ML20117J014
| ML20117J014 | |
| Person / Time | |
|---|---|
| Site: | Byron, Braidwood  |
| Issue date: | 08/19/1996 |
| From: | Stanley H COMMONWEALTH EDISON CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML20117J017 | List: |
| References | |
| NUDOCS 9609100121 | |
| Download: ML20117J014 (26) | |
Text
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ - _ _ _ _ _ - - _ _ _ _ _ _ _ _ _ _ _ - _ _ _ - _ - _ . _ _ _ _ _ _ _ _ - _ - _ _ _ _ _ _ _ - _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ - _ _ _ _ _ _ -_
. Commonwealth litiwn O>mpany i lir.tidwood Cecncrating Station )
Houte oI. Ilos 8i e liracculle. 11.60407-% I9 Tcl HI %A58 bull i
August 19,1996 United States Nuclear Regulatory Commission Attention: Document Control Desk <
Washington, D.C. 20555-0001
Subject:
Application for Amendment to Facility Operating Licenses:
Byron Nuclear Power Station, Units 1 and 2 NPF-37 and NPF-66: NRC Docket Nos. 50-454 and 50-455 Braidwood Nuclear Power Station, Units I and 2 NPF-72 and NPF-77: NRC Docket Nos. 50-456 and 50-457
Reference:
D. Lynch (NRC) letter to D. Farrar (Comed) dated November 9,1995, transmitting the Safety Evaluation Report (SER) Approving the Three Volt Interim Plugging Criteria for the Byron and Braidwood Unit i Steam Generators.
Pursuant to Title 10, Code of Federal Regulations, Past 50, Section 90 (10 CFR 50.90)
Commonwealth Edison Company (Comed) proposes to amend Technical Specification (TS) 3/4.4.5," Steam Generators," of Appendix A of Facility Operating Licenses NPF-37, NPF-66, NPF-72, and NPF-77.
The changes proposed to TS 3/4.4.5 will renew the 3.0 volt bobbin coil probe, Steam Generator (SG) Tube Support Plate (TSP) Interim Plugging Criteria (IPC) limit for Outside Diameter Stress Corrosion Cracking (ODSCC) indications at Locked-Tube Model TSP intersections as approved by the Nuclear Regulatory Commission (NRC) in Amendments 69 and 77 for Braidwood and Byron, respectively.
The renewal package is formatted to highlight information that was previously docketed to the NRC during the initial 3 volt licensing process. Additionally, Comed has addressed the specific concerns that were detailed in the Safety Evaluation Report for Braidwood and Byron Amendments 69 and 77, respectively.
This amendment request applies to Byron Unit I and Braidwood Unit 1 only. It is being docketed for Byron and Braidwood Units 1 and 2 because the Technical SpeciHcations for Units 1 and 2 are shared. \
O 9609100121 960819 i PDR ADOCK 05000454 p PDR
\
\
otfsyp\96038 doc A l'nicom Compan)
U.S. Nuclear Regulatory Commission August 19,1996 l
The amendment package consists of the following:
Attachment A: Description and Safety Analysis of Proposed Changes Attachment B: Byron /Braidwood Unit i Steam Generator Interim Plugging Criteria Methodology Attachment C: Proposed changes to the Technical Specification pages for Byron and Braidwood Attachment D: Evaluation of No Significant liarards Considerations Attachment E: Environmental Assessment.
l This proposed amendment has been reviewed and approved by the On-site and Off-site Review Committees in accordance with Comed procedures. Comed has reviewed this proposed amendment in accordance with l 10 CFR 50.92(c) and has determined that no significant hazards consideration exists.
l l
l Comed is notifying the State ofIllinois of our application for this proposed amendment by transmitting a l copy of this letter and the associated attachments to the designated state official.
l Comed requests that NRC review and approval of this proposed amendment be completed by March 3, l 1997.
l l
To the best of my knowledge and belief, the statements contained in this document are true and correct. In j some respects these statements are not based on my personal knowledge, but on information furnished by i other Comed employees, and/or consultants. Such information has been reviewed in accordance with company practice and I believe it to be reliable.
Please address any comments or questions regarding this proposed amendment to Denise Saccomando, Senior PWR Licensing Administrator at (708) 663-7283.
Sincerel ',
f./ ,
. Stanley fq TINAOFFICIAL SEA M TAMAYO SANTOLIN $
l Site Vice President NOTARY PUBUC. ST ATE oF ILLINOIS Braidwood Nuclear Station (>0.-h. $7"_ EI"'"_E*]j,'.,'_
1 Attachments I I
cc: A. B. Beach, Regional Administrator - Rill
~
M.D. Lynch, Senior Projects Manager - NRR G. F. Dick Jr., Byron Project Manager - NRR !
R. R. Assa, Braidwood Project Manager - NRR l S. Burgess, Senior Resident Inspector - Byron !
C. Phillips, Senior Resident inspector - Braidwood j Office of Nuclear Facility Safety - 1DNS l o V.fsyp\96038 doc ,
s
- . .- - - - - - . - ~ . ,
i
]
l l
ATTACHMENT A l
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 ., ;
i Commonwealth Edison (Comed) proposes to amend Braidwood and Byron Technical Specification (TS) 3/4.4.5, " Steam Generators" and the Bases for TS 3/4.4.5. l The changes proposed to TS 3/4.4.5 will renew the 3.0 volt bobbin i coil probe, Steam Generator (SG) Tube Support Plate (TSP) Interim l Plugging Criteria (IPC) limit for Outside Diameter Stress l Corrosion Cracking (ODSCC) indications at hot-leg (Locked-Tube Model) TSP intersections as approved by the Nuclear Regulatory Commission (NRC) in Amendments 69 and 77 for Braidwood and Byron, ,
respectively. l This renewal will also continue to require a 1.0 volt IPC be applied to ODSCC indications at the cold-leg and specific hot-leg TSP intersections (Free-Span Model), in accordance with Generic Letter 95-05, " Voltage-Based Repair Criteria for Westinghouse Steam Generator Tubes Affected By Outside Diameter Stress Corrosion Cracking," August 3, 1995 (GL 95-05). Administrative changes will be made to TS 3/4.4.5 and to the Bases for TS 3/4.4.5 to clarify the proper application of the SG tube plugging and repair criteria described in this amendment request. This renewal will be applicable for Braidwood Unit 1 Cycle 7, and for Byron Unit 1 Cycle 9.
Specific changes are discussed in detail in Section E of this attachment. Affected TS pages showing the actual changes are included in Attachment C.
B. DESCRIPTION OF THE CURRENT REQUIREMENT For Braidwood Unit 1 and Byron Unit 1, the Technical Specification Surveillance Requirement (TSSR) for TS 4.4.5 states, in part, that SG tubes with axial flaws indicative of ODSCC confined within the thickness of the TSP may remain in service provided that the following requirements are met:
A-1
\. .-
n the flaw-like bobbin coil signal is at a cold-leg intersection and is less than or equal to 1.0 volt; the flaw-like bobbin coil signal is at a hot-leg intersection and is less than or equal to 3.0 volts; i
the flaw-like bobbin coil signal is at a cold-leg
, intersection, is greater than 1.0 volt but less than or equal to the upper voltage repair limit, and a rotating j pancake coil (RPC) inspection does not detect degradation; I
the flaw-like bobbin coil signal is not in a location that l is susceptible to collapse ar deformation during a i postulated Loss Of Coolant Accident (LOCA) and Safe Shutdown Earthquake (SSE) event; or I
the flaw-like bobbin coil signal is not at a TSP j intersection that IPC can not be applied.
Axial flaws indicative of ODSCC confined within the thickness of j the TSP will be plugged or repaired under the following a conditions:
i the flaw-like bobbin coil signal is at a hot-leg intersection and is greater than 3.0 volts; the flaw-like bobbin coil signal is at a cold-leg intersection and is greater than the upper voltage repair limit; the flaw-like bobbin coil signal is at a cold-leg intersection, is greater than 1.0 volt but less than or equal to the upper voltage repair limit, and is confirmed by RPC; RPC confirmed flaws indicative of ODSCC at locations that are excluded from IPC; or the flaw-like bobbin coil signal is in a location that is susceptible to collapse or deformation during a postulated LOCA with a SSE event.
The upper voltage repair limit is required to be calculated in accordance with the methodology of Generic Letter 95-05, as supplemented. An IPC is not applied to the flaw-like bobbin coil signals at the Flow Distribution Baffle.
If, as a result of leakage due to a mechanism other than ODSCC at the TSP intersection, or some other cause, an unscheduled SG tube inspection is performed, bobbin coil voltage limits for cold-leg intersections are determined in accordance with an equation that takes into account the time remaining in the cycle, the A-2
structural limit voltage, and the bobbin voltage at the beginning-of-cycle (BOC) as directed by GL 95-05. The plugging criteria for hot-leg intersections during unsched' aled inspections remains the same as for a regularly scheduled inspection.
C. BASES FOR THE 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 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.
The voltage-based repair limits for Unit 1 in TSSR 4.4.5 implement the guidance in GL 95-05 for Westinghouse-designed SGs with the exception of the specific voltage limit and cycle applicability. GL 95-05 discusses a 1.0 volt Alternate Plugging Criteria (APC) that can be applied to more than one cycle of operation. Braidwood and Byron TSSR 4.4.5 implemented a 3.0 volt IPC for hot-leg intersections, and a 1.0 volt IPC for cold-leg TSP intersections, and selected hot-leg TSP intersections. This IPC is applicable to the Unit 1 SGs for a specified operating cycle. The TSP's at the hot-leg intersections have been " locked" to not allow movement of more than 0.1 inches during accident conditions. The higher voltage-based repair limit for hot-leg intersections can be applied due to credit being taken for the presence of the TSP's to virtually eliminate SG tube burst.
Projected end of cycle SG tube leakage and burst predictions are determined as required by GL 95-05.
The voltage-based repair limits of TSSR 4.4.5 are applicable only for dominantly axially oriented ODSCC located at the tube-to-TSP intersections of Westinghouse-designed SGs, with no ODSCC extending outside the thickness of the TSP. The voltage-based repair limits are not applicable to other forms of SG tube degradation nor are they applicable to ODSCC that occurs at other locations within the SG.
Implementation of TSSR 4.4.5 requires a derivation of the voltage structural limit from the burst versus voltage empirical correlation. The voltage repair limit is subsequently derived from the structural limit (which is then implemented by this surveillance). The cold-leg structural limit (4.745 volts) is determined based upon the methodology described in GL 95-05. The hot-leg structural limit has been determined to be in excess of A-3 I
' 1 ten volts. i TSSR 4.4.5.5 implements several reporting requirements recommended by GL 95-05 for situations which the NP.C is cc be notified prior to returning the SGs to service.
D. NEED FOR REVISION OF THE REQUIREMENT The current voltage-based repair limits in TSSR 4.4.5 are l applicable only to the end of Cycle 6 for Braidwood Unit 1, and !
to the end of Cycle 8 for Byron Unit 1. SG replacement is scheduled to take place at the end of Cycle 7 for Braidwood and the end of Cycle 8 for Byron. Therefore, this renewal amendment ;
is applicable for one cycle of operation at Braidwood Unit 1, with Byron Unit 1 implementation serving as a contingency if SG ;
replacement is delayed beyond the end of Cycle 8.
l At Braidwood and Byron, Unit 1 has four Westinghouse Model D-4 1 SGs. This model SG has 0.75 inch thick carbon steel, drilled hole TSPs. The tubes are mill annealed Inconel 600 which were hard rolled into the tube sheet during initial assembly.
Subsequently, the tubes were shot peened in the tube sheet area ;
and thermally stress relieved in the U-bend area. Over the past !
several refueling outages, the number of Unit 1 SG tubes with j ODSCC indications has been increasing at Braidwood and Byron.
Current repair projections for the Braidwood Unit 1 Cycle 6 Refueling Outage indicate that, using a 1.0 volt IPC, as many as 1450 SG tubes may need to be plugged or repaired by sleeving due to ODSCC at the TSP. Projections for Byron Unit 1 Cycle 8 Refuel Outage indicate that, using a 1.0 volt IPC, as many as 1500 SG tubes may need to be plugged or repaired by sleeving due to ODSCC. Plugging levels this high exceed currently analyzed maximum levels and would result in a significant reduction in the RCS flow rates, prevention of plant restart, excessive outage repair costs and 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 IPC for ODSCC indications at the hot-leg TSPs would reduce the projected maximum number of tubes needing plugging or repair due to ODSCC to 60 for Byron, and 50 for Braidwood. This represents a " savings" of 1440 tubes at Byron and 1400 tubes at Braidwood that would have had to be plugged or repaired using a 1.0 volt IPC. Since plugging levels this high(1440 tubes at Byron, 1400 at Braidwood) exceed currently analyzed maximums, sleeving these tubes would add as much as $7 Million apiece at Braidwood and Byron in outage inspection and repair costs.
Thus, in order to allow Braidwood and Byron to operate until SG A-4
1
, . I replacement, it is necessary to renew the current voltage-based repair criteria of TSSR 4.4.5.
This proposed amendment also requests administrative changes necessary to clarify the applicability of the repair criteria, and requests changes to the reporting requirements. The administrative changes and the changes to the reporting requirements are in response to NRC concerns. All of the changes are consistent with the discussions held in a meeting between Comed and the NRC on July 11, 1996.
E. DESCRIPTION OF THE REVISED REQUIREMENT For Braidwood Unit 1 and Byron Unit 1, Comed is requesting a one cycle renewal of the 3.0 volt bobbin coil probe, SG TSP IPC limit for ODSCC indications at the hot-leg TSP intersections (Locked-Tube Model) as approved by the NRC in Amendments 69 and 77 for Braidwood and Byron, respectively. This proposal also requests a one cycle renewal of the 1.0 volt IPC which will be applied to ODSCC indications at the cold-leg TSP intersections, and specific hot-leg TSP intersections (Free-Span Model), in accordance with GL 95-05. Administrative changes will also be made to TS 3/4.4.5 and to the Bases for TS 3/4.4.5 to further clarify the proper application of the SG tube plugging and repair criteria described in this amendment request.
Technical Specification 3/4.4.5 will be changed to be applicable through Cycle 7 for Braidwood Unit 1 and through Cycle 9 for Byron Unit 1.
TSSR 4.4.5.4.a will be modified to include new definitions 11 and
- 12. These definitions are intended to clarify the applicability of the 3.0 volt and 1.0 volt IPC to various SG tube-to-TSP intersections. The remainder of TSSR 4.4.5.4.a will be renumbered to accommodate the~e new definitions. These definitions read as follows:
"11) Locked-Tube Model Intersection means all steam generator hot-leg tube-to-tube support plate intersections which have been analyzed to experience a tube support plate displacement less than 0.1 inches during accident conditions, excluding the following:
a) All tube-to-tube support plate intersections where IPC cannot be applied per Generic Letter 95-05; b) All Flow Distribution Baffle intersections; c) All ster generator tube intersections adjacent to an intersection that contains a corrosion induced dent greater than 0.065 inches; and A-5
I d) All tube-to-tube support plate intersections that will be displaced more than 0.1 inches during accident conditions due to failure of the steam generator !
internal structures. ;
i 12) Free-Span Model Intersection means all steam generator tube- >
to-tube support plate intersections to which the Locked-Tube :
l Model does not apply and which meet the criteria of Generic Letter 95-05, excluding the following.
a) All tube-ta-tube support plate intersections where IPC cannot be applied per Generic Letter 95-05; and i b) All Flow Distribution Baffle intersections."
In the remainder of TSSR 4.4.5.4.a, the phrases " hot-leg tube I support plate" and " cold-leg tube support plate" will be replaced !
by the appropriate " Locked-Tube Model Intersection" or " Free-Span Model Intersection" term, respectively.
TSSR 4.4.5.4.11.e will be modified to indicate that the voltage- ,
based repair criteria of this amendment request do not apply to i flow distribution baffles. A sentence will be added to this TSSR to read as follows:
\
" Flow Distribution Baffle Intersections are also excluded from !
application of the voltage-based repair criteria." !
TSSR 4.4.5.5, " Reports," item "d" will be modified to add two new reports. These changes shall read:
i i
l A-6 l
"5) If cracking is observed in the tube support plates.
- 6) If any tube which previously passed a 0.610 inch diameter bobbin coil eddy current probe currently fails to pass a 0.610 inch diameter bobbin coil eddy current probe."
The remainder of the requirements listed in TSSR 4.4.5.5.d will be renumbered to accommodate these new requirements F. BASES FOR THE REVISED REQUIREMENT The technical bases for this amendment request were approved by the NRC in the Safety Evaluation Report for Braidwood and Byron Amendments 69 and 77, respectively. This amendment request proposes to renew the 3.0 volt bobbin coil probe, SG TSP IPC limit for ODSCC indications at the Locked-Tube Model TSP intersections, and the 1.0 volt bobbin coil probe, SG TSP IPC limit for ODSCC indications at the Free-Span Model TSP intersections.
While the IPC criteria of GL 95-05 is based on a structural limit derived from free-span tube burst conditions, the 3.0 volt IPC criteria is based on the constraining effects of the TSP to reduce burst probability to negligible levels.
Selected hot-leg tubes have been hydraulically expanded to serve as anchors to limit TSP motion during a postulated steam line break event. With TSP motion limited, the length of a crack confined within the TSP that would be subjected to free-span conditions due to TSP movement would be greatly reduced, thus reducing tube burst probabilities and leakage during accident conditions.
Degradation of SG internals has been identified in other plants.
Due to this, Comed developed a Byron /Braidwood SG internals inspection plan. This plan was implemented in refueling outage AlR05 for Braidwood, midcycle outage BlP02 and refueling outage BlR07 for Byron. No degradation of the integrity of the SG internal components necessary to support implementation of the 3.0 volt IPC was identified at either station.
Approach The approach applied to develop the 3.0 volt IPC methodology for the Locked-Tube Model Intersections was based on developing the i minimum requirements, establishing design objectives more limiting than the minimum requirements, and evaluating the ;
overall performance based on supporting analyses for the tube i expansion process. The general approach can be described as follows:
A-7
Defined acceptable TSP displacements to reduce the tube burst probability to negligible levels based on the conservative assumption that all Locked-Tube Model Intersections have through wall indications equal to the limited TSP displacement resulting from tube expansion.
3 Identified the tubes and locations that required expansion to limit TSP movement during a Main Steam Line Break (MSLB) event such that the displacements resulted in negligible tube burst probabilities.
Identified additional tubes and locations for expansion to provide sufficient redundancy in the unlikely event that one ,
or two expansions failed due to degradation. j Defined tube expansion functional requirements and process qualifications to ensure that design requirements were met.
i Verified, by inspection, the integrity of the SG internal '
components necessary to support implementation of the 3.0 volt Locked-Tube Model Intersection IPC. 1 Calculated a tube structural voltage limit based on limited l TSP displacement due to tube expansion. l Demonstrated that MSLB leakage, with limited TSP i displacement due to tube expansion, can be adequately I determined by the proposed leakage predictions.
Maintained the current primary-to-secondary leakage limits i and operational measures to monitor, trend, and respond to j SG tube leakage as specified in the original IPC submittal. '
Maintained existing eddy current inspection guidelines to increase detectability and reduce voltage variability.
Attachment B addresses the NRC's comments in the Safety Evaluation Report for Amendments 69 and 77 of the Braidwood and Byron TS, respectively, and the operational measures in place at l Braidwood and Byron relative to IPC implementation. l l
G. IMPACT OF THE PROPOSED CHANGE 1
With the implementation of this license amendment request, the l Braidwood and Byron Unit 1 SGs will continue to satisfy the requirements of Regulatory Guide (.R G) 1.121. For the Locked-Tube j Model Intersections, the use of tube expansion and stabilization i (performed during previous outages, as discussed above) limits l the tube-to-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. l A-8
Implementation of this amendment request could "save" as many as 1440 tubes at Byron and 1400 tubes at Braidwood that would have had to be plugged or repaired using the 1.0 volt IPC. This represents a dollar savings or $3 Million apiece at Braidwood and Byron assuming all these tubes were plugged. However, since plugging levels this high exceed currently analyzed maximums, sleeving these tubes could add as much as $7 Million apiece at Braidwood and Byron in outage inspection and repair costs.
Implementation of this amendment request will also minimize the RCS loop flow asymmetries and thermal power derates.
H. SCHEDULE REQUIREMENTS Comed requests that this proposed license amendment be approved to permit application of this 3.0 volt IPC during Braidwood's A1R06 refueling outage which begins March 29, 1997, and Byron's B1R09 refueling outage currently scheduled for the Spring of 1998. Approval of this license amendment request is required in order to declare the Braidwood Unit 1 and Byron Unit 1 SGs operable prior to entering Mode 4, Hot Shutdown. Based on this, Comed requests that this amendment be approved on or before March 3, 1997.
l l
l l
I A-9 l
l
ATTACHMENT B BYRON /BRAIDWOOD UNIT 1 STEAM GENERATOR INTERIM PLUGGING CRITERIA METHODOLOGY Introduction This amendment request proposes to renew the 3.0 volt bobbin coil probe Steam Generator (SG) Tube Support Plate (TSP) Interim Plugging Criteria (IPC) limit for Outside Diameter Stress Corrosion Cracking (ODSCC) indications at certain hot-leg TSP intersections (Locked-Tube Model Intersections), and renew the 1.0 volt SC 'SP IPC for ODSCC indications at cold-leg and selected hot-leg intersections (Free-Span Model Intersections) as approved by the Nuclear Regulatory Commission (NRC) in Amendments 69 and 77 for Braidwood and Byron Technical Specifications, respectively. The technical basis for this proposal was approved by the NRC in the Safety Evaluation Report (SER) for Amendments 69 and 77.
While a 1.0 volt IPC is based on a structural voltage limit (4.745 volts) derived from free-span tube burst conditions as described in Generic Letter 95-05, " Voltage-Based Repair Criteria for Westinghouse Steam Generator Tubes Affected By Outside Diameter Stress Corrosion Cracking," August 3, 1995 (GL 95-05),
the 3.0 volt IPC is based on the constraining effects of the TSP to reduce burst probability to negligible levels. Selected hot-leg tubes have been hydraulically expanded to serve as additional anchors to limit TSP motion during transient conditions. These tubes essentially become additional stayrods that restrict potential TSP displacements. With TSP motion limited, the length of a crack confined within the TSP that would be subjected to free-span conditions due to TSP movement would be greatly reduced, thus reducing tube burst probabilities during accident conditions.
The methodology used to develop the 3.0 volt IPC has been previously submitted and approved on an interim basis for Byron Unit 1 through Cycle 8 and for Braidwood Unit 1 for Cycle 6.
This proposed amendment is applicable for one cycle of operation at Braidwood Unit 1, with Byron Unit 1 implementation serving as a contingency if SG replacement is delayed beyond the end of Cycle 8.
The SER, for Braidwood and Byron Technical Specification (TS)
Amendments 69 and 77, respectively, granted interim approval of the 3.0 volt IPC for the hot-leg intersections and the 1.0 volt IPC for the cold-leg intersections. Contained within the SER B-1
were comments by the Staff which required resolution prior to extending approval beyond Cycle 6 for Braidwood Unit 1 and Cycle 8 for Byron Unit 1. The following sections paraphrase the NRC's comments contained in the SER and in the discussions held between the NRC and Commonwealth Edison (Comed) on July 11, 1996.
Comed's approach to addressing these comments, in the context of the 3.0 volt IPC renewal for one additional cycle of operation for Braidwood Unit 1 and Byron Unit 1, is also contained in the following sections. This proposed amendment is applicable until SG replacement at Braidwood Unit 1, with Byron Unit 1 implementation serving as a contingency if SG replacement is delayed beyond the end of Cycle 8.
Tube Expansion Integrity In SER Section 4.5.3 for Amendments 69 and 77 of the Braidwood and Byron TS, the Staff concluded that there is reasonable assurance of the structural integrity of the expanded SG tube joints for the proposed operating time interval for which these amendments are applicable. The Staff noted that additional information would be necessary to support the licensee's proposal not to inspect the expanded SG tubes during the forthcoming SG inspections if the license requested to continue operation of the Braidwood Unit 1 and Byron Unit 1 SGs beyond the limited operational time period approved by Amendments 69 and 77 for Braidwood and Byron, respectively.
Background
Tube expansion was used on selected tubes to limit relative tube-to-TSP motion during a postulated Main Steam Line Break (MSLB) event and resulted in negligible tube burst probabilities. The tube expansion process essentially converted the selected tubes into additional stayrods to restrict potential TSP displacements.
This was accomplished by hydraulically expanding an Inconel 690 sleeve and the SG tube into the TSP and creating a bulge larger than the TSP drilled hole above and below the TSP. This locked the tube to the TSP to limit motion in both directions. The Inconel 690 sleeve serves as a stabilizer and provides additional stiffness to the expansion. The tubes that were expanded were removed from service.
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 613 F.
Laboratory tests have indicated that reducing the temperature B-2
from an inservice tube to that of a plugged tube results in a reduction in the stress corrosion cracking initiation by a factor of sixteen for similarly stressed tubing. The estimated time to develop circumferential cracking in a tube at this lower temperature is approximately 15 years. In addition, the axial load during a MSLB is less than 500 pounds. In order to affect TSP displacement at this load, a circumferential crack must essentially sever the tube completely.
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 hydraulic or hard roll tube sheet expansions.
Discussion The integrity of the Locked-Tube expansions will be verified by an eddy current inspection of the expansion regions. The inspection technique selected will be sensitive to axial and circumferential indications and will be equivalent to that -
performed following the performance of the expansion process.
Twenty percent of the total expansions will be inspected. In i addition, the tubes containing the expansions to be inspected )
will be inspected at the top of the tube sheet. The tubes will '
be unplugged and inspected using a plus point coil. If a circumferential crack-like indication is detected at the TSP expansion, the indication will be evaluated for its effect on TSP ,
displacement. If it is determined that the indication would l result in TSP displacements greater than 0.1 inches during a MSLB l event, new expansions will be made to replace the affected l expansion or the Free-Span Model repair criteria will be applied to the TSP intersections that are analyzed to exceed 0.1 inch displacement. As a result of finding the circumferential crack-like indication, the inspection program will be enlarged to include 100% of the total TSP expansions.
If circumferential crack-like indications are detected at the top l of the tube sheet in the tubes whose expansions are to be inspected, an analysis will be done to deterrine the effect of these indications on TSP displacement. If the analysis shows that these indications would result in TSP displacements greater than 0.1 inches during a MSLB event, then c. inner a welded or mechanical sleeve will be installed in the tube to maintain TSP displacement less than 0.1 inches during a MSLB event, or the Free-Span Model repair criteria will be applied to the TSP intersections that are analyzed to exceed 0.1 inch displacement.
In addition, the inspection program will be enlarged to inspect the top-of-tube sheet roll transition region in 100% of the total number of tubes containing TSP expansions.
Axial indications at the top-of-tube sheet roll transition region l B-3 l
or at the tube-to-TSP expansion will not result in a displacement of the TSP by more than 0.1 inches. Therefore, finding axial indications in these expansion regions will not result in expanding the scope of the inspection nor will it result in the repair of the axial indication. Since Mixed Mode indications have axial and circumferential properties, their identification will require actions equivalent to that of circumferential indications.
SG Load Path Carrying Component Integrity In SER Section 4.1.4 for Amendments 69 and 77 of the Braidwood and Byron TS, the Staff noted that, for long-term implementation of a locked TSP model repair criterion, it will be necessary to develop a plan designed to address the long-term integrity of the load path carrying components.
Background
Comed developed a SG internals inspection plan to assure the integrity of those SG internal components that are subjected to loads during a MSLB and are necessary to support implementation of this amendment request. This inspection plan addressed the concerns in NRC Information Notice 96-09 and its supplement along with other foreign and domestic SG issues. Comed also had a meeting with a foreign utility that had identified degradation of their internal components prior to the development of the Comed SG internals inspection plan, and recently conducted a follow-up meeting with the foreign utility since the issuance of Information Notice 96-09.
The SG internals inspection plan was implemented during the previous Braidwood Unit 1 refueling outage (A1R05, Fall 1995) and during the previous Byron Unit 1 midcycle (B1P02, Fall 1995) and refuel outages (BIR07, Spring 1996). An extensive inspection of the load path components of the Braidwood 1B SG was conducted.
The inspections performed at Braidwood are considered to be representative of the D-4 SGs at Braidwood and Byron. Also, major components of the load paths in all of the Braidwood and Byron SGs were inspected. The inspections used visual and eddy current techniques. No load path degradation was observed in either the Braidwood or Byron inspections.
B-?
l i
1 i
! l 4 Discussion !
Since no indications of degradation of the load path components were uncovered in the previous Braidwood and Byron inspections, i and, to date, there have been no operational occurrences that would affect these load path components during the present operating cycle, it is expected that the load path integrity will not degrade for the one additional cycle of operation until SG j replacement.
l i
To ensure the integrity of the TSPs, an eddy current TSP !
inspection program will be conducted in accordance with the EPRI developed TSP program. Fifty tubes adjacent to each anti- !
rotation device in all four SGs will be inspected along with i twenty tubes along the patch plate seam in one SG. If a crack-like indication is identified, a plus point inspection will be conducted per the EPRI TSP program. If the plus point inspection verifies the existence of a crack-likc indication, the affect of i that indication on TSP displacement will be evaluated. If this l evaluation shows that TSP displacement would be greater than 0.1 !
inches during a MSLB event, the indication will either be i mechanically corrected (installation of additional expansions at ;
the affected TSP) or the Free-Span Model criteria will be applied '
to the affected area.
i Industry experience has shown that, in SGs with severe corrosion induced denting, TSPs 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 IPC. 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 0.065 inch diametral dent. Therefore, dents of a smaller size are not expected to produce stress levels that would pose a cracking :
concern. Braidwood Unit 1 and Byron Unit 1 SGs have not experienced corrosion induced denting at the TSP.
l To establish that denting does not produce a TSP cracking concern l in the future at Braidwood Unit 1 and Byron Unit 1, inspections j to evaluate service induced denting will continue and the bobbin ,
coil probe will be used as a go/no-go gauge to assess Locked-Tube :
Model Intersection dent sizes. The criteria used to ensure that dents are below the size necessary to cause excessive TSP stress levels (dents less than 0.065 inches) is the passage of a 0.610 inch diameter bobbin coil probe through the tube. If the tube does not allow passage of a 0.610 inch diameter bobbin coil probe due to a dent, then IPC will not be applied to that intersection and the Free-Span Model Intersection repair criteria will be applied to the adjacent intersections. IPC will not be applied to Locked-Tube Model or Free-span Model intersections with dents greater than 5.0 volts.
B-5
l Axial and Axial Tensile Burst Probability i In SER Section 4.5.4.2.3 for Amendments 69 and 77 of the
! Braidwood and Byron TS, the Staff concluded that: 1) all probabilistic calculations of SG tube tensile axial burst should be performed in accordance with the methodology described in GL 95-05, and 2) any future submittals on this issue should address a means of combining the axial and the axial tensile burst probabilities.
Background
As discussed in the responses to questions 38f and $4 of the NRC's Requests for Additional Information, dated July 21, 1995 and September 1, 1995, respectively, the probabilities of axial tensile burst are three orders of magnitude or more lower (3x104) than those obtained for axial free-span burst for a ten '
volt indication. Thus, for this probability to have a l significant contribution to the overall probability of burst, there would need to be a signif.icant number of indications greater than ten volts. With a 3.0 volt repair criteria, the likelihood of developing a significant number of indications greater than ten volts is small.
Discussion Based on the current voltage dittributions and growth rates, Monte Carlo projections were performed for Braidwood Unit 1 and Byron Unit 1 for the additional cycle of operation that this proposed amendment is requesting. The End of Cycle (EOC) voltage projections for Braidwood Unit 1 Cycle 7 predict that the maximum voltage will be less than 10.5 volts. The number of indications predicted greater than ten volts at the end of Cycle 7 is 0.3.
The EOC voltage projections for Byron Unit 1 Cycle 9 predict that the maximum voltage to be seen will be less than 13.5 volts. The ,
number of indications predicted greater than ten volts at the end l of Cycle 9 is 4.59.
Using a tensile rupture probability for a ten volt indication of 3x104, the probability of tensile rupture from the predicted 0.3 indications at Braidwood is 1-(1-3x104)'3 = 9.0x10". The probability of tensile rupture from the predicted 4.59 indications at Byron is 1-(1-3x104)'d' = 1.38x104 Both of these probabilities result in a negligible contribution to the total burst probability when compared to the 1x10-2 GL 95-05 requirement. Based on the tensile rupture probability of a ten volt indication being 3x104, it would take approximately 325 ten volt indications before a probability of 1x10-3 would be obtained. Thus, it is justified to neglect tensile rupture in the IPC evaluations, since few indications greater than ten volts are predicted for the next operating cycle at Braidwood and Byron. ;
B-6 l
l
Comed will calculate the probability of axial tensile burst in accordance with the guidance of GL 95-05. This probability will be combined with the conditional probability of burst if any indication with a voltage greater than or equal to fifteen volts is identified, or if a large number of indications between ten and fifteen volts are identified. This information will be included in the required 90 day inspection report. In addition to this calculation, Comed will perform axial tensile burst tests on any tube that is removed from the SG to meet the requirements of GL 95-05. Tubes are scheduled to be removed from the Braidwood Unit 1 and Byron Unit 1 SGs per the requirements of GL 95-05 during their next refuel outage.
1 4
IRB Leakage Estinate In SER Section 4.5.5.2 for Amendments 69 and 77 of the Braidwood and Byron TS, the Staff concluded that the 6.0 gpm leak rate for an Indication Restricted from Burst (IRB) was acceptable for one cycle of operation. However, the Staff was still evaluating the l acceptability of the 6.0 gpm value for long-term implementation.
Background
Although the probability of burst is greatly reduced at the Locked-Tube Model Intersections due to the constraining effects of the TSP, the probability of higher MSLB leak rate values has been evaluated. A finite probability exists that a crack may
- open to the limits of the tube-to-TSP gap and cause increased l leakage. This probability is equivalent to the probability of free-span burst.
In order to determine a bounding leak rate value for IRBs, Comed conducted an EPRI sponsored test program. The test program used actual cracked tube specimens which were artificially burst and leak tested while surrounded by a simulated TSP. An array of specimens were tested consisting of varying through wall crack lengths.
The largest indication detected at Braidwood or Byron (approximately 10 volts) had a maximum through wall length of 0.27 inches. This indication was centered within the 0.75 inch TSP. No field indications have been identified to date that are near the edge of the TSP. The IRB test program conducted by Comed included tubes with through wall cracks as long as 0.809 inches and tubes with multiple through wall cracks. The IRB test program was conducted with all of the crack tips at the edge of the TSP and with the crack tips exposed outside the TSP by 0.1 inches for 3/4 inch tubes. The tests determined thet the burst pressure and leakage, of the tubes with multiple cracks, were dominated by the largest crack.
Discussion B-7
The applicable time period for this amendment renewal request is one additional cycle of operation for Braidwood and Byron. As stated earlier, voltage values have been projected for the duration of this additional cycle and are not expected to exceed 10.5 volts for Braidwood and 13.5 volts for Byron. As demonstrated in the previous tube pulls, indications in this voltage range are expected to be significantly smaller than those tested in the IRB program. Specimens containing bounding through '
wall crack lengths were tested and provided a conservative leakage value of 6.0 gpm. Specimens with multiple through wall cracks were also tested and are bounded by the 6.0 gpm leakage value. This value will continue to be applied to all IRBs which '
are predicted to occur by Monte Carlo simulation.
Dented Intersections at Tubes Adjacent to Expanded Tubes In SER Section 4.5.6 for Amendments 69 and 77 of the Braidwood and Byron TS, the Staff noted that the criteria for assessing the 4 significance of dented intersections at SG tubes adjacent to expanded tubes would need to be addressed prior to approving the 3.0 volt repair criteria on a long-term basis.
l
Background
During the initial performance of expanding the selected tubes at the TSP, one of the requirements was that the tube intersections selected for tube expansion and the adjacent intersections must not contain dents greater than 5.0 volts and must pass a 0.610 inch diameter bobbin coil probe. If corrosion induced dents form during the present cycles of operation, the maximum requirement for TSP displacement (0.1 inches) during an accident could be i jeopardized if it is further postulated that the denting leads to ;
significant cracking of the TSP resulting in a reduction in plate stiffness.
l 1
l l
B-8
1 I
Discussion If corrosion induced denting, either greater than 5.0 volts or such that the affected tube is unable to pass a 0.610 inch diameter bobbin coil probe, is detected at an intersection adjacent to an expanded intersection, the dented intersection I will be inspected by an EPRI technique to determine if the TSP is cracked. If a crack-like indication is identified in a TSP, a plus point inspection will be conducted per the EPRI TSP program to disposition the crack-like indication. If the plus point inspection verifies the existence of a crack-like indication in the TSP, the effect of that indication on TSP displacement will be evaluated. If this evaluation shows that TSP displacement would be greater than 0.1 inches during a MSLB event, the affected area will either be mechanically corrected (installation of additional expansions at the affected TSP) or the Free-Span Model criteria will be applied to those intersections that are analyzed to exceed 0.1 inch displacement.
Leak Rate Calculation Method l In SER Section 4.5.5.2 for Amendments 69 and 77 of the Braidwood and Byron TS, the Staff was evaluating the need for a long-term approach for combining the SG tube leakage estimates from the Free-Span Model and the Locked-Tube Model, including a contribution from ODSCC indications which could burst when using the Free-Span model, prior to ordering the total leakage values.
Background
The EOC voltage distribution is predicted using a beginning-of- l cycle (BOC) voltage distribution, a Probability of Detection (POD) of 0.6, and by applying a growth rate, as defined in GL 95-
- 05. The Free-Span Model EOC leak rate is calculated per GL 95-05 using the 95% confidence value for the leak rate. The Locked-Tube Model EOC leak rate is calculated in a similar manner except that a 6.0 gpm leak rate is assigned to indications predicted to burst at the MSLB differential pressure. These two leak rate values are then added together for the total leak rate on a per SG basis.
The total primary-to-secondary tube leakage at MSLB conditions due to IPC application and any other approved alternate repair criteria is not to exceed the site allowable leak rate. The site allowable leakage calculated using a Reactor Coolant System Dose Equivalent Iodine-131 (I-131) level of 1.0 microcurie per gram (pci/gm) is 9.4 gpm for Braidwood and 12.8 gpm for Byron. Site allowable leak rates calculated using 0.35 pCi/gm Dose Equivalent I-131 (the current TS limit) are 26.8 gpm for Braidwood and 36.5 gpm for Byron. This leakage limit includes accident leakage, the allowed 0.1 gpm primary-to-secondary leakage (TS 3.4.6.2.c) for B-9
each of the 3 unfaulted SGs, and leakage from other approved 2 repair criteria. The 0.35 pCi/gm Dose Equivalent I-131 value !
! will remain in effect for the cycles for which this 3.0 volt IPC !
is being requested. i i ?
l Discussion [
Comed has evaluated the Staff's comment concerning application of I
, a contribution from ODSCC indications which could burst when :
using the Free-Span Model. The indications, to which the Free- l Span Model is applied, have historically been, and are expected i to remain, in the lower voltage ranges. This is because the 1.0 ;
j volt. repair criteria is applied to these indications causing them i
- to be removed from service prior to reaching high voltages, !
i (greater than ten volts). If it is assumed that a 10 volt :
I indication, which has a Probability of Burst (POB) of 1x10 were l I to develop a free-span leak rate of 100 gpm, the overall !
4 contribution to the total leak rate would be on the order of 0.10 gpm. This is due to the low burst probability and the 95% !
l '
4 ordered confidence level at which the leak rate is determined.
l Based on this assessment and the fact that the GL 95-05 POB sets j a limit of 1x104 below which free-span POB can be considered to ,
4 be negligible, Comed will continue to use its current leak rate [
j methodology as previously approved in the Braidwood and Byron !
, SER. l Comed performed an evaluation of the issue for a long-term approach to combine the SG tube leakage estimates from the Free- i Span i-iodel and the Locked-Tube Model. The result of this ,
evaluation showed that due to the low burst probability and the 95% ordered confidence level, combining the Free-Span and IRB L leakage models before taking the 95% confidence level will result ;
in a negligible impact (less than 0.1 gpm) on the total leakage 3 value. In fact, since the Free-Span Model voltages are typically I lower than the Locked-Tube Model voltages due to the 1.0 volt repair criteria compared to the 3.0 volt criteria, combining the e two distributions could result in lowering the overall predicted ,
leakage. Since thic submittal is for one additional cycle of .
operation with the 3.0 volt IPC, and the impact of combining the !
leakage models before taking the 95% confidence level is j negligible, the 95% confidence level will continue to be applied i to the Free-Span and the IRB models separately, then summed on a per SG basis. This methodology was previously approved in the .
Braidwood and Byron SER. ;
I B-10
O
- Probe Wear Criteria In SER Section 4.5.3 for Amendments 69 and 77 of the Braidwood and Byron TS, the Staff concluded that for future outages, the licensee should either: (a) provide an alternate probe wear methodology which provides detection and sizing capability equivalent to the probe wear guidance in GL 95-05; or (b) follow the GL 95-05 guidance with respect to probe wear.
Discussion l Braidwood and Byron will use the alternate probe wear criteria which was submitted to the NRC on March 19, 1996. This criteria was used during the Byron Unit 1 March 1996 IPC inspection. This !
approach is based on the Nuclear Energy Institute (NEI) alternate 1 probe wear criteria, and incorporates the NRC's provisions for I application.
Reporting Requirements In SER Section 4.5.6 for Amendments 69 and 77 of the Braidwood and Byron TS, the Staff noted that the reporting requirements !
need to be addressed prior to approving this repair criteria on a ,
long-term basis.
l
Background
Several reporting conditions were required by the SER, in the TS, and in the previous submittal. All of these requirements were met during the previous inspections at Braidwood and Byron.
These reporting requirements were as follows:
NRC notification prior to returning the SG to service (Mode
- 4) should any of the following arise:
Projected EOC or as-found MSLB leakage exceeds the site allowable limit. l Projected EOC or as-found probability of burst exceeds l x 10-2 , j If circumferential crack-like indications are found at TSP intersections.
If indications are identified that extend beyond the confines of the TSP.
If Primary Water Stress Corrosion Cracking (PWSCC) indications are found at TSPs.
B-ll
I e
- A safety assessment is to be provided to the NRC prior to i returning the SG to service should the MSLB leakage or probability of burst values exceed their respective limits, i or if a SG internals inspection identifies indications detrimental to the integrity of the load path components i necessary to support the 3.0 volt IPC. '
The complete results of the inspection, structural !
assessments, the Upper Voltage Repair limit used, and preliminary tube pull results are to be submitted to the NRC within 90 days of plant restart (Mode 2). !
i Prompt notification will be made to the NRC should corrosion induced denting greater than 5 volts be found. I l
A safety assessment is to be provided to the NRC if a l corrosion induced dent greater than 5.0 volts is found :
adjacent to an expanded tube. '
The NRC will be informed if a 0.610 inch diameter bobbin !
coil probe fails to pass through an intersection adjacent to !
an expanded tube.
The NRC will be informed if circumferential cracks are identified 2.n the expanded tubes at the top of the tube sheet or at the expanded TSP intersection. ;
i Discussion !
t Comed will retain each of these reporting requirements and the following NRC reporting requirements will be added to the TS. l These reports will be made prior to returning the SGs to serv. ice. ,
1 If cracking is observed in the tube support plates.
f If any tube which previously passed a 0.610 inch diameter i bobbin coil eddy current probe currently fails to pass a O.610 inch diameter bobbin coil eddy current probe."
Following a SG internals inspection, if indications detrimental to the integrity of the load path necessary to ;
support the Locked-Tube Model are found, notify the NRC and !
provide an assessment of the safety significance of the occurrence.
In addition to these reporting requirements, other requirements are necessary to support the Probe Wear issue. The following l information will be added to the 90 Day Report per the requirements of the probe wear criteria:
The root cause will be determined if a significant difference exists between the actual and projected end of B-12
cycle voltage distributions. The effects of probe wear will be explicitly considered in this evaluation. If probe wear is determined to be one of the factors for this difference, actions will be taken to prevent recurrence.
If a "large" indication is detected which was previously missed by a failed probe, an assessment of the significance will be performed. This assessment will specifically address the need to reinspect tubes which were inspected with the worn probe (i.e., implement the GL 95-05 probe wear check criteria).
An evaluation will address if "large" indications and/or a nonproportionate number of new indications are detected in l tubes which were inspected in a previous outage with a probe that failed the probe wear check.
An evaluation of the data acquired during the outage to ensure the adequacy of the 75% criteria.
RELAP5M3 Issues Discussion It is Comed's understanding that the Staff presented the presently approved 3.0 volt IPC amendment to ACRS. Following this presentation, ACRS commented on the supporting calculations as they relate to multidimensional behavior. This issue does not appear to be closed. Multidimensional effects were discussed l during the review process in some detail, and the following response is provided to address the issue.
All of the simulations have been done under the assumption that l
flow can be adequately described and quantified by a one-dimensional model. Some three dimensional effects can be postulated in the tube bundle. These effects have limited i importance in determining TSP loading for the following reasons: l l
- 1) The peak load occurs in the very early part of the transient (within a few seconds), and is primarily driven by inertial flow considerations.
- 2) The tube bundle is submerged within liquid water for a water l level well above the tube bundle (i.e., 487" elevation, right at the bottom of the swirlvane separators). The peak i load happens within a few seconds, while the flow regime is essentially limited within bubbly flow; flow regime transition is not experienced this early in the transient.
l 3) The fluid conditions at the time of the peak TSP load are relatively uniform in the tube bundle, because of the uniform tube layout, and uniform temperature conditions at the beginning of the MSLB event from a hot standby, zero B-13 i
power condition (a steam line break from hot standby, zero power is the most conservative case). No temperature difference exists within the tube bundle; both primary and secondary fluids are at the same initial temperature of 557 F.
- 4) For the Model D4 SGs, there are differences in some of the TSPs and baffles between the hot-leg and the cold-leg.
RELAP5M3 models these differences using separate nodes for the hot-leg and cold-leg. Thus, the model addresses the possible difference for the hot-leg and cold-leg of the TSPs.
- 5) Because of the uniform geometry and uniform temperature discussed above, the two-phase flow resulting from water flashing due to depressurization is expected to be essentially uniform radially. Axial variations exist in fluid flow conditions, such as velocity, pressure and void fraction. However, the flow regime is essentially bubbly flow within the very early part of the transient, during the peak TSP load, as mentioned above.
The following information summarizes the requirement.= of implementing a 3.0 volt IPC. !
Inspection Requirements ,
l Technical Speci fication Surveillance Requirement (TSSR) 4.4.5.2 requires bobbin coil inspections to be performed on 100% of the hot-leg and cold-leg intersections down to the lowest cold-leg TSP elevation having ODSCC. A minimum of a 20% random sample is !
also to be inspected over the full length of the tube. j Rotating Pancake Coil (RPC) inspections are to be performed on the following indications:
All Locked-Tube Model TSP indications greater than 3.0 volts. 1 All Free syan Model TSP indications greater than 1.0 volt. 1 All TSP intersections that contain dents greater than 5.0 volts and a 20% sample of the dents between 2.5 volts and 5.0 volts. If PWSCC or circumferential cracking is !
detected, 100% of the dents between 2.5 volts and 5.0 volts I will be inspected.
All intersections with large mixed residuals that could cause a 1.0 volt signal to be missed or misread.
All intersections with interfering signals from copper I deposits. Neither Braidwood nor Byron has significant B-14 x
copper deposits in the SGs. Guidance on conducting RPC inspections for interfering signals due to copper has been included in each station's inspection guidelines.
20% of the indications at the Locked-Tube Model TSP intersections between 1.0 volt and 3.0 volts concentrating on the larger indications.
All indications of cracks of the TSP in accordance with the EPRI TSP program.
Fifty tubes adjacent to each anti-rotation device in all four SGs will be inspected along with twenty tubes along the patch plate seam in one SG.
Any flaw-like indication confirmed by RPC at intersections with dent signals greater than 2.5 volts, large mixed residuals, or copper deposits will result in the intersection being repaired by sleeving or plugging of the tube. In addition, IPC will not be applied to any crack-like indication in a wedge area or the Flow Distribution Baffle (FDB).
Braidwood and Byron will use the alternate probe wear criteria approved for use by the NRC during the Byron Unit 1 March 1996 IPC inspection. This approach is based on the NEI alternate probe wear criteria, and incorporates the NRC's provisions.
Generic Letter 95-05 Review Comed will implement all the requirements contained in GL 95-05.
Below is a list which summarizes some of the key requirements contained in this Generic Letter and modifications due to application of the 3.0 volt IPC.
B-15
l ..
Exclusion of Intersections IPC 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 1.0 volt indication to be missed or misread.
Intersections with interfering copper signals.
Flow Distribution Baffles.
l PWSCC or Circumferential crack-like indications at TSP Intersections not inspected by a 0.610 inch diameter bobbin coil probe.
Repair Criteria The following indications / tubes will be repaired:
All Locked-Tube Model Intersections with ODSCC indications ,
greater than 3.0 volts, regardless of RPC confirmation. .
All Free-Span Model Intersections with ODSCC indications l greater than the upper _ voltage repair limit. i All Free-Span Model Intersections with ODSCC indications between 1.0 volt and the upper voltage repair limit that are confirmed by RPC.
Tubes with known leakage.
RPC confirmed flaws indicative of ODSCC at locations that are excluded from IPC, as described above.
Indications that extend beyond the edges of the TSP.
l 1
l B-16 l 1
I l
l The Free-Span Model Intersection repair criteria will be applied i to the following Locked-Tube Model Intersections, in lieu of the 3.0 volt IPC:
l Intersections adjacent to intersections that contain corrosion induced dents greater than 0.065 inches.
IPC Voltage Limit Determination A single voltage limit of 3.0 volts for Locked-Tube Model Intersections.
A lower voltage limit of 1.0 volt for Free-Span Model Intersections.
For Free-Span Model Intersections, an upper voltage limit is determined by reducing the structural voltage limit by voltage growth and Non-Destructive Examination (NDE) uncertainty.
Determined prior to each outage.
l
- Use the larger of the site specific growth rate or 30%/EFPY.
NDE uncertainty of 20% of the BOC voltage.
l l
Voltage Growth Distribution Growth rates are determined by indications identified at two
- successive inspections, except that indications that grow
! from No Detectable Degradation (NDD) to a relatively large voltage (e.g., 2.0 volts) will be included.
The most limiting growth rates will be used from the last two inspection cycles.
l Negative growth rates will be included as zero growth.
Re-evaluation of previous cycle data will be adjusted for changes made in data acquisition guidelines.
Effects of chemical cleaning will be evaluated, if performed.
B-17
i e .
Tube Pulls In 1994, four tubes were removed from Braidwood Unit 1. I These four tubes included nine TSP intersections along with the four FDB intersections. In 1994, three tubes were removed from Byron Unit 1. These three tubes included nine ;
TSP intersections along with the.three FDB intersections. A l minimum of one additional tube (minimum of two TSP i intersections) during the upcoming Braidwood and Byron :
refuel outages will be pulled for IPC evaluation. l Leak / burst tests will be performed under MSLB conditions to confirm that the failure mode is axial and to add to the industry correlation database.
Axial tensile pull force testing of the flawed TSP intersections will be performed as part of the testing program.
Axial tensile burst tests will be performed on any tube removed for IPC.
1 Destructive testing will also be performed,to confirm 1 degradation morphology.
Tube selection will be consistent with the GL 95-05 requirements. ,
Implemented 150 gallon per day (gpd) leakage limit (TS 3.4.6.2.c).
Implemented a primary-to-secondary leakage monitoring program.
Effectiveness of leakage monitoring procedures and operator actions have been assessed and appropriate procedure changes have been made.
Leakage instrumentation alarm setpoints have been reviewed and revised, as appropriate.
B-18 1
^
l 0
l l
l l MSLB Leakage and Burst Probability Assessments BOC voltage distribution will be determined by scaling upwards the as-found voltage distribution by 1/ (POD =0.6) and then subtracting the indications repaired.
EOC voltage distributions will be determined by Monte Carlo simulations that account for voltage growth, eddy current variability, and parameter uncertainty.
MSLB leakage will be based on the EPRI Probability of Leakage model and the 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.
For Locked-Tube Model Intersections, the MSLB leakage will include a bounding IRB leakage contribution (6.0 gpm).
Probability of Burst limit under postulated MSLB conditions l will not exceed lx10-2, Reporting Bequirements NRC notification will be made' prior to returning the SG to I
service (Mode 4) should any of the following arire:
Projected EOC or as-found MSLB leakage exceeds the site allowable limit. l I
Projected EOC or as-found probability of burst exceeds lx10-2 If circumferential crack-like indications are found at TSP intersections.
If indications are identified that extend beyond the confines of the TSP. l If PWSCC indications are found at TSPs.
A safety assessment is to be provided to the NRC prior to returning the SG to service should the MSLB leakage or !
, probability of burst values exceed their respective limits, i l or if a SG internals inspection identifies indications l detrimental to the integrity of the load path necessary to support the 3.0 volt IPC.
i B-19
The complete results of the inspection, structural assessments, the Upper Voltage Repair limit used, and preliminary tube pull results are to be submitted to.the NRC l within 90 days of plant restart (Mode 2). l Prompt notification will be made to the NRC should corrosion i induced denting greater than 5 volts be found.
A safety assessment is to be provided to the NRC if a corrosion induced dent greater than 5.0 volts is found adjacent to an expanded tube.
The NRC will be informed if a 0.610 inch diameter bobbin coil probe fails to pass through an intersection adjacent to an expanded tube. 1 The NRC will be informed if circumferential cracks are identified in the expanded tubes at the top of the tube sheet or at the expanded TSP intersection. .
l The NRC will be informed if cracking of the TSP is observed.
The NRC will be informed if any tube which previously passed a 0.610 inch diameter bobbin coil eddy current probe currently fails to pass a 0.610 inch diameter' bobbin coil eddy current probe.
1 Following a SG internals inspection, if indications detrimental to the integrity of the load path components j necessary to support the Locked-Tube Model are found, the i NRC will be notified and an assessment of the safety l significance of the occurrence will be provided. ,
The following reporting requirements will be added to the 90 Day Report per the requirements of the probe wear criteria:
The root cause will be determined if a significant difference exists between the actual and projected end of cycle voltage distributions. The effects of probe wear will be explicitly considered in this evaluation. If probe wear is determined to be one of the factors for this difference, actions will be taken to prevent recurrence.
If a large indication is detected which was previously missed by a failed probe, an assessment of the significance will be performed. This assessment will specifically address the need to reinspect tubes which were in=pected with the worn probe (i.e., implement the GL 95-05 probe wear check criteria).
An evaluation will address if "large" indications and/or a B-20 l
l
nonproportionate number of new indications are detected in tubes which were inspected in a previous outage with a probe that failed the probe wear check.
An evaluation of the data acquired during the outage to ensure the adequacy of the 75% criteria.
1 Inspection Requirements 100% bobbin coil probe of the hot-leg tubes down to the lowest cold-leg indication.
20% (Minimum) full length bobbin coil probe.
20% (Minimum) of the tube expansions.
RPC Inspection Requirements All Locked-Tube Model TSP indications greater than 3.0 volts.
All Free-Span Model TSP indications greater than 1.0 volt.
All TSP intersections that contain dents greater than 5.0 volts and a 20% sample of the dents between 2.5 volts and 5.0 volts. If 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 1.0 volt signal to be missed or misread.
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 interfering signals due to copper has been included in each station's inspection guidelines.
20% of the indications at the Locked-Tube Model TSP intersections between 1.0 volt and 3.0 volts concentrating on the larger indications.
Fifty tubes adjacent to each anti-rotation device in all four SGs will be inspected along with twenty tubes along the patch plate seam in one SG Data Acquisition and Analysis The bobbin coil will be calibrated against a reference standard in the laboratory by direct testing or by use of a transfer standard.
B-21 l l
l
The voltage response of new bobbin coil probes for the 40% l to 100% American Society of Mechanical Engineers (ASME) through wall holes will not differ from the nominal voltage by more than i 10%.
Braidwood and Byron will use the alternate probe wear criteria approved for use by the NRC during the Byron Unit 1 March 1996 IPC inspection. This approach is based on the NEI alternate probe wear criteria, and incorporates the NRC's provisions.
Data analysts will be trained in the use of the Comed Braidwood and Byron 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 utilixed in the tube integrity evaluations.
Quantitative noise criteria (resulting from electrical noise, tube noise, calibration 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.
I A 0.610 inch diameter bobbin coil probe will be utilized for ,
the inspection. If a 0.610 inch diameter bobbin coil probe 1 will not pass through a portion of a tube, IPC will not be I applied to the portion of the tube that is inspected by a i smaller probe. !
l A 0.610 inch diameter bobbin coil probe will be used as a go/no-go gauge to determine acceptability of dented intersections and adjacent intersections for 3.0 volt IPC.
The presence of the hot-leg TSPs will be verified by eddy current.
Data analysts will be trained on the potential for PWSCC cracking to occur at TSP intersections. The data analysts will be sensitized to identify indications attributed to PWSCC.
The bobbin coil and RPC examinations will be performed using enhanced inspection guidelines that are intended to increase detectability and reduce voltage variability in support of IPC implementation. The IPC guidelines that will be used in the Braidwood Unit 1 and Byron Unit 1 inspections are the same guidelines used to support the Braidwood Unit 1 Fall 1995 and the B-22 l
1
Byron Unit 1 Spring 1996 IPC inspections.
Operational Measures Comed's previous request for a 3.0 volt IPC contained a description of enhanced operational and procedural measures that Braidwood and Byron Stations have 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 Braidwood and Byron and are summarized below.
e Actions have been taken to mitigate the corrosive environment in the TSP crevices and to increase the likelihood that future growth rates and crack morphologies will be within expected bounds.
The alert and alarm setpoints on the main steam line and steam jet air ejector radiation monitors have been lowered to ensure early positive indication of primary-to-secondary '
leakage. !
Chemistry procedures have been revised to facilitate " quick '
counts" of chemistry samples to give rapid confirmation of ,
SG leakage. l SG chemistry sampling frequencies have been increased to a 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, the Braidwood Operating Abnormal Procedure (BwOA SEC-8) and the Byron-Operating Abnormal Procedure (BOA SEC-8), have been revised to require that radiation monitors be checked 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.
Braidwood and Byron Emergency Procedures require continuous monitoring for SG tube leakage. BwOA 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 j require that hourly trend readings of steam jet air ejector radiation monitor activity levels be reviewed on a daily basis.
B-23 l
i 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. Administrative limits exist should a large increase in primary-to-secondary leakage occur. These limits meet or exceed the requirements of the EPRI PWR Primary-to-Secondary Leakage Guidelines, May 1995.
B-24
.