ML20071L487
| ML20071L487 | |
| Person / Time | |
|---|---|
| Site: | Byron  |
| Issue date: | 08/01/1994 |
| From: | COMMONWEALTH EDISON CO. |
| To: | |
| Shared Package | |
| ML20071L473 | List: |
| References | |
| NUDOCS 9408030124 | |
| Download: ML20071L487 (24) | |
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i 2/.L.S . 5 STEAM GENERATORS LIMITING CONDITION FOR OPERATION t 3.4.5 Each steam generator shall be OPERABLE. 1 APPLICABILITY: M0'ES D 1, 2, 3 and 4. ACTIDN: , With one or more steam generators inoperable, restore the inoperable steam I generator (s) to OPERABLE status prior to increasing T, above 200*F. ; SURVEILLANCE REQUIREMENTS
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4.4.5.0 Each steam generator shall be demonstrated OPERABLE by performance of L the following augmented inservice inspection program and the requirements of - Specification 4.0.5. 4.4.5.1 Steam Generator Samole selection and Insoection - Each steam generator I shall be determined OPERABLE during shutdown by selecting and inspecting at least the minimum number of steam generators specified in Table 4.4-1. 4 4.4.5.2 Steam Generator Tube
- 5=le Selection and Insoection - The steam ,
generator tube minimum sample size, inspection result classification, and the corresponding action required shall be as specified in Table 4.4-2. The , inservice inspection of steam generator tubes shall be performed at the fre- ; quencies specified in Specification 4.4.5.3 and the inspected tubes shall be verified acceptable per the acceptance criteria of Specification 4.4.5.4. When applying the expectations of 4.4.5.2.a through 4.4.5.2.c, previous defects or ; imperfections in the area repaired by the sleeve are not considered an area requiring reinspection. The tubes selected for each inservice inspection shall 1
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include at least 3% of the total number of tubes in all steam generators; the ; tubes selected for these inspections shall be selected on a random basis except: ' a. Where experience in similar plants with similar water chemistry indicates critical areas to be inspected, then at least 50% of the
- tubes inspected shall be from these critical, areas; i
- b. The first sample of tubes selected for each inservice inspection i (subsequent to the preservice inspection) of each steam generator shall include: i i
*When referring to a steam generator tube, the sleeve shall be considered a part of the tube if the tube has been repaired per Specification 4.4.5.4.a.10. i r
t BYRON - UNITS 3 & 2 3/4 4-13
, AMENDMENT NO. 58 3
;ggai8aseZe83$34 P
g . REACTOP Cp0LANT SYSTEM - _. SURVEILLANCE REQUIREMENTS (Continued)
- 1) All tubes that previously had detectable tube wall penetrations greater than 7:0% that have not been plugged or sleeved in the affected area, and all tubes that previously had detectable sleeve wall penetrations that have not been plugged,
- 2) Tubes in those areas where experience has indicated potential -
.probl ems ,
3}, ' At least 3% of the total number of sleeved tubes in all four steam generators or all of the sleeved tubes in the generator chosen for , the inspection program, whichever is less. These inspections will include both the tube and the sleeve, and
- 4) A tube inspection (pursuant to Specification 4.4.5.4a.8) shall be performed on each selected tube. If any selected tube does not permit the passage of the eddy current probe for a tube inspection, this shall be recorded and an adjacent tube shall be selected and
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subjected to a tube inspection. 7 /c. The tubes selected as the second and third samples (if required by Table 4.4-2) during each inservice inspection may be subjected to a partial tube v V inspection provided:
- 1) The tubes selected for these samples include the tubes from those areas of the tube sheet array where tubes with imperfections were
, previously found, and a
%.- _ 2) The inspections include those portions of the tubes where d ia A t y imperfections were previously found. , s 's x r __.- / The results of each sample inspection shall be classified into one of the
! - following three categories:
Cateoorv Insnection Results C-1 Less than 5% of the total tubes inspected are degraded tubes and none of the inspected tubes ' are defective. r C-2 One or more tubes, but riot more than 1% of the ' total tubes inspected are defective, or between 5% and 10% of the total tubes inspected are i degraded tubes. - C-3 More than 10% of the total tubes inspected are degraded tubes or more than 1% of the inspected tubes are defective. Note: In all inspections, previously degraded tubes or sleeves . must exhibit significant (greater than 10%'of wall
' thickness) further wall penetrations to be included
"" in the above percentage calculations. ,
BYRON - UNITS 1 & 2 3/4 4-14 AMENDMENT NO. 58
INSERT A
- 5. For Unit 1, tubes in which the tube support plate IPC plugging limit has been applied.
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l INSERT B
- d. For Unit 1, implementation of the tube support plate interim plugging criteria ,
limit requires a 100% bobbin coil probe inspection for all hot leg tube support plate intersections and all cold leg intersections down to the lowest cold lug tube support plate with outer diameter stress corrosion cracking (ODSCC) indications. An inspection using a rotating pancake coil (RPC) probe is required in order to show OPERABILITY of tubes with flaw-like bobbin coil signal amplitudes greater than 1.0 volt but less than or equal to 2.7 volts. For tubes that will be administratively plugged or repaired, no RPC inspection is required. The RPC results are to be evaluated to establish that the principal indications can be characterized as ODSCC. s
REACTOR CDOLANT SYSTEM _ _ _ _ . _ . _ . ,_ __ _ SURVEILLANCE REOUIREMENTS (Continued) -. - _ -.--- .. 4.4.5.3 Insoection Frecuencies - The above required inservice inspections of steam generator tuces sna11 oe performed at the following frequencies:
- a. The first inservice inspection shall be performed after 6 Effective Full Power Months but within 24 calendar months of initial criticality.
Subsequent inservice inspections shall be performed at intervals of not less than 12 nor more than 24 calendar months after the previous inspection. If two consecutive inspections, not including the pre-service inspection, result in all inspection results falling into the C-1 category or if two consecutive inspections demonstrate that pre-viously observed degradation has not continued and no additional 1 degradation has occurred, the inspection interval may be extended to a maximum of once per 40 months;
- b. If the results of the inservice inspection of a steam generator conducted in accordance with Table 4.a-2 at 40-month intervals fall in Category C-3, the inspection frequency shall be increased to at least once per 20 months. The increase in inspection frequency shall apply until the subsequent inspections satisfy the criteria of Specification 4.4.5.3a.; the interval may then be extended to a maximum of once per 40 months; and
- c. Additional, unscheduled inservice inspections shall be performed on each steam generator in accordance with the first sample insp'ection specified in Table 4.4-2 during the shutdown subsequent to any of the following conditions:
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- 1) Reactor-to-secondary tube leaks (not including leak [s originating from tube-to-tube sheet welds) in excess of the limits of Specification 3.4.6.2c., or ,
- 2) A seismic occurrence greater than the Operating Basis Earthquake, or
- 3) A Condition IV loss-of-coolant accident requiring actuation of the Engineerec Safety Features, or
- 4) A Condition IV main steam' line or feedwater line break.
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BYRON - UNITS 1 & 2 3/4 4-15
- - . _ _ _ ~ . - - . . _ - - - . . --.
REACTDR C001 ANT SYSTEM . _, SURVEILLANCE REDUfREMENTS fContinued) i I 4.4.5.4 Accentance Criteria
- a. As used in this specification:
- 1) Imperfection means an exception to the dimensions, finish or contour of a tube or sleeve from that required by fabrication l;:
drawings or specifications. Eddy-current testing indications below 20% of the nominal tube or sleeve wall thickness, if ~ l,i detectable, may be considered as imperfections; ! i'
* ' 2)
Dearadation means a service-induced cracking,
wastage, wear or general corrosion occurring on either inside or outside of a , tube or sleeve; I;
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- 3) Deoraded Tube means a tube or sleeve containing unrepaired {'
imperfections greater than or equal to 20% of the nominal tube or sleeve wall thickness caused by degradation;
- 4) % Deoradation means the percentage of the tube or sleeve wall l-thickness affected or removed by degradation, ,
- 5) Defect means an imperfection of such severity that it exceeds !
the plugging or repair limit. A tube or sleeve containing an ! unrepaired defect is defective;
- 6) Pluacino or Renair Limit means the imperfection depth at or !
beyond which the tube shall be removed from service by plugging T or repaired by sleeving in the affected area. The plugging or ) repair limit imperfection depth is equal to 40% of the nominal ; hcT ,/ y wall thicknessi. ~ C ) 7) Unserviceable describes the condition of a tube if it leaks or Vg contains a defect large enough to affect its structural integ-rity in the event of an Operating Basis Earthquake, a loss-of-i coolant accident, or a steam line or feedwater line break as ; specified in 4.4.5.3c., above; !
- 8) Tube Insnection means an inspection of the steam generator tube i from the point of entry (hot leg side) com ;
U-bend to the top support of the cold leg.pletely around For a tube thatthe aas ; been repaired by sleeving, the tube inspection shall include the ' sleeved portion of the tube;..and- ,
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BYRON - UNITS 1 & 2 3/4 4-16 AMENDMEhT NO. 58
INSERT C For Unit 1, this definition does not apply to the region of the tube subject to the tube support plate interim plugging criteria limit, i.e., the tube support plate intersections. Specification 4.4.5.4.a.11 describes the repair limit for use within the tube suppcrt plate intersection;
INSERT D For Unit 1, for a tube in which the tube support plate interim plugging criteria limit has been applied, the inspection will include all hot leg tube support plate intersections and all cold leg intersections down to the lowest j cold leg tube support plate with outer diameter stress corrosion cracking ' (ODSCC) indications. s
REACTOR C00 ANT SYSTEM l ,
.. SURVEILLANCE REDUIREMENTS (Continued)
- 9) Preservice Insoettien means an inspection of the full length of each tube in each steam generator performed by addy current techniques prior to service to establish a baseline condition of t'he tubing. This inspection shall be performed prior to 1 initial POWER OPERATION using the equipment and techniques !
expected to be used during subsequent inservice inspections'.' ;
- 10) Tube Renair refers to a process that reestablishes tube
** serviceability. Acceptable tube repairs will be performed by the following processes:
a) Laser welded sleeving as described by Westinghouse report
. WCAP-13698, Rev. 1, or , b) Kinetic welded sleeving as described by Babcock & Wilcox I Topical Report BAW-2045PA, Rev.1. '
Tube repair includes the removal of plugs that were previously D- installed as a corrective or preventative measure. A tube , ,e inspection per 4.4.5.4.a.8 is required prior to returning LEKT s j v previously plugged tubes to service. ' E d. Tae' steam generator shall be determined OPERABLE after completing ' f the corresponding actions (plug or repair in the affected area all yr tubes exceeding the plugging or repair limit) required by ! Table 4.4-2. ! 4.4.5.5 Report s '
- a. Within 35 days following the completion of each inservice inspection of steam generator tubes, the number of tubes plugged or repaired in l each steam generator shall be reported to the Commission in a Special Report pursuant to Specification 6.9.2;
- b. The complete results of the steam generator tube inservice inspection -
shall be submitted to the Commission in a Special Report pursuant to Specification 6.9.2 within 12 months following the completion of the inspection. This Special Report shall include: ;
- 3) Number and extent of tubes inspected, *
- 2) Location and percent of wall-thickness penetration for each indication of an imperfection, and '
t
- 3) Identification of tubes plugged or repaired.
- c. Results of steam generator tube inspections which fall into Category ;
C-3 shall be reported in a Special Report to the Commission pursuant to Specification 6.9.2 within 30 days and prior to resumption of y plant operation. This report shall provide a descr~iption of investi-gations conducted to determine cauw of the tube degradation and
) 3E'T' j correcGve measures taken to prevent recurrence. ,
Fj > ' BYRDN - UNITS 1 & 2 3/4 4-17 AMENDMENT NO. 58
INSERT E
- 11) The Tube Sucoort Plate interim Pluooina Criteria Limit is used for the disposition of a steam generator tube for continued service that is experiencing outer diameter stress corrosion cracking confined within the thickness of the tube support plates. For application of the tube support plate interim plugging criteria limit, the tube's disposition for continued service will be based upon standard bobbin coil probe signal amplitude of flaw-like indications. The plant specific guidelines used for all inspections shall be amended, as appropriate, with respect to the voltage / depth parameters specified in Specification 4.4.5.2. An ASME standard calibrated against the laboratory standard will be utilized in Unit 1 steam generator inspections for consistent voltage normalization, pending incorporation of the voltage verification requirements in ASME standard verifications. The acceptance criteria are as follows:
- 1. A tube can remain in service with a flaw-like bobbin coil signal amplitude of less than or equal to 1.0 volt, regardless of the depth of the tube wall penetration.
- 2. A tube can remain in service with a flaw-like bobbin coil signal amplitude greater than 1.0 volt but less than or equal to 2.7 volts provided an RPC inspection does not detect degradation.
- 3. A tube with a flaw-like bobbin coil signal amplitude of greater than 2.7 volts shall be plugged or repaired. Detection of a tube or tubes with flaw-like bobbin coil signal amplitude of greater than 4.54 volts shall require an inspection report, as described in Specification 4.4.5.5.d.2, to be submitted to the Commission prior to plant startup.
- 4. Plant startup and operation is allowed following application of the above acceptance criteria if, as a result, the projected distribution of crack indications over the next operating period is verified to result in total primary-to secondary leakage less than or equal to 12.8 gpm (including operational and accident leakage). If the operating period is less than a full cycle, at the end of that operating period, the plant shall be shutdown and an inspection performed in accordance with Specification 4.4.5.2.d. Continued operation beyond that operating period, without a shutdown, may be permitted based on additional l licensee justification and subsequent approval by the Commission. i
INSERT E (cont.) Certain tubes identified in WCAP-14046, Section 4.7, shall be excluded from application of the tube support interim plugging criteria limit. It has been determined that these tubes may collapse or deform following a postulated LOCA+SSE.
INSERT F d.1 For Unit 1, if the flaw-like bobbin coil signal amplitudes detected during the inspection of tubes in which the tube support plate interim plugging criteria limit has been applied are less than or equal to 4.54 volts and if the leakage projected at end of the next cycle based on inspection results is less than or equal to 12.8 gpm, preliminary results of the inspection shall be reported to the Commission pursuant to Specification 6.9.2 prior to plant startup. The preliminary results to be reported include maximum indication voltage observed and predicted end of cycle leakage. The final results of inspection for all tubes in which the tube support plate interim plugging criteria limit has been applied shall be reported to the Commission pursuant to Specification 6.9.2 within 90 days following completion of the steam generator tube inservice inspection. This report shall include:
- 1. Listing of applicable tubes,
- 2. Locatt.n (applicable intersections per tube) and extent of degradation (voltage), and
- 3. Projected Steam Line (MSLB) Leakage s
d.2 For Unit 1, if a flaw-like bobbin coil signal amplitude of greater than 4.54 volts was detected during the inspection of tubes in which the tube support plate interim plugging criteria limit has been applied or if greater than 12.8 gpm leakage is projected at end of the next cycle based on inspection results, both the preliminary and final reports described in 4.4.5.5.d.1 shall be submitted to the Commission for approval prior to plant startup. In addition to the information identified above, the final report shall include justification to permit startup, definition of the operating period, and a description of the actions to be taken at the end of that operating period, if less than a full cycle.
l TABLE 4.4-1 l MINIMUM NUMBER OF STEAM GENERATORS TO BE .i e
. ,,; INSPECTED DURING INSERVICE INSPECTION ~ ~ - 1 ._ _ .. . J.C _ :.Z I
Preservice Inspection Yes
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l No. of Steam Generators per Unit Four ! i First Inservice Inspection Two Second & Subsequent Inservice Inspections One l TABLE NOTATION
- 1. The inservice inspection may be limited to one steam generator on a ,
rotating schedule encompassing 3 N % of the tubes (where N is the number of steam generators in the plant) if the results of the first l or previous inspections indicate that all steam generators are ! performing in a like manner. Note that under some circumstances, the i operating conditions in one or more steam generators may be found to i be more severe than those in other steam generators. Under such ! circumstances the sample sequence shall be modified to inspect the most severe conditions. Each of the other two steam generators not i inspected during the first inservice inspections shall be inspected i during the second and third inspections. The fourth and subsequent I inspections shall follow the instructions described above. ! l i l i I i
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n BYRON . UNITS 1 & 2 3/4 4-18 1 l
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" TABLE 4.4J ,
STEAM _ GENERATOR TUBE INSPECTION g 1ST SAMPLE INSPECTION 2ND 5 AMPLE INSPECTION - 3RD SAMPLE INSPECTION h Sample Sire Result Action Required Result Action Regidred
" Result Action Rgded A mininum of C-1 None N.A. N.A. N.A. .N.A.
! N d *# ~ g, g C-2 Plug or repolt C-1 None N.A. N.A. defective tubes and insput addW C-2 Plug or repele C-1 None l 25 tubes in this Afecdve the S* G* '"d'"spect C-2 Plug or repelr additional 45 l defective tubes . tubes in this S. G. C-3 Perform action for i C-3 result of first semple to C-3 Perform action for N.A. 1 N.A. C-3 result of first
? - W C-3 Inspect all tubes in All other None N.A. M.A.
tNs S. G., plug or S. G.s are repelt defective C-1 tubes and Inspect 25 tubes in each Some S. G.s Perform action for N.A. N.A. other S. G. C-2 but no C-2 result of addtlonel second semple Notification to NRC S. G. are C-3 . P"' I"
' Additional inspect all tubes N.A
.7 b ' N.A.
p 0 S. G.Is C-3 in each S. G. and plug or repele k.
= defective tubes. l Notification to k
NRC pursuant to 5 150.72ibH2) of 10 CFR Part 50 u, m N g 5-3 ilhere N is the ninnber of steam generators in the imit, and n is the ntpher of steam A generators inspected during an inspection .
J REAcTDR cpotANT SYSTEM ' nasts i 3 /4 . 4. 5 STEAM GENERATORS The Surveillance Requirements for inspection of the steam generator tubes ensure that the structural inteority of this portion of the RCS will be main-tained. The program for inservice inspection of steam generator tubes is based on a modification of Regulatory Guide 1.83 Revision 1. Inservict ' inspectionofsteamgeneratortubingisessentialinordertomaintainsurveil- ! lance 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 steam generator tubing also provides a means of characterizing the nature i and cause of any tube degradation so that corrective measures can be taken. ) The plant is expected to be operated in a manner such that the secondary coolant will be maintained within those chemistry limits found to result in negligible corrosion of the steam generator tubes. If the secondary coolant s chemistry is not maintained within these limits, localized corrosion may ' likely result in stress corrosion cracking. The extent of cracking during i plant operation would be limited by the limitation of steam generator tube
- leakage between the Reactor Coolant System and the Secondary Coolant System (reactor-to-secondary leakage - 500 gallons per day per steam generator !
Cracks having a reactor-to-secondary leakage less than this limit during). operation will have an adequate margin of safety to withstand the loads imposed during normal operation and by postulated accidents. Operating plants have demonstrated that reactor-to-secondary leakage of 500 gallons per day per steam generator can readily be detected by radiation monitors af steam generator blowdown. Leakage in excess of this limit will require plant J shutdown and an unscheduled inspection during which the leaking tubes will be located and plugged or repaired by slee, vin The technical bases for sleeving are described in Westinghouse report WCAP g.336g8 Rev. 3 and Babcock & Wilcox Topical Report BAW-2045PA Rev. 1. Wastage-type defects are unlikely with proper chemistry treatment of the secondary coolant. However even if a defect should develop in service, it will be found during scheduled inservice steam generator tube examinations. Plugging or sleeving will be required for all tubes with imperfections exceeding the plugging or repair limit of 40% of the tube nominal wall thickness. If a sleeved tube is found to contain a through wall penetration in the sleeve of equal to or greater than 40% of the nominal wall thickness, the tube must be plugged. The 40% plugging limit for the sleeve is derived from Reg. Guide 1.121 analysis and utilizes a 20% allowance for eddy current uncertainty and additional degradation growth. Inservice inspection of sleeves is required to ensure RCS integrity. Sleeve ins 1 described BAW-2045PA Report in Wes*.in ke%ouse Report WCAP-136g8 I and Babcock & Wilcox Rev.pection Topical techn
- y. 1. Steam Generator tube and sleeve inspections have demonstrated the capability to reliably detect degradation that has penetrated 20% of the pressure retaining portions of the tube or sleeve waH thickness.
Commonwealth Edison will validate the adequacy of any system that is used for 8
. periodic inservice inspection of the sleeves and, as deemed appropriate, will upgrade testing methods as better methods are developed and validated for ;
[] g omercial use. Ehenever the results of any steam generator tubing inservice inspection 4 ,, Mj
' fall into Category C-3, these results will be reported to the Commission pu suant to Specification 6.g.2 prior to resumption of plant operation. Such cases will be considered by the Commission on a case-by-case basis and may result in a requirement for analysis, laboratory examinations tests, additional eddy-current inspection, and revision of the Technical Specifications, iT necessary.
l BYRON - UNITS ] & 2 B 3/4 4-3 AMENDMENT NO. 58
4 1 INSERT G For Unit 1, tubes experiencing outer diameter stress corrosion cracking within the thickness of the tube support plates will be dispositioned in accordance with Specification 4.4.5.4.a.11. The operating period may be adjusted to less than the full operating cycle to meet the 12.8 gpm projected leakage limit. However, if greater than 12.8 gpm leakage is projected for end of cycle, the shortened period must be reported to the Commission for approval prior to plant startup in accordance with Specification 4.4.5.5.d.2. The maximum site allowable primary-to-secondary leakage limit,12.8 gpm, includes the accident leakage from a faulted steam generator and the operational leakage of the three remaining intact steam generators equal to the Specification 3.4.6.2.c leakage limit.
ATTACHMENT F EVALUATION OF SIGNIFICANT HAZARDS CONSIDERATIONS FOR PROPOSED CHANGES TO APPENDIX A TECHNICAL SPECIFICATIONS OF , FACILITY OPERATING LICENSES NPF-37 and NPF-66 Commonwealth Edison Company (Comed) has evaluated this proposed license amendment request and determined that it involves no significant hazards considerations. According to Title 10, Code of Federal Regulations, Part 50, Section 92, Paragraph c [10 CFR 50.92(c)], a proposed amendment to an operating license involves no significant hazards considerations if operation of the facility in accordance with the proposed amendment would not:
- 1. Involve a significant increase in the probability or consequences of an accident previously evaluated; or
- 2. Create the possibility of a new or d5fferent kind of accident from any :
accident previously evaluated; or
- 3. Involve a significant reduction in a margin of safety.
In the most recent Byron Unit 1 Cycle 5 Refueling Outage (B1R05), conducted in + the spring of 1993, a steam generator (SG) tube inservice inspection was performed in accordance with the current Technical Specification Surveillance Requirement (TSSR) 4.4.5.0. The results of this inspection identified a total of 1105 bobbin coilindications at the tube support plate (TSP) locations. Using a rotating pancake coil (RPC) probe to confirm these indications, 556 indications , were determined to be flawed due to outside diameter stress corrosion cracking (ODSCC) at the TSPs in 530 SG tubes. The 530 tubes were removed from service by plugging. This increased the overall plugging total for Byron Unit 1 to 847 tubes or 4.6% of the tubes. Of the 847 tubes plugged to date, 671 were plugged , due to ODSCC at the tube support plate locations. For the upcoming Byron Unit 1 Cycle 6 Refueling Outage (B1R06), predictions on the number of pluggable indications using the current depth-based acceptance , criteria are approximately 1950 tubes. With the approval of the voltage-based Interim Plugging Criteria (IPC) as proposed, the predicted number of tubes requiring repair by piugging or sleeving could be reduced to approximately 600. This F-1 1
represents a savings of approximately $5.2M in plugging and sleeving repair costs alone. In addition, IPC implementation saves a minimum of 24 days in critical path outage time and eliminates the associated replacement power costs. Also, permitting these tubes to remain in service maximizes RCS flow and heat transfer aroa availability and minimizes RCS loop asymmetries and loss of rated thermal power. Comed proposes to amend the following Byron Technical Specification: Specification 3/4.4.5 REACTOR COOLANT SYSTEM-STEAM GENERATORS This proposed license amendment request will modify Specification 3.4.5 to allow an eddy current bobbin coil probe voltage-based steam generator tube support plate IPC to be applied for Byron Unit 1. Technical Specification Bases Section 3/4.4.5, STEAM GENERATORS will also be modified to reflect these changes.
- 1. The proposed change does not involve a significant increase in the probability or consequences of an accident previously evaluated.
Consistent with Regulatory Guide (RG) 1.121, " Basis for Plugging Degraded PWR Steam Generator Tubes," Revision 0, August 1976, the traditional depth-based criteria for SG tube repair implicitly ensures that tubes accepted for continued service will retain adequate structural and leakage integrity during normal operating, transient, and postulated accident conditions. It is recognized that defects in tubes permitted to remain in service, especially cracks, occasionally grow entirely through-wall and develop small leaks. Limits on allowable primary-to-secondary leakage established in Technical Specifications ensure timely plant shutdown before the structural and leakage integrity of the affected tube is challenged. The proposed license amendment request to implement voltage amplitude SG tube support plate Interim Plugging Criteria for Byron Unit 1 meets the requirements of RG 1.121. The IPC methodology demonstrates that tube leakage is acceptably low and tube burst is a highly improbable event during either normal operation or the most limiting accident condition, a postulated main steam line break (MSLB) event. Adequate SG tube leakage integrity during normal operating conditions is assured by limiting allowable primary-to-secondary leakage to 150 gpd per SG or 600 gpd total. Currently, this limit is administratively controlled. However, a license amendment request was submitted on 06/03/94 to incorporate this limit into the Byron Technical Specifications. During normal operating conditions, the tube support plate constrains the ODSCC affected F-2
area of the tube to provide additional strength that precludes burst. Any leakage of a tube exhibiting ODSCC at the TSP is fully bounded by the existing SG tube rupture analysis included in the Byron UFSAR. Therefore, probability of failure of a tube left in service or consequences of tube failure during normal operating conditions is not significantly increased by the application of IPC. During transients, the TSP is conservatively assumed to displace due to the thermal-hydraulic loads associated with the transient. This may partially expose a crack which is within the boundary of the TSP during normal operations to free span conditions. Burst is therefore conservatively evaluated assuming the crack is fully exposed to free span conditions. The structural eddy current bobbin coil voltage limit for free-span burst is 4.54 volts. This limit takes into consideration a 1.43 safety factor applied to the steam line break differential pressure that is consistent with RG 1.121 requirements. $With additional considerations for growth rate assumptions and an upper 95% confidence estimate on voltage variability, the maximum voltage indication that could remain in service is reduced to 2.7 volts. For added conservatism, the allowable indication voltage is further reduced in the proposed amendment to a 1.0 volt confirmed ODSCC indication limit. Allindications between 1.0 and 2.7 volts will be subject to an RPC examination. Tubes with RPC confirmed ODSCC indications will be plugged or sleeved.. Any ODSCC indications between 1.0 volt and 2.7 volts which are not confirmed as ODSCC will be allowed to remain in service since these indications are not as likely to affect tube structural integrity or leakage integrity over the next operating cycle as the indications that are detectable by both bobbin and RPC inspections. The eddy current inspection process has been enhanced to address RG 1.83, 'mservice inspection of PWR Steam Generator Tubes," Revision 1, July 1975, considerations as well as the EPRI SG Inspection Guidelines. Enhancements in accordance with NUREG-1477 and Appendix A of the Catawba IPC report (WCAP-13698) are in place to increase detection of ODSCC indications and to ensure reliable, consistent acquisition and analysis ' of data. Based on the conservative selection of the voltage criteria and the increased ability to identify ODSCC, the probability of tube failure during an accident is also not significantly increased due to application of requested IPC. For consistency with current offsite dose limits, the site allowablo leakage limit during a MSLB has been conservatively calculated to be 12.8 gpm. This leakage limit includes maximum allowable operational leakage from the l unaffected SGs and the accident leakage from the affected SG. As a ' requirement for operation following application of IPC, the projected F-3
distribution of crack indications over the operating period must be verified to result in primary to secondary accident leakage less than the site allowable leakage limit. Thus, the consequences of a MSLB remain unchanged. Therefore, as implementation of the 1.0 volt IPC for Byron Unit 1 does not adversely affect steam generator tube integrity and results in acceptable dose consequences, the proposed license amendment request does not result in any significant increase in the probability or consequences of an accident previously evaluated within the Byron Updated Final Safety Analysis Report.
- 2. The proposed change does not create the possibility of a new or different kind of accident from any accident previously evaluated.
Implementation of the proposed SG tube IPC does not introduce any significant changes to the plant design basis. Use of the criteria does not 1 provide a mechanism which could result in an accident outside the tube l support plate elevations since industry experience indicates that ODSCC originating within the tube support plate does not extend significantly , beyond the thickness of the support plate. This criteria only applies to ODSCC contained within the region of the tube bounded by the tube support ) plate. In addressing the combined effects of Loss of Coolant Accident (LOCA) ! coincident with a Safe Shutdown Earthquake (SSE) on the SG (as required by General Design Criteria 2), it has been determined that tube collapse of select tubes may occur in the SGs at some plants, including Byron Unit 1. There are two issues associated with SG tube collapse. First, the collapse of SG tubing reduces the RCS flow area through the tubes. The reduction in flow area increases the resistance to flow of steam from the core during a LOCA which, in turn, may potentially increase Peak Clad Temperature (PCT). Second, there is a potential that partial through-wall cracks in tubes could progress to through-wall cracks during tube deformation or collapse. A number of tubes have been identified, in the " wedge" locations of the SG TSPs, that demonstrate the potential for tube collapse during a LOCA + SSE event. Because of this potential, these tubes have been excluded from , application of the voltage-based SG TSP IPC. Therefore, neither a single or multiple tube rupture event would be expected in a steam generator in which IPC has been applied. i F-4
Comed has implemented a maximum primary to secondary leakage limit of 150 gpd through any one SG at Byron to help preclude the potential for excessive leakage during all plant conditions. The 150 gpd limit provides for leakage detection and plant shutdown in the event of an unexpected single l crack leak associated with the longest permissible free span crack length. l The 150 gpd limit provides adequate leakage detection and plant shutdown criteria in the event an unexpected single crack results in leakage that is associated with the longest permissible free span crack length. Since tube burst is precluded during normal operation due to the proximity of the TSP to the tube and the potential exists for the crevice to become uncovered during MSLB conditions, the leakage from the maximum permissible crack must preclude tube burst at MSLB conditions. Thus, the 150 gpd limit provides a conservative limit to prompt plant shutdown prior to reaching critical crack lengths under MSLB conditions. Upon implementation of the 1.0 volt IPC, steam generator tube integrity continues to be maintained through inservice inspection and primary-to-secondary leakage monitoring. Therefore, the possibility of a new or different kind of accident from any previously evaluated is not created.
- 3. The proposed change does not involve a significant reduction in a margin of safety.
The use of the voltage based bobbin coil probe SG TSP IPC for Byron Unit 1 will maintain steam generator tube integrity commensurate with the criteria of RG 1.121 as discussed above. Upon implementation of the criteria, even under the worst case conditions, the occurrence of ODSCC at the TSP elevations is not expected to lead to a steam generator tube rupture event during normal or faulted plant conditions. The distribution of crack indications at the TSP elevations result in acceptable primary-to-secondary leakage during all plant conditions and radiological consequences are not adversely impacted by the application of IPC. The installation of SG tube plugs and sleeves reduces the RCS flow margin. As noted previously, implementation of the SG TSP IPC will decrease the number of tubes which must be repaired by plugging or sleeving. Thus, implementation of IPC will retain additional flow margin that would otherwise be reduced due to increased tube plugging. Therefore, no significant reduction in the margin of safety will occur as a result of the implementation of this proposed license amendment request. 1 I l F-5
Although not relied upon to prove adequacy of the proposed amendment request, the following analyses demonstrate that significant conservatisms exist in the methods and justifications described above: LIMITED TUBE SUPPORT PLATE DISPLACEMENT An analysis was nerformed to verify of limited TSP displacement during accident conditions (MSLB). Application of minimum TSP displacement assumptions reduce the likelihood of a tube burst to negligible levels. Consideration of limited TSP displacement would also reduce potential MSLB leakage when compared to the leakage calculated assuming free span indications. PROBABILITY OF DETECTION The Electric Power Research Institute (EPRI) Performance Demonstration Program analyzed the performance of approximately 20 eddy current data analysts evaluating data from a unit with 3/4" inside diameter and 0.049" wall thickness tubes. The results of this analysis clearly show that the detectability of larger voltage indications is increased which lends creditability for application of a POD of > 0.6 for ODSCC indications larger than 1.0 volt. RISK EVALUATION OF CORE DAMAGE As part of Comed's evaluation of the operability of Byron Unit 1 Cycle 7, a risk evaluation was completed. The objective of this evaluation was to compare core damage frequency under containment bypass conditions, with and without the interim plugging criteria applied at Byron Unit 1. i The total Byron core damage frequency is estimated to be 3.09E-5 per reactor year with a total contribution from containment bypass sequences of 3.72E-8 per reactor year according to the results of the current individual plant evaluation (IPE). Operation with the requested IPC resulted in an insignificant increase in core damage frequency resulting from MSLB with containment bypass conditions. Therefore, based on the evaluation above, Comed has concluded that this proposed license amendment request does not involve a significant hazards consideration. F-6
ATTACHMENT G ENVIRONMENTAL ASSESSMENT FOR PROPOSED CHANGES TO APPENDIX A TECHNICAL SPECIFICATIONS OF FACILITY OPERATING LICENSES NPF-37 AND NPF-6G Commonwealth Edison Company (Comed) has evaluated this proposed license amendment request against the criteria for and identification of licensing and regulatory actions requiring environmental assessment in accordance with Title 10, Code of Federal Regulations, Part 51, Section 21 (10 CFR 51.21). Comed has determined that this proposed license amendment request meets the criteria for a categorical exclusion set forth in 10 CFR 51.22(c)(9). This determination is based upon the following:
- 1. The proposed licensing action involves the issuance of an amendment to a license for a reactor pursuant to 10 CFR 50 which changes a requirement with respect to installation or use of a facility component located within the restricted area, as defined in 10 CFR 20, or which changes and inspection or a surveillance requirement. This proposed license amendment request changes the surveillance requirements for the Byron Unit 1 steam generator (SG) tube inservice inspection program;
- 2. this proposed license amendment request involves no significant hazards considerations;
- 3. there is no significant change in the types or significant increase in the amounts of any effluent that may be released offsite; and
- 4. there is no significant increase in individual or cumulative occupational radiation exposure.
Therefore, pursuant to 10 CFR 51.22(b), neither an environmental impact statement nor an environmental assessment is necessary for this proposed license amendment request.
I I i ATTACHMENT H Westinghouse Report WCAP-14046 (Proprietary) and Westinghouse Report WCAP-14047 (Non-Proprietary), "Braidwood Unit 1: Technical Support for Cycle 5 Steam Generator Interim Plugging Criteria," dated May,1994
gv l Westinghouse Energy Systems Nucles Technology Division Electric Corporation en ass Pittsburgh Pennsylvania 15230-03ss July 28,1994 CAW-94-699 l Document Control Desk US Nuclear Regulatory Commission Washington, DC 20555 Attention: Mr. William T. Russell, Director APPLICATION FOR WITHHOLDING PROPRIETARY INFORMATION FROM PUBLIC DISCLOSURE
Subject:
"Braidwood Unit 1 Technical Support for Cycle 5 Steam Generator Interim Plugging Criteria" (WCAP-14046)
Dear Mr. Russell:
The proprietary information for which withholding is being requested is further identified .in Af6 davit CAW-94-699 signed by the owner of the proprietary information, Westinghouse Electric Corporation. The affidavit, which accompanies this letter, sets forth the basis on which the information may be withheld from public disclosure by the Commission and addresses with specificity the considerations listed in paragraph (b)(4) of 10 CFR Section 2.790 of the Commission's regulations. Accordingly, this letter authorizes the utilization of the accompanying Affidavit by Commonwealth Edison Company. Correspondence with respect to the proprietary aspects of the application for withholding or the Westinghouse affidavit should reference this letter, CAW-94-699, and should be addressed to the undersigned. Very truly yours, j N. J. Liparu o, k anager Enclosures Nuclear Safety Regulatory and Licensing Activities cc: Kevin Bohrer/NRC (12H5) j- .- f - - -
CAW-94-699 AFFIDAVIT COMMONWEALTH OF PENNSYLVANIA: ss COUNTY OF ALLEGHENY: Before me, the undersigned authority, personally appeared Henry A. Sepp, who, being by me duly sworn according to law, deposes and says that he is authorized to execute this Affidavit on behalf of Westinghouse Electric Corporation (" Westinghouse") and that the averments of fact set forth in this Affidavit are true and correct to the best of his knowledge, information, and belief: i h - < M, Henry A. Sepp, Manager Regulatory and Licensing Initiatives Sworn to and subscribed before me this _88 day of J <<044 ,1994 , O DeniseKHenderson NotaryPutic My asen Expos 28
~~~~
Oml< Hendmvm Notary Public wxmsenm
i CAW-94-699 (1) I am Manager, Regulatory and Licensing Initiatives, in the Nuclear Technology Division, of the Westinghouse Electric Corporation and as such, I have been specifically delegated the function of reviewing the proprietary information sought to be withheld from public disclosure in connection with nuclear power plant licensing and rulemaking proceedings, and am authorized to apply for its withholding on behalf of the Westinghouse Energy Systems Business Unit. (2) I am making this Affidavit in conformance with the provisions of 10CFR Section 2.790 of the Commission's regulations and in conjunction with the Westinghouse application for withholding accompanying this Affidavit. (3) I have personal knowledge of the criteria and procedures utilized by the Westinghouse Energy , Systems Business Unit in designating information as a trade secret, privileged or as confidential commercial or financial information. (4) Pursuant to the provisions of paragraph (b)(4) of Section 2.790 of the Commission's , regulations, the following is furnished for consideration by the Commission in det a k ing whether the information sought to be withheld from public disclosure should be witu.d. (i) The information sought to be withheld from public disclosure is owned and has been held in confidence by Westinghouse. t (ii) The information is of a type customarily held in confidence by Westinghouse and not customarily disclosed to the public. Westinghouse has a rational basis for determining the types of information customarily held in confidence by it and, in that connection, utilizes a system to determine when and whether to hold certain types of information in confidence. The application of that system and the substance of that system constitutes Westinghouse policy and provides the rational basis required. Under that system, information is held in confidence if it falls in one or more of several types, the release of which might result in the loss of an existing or potential competitive advantage, as follows: , I 132SC-RJM 29722e4
CAW-94-699 (a) De information reveals the distinguishing aspects of a process (or component, structure, tool, method, etc.) where prevention of its use by any of Westinghouse's competitors without license from Westinghouse constitutes a competitive economic advantage over other companies. (b) It consists of supporting data, including test data, relative to a process (or component, structure, tool, method, etc.), the application of which data secures a competitive economic advantage, e.g., by optimization or improved marketability. (c) Its use by a competitor would reduce his expenditure of resources or improve his competitive position in the design, manufacture, shipment, installation, assurance of quality, or licensing a similar product. (d) It reveals cost or price information, production capacities, budget levels, or commercial strategies of Westinghouse, its customers or suppliers. (e) It reveals aspects of past, present, or future Westinghouse or customer funded development plans and programs of potential commercial value to Westinghouse. (f) It contains patentable ideas, for which patent protection may be desirable. There are sound policy reasons behind the Westinghouse system which include the following: (a) The use of such information by Westinghouse gives Westinghouse a competitive advantage over its competitors. It is, therefore, withheld from disclosure to protect the Westinghouse competitive position. (b) It is information which is marketable in many ways. The extent to which such information is available to competitors diminishes the Westinghouse l ability to sell products and $arvices involving the use of the information. l I nr.3c.nMsS7:su ,
CAW-94499 (c) Use by our competitor would put Westinghouse at a competitive disadvantage by reducing his expenditure of resources at our expense. (d) Each component of proprietary information pertinent to a particular competitive advantage is potentially as valuable as the total competitive advantage. If competitors acquire components of proprietary information, any one component may be the key to the entire puzzle, thereby depriving Westinghouse of a competitive advantage. (e) Unrestricted disclosure would jeopardize the position of prominence of Westinghouse in the world market, and thereby give a market advantage to the competition of those countries. (f) The Westinghouse capacity to invest corporate assets in research and development depends upon the success in obtaining and maintaining a competitive advantage. (iii) The information is being transmitted to the Commission in confidence and, under the provisions of 10CFR Section 2.790, it is to be received in confidence by the Commission. (iv) The information sought to be protected is not available in public sources or available information has not been previously employed in the same original manner or method to the best of our knowledge and belief. (v) The proprietary information sought to be withheld in this submittal is that which is appropriately marked in "Braidwood Unit 1 Technical Support for Cycle 5 Steam Generator Interim Plugging Criteria", WCAP-14046 (Proprietary), May,1994 for Byron Unit 1, being transmitted by Commonwealth Edison Company letter and Application for Withholding Proprietary Information from Public Disclosure, to 1 Document Control Desk, Attention William T. Russell. The proprietary information as submitted for use by Commonwealth Edison Company for Byron Unit I is expected ; to be applicable in other licensee submittals in response to certain NRC requirements for justification of steam generator tube interim plugging criteria. , 1 I srxnum:m j
CAW-94-699 This information is part of that which will enable Westinghouse to: I (a) Provide documentation for steam generator tube interim plugging criterion. (b) Provide a basis for the form of the steamline break (SLB) leak rate correlation. (c) Provide SLB leak rate analyses. (d) Assist the customer in obtaining NRC approval. Further this information has substantial commercial value as follows: (a) Westinghouse plans to sell the use of similar information to its customers for purposes of meeting requirements for licensing documentation. (b) Westinghouse can sell support and defense of the technology to its customers in the licensing process. Public disclosure of this proprietary information is likely to cause substantial harm to the competitive position of Westinghouse because it would enhance the ability of competitors to provide similar methodologies and licensing defense services for commercial power reactors without commensurate expenses. Also, public disclosure of the information would enable others to use the information to meet NRC requirements for licensing documentation without purchasing the right to use the information. The development of the technology described in part by the information is the result of applying the results of many years of experience in an intensive Westinghouse effort and the expenditure of a considerable sum of money, in order for competitors of Westinghouse to duplicate this information, similar technical programs would have to be performed and a significant manpower effort, n:se amona
CAW-94-699 having the requisite talent and experience, would have to be expended for developing testing and analytical methods and performing testing. Further the deponent sayeth not. l t t 6 i l t i r i f P b a 13:5C-RM427 :Fa4
Proprietary Information Notice Transmitted herewith are proprietary and/or non-proprietary versions of documents furnished to the NRC in connection with requests for generic and/or plant-specific review and approval. In order to conform to the requirements of 10 CFR 2.790 of the Commission's regulations concerning the protection of proprietary information so submitted to the NRC, the information which is proprietary in the proprietary versions is contained within brackets, and where the proprietary information has been deleted in the non-proprietary versions, only the brackets remain (the information that was contained within the brackets in the proprietary versions having been deleted). The justification for claiming the information so designated as proprietary is indicated in both versions by means of lower case letters (a) through (f) contained within parentheses located as a superscript immediately following the brackets enclosing each item of information Scing identified as proprietary or in the margin opposite such information. These lower case letters refer to the types of information Westinghouse customarily holds in confidence identified in Sections (4)(ii)(a) through (4)(ii)(f) of the af'idavit accompanying this transmittal pursuant to 10 CFR 2.790(b)(1).
Copyright Notice l l i i The reports transmitted herewith each bear a Westinghouse copyright notice. The NRC is permitted to make the number of copies of the information contained in these reports which are necessary for its internal use in connection with generic and plant-specific reviews and approvals as well as the issuance, denial, amendment, transfer, renewal, modification, suspension, revocation, or violation of a license, permit, order, or regulation subject to the requirements of 10 CFR 2.790 regarding restrictions on public : disclosure to the extent such information has been identified as proprietary by Westinghouse, copyright protection notwithstanding. With respect to the non-proprietary versions of these reports, the NRC is , permitted to make the number of copies beyond those necessary for its internal use which are necessary in order to have one copy available for public viewing in the appropriate docket files in the public document room in Washington, DC and in local public document rooms as may be required by NRC regulations if the number of copies submitted is insufficient for this purpose. Copies made by the NRC must include e the copyright notice in all instances and the proprietary notice if the original was identified as proprietary. { CINB8.KSwoud
WESTINGHOUSE CLASS 3 WCAP-14047 SG-94-06-002 BRAIDWOOD UNIT 1 TECHNICAL SUPPORT FOR CYCLE 5 STEAM GENERATOR INTERIM PLUGGING CRITERIA MAY 1994 Approved by: Esposito,%anager
/ team Generator Technology & E gi n neering WESTINGHOUSE ELECTRIC CORPOPATION NUCLEAR SERVICES DIVISION P. O. BOX 158 MADISON, FENNSYLVANIA 15663-0158 C 1994 Westinghouse Electric Corporation
. All Rights Reserved
.h hhb - =A
l BRAIDWOOD UNIT 1: TECHNICAL SUPPORT FOR CYCLE 5 STEAM GENERATOR INTERIM PLUGGING CRITERIA TABLE OF CONTENTS SEC110N PAGE 1.0 Introduction 1-1 2.0 Summary and Conclusions 2-1 2.1 Overall Conclusions 2-1 2.2 Summary 2-2 3.0 Crack Morphology 3-1 3.1 General Discussion 3-1 4.0 Accident Considerations 4-1 4.1 General Considerations 4-1 4.2 Thermal Hydraulic Loads on TSP in a SLB Event 4-2 4.3 Structural Modeling for SLB TSP Displacement Analyses 4-5 4.4 Results of SLB TSP Displacement Analyses 4-10 4.5 SLB TSP Displacements by Tube Location 4-13 4.6 SLB Frequency at Hot Standby and Full Power Conditions 4-15 4.7 Tubes Subject to Deformation in a SSE + LOCA Event 4-16 4.8 Allowable SLB Leakage Limit 4-18 4.9 Acceptability of the Use of TRANFLO Code 4-20 4.10 References 4-24 5.0 Database Supporting Altemate Repair Criteria 5-1 5.1 Data Outlier Evaluation 5-1 5.2 Database for ARC Correlations 5-6 5.3 NDE Uncertainties 5-6 5.4 References 5-7 6.0 Burst and SLB Leak Rate Correlations 6-1 6.1 EPRI ARC Correlations 6-1 6.2 Burst Pressure vs. Bobbin Voltage Corelation 6-1 6.3 Burst Pressure vs. Throughwall Crack Length Correlation 6-2 6.4 NRC Draft NUREG-1477 SLB Leak Rate POD and Uncertainty 6-5 Methodology 6.5 Probability of Leakage Correlations 6-5 6.6 SLB Leak Rate vs. Voltage Correlation for 3/4" Tubes 6-9 6.7 SLB Leak Rate Analysis Methodology 6-11 6.8 Simulation of Equation Parameter Uncertainties 6-13 i
BRAIDWOOD UNIT 1: TECHNICAL SUPPORT FOR CYCLE 5 STEAM GENERATOR INTERIM PLUGGING CRITERIA TABLE OF CONTENTS (Continued) , SECTION PAGE . 7.0 . Braidwood-l Eddy Current Inspection Results 7-1 i 7.1 General 7-1 i 7.2 Inspection Results 7-2 7.3 Voltage Growth Rates 7-3 7.4 Historical Operating Chemistry 7-5 7.5 Relation Between Operating Chemistry and ODSCC Growth 7-6 . 7.6 Pulled Tuoe Eddy Current Data 7-7 i 8.0 Braidwood-l IPC Criteria and Evaluation 8-1 8.1 General Approach to IPC Assessment 8-1 8.2 IPC Repair Criteria Implemented at Braidwood-l 8-2 ; 8.3 Operating Leakage Limit 8-3 i 8.4 Projected EOC-5 Voltage Distributions 8-5 8.5 SLB Leakage Analyses 8-6 5.5.1 Reference SLB Leakage Analyses (Log logistic POL) 8-6 l 8.5.2 SLB Leak Rate Sensitivity to POL Correlations 8-7 8.6 Assessment of SLB Burst Margins and Probability of Burst 8-7 i 8.6.1 Deterministic Burst Margin Assessment 8-7 8.6.2 Method of Analysis for SLB Tube Burst Probability 8-8 { 8.6.3 Demonstration of Method for SG-D at EOC-4 8-11 ! 8.6.4 Conservative Burst Probability for SLB at Normal Operating 8-11 ! , Conditions ; 8.6.5 Burst Probability for SLB at Hot Standby Conditions 8-12 8.6.6 Braidwood-l Frequency of SLB Event with a Tube Rupture 8-13 8.7 Summary of Results 8-13 ; I : l
?
ii ! l N l ~
BRAIDWOOD UNIT 1: TECHNICAL SUPPORT FOR CYCLE 5 STEAM OZNERATOR INTERIM PLUGGING CRITERIA
1.0 INTRODUCTION
Following the completien of Cycle 4 operation, eddy current inspections of the tube support plate (TSP) intersections of the steam generator (S/G) tubes have identified 2733 bobbin coil indications of which 1566 were confirmed as being axial crack like ODSCC indications using RPC inspection techniques. The size and number of indications could result in significant tube repairs with current plugging criteria and repairs that are not required to meet NRC Regulatory Guide 1.121 guidelines for tube repair. Braidwood Station has therefore requested a Technical Specification change to implement an interim plugging criteria (IPC) for ODSCC at TSP intersections. The requested IPC repair limits and inspection requirements have been based on the Catawba-1 NRC SER which approved a 1.0 volt repair limit. 'Ihe methodology to support the Braidwood-l IPC differs from previously approved IPCs in that it applies the EPRI data outlier evaluation methodology and SLB leak rate versus voltage correlation based on the NRC guidance of the February 8,1993 NRC/ industry meeting en resolution of comments on draft NUREG-1477. In addition, Braidwood-l IPC analyses demonstrate limited TSP displacement relative to the tube in a SLB event, and show structural integrity with respect to tube burst considerations. The evaluations supporting the Braidwood-l IPC are based upon bobbin coil voltage amplitude which is correlated with tube burst capability and leakage potential. Detailed analyses provided in this report (Section 4) have demonstrated limited relative tube support plate to tube movement which minimizes the potential for significant leakage or tube burst during both normal and accident conditions. For SLB leakage analyses, the tube support plate crevices are assumed to be free span or open crevices, which lead to more conservative leak rates compared to the expected packed crevices under normal and accident conditions. The analyses for demonstrating limited TSP displacement utilize thermal-hydraulic loads for a postulated SLB at normal operating conditions and for a SLB at hot standby conditions. The loads utilize existing analyses and the hot standby loads are very conservative as the initial { conditions include low water level combined with an excess feedwater transient, both of which tend to increase the loads. The dynamic structural analyses yield TSP displacements as l a function of tube location. Tube burst analyses performed for the crack length exposed by ; the TSP displacements have been conservatively performed by assuming that the exposed ! crack length is throughwall. Even with these conservative assumptions, it is demonstrated j that Braidwood-l has adequate tube burst margin. { In accordance with draft NUREG-1477, SLB leak rates were calculated for a total of six probability of leak (POL) correlations including the EPRI reference log logistic correlation. 1-1 l l I
l The six correlations (Section 6) evaluated included linear and log voltage formulations for , logistic, normal and Cauchy cumulative distribution functions. The reference leak rate with j the log logistic correlation and five additional leak rates for assessing the sensitivity to the 1 POL correlation are given in this report (Section 8). The SLB leak rate analyses utilize voltage distributions consistent with the draft NUREG-1477 guidance including adjustments for probability of detection. The plugging criteria were developed from testing of tube specimens with laboratory-induced ODSCC, extensive examination of pulled tubes from operating S/Gs and field experience for leakage due to indications at TSPs. The recommended criteria represent conservative criteria, based upon Electric Power Research Institute (EPRI) and industry-supported development programs that are continuing to further refine the plugging criteria. At the end of Cycle 4, four tubes with 13 intersections and 6 RPC confirmed indications were pulled at Braidwood-l for future enhancement of the EPRI database and validate the industry developed EPRI leak and burst correlations applied in this report. Implementation of the tube plugging criteria was supplemented by 100% bobbin coil inspection requirements at TSP elevations having ODSCC indications, reduced operating leakage requirements, inspection guidelines to provide consistency in the voltage normalization, and rotating pancake coil (RPC) inspection requirements to establish repair requirements for indications above the 1.0 volt repair limit and to characterize the principal degradation mechanism as ODSCC. In addition, potential SLB leakage was calculated for tubes with indications left in service at TSPs to demonstrate that the cumulative EOC-5 leakage is less than the allowable limits. 1-2
2.0
SUMMARY
AND CONCLUSIONS This report documents the technical support for a Braidwood Unit 1, Cycle 5 Interim Plugging Criteria (IPC) of 1.0 volt for ODSCC indications at TSPs. 1 2.1 Overall Conclusions An IPC with a 1.0 bobbin voltage repair limit has been developed for Braidwood-1, Cycle 5 operation. Inspection requirements typical ofIPC practice, such as the guidelines of the Catawba-1 NRC SER, were applied at the Cycle 4 refueling outage to support implementation , of the IPC. These requirements include eddy current analysis guidelines, training of analysts, l cross calibration of ASME standards to a reference standard, use of probe wear standards, I 100% bobbin probe inspection and RPC inspection of bobbin indications above 1.0 volt together with a sample of dented TSP intersections. R.G.1.121 guidelines for tube integrity are conservatively satisfied at end-of-cycle five (EOC-5) conditions for the 1.0 volt IPC. The results of the Braidwood-l assessment can be summarized as follows: The projected EOC-5 SLB leakage is 3.1 gpm for the limiting SG, which is less than the allowable limit of 9.1 gpm for Braidwood-1. The SLB leak rate was evaluated for the six altemate formulations of the probability of leak versus voltage correlation identified in draft NUREG-1477 and found to be essentially (within 0.1 gpm) independent of the correlation applied in the analysis. The SLB leak rates were obtained by applying the leak rate versus voltage correlation based on the EPRI database and outlier evaluation consistent with the NRC guidance of the February 8,1994, NRC/ industry meeting on resolution of draft NUREG-1477 comments. The tube burst probabilities estimated at EOC-5 are 5x10 s for a SLB at normal operating conditions and 8x10" for a SLB at hot standby conditions. Weighting these probabilities by the relative operating times leads to a combined burst probability of 3.1x10'5. These burst probabilities are significantly lower than the IPC acceptance guideline of 2.5x10 2 shown to be acceptable in NUREG-0844. When combined with the corresponding SLB event frequencies, the frequency of a postulated SLB event with a subsequent tube 4 rupture is very low at 5.5x10 per year. The tube burst probabilities are developed based on limited TSP displacements calculated during a SLB event for the Braidwood-l S/Gs, even when applying very conservative load conditions for the hot standby SLB. Deterministic tube burst analyses show that the projected EOC-5 voltage obtained with voltage growth rates up to 99% cumulative probability on the Cycle 4 measured growth distribution, is less than the R.G.1.121 structural limit of 4.54 volts for a 1.43xAPm 2-1
accident condition burst margin. The R.G.1.121 structural limit guideline of three times normal operating pressure differential is inherently satisfied by the tube constraint provided by the tube support plates at normal operating conditions. The modest SLB leakage, acceptable tube burst margins and low tube burst probabilities l presented in this report support full cycle operation for Cycle 5 at Braidwood-l following - implementation of the 1.0 volt IPC 2.2 Summary l Draidwood-l Interim Pluccine Criteria The implementation of the IPC at Braidwood-l for ODSCC at TSPs can be summarized as follows: Tube Pluccine Criteria Tubes with bobbin flaw indications exceeding the 1.0 volt IPC voltage repair limit and
$2.7 volts are plugged or repaired if confirmed as flaw indications by RPC inspection.
Bobbin flaw indications >2.7 volts attributable to ODSCC are repaired independent of RPC confirmation. Insnection Recuirements A 100% bobbin coil inspection was performed for all TSP intersections. All bobbin i flaw indications greater than the 1.0 volt repair limit were RPC inspected and the RPC inspection included a sample of dented TSP intersections. Ooeratine Leakane Limits Plant shutdown will be implemented if normal operating leakage exceeds 150 gpd per SG. SLB Leakane Criterion Predicted end of cycle SLB leak rates from tubes left in service, including a POD = 0.6 adjustment and allowances for NDE uncertainties and ODSCC growth rates, must be less than 9.1 gpm for the S/G in the faulted loop.
. Exclusions from Tubs _Pluecine Criteria Certain tube locations, as identified in Section 4 of this report, are excluded from l application of the IPC repair limits. 'Ihe analyses indicate that these tubes may potentially deform or collapse following a postulated LOCA + SSE event.
l 2-2 !
EOC-4 Insoection Results Eddy current inspection at EOC-4 resulted in the identification of 2733 bobbin indications at the TSP intersections and 1566 or 57% of the bobbin indications were confirmed by RPC inspection. The indications ranged from 272 in S/G B to 1061 in S/G C. To evaluate Cycle 4 voltage growth, all indications of ODSCC at TSP intersections at EOC-4 had the EOC-3 bobbin data reevaluated to obtain Cycle 4 growth rates. In addition, Braidwood-l had a 100% inspection of S/G C during October,1993 as ti.c result of a primary to secondary tube leak unrelated to ODSCC at the TSPs. This allowed a growth evaluation for S/G C from October 1992 to October 1993, a S/G C evaluation from November 1993 to March 1994 and a growth evaluation on S/Gs A, B and D for the entire Cycle 4. The results of this growth rate analysis were conservatively applied to the BOC-5 indications left in service to project , the EOC-5 voltage distributions for tube integrity analyses. The average growth for all 4 l S/Gs over Cycle 4 was 0.23 volts per EFPY or 48% of the BOC-4 average voltage l amplitudes. The average growth for S/G C over the first part of Cycle 4 was 0.19 volts per i EFPY (48%) and was 0.11 volts per EFPY (16%) over the second part of Cycle 4. A few indications (-l%) showed larger than typical growth with the largest growth rate being 9.76 , volts. l l The Braidwood-1, RPC confirmed TSP bobbin indications show axially oriented indications i that are typical of those of other plants which have been confirmed as having ODSCC; i.e.,
]
the Braidwood-l results are consistent with axial ODSCC as the degradation mechanism and ' the associated EPRI database is applicable for the Braidwood-l IPC. Four tubes including 13 TSP intersections and six RPC confirmed bobbin indications ranging from 1.0 to 10.4 volts I were pulled during the outage for subsequent laboratory testing and destructive examination. The results from these pulled tube examinations will be used to enhance the EPRI database l and leakage / burst correlations. The effect of these data on the correlations and results of this I report will be assessed upon completion of the destructive examinations. Correlations of bobbin voltage to burst pressure and to SLB leakage and a correlation for the prcbability of SLB leakage are provided which are consistent with NUREG-1477 and the i Catawba-1 SER. These correlations form the basis for determining repair limits and the corresponding margins for burst and leakage as summarized below. l Structural Intecrity Assessment To support the Cycle 5 tube integrity assessment under the conservative assumptions of the larger Cycle 4 growth rates reoccurring in Cycle 5 and a probability of detecuan of 0.6 (draft i NUREG 1477 guidance), additional analyses were performed to demonstrate limited TSP displacement in a postulated SLB event. With limited displacement, the part of the overall 2-3 I
1 l I 1 ODSCC crack length covered by the TSP is constrained against burst and the burst capability of the indication is that associated with the exposed crack length. Thus, limited relative displacement of the tubes and TSPs realts in increased tube burst margins and an associated low probability of tube burst. The two sets of Model D4 S/G thermal-hydraulic loads available for this report are (a) those for a SLB at normal full power operating conditions and (b) those for a very conservative SLB at hot standby conditions with low water level combined with an excess feedwater transient. The initial conditions for the latter hot standby SLB event are excessively conservative as shown by comparison with a Model D3 S/G, hot standby SLB event with normal water levels and no feedwater transient. TSP displacements for each TSP and each tube location were obtained by dynamic, finite element analyses for each of the aforementioned SLB loading conditions. The results of the Model D4 S/G SLB analyses at normal operating conditions and for the Model D3 S/G at hot standby conditions show maximum TSP displacements at tube locations of <0.44 inch. These displacements expose a crack length less than the 0.51 inch throughwall crack length that satisfies R.G 1.121 criteria for the structural limit of 1.43xAPsts. The estimated tube burst probability for the SLB at normal operating conditions, very conservatively assuming a throughwall crack equal to the exposed crack length, is 5x104 which is negligible for tube integrity considerations. Thus structural integrity is maintained throughout Cycle 5 for a SLB at normal operating conditions. Since the time at power operation is typically 96% of the operating cycle for Braidwood-1, large structural margins exist for the dominant part of the operating cycle. Even for the very conservative Model D4 hot standby loads, TSP displacements are limited to less than 0.35 inch for all TSPs having bobbin indications at Braidwood-l except for plates 3 and 7. At plate 3, the maximum TSP displacement at a tube location is 0.57 inch which is l well less than the 0.75 inch length for burst at the SLB pressure differential of 2560 psi for l tubes with LTL material properties. The probability of tube burst for an assumed 0.57 inch throughwall crack is about 6x10" which is negligible compared to allowables since only 12 l (0.26% of TSP intersections) tube locations on plate 3 have TSP displacements greater than I the 0.51 inch structural limit. At the EOC-4 inspection, only 1 indication was found on plate 3 at a location with displacements >0.5 inch. This indication had a small 0.59 volt amplitude I at a tube location with 0.51 inch TSP displacement. Thus the number and voltage amplitudes of indications found at plate 3 locations with significant TSP displacements is negligible for tube integrity considerations. Since maximum TSP displacements maintain adequate tube burst margins even if throughwall cracks are assumed and since the larger tube displacements involve only a few tubes, it is concluded that adequate structural margins are maintained for I Cycle 5 operation for all potential indications at plate 3. l l 2-4
3 Only plate 7 has significant tube-to-TSP displacements which provide potential concerns for exceeding EOC-5 structural integrity considerations. At plate 7,124 tubes (2.6% of TSP intersections) have TSP displacements exceeding 0.5 inch corresponding to the R.G.1.121 structural margin for throughwall cracks and the maximum TSP displacement at any tube location is 0.87 inch. Based on the EOC-4 inspection results of plate 7 locations, only 8 indications in any one S/G, and a total of 20 indications in all 4 S/Gs (0.7% of all indications) have SLB displacements exceeding 0.5 inch. The maximum bobbin voltage at any tube location with SLB displacements exceeding 0.35 inch was 1.24 volts and the maximum voltage indication found in any S/G at plate 7 was 2.74 volts. This is well below the 4.54 volts corresponding to R.G.1.121 margins against burst for free span indications. Thus it is concluded that only a few, relatively low voltage indications are likely to occur at the plate 7 locations with significant SLB displacements at hot standby conditions. A statistical assessment is necessary to assess the potential for a structurally significant indication to occur at a plate 7 location with relatively large TSP displacements. A tube burst probability ' assessment was performed for SLB hot standby conditions (conservative Model D4 loads) and the resulting probability of a tube burst at EOC-5 conditions was only 8x10"; 4 this is negligible compared to IPC acceptance guidelines of 2.5x10 . The burst probability for an SLB during power operation at EOC-5 is 5x10 4 Since only about 3.8% of the Braidwood-l operating time is at hot standby (Mode 3) conditions, the combined burst probability is only about 3x104 The Braidwood-l SLB event frequeraies and conditional tube rupture probabilities described 4 above have been combined to obtain a frequency of 5.5x10 per year for a SLB event with a subsequent tube rupture. This very low frequency has negligible influence on the core damage frequency and supports full cycle operation at Braidwood-l for Cycle 5. Leakace Intecrity Based on sensitivity analyses for SLB leakage, it was concluded that S/G D is the most limiting S/G and was analyzed for potential SLB leak rates at EOC-5. The analysis utilized the EPRI IPC database, probability of leakage correlation and SLB leak rate versus voltage correlation following the NRC guidance at the February 8,1994, meeting on resolution of draft NUREG-1477 comments. Projected EOC-5 bobbin voltage distributions were obtained includiig a POD adjustment of 0.6, an allowance for NDE uncertainties, and an allowance for voltage, growth based on the S/G D voltage growth distribution obtained for Cycle 4. The resulting SLB leak rate for the limiting SG at EOC-5 was 3.1 gpm, which is'significantly less f than the allowable leak rate of 9.1 gpm obtained for Braidwood-1.
)
1 Based on draft NUREG-1477 guidance, the SLB leak rate was assessed for six alternate l formulations of the probability of leakage correlation including linear and log voltage forms l 2-5 1
=
for logistic, normal and Cauchy distributions. A negligible leak rate dependence on the probability of leakage form was found, with a variation of only 0.1 gpm between the six distributions. 2-6
l 3.0 CRACK MORPHOLOGY 3.1 General Discussion Four tubes were pulled from Braidwood-l including 13 TSP intersections with 6 reported bobbin and RPC indications. The resulting tube examinations will confirm the crack morphology for indications at the tube support intersections. The schedule for the tube exams will be based on obtaining the appropriate technical results and the results will be available for review after the tests are completed. In the interim period, comparisons of RPC data from the current Braidwood-l inspection are compared in Section 3.2 below with RPC results for pulled tubes with known morphology of dominantly axial ODSCC typical of the EPRI database. With the performance of the tube metallography on the pulled tube specimens from Braidwood-1, the 3/4" database will be expanded by 6 TSP intersections with clearly identifiable degradation and 7 other intersections for which EC interpretation guidelines, as practiced in the field, did not find a basis for reporting as possible flaws; these NDD specimens will help to define the extent of ODSCC which may be present at such locations. The Braidwood 1 pulled tubes can be expected to demonstrate a crack morphology of dominantly axial ODSCC typical of the EPRI database. Together with leak and burst testing, the ground truth provided from these samples is expected to support the detection probability conceming the adequacy of bobbin EC testing of non-dented TSPs as the appropriate NDE technique for TSP interim plugging criteria. The bobbin results from the SH level of R37C34 in particular are suggestive of possible fiaw conditions, but both the bobbin and the RPC field analyses were reported as NDD; the metallography results could confirm the sensitivity of the bobbin probes' integration of many small cracks, producing a detectable signal, while the RPC probe response is too small to distinguish a signal produced from only a fraction of the total cracks present in its helical path at any instant. In either case, the voltage range of 1.0 to 10.4 volts for the ; Braidwood-l pulled tubes will enhance the EPRI database and resulting correlations while the l 7 NDD intersections will supplement the bobbin and RPC detectability data. I 3.2 Crack Morphology Inferred from Inspection Data Comparison of typical MRPC pseudo-isometric graphics (C-scans) for some of TSP indications which were confirmed shows that the Braidwood-l TSP degradation is enveloped by examples ! from other plants and that the condition represented by the C-scans is quite consistent with l ODSCC. Figures 7-1 to 7-6 in Section 7 illustrate the distributions of axial indications, all l confined within the edges of the support plates; the distributions of bobbin indications with l elevation and voltage are similar to that found in plants with axial indications verified by previous investigations to be ODSCC by metallographic studies of pulled tubes. 3-1 l l l
The intersections pulled during the EOC-4 inspection which exhibited EC indications were R37C34-3H and SH and R16C42-3H from SG D, followed by R27C43-3H and R42C44-3H and SH, both from SG A; these MRPC indications are shown in Figures 7-42 to 7-47 and are typical of the variety of TSP ODSCC in Braidwood-l confirmed bobbin indications from 1.04 volts to 10.4 volts. Comparable C-scan results from Plant R and Plant S, both with SG's of similar design to the Braidwood-l SGs, shown in Figures 3-1 to 3-5, confirm the appropriateness of the judgment that all of these indications represent TSP ODSCC within the definition relevant to the IPC. l I 3-2
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{ l l l 4.0 ACCIDENT CONSIDERATIONS .; i 4.1 General Considerations for Accident Condition Analyses ; ) The approach being applied to demonstrate tube integrity at Braidwood-l is based on applying 1- SLB analyses demonstrating limited TSP displacement to reduce the likelihood of a tube burst , in a SLB event to negligible levels. In addition, it is demonstrated that the SLB leak rate, ; even under the conservative assumption ofleak rates for free span indications, is within , acceptable limits. The allowable limit on the SLB leak rate is developed in Section 4.8. Section 4.2 develops the SLB thermal hydraulic loads on the TSPs which are used in the structural analyses of Sections 4.3 to 4.5 to obtain TSP displacements. At this time, Model , D4 S/G loads are available for an SLB at normal operating conditions and for a very ' conservative SLB at hot standby conditions. The hot standby loads include conservatisms based on low water levels (at level of the top TSP) and include a simultaneous feedwater transient. He potential level of conservatism in the Model D4 hot standby loads is demonstrated by comparing the loads with those obtained from a Model D3 S/G analysis with ! normal water level and no feedwater transient. Both SLB analyses, at normal operating , conditions and at conservative hot standby conditions, for TSP displacements developed in j this section are applied in Section 8 to develop tube burst marg; ins. He TSP displacements i are calculated relative to the tube location at the start of the trusient, as discussed in ! Section 4.5. Section 4.4 includes an assessment of the structural integrity of the TSPs and ! their supports (bar, wedge welds). Section 4.6 develops the frequencies of occurrence for an ! SLB at Braidwood l at both normal operating and hot standby (Mode 3) conditions. It is l shown that the frequency of an SLB at hot standby conditions, for which the TSP l displacements are higher, is significantly lower than that for an SLB at normal operating ) conditions. l For a postulated accident condition combining a LOCA simuhaneously with a SSE, it is possible to have some tubes near TSP wedges deformed by the resulting loading condition. l Due to the potential for secondary to primary leakage in the ccimbined LOCA plus SSE, the i tubes subject to significant tube deformation near the wedges are excluded from application of ! the IPC repair limits. The analyses describing this consideration are described in Section 4.7. t Some of the analyses described in this section use the Westinghouse labeling system for numbering TSPs which differs from that applied at Braidwood 1. The following relates the l Westinghouse and Braidwood-l nomenclatures for hot leg TSP identification: i l 4-1 I
1 l Westinchouse TSP Braidwood-l TSP A 1 C 3 F 5 J 7 L 8 M 9 N 10 P 11 TSP 1 is the Flow Distribution Baffle (FDB). The FDB has large tube to plate clearances (nominal [ ]' diameter) in the central region of the plate and radialized holes (nominal [ ]* width) in the outer region. No indications have been found at the FDB in the Braidwood-l SGs. For comparison, the Model D3 SG, for which indications have been found at the FDB, has a nominal hole diameter of [ J'. 4.2 Thermal Hydraulic Loads on TSP in a SLB Event 4.2.1 Introduction A postulated steam line break (SLB) event results in blowdown of steam and water. The fluid blowdown leads to depressurization of the secondary side fluid. Pressure drop develops and exerts hydraulic loads on the tube support plate (TSP) or flow baffle. These hydraulic loads were determined for the Model D4 and D3 steam generator using the TRANFLO Code. This code is a network flow based code that can model the thermal and hydraulic characteristics of fluid through the steam generator intemals. TRANFLO code predicts the transient flow rate, pressures and pressure drops. The hydraulic loads vary with initial conditions and boundary conditions of the SLB event. The significant initial conditions are mode of operation and water level. The important boundary conditions are those associated with feedwater nozzle and steam nozzle; these include the size and location of break, and flow rate through the feedwater nozzle during the event. The most likely initial conditions are of full power operation with a normal water level. When fluid moves in the tube bundle, water will exert a higher pressure drop across the TSP when compared to steam. Hot standby at zero power provides a solid water pool in the tube bundle while power operation generates a steam and water mixture. Thus, hot standby would be conservative in estimating the hydraulic loads on the TSPs, although the most likely mode of operation is power operation if a SLB event occurred. Previous studies confirmed that the 4-2 l l
i l l l l l hot standby yields the largest hydraulic loads when compared to full or partial power operation. Once a SLB event begins, it triggers a rapid depressurization, which leads to water flashing across the water level. The rapid water flashing generates water motion, and the closer the TSP to the water level the higher the flow rate, and thus the larger the pressure drop. Previous parametric evaluations indicate that a lower water level tends to yield higher hydraulic loads on the tube support plates or baffles. It would be ideal to calculate the hydraulic loads on the TSPs of the Model D4 steam generator under the no load, hot standby conditions. Although there are currently no such calculations, there are other calculations of Model D3 and D4 for developing conservative, , bounding loads for the Model D4. This section presents such a task. These bounding loads for the Model D4 and the more applicable Model D3 loads at hot standby with normal water level. 4.2.2 Hydraulic Imads of Model D3 under No Load, Hot Standby with Normal Water Level In 1993, a TRANFLO calculation of hydraulic loads on the TSP under a SLB event was made for a Model D3 steam generator. The calculation considers the initial conditions of zero load, hot standby and a water level at about normal setting. The following describes the calculation model. The Model D3 steam generator maintains a normal water level of [ ]' above the top of the tubesheet during no load, hot standby. The computational model considers a water level of [ ]' above the top of the tubesheet. Use of the no load, hot standby and a water level of [ J' is thus conservative in estimating the pressure loads to tube support plates. Water and steam temperature is initially at 557'F, and primary coolant pressure is at 2350 psia, and secondary side steam pressure is at 1106 psia, and feedwater temperature at 75'F. A network of nodes and connectors was created to represent the secondary side fluid, tube metal heat transfer and primary coolant. Figures 4-1 and 4-2 show the nodal layout of the secondary side of the Model D3 steam generator. Figures 4-3 and 4-4 present the nodal network of the secondary fluid, primary fluid and tube metal. In the tube bundle area, the space between support plates or baffles forms a fluid node, and a flow connector links the adjacent nodes. Pressure drops through support plates or baffles are calculated by the code for each flow connector, which represent a plate or baffle. Blowdown flow induces fluid flow in the secondary side, and thus pressure loads to various TSPs and baffle plates. Figures 4-5 through 4-7 show pressure loads through TSPs and baffle 4-3
plates outside the preheater. The peak of pressure loads across TSP or baffle plates develops within one second, and it then drops to a small value or becomes a quasi-steady state. The flow splits take place in the lower tube bundle; it occurs at about TSP L (see Figure 4-1). Plates A, C and G experience downward flow because the fluid leaves in a downward direction from the tube bundle up into the downcomer. Plates above TSP L experiences upward flow as the fluid leaves in the upward direction through the tube bundle. Maximum loads occur at TSPs A, B and T; about [ ]' at the peak for TSP B on the cold leg, [ ]' for TSP A on the hot leg, and [ ]* for TSP T (i.e., the uppermost TSP). 4.2.3 Hydraulic Loads of Model D4 under Full Power with Normal Water Level Although there are differences in the preheater design between the Model D3 and D4 steam generator, it is judged that there would be no significant differences in the hydraulic loads on the TSPs outside the preheater. It would be ideal to have a TRANFLO calculation for the Model D4 steam generator with initial conditions and boundary conditions like Case 1 for the Model D3. However, no such run is currently available. Calculations are available for , hydraulic loads on the TSPs for the Model D4 steam generator under full power operation j with a normal water level when a SLB begins. Figure 4-8 illc.strates the nodal layout of the secondary side of the Model D4 steam generator, ! which is similar to Figure 4-1 for the Model D3. The calculation was made for design l analyses in the 1970's. Table 4-1 lists the initial and boundary conditions for three cases for l which SLB loads are available; Case 3 will be discussed later. l Results of Case 2 are presented in Figures 4-9 through 4-11. As discussed earlier, hydraulic loads for a steam and water mixture in the tube bundle are less than a solid water pool. Therefore, hydraulic loads of Case 2 for the Model D4 is less than those of Case 1 for the Model D3. When a SLB event initiates from a power operation, the blowdown flow path is essentially in the upward direction from the tubesheet towards the riser barrels. Therefore, hydraulic loads tend to be higher at the upper TSPs, as shown in the above figures. Since the event begins from full power operation, the steam content increases with the bundle height. The uppermost TSP is thus lower in water content, and the resulting hydraulic load is less than the N plate below it. In addition, the highest loads occurs at the TSP L on the hot leg because the flow area is half of a whole TSP and the majority of flow is passing through the l hot leg side. 1 Compared to Case 1 for the Model D3, which experiences flow splits, loads of Case 2 for l Model D4 are less even under the situation of no flow splits. The reason for this is because of its relatively mild initial conditions. l 4-4
4.2.4 Hydraulic Loads of Model D4 under No Load, Hot Standby with a Water Level at the Uppermost TSP and an Excessive Feedwater Flow Transient The TRANFLO computational model for this case is identical to Case 2 except for its initial and boundary conditions. This calculation of Case 3 uses extremes of both initial and boundary conditions. No load at hot standby is already conservative compared to a most likely mode of full power operation; it considers a water level at the uppermost TSP, which is by itself a very rare transient. In addition, it imposes an excessive feedwater flow transient. As discussed already, a water level at the uppermost TSP generates higher hydraulic loads than a normal water level. An excessive feedwater flow introduces more solid water into the tube bundle, which provides additional source of water for flashing action to trigger more water motion. Figures 4-1,2 through 4-14 presents hydraulic loads on various TSPs. Like Case 1, flow splits take place for Case 3 since both cases initiate from a no load, hot standby condition. However, Case 3 yields much higher loads than case I because of severe initial and boundary conditions discussed above. 4.2.5 Summary Table 4-2 summarizes the key parameters regarding the loads. As far as the maximum peak load is concerned Case 2 for Model D4 yields slightly higher loads than Case 1 for Model D3. This is because the flow area for the plate with maximum load is half of the whole plate only, and there is no flow split. The lower TSPs of Case 2 experience hydraulic loads much less than those of Case 1, because there is almost no downward flow split for Case 2. Peak loads of Case 3 are more than twice those of Case 2. Use ofloads of Case 3 is conservative. It is believed that loads for Model D4 would be about the same as those of Case 1 for Model D3, if the same initial and boundary conditions are used in the computational model. 4.3 Structural Modeling for SLB TSP Displacement Analyses This section summarizes the structural modeling of the Model D4 tube bundle region. A finite element model of the hot leg region of the tube bundle is prepared, and corresponding mass and stiffness matrices are generated. The mass and stiffness matrices are then used in a subsequent dynamic analysis to determine TSP displacements under SLB loads. Structural 4-5
members included in the model include all TSPs, the tierods and spacers.' Since the present analysis considers only the response of the hot leg to the SLB loading, the finite element model includes 90* of the tube bundle. 4.3.1 Material Properties A summary of component materials is contained in Table 4-3, with the corresponding material properties summarized in Tables 4-4 through 4-6. The properties are taken from the 1971 edition (through summer 1972 addenda) of the ASME Code, which is the applicable code edition for Braidwood Unit 1. Since temperature dependent properties cannot be used in substructures, properties for the finite element model correspond to the values at 550*F. The material properties for the tube support plates are modified to account for the tube penetrations and flow holes. The density of the TSPs is also modified to account for the added mass of the secondary side fluid. 4.3.2 TSP Support System The support system for the TSPs is a combination of several support mechanisms. A schematic of the tube bundle region is shown in Figure 4-15, with each of the plates itientified. [ P
' For the analysis of the Model D3 steam generators under SLB loads, the finite element model also included the shell, wrapper, partition plate, and channel head. Except for the tubesheet, these structures were included to account for support locations for the TSPs and baffle plates. However, compared to the stiffness of the TSPs, bafIle plates, and tierods, these structures are essentially infinitely stiff and have insignificant displacements (<0.010) under SLB loads. Therefore, it is acceptable to treat these structures as points of rigid support for the plates, and not include them explicitly in the model.
Regarding the tubesheet, although not considered explicitly in the finite element model, tubesheet i displacements are considered in the analysis. Due to similarities in geometry of the tubesheet, shell, and channel head, displacements are scaled from the Model D3 analysis. The tubesheet displacements are quite small relative to the TSP displacements, and scaling of Model D3 displacements is an acceptable approximation. Further discussion of the tubesheet displacements
- is provided in Section 4.4.
l < The Model D3 analysis also considered the non-linear interaction between tubes and TSP due to l TSP rotation. The present analysis has not incorporated this effect, primarily due to the limited time l available to develop the system model. This effect may be considered in subsequent evaluations to limit plate displacements. 4-6 L-_____________________________
I
\
l i l'. The lack of a rigid link between the spacers and TSPs for the outer tierods / spacers results in i j a non-linear dynamic system. However, the nature of the SLB transient results in an j l essentially linear system response. During installation a small positive preload is introduced i { into the tierod/ spacer system. As shown in Section 4.2, the plates are subject either to an I ( upward or downward pressure loading, with the exception being Plate J, which sees a both a significant upward and downward loading. Thus, the response is essentially linear either ; upward or downward. The tierods/ spacers have a different stiffness characteristic for upward ! and downward loads. The'se differences have been incorporated into the model. For Plate J, the weaker of the two stiffnesses has been incorporated to provide a conservative response. i I
]'
I l' 4-7 in m is
The various support locatio ts for the plates are shown in Figures 4-16 through 4-24. Figure 4-16 shows the locations of the tierods and spacers. Plate / wrapper support locations are shown in Figures 4-17 through 4-24. The finite element model representation of the plates ed tieroMpacers is shown in Figure 4-25. 4.3.3 Revised Material Properties As noted earlier, the material properties for the tubesheet and tube support plates are modified to accoGnt for the tube penetrations, flow holes, and various cutouts. The properties that must be modified are Young's modulus, Poisson's ratio, and the material density. The density must be additionally modified to account for the added mass of the secondary side fluid. In calculating revised values for Young's modulus and Poisson's ratio, separate formulations are used for plates with and without flow holes. Due to square penetration pattems, different properties exist in the pitch and diagonal directions. The first step is to establish equivalent parameters for Young's modulus and Poisson's ratio in the pitch and diagonal directions (E,*/E, E,*/E, v/, y,*), respectively. The equivalent Young's modulus for the overall plate is taken as the average of the pitch and diagonal directions. The next step in the process is to determine an equivalent value for the sherr modulus, G'/G, for the plate. This is done in a similar manner as for Young's modulus, starting with values in the pitch and diagonal directions, and then taking an average of the two values. The final equivalent value for Poisson's ratio is determined from the relationship between Young's modulus and the shear modulus. A summary of the revised values for Young's modulus and Poisson's ratio is provided in Table 4-7. There are two aspects to revising the plate density. The first is based on a ratio of solid area to the modeled area. The second aspect corresponds to the plate moving through the secondary side fluid, displacing that fluid, and creating an "added mass" effect. The added hydrodynamic mass is a direct function of the fluid density. Because the dynamic analysis cannot account for the change in fluid density with time, the analysis uses the average density value for the duration of the transient. Results of the calcu!stions to determine effective plate densities are summarized in Table 4-8. This table provides s summary of the actual (structural) and modeled plate areas, the metal and added fluid masses, and the final effectwe plate densities. The fluid densities correspond to SLB events initiating from hot shutdown conditions (as opposed to full power operrtion). Calculations were also performed for densities corresponding to full power operation. The change in effective plate densities did not have a significant effect on the dynamic response of the plates. 4-8
4.3.4 Dynamic Degrees of Freedom In setting up the dynamic substructures, it is necessary to define the dynamic fegrees of freedom. In order to define dynamic degrees of freedom for the TSPs, twc sets of modal calculations are performed for each of the plates. The first set of calculations determine plate mode shapes and frequencies using a large number of degrees of freedom (approximately 120 per plate). The second set of calculations involves repeating the modal analysis, using a significantly reduced set of degrees of freedom (DOF). The reduced DOF are selected to predict all frequencies for a given plate below 50 hertz to within 10% of the frequencies for the large set of DOF. A frequency of 50 hertz was selected as a cutoff, as it is judged that higher frequencies will have a small energy content compared to the lower frequencies. This can be confirmed by noting that the highest frequency content in the first one and a half seconds of the pressure drop time-history input loadings is typically less than 10 hertz. For each of the modal runs, in addition to symmetry boundary conditions along the "Y-axis", and vertical restraint at vertical bar locations, all the plates are assumed to be constrained vertically at tierod/ spacer locations. A sample set of mode shape plots is provided for Plate A. Mode shape plots for the full set of DOF are shown in Figures 4-26 through 4-28, while mode shapes for the reduced set of DOF are shown in Figures 4-29 through 4-31. A comparison of the natural frequencies for the full and reduced sets of DOF for the plates is provided in Table 4-9. Based on the tabular summary, the reduced set of DOF are concluded to provide a good approximation of the plate response. Note that for Plate P, the frequency for Modes 3 and 5 for the reduced set of DOF slightly exceeds the 10% objective for matching frequencies. These variations are not considered to be significant, and the selected DOF are judged to give an acceptable representation of the Plate P response. The reduced set of DOF consists of 8 - 10 DOF for each of the plates. 4.3.5 Displacement Boundary Conditions The displacement boundary conditions for the substructure generation consist primarily of prescribing symmetry conditions along the "Y" axis for each of the components. Vertical constraint is provided where the plates are constrained by the vertical bars welded to the partition plate and wrapper, and to the tierods at there bottom end. For the TSPs, rotations normal to the plate surface are also constrained, as required by the stiffness representation for the plate elements. 4-9 l
4.3.6 Application of Pressure Loading The SLB pressure loads act on each of the TSPs. To accommodate this, load vectors are l prescribed for each of the plates using a reference load of 1 psi. The reference loads are i scaled during the dynamic analysis to the actual time-history (transient) loading conditions, as defined in Section 4.2. The transient pressures summarized in Section 4.2 are relative to the control volume for the thermal hydraulic analysis. The area over which the hydraulic pressure acts corresponds to the area inside the wrapper minus the tube area. These pressures must be scaled based on a ratio of the plate are:in the structural model to the control volume area in the hydraulic model. A summary of the transient pressure drops is given in Section 4.2. These pressure drops were modified as discussed above and applied to the structural model for the dynamic analysis. 4.4 Results of SLB TSP Displacement Analyses As discussed in Section 4.2, several sets of SLB loads were considered in performing this analysis. In addition to the system analysis, some preliminary single-plate evaluations were performed to estimate the plate response to the applied loadings. Calculations were also performed using the single plate models to estimate the effects of expanding tubes at various locations in the tube bundle to limit plate motions. The results for each set of calculations is summarized within this section of the report. An overall summary of the limiting displacements for each of the plates for the various cases considered is provided in Table 4-10. The displacements in this table are relative to the initial starting plate positions. The magnitude of the tubesheet displacements and there affect i on these results is discussed below. The first two sets of results in Table 4-10 are for the most limiting SLB loading (SLB with a simultaneous Feedwater Transient) using the single plate models, with and without tube expansion. These resuits show that tube expansion significantly reduces plate displacement for all of the plates. The third set of results is again for the limiting SLB transient for the tull system model. Comparing these results to the single plate models shows that the single plate models provide a good indication of the relative plate motions, but that plate interaction does result in an increase in the plate responses, more for some plates than others. Comparing the results for the three SLB sets ofloads using the system model shows that for the limiting SLB loads, Plates A (lH), C (3H), and J (7H) experience displacements greater 4 10
than 0.350 inch. For a transient initiating from nermal operation that only Plate J (7H) sees any significant motions, and for the Model D3 SLB loads case, only Plates A (IH) and C (3H) show any significant response. Based on the single plate response to the limiting load with expanded tubes, it is concluded that expansion of a limited number of tubes would be effective in reducing the response of each of these plates to very low levels. The limiting plate displacements in all cases are limited to a small region of the plate at their outer edge near the tube lane, where the distance between vertical supports is greatest. Displaced geometry plots for Plates A (lH), C (3H), and J (7H) for the limiting set of SLB loads are shown in Figures 4-32 through 4-35. The consistent displacement pattern is apparent for the three plates. Displacement time histories for each of the plates for the limiting transient loads are provided in Figures 4-36 and 4-37. The bottom four plates are shown in Figure 4-36 and the upper four plates in Figure 4-37. As discussed previously, tubesheet displacements are not significant and were scaled from the Model D3 analysis. The geometry of the tubesheet and supporting structures for the two designs is nearly identical. A summary of key dimensions for the two models of steam generators is provided in Table 4-11. Displacement results for the tubesheet from the Model D3 analysis as a function of distance from plate center for several transient times are summarized in Table 4-12. At the bottom of this table a summary of the tubesheet displacements relative to time zero are presented. The relative displacements are shown to be quite small relative to the plate displacements. This is especially true at the outer edge of the . tubesheet where the plate displacements are a maximum. Since the dynamic analysis is based on elastic response, calculations were performed to assure that the tierods, a significant support element for the plates remain elastic throughout the l transient. The dynamics analysis results establish that the stayrods do, in fact, remain elastic l throughout the transient. [ ] i l J' In both instances, these elongations are l well below the yield point for the stayrods. Also relevant in assessing the approptiateness of the elastic solution, are the stresses in the pla:es. Thus, in conjunction with the displacement results from the dynamic analysis, stresses are calculated for the hot leg plates at the times corresponding to the maximum plate displacements. The stresses are calculated by extracting displacements from the dynamic analysis for each plate degree of freedom, and then applying those displacements to the finite element model. The finite element code then back-calculates the displacements and stresses i for the overall plate model. j 1 4 - 11
l l In order to extract the appropriate displacements from the tape created by the dynamic analysis, a special purpose computer program is used. This program extracts the displacements for a given plate at specific transient times and writes the resulting nodal displacements to output in a form that can be input directly to the WECAN program as displacement boundary conditions. Using this program, displacement boundary conditions are extracted at the times of maximum relative displacement for Places A (IH), C (3H), and J (7H) at the critical times for the SLB + Excess Feedwater transient and for Plates A (IH) and C (3H) for the Model D3 transient. Note that for Plate J for the SLB + Excess Feedwater transient, stresses are calculated for the times corresponding to both the maximum upward displacement and also for the maximum downward displacement. These are the transients and plates that are judged to be limiting based on the plate displacement results. Additional boundary conditions corresponding to lines of symmetry and appropriate rotational constraints are also applied to the model. The finite element results give a set of displacement and stress results for the overall plate. The resulting plate stresses, however, correspond to the effective Young's modulus, and must be multiplied by the inverse ratio of effective-to-actual Young's modulus to get the correct plate stresses. The stress multiplication is performed by another special purpose computer program, SRATIO. In order to interpret the stress results, stress contour plots for the maximum and minimum stress intensities have been made for each plate. The limiting stresses for each of the plates occur for the SLB + Excess Feedwater transient. Plots showing the maximum and minimum stress intensities for Plates A(lH), C(3H), and J(7H) are shown in Figures 4-38 to 4-45, respectively. These plots show the distribution of stress throughout the plate. As expected, the maximum stresses occur near the locations of vertical support, the tierod / spacers and vertical bars. The ASME Code minimum yield strength for the TSP material is 23.4 ksi. Except for one very local area for Plate J corresponding to the upward loading on the plate (Figure 4-42), the stresses are elastic throughout the plate. Recalling that the present analysis does not account for either the wedge support for Plate J at the 10' location, or the potential for tube / plate interaction due to plate rotation, the stresses in Figures 4-42 and 4-43 for Plate J are judged to be conservative. Thus, it is judged that the effective plate stresses will be judged to be elastic for all transient cases. The plate stresses cannot be compared directly to the material yield strength, as these stresses correspond to an equivalent solid plate. In order to arrive at the plate ligament stresses, additional detailed stress analysis of the plates is required. Such an analysis is outside the scope of this program. The equivalent plate stresses do provide a general guideline as to those areas of the plate that are most limiting from a stress viewpoint. The plate stresses are meaningful in that they indicate that the stresses are generally low throughout the plate, and l that the elastic analysis is a good approximation of the transient plate response. 4 - 12
Calculations have also been performed to determine the stresses in the welds between the vertical bars and the partition plate and wrapper. The loads at the various support points are extracted from the static WECAN runs in the form of reaction forces at the times of maximum plate deflection. Loads have been extracted for the limiting plates (based on plate motions) for each of the SLB load cases, and for Plate P, which experiences the highest pressure loads, for the SLB + Excess Feedwater transient. [
]* The corresponding stress intensity is twice the shear stress.
A summary of the reaction forces and corresponding stresses for each of the bar locations for the locations considered is provided in Table 4-13. The results show all of the stresses to be low (<2 ksi) for a faulted event. The allowable stress for the welds is based on 2.4S, x 1.5 x 0.35 (for fillet welds with visual examination) for carbon steel. S, at 550'F is 15.5 ksi. The resulting allowable stress intensity is 19.53 ksi, and the weld stresses are acceptable. Overall, it is concluded that the elastic analysis provides a good approximation of the dynamic response of the TSPs to the applied loading. 4.5 SLB Displacements By Tube Location In order to establish probabilities for tube burst as a result of relative plate / tube movement, calculations are performed to determine how many tubes are associated with a given displacement magnitude for a given plate. The plate displacements are categorized into groups, starting at 0.35 inch, and increasing in 0.05 inch increments to a maximura displacement > 0.80 inch. It is the relative plate / tube displacement that is of interest, with the tube and plate positions at the start of the SLB transient def'med as the reference position. At hot standby, the TSP positions relative to cracks inside the TSP are essentially the same as at cold shutdown. Every known S/G cold condition inspection shows ODSCC cracks within the non-dented TSP with a trend towards being centered within the TSP. Therefore, the cold condition TSP location relative to tha tubes is essentially the same as for the full power condition where the cracks formed, which is also the position during hot shutdown. 'Ihese inspections indicate that there is little relative movement between the tubes and plates throughout the operating cycle. Thus, this analysis calculates relative tube / TSP motions based on the tube / plate positions at the initiation of the SLB transient. ! I i 4 - 13
l I The algorithm for calculating the relative displacements is as follows: AD = (D, . y - D, . o ),w - (D, . y - D, . o )toww, , where Dr = Plate Displacement D2,ww, = Tubesheet Displacement T = Time of maximum displacement from dynamic analysis In order to calculate the relative displacements across the full plate, displacement (stress) solutions are performed for the limiting plates at the times of maximum displacement. Calculations were performed for each set of transient loads for those plates where the maximum absolute displacement exceeded 0.350 inch. The displacement solutions are performed using the finite element representations for the plates. Displacements for the dynamic degrees of freedom for the limiting plates are extracted at the times ofinterest from a file containing the DOF displacements for the full transient. These displacements are applied to the finite element model as boundary conditions (along with any other appropriate boundary conditions representing symmetry or ground locations), and displacements for the entire plate are then calculated. These results are then combined with the scaled tubesheet displacements, to arrive at a combined relative displacement between the tubes and plates. The combined relative displacements are then superimposed on a tube bundle map, and the results interpolated to arrive at a displacement value for each tube location. A summary of the number of tubes falling into each of the displacement groupings for the limiting plates is provided in Table 4-14. Note that the numbers of tubes in Table 4-14 correspond to the full plate. He number of tubes in each plate quadrant is one-half of the values listed. A summary of the total number of tubes having displacements > 0.35 inch for each of the SLB loads is provided in Table 4-15. Note that at the top of Table 4-14, the limiting displacements as reported in Table 4-10 are repeated, while the number of tubes where the relative plate / tube displacements exceed 0.350 inch are summarized at the bottom of the table. Summarized in Table 4-16 is a comparison of the maximum plate displacement to the plate displacement at the limiting tube location (the tube having the highest displacement), RIC1. ) As can be observed in the displaced geometry plots in Figures 4 4-35, the displacement ; gradients at the corner of the plate are high, so the maximum differential displacement at l RICI is hss than the maximum plate displacement reported in Table 4-15.
)
l l l 4 - 14
i I I 1 l l 4.6 SLB Frequency at Hot Standby and Full Power Conditions , In order to identify the frequency of main steamline break in both the hot standby and full power conditions to support the steamline break tube support plate displacement analysis for Braidwood Unit 1, a review of References 4-1 and 4-2 for the Byron Nuclear Power Station Units 1 and 2 was completed. 4.6.1 Secondary Side Breaks Two main feedline pipe breaks have occurred on Westinghouse designed PWRs. The feedline breaks were downstream of the main feedwater isolation valves (MFWIVs), outside containment. The number of years at criticality calculated for all Westinghouse designed PWRs is 1370 years (Reference 4-1). Using the Bayes theorem, the mean frequency of occurrence may be determined (Reference 4-2) by:
,2r+1 2r where r is the number of failures and t is the time interval. Substituting r = 2 and t = 1370, mean = *M * ' = *b = 1.8E-03l year 2(1370) 1370 Since no secondary side breaks have occurred, other than these two main feedline breaks, the mean of the frequency for this event is 1.8E-03/ year (Reference 4-1).
Based on the plant response to steamline/feedline breaks, this event is split into two initiators: (1) secondary side breaks downstream of the main steam isola': ion valves (MSIVs) or upstream of the MFWIVs and (2) secondary side breaks upstream of the MSIVs or downstream of the MFWIVs. The same frequency is used for both types of steamline/feedline breaks. Hat is, Secondary side breaks upstream of MSIVs or downstream of MFWIVs = 1.8E-03/ year Secondary side breaks downstream of MSIVs or upstream of MFWIVs = 1.8E-03/ year. , l l 4 - 15 < l l
4.6.2 Hot Standby and Full Power Conditions Evaluations A review of the operating histories for Braidwood Unit 1 Cycle 3 and 4 was completed to determine the amount of time spent in Mode 3 versus full power operation. The result of this evaluation is shown in Table 4-17. The frequency of Mode 3 operation is defined as: Days k Mode 3 , 36.1,9,93g Frequency of Mode 3, Days in Cycles 3 & 4 959 Frequency of Mode 1 = 1 -Mode 3 = 0.962 The results of these calculations show a frequency in Mode 3 of 0.038 and frequency of Mode 1 of 0.962. Combining these frequencies with the IPE frequency of secondary side break upstream of the MSIVs gives a frequency of secondary side break upstream of the MSIVs in the Mode 3 condition r.nd in the Mode I condition of: Mode 3 Secondary Side Break = (1.8E-03l year)x 0.038 = 6.8E-0$fyr. Mode 1 Secondary Side Break = (1.8E-03l year) x 0.962 = 1.7E-03fyr. 4.7 Tubes Subject to Deformation in a SSE + LOCA Event This section deals with accident condition loadings in terms of their effects on tube defor'". ion. The most limiting accident conditions relative to these concems are seismic (SSE) plus loss of coolant accident (LOCA). For the combined SSE + LOCA loading condition, the potential exists for yielding of the tube support plate in the vicinity of the l wedge groups, accompanied by deformation of tubes and subsequent loss of flow area and a postulated in-leakage. Tube deformation alone, although it impacts the steam generator cooling capability following a LOCA, is small and the increase in PCT is acceptable. Consequent in-leakage, however, may occur if axial cracks are present and propagate throughwall as tube deformation occurs. This deformation may also lead to opening of pre-existing tight through wall cracks, resulting in primary to secondary leakage during the SSE + LOCA event, with consequent in-leakage following the event. In-leakage is a potential I concern, as a small amount of leakage may cause an unacceptable increase in the core PCT. Thus, any tubes that are defined to be potentially susceptible to deformation under SSE + LOCA loads are excluded from consideration under the IPC. 4 - 16
I I i In the absence of plant specific LOCA and SSE loads for Braidwood Unit 1, a conservative upper bound estimate was made of the maximum number of tubes that would be affected at each wedge location. Using the results of an analysis for another plant having the same model steam generators, a conservative upper bound of [ ]* per wedge group was established for the Braidwood Unit I steam generators. A summary of the applicable tubes l I for each of the wedge locations is provided in accompanymg tables and figures. i Braidwood Unit 1 is a four-loop plant. As such, there are two loops with "left-hand" steam generators and two loops with "right-hand" steam generators. These designations refer to the orientation of the nozzles and manways on the channel head. For the purpose of this analysis, .
"left-hand" units are defined to be those loops where the primary fluid flows from the reactor ;
to the steam generator to the pump and back to the reactor vessel in a counter-clockwise disection. Conversely, for the "right-hand" units, the flow is in the clockwise direction. The left- versus right-hand designation affects the location of the nozzles and manways, and the manner in which the columns are numbered for tube identification purposes. Reference configurations used in identifying wedge locations are shown in Figures 4-46 and 4-47 for the left-hand and right-hand units, respectively. As shown in the figures, for left-hand units, the nozzle and tube column 1 are located at 0*, while for right-hand units they are located at 180*. l Tabular summaries of the tubes that are potentially susceptible to collapse and subsequent in-leakage are summarized in Tables 4-18 to 4-23 for the left-hand units, and in Tables 4-24 . to 4-29 for the right-hand units. For the Braidwood Unit I steam generators there is a flow , distribution baffle, seven tube support plates, and three baffle plates. The plate configuration is shown in Figure 4-15. Plate A corresponds to the flow distribution baffle, Plates B, E, and ; H are the flow baffles, and Plates C/D, F/G, J/K, and L, M, N, and P are the tube support plates. Prior analysis for steam generators of similar design show the flow distribution baffle to not impact the wrapper /shell under seismic loads. Thus, it is judged that there will not be any , tubes at the flow distribution baffle location that are potentially susceptible to collapse under i combined LOCA+SSE. It will be noted that separate summary tables are provided for the lower TSPs, B-K (except E and H where a table common to both is used), and a single table for the upper TSPs L-P. This is due to the orientation of wedge groups for each of the TSP. For the lower TSPs, the wedge groups are rotated in some instances relative to the other TSPs, while for the upper TSPs, the wedge groups have the same angular orientation. Maps showing the location of the potentially susceptible tubes are provided in Figures 4-48 to 4-57. The maps provide row and column designations relative to the left-hand units. Column numbers for the right-hand units are shown in brackets. Identification of the potentially susceptible tubes is based on crush test results for both Model D and Series 51 steam 4 - 17
r generators. For both sets of tests, however, wedge / tube configurations identical to those for the Braidwood Unit I steam generators were not tested. As such, it was not possible to iden:ify exactly the [ ]' that might be limiting at each wedge group. Thus, fue to the uncertainties involved, there are generally [ ]' identified at each wedge group as being limiting. Finally, Table 4-30 provides an index of the applicable tables and figures identifying the potentially susceptible tubes for each TSP. 4.8 Allowable SLB Leakage Limit An evaluation has been performed to determine the maximum permissible steam generator primary to secondary leak rate during a steam line break for the Braidwood Nuclear Plant Unit 1. The evaluation considered both pre-accident and accident initiated iodine spikes. The results of the evaluation show that the accident initiated spike yields the limiting leak rate. This case was based on a 30 rem thyroid dose at the site boundary and initial primary and secondary coolant iodine activity levels of 1 pCi/gm and 0.1 pCi/gm I-131, respectively. A leak rate of 9.1 gpm was determined to be the upper limit for allowable primary to secondary leakage in the SG in the faulted loop. The SG in each of the three intact loops was assumed to leak at a rate of 150 gpd (approximately 0.1 gpm), the proposed Technical Specification LCO for implementation of IPC. The allowable leak rate will increase in inverse proportion to a reduction in the primary and secondary equilibrium coolant activity. Thirty rem was selected as the thyroid dose acceptance criteria for a steam line break with an assumed accident initiated iodine spike based on the guidance of the Standard Review Plan (NUREG-0800) Section 15.1.5, Appendix A. Only the release ofiodine and the resulting thyroid dose was considered in the leak rate determination. Whole-body doses due to noble gas immersion have been determined, in other evaluations, to be less limiting than the corresponding thyroid doses. The salient assumptions follow. m Initial primary coolant iodine activity - 1 pCi/gm DE I 131 The calculation of primary coolant DE I-131 is based on a mixture of 5 iodine nuclides (I-131 through I-135) and the dose conversion factors of TID-14844, consistent with the Braidwood Technical Specification definition of DE I-131. 4 - 18
l l i l m Initial secondary coolant iodine activity - 0.1 pCi/gm I-131 i The calculation of secondary coolant iodine activity is based on actual I-131 activity rather than DE I-131. Although, this is somewhat more conservative than the Technical Specification LCO which is based on DE I-131, secondary coolant activity still accounts for less than 6% (1.75 rem) of the allowable offsite dose, a Steam released to the environment (0 to 2 hours) from 3 SGs in the intact loops,416,573 lb from the affected SG,96,000 lb (the entire initial SG water mass) m Iodine partition coefficients for primary-secondary leakage SGs in intact loops,1.0 (leakage is assumed to be above the mixture level) SG in faulted loop,1.0 (SG is assumed to steam dry) h Iodine partition coefficients for activity release due to steaming of SG water SGs in intact loops, 0.1 SG in faulted loop,1.0 (SG is assumed to steam dry) e Atmospheric dispersion factor (SB 0 to 2 hours),7.70E-4 sec/m' s Thyroid dose conversion factors (I-131 through I-135) utilized in offsite dose calculation, ICRP-30 The activity released to the environment due to a main steam line break can be separated into two distinct releases: the release of the iodine activity that has been established in the secondary coolant prior to the accident and the release of the primary coolant iodine activity that is transferred by tube leakage during the accident. Based on the assumptions stated previously, the release of the activity initially contained in the secondary coolant (4 SGs) results in a site boundary thyroid dose of approximately 1.75 rem. The dose contribution from 1 gpm of primary-to-secondaiy leakage (4 SGs) is approximately 3 rem. With the thyroid dose limit of 30 rem and with 1.75 rem from the initial activity contained in the secondary coolant, the total allowable primary-to-secondary leak rate is (30 rem - 1.75)/3 rem per gpm, or 9.4 gpm. Allowing 0.1 gpm per each of the 3 intact SGs leaves (9.4 - 0.3) or 9.1 gpm for the SG on the faulted loop. 4 - 19
i I l 4.9 Acceptability of the Use of TRANFLO Code 4.9.1 Background in the early 1970's, there was a need to accurately predict the steam generator behavior under transient conditions, such as a steam line break (SLB) event; a transient can develop thermal hydraulic loads on the intemal components and shell of the steam generator. Structural analyses are required to analyze the adequacy of the individual components and the whole steam generator under various thermal and hydraulic loads. With the assistance of MPR Associates, Westinghouse developed and verified the TRANFLO computer code to conservatively model the thermal and hydraulic conditions within the steam generator under transient conditions. The secondary side of the steam generator involves water boiling under high pressure during normal operating conditions. During a transient such as a SLB event, it may be subject to vapor generation due to rapid depressurization. Therefore, analysis methods have to recognize this characteristic of two-phase fluid behavior. In the early stage of the computer code development and technology of two phase flow, a homogeneous model was used. For current analyses, a more accurate slip flow model is used which takes into consideration the relative velocity between the liquid and vapor phases. Development of the TRANFLO code reflects this general trend of the two-phase flow modeling. The first version of TRANFLO was a homogeneous model, and it was later updated to a drift flux model to simulate the effect of two-phase slip. Since the original issue of the code, Westinghouse has made several enhancements to the code and has performed the appropriate verification and validation of these changes. These changes do not significantly affect the calculated pressure drops across the steam generator tube support plates. 4.9.2 Acceptability of Application of TRANFLO The original version of the TRANFLO code (Reference 4-3) was reviewed and approved by the NRC in Reference 4-4. TRANFLO was used as part of the Westinghouse mass and energy release / containment analysis methodology. Specifically, the code was used to predict steam generator (SG) secondary side behavior following a spectrum of steam line breaks. Its output was the prediction of the quality of the steam at the break as a function of time. The quality is calculated as a function of power level, as well as break size. In order to assure that the TRANFLO code evaluates a conservatively high exit quality, Reference 4-4 states that the calculational sequences were reviewed for the determination of " conditions prior to entering into the separation stages. The calculated rate, quality and energy content of the two-phase mixture entering the separation stages must be evaluated conservatively". This review was completed and found to be acceptable, as the NRC staff concludes in 4 - 20 t 1
Reference 4-4 that the TRANFLO code is an acceptable code for calculating mass and energy release data following a postulated MSLB. Therefore, it is concluded that the TRANFLO model is appropriate for predicting SG behavior (including tube bundle region) under the range of SLB conditions. For the current application, TRANFLO is used in conjunction with a structural analysis code l to predict TSP movement following the same SLB event. The key data transferred between the transient code and the structural code is the pressure drop across the TSP as a function of time. This pressure drop calculation depends on the fluid conditions in the steam generator and on the adequacy of the loss coefficients along the flow paths. The conditions in the tube i bundle as calculated by TRANFLO have been previously reviewed. Furtherjustification of the adequacy of the pressure drop calculation is discussed in Section 4.9.4. 4.9.3 Different Versions of TRANFLO The original version of the TRANFLO code has been reviewed and approved by the NRC. Westinghouse has continued to update the code with new models that more accurately predict ' steam generator behavior. Four versions of TRANFLO have been used in calculation. The following are descriptions of each of them. The Oricinal Version (Aoril 1974) This is the original homogeneous model, which MPR Associates developed in April 1974. The code predicts mass flow rate, pressure, pressure drop, fluid temperature, steam quality and void fraction. The code document includes results of TRANFLO calculations for a 51 Series steam generator subject to water and steam blowdown due to an SLB event. The document also presents code verification using blowdown test data from pressurized vessels. Westinghouse documented this version in detail in September 1976, including code verification using vessel blowdown data. Sensitivity analyses were also performed and documented to show that the modelling was conservative. This included sensitivities to loss coefficient. The TRANFLO code uses an elemental control volume approach to calculate the thermal-hydraulics of a steam and water system undergoing rapid changes. Fluid conditions may be. subcooled, two-phase or superheated. The code considers fluid flows being one-dimensional. Control volumes simulate the geometrical model, and flow connectors allow mass and energy exchange between control volumes. Each nodal volume has mass and energy that are homogeneous throughout the volume. Flow connectors account for flow and pressure drops. The system model allows flow entering or leaving any control volume. This then allows that 4 - 21
l feedwater flows into a steam generator and steam flows out ofit. The system models also permit a heat source, which then can simulate the tube bundle with hot water flow. l TRANFLO solves for system conditions by satisfying mass, momentum and energy equations ! for all control volumes. It models the effects of two-phase flows on pressure losses. The code allows a variety of heat transfer correlations for the tube bundle. It covers all regimes from forced convection to subcooled liquid through boiling and forced convection to steam. The Drift-Flux Version (November 1980) This version implements a drift-flux model to better simulate relative flow velocity between water and steam. For example, it allows a realistic simulation of counter-current flow of steam and water. It required modification of the mass, momentum and energy equations of the two-phase flow. A capability is provided for monitoring calculated variables for convenient examination of results. TRANFLO Version 1.0 (November 19911 This version accepts transient data of parameters as direct irputs, rather than supplying input subroutines, as used in the drift-flux version. It also improves printouts and plots. This version maintains the drift-flux model, and includes the addition of thermal conductivity of Alloy 690 tubing. TRANFLO Version 2 0 Oanuary 1993) i This version provides an option for two inlets of feedwater flow into the steam generator. It involves minor changes to a subroutine for specifying feedwater flow. This version is used for separate inlets of simultaneous feedwater flow from main and auxiliary feedwater nozzle. 4.9.4 Verification of Loop Pressure Drop Correlations As discussed earlier, an accurate prediction of mass and energy release from the vessel means that the TRANFLO code properly calculates local thermal-hydraulics in various nodes (i.e., elemental control volume and flow connector). It is critical to accurately simulate the pressure drop inside a steam generator that consists of various components, such as the tube bundle with tube support plates, moisture separators, and downcomer. Hydraulic loads on various components depend on accurate pressure drop calculations. Thus, it is important to verify the pressure drop calculations through the circulation loop. The TRANFLO code uses the same pressure drop correlations as the Westinghouse GENF code, which is a performance program. The GENF code predicts one-dimensional steady 4 - 22
state conditions, which include pressure drops along the circulation flow loop. Both laboratory tests and field data validate the accuracy of the GENF code. The GENF code is used extensively for steam generator performance analysis and has been shown to accurately predict operating steam generator conditions. When provided with all geometrical input and operating conditions, GENF calculates the ! steam pressure, steam flow rate, circulation ratio, pressure drops, and other thermal-hydraulic data. The circulation ratio is a ratio of total flow through the tube bundle to feedwater flow. For a dry and saturated steam generator, there exists a hydrostatic head difference between the downcomer and the tube bundle. This head difference serves as the driving head to circulate flow between them (see Figure 4-58). The driving head is constant for given operating specifications, such as power level and water level. The total pressure drop through the circulation loop is equal to the driving head. Pressure drops depend on loss coefficient and flow rate (i.e., velocity). Loss coefficient consists of friction loss and form loss; the majority of the loss is due to the form loss in the steam generator. Since the driving head is constant, a higher loss coefficient means a lower circulation flow rate and a lower circulation ratio. A lower loss coefficient yields a higher circulation ratio. Therefore, an accurate prediction of the circulation ratio depends on an accurate loss coefficient. - Model boiler and field tests are used in qualifying the loss coefficients in the flow loop of the steam generator. For example, the major contributors of the pressure drop are the primary separator and tube support plates. The loss coefficient of the primary separator has been verified usir.g model boilers and field steam generators (Reference 4-5). Similarly, loss coefficients of tube support plates have been developed using test data; Figure 4-59 presents the correlation of the loss coefficient and test data. Figure 4-60 shows a typical comparison between predicted and actual measured circulation ratio. There is good agreement in circulation ratio between the prediction and measurement. l The TRANFLO model uses the same los coefficient correlations as GENF code. This provides assurance in properly calculating the pressure drops throughout the steam generator. 4.9.5 Summary This section presents a summary of the adequacy of the TRANFLO code for its current applications. Blowdown test data of simulated reactor vesseis validate the adequacy of the code in predicting the steam and water blowdown transient. The NRC has accepted the i TRANFLO code in calculating mass and energy release to the containment during a steam generator blowdown due to feed or steam line break. 4 - 23 I
As part of its review, the NRC accepted the code's ability to accurately predict local thermal-hydraulics in die vessel. The calculated pressure agrees well with the measured vessel pressure. Flow through the internals of the steam generator depends on accurate prediction of pressure drops, which relies on the accuracy of the loss coefficients along the flow paths. Test data of pressure drops from model boiler and field steam generators have been applied to verify the correlations for the loss coefficients. Westinghouse has made modifications to the code to better predict steam generator behavior following a SLB event. Westinghouse has performed the verification and validation consistent with the methods approved by the NRC staff for the original version. In conclusion, the TRANFLO code is a verified program for adequately predicting thermal-hydraulic conditions during the blowdown transient of a steam generator due to a feed or steam line break. 4.10 References 4-1. "Quantification of Byron IPE Steamline/Feedline Break Frequency", CN-COA-92-537-R1, Appendix Rl-B, April 1993. 4-2. " Byron IPE Initiating Event Calculations and Notebook - Draft", CN-COA-92-537-RO, December 1993. 4-3. R. E. Land, "TRANFLO Steam Generator Code Description", Westinghouse Nuclear Energy System, WCAP-8821, September 1976. 4-4. Memo from C. O. Thomas to E. P. Rahe, " Proprietary Content Review of SER on WCAP-8821 and WCAP-8822", October 14,1982. 4-5. P. W. Bird and P. J. Prabhu, " Review of Primary Separator Loss Coefficient", WTD-TH-80-010, July 1980. l l l l 4 - 24
Table 4-1 Initial and Boundary Conditions of the TRANFLO Calculation Models for Model D3 and D4 Steam Generator Initial Conditions Boundary Conditions SG Mode of Steam Nozzle Cnc Model Operation Water Level Flow Limiter FeedwaterFlow 1 D3 Hot Standby @ ~ Normal Setting Yes Small 2 D4 Full Power @ Normal Setting Yes Full Flow 3 D4 Hot Standby @ Uppermost TSP Yes Excessive 0 9 4 - 25 1
l l Table 4-2 Peak Pressure Drop at Different Tube Support Plates (Hot Leg Only for Half Plate) ' i SG & Case SG & Case SG & Case Parameter D1:_1 D4_ _2 D4-1 Flow splits within tube bundle Yes No Yes ; TSP with max peak Dp
- Peak Dp @ uppermost TSP Max peak Dp, psi ,
Peak max Dp @ bottom Plate Dp @ Hot Leg Top TSP P i 1 I 4 - 26 I i l t .
1 l l l Table 4-3 { Summary of Component Materials
! Component Material l Tube Support Plate SA-285 Grade C l
Stayrod SA-106 Grade B Spacer SA-106 Grade B , ! Tube Inconel 600 l l 4 - 27 DISK 215 - BRDWD\TBL431 - 04/18/94
Table 4-5 Summary of Material Properties SA-106, Gr. B li TEMPERATURE ! I PROPERTY ICODEEDI 70 200 l 300 l 400 l 500 -l 600 I 700 l Young's Modulus 71 27.90 27.70 27.40 27.00 26 40 25.70 24.80 r l t l CoefficientofThenna! 71 6.07 6.38 6.60 6.82 7.02 7.23 7.44 l Expansion i Density 0.284 0.283 f -- 0.283 0.282 0.281 0.281 0.280 j 7.35 7.33 7.32 7.30 7.28 7.26 7.25 l 1 PROPERTY ! UNITS l l Young's Modulus psi x 1.0E06 i I Coeflicient of Thennal in/m/deg. F x 1.0E 06 Expansion r l Density Ib/m^3
! lb-sec^2/m^4 x 1.0E-4 l
4 - 29 i i DISK 215 - BRDWD\TBl/'2 - 04/19/94 I
l l 1 Table 4-7 ! l Summary of Equivalent Plate Properties j Reference Effective Effective l ! Young's Young's Poisson's ! l Plate Modulus Modulus Ratio A -Inside 32" Radius 2.60SE+07 4.810E+06 0.2466 A - Outside 32" Radius 2.605E407 5.850E+06 0.2654 C. F. J,_L m mM N. P* 2.60SE+07 2 470E+06 OI>445 l
- - These plates have flow holes, resulting in a signincantly reduced value for Young's Modulus 4 - 31 DISK 215 - BRDWD\TBL435 - 04/18/94
Table 4-9 Comparison of Natural Frequencies Full Versus Reduced DOF
.a i
l \ l l \ l 4 - 33 DISK 215 - BRDWDiTBL437 - 04/19/94
i Table 4-11 i Comparison of Component Dimensions Model D3 versus Model D4 Steam Generators 1 i l Dimension I Model D3 i Model D4 l
~ ~
ShellID l a i Shell Thickness ' l [ j ! ! 1
! Channel Head Bowl Radius :
Channel Head T.'ackness I Tubesheet Thickness , Hole Diameter Number Holes - i Tube Pitch .
)
i l l l 1 a b i l l i 1 4 - 35 ! DISK 215 - BRDWDiTBL442 - 04/19/94
Table 4-13 Summary of Vertical Bar Stresses Model D4 Steam Generators i l I i l W W 4 -37 DISE215 BRDWD\TBL444 04/20/94
i Table 4-15 i i Summary of Tubes Having Relative Tube / Plate Displacements That Exceed 0.400 inch ' t a' l r i i i b i h P L 8 i l i l I I h i t t I 5 h f i I r 1
- l mum 6
4 -39 DISK 215 - BRDWDiTBIA52 -04/19/94 {
\
l I i l
-- _ _ . _ . --=.
Table 4-17 Braidwood Unit 1 Mode 3 Durations Hours in Event Offline Date Mode 3 Online Date Online Days Cycle 3 A1R02 N/A 360
- 5/18/91 AIF19 7/16/91 0 7/27/91 60 AIF20 10/9/91 0 10/14/91 74 AIF21 11/6/91 54 11/11/91 24 A1F22 2/5/92 62 2 0/92 86 A1F23 3/21/9 8 3/21/92 43 A1R03 9/1/92 26' N/A 165 Hours in Mode 3 = 510 Online Days = 452 Days in Mode 3 = 21.2 Days in Cycle = 472 Cycle 4 A1R03 N/A 56* 11/3/92 AIM 03 11/20/92 124 11/25/92 18 AIF24 In/93 38 1/14/93 44 A1M04 5/29/93 35 5/30/93 136 A1F25 6/2/93 65 6/7/93 4 AIF26 10/24/93 21 11/11/93 140 A1R04 3/4/94 18' N/A 114 Hours in Mode 3 = 357 Online Days = 456 Days in Mode 3 = 14.9 Days in Cycle = 487
- Mode 3 times associated with planned refueling outages.
Cycle 3 percent of time spent in Mode 3 = 4.50% Cycle 3 percent of time spent in Mode 3 minus Refuelling Mode 3 hours = 1.09% Cycle 4 percent of time spent in Mode 3 = 3.05% Cycle 4 percent of time spent in Mode 3 minus Refuelling Mode 3 hours = 2.42% 4 - 41
Table 4-19 Tubes Potentially Susceptible to Collapse and In-Leakage TSP F, G Left-Hand Unit _ A l I i 4 - 43 DISK 215- BRDWO\TBL42 - 04/19/94 I l
Table 4-21 Tubes Potentially Susceptible to Collapse and In-Leakage TSPleP Left-Iland Unit
= 8 i
i m. l l 4 - 45 DISK 215 - BRDWD\TBL42 - 04/19/94
Table 4-23 Tubes Potentially Susceptible to Collapse and In-Leakage TSP E, H Left-Iland Unit
- a i
t oen m 4 - 47 DISK 215 - BRDWD\TBL42 - 04/19/94
l Table 4-25 Tubes Potentially Susceptible to Collapse and In-Leakage TSP F, G Right-Hand Unit
- A
~-
4 - 49 DISK 215- BRDWD\TBL42- 04/19/94
1 Table 4-27 ! Tubes Potentially Susceptible to Collapse and In-Leakage TSP L-P Right-Hand Unit
- a V
[ [ r i s i f t f i r t t
.I 4 - 51 i
DISK 215- BRDWD\TBL42 - 04/19/94 ;
, . . . ., ,r_ ,-.-n.- - - - - - -
4 i t l 4 , Table 4-29
- Tubes Potentially Susceptible to Collapse and In-Leakage ,
TSP E, H [ Right-Hand Unit i _. a r a e L i f i f t L 4 - 53 ; DISK 215 - BRDWD\TBL42 - 04/19/94 ; t h
,_ _a Figure 4-1. Secondary Side Nodes, and Tube Support Plate Identification (See Figure 4-2 for Preheater Detail) 4 - 55 l
a Figure 4-3. Secondary Side Fluid Nodes and Flow Connectors for Model D3 Steam Generator 4 - 57 l
l
.l ,
- a i A
b I l I l t Figure 4-5. Pressure drop through tube support plates T, S and R during steam line break of a Model D3 (Case 1: E - TSP T, O - TSP S, * - TSP R)
- a i
i l. P i l
?
I
\
l i a Figure 4-6 Pressure drop through tube support plates Qhot, L and G during steam line break of a Model D3 (Case 1: 3 - TSP Qhot, Q- TSP L, + - TSP G) 4 - 59 l l l
r p a ? i P i t L t b I Figure 4-8. Secondary Side Nodes and Tube Support Plates Identification of TRANFLO Model for Model D4 Steam Generator 4 - 61 L
1 I l
\
\
_a Figure 4-11. Pressure drop through tube support plates A and C during steam line break of a Model D4 (Case 2 O TSP A, E - TSP C)
- a Figure 4-12. Pressure drop through tube support plates M, N and P during steam line break of a Model D4 (Case 3; E - TSP P, - TSP N + - TSP M) 4 - 63
_ _a 1 l l l I Figure 4-15. Tube Bundle Geometry 4 - 65 l l l l l < l l
a l l l i l l Figure 4-17. Plate A (III) Support Locations 4 - 67
~
i l
-a Figure 4-19. Plate F (SH) Support Locations 4 - 69 l
l
- a
- r.
l i 1 l 4_ 1 Figurr 4-21. Plate L (8H) Support Locations 4 - 71 )
=
_ _a l Figure 4-23. Plate N (1011) Support Locations
)
1 4 - 73 l
P Anw gge > i NSP l l : Figure 4 25. Overall Finite Element Model Geometry i 4 75
- , . ;pQ
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I i Figure 4-27. Mode Shape Plot - Plate A Full Set of DOF Mode 2 4 - 77 l 1
s ~, ,-
' -- nx. ..,_=- . '
s 's ,- ~, -/,
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Figure 4-29. Mode Shape Plot - Plate A Reduced Set of DOF Mode 1 4 - 79 4 I
Jw I t b 1
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/ ,
- * % $ > e---....n._s_-
~s *
,o .,Y , ,/. ,
, .y, p
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T-I j Figure 4-31. Mode Shape Plot - Plate A i Reduced Set of DOF l Mode 3 4 - 81
~
n- .
, , . 9 R?(. . . . y':,-' :: : - - ' .M,-- , ' , ' _
'~
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)
Figure 4-33. Displaced Geometry Plate C(3H) : Time = 1.886 sec SLB + Excess Feedwater Transient , a 1 1 4 - 83 l
,1
L
^
A , N' f ',S' . 5, , l~ 'S' W ' ' Nh j- S'f ' ff:<,';~,:,-:_'?> y'
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~ Y ,
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Nih\ X T~ ' . ;j / s
.f '/' '
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-% / '
sf ~. '
~/
Figure 4-35. Displaced Geometry Plate J(7H) : Time = 1.926 sec SLB + Excess Feedwater Transient 4 - 85
i l i l a i i l Figure 4-37. Displacement Time IIistory Response SLB + Excess Feedwater Transient Plates L(8H), M(9H), N(IDH), P(11H) 4 - 87
_ _a l Figure 4-39 , Minimum Stress Intensity SLB + Excess Feedwater Transient Plate A (1H) 1 4 89 l l l
i i l l i
- a 1 Figure 4-41 Minimum Stress Intensity SLB + Excess Feedwater Transient Plate C (311) 4 - 91
t I i I
- a i t
i i I i t 1 i l l t t i I i i i 1 l t i i i
~
~
Figure 4-43 Minimum Stress Intensity ! SLB + Excess Feedwater Transient : Plate J (7H) (Maximum Upward Response) l l i l t l l 4 - 93 .; e t 6 t m a y g.4e- - --w .r, n d+-
- a
~
Figure 4-45 Minimum Stress Intensity , SLB + Excess Feedwater Transient ! Plate J (7H) (Maximum Downward Response) 1 4 - 95 l
90~ Ouadrant 2 Quadrant 1 Hot Leg DMder Plate Manway Nonle
- 0:
180 N - 360-Column 114 coiumn 1 Quadrant 3 Cold Leg Quadrant 4 e 270 Figure 4-47. Reference Configuration Looking Down on Steam Generator Right-liand Unit i 1 a . 47
)
. l l
l l DISK 215 - PDDWD-We A o'*-.'o c'9-- "r
i i a i t i
?
f 1 l t i i f
.I f
i i f
~
Figure 4-49. Tubes Potentially Susceptible to Collapse and In-Leakage Braidwood Unit 1 TSP C, J Quadrant 2 4 - 99 l l
I
-. a I
~
~
Figure 4 51. Tubes Potentially Susceptible to Collarte and In-Leakage Braidwood Unit I TSP D, G Quadrant 4 i l 4 - 101 i I i l
_a b L - Figure 4-53. Tubes Potentially Susceptible to Collapse and in-Leakage i Braidwood Unit 1 1 TSP E, H l Quadrant 4 4 - 103 l l l l l l l
- a i
l l
~
~
Figure 4-55. Tubes Potentially Susceptible to Collapse and In-Leakage Braidwood Unit 1 TSP F Quadrant 2 4 - 105 I j
i _ a 1 l Figure 4 57. Tubes Potentially Susceptible to Collapse and In Leakage Braidwood Unit 1 TSP L, M, N, P Quadrant 2 4 - 107 1 I
=
- _a r
Figure 4 59. Counterbored Structural Quatrefoil Loss Coefficients 4 - 109
1 l I 5.0 DATABASE SUPPORTING ALTERNATE REPAIR CRITERIA This section describes the database supporting the alternate repair criteria (ARC) burst and leak rate correlations. The database for 3/4 inr.h diameter tubing is described in EPRI Report NP-7480 L, Volume 2 (Reference 5-1). Howaver, at the February 8,1994 NRC/ Industry meeting, the NRC presented resolution ofinGustry comments on draft NUREG-1477. The NRC identified guidelines for application of leak rate versus voltage correlations and for removal of data outliers in the burst and leak rate correlations. This section applies the NRC guidance on removal of outliers to update Ge database for the 3/4 inch tubing correlations. 5.1 Data Outlier Evaluation At the February 8 meeting, the NRC provided the following guidance for removal of data outliers: Data can be deleted in case of an invalid test. Any morphology criteria for deleting outliers must be rigorously defined and applied to all the data. Criteria for deleting outliers must be able to be unambiguously applied by an independent observer. It is acceptable to modify data or a model in a conservative manner. Based on the above NRC guidance, the outlier evaluation of Reference 5-1 is updated in this section. Consistent with the NRC guidance, criteria for removal of outliers are defined in this section and applied to the database. These criteria were developed and approved by the EPRI Adhoc Altemate Repair Criteria (ARC) Committee. Consistent with Reference 5-1, only conservative outliers which are high on the burst correlation or low on the leak rate correlation are evaluated for removal from the database. Although the outliers are conservative in this manner, their retention in the database can increase the uncertainties from the regression analyses such that their removal from the databe.se can lead to non-conservatisms in analyses applying uncertainties at upper or lower tolerances. Cnterion 1 for outlier removal applies to invalid data including unacceptable specimens, invalid measurements, etc. To describe the invalid test condition, Criteria la to le are defined as described in Table 5-1. Table 5-1 provides examples ofinvalid data that are applicable to the EPRI database. , I 5-1
crack width is about 1 mil at 2560 psid and increases to about 10 mils for a 0.5" long crack. Thus, crack lengths < 0.3" are more susceptable to plugging from deposits. l From Figure 5-1, it is seen that model boiler specimens 598-3 and 604-2 have very low leak rates for their respective throughwall crack lengths. The remaining data are reasonably clustered with trends similar to that expected as shown for the CRACKFLO analyses in Figure 5-1. There is no indication through spread in the data that other specimens are significantly influenced by probable deposits in the crack face. Criterion 3 has been applied to specimen 598-3 to eliminate this indication from the leak rate correlation, as this specimen is more than a factor of 100 lower than the mean of the other data at about the 0.27" crack length of this specimen. Criterion 3 has not been applied to specimen 604-2, as this specimen - is not clearly a factor of 50 less than the mean of the data, although the leak rate is apparently affected by deposits. Criterion 3 can be unambiguously applied by an independent observer to all measured leak rates given the results from leak rate measurements and/or destructive examinations and thus satisfies the NRC guidance for removal of outliers. This criterion is applied only to low leak rate measurements. For conservatism, high leak rate measurements are not considered for removal from the database Based on Criteria 1 to 3 as desenbed in Tables 5-1 to 5-3, the EPRI database of Reference 5-1 was reviewed for identification of data outliers to be removed from the database. Tables 5-4 to 5-6 summa. tine the data points removed from the database applied to the burst, leak rate and probability of leak correlations, respectively. Data were removed from the EPRI database in Reference 5-1 based on the same technical considerations, although less formal, as the criteria of Tables 5-1 to 5-3. However, the updated criteria lead to no changes from Reference 5-1. Plant S pulled tube R28C41 was deleted from the database of Reference 5-1 and would also be deleted by the more explicit criteria of this section. However, special considerations have been applied to this indication as described below. Special Consideration for Plant S Pulled Tube R28C41 Plant S pulled tube R28C41 had leak rates exceeding the initial hot cell leak rate facility capacity at pressure differentials near SLB conditions. Test results are given in Table 5-7. Measured leak rates of 43.4 and 95.11/hr at 2335 and 2650 psid, respectively, exceeded facility capacity and are not valid measurements. At 1500 psid, a measured leak rate of 12.31/hr was within the facility capability (- 251/hr) and represents a valid measurement. The facility capacity was increased and attempts to reach 2650 psid for a valid leak rate measurement (i.e., without hysteresis effects) were not successful as the leakage exceeded the 5-3 1 1
area was calculated as a function of crack length. These results are presented in Figure 5-3, along with a curve fit to the calculations. The curve fit was used to develop a modified version of CRACKFLO which maintains the minimum plastic opening resulting from the pressurization to 2650 psid and combines it with an additional clastic opening due to the pressure differential of subsequent tests.
- 3. Using the modified CRACKFLO code with plastic crack opening at 2650 psid, the leak rate as a function of crack length was determined for the conditions of Test 4, Table 5-7. The results are presented in Figure 3-4. The figure shows that a crack length of 0.42 inch is inferred from the measured leak rate of 79.81/hr. Some additional tearing of the ligaments and throughwall crack extension from the 2650 psid pressurization is suggested by the throughwall crack length increase from 0.38 to 0.42 inch between Tests I to 3 and Test 4.
- 4. The modified code, a 0.42 inch crack length and the conditions for Test 6 give a leak rate of 1141/hr at 1615 psid. This is substantially less than the 4481/hr measured for this test, suggesting significant tearing of the crack has occurred from thermal cycling and pressurization between Tests 4 and 6.
- 5. Destructive examination of the tube after a tube burst test indicated a crack length up to 0.67 inches was possible. Using this crack length, a leak rate of 3751/hr is obtained for the conditions of Test 6. This value is reasonably close to the measured leak rate of 4481/hr. For this calculation CRACKFLO was used since the plastic opening area, 2.0x10 inch, was greater than the 1.5x10 ' inch calculated to be present after the pressurization to 2650 psid. Thus it is expected that complete tearing of all ligaments and the 5% wall thickness occurred between Tests 4 and 6.
- 6. Using the desired steam line break conditions (2560 psid and 616'F primary temperature) for the EPRI database, the as-pulled crack length of 0.38 inch (Step 1) is expected to have torn to 0.42 inch and a leak rate of 1111/hr is calculated.
The estimated leak rate for Plant S tube R28C41 at SLB conditions (2560 psid)is therefore 1I11/hr. This result is reasonably consistent with Plant S tube R33C20, which was measured in the large capacity facility. Tube R33C20 had a throughwall corrosion length of 0.33", compared to the 0.26" continuous length for R28C41. Both indications likely had ligament tearing and crack extension from tube pulling and pressurization to 2560 psid. The measured leak rate for R33C20 at 2560 psid was 1371/hr, compared to the estimate of 1111/hr for R28C41. Based on similar analyses using a few runs with the LABOLEAK code and analytical ratios of crack areas between 2650 and 1200 psid, Paul Hernalsteen of Laborelec estimated a 5-5
l 5.4 References 5-1. " Steam Generator Tubing Outside Diameter Stress Corrosion Cracking at Tube Support Plates - Database for Alternate Repair Criteria, Volume 2: 3/4-Inch Diameter Tubing", NP-7480-L, Volume 2, October 1993. 5-2. "PWR Steam Generator Tube Repair Limits - Technical Support Document for Outside Diameter Stress Corrosion Cracking at Tube Support Plates", TR-100407, Resision 1, ' Draft Report, August 1993. 5-7
Table 5-2 Criteria 2a and 2b for Excluding Data from Correlations Criterion 2a: Atypical Ligament Morphology
+ Cracks having 5 2 uncorroded ligaments in shallow cracks < 60% maximum depth should be excluded from the database as having bobbin voltages significantly higher than the dominant database which shows more uncorroded ligaments in shallow cracks
- Results in atypical voltages and associated specimens are excluded from all corr.
- No 3/4" specimens are excluded from the database due to this criterion Criterion 2b: Severe Degradation Exclude data points having bobbin voltages > 20 volts larger than next data point from correlations, as singular data points at the tail of distributions can have undue influence on regression correlation. In this case, there is insufficient data at comparable voltages to assess the prototypicality of the crack morphology and applicability to the database.
- Results in atypical voltages and associated specimens are excluded from all corr.
- Excludes 3/4" model boiler specimen 598-1 (64.9 volts) which is > 40 volts larger than the next highest voltage point (22 volts) -
I 5-9 ) l l.
-M
l Table 5-4 Basis for Excluding Data from the 3/4" Burst Correlation Basis for Excluding Indications . EPRI* Tube Exclusion TSP from Tube Burst Correlation Report Category Ss Plant E-4 R19C35 2 Burst inside TSP. Yields much higher burst Ib 4.4 , pressure than free span burst tests of ARC data ; base. R45C54 2 Burst inside TSP lb
' R47C66 2 Burst inside TSP lb Piet S :
R28C41 1 Incomplete burst test - burst opening length Ib 2.5, 4.5 less than macrocrack length (no tearing) Plant R-1 R7C71 3 Test recorder malfunction Ib 2.2,4.3 RSCI12 2,3 Incomplete burst test 1b R10C6 2,3 Incomplete burst test Ib ; R10C69 2,3 Incomplete burst test Ib R20C46 2,3 Incomplete burst test Ib R7C47 3 Incomplete burst test Ib Model Boiler Specimens 591-3 Unacceptable specimen preparation due to la 5.6 bobbin voltage influenced by cracks in model boiler Teflon spacer below TSP as well as , cracking within TSP. This results in two bands of cracks. 598-1 Bobbin voltage (64.93 volts) and three large 2b 5.6 throughwall indications not prototypic of field indications and single data point >20 volts unduly influences burst correlation. 593-4,595-4, These bobbin NDD specimens all burst at a Ib 596-1, 597-4, welded joint made to extend the specimen 603-4, 604-4 length for burst testing and are not valid tests. These data have been excluded from the 3/4 inch data base discussed in the EPRI report. EPRI Report NP-7480-L, Vol. 2 (Reference 5-1) I 5 - 11
l l Table 5-6 l Basis for Excluding Data from the 3/4" Prob of Leak Correlation Basis for Excluding Indications Exclusion i Tube TSP from Prob. of Leak Correlation Report '
"I*E 'Y Section 1 1
Plant R-1 R7C47 2 No destructive exam data or burst test to le 4.3 estimate probability ofleakage. R5Cl12 3 Max. corrosion depth of 97%. Remaining TW Id 2.2,4.3 ligament torn during tube pull as indicated by post pull voltage and leak at 500 psi. Analyses indicate ligament would not have tom at accident conditions. Plant B-1 R4C61 5 No leakage identifiable during pressure test le 2.2,4.3 above SLB conditions. Test accuracy not sufficient to conclude no leakage. Model Boiler Specimens 591-3 Unacceptable specimen preparation due to la 5.6 bobbin voltage influenced by cracks in model boiler Teflon spacer below TSP as well as cracking within TSP. This results in two bands of cracks. 598-1 Bobbin voltage (64.93 volts) and three large 2b 5.6 throughwall indications not prototypic of field indications and single data point >20 volts unduly influences correlation. EPRI Report NP-7480-L, Vol. 2 (Reference 5-1) 5 - 13
Table 5-8 Plant S SG Tube Macrocrack Profile for R28C41 Length vs. Depth Ductile Ligament Tube. Location (inchF4 throur.hwalh Location R28C41, FDB 0.00 / 0 0.07 / 100 0.13 / 100 0.19 / 95
- Ligament 1,0.013" wide 0.25 / 95 0.32 / 95
- Ligament 2,0.004" wide 0.38 / 95 j 0.44 / 100
- 0.52 / 100
- Ligament 3,0.007" wide 0.60 / 100 0.70 / 100
- Ligament 4,0.008" wide 0.75 / 70 0.80 / 0 5 - 15
Table 5-10 Burst Pressure and Leak Rate Data Base for 3/4 inch Tubing Adjusted Correlation (4) Destructive Exam SLB Leak (2) Burst (3) Application Row / Col or Bobbin Bobbin RPC Max. Specimen No. Rate (1/hr) Pressure Leak Plant TSP Volts Depth Volts Depth Length (1) 2560 psid (ksi) Rate Burst _. e l l
Table 5-10 (continued) Burst Pressure and Leak Rate Data Base for 3/4 Inch Tubing Adjusted Correlation (4) Row / Col or Destructive Exam SLB Leak (2) Burst (3) Application Bobbin Bobbin RPC Max. Plant Specimen No. TSP Volts Depth Rate (1/hr) Pressure Leak Volts Depth Length (1) 2560 psid (ksi) Rate Burst
- C l
l l l l l l l W
,w - -
e -
i i Figure 5-1 Comparison of 3/4" Leak Test Data with CRACKFLO Predictions
- 1,e 1
f l i
Figure 5-3 Plastic Correction Area 2650 psi Pressure Difference _y l t i h e i L l l
l 6.0 BURST AND SLB LEAK RATE CORRELATIONS 6.1 EPRI ARC Correlations As part of the development of attemate repair criteria (ARC), correlations have been de for tubes containing ODSCC indications at TSP locations between the bobbin amplitude, expressed in volts, of those indications and the free-span burst pressure, the probability and the free-span leak rate for indications that leak, References 6.1 and 6.2. The database for the development of the correlations is presented and discussed in Reference 6.2. Gui for the identification and exclusion of inappropriate data, termed outliers, are provided in Reference 6.3. In addition to the aforementioned, an empirical correlation curve for the burs pressure as a function of crack length has been developed for tubes with free-span, through-wall, axial cracks. In 1993, the NRC issued draft NUREG-1477, Reference 6.4, for public comment. The draft NUREG delineated a set of guidelines for criteria to be met for the application ofInterim Plugging Criteria (IPC) for ODSCC indications. The criteria guidelin permitted the use of, with adequate justification, a burst pressure to bobbin amplitude correla tion and a probability ofleak to bobbin amplitude correlation. The criteria guidelines did not permit the use of a leak rate to bobbin amplitude correlation for the estimation of end o (EOC) total leak rates. In essence, References 6.1 and 6.2.provided comments on the Reference 6.4 guidelines. Reference 6.5 provided an NRC response and position relative to resolving the differences between References 6.1 & 6.2 and Reference 6.4, along with responses to other public comments. Of significance to this report, is that Reference 6.5 indicated that a correlation between leak rate and bobbin amplitude could be employed correlation could be statistically justified at a 95% confidence level, and provided direction for the development of guidelines, e.g., Reference 6.3, that could then be employed for the identification and exclusion of outlying experimental data. Subsequent discussions with personnel have revealed potential issues associated with the manner in which the leak rate to bobbin amplitude correlation is used, thus, the potential leak rate during a postulated ste break (SLB) is herein estimated by attemate Monte Carlo and deterministic methods to demonstrate that either method yields acceptable results. The purpose of this section is to provide information and justification for all of the correlat developed in support of the application of an IPC for the Braidwood I nuclear power pl Information is first presented relative to the correlation of burst pressure to bobbin amp and to through-wall crack length, followed by a discussion of the correlation between the probability ofleak and the bobbin amplitude, and lastly a discussion of the correlation ofleak rate to bobbin amplitude. The use of each of the correlations is also documented. 6-1
6.3 Burst Pressure versus Through-Wall Crack Length Correlation For a tube with a mean radius of r, and a thickness t, the normalized burst pressure as a function of the actual burst pressure, P,, is given by P, r" P'~ = _ (6.2)
\ 'Su )t Thus, P,,,is the ratio of the maximum Tresca stress intensity, taking the average compressive stress in the tube to be P,/2, to twice the flow strength of the material. The normalizing parameter for crack length, a, is given by a
A" - (6.3)
} r,,,1 a form which arises in the theoretical solutions. The burst pressure as a function of axial crack length for a specific tube size is then easily obtained from the non-dimensionalized relation-ship.
Examination of the normalized burst pressure data indicated that a variety of functional forms would result in similar fit characteristics An exponential function, i.e., P,,, = b, + b, c , (6.4) was finally selected based on the combination of maximizing the goodness of fit, and minimiz-ing the number of coefficients in the function. Equation (6.4) was also found to be advanta-geous in that it can easily be inverted to yield A as a function of P ,,. For the data analyzed, the coefficients of equation (6.4) were found to be
~
P,,, = 0.0615 + 0.534 e 5'" (6.5) i The index of determination for the fit was 98.3%, with a standard error of the estimate of 0.015. The F distribution statistic for the regression, the ratio of the mean square due to the regression to the mean square due to the residuals, was 4625. Thus, the fit of the equation to l the data is excellent. Note that this does not mean that equation (6.4) is the true form of a I l 1 6-3 l _9
1
. i calculated using randomly generated independent r-variates and the respective estimated l standard deviations of P,,, about the regression curve and Sfabout the mean of the database.
These are then combined using equation (6.7) to obtain a burst pressure for a single simulation. The number of occurrences of the calculated burst presrure being less than the SLB pressure is ; then an estimate of the probability of burst. Based on the specific simulation results, an upper ' bound for the estimate of the probability of burst may then be made using non-parametric methods. The results of the calculational and the Monte Carlo simulation determinations are depicted on Figure 6-3. Also shown are the 99% upper confidence bounds for the Monte Carlo estimated values. The calculational procedure is seen to lead to a conservative estimate of the probability of burst for a given crack length. An examination of the distribution of the burst pressures from the Monte Carlo simulations reveals that is skewed right. Thus, the tail of the distribution is shorter for the lower burst pressures, hence the lower probabilities of burst. 6.4 NRC Draft NUREG-1477 SLB Leak Rate POD and Uncertainty Methodology The NRC methodology of draft NUREG-1477 obtains the number ofindications that are to be considered as being retumed to service, N, as-N N = N, + N" - N' = N, + 1 - POD y# _ g' , d _ y' ' (6.9) POD POD where, N, = number of detected bobbin indications N, = number of repaired indications Na = number ofindications not detected by the bobbin inspection POD = probability of detection (0.6 for NRC methodology). The above adjustments for POD have been incorporated in the BOC and EOC voltage distributions so that no further adjustments are required for the leakage calculation. Section 3.3 of draft NUREG-1477 states that the total leak rate, T, should be determined as: T -pF +2 2 cP+pp_ 2 (y,p,2) , (6.10) where, p = mean of the leak rate data independent of voltage c = standard deviation of the leak rate data independent of voltage P, = probability that a tube leaks for the f voltage bin : N, = number of indications (after POD adjustment) in the f voltage bin P = I(N,P,) = expected number of indications that leak summed over all voltage bins 2 = standard normal distribution deviate (establishes level of confidence on leakage). 6-5
l 1 The use of the logistic function for the analysis of dichotomous data is standard in many fields. i The differential form assumes that the rate of change of the probability ofleak is proportional i to the product of the probability of leak and the probability of no leak. As noted, the function i is sigmoidal in shape, and is similar to the cumulative normal function, and likewise similar to ; using a probit model (which is a normal function with the deviate axis shifted to avoid dealing I with negative values). In principle, any distribution function that has a cumulative area of , unity could be fit as the distribution function, a limitless number of possibilities. Trying to identify a latent, or physically based, distribution for the probability of leak would be consid-ered to be unrealistic and unnecessaiy. For most purposes the logistic and normal functions will agree closely over the mid range of the data being fined. The tails of the distributions do not agree as well, with the normal function approaching the limiting probabilities of 0 and 1 more rapidly than the logistic function. Thus, relative to the use of the normal distribution, the use of the logistic function is conservative. Given its wide acceptance in multiple fields it was judged that the logistic function would be suitable for use in determining a probability ofleak as a function of voltage. 9 In addition, consideration was given as to whether the bobbin amplitude or the logarithm of the bobbin amplitude should be used Since the logistic, normal and Cauchy distribution functions are unbounded, the use of volts would result in a finite probability ofleak from non-degraded tubes, and would be zero only for V=-m. By contrast, the use of the logarithm of the voltage results in a probability of leak for non-degraded tubes of zero. Clearly, the second situation is mere realistic than the first, especially in light of the fact that a voltage threshold is a likely possibility. To comply with the NRC request, however, each distribution function was fitted to the data using the logarithm of the bobbin amplitude and the bobbin amplitude as the regressor. The three functions to be evaluated fall into a category of models referred to as Generalized Lincar Madcls (GLMs). This simply means that the models can be transformed into a linear form, e.g., equation (6.12). The left side of equation (6.12) is referred to as the link function for the logistic model. For the normal or cumulative Gaussian distribution function, the model to be fitted is: p, < t,ws m ,, I 7 P(Icak) = I c dr, (6.13) [2ii L and the model to be fitted for the Cauchy distribution function is: P(Icak) = 1 + 1 tan ~'(p, + p, log (P)]. (6.14) 2 x 6-7 ,
The results of fitting each of the equations are depicted on Figures 6-4 and 6-5. A comparison of the results shown on Figure 6-4 with those shown on Figure 6-5 indicates that the use of the logarithm of the volts results in a spreading of the functions with the probability ofleak at, say,3 volts being higher for the logarithmic forms. In the very low voltage range, less than 1 volt, the probability ofleak is lower for the logarithmic forms. This is because the tails must extend to -e. In general, the Cauchy cumulative distribution function has longer tails than either the logistic or normal functions. It also rises much more sharply in the middle of the data range. The regression results on Figure 6-2 illustrate the non realistic nature of the Cauchy fit for the non-logarithmic form, in spite of its similar deviance value. Examination of the figures indicates that the Cauchy distribution is significantly less representative of the data in the regions where the no-leak and leak test data overlap. A listing of probability of leak results for selected volts is provided in Table 6-3. Up to a bobbin amplitude of 1 volt, predictions based on the log-normal function are less than predictions based on the log-logistic function. For very high voltages the Cauchy distribution forms rise to a probability ofleak of one slower than the other distribution functions. Taken in conjunction with the leak rate versus voltage correlation, the cbse of a probability ofleak function is relatively moot. The final total leak rate values tend to differ by only a few percent across the spectrum of POL functions. 6.6 SLB Leak Rate Versus Voltage Correlation for 3/4" Tubes The bobbin coil and leakage data previously reported were used to determine a correlation function between the SLB leak rate and the bobbin amplitude voltage. Since the bobbin amplitude and the leak rate would be expected to be functions of the crack morphology,it is to be expected that a correlation between these variables would exist. Previous plots of the data on linear and logarithmic scales indicated that a linear relationship between the logarithm of the leak rate and the loganthm of the bobbin amplitude would be an appropriate choice for establishing a correlating function via least squares regression analysis. Thus, the functional form of the correlation is log (G ) = b, + b, log ( V), (6.19) where G is the leak rate, Vis the bobbin voltage, and b, and b, are estimates obtained from the data of some coefficients, p, and p,. The final selection of the form of the variable scales, i.e., log log, was based on performing least squares regression analysis on each possible combination and examining the square of the correlation coefficient for each case. He largest index of determination,58.2%, was found for the log (G) on log (V) regression. The second largest index, for G on V, was found to be on the order of 24%, clearly indicating the appropriate choice of scales to be log-log. 6-9 l l
i To complete the analysis for the leak rate, the expected leak rate as a function of log (P) was determined by multiplying the AA leak rate by the probability ofleak as a function oflog(V). ; The results of this calculation are also depicted on Figure 6-6 for a steam line break differential pressure of 2560 psi. 6.6.1 Analysis of Regression Residuals As previously noted, the correlation coefficients obtained from the analyses indicate that the log-log regressions at the vanous SLB APs are significant at a level greater than 99.8% Additienal verification of the appropriateness of the regression was obtained by analyzing the regression residuals, i.e., the actual variable value minus the predicted variable value from the . regression equation. A plot of the log (G) residuals as a function of the predicted log (G) was t found to be nondescript, indicating no apparent correlation between the residuals and the predicted values. A cumulative probability plot of the residuals on normal probability paper approximated a straight line, thus verifying the assumption inherent in the regression analysis that the residuals are normally distributed. Given the results of the residuals scatter plots and the normal probability plots, it is considered that the regression curve and statistics can be used for the prediction ofleak rate as a function of bobbin amplitude, and for the establishment of statistical inference bounds. 6.7 SLB Leak Rate Analysis Methodology . The leak rate versus voltage correlation can be simulated in conjunction with the EOC voltage distributions obtained by Monte Carlo methods, or by applying the POL and leak rate correlations to the EOC voltage distribution obtained by Monte Carlo methods as applied for the uraft NUREG methodology. This second approach is a hybrid that joins Monte Carlo and deterministic calculations. Parallel analyses verified that the full Monte Carlo leak rates and the direct application of the correlations to the EOC voltage distribution yield essentially the same results. Thus, it is adequate to apply the correlations to the EOC voltage distributions. The determination of the end of cycle leak rate estimate proceeds as follows. The beginning of ! cycle voltages are estimated using the methodology provided in draft NUREG-1477. The distribution ofindications is binned in 0.lV increments. The number ofindications in each bin is divided by 0.6 to account for POD. The resulting ramber ofindications in each bin is reduced by the number ofindications plugged in each bin. The final result is the beginning of cycle distribution used for the Monte Carlo simulations. The NDE uncertainty and growth rate distributions are then independently sampled to estimate an end of cycle distribution, also reported in bins of 0.lv increment. Given the EOC voltage distribution the calculational steps to obtam an estimate of the total leak rate are as follows (1) For each voltage bin, the leak rate versus bobbin amplitude correlation is used to estimate an expected, or average, leak rate for indications in that bin. ! i 6 - 11 !
individual leak rates, i.e., from the covariance, which arises as a consequence of using the regression equations. Thus, the second term accounts for the variances of the positions of the regression equations. A linearized approximation (via Taylor's Theorem) of the variance of the mean of the regression prediction, T,, is given by [Cor(p,,p,)] O O dT ' dT V(T, ) = f, , dp# n, < 0 [Cov(p3,p,)] O
', (6.25) 0 0 '
dp, V(of) where the derivative of the total leak rate vector contains five elements forj=1,...,5, and the Covahancc Mardx is a square 5x5 matrix consisting of the estimated variances and covariances of the estimated individual regression coef6cients and c,. Note that here [Cov(p,, E2)] and [Cov(p3, p.)] are each 2x2 matrices, where the p's are estimated by b, through b,, and recall that c, is an estimate of p5 The variance of the variance is estimated as V(o,') = (6.26) n~2, where n is the number of data pairs used in the leak rate regression analysis. The standard deviation of the total leak rate is then taken as the square root of the variance of the total leak rate. The upper bound 95% con 6dence limit on the total leak rate is then obtained as the expected total leak rate plus 1.645 times the standard deviation of the total leak rate. The results obtained with this approach have been compared to results obtained from the Monte Carlo simulation without signi6 cant differences being observed. For a calculation utilizing only equation (6.24), the total leak rate from SG "D" at the EOC is estimated to be 3.0 GPM. By including the variance from equation (6.25), the estimated total leak rate was estimated to be 3.1 GPM. The value obtained from the Monte Carlo simulation of the total leak rate was 3.2 GPM, as described in Section 6.8.1 below. Thus, for the distribution analyzed, the contribution of terms associated with the covariance, i.e., the uncertainty of the prediction of the mean total expected leak rate,is small (being on the order of 3%) when compared to the variance of the total leak rate about the mean value. The results obtained provide independent veri 6 cation of the Monte Carlo and hybrid techniques. 6.8 Simulation of Equation Parameter Uncertainties The estimated, total end of cycle leak rate can also be calculated using Monte Carlo tech-niques, e g., the method documented in the EPRI ODSCC report (TR-10047, Rev.1). In the Monte Carlo analysis the variation in the parameters, i.e., coef6cients, and the variation of the dependent variable about the regression line is simulated. A 95% con 6dence bound on the total leak rate from SG "D" of Braidwood 1 was calculated using a Monte Carlo simulation to l l 6 - 13 l l
i l 1 i distribution. The total leak rate for the SG simulation is calculated as the sum of the leak rates from all of the indications in the SG. The expression for the total leak rate is {
\
T= R,(pi, p,) G,(p,, p , p,), (6.28) where N = the total number of indications in the SG at EOC, R,(pi, p2) = 0 or 1 is the POL from a single indication, i, in a tube, G,(p3, E., p3) = is the conditional leak rate of indication i, i.e., the leak rate if the indication is leaking, p,,p2= the coefficients of the POL equation, p3, p. = the coefficients of the leak rate versus bobbin amplitude equation, and E3 = the standard error of the log of the leak rate about the correlation line, also referred to herein as o. To simulate the total leak rate from all of the indications in the generator, random coefficients for the probability ofleak, POL, and leak rate correlation equations are generated, and then those coefficients are used to simulate the POL and leak rate for each indication. The POL, R,, for each indication, i, is simulated as, R,(p ) = 0 otherwise Wi
- 2 ' Ef 'O, (6.29) where U,is an independent draw from a uniform distribution. The step of determining an integer value for the POL accounts for the variation of the distribution of probabilities about the log-logistic regression line. Discussion of the generation of pi and p2 is left until after the discussion of the coefficients for the leak rate equation.
Leak Rote versus Bobbin Amplitude Simulation To simulate the leak rate from the regression line, random coefficients p3 and D, must be simulated Each of these has a variance that is dependent on the variance of the error of the log of the leak rate about the regression line. Thus, the first step is to simulate a random error 2 variance by picking a random x deviate for n-2 degrees of freedom and then calculating a L 2 random error variance, c , for the correlation equation from the regression error variance as o' = (n - 2) 62 =f,, c ' , (6.30) i
% ( a - 2), readam I
l J 6 - 15
Probability of Leak Simulation The generation of the coefficients of the POL relation to be used in the simulation of the total leak rate proceeds in the same manner as for the coefficients of the leak rate relation. The elements of the covariance matrix are obtained from the GLM regression analysis and used with the estimated coefficients in equations like (6.32) and (6.33) to obtain p, and p2 for a random population POL equation. However, for the simulation of the POL, there is no term of the form 2,o in the simulation of the total leak rate. This exception is due to the fact that the data are binary. In effect, this additional term is being simulated through the use of the random sampling to determine if R, is 0 or 1 in equation (6.29). It is noted that the elements of the covariance matrix obtained from the GLM regression are scaled to a mean square error (mse) of 1. This is because the mse for the binary variables is asymptotically 1. A check of this assumption can be made by calculating an estimate of the square root of the mse from the regression results as 6= 1 ($' #'} (6.35) g n - 2 {, p , ( 1 p ,) , where the yls are the observed probabilities of leak, either zero or one, from the leak and burst testing, and the pls are the calculated probabilities ofleak from the logisuc regression equation. A significant departure from 1 for this quantity could be indicative of an inadequate model For the simulation of the POL data for 3/4" tubes the root mse was found to be 1.1. This is not significantly different from 1. A 95% con 0dence bound on the total leak rate from SG "D" at the end of the fuel cycle was found to be 3.2 GPM. This is in very close agreement with the value found using the : deterministic estimate. 6.8.2 EPRI Monte Carlo Simulations The simulation methodology documented in the EPRI ODSCC report, Reference 6.1, was also used for the estimation of a EOC leak rate for the Braidwood 1 SG "D" The resulting value, 3.1 GPM is provided for information since this analysis was not the reference methodology employed for the evaluation of the Braidwood SG's. Thus, the following discussion of the EPRI model is also for information purposes to clarify how it relates to the methodology em-ployed Application of the EPRI model involves two major steps. In the first step, an EOC leak rate table as a function of BOC volts is generated from Monte Carlo simulations of NDE uncertainties, plant specific growth rates, and uncertainties associated with the correlation analyses. In the second step, the total leak rate is estimated as the sum of the individual EOC leak rates from each indication using the tabulated leak versus BOC volts values. 6 - 17
the slope can be generated from equation (6.38), where the sign of the random t-variate govems the sign of the second expression, i.e., c' p,=b,+t, (6.39) {(V - F)2 j The coefficients of the regression equation, i.e., equation (6.27), are not statistically indepen-dent. Thus, selecting a random value for the intercept must account for the already selected slope. In this case, a joint 100-(1-cz)% con 6dence ellipse for the coef6cients is given by (D - b )2 + 2 F(E - b )(p - b ) + [ V (p, - b,)2 s2 0' F2-* 3 3 3 3 , (6.40) n n where p3 and p, are the true, but unknown, coef6cients of the regression equation. Thus, given the random slope from equation (6.39), a random F-distribution value, F, for 2 and v degrees of freedom, is selected and equation (6.40) is solved (considering the equality) to obtain a random value for p3 Since there are multiple roots of equation (6.40), i.e., 3 Q, = b - V(p, - b ) ( p, - b,)' V 2
-{V' n
+
2 c,'F,' n (6.41) an additional random selection must be made to account for the sign of the radical in equation (6.41). It is also noted that the selection of a random F deviate may result in the radical of (6 41) being imaginary. In this case, it is necessary to sample F until the radical is real. To complete the leak rate versus voltage correlation for the simulation, only the variation about the regression line remains. The standard error, o,, from the regression analysis has been shown to be approximately normally distributed with a mean of zero. Since the true variance of the residual population is estimated, the distributiw is simulated using a random t-variate, and the 6nal leak rate for each simulation case is given by G, = 10 b'"'. (6.42) It is noted that the method described in the UKl ODSCC report indicates thst the effective standard deviation of the residuals, o,, from equation (6.22) is to be used instead of the actual standard deviation of the residuals, o,, in equation (6.42). This is considered to be an unnecessary conservatism because the variance of the coef6cients would enter equation (6.42) twice, i.e., through the simulation of 3 and p, and through o,. The net effect would be to 6 - 19
l 6.6 Regulatory Guide 1.121 (draft), " Bases for Plugging Degraded PWR Steam Generator Tubes," United States R clear Regulatory Commission, issued for comment in August, 1976. 6.7 Docket STM-50-456, " Safety Evaluation by the Office of Nuclear Reactor Regulation Related to Amendment No. to Facility Operating License No. NPF-72 Commonwealth Edison Company Braidwood Station, Unit No.1," United States Nuclear Regulatory Commission, May,1994. 6 - 21 ; l
l l l i Table 6-2: Results of Regression Fits of Logarithmic Forms of POL Distribution Functions to 3/4" OD Tube Data
@ 620'F and AP = 2560 psi Parameter Log-Logistic Log-Normal Log-Cauchy Values Values Values b, -5.5998 -2.7157 -13.8413 l b, 9.1924 4.6317 21.3183 V,, 2.1145 0.3664 46.5125 V,, -2.9538 -0.4985 -71.2114 V,, 4.5779 0.7993 110.22 Deviance 32.52 33.84 32.43 Results of Regression Fits of Non Logarithmic Forms of POL Distribution Functions to 3/4" OD Tube Data.
l Parameter I,ogistic Normal Cauchy Values Values Values b, -5.3890 -2.8544 -10.5327 b, 1.1945 0.6395 2.3085 l ', , 1.4958 0.2905 24.4371 V,, -0.3141 -0.0617 -5.3943 V,, 0.0787 0.0169 1.2223 Deviance 28.87 28.94 32.47 j 6 - 23 l i __________.____.__.__.________.-._---_____--___-.-_------------_----------------------------U
I l l Table 6-4: Regression Analysis Results: log (Leak Rate) vs log (Volts) for 3/4" x 0.043" Alloy 600 SG Tubes
@ 620'F and AP = 2560 psi Parameter Value Value Parameter ,
b, 3.132 -1.888 b, SE b, 0.431 0.425 SE b, ! 2 r 58.2 % 0.653 SE log (G) F 55.88 38 DoF SS,,, 22.56 16.21 S S,,, Pr(F) <0.000001% 2.300 SS io,c,3 pi-value <0.000001 % 0.01% po-value i 6 - 25 r
i Figure 6-2: Burst Pressuit vs. Crack length 0.750" x 0.043", Alloy 600 MA Steam Generator Tubes @ 650*F, Average Flow Stress ae ' f 8 gw,consT xtst 34 curve 47's98. s si ru
. . . ____ . _ _ .. _ 'v M :_ . . . ,
u
- s i'
Figurt 6-4; Probability of Leak for3/4" SG Tubes i Comparison of Logarithmic Forms of legistic, Normal & Cauchy Functions ' k l i i I t h,
.g.
$5 A
n. s
., a
.??
l 1 f o 1 1 i iscURVE34 XLS) Pot %(v) , ocv ....-. .. -..
.;(\\
Figure 6-6: 2560 psi SLB Leak Rate vs. Bobbin Amplitude 3/4" x 0.043" Alloy 600 SG Tubes, Model Boiler & Field Data (EPRI) R,C F i p40V_CCE XLS) O vs V EPRI nm er%. .=m
7,0 BRAIDWOOD 1 EDDY CURRENT INSPECTION RESULTS 7.1 General The March-April 1994 refueling shutdown was accompanied by 100% full length bobbin probe inspection of all four steam generators. In anticipation of the potential finding of significant ODSCC at support plate intersections, the ASME standards were calibrated to be consistent with IPC guidelines (such as incorporated into Appendix A of WC'AP-13854), wear standards were employed to allow tracking of voltage measurement variation, and the eddy current analysts were required to demonstrate their capability to report and to measure indication voltages. TSP indications have been assessed against the prior inspection conditions at the corresponding locations to develop voltage growth rates for the preceding periods of operation. ' Previous inspec't ions of the Braidwood-l steam generator tubes were conducted in November 1993 during an unplanned outage (SG C only), in September 1992 (EOC-3), and in April 1991 (EOC-2); the EOC-1 inspection in September 1989 was not included in the growth rate studies. For each indication reported during the 1994 inspection, both the 1993 (SG C) and the 1992 (all SGs) data were reevaluated to determine, as far as possible, the pre existing signal amplitude which could be attributed to any detectable precursor condition. Only if a possible flaw indication was observed in the earlier inspection was a growth point calculated for the particular 1994 indication; i.e. no assumptions were made about prior year signal voltages Because of the unplanned outage during Cycle 4, comparisons in SG C were made to both the 1993 and 1992 inspection results; furthermore,1992 data for tubes reported in ! 1993 were compared to obtain an estimate of the partial cycle (4a) growth rate. Cycle 4b growth was determined by comparing the 1993 and 1994 data for SG C only; an overall Cycle 4 growth rate based on comparison of 1994 with 1992 data was also calculated. All the tubes plugged in 1992 were used to develop growth rate data for Cycle 3 by reanalyzing the 1991 data Table 7-1 presents a summary tabulation of all the growth rates on a per cycle as well as a per Effective Full Power Year (EFPY) basis; also shown for each case are the number of comparisons used, the average BOC voltages, the voltage growth (AV), and the length of the operating period in EFPY. For each cycle evaluated, the data was subdivided into indication populations less than 0.75 volt and those equal to or greater than 0.75 volt. This was done to demonstrate the consistency in behavior with prior cases, which have consistently shown higher average percentage growth rates for low voltage indications. l The distribution of the TSP ODSCC indications among the four SGs for the 1994 inspection is shown in Table 7-2, which tabulates the number ofindications for each TSP elevation for which indications were observed. For the D4 SGs of Braidwood-1, the IH level represents the Flow Distribution Baffle (FDB), a plate with oversize tube holes and no flow holes; for i this reason the incidence of ODSCC is expected to be low in the absence of unusual 7-1 c
provides detailed RPC confirmation statistics as a function of bobbin voltage for each of the individual SGs, as well as cumulative confirmation data for the four SG composite results. An RPC sampling plan was performed to inspect TSP intersections with dent signals greater than 5 volts and artifact / residual signals that could potentially mask bobbin indications of about 1.0 volt. Denting in Braidwood-l is minor and most of the dents represent mechanical dings rather than corrosion induced denting. The RPC sampling plan was performed on all identified hot leg dents > 5.0 volts in SGs A and B. It included 21 dents (18 in SG A,3 in SG B) at TSP intersections. There are only 6 dents in SG C (one additional dent was in a tube plugged for other causes) and 2 in SG D left in service above 5 volts that were not RPC inspected. The RPC sample included 40 mix residuals in SG A and 41 in SG B. The mix residuals inspected had greater than a one volt signal and were manually selected to represent the larger residual signals. In addition to this RPC sampling plan,85 intersections with no bobbin indications were RPC inspected. No RPC flaw indications were found in the RPC sampling plan. In both this RPC sample and the RPC inspection of bobbin flaw indications, ' no circumferential indications or indications extending outside of the TSP thickness were , detected. Limiting the RPC sampling to only SGs A and B left only 8 dented TSP intersections unmspected in SGs C and D. Reviews of data from previous outages indicate that all 8 of : these dent indications were present. The uninspected dent indications lead to a negligible risk of leakage or rupture due to the small number of dents, the fact that no flaw indications were found at the inspected dent locations and the fact that a conservative POD of 0.6, independent of voltage, is applied for the SLB leak rate and tube burst probability estimates. Similarly, uninspected mix residuals in SGs C and D would have negligible concern for leakage or burst considerations. The two dents in SG D have bobbin voltages of 19.1 and 5.1 volts. The bobbin data for these indications have been reviewed for the 1989,1991,1992 and 1994 inspections. There . have been no discernable changes in the dent voltages or phase angles. In all inspections, the phase angles are within 3 degrees of the expected 180 degrees for a dent. If a flaw were present, some change to the voltage and phase angle would be expected. Thus,it is judged that the dents are not growing in size and there is a low likelihood of a flaw being present in the dents. SG D is the most limiting SG for tube leakage and burst considerations. Since only two iminspected dents are present, even the assumption of a flaw being present in the dent (a flaw too small to influence the phase angle of the dent) would have negligible : influence on leakage or burst. The POD = 0.6 adjustment results in 7.3 indications (actual indications plugged) above 2.7 volts left in service and 2 indications above 5.0 volts left in service. The contributions of these postulated indications to leakage and. burst probability would be expected to exceed that of a potential indication in the two dented intersections not RPC inspectei SG C is not a limiting SG for leakage or burst considerations due to the 7-3
1 1 l 7.3 TSP Voltage Growth Rates ! The progression of ODSCC indications at the TSPs is determined by re-evaluation of prior inspection EC records at the locations identified with indications in the 1994 inspection In most cases, some element of the precursor is identified as corresponding to the flaw signal reported in 1994. However, it should be noted that rather conservative analysis criteria are invoked to accomplish this task. In this process analysts are required to forego the behavior t criteria they may have employed to screen out low signal-to-noise indications, and to report possible flaw-like behavior in the TSP mix residual regardless of clarity. Review of the growth data identifies any anomalous growth data, and these are subjected to further scrutiny to eliminate spurious data. , The evaluation of voltage growth based on reevaluating the prior inspection data for a:1 indications found during the latest inspection is the same approach used for other IPC/APC evaluations This method of growth evaluation includes the largest growth values (typically repaired at the EOC) for each cycle, and can result in large, conservative average growth values llowever, because of tube repair and the occurrence of new indications, there are differences in the population of tubes when comparing growth rates between cycles. This introduces some uncertainty in assessing growth trends between cycles, such as those which may be due to chemistry improvements. A more desirable growth evaluation would track the same population of indications for multiple cycles to more accurately assess growth trends. liowever, if the !r. mspection indications are tracked back in time, the larger prior cycle indications which were repaired are not included in the analysis and this method can lead to an underestimate of average prior cycle growth. This method has been applied to SG C over the first and second parts of Cycle 4 as described below. A third option for evaluating , growth would be to track the latest inspection results back in time and to add plugged tubes ' into the population evaluated for prior cycles. This method has not been systematically : evaluated. A more systematic evaluation of these three options would be desirable to assess the best option for evaluating both cycle to cycle growth trends and the influence of operational chemistry improvements. Such an evaluation has not been performed for Braidwood l in this report. The operational periods for which growth values were determined included Cycle 3 - plugged ' tubes only; Cycle 4a (9/92-10/93) - SG C only but in three subgroups: all plugged tubes at 10/93, all indications reported at 10/93, and all indications reported at 4/94; Cycle 4b (11/93-4/94) for SG C only for all indications reported in 4/94; and the overall Cycle 4 for all four SGs. For each of these periods, growth data for indications <0.75 volt and those >0.75 volt were contrasted with the composite growth data for all indications. Table 7-6 shows a summary of the growth rates developed in this fashion for all four SGs. Figure 7-11 : illustrates the overall growth / amplitude relationship for all the comparisons obtained in [ A 1 R04. 7-5 l 1
caustic crevice conditions conducive to initiation and propagation of Alloy 600 alkaline stress corrosion cracking. Figures 7-19 through 7 27 show the power history, steam generator blowdown sodium to chloride molar ratios, and steam generator blowdown sodium and chloride concentrations during power operation for Braidwood Unit I during Cycles 2 through 4. During Cycle 2, SG blowdown sodium to chloride molar ratios (Figure 7-22) were slightly higher than molar equivalency with ratios typically less than 2. These ratio values fluctuated along with variations in plant operating conditions and minor contaminant ingresses - condenser leakage and demineralizer leakage. It should be noted that ratios maintained in this range can lead to development of caustic conditions in steam generator crevice regions. During Cycle 3, SG blowdown sodium to chloride molar ratios (Figure 7-23) were very elevated - both with respect to prior cycles of operation and with respect to good operating chemistry conditions. It is believed that this notable increase is likely to primarily be due to increased attention paid to SG blowdown cation conductivity values and attempts to lower them. As chloride conc:ntration affects cation conductivity, lower chloride concentrations resulted in lower cation conductivity and, consequently, higher sodium to ' chloride molar ratios. Sodium concentrations were elevated during the first half of Cycle 3 (Figure 7-26). As these concentrar,ons were decreased during the latter part of the fuel cycle, however, chloride concentrations were also decreased Sodium to chloride molar ratios typically in the range of 2 to 3 and up to 5, as observed during Cycle 3, are strongly indicative of potentially caustic environment development in SG crevice regions as described above. During Cycle 4, a period of operation with higher molar ratios around 2 to 3 was followed by attempts to control molar ratio by modification of blowdown demineralizer operation and, subsequently, ammonium chloride addition (Figure 7-24). Ammomum chloride addition has had the greatest effectiveness at Braidwood Unit 1 in controlling steam generator blowdown sodium to chloride molar ratios in the desired band. The success of this method at ! controlling crevice chemistry appears to be positive as a result of shutdown hideout return evaluations performed in May and at the end of the cycle. Ilideout return data obtained during Cycle 4 has been evaluated to ascertain the success of the molar ratio control program in modifying the steam generator crevice pH environment. M olar ratios of highly soluble species (sodium, potassium, and chloride) indicate a decreasing trend over the entire cycle (Figure 7-28) In addition, it has been reported that the crevice pH calculated by the MULTEQ program indicates an approximate 1.5 pH unit reduction to around 7.5 prior to the end of cycle shutdown. The end of cycle shutdown indicated more acidic conditions and lower molar ratio due to the occurrence of circulating water leakage. 7.5 Relationship Between Operating Chemistry and ODSCC Growth Corrective actions ,aken at Braidwood Unit I specifically to slow the progression of Alloy 600 tubing ODSCC include molar ratio chemistry control and boric acid addition beginning in 7-7
l 7.6 Pulled Tube Eddy Current Data TSP intersections from 4 tubes were removed from the Braidwood-l SGs to provide the basis for application ofInterim Plugging Criteria and to demonstrate the consistency of the Braidwood-l experience with other plants in which those criteria have been accepted. From SG A,2 tubes (R37C43 and R42C44) were pulled, and from SG D,2 tubes (R37C34 and R16C42). Tube R42C44 was cut above the 7H intersection, permitting the extraction of 4 intersections at the IH,3H, SH and 7H elevations. The three remaining tubes were cut below the 7H TSP level on inlet side, permitting the extraction of 9 additional intersections (total of 13),3 at each of the IH,3H, and SH elevations. Bobbin and RPC data weie collected for each of the removed intersections, which resulted in 6 field bobbin indications with corresponding RPC confirmations and 7 NDD intersections. The bobbin field EC graphics for each of the intersections are given in Figures 7-30 to 7-42. The corresponding RPC field graphics for the tubes reported to have bobbin indications are given in Figures 7-43 to 7-48. Table 7-8 summarizes the field analysis results for each of the intersections. With the exception of the 1.04 volt indication at the 3H level on R37C34 and the 2.09 volt indication at TSP-5H on R42C44, the field calls represent voltages in excess of the full APC limit calculated for the 3/4" tubes in Braidwood 1. The SH level on R16C42 is considered as representing a possible bobbin indication of 0.61 volt, but field RPC was reported as NDD, suggesting the absence of significant ODSCC; evaluation of the tube metallography for this tube may provide some insight into the relative sensitivities of the bobbin and RPC probes for the less developed areas of ODSCC. i e 1 7-9
+
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Table 7-2. Braidwood #1 TSP ODSCC Indications (A1R04) March,1994 Steam Generator A Steam Generator 8 Steam Generator C Steam Generator O All Steam Generators Volte Volts Growth Volts Volts Growth Volts Volts Growth Volte Volts Growth Volts Volts Growth T5P # Man. Ave _ volts # Men. Ave. volts # Men. Ave. volts # Max. Ave. volts # Men. Ave. volts 1H 0 0 0 0 0 3H 344 4 99 0 86 0 37 134 4 25 0 68 0 13 708 2 38 0 72 0 21 403 8 82 0 82 03 1500 8 82 0 78 0 27 5H 238 8 33 0 95 05 116 2 75 0 59 0 23 235 2 46 0 62 0 16 180 10 44 0 75 0 28 770 10 44 0 75 0 26 1H 91 2 42 08 0 35 18 1 37 06 0 13 94 2 10 0 64 0 25 77 1 24 0.58 0.17 280 2.74 0 67 0 26 BH 28 3 46 0 83 0 44 3 0 44 0 41 0 08 20 0 92 0 55 0 24 23 1 59 0 57 0 25 74 3 46 O rc 0.31 9H 3 1 02 0 77 0 37 1 0 39 0 39 0 13 1 0 63 0 63 01 9 0 53 0.43 0 16 to 1 02 0 51 02 10H 2 0 76 0 63 0 22 0 1 0 45 0 45 0 18 1 0 67 0 87 0 43 4 0 76 06 0 26 I 11H 0 0 0 1 0 52 0 52 1 0 52 0 52 l l
1 i Table 7-4. Braidwood Unit 1 10/93 Inspection S/G C Only Elevation Number ofIndications IH 0 3H 346 5H 75 7H 23 r 8H 2 9H I 10H I 11H 1 Note: All Bobbin Indications: No RPC Confirmations _ CCEM!sC..\'L5
Table 7-6 Braidwood Unit 1 Cumulative Probability Distributions for Voltage Growth (per EFPY) I 1991 to 1992 1992 to 1993 1992 to iD94 As Scs SC C SG A 5G B 5G C SG D 6 we sous cod sota cod sous cod scos cod ses cod' sons cod Een sous cod 4 76 60 14 01 161 23 68 75 2/.57 268 26 17 196 28 96 702 26 67 0 8 56 27 10 76 34 85 70 53 31 167 42 de 91 42 31 404 40 54 01 15 13 77 42 76 94 48 68 de 70 96 159 58 01 121 60 03 422 56 10 02 16 23 35 67 68 10 64 63 57 94 40 85 66 157 73 34 46 72 62 346 03 21 35 93 57 71 48 50 49 69 16 59 66 62 16 91 54 97 82 81 59 81.26 231 77 00 04 21 05 61 66 20 73 83 39 72 35 12 95 96 62 86 87 30 85 65 143 8294 22 26 32 77 06 2 96 69 36 92 36 28 80 75 96 86 61 06 12 68 86 79 91 81 62 0 96 69 32 95 51 16 92 09 79 89 91 07 9 74 25 10 82 24 31 14 23 85 00 0 96 60 16 97 07 12 93 85 51 92 25 08 10 80 24 85 51 88 79 88 09 97 06 6 97 66 9 95 17 37 94 03 00 6 83 83 14 21 1 85 63 7 90.42 16 90 44 1 97 43 8 98 44 6 96 05 31 95 14 1 3 91 59 17 92 94 97 79 5 98 93 6 96 93 29 96 46 11 6 69 22 5 1 93 82 0 97 79 2 99 12 4 97.51 12 97 11 12 5 92 22 7 93.22 6 4 4 94 16 94 71 9616 2 99 32 3 97 95 12 97 59 13 94 61 6 1 95 33 4 95 29 98 53 3 99 61 0 97 95 8 97 77 14 1 95 21 5 1 96 03 4 95 68 0 98 53 1 99 71 2 9624 7 98 11 15 1 95 81 3 16 0 95 81 3 96 73 3 96 32 1 96 90 0 99 71 0 96 24 4 96 33 17 0 95 01 1 96 96 3 96 76 0 96 90 1 99 80 1 96 39 5 96 52 18 0 95 81 3 97 66 3 97.21 1 99 26 1 99 90 0 96 39 5 96 66 19 1 96 41 1 97 90 1 97 35 0 99 26 0 99 90 2 96 88 3 90 81 2 3 98 20 2 96 36 4 97 94 0 99 26 0 99 90 0 96 68 4 98 96 21 0 98 20 0 98 36 0 97 94 0 99 26 0 99 90 0 98 86 0 90 00 22 0 96 20 1 98 60 2 96 24 0 90 26 1 100 00 0 96 66 3 99 07 2J 0 96.20 0 96 60 1 98 38 1 90 63 0 100 00 2 96 98 4 99 22 24 0 98 20 0 96 60 2 96 68 0 99 63 0 100 00 0 96 98 2 99 30 25 1 96 60 0 96 60 1 98 82 0 99 63 0 10J 00 0 98 96 1 99 37 26 0 96 60 0 96 60 0 9682 0 99 63 0 100 00 0 96 96 0 99 37 9880 99 07 99 12 0 99 63 0 100 00 1 99 12 3 fr9 48 27 0 2 2 28 0 98 80 0 9W 07 0 99 12 0 99 63 0 100 00 0 9912 0 9952 29 0 98 80 1 99 30 0 99 12 0 99 63 0 100 00 1 90 27 1 99 55 3 0 98 80 0 99 30 2 99 41 0 99 63 0 100 00 0 99 27 2 99 63 32 0 96 60 1 99 53 1 99 56 0 93 63 0 100 00 1 99 41 2 99 70 34 0 96 80 0 99 53 0 99 56 1 100 00 0 100 00 1 99 56 2 99 78 36 0 98 80 1 99 77 0 99 56 0 100 00 0 100 00 0 99 56 0 99 78 38 0 98 80 0 99 77 0 99 56 0 100 00 0 100 00 1 99 71 1 9981 4 1 99 40 0 99 77 0 99 56 0 100 00 0 100 00 0 99 71 0 99 81 42 0 99 40 0 99 77 1 99 71 0 100 00 0 100 00 0 99 71 1 99 85 44 0 9'd 40 i 100 00 1 93 85 0 100 00 0 100 00 0 99 71 1 99 89 46 1 100 00 0 100 00 0 99 85 0 100 00 0 100 00 0 99 71 0 9989 48 0 100 00 0 100 00 0 99 65 0 100 00 0 100 00 0 99 71 0 99 89 5 0 100 00 0 100 00 0 99 85 0 100 00 0 100 00 0 99 71 0 99 89 55 0 100 00 0 100 00 0 99 85 0 100 00 0 100 00 0 99 71 0 99 89 6 0 100 00 0 100 00 1 100 00 0 100 00 0 100 00 0 99 71 1 99 93 65 0 100 00 0 100 00 0 100 00 0 100 00 0 100 00 0 99 71 0 9993 7 0 100 00 0 100 00 0 100 00 0 100 00 0 100 00 0 99 71 0 99 93 75 0 100 00 0 100 00 0 100 00 0 100 00 0 100 00 1 99 85 1 99 96 8 0 100 00 0 100 00 0 100 00 0 100 00 0 100 00 0 99 85 0 99 96 85 0 100 00 0 100 00 0 100 00 0 100 00 0 100 00 0 99 85 0 99 96 0 0 100 00 0 100 00 0 100 00 0 100 00 0 100 00 1 100 00 1 100 00 95 0 100 00 0 100 00 0 100 00 0 100 00 0 100 00 0 100 00 0 100 00 10 0 100 00 0 100 00 0 100 00 0 100 00 0 100 00 0 100 00 0 100 00 10 5 0 100 00 0 100 00 0 100 00 0 100 00 0 100 00 0 100 00 0 100 00
l Table 7-8 Braidwood Unit 1 AIRO4 Pulled Tube EC Results Tube I.D. Bobbin Bobbin RPC RPC Voltage Voltage Call Call SG A ' R27C43 IH - NDD NDD - 3H 4.88 85% SAI 5.28 - SH - NDD NDD - i R42C44 IH - NDD NDD - 3H 3.73 68 % MAI 3.24 max. 5H 2.09 49% SAI 1.62
- 7H -
NDD ,NDD - l 1 SG D f I R37C34 IH - NDD NDD - l 3H 1.04 92 % SAI 0.31 1 l 5H IO 44 82 % SAI 8.77 R16C42 IH - NDD NDD - 3H 3.12 70% > MAI 1.70 max. t SH 0.61
- NDD NDD -
t
- Indication not reported in field inspection. !
l 7 - 17 l l
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Figure 7-20 Braidwood Unit 1 - Cycle 3 Reactor Power Level 120 - - --- - - - - - - - - - - - - - 100 g, pg,j\ g ,ig {gy s.
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'Braidwood Unit 1 Cycle 2 Sodium to Chloride Molar Ratio 4
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Figure 7-24 Braidwood Unit 1 - Cycle 4 SG Blowdown Sodium to Chloride Molar Ratio 5 -- I 4
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Figure 7-26
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8.0 BRAIDWOOD-1 IPC CRITERIA AND EVALUATION This section summarizes the 1.0 volt IPC implemented for Cycle 5 at Braidwood-l and the supporting evaluations. The supporting evaluations include projected EOC-5 voltage distributions, SLB leak rates and tube burst assessments. Both deterministic and probabilistic tube burst assessments are given in this section. 8.1 General Approach to the IPC Assessment The tube integrity assessment approach applied to support the Braidwood-l IPC is based on demonstrating limited TSP displacement in a SLB event to reduce the likelihood of a tube burst to negligible levels and to conservatively ca;culate SLB leahage as free span leakage even though the limited TSP displacement would : reduce leakage compared to free span tube conditions. The structural analyses of Section 4 fx obtaining TSP displacements in a SLB event are applied to a conservative assumption that the TSP displacements expose a throughwall crack length equal to the TSP displacement. By applying the burst pressure versus throughwall crack length correlation of Section 6.2, both deterministic and probabilistic burst assessments are made for the assumed exposed throughwall crack length. That is, the burst capability is a function of the exposed throughwall crack length. This analysis is equivalent to assuming that the indication at the TSP has a throughwall crack length approximately equal to the TSP thickness. This is an extremely conservative assumption l since the bobbin voltages associated with such long throughwall cracks would be in the many l tens of volts and much higher than that found at Braidwood-l which are bounded by a maximum indication of 10.4 volts at EOC-4. Consequently, the conservatism of the burst assessment bounds any realistic growth rate for Braidwood-l and the burst margins obtained at EOC-5 based on limited SLB TSP displacements are essentially independent of growth rates. The limited SLB TSP displacement would result in most of the crack length for indications at TSPs covered by the TSPs and associated crevice deposits. This effect would tend to reduce leakage below that of free span indications which is the basis for data developed to support the EPRI SLB leak rate correlations of Section 6.5 which are used for the leakage analyses of this report. EdF has performed system leak rate measurements on French S/Gs at pressure differentials exceeding SLB conditions. Bobbin voltage levels in the French units at the time l of these te:;ts exceeded that found at Braidwood-1. In addition, the French units included I axial free span cracks in the roll transition at the top of the tubesheet which are left in service per repair criteria implemented by EdF. The total system leakage at pressure differentials typical of SLB conditions from these tests was on the order of a few gpm This leak rate is much lower than would be predicted by the EPRI leak rate correlations considering only the indications at TSPs and ignoring the roll transition indications. Thus the E@ tests 8-1
i i l l l Braidwood-1 EOC-4 Inspection Eddy current analysis guidelines and voltage normalization consistent with the EPRI ISI guidelines and with prior IPC applications (typical of Appendix A for prior Westinghouse IPC WCAPs such as WCAP-13854). Eddy current analysts were trained specifically to voltage sizing per the analysis guidelines and 52% of the analysts were qualified to the industry standard Qualified Data Analysis program. Use of ASME calibration standards cross-calibrated to the reference laboratory standard and use of a probe wear standard requiring probe replacement at a voltage change of 15% from that found for the new probe. 100% bobbin coil, full length inspection of all active tubes with a 0.610 inch diameter bobbin probe for all straight length tubing. RPC inspection of all bobbin indications greater than the 1.0 volt repair limit (actual implernented was all bobbin indications). RPC inspections were performed with a 0.620 inch diameter,3 coil motorized RPC probe. IU'C sample inspection of more than 100 TSP intersections with dents (at Braidwood-1, these are typically mechanically induced " dings") or artifact / residual signals that could potentially mask a 1.0 volt bobbin signal. Any RPC flaw indications in this sample will be plugged er repaired. The NRC will be informed, prior to plant restart from the refueling outage, of any unexpected inspection findings relative to the assumed characteristics of the flaws at the i TSP intersections. This includes any detectable circumferential indications or detectable indications extending outside the thickness of the TSP. The IPC eve.luations given in this report are based on the inspection results implementing the i above guidelines and the 1.0 volt IPC repair limit. 8.3 Operating Leakage Limit Regulatory Guide 1.121 acceptance criteria for establishing operating leakage limits are based
- on leak before break (LBB) considerations such that plant shutdown is initiated if the leakage associated with the longest permissible crack is exceeded. The longest permissible crack length is the length that provides a factor of safety of 1.43 against burst at SLB conditions i i
8-3
8.4 Projected EOC-5 Voltage Distributions The BOC-5 voltage distributions are obtained by applying the draft NUREG-1477 POD = 0.6 adjustment to all indications found in the EOC-4 inspection and subtracting the repaired indications. Data to develop the BOC-5 bobbin voltage distributinns are given in Table 7.3. Monte Carlo analyses are then applied to develop the EOC-5 voltage distribunons from the BOC distributions. The BOC voltages are increased by allowances for NDE uncertainties (Section 5.3) and voltage growth (Section 7.3) to obtain the EOC values. In the Monte Carlo i analyses, each voltage bin of the BOC distributions (Figure 8-2 for S/G D, for example) is increased by a random sample of the NDE uncertainty and growth distributions to obtain a EOC voltage sample. Each sample is weighted by the number of indications in the voltage bin. The sampling process is repeated 100,000 times for each BOC voltage bin and then repeated for each voltage bin of the voltage distribution. Since the Monte Carlo analyses yield a cumulative probability distribution of EOC voltages, a method must be defined to obtain a discrete maximum EOC voltage value. The method adopted in this report is to integrate the tail of the Monte Carlo distribution over the largest 1/3 of an indication to define a discrete value with an occurrence of 0.33 indication. For N indications in the distribution, this is equivalent to evaluating the cumulative probability of voltages at a probability of (N-0.33)/N. The largest voltages for all distributions developed by Monte Carlo in this report have been obtained with this defimtion for the maximum EOC discrete voltage. The next largest discrete EOC voltage indication is obtained by integrating the tail of the Monte Carlo distribuuon to one indication and assigning the occurrence of 0.67 indication. This process for developing the largest EOC voltage indications provides appropriate emphasis to the high voltage tail of the distribution and permits discrete EOC voltages for deterministic tube mtegrity analyses. As described m Section 8.5 below, S/G D is the most limiting S/G for SLB leakage analyses and has been evaluated using final Braidwood-l mspection results and tube plugging data. The Cycle 4 voltage growth distribution of Table 7.6 for S/G D has been used to obtain the EOC voltages by Monte Carlo analyses as described above. The resulting BOC-5 and EOC-5 { bobbin voltage distributions are shown in Figure 8-2. Based on applying the POD - l adjustment, the largest BOC voltage indication left in service is 0.7 indication at 10 4 volts. ; At EOC-5, the largest voltage indication is projected to be 11.2 volts. The EOC-5 distribution of Figure 8-1 is used for the S/G D SLB leakage analyses in Section 8.5. l As shown in Table 7.3, the number of indications found at EOC-4 in S/G B was 277 compared to 741 in S/G A,1062 in S/G C and 696 in S/G D. It is clear that S/G B is not limiting for tube integrity considerations and this S/G was not analyzed to obtain EOC distributiens or leak rates. S/Gs A and C were analyzed using preliminary inspection results and growth rate data which have not had large changes in the fmal data. The voltage growth distribution for S/G A was applied in the Monte Carlo analyses for both S/Gs A and C. The ; 8-5 4
provides the projected EOC-5 voltage distribution including the POD = 0.6 adjustment. The P.i and 0.i columns represent the POL and expected leak rate for each voltage bin. The remaining columns provide data for the upper bound confidence of 95% applied to the leak rate. l Application of the POD adjustment to the EOC-4 voltage distribution leads to large voltage indications postulated to have been missed in tne inspection and left in service at BOC-5. i With the 1.0 volt repair limit and only RPC NDD indications above 1.0 volt left in service, the expec:ed SLB leakage at BOC-5 would be about zero. The influence of the POD adjustment on predicted leakage values can be estimated by calculatmg the leak rate for the , BOC-5 voltage distribution. The resulting SLB leak rate for S/G D at BOC-5 is 1.7 gpm compared to the expected near zero value. The leak rate thus increases only from 1.7 gpm at BOC to 3.1 gpm at EOC. Thus growth to the EOC only increases the SLB leak rate by about 1.4 gpm which would be near the projected leak rate assuming a POD of about 1.0. 8.5.2 SLB Leak Rate Sensitivity to POL Correlations The NRC has requested that the projected EOC-5 SLB leak rate be provided for all six POL correlations discussed in draft NUREO-1477. These results provide sensitivity estimates to the form of the POL correlation. As discussed in Section 6.4, the linear and log Cauchy distributions are not consistent with the pulled tube database for low voltage (< 2.0 volt) probability of leakage and are not recommended for considerr. tion as acceptable POL l correlations The estimated BOC-5 and EOC-5 SLB leak rates for all six POL correlations are given in Table 8-2. The results for the reference log logistic POL correlation have been described above and are repeated in Table 8-2. It is seen from Table 8-2 that the SLB leak rates are essentially independent of the POL correlation applied to obtain the leak rates. The low leak rates for indications below I to 2 volts tend to offset the effects of the differences in POL correlations. As seen in Table 8-1 for the column titled N.i'P.i'Q.i, which gives the expected leak rate, the SLB leak rates are dominated by EOC indications above about 3 volts even though only a small fraction of the EOC indications are in this voltage range. 86 Assessments of SLB Burst Margins and Probability of Burst S.6.1 Deterministic Burst Margin Assessments Although the technical support for the Braidwood-l IPC is based on tube burst for limited TSP displacement, significant margins exist for free span burst considerations for voltage growth in excess of 95% cumulative probability. Limited TSP displacement considerations 8-7
pucked crevices with associated tube corrosion at the FDB intersections. Since no Braidwood-l indications at the FDB have been found, the FDB is not included in the tiibe burst assessment The projected EOC-5 voltage distributions of Section 8.4 above are total mdications independent of TSP elevation and tube location. The EOC-4 inspection results can be used to develop the distribution ofindications between TSP elevations and the fraction of indications occuring at tube locations where tne TSP displacements are significant. TSP displacements as a function of tube location were developed from the analyses described in Section 4 and the number of tube locations as a function of displacement are summarized in Table 4.5.3. Table 8-4 provides the inspection results for S/Gs A, C and D as a function of TSP elevation and TSP displacement. S/G B is not included due to the smaller number ofindications found in this S/G The table includes the fraction, Fo, ofindications found as a function of displacement. Also given in the table are the number and fractions ofindications for a uniform distribution of all tube intersections. Only 9 indications on plate 7 have been found in all S/Gs at tube locations having displacements large enough (greater than abor; 0.6 inch) to signi6cantly influence the tube burst probability. The largest bobbin voltage for any of these 9 indications was 1.24 volts and the largest indication found anywhere on plate 7 was 2 74 volts. These indications would have a high burst pressure even as free span indications. Thus, the inspection results indicate a low frequency of indications and low voltages at tube locations subject to signi6 cant SLB TSP displacements. The data of Table 8-4 can be used to define bounding distributions for indications as a function of TSP elevation and displacement. The highest fraction of indications at TSPs 3 and 7 were 67% at TSP 3 in S/G C and 13% at TSP 7 in S/G A. These values are used for the fraction of total indications at these TSP elevations. The bounding distribution for the fraction ofindications on the TSP as a function of TSP displacement is obtained as the larger found by inspection or the uniforin distribution. The resulting bounding distributions for plates 3 and 7 are given in Table 8-4. Also given is the weighted sum for the fraction of TSP indications as a function of displacement. This is obtained as the sum of the individual plate fractions multiplied by the fraction of indications for the TSP elevation. This weighted sum of the bounding distributions is applied in the tube burst probability analyses as described below. The number of indications as a function of TSP displacement can be obtained as the product of the total number ofindications times the bounding fractional distribution of Table 8-4. This product can be obtained as a function of bobbin voltage by applying the number of indications in each voltage bin. The voltage bins and the number of EOC-5 indications in each voltage bin are shown in Figure 8-2 and Table 8-1 for S/G D, the most limiting S/G. Conservatively assuming that the TSP displacements expose throughwall cracks, the 8-9
8.6.3 SLB Burst Probability for S/G D at EOC-4 The burst probability for S/G D at EOC-4 with limited TSP displacement can be obtained directly from the indications found and the TSP displacement at each cpecific indication. This application demonstrates the general methodology for the limited TSP displacement, burst probabilities without the need for distributing the indications as described in ' Section 8.6.2 above. Table 8-5 identifies the indications fcund in the inspection for the larger voltage indications and for indications at locations having the largest TSP displacements in the hot standby SLB event. The bobbin voltage and free span burst probability at the given voltage level are provided for each indication. Also given in the table are the local TSP displacement and the burst probability for a throughwall crack length equal to the TSP ! displacement (conservatively assumed exposed throughwall crack length). The applicable ! SLB burst probability column shows the lower of the free span or throughwall burst probability for each indication. The lower of the two burst probabilities is the appropriate i value since the limited TSP displacement can reduce the free span burst probability but the free span probability cannot be exceeded The throughwall burst probability can exceed the free span value only because it is conservatively calculated for a throughwall crack while the free span value, based on bobbin voltage, is more realistically based on the actual crack morphology as reflected in the voltage amplitude. For the S/G D indications given in Table 8-5, ie total burst probability calculated assuming free span (very large SLB TSP displacements) conditions is 3.7 x 10 4 Accounting for the hmited SLB TSP displacements at the locations of the indications, the total burst probability is 1.7 x 10 4 Thus the limited TSP displacements reduce the burst probability by three orders of magnitude. It can be noted that none of the high voltage indications occurred at locations of high TSP displacement and the TSP constraint reduces the burst probability for these high voltage indications to approximately zero. Only the small voltage indications found at the corners of plate 7, where SLB displacements are significant, contribute to the burst probability. The results of Table 8 5 show the effectiveness of limited TSP dispiacements in reducing the tube burst probability to small values and also show that Braidwood-l had an acceptably low burst probability at EOC-4. l 8.6.4 Conservative Burct Probability for SLB at Normal Operating Conditions For a SLB at normal operating conditions, it is shown in Section 4, Table 4.5.1 that TSP displacements are small and significantly less than that for an SLB at hot standby conditions. The maximum TSP displacement occurs for plate J and is limited to 0.438 inch. The maximum displacements for all other plates are < 0.2 inch. An extremely conservative or boundmg burst probability for this event can be obtained by assuming that the SLB B - 11 I
l of indications, free span burst probability, the distribution of indications and throughwall burst probability as a function of the SLB TSP displacement are given in Table 8-7. By applying Equation 2, the net probability of burst for each voltage level is obtained as given in the last column of the table. The total limited TSP displacement burst probability is obtained as 8 x ; 10 The influence of the limited TSP displacement can be seen by comparison with the estimated free span burst probability (column 3) of 9 x 10 4 The latter free span result is dominated by the large projected EOC-5 voltage indications up to 11.2 volts which are traceable to applying the POD adjustment to all indications found in the last inspection prior to reducing the population for tubes repaired at EOC-4. The estimated SLB tube burst probability of 8 x 10 is significantly less than the acceptance guideline for IPC applications of 2.5 x 102, which was found acceptable in NUREG-0844. The normal operating and hot standby burst probabilities can be combined by weighting the separate burst probabilities by the fraction of operatmg time in each operating condition. Applying the Section 4.6 Braidwood I fractions of 0.962 for normal operation and 0.038 for hot standby, the combined burst probability is 3.1 x 10 4 8.6.6 Braidwood-l Frequency of SLB Event with a Tube Rupture In Section 4.6, Sraidwood-l frequencies of occurrence were developed for an SLB at both normal operating and hot standby (Mode 3) conditions. The frequencies are summarized in Figure 8-5. The frequency for at ' LB event at hot standby conditions is a factor of 25 lower than at operating conditions and is only about 6.8 x 104 per year. Figure 8-5 includes the conditional probability of a tube rupture at normal operating and hot standby conditions as developed in Sections 8.6.4 and 8.6.5, respectively. The SLB event frequencies and conditional tube rupture probabilities are combined in Figure 8-5 to obtain a frequency of 4 about 5.5 x 10 per year for a Braidwood l SLB event with a subsequent tube rupture. This very low frequency has negligible influence on the core damage frequency and supports full cycle operation at Braidwood l following implementation of the IPC for Cycle 5. 8.7 Summary of Results ; i An IPC with a 1.0 bobbin voltage repair limit has been implemented for Braidwood-l Cycle 5 i operation. Inspection requirements typical ofIPC practice, such as the guidelines of the Catawba-1 NRC SER, were applied at the Cycle 4 refueling outage to support implementation of the IPC An operating leakage limit of 150 gpd is being applied for Cycle 5 operation. . The results of the Braidwood-l IPC assessment can be summarized as follows: ! l
. The projected EOC-5 SLB leakage is 3.1 gpm which is less than the allowable limit of 9.1 gpm for Braidwood 1. The SLB leak rate was evaluated for the six alternate formulations of the probability of leak versur voltage correlation identified in draft NUREG-1477 and 8 - 13 i
l
Table 81: Braldwood 1, SG "D*, pod = 0.6, EOC 5 Volts Caveny i EOC Volts Cum Prob [ N.i P.i O
@2560 psi Variance O.1 N.f*P.l*C.i p,[
l 0.2 0.000984 1016.00 1.0 3.11E 02 5.17E-04 6.15E 05 1.61 E-05 1.92E 06 ) 0.3 0.010827 1015.33 10.0 319E 02 1.78E 03 3 49E 04 5.67E 04 1.12E 05 O.4 0.049213 1005.09 39 0 3.26E 02 4.12E 03 1.22E-03 5.24E 03 4 02E 05 0.5 0.123031 966 28 75.0 3.34E-02 7.83E 03 3.26E 03 1.96E-02 1.11 E-04 0.6 0.222441 891.35 101.0 3 42E 02 1.32E 02 7.40E 03 4.55E 02 2.59E 04 l 0.7 0.334646 790.25 114.0 3.51E 02 2.04E-02 1.50E 02 8.17E 02 5.40E-04 ' O.8 0.447835 675.79 115.0 3 60E 02 2.99E-02 2.78E 02 1.24E 01 1.03E 03 , 0.9 0.550197 561.22 104.0 3.70E 02 4.18E 02 4.84E 02 1.61 E-01 1.85E-03 l 1.0 0.639764 456.55 91.0 3.80E 02 5.64E-02 8.00E-02 1.95E-01 3.16E 03 1.1 0.712598 366.30 74.0 3 91E 02 7.41E 02 1.27E-01 2.14E-01 5.16E-03 1.2 0.771654 291.82 60.0 4.02E 02 9.51E-02 1.94E 01 2.29E 01 8.13E-03 1.3 0.817913 231.92 47.0 4.14E 02 1.20E-01 2.87E-01 2.33E-01 1.25E 02 1.4 0.853346 184.b6 36.0 4 27E 02 1.48E 01 4.15E 01 2.27E 01 1.86E-02 1.5 0.880906 148 63 28.0 4 40E 02 1.81 E-01 5.86E 01 2.23E-01 2.72E-02 1.6 0.902559 120.69 22.0 4.55E 02 2.18E 01 8.12E-01 2.18E 01 3.90E-02 1.7 0.919291 99.09 17.0 4.70E42 2 60E-01 1.11 E+00 2.07E 01 5.50E 02 1.8 0 932087 82.01 13.0 4.86E 02 3.06E-01 1.48E+ 00 1.94 E-01 7.65E 02 1.9 0.942913 69.04 11.0 5.04 E-02 3.59E-01 1.96E+00 1.99E-01 1.05E-01 2.0 0.950787 58.50 8.0 5.23E 02 4.16E-01 2.56E+ 00 1.74E 01 1.42E-01 2.1 0.956693 50.34 6.0 5.43E 02 4.80E 01 3.30E+ 00 1.57E-01 1.91E 01 2.2 0.961614 43.86 5.0 5.66E-02 5.50E-01 4.22E+00 1.C6E-01 2.55E-01 2.3 0.965551 38.83 4.0 5.89E 02 6.27E-01 5.34E+00 1.48E 01 3.36E 01 24 0 968504 34.97 3.0 6.15E 02 7.11E 01 6.69E+00 1.31E 01 4.41E 01 2.5 0.971457 31.96 3.0 6 44E 02 8.01 E-01 8.33E+00 1.55E 01 5.75E-01 2.6 0.973425 29.39 20 6.75E 02 9.00E 01 1.03E+01 1.21E 01 7.45E 01 2.7 0.975394 27.19 2.0 7.09E C2 1.01 E+00 1.26E+ 0 i 1.43E-01 9.60E41 2.8 0.976378 25.24 1.0 7.47E 02 1.12E+ 00 1.54E+01 8.36E 02 1.23E+00 2.9 0.97834C 23.55 2.0 7.89E-02 1.24 E+ 00 1.86E+01 1.96E.01 1.58E+00 3.0 0.979331 21.99 1.0 8.35E 02 1.37E+00 2.24E+01 1.15E 01 2.01 E+00 3.1 0.981299 20.55 2.0 8.88E 02 1.52E+00 2.68E+01 2.69E 01 2.57E+00 3.2 0.982283 19.34 1.0 9 47E 02 1.67E+00 3.19E+01 1.58E-01 3.26E+00 3.3 0.983268 18.25 1.0 1.01E 01 1.83E+00 3.79E+01 1.85E-01 4.15E+00 34 0.984252 17.35 1.0 1.09E-01 2.00E+ 00 4.47E+01 2.18E-01 5.27E+00 36 0.98523G 15.74 1.0 1.29E 01 2.37E+00 6.15E+01 3.05E 01 8.55E+ 00 3.7 0.986220 15.01 1.0 1.41E 01 2.57E+00 7.18E+01 3.63E-01 1.09E+01 39 0.987205 13.56 1.0 1.74E-01 3.01 E+00 9.67E+01 5.24E 01 1.81 E+01 4.0 0.988189 1203 1.0 1.96E 01 3.25E+ 00 1.? ?E+02 6.37E 01 2.35E+01 4.1 0.989173 12.08 1.0 2.23E 01 3.50E+00 1.28E+02 7.83E 01 3.08E+01 4.3 0.990157 10.55 1.0 3.01E 01 4.05E+ 00 1.69E+02 1.22E+ 00 5 42E+01 44 0.991142 9.71 1.0 3.55E-31 4.34 E+ 00 1.93E+ 02 1.54E+00 7.26E+01 4.5 0.992126 8.94 1.0 4.19E41 4.64E+00 2.19E+02 1.95E+ 00 9.71E+01 4.7 0.903110 7.51 1.0 5.63E 01 5.30E+00 2.82E+02 2.99E+ 00 1.66E+02 4.8 0.994094 6.90 1.0 6 30E 01 5.65E+00 3.19E+02 3.5GE+00 2.08E+ 02 5.1 0 995079 5.62 1.0 7.69E 01 6.80E+ 00 4.54E+02 5.22E+ 00 3.57E+02 5.7 0.996063 4.60 1.0 8.79E 01 9.55E + 00 8.75E+02 8.40E+00 7.80E+ 02 7.4 0.997047 3.52 1.0 9 51E 01 2.14E+01 4.24E+03 2.04E+ 01 4.05E+03 8,9 0.998031 2.52 1.0 9 68E-01 3.81 E+ 01 1.33E+04 3.69E+ 01 1.29E+04 9.7 0.999016 1.58 1.0 9 73E 01 5.00E+ 01 2.29E+04 4.87E+01 2.24E+04 10.5 0.999705 0.65 0.7 9.77E-01 6.43E + 01 3.80E+ 04 4.40E+01 3.72E + 0
- 11.2 1.000000 0 33 03 9 79E-01 7.89E+01 5 76E+04 2.32E+01 5 65E+04 Flegression Equations Analysis Sum [ Ni
- E(Qi)
- Pi ) = 205.592 Sum [ Var + Cov } = 9.17E+04 Effectwe Standard Deviaton = 3.03E+02 Contdonce = E 5.0%
Z - Deviate = 1.645 Q. total (LPH) = 703.6
- 0. total (GFM) = 3.098 8 - 15 lCasw 34al930 toc W me. F 10 N
Table 8 3 Summary of Deterministic Margms Against Burst at SLB Conditions (95% Confidence) Parameter S/G A S/G B S/G C S/G D RPC Confirmed Ir.dications Left in Service Largest bobbm voltage 1 00 1.00 1.00 1.00 NDE uncertainty at 95% 0.20 0.20 0.20 0.20 confidence 20% of bobbin voltage Voltage growth at 95% 1.40 0.50 1.40m 1.00 cumulative probability Projected EOC-5 Voltage 2.60 1.7 2.60 2.20 Allowable EOC Voltage at 4 54 volt 1.43xAP3tn Largest Bobbin Voltage, RPC NDD Left in Service Largest bobbin voltage 1.48 2.03 1.55 1.8 NDE uncertainty at 95% 0.30 0.41 0.31 0.36 confidence 20% of bobbin voltage Voltage growth at 95% 1.40 0.50 1.40m 1.00 cumulative probability Projected EOC-5 Voltage 3.18 2.49 3.26 3.16 Allowable EOC Voltage at 4.54 1.43xAPst , Notes: 1. Growth rate for S/G A conservatively applied to S/G C 4 I 8 - 17 I
I l Table 8 5 ' Braidwood 1, SG D - Estimated Hot Standby SLB Burst Probability at EOC-4 Tube / Location Free Span Burst Ltmited TSP Disp Burst (1) Applicable SLB f Row Col Volts Burst Prob (2) j TSP Burst Prob Local TSP Disp TW Burst Prob l l
\
37 34 5 10 44 2.0E-02 < 0.12 < 1 OE-12 -00 23 12 3 8.82 1.2E-02 < 0.3 5 < l.0E-11 -00 12 9 3 5.02 1.5E-03 < 0 35 < 1 OE 11 -00 l 11 9 3 4.28 8 OE-04 < 0 35 < 1 OE-11 -00 19 7 3 3.95 5.7E-04 < 0.35 < l .0E l 1 - C.0 1 33 20 3 3.83 5.0E-04 < 0.35 < l.0E 11 - 0.0 1 35 29 3 3.62 3.9E-04 < 0.35 < l.0E-11 -00 11 12 3.21 2.3 E-04 < l .0E 11 3 < 0.3 5 -00 16 42 3 3 12 2.0E-04 < 0.35 < l.0E 11 - 0.0 2 105 3 2.84 1.3E 04 < 0 35 < 1 OE 11 - 0.0 8 20 3 2.77 1.2E-04 < 0.35 < l.0E 11 -00 43 56 3 2.60 8 8E 05 < 0.35 < l.0E-11 -00 32 27 5 2 48 7. lE-05 < 012 < l .0E-12 - 0.0 45 53 3 2.30 4.9E-05 < 0.35 < l.0E-11 - 0.0 l 31 20 3 2.20 4.0E-05 < 0.35 < l.0E 11 - 0.0 1 27 35 3 2.18 3.8E-05 < 0 35 < 1.0E-11 -00 41 55 3 2.16 3.7E-05 < 0.35 < l.0E-11 - 0.0 43 53 3 2.11 3.3E-05 < 0.35 < l.0E-11 - 0.0 2 113 3 0.59 2.2E47 0.514 1.9E-05 2.2E-07 I 3 110 3 0.58 2.lE-07 0 406 3.5E-09 3.5E-09 2 113 7 0.56 1.9E-07 0.804 4.5E-01 1.9E-07 2 108 7 1.10 3.5E-06 0.631 9.0E-03 3.5E-06 2 105 7 0 61 3.5E-07 0.530 5.3E-05 3.5E-07 2 11 7 0 72 5 6E-07 0 498 4.9E-06 5 6E 07 4 106 7 0.52 1.4 E-07 0.532 6.3E-05 1.4E-07 4 112 7 1.24 6 OE-06 0.718 1.2E-01 6.0E-06 5 112 7 1.24 6.0E-06 0 692 6.4E-02 6.0E-06 (continued on next page)
l l l Table 8-6. Bounding SLB Burst Probability at Normal Operating Conditions EOC-4 Bounding SLB Burst Probability Indications Maximum TSP Max. Exposed TSP Displacement Max. Volts Length Burst Prob. for (inch) No. Ind. at Number Burst Ind. at All at TSP TSP Tubes Prob.m H.L. Int?
-. a 1/A 3/C 5/F 7/J 8/L ,
9/M 10/N 11/P Total Burst <$ x 10 4 Probability Notes: 1. Maximum number of indications in any S/G at the noted TSP.
- 2. Burst probability for a throughwall crack length equal to the <
maximum TSP displacement of column 2.
- 3. Burst probability assuming all hot leg TSP intersections have a throughwall crack length at maximum TSP displacement. ,
8 - 21
Table 8-7 Braldweed-I SG D: EOC-5 Burst Probability for list Standby SLB with Limited TSP Displacement Free EOC-5 Span Plate 3 and 7 Conation F, and PRBoas a Function of TSP Displacement No. of Butst < 045* O 45* - 0 50- 0.50* - 0.55' O 55' - 0 60* 060*-065* 2065* (2) Net Prob I Voltage Ind. Prob ef Durst Din NV PRD(V,) F. PR. l o PRDg" 6 F. PRBo Fo Fo PRBg" Fo PRHg" Fo Pray" PRB, 2.7 2.0 1.7E-4 8.5E-9 (Note 3) 6 lE-9 (Note 3) 2 0E-7 (Note 3) 0 003I 1.7E-4 0 0017 1.7E-4 0 0068 I 7E-4 4 4E4 2.8 1.0 2.0E-4 8.5E-9 6.lE-9 2 OE-7 0 0031 2 OE-4 0 0017 2 OE-4 0 0068 2OE-4 2SE4 2.9 20 2.3E-4 8.5E-9 6 lE-9 2 0E-7 0 003I 2.3E-4 0 0017 2 3E-4 0 0068 2.3 E-4 5 8E4 ' 30 10 2 6E-4 8SE-9 6.lE-9 2 OE-7 0 0031 2 6E-4 0 0017 2 6E-4 0.0068 2.6E-4 32E4 i i 31 20 3 OE-4 8 SE-9 6. l E-9 2.0E-7 0.0031 3 OE-4 0 0017 3 OE-4 0 0068 3 OE-4 7.4E4 3,2 10 3 4E-4 8. 5E-9 61E-9 2.0E-7 0 0031 3 4E-4 00017 3 4E-4 0 0068 4 3 4E-4 4 2E4 3.3 1.0 3.8E-4 8 SE-9 6 lE-9 2 OE-7 0 0031 3.8E-4 0 0017 3 BE-4 0 0068 3 RE-4 4 4E4 l 34 10 4.3E-4 8.5 E-9 6.IE-9 2 0E-7 0 0031 4 3E-4 0 0017 ME 4 0.0068 5 2E4 t 4.3 E-4 y 36 10 5.4E-4 8.5E-9 6.IE-9 2.0E-7 0 0031 5 4E-4 0 00 D 5 4E-4 0 0068 5 4E-4 6.5E4 3.7 1.0 6 OE-4 8SE-9 6 iE-9 2 OE-7 0 0031 6.0E-4 0 00I7 6 OE-4 0.0068 6 OE-4 7.2E4 39 10 7 4E-4 8 SE-9 6 IE-9 2OE-7 0 0031 6 IE-4 0 0017 7 4E-4 0 0068 7 4E-4 84E4 4.0 1.0 8 2E-4 8 SE-9 6 lE 9 2 OE-7 19E4 (Note 3) 0 0017 8 2E-4 0 0068 8 2E-4 9 IE-6 l 4.1 to 9.0E-4 8.5E-9 6 1E-9 2 0E-7 1.9E4 0 0017 9 0E-4 0.0068 9.0E-4 9 8E4 4.3 1.0 1.lE-3 8 SE-9 6 IE-9 2.0E-7 1.9E-6 0 0017 l . I E-3 0 0068 I . lE-3 1. l E-5 4.4 1.0 1.2E-3 8.5E-9 6.lE 9 2.0F-7 1.9E-6 0 0017 12E-3 0 0068 12E-3 12E-5
- 4.5 10 1.3 E-3 8.5E-9 6.lE-9 2 DE-7 1 I .9E-6 0.0017 I 3E-3 0 006R I 3E-3 13E-5 4.7 10 1.5E-3 8SE-9 6.lE-9 20E-7 1.9E-6 0 0017 i SE-3 0 0068 i SE-3 i SE-5 I
i r 1 a e _ i 4 i t t t Figum 8-1. Leak Rate Under Normal Opemting Conditions versus Crack Length for 3/4 Inch Tubing
- - - . .,--.,..----.,,,,,.....-.,..c,
- - - ~
Figure 8-3: Braidwood 1, SG "A" BOC & EOC 5 Indications BOC Indications (Preliminary) Adjusted for pod = 0.6 160 0 BOC 5 Indications 140 - E EOC 5 Indications 120 - p too _ _ _ e 8 s
$ 80 - - - - -
e Largest RPC NDD Z 60 - - _ _ indication Left in Service. yo _ _ _ _ _ _ _ 20 - - - - - - - - 0 -h '+ 1 1 1 1 1 1 1 4 i , ; ; J ;r ;r ; ; ; th W pfp W w ;a:-;:;:;_;#,;;_,-p.y.r %
; amass aaneaanaaa an: : : : : : : : : : :
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i' . l Figure 8-5. Estimated Braidwood-1 EOC-5 Frequency of SLB Event with a Tube Repair l Braidwood-l SLB ) Frequency 1.8 x 10-3/yr i Fraction of Time at Fraction of Time at Normal Operation Hot Standby . Mode 3 0.96 0.038 I l Full Power SLB Frequency Hot Standby SLB Frequency 4 1.7x10 /yr 6Jul04/yr e Limited TSP Displacement o IJahed TSP Displacement o Free Span e Conditional Probability of o Conditsonal Probability of o Conditional Probability of Rupture for SLB Rupture for SLB Rupture for SLB ' e Normal Operation Conditions o Hot Standby Condition o Hot Standby Condition l
# 4
< 5410 8x10' 9x10 :
h,A* For Information Only I l Combined Frequency of SLB Combined Frequency of SLB at Normal Operation and at Hot Standby and a Tube Rupture Tube Rupture 8.5x10*/yr 5.4x10*/yr Frequency of SLB - and a Tube Rupture 5.5x10*/yr l M ' I
~ l ATTACHMENT I 1 Byron /Braidwood Eddy Current inspection Guidelines July 1994 i
Commonwealth Edison Company Byron & Braidwood Stations Units 1 & 2 Eddy Current Analysis Guidelines
+
l' l y r ,T, l h . E jh '
, MLu l, D
Rev.7 July 1994 1
Table of Contents Section Title Eggg I 1 1.0 Purpose 1 2.0 Scope 3.0 Responsibilities 1 Personnel Qualifications 2 4.0 General Analysis Requirements 2 S.0 Bobbin Probe Analysis Requirements 3 6.0 Rotating Probe Analysis Requirements 11 7.0 8.0 Recording and Reporting Requirements 14 Resolution Criteria 15 9.0 APPENDICES Appendix A Data Acquisition and Analysis Requirements for TSP ODSCC APC Appendix B Analysis Guidelines Change Forms Appendix C Analysis and Retest Codes Appendix D Support Structures Nomenclature and Measurements
\ COMMONWEALTH EDISON Rev. 7 Jufy 1994 Byron & Braidwool Units 1 & 2 Analysis Guidehnes 1.0 PURPOSE eddy current vendor with CECO concunence.
Responsibilities of these Analysts are as follows: 1.1 The purpose of this guideline is to provide general instructions and to define specific 3.2.1 Senior Analyst requirements for the analysis of eddy current data acquired from the Commonwealth Edison a. Analyze eddy current data in accordance Company (CECO) 13yron and Braidwood Units 1 with this guideline. & 2 steam generatr,rs.
- b. Identify and process required changes to 1.2 Analysis guidelines provide a structure to the guideline during the course of the ensure that data is (a) analyzed in accordance examination as circumstances may warrant.
with the appropnate techniques and practices Changes are documented using the Analysis that reflect current industry experience, (b) in a Guideline Change Form in Appendix B to this consistent and repeatable manner and (c) in guideline and are subject to CECO approval. compliance with CECO requirements.
- c. Promptly inform all data Analysts of 1.3 Conditions encountered during the course changes to this guideline as such changes occur.
of a steam generator examination not foreseen The Analysis Guideline Change by this guideline are to be reported by data Acknowledgment Form in Appendix B is used to analysts to the Lead or Senior Analyst . document receipt and review of changes by all l 1 Analysts. 2.0 SCOPE
- d. Perform duties of Lead Analyst or Analyst '
2.1 This guideline provides instructions and as required. define specific requirements for bobbin and rotating probe eddy current data analysis for the 3.2.2 Lead Analyst Byron and Braidwood Station steam generators.
- a. Analyze eddy current data in accordance 2.2 This guideline also provides direction in with this guideline.
applying analysis requirements for an outer diameter stress corrosion cracking at tube b. As a Resolution Analyst, resolve l support plates Alternate Plugging Criterion discrepancies between primary and secondary (APC). Analysts and resolve LAR (Lead Analyst Resolution) calls in accordance with the 3.0 RESPONSIBILITIES resolution criteria in Section 9 of this guideline. 3.1 Commonwealth Edison is responsible for c. Promptly inform tne Senior Analyst of I interpreting, maintaining and implementing these circumstances that arise during the course of guidelines, and determining plant specife APC data analysis that are not consistent with or not eddy current data analysis applicability. addressed by this guideline and may require changes. 3.2 The Senior Analyst, shift Lead Analysts, and data Analysts are selected by CECO or the 1
l l
\ COMMONWEALTH EDISON I
Byron & Braktwood Units 1 & 2 Analysrs Guuselines Rev. 7 Jufy 1994 3.2.3 Analyst 5.3 Data analysis consists of reviewing Lissajous and strip chart displays to the extent
- a. Analyze eddy current data in accordance ' that all indications of tube wall degradation and with this guideline. other signals as defined by this document are reported and dispositioned in accordance with
- b. For each calibration group of data the requirements of this document.
analyzed, prepare and submit a final report consistent with this guideline that is complete 5.3.1 All recorded data shall be evaluated and free of errors. regardless of the extent tested.
- c. As a Resolution Analyst, resolve 5.3.2 Phase angle measurements shall be discrepancies between primary and secondary made utilizing VOLTS MAXRATE for signals Analysts in accordance with the resolution which have a well-defined transition. For cases entena in Section 9.0 of the guideline. where no clear transition exists, a VOLTS PEAK-TO-PEAK approach shall be used. The 4.0 PERSONNEL QUALIFICATIONS use of guess angle shall be kept to a minimum and only used when the latter two analysis 4.1 Personnel analyzing data shall be functions do not give a good representation of qualified in accordance with SNT-TC-1 A and the signal phase angle.
certified to Level llA or Level 111. 5.3.3 Indications for which there are no 4.2 in addition, the analyst shall have applicable reporting criteria or which the Analyst received training in the evaluation of eddy considers to be ambiguous or indeterminate current data for nonferromagnetic tubing, should be reported as LAR. The Lead Analyst must resolve such indications with the 4.3 Data analysts will successfully pass a concurrence of the Senior Analyst. CECO eddy current data Analyst performance demonstration program consisting of site-specific 5.4 All acquired data shall be subject to two training and testing prior to analyzing production independent analyses. These are referred to as data. " primary" and " secondary" analyses. 5.0 GENERAL ANALYSIS REQUIREMENTS 5.4.1 The two individual analysis results shall be reviewed for discrepancies in 5.1 All recorded indications shall be accordance with Section 9.0 of this guideline. evaluated in accordance with this guideline. Guideline changes must be implemented using 5.4.2 If no discrepancies exist between the the change form given in Appendix B. primary and secondary analyses, then the primary analysis results shall be considered as 5.2 There is no minimum voltage threshold for final. ceporting indications believed to be attributable to tube wall degradation. 5.5 All previous history must be addressed. If no indication is identified at the previous reported location an INF or INR 2
~ n l COMMONWEALTH EDISON t L. J j Byron & Braidwood Units 1 & 2 Analysis Guidelines Rev,7 July 1994 l analysis code (See Appendix C) will be used. 5.10.3 Support structure (landmark) !
nomenclature and measurements are identified ' 5.6 Axial locations in the hot leg shall be in Appendix D of this guideline. ! reported in a positive direction from supports, i AVB's, tube sheet, and tube end up to but not 5.11 Calibration Verification r including 011C. - l i 5.11.1 ASME Standard ! l 5.7 Axial locations in the cold leg shall be ; reported in a positive direction from supports, a. Calibration verification shall be performed ; tub, sheet, and tube end up to 011C. at the beginning and end of each calibration ! group. If the requirements are not met for bobbin 5.8 Probe speed (axial traverse speed and probe data then the data Analyst will identify the RPM as applicable) should be verified on the affected data and determine which tubes, if any, ; following occasions: require retest. ! 5.8.1 At each calibration run. b. The ASME calibrations shall be compared ! , within the following parameters using Channel 1: ( 5.8.2 At any time probe speed is ; questionable. (1) The phase angle of the 100% through-wall ! hole response should be at 40" +/- 5 . l 5.9 Storina Analysis Setuos ! (2) The phase angle of the 20% drill hole l 5.9.1 The analysis setup established for each response should be between 50* and 130" ( calibration group shall be stored to the data clockwise from the 100% drill hole response. , recording medium. i (3) Responses from the calibration ! 5.9.2 Each primary, secondary or resolution discontinuities should be clearly indicated and l Analyst shall store results to primary, secondary, discernible from each other and probe rWion. i or resolution files respectively. : 6.0 BOBBIN PROBE ANALYSIS 5.10 Reportina Criteria , 6.1 Setuo and Calibration ; 5.10.1 The record of each tube analyzed shall include the Tube ID; VOLTS, DEG, % or three 6.1.1 Examination Freauencies letter code, CH# and axial location l corresponding to any reported indication (s); and Examination frequencies and channel the extent tested. assignments are given in Table 6-1. 5.10.2 Acceptable three letter analysis codes for reported indications that are not assigned a percent through-wall are identified in Appendix C of this guideline. 1 3 1 1
COMMONWEALTH EDISON C . .. J . . . Byron & Braidwood units 1 & 2 Anatyees Guidehnes Rev. 7 July 1994 reporting indications at support structures (other ' Table 6-1 than AVB's). Tube Examination Frequencies
- b. Mix 2: 300/130 KHz absolute; mix on Frequency Differential Absolute ASME support ring signal. Set amplitude (kHz) Channel Channel (voltage) .3-point calibration curve (VERTMAX) '
550 1 2 using the 0%, 20%, and 40% AVB wear scar signals. (Note: 50% wear scar may by substituted 300 3 4 f 40% wear scar does not exist in standard). Mix 130 5 6 2 is used for reporting indications at AVB's. 10 7 a
- c. Mix 3 (optional): 550/300/130 KHz 6.1.2 Settino Mixes differential; suppress ASME support plate and normal in-generator roll expansion signal; The mixes in Table 6-2 shall be established. save signals from ASME standard drill holes. -
Mix 3 is used to screen TTS expansion regions Table 6-2 for indications and to aid in the confirmation of Mix Setup other indications. Mix Channel Suppress Save 6.1.3 Settino Rotations Sequence on: on: Mix 1 1-5 Support N/A Ring so that the phase angle of the signal from the 100% through-wall hole is 40 degrees (+/- 2 Mix 2 4-6 Support N/A degree) with initial signal excursion down and Ring to the right as the probe is pulled through the Support ASME Cal calibration standard. Mix 3 1-3-5 Ring + Std Drill (Optional) Clean TTS Holes & OD
- b. Channels 2,4, 6, and Mix 2: Adjust the rotation so that probe motion is horizontal with Additional mixes may be established for screening and diagnostic applications at the c. Channel 6: As an option, the signal discretion of the analyst. However, as a response from the ASME 100% drill hole may be minimum, data screening and reporting shall be conducted using the applicable channels rotated to 32* (+/- 2').
specified in Section 6.2. d. Channels 7 and 8: Adjust the rotation so that the initial excursion of the signal from the
- a. Mix 1: 550/130 KHz differential support support ring is oriented vertically starting mix: mix on ASME standard support ring. Set downwards.
3-point phase angle-depth calibration curve using ASME 100%, 60%, and 20% drill hole
- e. Mix 1 and Mix 3: Set probe motion signals. Mix #1 is the primary channel for horizontal with the signal from the 100% drill 4
= COMMONWEALTH EDISON t 1 Byron & Braicwood Units 1 & 2 Analysis Guidehnes Rev. 7 July 1994 hole starting oownwards and to the right (dgnal l 6.1.6 Calibration Curves l will be at about 35 degrees). l
- a. Calibration Standard Hole Depths:
6.1.4 Settina Soans (1) The actual depths corresponding to the
- a. Channel 1 and Mix 1: As a minimum, set nominal depths provided below shall be used in span so that the magnitude of the ASME 20% establishing calibration curves. "As built" hole drill hole response is approximately 25% of the dimensions shall be obtained from the applicable ;
calibration standard drawings. full screen height (FSH) of the Lissajous display. Verify that the magnitude of the ASME 100% drill hole response is at least 50% of FSH. (2) Normalized calibration curves generated using phase angles based on a nominal wall ,
- b. Mix 2: Set span so that the magnitude of thickness and a standard depth of penetration of the AVB 20% wear scar response is 37% are permitted if the requirements of Section 1 approximately 25% of FSH. 6.1.6.a.1 cannot be satisfied. ,
- c. Locator Channels 7 and 8: Set span so b. Use of Artificial Curves: The use of that the magnitude of the support plate response artificial curves e.g., set 4.1, is prohibited, on Channels 7 and 8 are at least 50% and 25%
of FSH, respectively. ;
- c. Mix 1 and Channels 1,3, and 5: Establish 6.1.5 Settina Volts phase angle versus depth curves using the following nominal set points:
- a. Channel 1: Set the ASME 20% FBH signal to 4 volts +/- 0.1 volts peak-to-peak in Set Point 1: 100% -
Channel 1 and save/ store to all other channels Set Point 2: 60 % and mixes. Set Point 3: 20%
- b. Mix 1: If an ARC calibration standard is d. Mix 2: Establish a VERT MAX voltage used to establish a voltage scale, then the versus depth curve using either of the following ,
voltage shall be set to the normalized value on two cases of typical nominal set points, the applicable transfer standard drawing. depending on the AVB calibration standard used: Save/ store to Mix 1. If an ASME calibration t standard is used, then set the 20% FBH signal to Case 1 Case 2 , 2.75 volts +/- 0.1 volts peak-to-peak in Mix 1. Set Point 1: 0% 0% , Save/ store to Mix 1. Set Point 2: 20% 30 % ; Set Point 3: 40% 50 %
- c. Mix 2: Set the 40% wear scar signal (or 50% wear scar signal if applicable) to 5 volts e. Mix 3 (Optional Turbo Mix): No (VERTMAX). Save/ store to Mix 2. calibration curve is required. )
l 1 I 5
~ w-w COMMONWEALTH EDISON L ..J !
Byron & Braidwood Units 1 & 2 Anarysts Guiden..c3 Rw. 7 July 1994 6.1.7 Data Disolav c. Axial locations of indications are measured with a positive offset and physically upward in
- a. As a minimum, set up the display relation to the adjacent landmark.
configuration for initial data screening according to Table 6-3 using the span settings established (1) Locations of indications within the in Section 6.1.4. boundaries of support and baffle plates are referenced (+) or (-) as they occur above or Table 6-3 below the support structure centerline. Minimum Display Configuration Requirements i (2) Indications within the expansion transition Display Channel region near the secondary tubesheet face are referenced relative to the top of the tubesheet. Lissajous CH1 Left Strip Chart CH 6 Vertical (3) U-bend indications are referenced (+) in Right Strip Chart Mix 1 Vertical relation to the adjacent AVB toward the hot-leg or upper hot-leg support plate as appropriate. 6.1.8 Settina Scale and Axial Locations (4) AVB indications are referenced to (0.00) at the corresponding AVB.
- a. Set the axial scale to the nearest one-hundredth (0.00) of an inch using Appendix d. Location landmarks are identified using the C for dimensions and verify proper setting each appropriate three-letter codes as specified in time an indication is reported. Appendix C.
- b. Scale should be set using the two support 6.2 DATA EVALUATION structures which bound the region of interest. For U-Bend indications, set scale using the two 6.2.1 This section defines special augmented uppermost TSP's on either leg of the steam data screening and analysis requirements for i generator. various classes of indications. Particular attention should focus on analysis procedures for (1) Use the TSP centerline as the zero 1) free-span indications, and dings. Both of these reference point when setting scale between types of indications have been associated with TSP's. recent industry forced outages in preheater steam generators.
(2) Use the top of the tubesheet and next TSP or baffle plate centerline when setting scale in addition, evaluation requirements for l between the top of the tubesheet and the lowest screening support structures, e.g., support and ! TSP or baffle plate. baffle plates, AVB's, and the tubesheet j secondaly face, are described. (3) Use the tube end and top of tubesheet when the region of interest is within the tubesheet. 6
) ; COMMONWEALTH EDISON b J Byron & Bracwood Units 1 & 2 Analysis Guide':nes Rev. 7 July 1994
- a. Free-Span Sections (Byron 1 and 4. Single indications may be reported using a Braidwood 1 Only): discrete location while multiple indications in !
close proximity may be reported using a to-from
- Ding Signal Screening location.
- 1. Free-span ding signals discovered during 5. Figure 6-1 shows a flowchart illustrating ,
data screening shall be scrolled in the Lissajous U-bend data screening and reporting window using Channels 1,3 and 5. requirements. ,
- 2. Distorted indications observed during data seron u-bend 8
review shall be reported as FSI for subsequent $",'nn]"3 e , disposition by rotating probe diagnostics. . span 10 '
- 3. It should be noted that generally distorted j indications are more apparent in Channels 3 and 5, and often are not evident in Channel 1 t because of the overwhelming horizontal response caused by local tube indentation or po ,3i, deformation. indication?
r
- U-bend region Data Screenina (Data Analysts) y,, n99 1
- 1. The U-bend region between the uppermost c support plates shall be scrolled in the Lissajous window using Channel 5 at a numerical span p&
setting of 10 orless. confirmed \ i using Channel h No-37
- 2. Possible indications observed in Channel 5 should be confirmed using Channel 3. It is emphasized that definitive iidications may not
\[/
always be observedin eitherof the two channels. ve, Rather, the indications may assume a noise-like structure, with multiple discrete indications , occurring in close proximity over a longer axial ,/ distance. ( Report as , Fss '
- 3. Report all confirmed indications using an Free-Span Signal (FSS) analysis code. . ,
Subsequent disposition of all reported indications will be accomplished by a resolution analyst. Figure 6-1. Data screening requirements for U-bend free-span indications. 7
r COMMONWEALTH EDISON L a
. . . ~ . . .
Byron & Braicwood Units 1 & 2 Analysrs Guidehnes Rev. 7 July 1994 Disposition fResolution Analvsts) measurement points between the identifying frequency and the Mix 1 channel to obtain proper
- 1. Previous history or rotating probe placement. ,
diagnostics shall be used to disposition U-bend l free-span signals. 3. The largest amplitude portion of the I Lissajous signal (not necessari!y the MAXRATE l
- 2. U-bend free-span signals may be further position) representing the indication should then reclassified as Free-Span Differential (FSD), be reported using Mix 1 to establish the voltage.
Manufacturing Burnish Mark (MBM) etc., depending on the relative response of the absolute / differential bobbin coil modes. Scroll Tube
- 3. U-bend free-span signals identified for support using Chan s 3 and repair shall be reclassified as a Free-Span Indication (FSi). I
- b. Support Plates and Baffle Plates:
v Conventional Pluccino Criterion: .
- 1. Scroll support plates using Channels 3 and ,("[i[rted No Mix 1. There is no minimum threshold voltage for Incication?
reporting.
- 2. Channel 3 is usually a very useful channel ,
for data screening and locating the initial position for phase angle measurement. Yes NDD I
- 3. Mix 1 shall be used to determine the final , y phase angle measurement point.
f Alternate Plucoino Criterion: I/ Repon using , Mix 1
- 1. Scroll support plates using Channels 3 and Mix 1. There is no minimum threshold voltage for reporting purposes.
I
- 2. Initial placement of the dots for identification of the flaw location may be performed using Channels 1 or 3, but the final Figure 6-2 peak-to-peak measurements must be performed Flowchart showing data screening for using the Mix 1 Lissajous signal to include the indications at tube support plates.
full flaw segment of the signal. It may be necessary to iterate the positions of the 8
r- - COMMONWEALTH EDISON t m . . . . ; Byron & Braidwood Units 1 & 2 Anaysts Guxielines Rev. 7 July 1994
- c. Antivibration Bars: 1 I
1
- 1. Scroll antivibration bars locations using Mix I 1 or Mix 2. i scroll j
- 2. Report indications using the Mix 2 Antivibration Bar l using VERTMAX analysis function. Signal amplitude, Mix 1 r Mix 2 ;
as measured on the conservative leg of the indication, shall be utilized for sizing indications at AVB's.
- 3. Figure 6-3 shows a flowchart illustrating i data screening and reporting requirements. ;
Possible Indication? i u Yes NDD 1
' v Report using Mix 2 i
l-i
)
Figure 6-3 Flowchart showing data screening for ; indications at AVB's. l l 9 I
(" O ' [ j COMMONWEALTH EDISON l Byron & Braiowood Units 1 & 2 Anatysis Guidehnes Rev. 7 Juty 1994
- d. Tubesheet Secondary Face:
- 1. Scroll all tubesheet :iecondary face expansion transitions using Channels 1, 3, 5, and Mix 1 at span settings such that the expansion signal (except for Mix 1) occupies the Scroll Tubesheet maximum extent of the Lissajous display without Secondary Face saturating. Chann 1,3 & 5,
& Mix 1
- 2. As an option, Mix 3 (Turbo mix) may be Mix 3 (optional) used to carefully screen for degradation-like indications at the top of the tubesheet.
v
- 3. Distorted tube sheet entry signals or possible indications should be reported using the Distorted appropriate analysis code. Tubesheet No
- 4. Figure 6-4 shows a flowchart illustrating data screening and reporting requirements.
v Yes NDD : Report Using Appropriate ; Analysis Code ; i Figure 6-4 Flowchart showing data screening for indications at tubesheet secondary face. l l f ' 10
I COMMONWEALTH EDISON : La ' Byron & Braidwood Unds 1 & 2 Analysis Guidehnes Rev. 7 Ny 1994 7.0 ROTATING PROBE ANALYSIS 7.1.3 Filters (Octional) 7.1 Setup and Calibration a. At the option of the data analysts or at the direction of the Lead Analyst, bandpass filters on , 7.1.1 Examination Frecuencies process channels P1, P2 and P3 using Channels 1,2 and 3 (300 KHz), respectively, may be
- a. Examination frequencies and channel established using the nominal settings of Table assignments for a three-coil rotating probe are 7-2. Settings may be adjusted slightly to improve given in Table 7-1. signal-to-noise.
Table 7-1 Three-Coil Rotating Probe Table 7-2 Bandpass Filter Setup Channel Frequency Coil Coil Function (kHz) Type Parameter Value 1 300 1 Pancake General Sharpness 23 coefficients Detection Low cutoff 10 Hz 2 300 5 Circ Axial Wotnd Detection frequency 3 300 7 Axial Circumferential High cutoff 100 Hz Wound Detection frequency 4 200 1 Pancake General Confirmation 5 200 5 Circ Axial 7.1.4 Settina Volts Wound Confirmation 6 200 7 Axial Circumferential Pancake Coil i Wound Confirmation 00 1 Pancake a. Set tha voltage for Channel 1 to 20.00 +/- j , Co f lon , 0.3 volts on the largest pt ak-to-peak response of , 8 100 4 Pancake Trigger o@~ 9 100 5 Circ A <ial , Wound Conf,rmation
- b. Normalize the voltage for other pancake ;
10 100 7 Axial Circu/nferential Wound Confirmation coil channels (CH4 and CH7) in reference to , 11 10 1 Pancake ' Locator Channel 1. Store to all other channels for that coil. 7.1.2 Settina Mixes (Octional) Circumferential Wound Coil
- a. At the option of the data analysts or at the a. Set the voltage for Channel 2 to 20.00 +/- !
direction of the Lead Analyst, mixes may be 0.3 volts on the largest peak-to-peak response of l established for information only. the 100% EDM notch. l l 11 l
1 1 COMMONWEALTH EDISON L .) Byron & Bradwood Units 1 & 2 Anatysis Gudelines Rev. 7.luty 1994
- b. Normalize the voltage for all other pancake c. Channel 11: Set the response of the coil channels (CHS and CH 9) in reference to support plate vertically downward at Channel 2. Store to all other channels for that approximately 270".
coil. 7.1.7 Settina Curves e_xial Wound Coll
- a. Depth calibration curves are not required.
- a. Set the voltage for Channel 3 to 20.00 +/- Phase angle or amplitude curves may be 0.3 volts on the largest peak-to-peak response of established at the Analysts' option for information tha 100% EDM notch. only.
- b. Normalize the voltage for all other pancake 7.1.8 Settina Scale and Axial Locations coil channels (CH6 and CH10) in reference to Channel 3. Store to all other channels for that a. Using Chr.nnel 1, set scale between the coil. centerlines of two known reference locations of greatest separation on the EDM notch standard.
7.1.5 Settina Scans
- b. Verify proper scale setting when reporting
- a. Channels 1,2,4,5,8 & 9: Set spans such each indication.
that the peak-to-peak response of the axially oriented 40% EDM notch is at least 25% FSH. c. For sspport plate indications, axial locations should be referenced positively (+)
- b. Channels 3,6 & 10: Set spans to same upward or negatively (-) downward from the nominal numerical values as Channels 2,5, and 9 centerline (0.00) uf the nearest support plate.
respectively.
- d. For top of tubesheet indications, axial
- c. Channel 8: Set span so that the trigger locations should be referenced positively (+)
pulse occupies approximately 50% FSH. upward or negatively downward from the top of the tubesheet zero (0.00) reference.
- d. Channel 11: Set span so that the support plate occupies 25%-50% FSH. 7.1.9 Display Confiauration 7.1.6 Settina Rotations a. Setup the display configuration for initial data screening according to Table 7-3 using
- a. Detection / Confirmation Channels: Set span settings established above.
probe motion to within +/- 5' of horizontal with flaw excursions directed upwards. 7.1.10 C-Scan
- b. Channel 8: Set the trigger pulse vertically a. C-scan features shall be adjusted upwards at 90*-120 consistent with the software suppliers recommended practice.
12
t 1 __ j COMMONWEALTH EDISON : L Byron & Braidwood Units 1 & 2 Analysis Guidelines Rev.7 Juty 1994 irrespective of the extent to which the channels Table 7-3 correlate. Display Configuration 7.2.2 Analysis Display Channel Lissajous
- a. Graphic displays and relative three-coil l CH 1 (300 kHz) amplitude response shall be used to determine Left Chart CH or C P1 f aw orientation and dimensionality using the ;
basic logic summarized in Figure 7- 1. Right Chart CH 2 or CH 3 Vertical ,,,,,, ;H ,,,
, j iIeTeo'ii Amplitude 7.1.11 Indication Lenoth Measurements
- a. Indication length measurements are required. o
- b. Software features for measuring indication v ,
lengths will be invoked consistent with the software supplier's recommended practice.
,g[,y o
- c. Setup of measurement features should be ina, noni.g l
done using the nominal tube ID and the as-built - dimensions of the EDM notch standard ReQusng discontinuit,es. i
. nag,.
va eco v 7.2 Data Evaluation ,,,,,,,,,,,' applicatae 7.2.1 Screenina i i
- a. Review strip chart data while scrolling ali -
acquired data using Channel 1 to establish the - presence of an indication. Other analysis channels may be used for additional Figure 7-1. confirmation. Rotating Probe Analysis
- b. Decrease initial span settings (higher gain) as required such that proper detailed analysis is b. Three-coil relative signal response as conducted on all data. shown in Table 7-4 may be used to assist in determining flaw dimensionality and orientation. r
- c. Indications which are flaw-like on any of the degradation channels shall be reported 13 ,
i
~
3
; COMMONWEALTH EDISON C. J Byron & Brtiidwood Unns 1 & 2 Analysts Guidelines Rev. 7 July 1994 Table 7-4 a. All quantifiable ind cations of tube wall Three-coil Relative Amplitude Response degradation shall be reported. For AVB indications, the reporting threshold is 15%.
Flaw Dimensionality / Orientation Coil Vol Axial Cire b. All non-quantifiat >le indications (See Appendix -B, Category 11) shall be reported. As Pancake l + + + a general rule, Category 11 indications shall be Axial + + - considered a repairable condition unless proven Cire + - + otherwise using suoplemental diagnostic techniques, e.g. RPC or equivalent, or historical i review, Three-dimensional discontinuities in general will have a comparable response from the : pancake and axial /cire coils. Linear or c. Dents or dings > 5 volts peak-to-peak (Mix , two-dimensional discontinuities will typically 1 )- show a preferred response to either the axial or d. Distorted dents or dings having flaw-like circ coils (or both) dependent on flaw orientation. characteristics shall be reported as LAR. The pancake coil is equally sensitive to linear ! discontinuities independent of their orientation. e. Actual test extent shall be reported as the i furthest landmark from the entry leg observed.
- c. Indications with a preferred amplitude !
response from either the axial or circ coil shall be 8.1.2 Recordina Qeauirements analyzed using a three-letter analysis code indicative of the orientation (axial or a. As a minimum, the following graphic , circumferential) and frequency of occurrence in a printouts shall be generated for each reported l given plane. Indications with comparable quantifiable indication, "I" code indication, amplitude responses from all three coils shall be Free-Span Signal (FSS) and LAR indication: analyzed as three-dimensional (volumetric) using an appropriate analysis code. Section 8.2 1. Multiple-channel Lissajous graphics as defines the applicable analysis codes. specified in Tables 8-1 or Table 8-2.
- e. Locations with both axial and b. The following information will be circumferential indications present concurrently recorded in the FINAL REPORT section of the ;
shall be analyzed as mixed-mode. RECORDING MEDIUM: i 8.0 REPORTING AND R.ECORDING 1. For each tube evaluated, an entry must be REQUIREMENTS made that, as a minimum, contains the S/G, ROW, COL, and EXTENT tested. j 8.1 Bobbin Probe .
- 2. The evaluation of all indications to 8.1.1 Reportina Reauirements include the S/G, ROW, COL, VOLTS, DEG, %,
CH#, LOCATICN, and EXTENT tested. 14 l
t j COMMONWEALTH EDISON Dyron & Braidwood Units 1 & 2 Analysis Guidelines Rev. 7 Juty 1994 1
- 3. Any RESTRICTED tubes and the location 8.2 Rotatina Probe :
where probe passage is obstructed. Restricted ! locations must include elevation where 8.2.1 Reportina Reauirements restriction occurs.
- a. The voltage of an indication will be
- c. The
SUMMARY
portion of the measured at the peak signal for each indication. RECORDING MEDIUM shallinclude: This will generally be at the centermost " hit" of i the indication using the detection channel (CH 1
- 1. All information recorded on the typically). Peak-to-peak voltage should be used RECORDING MEDIUM and updated to reflect for the voltage reading, adjusting the window >
the actual spans and rotations used during data width to minimize noise in the signal. ; evnluation.
- b. Indication location will be derived from the
- 2. The NAME(S) and LEVEL (S) of the centermost " hit" point of the calling channel.
e taluator(s) along with the date of the evaluation. c. Indications will not be reported as a percent depth, but assigned an analysis code indicative of the dimensionality, orientation and Table 8-1 frequency of occurrence of the flaw in a given . Eight Channel Graphics plane. Permissible analysis codes are listed in Appendix D. , Location Lissajous Charts Supports 1,3,5, Mix 1 Mix 1 8.2.2 Recordino Reauirements 2,4,6, Mix 2 , AVB's 1,3,5, Mix 1, Mix 2 The following graphic printouts should be l 2,4,6, Mix 2 generated for each reported indication: , Free Span 1,3,5, Mix 1 5
- a. Main display screen typically with the Lissajous of the calling channel (CH 1), left strip TTS 1,3,5, Mix 1 Mix 1 2,4'6 Mix 2 or chart of a low frequency channel adequate to 1x 3 display the bounding or nearest support and right '
strip chart with the vertical component of a Table 8-2 Four-Channel Graphics b. C-scan of indication with the low frequency channel displayed on the strip chart and either Location Lissajous Charts the calling channel or corresponding filtered Supports 1,3,5, Mix 1 0, Mix 1 channel for the C-scan plot. ; AVB's 1,3,6, Mix 2 6, Mix 2 l Free Span 1,3,5,6 1, 5
.0 RESOMG CNEMA I TTS 1,3,5, Mix 1 5, Mix 1 9.1 Primary and secondary analyses results will be compared and referred to the Senior 15
v_ t . COMMONWEALTH EDISON Byron & Braidwood Units 1 & 2 Analysm Guidelines Rev. 7 July 1994 and/or Lead analysts for resolution and probe type, extent tested, analysis code 1 disposition. assignment, etc. 9.2 Conditions requiring resolution include: 9.2.7 One analyst reports a tube not reported by another. 9.2.1 All quantifiable indications >_ 40% through-wall, and Category 2 indications listed in 9.3 Any tube with an initially reporied Appendix C where primary and secondary repairable condition - by either the primary or t analysis results do not match. secondary analyst, or both - that is subsequently resolved to a non-repairable condition during I 9.2.2 Quantifiable indications between 20% resolution - shall be reported to a CECO and 39% reported by one Analyst but not the representative for information. Other. t 9.2.3 Indications in which the depth estimate differs by more than 10% through-wall 9.2.4 Indications for which location measurements differ by more than; , s
- a. +/- 1" for free-span. ,
- b. +/- 0.5" at support structures.
9.2.5 Indications at tube support plates for , plants implementing APC fur which; l
- a. Bobbin coil indications are greater than the !
repair limit voltage where primary and secondary l analysis results do not match.
- b. The reported location extends beyond either support plate edge. ,
r
- c. Indications are diagnosed as circumferential cracking. by RPC.
t
- d. The bobbin coil voltage values called by f primary and secondary analysts deviate by more l than 20% and one or both calts exceeds 1 volt. 1 9.2.6 Reporting errors or discrepancies in such items as steam generator, tube or reel ID, 16
.,.A _:.A.. _,. _ m 4&J J.gu- ---A 4- S ,----i dM-e -- - + - .s-- - + -e O APPENDIX A NDE DATA ACQUISITION AND ANALYSIS GUIDELINES FOR ODSCC AT TSP APC
-w COMMONWEALTH EDISON l Byron & Braidwood Unas 1 & 2 AnaWis Guidelines. Appendix A Rev. 7 July 1994 A.1 INTRODUCTION A.2.2 Probes This appendix documents techniques for the A.2.2.1 Bobbin Coil Probes inspection of Byron and Braidwood Unit 1 steam generator tubes related to the identification of To maximize consistency with laboratory APC ODSCC or IGA / SCC at tube support plate (TSP) data, differential probes with the following regions, parameters shall be used for examination of APC tube support plate intersections:
This appendix contains guidelines which provide direction in applying the ODSCC - 0.610 outer diameter alternate plugging criteria (APC) described in this report. The procedures for eddy current testing - two bobbin coils, each 60 mils long, with 60 using bobbin coil (BC) and rotating pancake coil mils between coils (coil centers separated by 120 (RPC) techniques are summarized. The mils) . procedures given apply to the bobbin coil inspection, except as explicitly noted for RPC in addition, the probe design must ; inspection. The methods and techniques detailed incorporate centering features that provide for in this appendix are requisite for implementation minimum probe wobble and offset; the centering , of TSP APC. features must maintain constant probe center to tube ID offset for nominal diameter tubing. For The following sections define specific locations which must be inspected with smaller acquisition and analysis parameters and than nominal diameter probes, it is essential that methods to be used for the inspection of steam the reduced diameter probe be calibrated to the generator tubing, reference normalization (Section A.2.6.1 and A.2.6.2) and that the centering features permit A.2 DATA ACQUISITION constant probe center to tube ID offset. Byron and Braidwood Unit 1 steam A.2.2.2 Rotatina Pancake Coil Probes generators utilize 3/4" OD x 0.043" wall, Alloy 600 milll-annealed tubing. The carbon steel Pancake coil designs (vertical dipole moment) support plates and baffle plates are designed with a coil diameter d, where d is 0.060" 5 d 5 '
- with drilled holes. The following guidelines are 0.125", shall be used. While other multi-coil (i.e.,
specified for non-destructive examination of the 1,2 or 3-coil) probes can be utilized, it is tubes within the TSP at Byron Unit 1. recommended that if a 3-coil probe is used, any voltage measurements should be made with the A.2.1 Instrumentation probe's pancake coil rather than its circumferential or axial coil. Eddy current equipment used shall be ti e 4 Zetec MlZ-18, the Echoram ERDAU or other The maximum probe pulling speed shall be i equipment with similar specifications. 0.2 indsec for the 1-coil or 3-coil probe, or 0.4 in/sec. for the 2-coil probe. The maximum rotation shall be 300 rpm. This would result in a 1 pitch of 40 mils for the 3-coil probe. A-1
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, COMMONWEALTH EDISON L
4 Byron & Braidwood Units 1 & 2 Analysis Guidehnes. Appenda A Rev.7 Juty1994 A.2.3 Calibration Standards
- Probe Wear Standard A.2.3.1 Bobbin Coil Standards
- A probe wear standard for monitoring the i The bobbin coil calibration standards contain degradation of probe centering devices leac?ng l the following items: to off-center coil positioning and potential variations in flaw amplitude responses. This
- Voltage Normalization Standard standard shall include four 0.052" +/- 0.001 inch diameter through-wall holes, spaced 90 degrees ;
- One 0.052" diameter 100% through wall apart around the tube circumference with an '
i hole axial spacing such that signals can be clearly distinguished from one another. See Figure A-1.
- Four 0.028" diameter through wall holes, 90 l degrees apart in a single plane around the tube ,
circumference; the hole diameter tolerance shall be +/- 0.001" (optional). ,I :
- One 0.109" diameter flat bottom hole, 60% ~P-through from OD .
4 ik ?
- One 0.187" diameter flat bottom hole, 40% i through from the OD i
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- Four 0.187" diameter flat bottom holes, 20% .wi o through from the OD, spaced 90 apart in a single DI""'".
plane around the tube circumference. The j
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tolerance on hole diameter and depth shall be b :
+/-0.001" !
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- A simulated support ring, 0.75" long, ' . T" comprised of SA-285 Grade C carbon steel or equivalent.
All holes shall be machined using a mechanical drilling technique. This calibration A.2.3.2 Rotatina Probe Standard standard will need to be calibrated against the reference standard used for the APC laboratory A satisfactory RPC standard may contain: work by direct testing or through the use of a transfer standard- - Two axial EDM notches, located at the same axial position but 180 degrees apart circumferential, each 0.006" wide and 0.5" long, one 80% and one 100% through wall from the OD. 1 4 A-2
j COMMONWEALTH EDISON l a Byron & Bracwood Unas 1 & 2 Analysis Guidehnes . Appendu A Rev. 7 Jufy 1994 i replaced. If any of the last probe wear standard
- Two axial EDM notches, located at the same signal amplitudes prior to probe replacement axial position but 180 degrees apart exceeds the 15% limit, say by a variable value, ,
circumferentially, each 0.006" wide and 0.5" x%, then indications measured since the last long, one 60% and cne 40% through-wall from acceptable probe wear measurement that are the OD. within x% of the repair limit must be re-inspected with the new probe.
- Two circumferential EDM notches, one 50% '
through wall from the OD with a 75 degree A.2.4.1 Bobbin Coil Wear Standard (0.57") are length, and one 100% through wall Placement with a 26 degree (0.20") arc length, with both notches 0.006" wide. Under ideal circumstances, the incorporation of a wear standard in line with the conduit and
- A simulated support segment 270 degrees guide tube configuration would provide in circumferential extent, 0.75" thick, comprised continuous monitoring of the behavior of bobbin of SA-285 Grade C carbon steel or equivalent. probe wear. However, the curvature of the channelhead places restrictions on the length on -
Similar configurations which satisfy the intent in line tubing inserts which can be of calibrating RPC probes for OD axial and accommodated. The spacing of the ASME circumferential cracking are satisfactory. The Section XI holes and the wear standard results in center to center distarice between the support a length of tubing which cannot be freely plate simulation and the nearest slot shall be at positioned within the restricted space available. least 1.25" The center to center distance The flexible conduit sections inside the i between the EDM notches shall be at least 1.0". channelhead, together with the guide tube, limit The tolerance for the widths and depths of the the space available for additional in line ' notches shall be 0.001" The tolerance for the components. Voltage responses for the wear slot lengths shall be 0.010" standard are sensitive to bending of the leads, l and mock up tests have shown sensitivity to the , A.2.4 Application of Bobbin Coil Wear robot end effector position in the tubesheet, even Standard when the wear standard is placed on the bottom of the channelhead. Wear standard A calibration standard has been designed to measurements must permit some optimization of j monitor bobbin coil probe wear. During steam positions for the measurement and this should be generator examination, the bobbin probe is a periodic measurement for inspection efficiency. ; inserted into the wear monitoring standard; the The pre-existing requirement to check calibration ! initial (new probe) amplitude response from each using the ASME tubing standard is satisfied by of the four holes is determined and compared on periodic probing at the beginning and end of i an individual basis with subsequent each probe's use as well as at four hour : measurements. Signal amplitudes or voltages intervals. This frequency is adequate for wear from the individual holes - compared with their standard purposes as well. Evaluating the probe i initial amplitudes - must remain within 15% of wear under uncontrollable circumstances would their initial amplitude (i.e., {(worn-new)/new} for present variability in response due to an acceptable probe wear condition. If this channelhead orientations rather than changes in . condition is not satisfied, then the probe must be the probe itself. A-3 l l 1
(~ 3 COMMONWEALTH EDISON
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Byron & Braidwood Units 1 & 2 Analysis Guuselines Appendix A Rev.7 July 1994 j } A.2.5 Acouisitior Parameters such as spans, rotations, mixes, voltage scales, l and calibration curves. Although indicated depth i The following parameters apply to bobbin cail measurement may not be required to support an data acquisition and should be incorporated in attemative repair limit, the methodology for the applicable inspection procedures to establishing the calibration curves is presented. supplement (not necessarily replace) the The use of these curves is recommended for parameters normally used. consistency in reporting and to provide compatibility of results with subsequent A.2.5.1 Test Frecuencies inspections of the same steam generator and for comparison with other steam generators and/or This technique requires the use of bobbin coil Pl ants. 550 kHz and 130 kHz test frequencies in the differential mode it is recommended that the A.2.6.1 Bobbin Coil 550 kHz Differential absolute mode also be used, at test frequencies Channel of 130 kHz and 10 - 35 kHz. The low frequency (10-35 kHz) channel should be recorded to Scans and Rotations: Spans and rotations provide a means of verifying tube support plate can be set at the discretion of the user and/or in edge detection for flaw location purposes. The accordance with applicable procedures. 550/130 kHz mix or the 550 kHz differential channel is used to access changes in signal Voltace Scale: The peak-to-peak signal amplitude for the probe wear standard as well as amplitude of the signal from the four 20% for flaw detection. through-wall holes should be set to produce a voltage equivalent to that obtained from the APC RPC frequencies should include channels lab standard. The laboratory standard adequate for detection of OD degradation in the normalization voltages are 4.0 volts at 550 kHz range of 100 kHz to 550 kHz, as well as a low and 2.75 volts for the 550/130 kHz mix. frequency channel to support location of the TSP edges. The transfer / field standard will be calibrated against the laboratory standard using a reference A.2.5.2 Dialtizina Rate laboratory probe to establish voltages for the field standard that are equivalent to the above A minimum digitizing rate of 30 samples per laboratory standard. These equivalent voltages inch should be used. Combinations of probe are then set on the field standard to establish speeds and instrument sample rates should be calibration voltages for any other standard. chosen such that: Voltage normalization to the standard Samole Rate (samoles/sec3 130 (samples /in.) calibration voltages at 550 kHz is the preferred Probo Speed (in/sec) normalization to minimize analyst sensitivity in establishing the mix. However, if the bobbin A.2.6 Analvsis Parcmeters probes used result in a 550/130 4Hz mix to 550 kHz voltage ratios differing frorn the laboratory This section discusses 1) the methodology for standard ratio of 0.69 by more than 5% (0.66 to establishing bobbin coil data analysis variables 0.72), the 550/130 kHz mix calibration voltage should be used for voltage normalization. A-4
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t COMMONWEALTH EDISON ! WJ Byron & Braidwood Unds 1 & 2 Analysts Gwdelines. Appendix A Rw.7 Jufy1994 l indications of interest within the support plate Calibration Curve: Establish a phase versus signal. The largest amplitude portion of the depth calibration curve using measured signal Lissajous signal representing the flaw should phase angles in combination with the "as-built" then be measured using the 550/130 kHz Mix 1 flaw depths for the 100%,60%, and 20% holes. channel to establish the peak-to-peak voltage as shown in Eigure A-2. Initial placement of the dots i A.2.6.2 Bobbin Coil 550/130 kHz for identification of the flaw location may be Differential Mix Channel performed as shown in Figures A-3 and A-4, but the final peak-to-peak measurements must be Soans and Rotations: Spans and rotations performed on the Mix 1 Lissajous signal to can be set at the discretion of the user and/or in include the full flaw segment of the signal. It may accordance with applicable procedures. be necessary to iterate the positions of the dots between the identifying frequency and the Voltaoe scale: See Section A.2.6.1 550/130 kHz mix to obtain proper placement. As can be seen in Figure A-4, failure to do so can Calibration Curve: Mix 1 is a 550/130 kHz reduce the voltage measurement of Mix 1 by as differential support mix; mix on ASME standard much as 65% tc 70% due to the interference of support ring. Set 3-point phase angle-depth the support plate signal in the raw frequencies. calibration curve using ASME 100%, 60%, and The voltage as measured from Mix 1 is then 20% drill hole signals. Mix 1 is the primary entered as the analysis of record for comparison channel for reporting indications at support with the repair limit voltage. structures. To support the uncertainty allowances A.2.6.2 Rotatina Pancake Coil Channel maintained in the APC, the difference in amplitude measurements for each indication will Voltaoe Scale: The RPC amplitude will be be limited to 20%. If the voltage values called by referenced to 20 volts for a 0.5 inch long 100% the independent arr'ysts deviate by more than through wall notch at 300 kHz. Each channel 20% and one or both of the calls exceeds 1.0 ) shall be set individually to the desired amplitude volts, analysis by the resolution analyst will be i for the EDM notches on the plant standards; performed. These triplicate analyses result in l cross calibration will be achieved by comparison assurance that the voltage reported departs from j of the RPC responses from the 100% drilled the correct call by no more than 20%. ! hole. A.2.6 Reportina Guidelines A.2.7 Analysis Methodoloav The reporting requirements identified below, Bobbin coil indications at support plates are in addition to any other reporting attributable to ODSCC are quantified using the requirements specified by the user. Mix 1 (550 kHz/130 kHz) data channel. This is illustrated with the example shown in Figure A-2. A.2.8.1 Minimum Reauirements The 500/130 kHz mix channe! or other channels appropriate for flaw detection (550 kHz, 300 kHz, All bobbin coil flaw indications in the 550/130 or 130 kHz) may be used to locate the kHz mix channel at the tube support plate A-5 1
l
! COMMONWEALTH EDISON l ;
Byron & Bradwood Units 1 & 2 Analysis Guidehnes. Appendtx A Rev. 7 July 1994 intersections regardless of the peak-to-peak A.3 DATA EVAL.UATION signal amplitude must be reported. All TSP locations with indications exceeding 1.0 volts A.3.1 Use of 550/130 Differential Mix for must be examined with RPC probes. Extractino the Bobbin Flaw Sianal A.2.8.2 Additional Reauirements in order to identify a discontinuity in the composite signal as an indication of a flaw in the For each reported indication, the following tube wall, a simple signal processing procedure information should also be recorded: of mixing the data from the two test frequencies is used which reduces the interference from the Tube identification (row, column) support plate signal by approximately one order Signal amplitude (volts) of magnitude. The test frequencies most often Signal phase angle (degrees) used for this signal processing are 550 kHz and Indicated depth (%)* 130 kHz for 43 mit wall Alloy 600 tubing. Any of Test Channel (ch#) the differential data channels including the mix Axial position of tube (location) channel may be used for flaw detection (though Extent of test (extent) the 130 kHz is o' ten subject to the influence from many different effects), but the final evaluation of
- It is recommended that a percent through wall signal detection, amplitude and phase angle will be reported rather than a three-letter analysis code. be made from the 550/130 kHz differential mix While this measurement is not required, this channel. Upon detection of a flaw signal in the information might be found useful at a later date. differential mix channel, confirmation from other raw channels in not required; all such signals RPC reporting requirements should . include must be reported as indications of possible as a minimum: type of degradation (axial, ODSCC. The voltage scale for the 550/130 kHz circumferential or other), maximum voltage, differential channel should be normalized as phase angle, crack lengths, and location of the described in Section A.2.2.6.1 and A.2.2.6.2.
center of the crack within the TSP. The crack axial center to edge need not coincide with the The present evaluation procedure requires position of maximum amplitude. Locations which that there is no minimum voltage for flaw do not exhibit flaw-like indications in the RPC detection purposes and that all flaw signals, isometric plots may continue in service, except however small, be identified. The intersections that all intersections exhibiting flaw-like bobbin w th flaw signals > 1.0 volt will be inspected with behavior and bobbin amplitudes in excess of the ._ RPC, unless the tube is to be plugged or repair limit voltage must be repaired' sleeved. Although the signal voltage is not a notwithstanding the RPC analyses. RPC measure of flaw depth, it is an indicator of the isometrics should be interpreted by the analyst t tube burst pressure when the flaw is identified as characterize the signals observed; only axial ODSCC with or without minor IGA. featureless isometrics are to be reported as NDD. Signals not interpreted as flaws include A.3.2 Amolitude Variabilitt dents, liftoff, deposits, copper, magnetite, etc. It has been observed that voltage measurements taken from the same data by A-6 i
~7 ~ ! l COMMONWEALTH EDISON L___ J Byron & Braidwood Units 1 & 2 Analysis Guidehnes - Appendix A Rev. 7 Juty 1994 different analysts may vary, even when using In some cases, it will be found that little if any identical analysis guidelines. This is largely due definitive help is available from the use of the to differences in analyst interpretation of where raw frequencies. Such as example is shown in to place the dots on the lissajous figure for the Figure A-11, where there are no significantly ;
peak-to-peak amplitude measurement. Figures sharp transitions in any of the raw frequencies. l A-5 and A-6 show the correct placement of the Consequently, the placement of the i dots on the Mix 1 Lissajous figures for the measurement dots must be made completely on peak-to-peak voltage amplitude measurements the basis of the Mix 1 channel Lissajous figure as for two tubes from Plant S. In Figure A-5, the shown in the upper left of the graphic. An even placement is quite obvious. In Figure A-6, the more difficult example is shown in Figure A-12. i l placement requires slightly more of a judgment The logic behind the placement of the dots in Mix call. Figures A-7 and A-8 show these same two 1 is that sharp transitions in the residual support tubes with peak-to-peak measurements being plate signals can be observed at the locations of made, but in both cases the dots have been both dots. In the following graphic, Figure A-13, placed at locations where the normal max-rate somewhat the same logic could be applied in i dots would be located. The reduction in the determining the flaw-like portion of the signal { voltage amplitude measurement is 19.3% in from the Mix 1 Lissajous pattem. However, Figure A-7 and 16.3% in Figure A-8 While this is inasmuch as there is no sharp, clearly defined an accepted method of analysis for phase-angle transition, coupled with the fact that the entry measurements, it is not appropriate for the lobe into the support plate is distorted on all of voltage amplitude measurements required. the raw frequencies, the dots should be placed as shown in Figure A-14. This is a conservative In Figures A-5 and A-6, the locations of the approach and should be taken whenever a I dots for the peak-to peak measurements being degree of doubt as to the dot placement exists. performed from Mix 1 show the corresponding dots on the 550 kHz raw frequencies as also it is noted that by employing these being located at the peak or maximurn points of techniques, identification of flaws is improved ! the flaw portion of the Lissajous figure. In no and that conservative amplitude measurements case should the should the dots to measure the are promoted. The Mix 1 traces which result from voltage amplitude be at locations less that the this approach confirm to the model of TSP maximum points of the flaw portion of the 550 ODSCC which represents the degradation as a , kHz raw frequency. series of microcrack segments axially integrated ! by the bobbin coil; i.e., short segments of l Figure A-9 is an example of where the dots changing phase angle direction represent have been placed on the transition region of the changes in average depth with changing axial 550 kHz raw frequency data Lissajous figure. It is position. This procedure may not yield the clear from the N 1 Lissajous figure that this maximum bobbin depth call. If maximum depth is does not correspond to the maximum voltage desired for information purposes, shorted l measurement. The correct placement on the Mix segments of the overall crack may have to be l 1 Lissajous figure us shown in Figure A-10. This evaluated to obtain the maximum depth estimate. placement also corresponds to the maximum However, the peak to peak voltages as described voltage measurement on the 550 kHz raw herein must be reported, even if a different frequency data channel. segment is used for the depth call. A-7 l l
r 7
, COMMONWEALTH EDISON L .. ... J Byron & Bra cwood Uruts 1 & 2 Analysis Guidelines- Appendix A Rev.7 July 1994 A.3.3 Allov Procerty Chanaes denting nor do they have reported indications indicative of copper deposits.
This signal manifests itself as part of the support plate " mix residual" in both the A.3.5 RPC Flaw Characterization differential and absolute mix channels. It has often been confused with copper deposit as the The RPC inspection of some support plate cause. Such signals are often found as support intersections with bobbin coil indications > 1.0 plate intersections of operating plants, as well as volts is recommended in order to verify the in some model boiler test samples, and are not applicability of the alternate repair limit. This is necessarily indicative of tube wall degradation. based on establishing the presence of ODSCC Six support plate intersections from Plant A, with minor IGA as the cause of the bobbin judged as free of tube wall degradation on the indications. basis of the mixed differential channel using the guidelines given in Section A.2.7 of this The signal voltage for RPC data evaluation document, were pulled in 1989. Examples of the will be based on 20 volts for the 100 % bobbin coil field data are shown in Figure A-15. throughwall 0.5" long EDM notch at all (inspection data from a plant with 7/8 inch frequencies. diameter tubing. The mix residual for this example is approximately 3 volts in the The nature of the degradation and its differential mix channel and no discontinuity orientation (axial or circumferential) will be suggestive of a flaw can be found in this channel. determined from careful examination of the An offset in the absolute mix channel which could isometric plots of the RPC data. The presence of be confused as a possible indication is also axicl ODSCC at the support plates has been well i present. These signals persisted without any documented, but the presence of circumferential l significant change even after chemically cleaning indications related to ODSCC at support plate l the OD and the ID of the tubes. The destructive intersections has also been established by tube examination of these intersections showed very pulls at two plants. Figures A-16 to A-18 show minor or no tube wall degradation. Thus, the examples of single and multiple axial ODSCC overall " residuals" of both the differential and from Plant S. absolute mix channels were not indications of tube wall dagradation. One needs to examine the Figure A-19 is an example of a detailed structure of the " mix residual" (as circumferential indication related to ODSCC at a outlined in Section A.2.7) in order to assass the tube support plate location from another plant. If possibility that a flaw signal is present in the circumferential involvement results from residual composite. Verification of the integrity of circumferential cracks as opposed to multiple TSP intersections exhibiting alloy property or axial cracks, discrimination between axial and artifact signals is accomplished by RPC testing circumferentially oriented cracking can be of a representative sample of such signals. generally established for affected arc lengths of about 45 degrees to 60 degrees or larger. Axial A.3.4 Dentina and Cooper influences cracking has been found by pulled tube exams for RPC arcs of 150 degrees when the axial The Byron and Braidwood Units have r extent is significant, such as > 0.2 inch. experienced significant corrosion-assisted A-8
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! COMMONWEALTH EDISON L J l
Byron & Bracwood Units 1 & 2 Anafysis Gun:iehnes - Appends A Rev. 7 July 1994 l Pancake coil resolution is considered interest, the low frequency channel (e.g.10 kHz) adequate for separation between circumferential is used to set a local scale for measurement. By l and axial cracks. This can be supplemented by establishing the midpoint of the support plate ; careful interpretation of 3-coil results. Since response, a reference point for indication l denting has not occurred at the Byron or location is established. Calibration of the Brsidwood units, circumferential cracking is not distance scale is accomplished by setting the ; expected to happen. displacement between the 10 kHz absolute, upper and lower support plate transitions equal The presence of IGA as a local effect directly to 0.75 inch. ; adjacent to crack faces is expected to be i indistinguishable from the crack responses and A.3.7 Lenoth Determination with RPC as such of no structural consequence. When IGA Probes exists as a general phenomenon, the eddy current response is proportional to the volume of The number of scan lines indicating the i affected tube material, with phase angle presence of the flaw times the pitch of the i corresponding to depth of penetration and rotating probe provides a conservative estimate amplitude relatively larger than that expected for of crack length which may then be corrected for ; small cracks. The presence of distributed beam spread. , cracking, e.g., celluiar SCC, may produce : responses from microcracks of sufficient A.3.8 RPC Insoection Plan i individual dimensions to be detected but not resolved by the RPC, resulting in volumetric The RPC inspection plan will include the responses similar to three-dimensional following upon implementation of the APC repair degradation. limits: l For hot leg TSP locations, there is little
- Bobbin voltage indications > than 1 volt !
industry experience on the basis of tube pulls for volumetric degradation, i.e., actual wall loss or
- A representative sample of 100 TSP 1 general IGA. For cold leg TSP locations, intersections based on the following: ;
considerable experience is available for
- volumetric degradation in the form of thinning of 1) Artifact signals (alloy property changes) peripheral tubes, favoring the lower TSP spanning the range of amplitudes observed ;
elevations. Therefore, in the absence of during bobbin coil examination ! confirmed pulled tube experience to the contrary, volumetric OD indications at hot-leg tube support 2) Dented tubes at TSP intersections with plates should be considered to represent bobbin dent voltages exceeding 5 volts , ODSCC.
- 3) Bobbin indications less than 1 volt for A.3.6 Confinement of ODSCC/lGA Within justification of these indications as typical of the Suocort Plate Reaion ODSCC. i The measurement of axial crack lengths from The 100 TSP intersections for RPC RPC isometrics can be determined using the inspection would be targeted toward a l following analysis practices. For the location of distnbution on the order of 40 dents,40 artifacts, !
A-9 l
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! ) COMMONWEALTH EDISON o . . . .
Byron & Braidwood Units 1 & 2 Anatysis Guidehnes - Appendix A Rev.7 July 1994 artifacts, and 20 indications with bobbin voltages
< 1.0 volts; this distribution will be adjusted to ,
reflect field observations as appropriate. Consideration for expansion of the RPC inspection program would be based on id:ntifying unusual or unexpected indications such as clear circumferential cracks. In this casa, structural assessments of the significance of the indications would be used to guide the need for further RPC inspection. A.3.8.13-coil RPC Usaae It is Commonwealth Edison's standard practice to use 3-coil RPC probes, incorporating a pancake coil, an axial preference coil, and a circumferential preference coil. Comparisons for ODSCC with bobbin amplitudes exceeding 1.0 . volts have shown that the pancake coil fulfills the need for discrimination between axial and circumferential indications, when compared against the outputs of the preferred direction coils. Pancake coils have been the basis for reporting RPC voltages for model boiler and pulled tube indications in the APC database; these data permit semi-quantitative judgments on the potential significance of RPC indications. The requirements for a pancake coil is satisfied by the single coil, 2-coil, and 3-coil probes in , common use for RPC inspections. l l l l l A-10 l
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! . COMMONWEALTH EDISON l L J Byron & Braidwood Units 1 & 2 Anatysis Guidelines. Appenduc A Rev. 7 July 1994 l in, ...i..i.i... ......i a, .n in a . o ,
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r l t COMMONWEALTH EDISON ! I Cd I Byron & Braidwood Units 1 & 2 Anays,s Guidehnes . Appenda A Rev. 7 Jufy 1994
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1 Figure A-6. Correct Placement of Vector Dots on Mix 1 Lissajous Traces for R22C40. 1 A-15 l I l i I
L a COMMONWEALTH EDISON Byron & Braidwood Units 1 & 2 Analysis Guidelines - Appendtx A Rev. 7 July 1994 l l ai c., . . . . . .i. ,,. . o, i o ... . i....> u a K q [4 $
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Figure A-7. Incorrect Placement of Vector Dots on Mix 1 Lissajous Traces for R18C103. I A-16 l
4 i l COMMONWEALTH EDISON ; 1 k -) Byron & Braiowood Units 1 & 2 Analysen Guidelines- Appendix A Rev.7 Jufy1994 ! e se til att 4 183 7 11 %%8 tas CM l 852 34 j CM &W i uts 4 y Ttt I*CE - " . 91 := IM l *G.M l el {ted
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u_, COMMONWEALTH EDISON Byron & Braidwood Units 1 & 2 Analysis Guidehnes- Appendix A Rev.7 July 1994 I 36 6 Cao , e f als a V I 3.2e t5 aan a t. 6.71 15. Esee on i 29 9 ~
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i E T-~' Fi r ::: i ' l Figure A-9. Incorrect Maximum Voltage Derived from Placement of Vector Dots on Transition Region of 550 kHz Raw Frequency Data Lissajous Trace for R42C44. A-18
[L > COMMONWEALTH EDISON Byron & Braidwood Units & Analysis Guidelines - Appendut A Rev. 7 Juty 1994 36 4 CM 4 V i 415 4V 3.38 L:5 sit t 1 to 6.11 154 ths CM i 2e
- e. -: :
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T -<_ __ i < N -;;; 1 i e r i c __.i. ni,. 1 Figure A-10. Correct Placement of Vector Dots on Mix 1 Lissajous Figure for R42C44. A-19
y i
't .
g COMMONWEALTH EDISON Dyron & Braidwood Unds 1 & 2 Analysis Guidelines. Appendix A Rev.7 July 1994
$3ENF
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s i r s i / i' Figure A-11. Placement of Vector Dots Based Solely on Mix 1 Lissajous Figure (no significantly sharp transitions in any of the raw frequencies)- R10C44. A-20
I l COMMONWEALTH EDISON o Byron & Braidwood Units 1 & 2 Analysis Guidelines - Appendix A Rev. 7 Jufy 1994 se s c.n a v imsv a.s2 1.5 als a to 6.11 sta tha c.n a to ttt x j in !it. seq,I
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Figure A-12. Placement of Dots Marking Mix 1 Lissajous Figure for R16C26. i I 1 A-21
COMMONWEALTH EDISON
!N-- )! l Eyron & Bradwood Units 1 & 2 AnaWis Guidelines - Appendix A Rn74 W l
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Figure A-13. Incorrect Placement of Vector Dots Marking Mix 1 Lissajous Figure for R30C74. A-22
(- . I COMMONWEALTH EDISON L_J' . - . . . . . . . . . . . _ . . _ . _ . , _ , , , , , , , , , Byron & Branchvood Unsts 1 & 2 Analysis Guidehnes - Appenda A Rev. 7 .'uly 1994 i 1.5 nit i le i s.72 55e na CM i 21 i f 25 s :n a v i cM 5 , i 2.99 ' 1 2M l+23.9e4 l :lta avaitta i se j g 18 , seus ias.se68.e .tania , [C. m
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Ul , t l l Figure A-14. Correct Placement of Dots to Effect Maximum Voltage - R30C74. l l l l l A-23 I l 1 l
l
!LJ ! COMMONWEALTH EDISON Byron & Braidwood Unds 1 & 2 Anatysis Guidelines. Appendut A Rev. 7 Jufy 1994 l
j 23i :n s v i mis a e i 6 se *es un cm i Jae e a 22 2.s ais 2 ea l E -- 4 400/100 A'bsolute **" E- ! S - g ,. // f m la .ano , .ss .ug . _ , LIf Laf fl_ 08 $ (ses _e
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l F' ' ' l I j { 'T I T 1 Figure A-15. Example of Bobbin Coil Field Data - Mix Residual Due to Alloy Change. l l i A-24 i 1 _ _ - - _ _ - - - - - - - _ - _ - - _ - - - _ - - _ - - - - - - _ - - _ - - - - _ - )
e q t J COMMONWEALTH EDISON Byron & Bracwood Units 1 & 2 Analysis Gudelines- Appendtx A Rev. 7 Jury 1994 1 I se i a . , cm i , ..se see o. cm . se < g; w a p 3 gj sian in 1 "is eneri ." asuuns a:Walesanw eet 3e g g,g g4 tg g,4
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i i I Figure A-16. Example of RPC Data for Single Axial Indication (sal) Attributed to ODSCC - A-25
o COMMONWEALTH EDISON l l Byron & Braidwood Units 1 & 2 Analysis Guidelines - Appendtx A Rev. 7 Jufy 1994 30 i O, 4 V Og 9 T e.49 38 Das Ose .9 @ M E M 8 A g ".*:" E l
. . - , , .........e,,,,, i. i . , i,, ,,,
,,,,,,,, 2 are ra i ro i ,
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a.--- t .) COMMONWEALTH EDISON Byron & Braidwood Units 1 & 2 Analysis Guidelines . Appendtx A Rev. 7 July 1994 weo..l oe i , , a.. we e. a . in a 4 m w y :. __ _
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. mmEL W SEM LIEle.iiim .
iime . i .. i,i it,, enom 'm i ro i M C 5 7 Itoisaal leiscluis 8'eam 6 e.se iiwame l'esisil
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='
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i l COMMONWEALTH EDISON l l
-=.e. a.m n. . - . . , , ,
i
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i Figure A 19. RPC Data for Circumferential ODSCC Indications at Dented Upper and Lower TSP Edges. A-28 l 1 l
Y f 1 APPENDIX B ANALYSIS GUIDELINES CHANGE FORMS
?
P f P l
.--.-. . - - , . - - ~ -- , - --
I i l APPENDIX B ANALYSIS GUIDELINES CHANGE FORMS i (PAGE 10F 2) ANALYSIS GUIDELINES CHANGE FORM ; i
Subject:
DESCRIPTION OF CHANGE: REASON FOR CHANGE: , TECHNICAL BASIS: i EXAMINATION IMPACT: AUTHORIZATIONS: ! Lead Analyst Date: / / CECO Acknowledgment Date / / " b n B-1 i f i
APPENDIX B ANALYSIS GUIDELINES CHANGE FORMS (PAGE 2 0F 2) i ANALYSIS GUIDELINES CHANGE ACKNOWLEDGMENT FORM Change Notice # : EFFECTIVE DATE OF CHANGE / / TIME / am pm Analyst Sianature Qgig Time
/ / __
/ / _._
/ / __
/ / .
i I I _
/ / _._
/ / __
/ / . !
/ / __
/ / _._ i
/ / __
/ / _._
B-2 !
APPENDIX C ANALYSIS & RETEST CODES i
Appendix C (Page 1 of 2) Analysis & Retest Codes Category 1 - No Further Action Analysis Retest No Detectable Degradation NDD RND Plugged PLG - Sleeved SLV RSV Positive indentification PID - Category 2 - Possible Flaw, Further Action Required Non-quantifiable indication NQI RNQ _ Absolute Drift Indication ADI RAD Distorted Support Indication DSI RDI Distorted Tubesheet Indication DTI RTl Distorted Roll Indication DRI RTl Single AxialIndication SAI RSA Multiple AxialIndications mal RMA Single Circumferential Indication SCI RSC Multiple Circumferential Indications MCI RMC Mixed-Mode Indications MMI RMI Free-Span Signal FSS RSS Free-Span Indication FS! RSI Lead Analyst Resolution LAR RAR Category 3 - Possible Loose Part, Further Action Required Possible Loose Part PLP RLP Category 4 - Further Action Required. Retest Condition Bad Data RBD RBD incomplete Test INC RIC i Obstructec ODS ROB i Template Plog TMP RTP l Tube No Test TNT RNT To Be Retested TBR - Fixture FlX RFX l Tube Number Check TNC RNC C-1
Appendix C (Page 2 of 2) Analysis & Retest Codes (Cont'd) Category 5 - No Further Action Required Analysis Retest Bulge BLG RBL Copper Deposit CUD RCD Dent DNT RDN ,
.q .,,
Deposit DEP RDP Ding DNG RDG Distorted Roll Transition Signal DRT RRT Distorted Support Plate Signal DSS RDS Distorted Tubesheet Signal DTS RDT Expansion EXP REX Indication Not Reportable INR RNR Indication Not Found INF RNF Manufacturing Sumish Mark MBM RBM Manufacturing Anomaly Mark MAM RAM l Noisy Tube NSY RSY Over Roll OVR RVR Overexpansion OXP RXP Partial Tubesheet Expansion PTE RTE Permeability Variation PVN RPV Skipped Roll SKR RSR Sludge SLG RSG Top Main Roll TMR RTM Volumetic Indication (s) VOL RVL Free-Span Differential FSD RSD Shot Peening Anamoly SPA RPA C-2
1.s - --+a -- - aaJ.A - . _ . . -_. APPENDIX D SUPPORT STRUCTURES NOMENCLATURE AND MEASUREMENTS 4
Appendix D Support Structures Nomenclature and Measurements l (Page 1 of 3) Westinghouse Model D4 S/G Support Structures Measurements AV V3 Elevation Spacing av v4 Level (Inches) CoWeg ( 11H itc Tube End 0 0 Tu5esheet 21.2 21.2 10H 100 top Center of ist 6.4 6.4 09H structure 09C Center of - 12 2nd structure 08H 08c Center of 3rd 30 18 structure 07H 07C Center of 4th - 18 structure 08C Center of 5th 36 18 l
]'
osH lolc structure l Center of 6th - 18 3H p 020 structure Center of 7th 36 18
# structure i l Tsn o,g -- oc Tsc l Center of 8th 43 -
TEH h h-TEC structure i l Center of 9th 43 - J structure l Center of 43 - , 10th I structure Center of 43 1 - 11th structure D-1
i Appendix D Support Structures Nomenclature and Measurements (Page 2 of 3) Westinghouse Model D5 SIG Support Structures Measurements
-- - _ _ Elevation spacing AV VS Level (Inchee)
Av v4 Hot-leg Cold-leg Tube End 0 0 n ; HH 11C Tubesheet 21.2 21.2 top toH toc Center of 1st 8.4 6.4 l structure Center of - 12 09H 09C 2nd structure Center of 3rd 28 18 structure Center of 4th - 18 . structure { 07H 07C Center of 6th 36 18 [ ute is 06C C5H C i
- j. structure a Center of 7th 36 18 03H 03C dm ure {
l, 02C 01C Center of 8th 43 - TSH 01H .; Center of 9th 43
} TSC TEH -
{ -*- TEC structure f Center of 43 - ; 10th structure , Center of 43 11th structure i c h d D-2 t
Appendix D Support Structures Nomenclature and Measurements (Page 3 of 3) Structures Nomenclatur's Notation Description TEH Tube end hot TSH Top of tubesheet- hotleg 01H ist support plate - hot leg 03H 3rd support plate - hot leg 05H 5th support plate - hotiog 07H 7th support plate - hot leg 08H 8th support plate - hot leg 09H 9th support plate - hot leg 10H 10th support plate - hot leg 11H 11th support plate - hot leg 3 AV1 1st anti-vibration bar AV2 2nd anti-vibration bar AV3 3rd anti-vibration bar AV4 4th anti-vibration bar 11C 11th support plate - cold leg 10C 10th support plate - cold leg 09C 09th support plate - cold leg 08C 08th support plate - cold leg 07C 07th support plate - cold leg 06C 06th support plate - cold leg OSC 05th support plate - cold leg 04C 04th support plate - cold leg 03C 03th support plate - cold leg 02C 02th support plate - cold leg 01C 01st support plate - cold leg TSC Top of tubesheet - cold leg TEC Tube end cold D-3 _ _ _ _ - i
r n 1 i l ATTACHMENT J REFERENCES
- 1. Regulatory Guide 1.121, " Basis for Plugging Degraded PWR Steam Generator Tubes," Revision 0, August 1976 (issued for comment)
- 2. Draft NUREG-1477, " Voltage-Based Interim Plugging for Steam Generator Tubes-Task Group Report," June 1,1993
- 3. EPRI Draft Report bio-6864-L, "PWR Steam Generator Tube Repair Limits:
Technical Support Document for Expansion Zone PWSCC in Roll Transitions
" Revision 2, August 1993
- 4. EPRI Draft Report TR-100407, "PWR Steam Generator Tube Repair Limits -
Technical Support Document for Outside Diameter Stress Corrosion Cracking at Tube Support Plates," Revision 1, August 1993
- 5. Westinghouse Letter Report NSD-TAP-3069, "Braidwood 1: Technical Support for Cycle 5 S/G interim Plugging Criteria, Pre-WCAP Release," April 21,1994
- 6. Westinghouse Letter CAE-94-200, " Byron Unit 1: Steam Generator Plugged Tube Growth Data," July 29,1994 1}}