacement outage (BIR08)is scheduled to start November'7,1997.
- 12. During the SG blowdown following a postulated main steamline break (MSLB), the pressure drop across a TSP will be determined by the position dependent flow distribution across a TSP. Because of the differences in resistances between fluid j
flows parallel and perpendicular to the SG tube bundles above the topmost TSP, a multidimensional flow pattern exists. This effect will be most pronounced at the upper TSP. Accordingly, assess the effect of the multidimensional flow pattern on the position dependent pressure drop across the TSPs.
Response
Analyses are underway to responds to this question at a later date.
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References I
- 1. Comed letter dated March 5,1996,"Braidwood Station Unit 1 Steam Generator i
Interim Plugging Criteria 90 Day Repon"
- 2. Comed letter dated September 9,1996," Byron Station Unit 1 Steam Generator
)
Interim Plugging Criteria 90 Day Repon for the End-of-Cycle 7 Inspection" l
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