ML20202H977
| ML20202H977 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 02/16/1998 |
| From: | HOUSTON LIGHTING & POWER CO. |
| To: | |
| Shared Package | |
| ML20202H951 | List: |
| References | |
| NUDOCS 9802230055 | |
| Download: ML20202H977 (14) | |
Text
ATTACHMENT 4 PROPOSED CHANGES TO CURRENT TECHNICAL SPECIFICATIONS 9002230055 980216 PDR ADOCK 05000499 p
PDR c;\\wp\\ntbrc ap\\TSC-98WT74 doc STI 30526238
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EfACTOR COOLANT SYSTEM STEAM GENERATORS SURVEILLANCE RE0VIREMENTS (Continued) 3)
A tube inspection (pursuant to S)ecification 4.4.5.4a 8) shall be performed on each selected tu)e.
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 subjected to a tube inspection.
4)
Indications left in service as a result of application of the tube support plate voltage-based repair criteria shall be inspected by bobbin coil probe during all future refueling
- outages, The tubes selected as the second and third samples (if required by c.
Table 4.4-2 or Table 4.4-3) during each inservice inspection may be subjected to a partial tube 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 2)
The inspections include those portions of the tubes where imperfections were previously found, d.
For Unit 1, any tube allowed to remain in service per Acceptance Criterion 11 (of Technical Specification 4.4.5.4a) shall be l
inspected via the rotating pancake coil (RPC) eddy current method over the F* distance.
Such tubes are exempt from eddy current inspectiun over the portion of the tube below the F* distance which is not structurally relevant.
' " " ' 1mplementation of the steam generator tube / tube support e.
plate repair criteria requires a 100-percent bobbin coil inspection for hot-leg and cold leg tube support plate intersections down to the lowest cold-leg tube support plate with known outside diameter stress corrosion cracking (0DSCC) indications. The determination of the lowest cold-leg tube support plate intersections having ODSCC indications shall be based on the performance of at least a 20-percent random sampling of tubes inspected over their full length.
The results of each sample inspection shall be classified into one of the following three categories.
Cateo n Insnection Results C-1 Less than 5% of the total tubes inspected are degraded tubes and none of the inspected tubes are defective.
SOUTH TEXAS - UNITS 1 & 2 3/4 4-13 Unit 1 - Amendment No. 62783,90 Unit 2 - Amendment No. 77
REACTOR COOLANT SYSTEM STEAM GENERATORS SURVEILLANCE REOUIREMENTS (Continued) 4.4.5.4= Acceptance Criteria a.-
As used in-this specification:
1)-
Tubinc or Tube means that portion of the tube or sleeve which forms the primary system to secondary system pressure boundary; 2)-
Imoerfection means an exception to the dimensions, finish, or contour of a tube from that required by fabrication drawings or l s )ecifications.
Eddy-current testing indications below 20% of-tie nominal tube wall thickness,11f detectable, may be considered as imperfections; 3)
Dearadation means a service ~ induced cracking,
wastage, wear, or l general corrosion occurring on either inside or outside of a-
-tube; 4)
Dearaded Tube means a tube containing imperfections greater l
than or equal to 20% of the nominal wall thickness caused by degradation; 5)
% Dearadation means the percentage of the tube wall thickness l
affected or removed by degradation; 6)
Defect means an imperfection of such severity that it exceeds the pluggin defective; g or_ repair limit
_A tube-containing a defect-is 7)
Pluaoina Limit or Renair Limit means the imperfection depth a't>
or beyond which the tube shall be rtmoved from service by plugging or repaired by sleeving in the'affected area because it may become unserviceable prior to the next inspection. The' plugging.or repair limit imperfection -depths are specified in percentage of the nominal wall thickness as follows:
a.
original tube wall-40%
b.
Westinghouse laser welded sleeve wall 40%
NrU.,RAIisdefinitiondoesnotapplytotubesupport plate intersections for which the voltage-based repair criteria are being applied. Refer to 4.4.5.4.a.12 for the' repair limi'.
applicable to these intersections.
8)
Unserviceable describes the condition of a tube if it leaks or l contains a defect large enough.to affect its structural integrity in the event of an Operating Basis Earthquake, a loss-of-coolant accident, or a steam line or feedwater line break as specified in Specification 4.4.5.3c., above; 9)
TubeInspectionmeansaninspectionofthesteamgeneratortubel from the point of entry (hot leg side) completely around the U-bend to the top support of the cold leg; and SOUTH TEXAS - UNITS 1 & 2 3/4 4-15 Unit 1 - Amendment No. 83,90 Unit 2 - Amendment No. 77 l
REACTOR COOLANT SYSTEM STEAM GENERATORS SVRVFILLANCF RE0VIREMENTS (Continued) 10)
Preservice Inspection means an inspection of the full length of l each tube in each steam generator performed by eddy current techniques prior to service to establish a baseline condition of the tubing. This inspection shall be performed prior to initial POWER OPERATION using the equipment and techniques expected to be used during subsequent inservice inspections.
-11)
F* criteria IFor Unit 1 onlvl Tube degradation below a l
s)ecified distance from the hard roll contact point at or near tie top-of-tubesheet (the F* distance) can be excluded from consideration to the acceptance criteria stated in this section (i.e., plugging of such tuber is not required). The methodology for determinatioc for the F* distance as well as the list of tubes to which the F* criteria is not applicable is described in detail in Topical Report - BAW 10203P, Revision 0.
-MitL 44Nr4tr>
12) f:r "att ' Tube Lunoort Plate Pluacina limit is used for the l
dispositio,n of agalloy 600 steam generator tube for continued service that is experiencing predominately axially oriented outside diameter stress corrosion cracking confined within the thickness of the tube support plates. At tube support plate intersections, the plugging (repair) limit is based on maintaining steam generator tube serviceability as described below:
a)
Steam generator tubes, whose degradation is attributed to outside diameter stress corrosion cracking within the bounds of the tube support plate with bobbin voltage less than or equal to the lower voltage repair limit (Note 1),
will be allowed to remain in service, b)
Steam generator tubes, whose degradation is attributed to outside diameter stress corrosion cracking within the bounds of the tube scpport plate with a bobbin voltage greater than the lower voltage repair limit (Note 1), will be repaired or plugged, except as noted in 4.4.5.4.a.12.c l
- below, c)
Steam generator tubes, with indications of potential degradation attributed to outside diameter stress corrosion cracking within the bounds of the tube support plate with a bobbin voltage greater than the lower voltage repair limit (Note 1) but less than or equal to the upper repair voltage limit (Note 2), may remain in service if a rotating pancake coil inspection does not detect degradation. Steam generator tubes, with indications of outside diameter stress corrosion cracking degradation with bobbin voltage greater than the upper voltage repair limit (Note 2) will be plugged or repaired.
SOUTH TEXAS - UNITS 1 & 2 3/4 4-16 Unit 1 - Amendment No. &%83,90 Unit 2 - Amendment No. 77 l
I i
@g SAIMLGENERATORS pjtRVElltANCE RE001REMENTS (Co inued) d)
Certain ntersections as identified in Framatome Technologies, Inc. Topical Report BAW-10204P, " South Texas Project Tube Repair Criteria for ODSCC At Tube Support Plates" will be excluded from application of the voltage-based repair criteria as it is determined that these intersections may collapse or deform following a postulated LOCA + SSE event.
e)
If an unscheduled mid-cycle inspection is performed, the mid-cycle repair limits apply instead of the limits identified in 4.4.5.4.a.12.a. 4.4.5.4.a.12.b, and 4.4.5.4.a.12.c.
The mid-cycle repair limits will be determined from the equations for mid-cycle repair limits of NRC Generic Letter 95-05, Attachment 2, page 3 of 7.
Implementation of these mid-cycle repair limits should follow the same approach as in TS 4.4.5.4.a.12.a.
4.4.5.4.a.12.b, and 4.4.5.4.a.12.c.
Note 1:
The lower voltage repair limit is 1.0 volt for 3/4-inch diameter tubing.:r ? O ;;lt; f:r 7/S 'rd. &--ter tdh;;.
Note 2:
The upper voltage repair limit (V methodology in Generic Letter 95M)as supplemented.is calculated according to the V
may on differ at the TSPs and flow distribution baffle.
- 13) Tube Reoair refers to a process that reestablishes tube serviceability. Acceptable tube repair will be performed in accordance with the methods described in Westinghouse Reports WCAP-13698, Revision 2, " Laser Welded Sleeves for 3/4 Inch-Diameter Tube Feedring-Type and Westinghouse Preheater Steam Generators," April 1995 and WCAP-14653, " Specific Application of Laser Welded Sleeves for South Texas Project Power Plant Steam Generators," June 1996, including post-weld stress relief; Tube repair includes the removal of plugs that were previously installed as a corrective or preventive measure. A tube inspection per 4.4.5.4.a.9 is required prior to returning previously plugged tubes to service.
b.
The steam generator shall be determined OPERABLE after completing the corresponding actions (plug or repair all tt.bes exceeding the plugging or repair limit and all tubes containing through-wall cracks) required by Table 4.4-2 and Table 4.4-3.
4.4.5.5 Reoorts a.
Within 15 days following the completion of each inservice inspection of steam generator tubes, the number of tubes plugged or repaired in j each steam generator shall be reported to the Commission in a Special Report pursuant to Specification 6.9.2; SOUTH TEXAS - UNITS 1 & 2 3/4 4-16a Unit 1 - Amendment No. 83,90 Unit 2 - Amendment No. 77
1 TEAM GENERATORS ggVEILLANCEREQUIREMENTS(Continued)
-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:
1)
. Number and extent of tubes inspected, 2) location and percent of wall-thickness penetration for each indication of an imperfection, and 3)
Identification of tubes plugged or repaired.
l Results of. steam generator tube inspections which fall into Category c.
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 plant operation. This report shall provide a description of-investigations conducted to determine cause of the tube degradation and corrective measures taken to prevent recurrence.
d.
For L;. A implementation of the voltage-based repair criteria to tube support plate intersections, notify the Staff prior to returning the steam generators to service should any of the following; conditions arise:
1)
If estimated leakage based on the projected end-of-cycle (or if l-not practical, using the actual measured end-of-cycle) voltage distribution exceeds the-leak limit-(determined from the licensing basis dose calculation for the postulated main steam line break) for the next operating cycle.
2)
If circumferential crack-like indications are detected at the
-l tube support plate intersections.
3)
If indications are identified that extend beyond the confines l
of the tube support plate.
4)
If indications are identified at the tube support plate l-elevations that are attributable to primary water stress corrosion-cracking.-
5)
If the calculated conditional burst probability based on the l
projected end-of-cycle (or if not practical, using the actgal measured end-of-cycle) voltage distribution exceeds 1 x 10',
notify the NRC and provide an assessment of the safety significance of the occurrence.
SOUTH TEXAS - UNITS 1 & 2 3/4 4-16b Unit 1 - Amendment No. 88,90 Unit 2 - Amendment No. 77
BEACTOR COOLANT SYSTEM BAsrs STEAM GENERATORS (Continued) plants have demonstrated the capability to reliably detect degradation that has penetrated 20% of the original tube wall thickness. Repaired tubes are also included in the inservice tube inspection program.
Exclusion of certain areas of Unit I tubes from consideration has been analyzed using an F* criteria.
The criteria allows service induced degradation deep within the tubesheet to remain in service. The analysis methodology determiner the length of sound fully rolled expanded tubing required in the uppeiinost area within the tubesheet to preserve needed structural margins for all service conditions.
The remainder of the tube, below the F* distance, is considered not structurally relevant and is excluded from consideration to the customary plugging criteria of 40% throughwall.
The amount of primary to secondary leakage from tubes left in service by application of the F* criterion has been determined by verification testing.
This leakage has been considered in the calculation of postulated primary to secondary leakage under accident conditions.
Primary to secondary leakage during accident conditions is limited such that the associated radiological consequences as a result of this leakage is less than the 10 CFR 100 limits.
Fr "dt d5e voltage-based repair limits of SR 4.4.5 implement the guidance in GL 95-05 and are applicable only to Westinghouse-designed steam generators (SGs) with outside diameter stress corrosion cracking (ODSCC) located at the tube-to-tube support plate intersections. The voltage-based repair limits are not applicable to other forms of SG tube degradation nor are they applicable to ODSCC that occurs at other locations within the SG.
Additionally, the repair criteria apply only to indications where the degradation mechanism is dominantly axial ODSCC with no significant cracks extending outside the thickness of the support plate. Refer to GL 95-05 for additional description of the degradation morphology.
Implementation of SR 4.4.5 requires a derivation of the voltage structural limit from the burst versus voltage empirical correlation and then the subsequent derivation of the voltage repair limit from the structural limit (which is then implemented by this surveillance).
The voltage structural limit is the voltage from the burst pressure / bobbin voltage correlation, at the 95-percent prediction interval curve reduced to account for the lower 95/95-percent tolerance bound for tubing material properties at 650*F (i.e., the 95-percent LTL curve). The voltage structural limit must be adjusted downward to account for potential flaw growth during an operating interval and to account for NDE uncertainty.
The upper voltage repair limit; V
'w, is determined from the structural voltage limit by applying the folio ing equation:
V, = V
-V
-V st ca uot _
where V represent the allowance for flaw growth between inspections and V,o c
represenks the allowance for potential sources of error in the measurement ok the bobbin coil voltage. Further discussion of the assumptions necessary to determine the voltage repair limit are discussed in GL 95-05.
SOUTH TEXAS - UNITS 1 & 2 B 3/4 4-3 Unit 1 - Amendment No. 82d3,90 Unit 2 - Amendment No. 77 I
REACTOR' COOLANT SYSTEM BASES DPERATIONAL LEAKAGE (Continued)
, d e leakage limits incorporated into SR 4.4.6 are more T;, "
restrictive than the standard operating leakage limits and are intended to provide an additional margin to accommodate a crack which might grow at a greater than expected rate or unexpectedly extend outside the thickness of the tube support 11 ate.
Hence, the reduced leakage limit,-when combined with an effective lea ( rate monitoring program, provides additional assurance that should a significant leak be experienced in service, it will be detected, and the plant shut down in a timely manner.
Tr ":"
' =f de steam generator tube leakage limit of 150 gpd for each steam generator not isolated from the RCS ensures that the dosage
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contribution from the tube leakage will be limited to a small fraction of 10 CFR Part 100 dose guideline valves in the event of either a steam generator tube rupture or steam line break. The 150 gpd limit per steam generator is conservative compared to the assumptions used in the analysis of these accidents. The 150 gpd leakage limit per steam generator ensures that steam generator tube integrity is maintained in the event of a main steam line 4
rupture or under LOCA conditions.
The 10 gpm IDENTIFIED LEAKAGE limitation provides allowance for a limited amount of leakage from known sources whose presence will not ;nterfere with the detection of UNIDENTIFIED LEAKAGE by the Leakage Detection Systems.
The specified allowed leakage from any RCS pressure isolation valve is sufficiently low to ensure early detection of possible in-series check valve failure.
It is-apparent that when pressure isolation is provided by two in-series check valves and when failure of one valve in the pair can go undetected for a substantial length of' time, verification of valve integrity is required.
Since these valves are impor). ant in preventing overpressurization and rupture of the ECCS low pressure piping which could result in a LOCA that bypasses containment, these valves should be tested periodically to ensure low probability of gross failure.
The Surveillance Requirements for RCS pressure isolation valves provide added assurance of valvt integrity thereby reducing the probability of gross valve failure and consequent intersystem LOCA. Leakage from the RCS pressure isolation valve is IDENTIFIED LEAKAGE and will be considered as a portion of the allowed limit.
3/4.4.7 CHEMISTRY The limitations on Reactor Coolant System chemistry ensure that corrosion of the Reactor Coolant System is minimized and reduces the potential for Reactor Coolant System leakage or failure due to stress corrosion. Maintaining SOUTH TEXAS - UNITS 1 & 2 B 3/4 4-4 Unit 1 - Amendment No. 83,90 Unit 2 - Amendment No.77
ATTACHMENT 5 PROPOSED CHANGES TO IMPROVED TECHNICAL SPECIFICATIONS c3wp\\nNmap\\TSC 98VX)74. doc STI 30526288
Programs and Manuals 5.5 5.5 Prograats and Manuals 5.5.9.2 Steam Generator Tube Samnle Selection and Insoection (continued) 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. r-and 2.
The inspections include those portions of the tubes where imperfections were previously found.
d.
For Unit 1. any tube allowed to remain in service oer accentance Criterion 11 (of Technical Soecification 5.5.9.4.a shall be ins 3ected via the rotatina cancake coil (RPC) eddy current met 1od over the F* distance. Such tubes are exemot from eddy current insSection over the nortion of the tube below the F* distance w11ch is not structurally relevant.
g.
- "^'
molementation of the steam aenerator tube / tube sunoort olate recair criteria reouires a 100-oercent bobbin co11 insoection for hot-lea and cold-lea tube succort olate
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intersections down to the lowest cold-lea tube subcort'olate with known outside diameter stress corrosion crac tina (ODSCC) indications. The determination of the lowest cold-lea tube suonort olate intersections havina ODSrc
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indications shall be based on the nerformance of at least a 20-oercent random samolina of tubes insoected over their full lenath.
The results of each sample inspcction shall be classified into one of the following three categories:
Cateaorv Insoection Results C-1 Less than 5% of the total tubes inspected are degraded tubes and none of the inspected tubes are defective.
C-2 One or more tubes but not more than 1% of the total tubes inspected are defective, or between 5%
and 10% of the total tubes inspected are degraded tubes.
C-3 More than 10% of the total tubes inspected oi_
degraded tubes or more than 1% of the inspected tubes are defective.
(continued)
South Texas Units 1 & 2 5.0-15 Rev 0, 07/18/97 I.
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Programs and Manuals 5.5 5.5 Programs and Manuals 5.5.9.4 Acceotance Criteria (continued) to the next insoection. The nluoaina or renair limit imoerfection denths are soecified 1n oercent' ace of the
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nominal wall thickness as follows-jL oriainal tube wall El h
Westinghouse laser welded sleave wall 101 m m,4 4,
mm. s1
+m Any mr +nm nmm4 g1 +nsm..s 1,
+ k 4 r t. nme r,
fb b5i!1 Mis IefinitionlSes nok an[v'to'EubS
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suonort nlate intersections for which t ie voltaae-based renair criteria are beina ao311ed Refer to R.6.Q 4.a.12 m
fo'r the renair limit anolica31e to these intersections.
78, linserviceable describes the condition of a tube if it leaks or contains a defect large enough to affect its structural integrity in the event of an Operating Basis Earthquake, a loss-of-coolant accident, or a steam line or feedwater line break as specified in Specification 5.5.9.3.c. above:
89, Tube Insoection means an inspection of the steam generato'r tube from the Joint of entry (hot leg side) completely around the U-3end to the top support of the cold leg: and 91Q. Prcservice insnection means an inspection of the full length of each tube in each steam generator performed by eddy current techniques prior to service to establish a baseline condition of the tubingJEP OPEPATMpection shall This ins be perfomed prior to initial P.
Power Ooeration (Mode 11 using the equipment and techniques e'xpected to be used during subsequent inservice inspections.
IL F* criteria fFor Unit 1 onivl Tube dearadation below a sDecified distance from the hard roll contact noint at or near the ton-of-tubesheet (the F* distance) can be excluded from consideration to the acceotance criteria stated in this section (i.e.
olugaina of such tubes is not reouired).
The methodoloav for determination for the F* distance as well as the list of tubes to which the F*
criteria is not a30licable is described in detail in Tonical Reoort - MW 10203P. Revision 0.
(continued)
South Texas Units 1 & 2 5.0-21 Rev 0, 07/18/97
Programs and Manuals 5.5 5.5 Programs and Manuals 5.5.9.4 Accentance Criteria (continued)
- 12. F r Unit 1. Tube Suonort late Pluacina limit is' used for the disoosition of anFallov 600 steam aenerator tube for continued service tnat is exDeriencina credominately axially oriented outside diameter stress corrosion crackina confined within the thickness of the tube sunnort olates. At tube suinort olate intersections. the cluacina'fre3 air) limit is 3ased on maintainina steam aenerator tu3e serviceability as described below-a.
Steam aenerator tubes. whose dearadatien is attributed to outside diameter stress corrosion crackino within the bounds of the tube suonort olate with bobbin voltaae less than or eaual to the lower voltage renair limit (Note 1). will be allowed to remain in service.
b.
Steam aenerator tubes. whose dearadation is attributed to outside diameter stress corrosion crackina within the bounds of the tube suo3crt plate with a bobbin voltaae areater than t 1e lower voltaae renair limit (Note 1). will be reoaired or cluaaed. e'xceot as noted in 5.5.9.4.a.12.c below.
C.
Steam aenerator tubes. with indications of potential degradation attributed to outside diameter stress corrosion crackina within the bounds of the tube suo3crt olate with a bobbin voltaae areater than t ie lower voltaae reoair limit
~
(Note 1) but less than or ecual to the unber renair voltaae limit (Note 2). may' remain in se'vice if' a r
rotatino cancake coil insoection does not detect dearadation. Steam t'nerator tubes. with indications of outside diameter stress corrosion crackino deartdation with bobbin voltaae areater Unst than the unber voltaae rega,ir limit (Note 2) will be 01oaaed or renair,d.
IL Cettai nh ntersecti ons.ar_jfienti fi ed i n Fran1atome Technoloaies. Inc. TOD.ical Reoort BAW-10204P.
" South Texas Proiect Tgbe Reoa' ir Criteria for ODSCC At Tube Suncort Plates" will'be excluded from (continued)
South Texas Units 1 & 2 5.0-22 Rev 0. 07/18/97
Programs and Manuals 5.5 l
5.5 Programs and Manuals t
5.5.9.4.
Accentance Criteria (continued) aonlication of the voltaae-based reoair criteria as it is determined that these intersections may collanse or deform followino a costulated LOCA + SSE event.
g.
If an unscheduled mid-cycle insoection is nerformed. the mid-cycle reoair limits anolv instead of the limits ident1fied in 5.5.9. A.a.12.a.
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5.5.9.4.a.12.b. and 5.5.9.4.a 12.c.
The mid-cycle renai.* limits will be determined from the ecuations for mid-cycle reoair of NRC Generic Letter 95-05.. Daae 3 of 7.
Imnlementation of these mid-cycle reoair limits should follow the same aggroach as in TS 5.5.9.4.a.12.a. 5.5.9.4.a.12.b.
and 5.5.9.4.a.12.c.
Note 1: The lower voltaae re3 air limit is 1.0 volt for 3/4-inch diameter tu3ino cr 2.0 colt-f r '!B 'r.ch-
-di^2:::: tubin:.
Note 2: The unoer voltaae re3 air limit (V,1)is calculated accordina to the met lodoloov in Generic Letter 95-05 as sucolemented.
V in and flow distribution baff$e.av differ at the TSPs
- 13. Tube Renair refers to a 3rocess that reestablishes tube serviceability. Accenta 31e tube reoair will be nerformed in accordance with the methods described in Westinahouse Reoorts WCAP-13698. Revision 2. " Laser Welded Sleeves for 3/4 Inch Diameter TLbe Feedrino-Tvoe and Westinahouse Preheater Steam Generators. " Aoril' 1995 and WCAP-14653.
"Soecific Ano11 cation of Laser Welded Sleeves for South
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Texas Proiect Power Plant Steam Generators." June 1996.
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includina oost weld stress relief.
Tube renair includes the removal of cluas that were oreviously installed as a corrective or oreventive b9asure. A tube insnection oer 6.5.9.4.a.9 is reauired orior to returnina oreviousl' oluaaed tubes to service.
v b.
The steam generator shall be determined OPERABLE after completing the corresponding actions (plug or reoair all (continued)
South Texas Units 1 & 2 5.0-23 Rev 0. 07/18/97 l
Reporting Reqw rements 5.6 5.6 Reporting Requirements (continued) 5.6.98 Tendon surveillance Reoort Any abnormal degradation of the containment structure detected during the tests required by the Pre stressed Concrete Containment Tendon Surveillance Program shall be reported to the NRC within 30 days. The report shall include a description of the tendon condition, the condition of the concrete (especially at tendon anchorages), the inspection procedures, the tolerances on cracking, and the corrective action taken.
5.6.M2 steam Generator Tube insocction Recor.t The Steam Generator Tube Surveillance Program shall be documented in reports submitted to the NRC in accordance with the following:
a.
The number of tubes plugged or renaired in each steam generator shall be reported within 15 days following completion of the progre: insnection, b.
Thecomp:leteresultsoftheStenGeneratorTube Surv011. n 0 "r-egram insoelion shall be re months following complefion of the progr= ported within 12 insoection and shall include:
1.
Number and extent of tubes inspected, 2.
Location and percent of wall thickness penetration for each indication of an imperfection, anu 3.
Identification of tubes plugged or renaird, c.
The results of steam cerettor tube ins)ections which fall into Category C 3 shall be reported wit 11n 30 days ef 4he c0 plction 0. the prc^{r : and prior to resumption of plant operation. The repor shall include a description of investigations conducted to determine the cause of the tube degradation and corrective measures taken to prevent recurrence.
i For M im31ementation of the voltaae-based renair criteria to tu3e sunoort olate intersections. notify the
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Staff orior to return' na the steam aenerators to service should any of the fol hina conditions arise-1.
If estimated leakaae based on the orciected end of evele for if r.ot oractical. usina the actual moasured end-of-(continued)
South Texas Units 1 & 2 5.0 38 Rev 0. 07/18/97
ATTACHMENT 6 WESTINGHOUSE STEAM GENERATOR REPORT SG-98-01-004 4
)
e \\wp\\ntinre apATSC-98W174 doc STI 30526288
SG 98 01-004 SOUTH TEXAS PROJECT UNIT 2 Technical Bases Supporting Application For License Amendmentt Voltage Based Repalr Criteria per GL 95-05 i
1.0 Introduction i
The BTP Unit 2 Technical Specifications currently assess steam generator tube operability based on an indicated <10% (by NDIC) degradation depth. Accurate depth sizing of stress corrosion i
cracking in SG tubes is difficult, and SG tube burst and leakage integrity is ultimately dependent upon both flaw depth and length, the latter not incorporated into the current Unit 2 depth based Technical Specification tube repair criteria, llobbin coil voltage analysis has been 3
shown to provide a more accurate akscasment of tube structuralintegrity than depth based
+
phase analysis for tubes affected by outer diameter stress corrosion cracking (ODSCC).
i Therefore, the Voltage liased Hepair Criteria for ODSCC at tube support plate (TSP) intersections, addressed by NitC Generic letter 95 05, provides an siternative method for the assessment of SG tube repair requirements due to predominantly axially oriented ODSCC at TSP intersections, lly directly relating bobbin voltage response to burst capability, the voltage based repair criteria represents a more approprinto tube integrity r4ssessment tool compared to
+
depth sizing alone. The voltage based repair criteria has been implemented at 5 plants using Westinghouse steam generators with 7/8" OD mill annealed Alloy 600 tubing and 4 plants with Westinghouse steam generators using 3/4" OD mill annealed Alloy 600 tubing (the latter being Catawba 1, Byron 1, liraidwood I and South Texas Unit 1). The implementation of the criterin at these plants has jvstified continued operation fer thousands of steam generator tubes with 1
bobbin eddy current signals at TSP intersections which would have required repair using the current depth based criteria and industry plugging practices.
i STPNOC requests approval for use of the voltage based repair criteria per GL 05 05 for the upcoming 1998 Cycle 0 inspection (2HE00 outage) Imsed on the detection of ODSCC at TSP I
intersections in 2HE05 and 2itE01 l'herefore, the criteria will be implemented beginning with the Cycle 7 operating period.,% the ODsCC mechanism at STP Unit 2 is in its early stages, I
application of the voltage based plugging criteria will prevent the unnecessary plugging of steam generator tubes at TSP intercections due to the uncertainty related to depth estimation of i
4 The purpose of this attachment is to provide the technical basis supporting a license amendment request implementing the 1.0 volt repair criteria for steam generator tubes affected by ODSCO, t
according to the guidance of NHC Generic Letter 95 05 (Heference 1) at South Texas Unit 2.
This attachment describes the STPNOC plan for implementation of the 1.0 volt repair limit and the requirements of GL 05 05. Sections I to 6 of Attachment 1 to GL 95 05 are addressed herein
)
to summarize the STP Unit 2 plan, which meets the intent of GL 05 05, and is consistent with i
1
SG.98-01-004 NitC approved updates to the origim'lly issued 01,05 05 methods. Clarificationn to the Section 3 " Inspection Criteria" articles are identified in the corresponding section of this attachment.
These relate to implementation of tho bobbin probe variability requirements (Section 3.c.2), the probe wear requirements (Section 3.c.3) and the use of alternate probes to the itPC probe, in addition, STPNGC is requenting the use of a voltage dependent probability of detection, the methodology of which was originally submitted to the NitC for review by NEl in December of 1990.
1.1 South Texas Unit 2 Design Features STP Unit 2 is a Westinghouse 4 loop pressurized water reactor plant which utilizes Model E2 steam generators (SG) with 3/4 inch diameter mill annealed Alloy 600 tubing and drilled hole stainless steel tube support plates (TSPs). A total of 15 tubes in SG D use thermally treated Alloy 600 tubing, and these tubes, identified later, are excluded from application of the criteria since they are not constructed nf Alloy 600 mill annealed tubing. While thermally treated Alloy 600 tube material is less susceptible to stress corrosion cracking than mill annealed Alloy 600 tube material, should ODSCC develop in these tubes, the postulated corrosion morphology cannot be adequately determined without a tube pull. The benefit obtained by application of the criteria to these tubes is not perceived to be greater than the economic impact of a tube pull, should degradation occur in these tubes. The Model E2 SG incorporates a flow distribution baffle (FDil) plate located approximately 8 inches above the top of the tubesheet, like the Unit 1 SGs, and similar to other SGs in which the voltage based plugging criteria are applied, such as the Model D 1 steam generator. The tube holes located in the FDil design include an increased nominal tube to plate diametrical gap ranging from approximately 0.083" to 0.120", compared to a 0.017" to 0.021" nominal gap at the TSPs. Ilased on this increased tube to plate gap at the FDil, an upper voltage repair limit based on providing tube structural integrity against a pressure equivalent of three times the normal primary to secondary tubo differential pressure is provided. The design features of the South Texas Unit 2 steam generators are consistent with the scope of applicability of GL 95 05. While not specifically addressed by GL 05 05, the voltage based repair criteria can be applied to the TSP intersections at STP Unit 2 without modification or exception due to the TSP material (105 SS). A large portion of the %" pulled tube data base is i
taken from pulled tube data from the Doel.4 plant, which originally used Model El SGs with 405 SS TSPs, prior to SG replacement. Confirmatory eddy current testing was performed using both carbon steel and stainless steel TSP simulants to show that the primary mix channel bobbin coil voltage response is unaffected by the TSP material. The results of this testing is discussed in greater detailin report section 3.0, "GL 95 05 Section 2."
2
~
SG 98-01004 1.2 Summary of the Voltage Hased Hepair Criteria The following items outlino the specific requirements and actions associated with the implementation of the voltage based repair criteria at STP Unit 2.
l All tubes shall bo inspected using the bobbin coil. The inspection shall include all hot leg i
e TSP intersections and cold leg intersections down to the lowest TSP for which ODSCC has been identified.
l llobbin coil flaw indications greater than 1.0 volt shall be inspected by a rotating coil probe e
(or equivalent) to evaluate the presence of detectable ODSCO and to confirm that the I
dominant corrosion mechanism occurring is axially oriented ODSCC.
Eddy current analysis guidelines shall be compatible with and satisfy GL 05 05 i
requirements.
{
Technical Specification operational leak rate limit (LCO 3A.0.2) shall be reduced to 150 gpd e
per steam generator. The STP Unit 2 normal operating condition leakage limit has been 7
previously reduced to the GL 05 05 value of 150 gpd.
Axial ODSCC indications less than the lower voltage repair limit,1.0 volt, as measured by bobbin coil, may remain in service without further inspection or analysis.
Axial ODSCC bobbin coil indications greater than 1.0 volt and less than or equal to the upper voltage repair limit (%w.) can remain in service if MllPC inspection indicates no detectable degradation.
Axial ODSCC bobbin coil indications greater than 1.0 volt and less than or equal to the upper voltage repair limit (Vma.) must be repaired if MHPC inspection indicates detectable degradation.
Axial ODSCC bobbin coil indications exceeding the upper voltage repair limit must be repaired.
Postulated Faulted condition primary to secondary leakage through indications to which the criteria is applied shall be calculated using accepted industry and NilC approved practices.
Postulated leakage in the limiting steam generator rihall be less than the bounding faulted condition leakago necessary to ensure that offsite doses remain within the 10 CFR 100 siting criteria and that control doses remain within ODC 10 limits.
i Projected tube burst probability at a pressure differential equal to the limiting faulted e
condition pressure differential shall be calculated using accepted industry and NRC approved practices and compared to the reporting value of 1.0 x loiin the limiting steam generator.
1.3 Acknowledgment of GL 95-05 Performance Requirements Table 1 (provided on the following pages) presents an item by item identification of the individual points of GL 05 05 which require utility action or present a specific analysis methodology.
3 J
SG 08-01-004 Table 1 Acknowledgment ofIndividual GL 95-05 Performance Criteria OL 05 05 0L Methodology Comments item Concurrence 1.b Followed The exclusion criteria listed will be followed. Nbintersections are excluded due to permanent deformation potential from a combined LOCA + SSE event. Table 2 lists tubes excluded based on material properties. b for FDll intersections is dermed in Section 2.
2.n.1 Modified from The latest NitC approved database at the time of the inspection will be original version, utilized. Currently, the database defined in Iteference 0, EPit! NP 7480.L.
approved by NitC Addendum 1. is the latest NitC approved database for %" tubing. This database supersedes the database identified in GL 95 05.
2.a.2 Followed See response to section 2.a.l.
2.a.3 Followed See recponse to section 2.a.l.
2.b.1 llequest for NitC Distribution of bobbin indications included in the Stil lenkrate projection approval will be based on the voltage dependent probability of detection, or POPCD, as described in lleference G.
2.b.4 Followed Consistent with the STP UFSAlt, ICitP 2 dose conversion factors were used for calculation of maximum allowable SLB leak rates. These dose conversion factors are more conservative than the ICitP 30 data.
3.b Followed STPNOC will utilize the rotating pancake probe (ItPC) or equivalent probe for confirmation of bobbin indications.
3.b.1 Followed itPC (or equivalent) will be used for inspection of bobbin voltages > 1.0 volt.
3.b.2 Followed itPC (or equivalent) will be used for inspection where copper could innuence bobbin signal, possibly masking a 1,0 volt indication.
3.b.3 Followed itPC (or equivalent) will be used for inspection of all dents
> $ volts, possibly masking a 1.0 volt indication.
3.b.4 Followed itPC (or equivalent) will be used for inspection oflarge mixed residuals, possibly masking a 1.0 volt indication.
3 c.2
- Modified, The probe variability limits dermed in the NitC letter dated March 18,1990 accepted by NitC will be implemented.
3.c.3
- Modified, Limits on reinspection of tubes due to out of specification probe wear will be accepted by NitC followed according to the NitC letter dated February 9,1990.
3.c.4 Followed Data analysts will be trained and qualified in the use of the analysis guidelines and procedures specific for application of the criteria 4.
Followed Tube removal guidance will be followed.
5.a Followed Operationalleakage (LCO 3.4..G.2) has previously been reduced to 150 gpd /
SG 5.b Followed STPNOC leakage monitoring techniques are consistent with lteference 7, and are adequate to meet GL 95-05 recommendations.
5.c Followed Known leaking tubes will be repaired.
6.
Followed llepos ting requirements will be followed.
4
SG-98-01-004 y
2.0 GL 05-05 Section 1: APPLICAlllLITY The repair critHa will be applied to axially oriented ODSCC indications at tube to TSP and FDilintersections (within the plate thickness) of tho steam generator tube bundle. The relatively small bobbin voltages observed indicate that the degradation morphology is currently in its early stages of development. Of the 1050 observed bobbin indications at the TSPs,099 were removed from service due to the total plugging effort (including plugging for top of tubenheet, AVils, etc). Of the 1050 total DSis,000 (02.5%) were confirmed by llPC as either multiple axial indications (mal, 28 indications), single axiol indications (sal, 030 indications), or volumetric (2 indications). Consistent with Section 4.a of Attachment I to GL 05 05, a minimum of two tubes (and 4 inter *ections) will be removed from STP Unit 2 for destructive examination upon initialimplementation of the criteria. Tubes pulled from other plants using both 7/8" and 3/4" OD tubing for indications of ODSCC at TSPs have been shown to have crack morphology consistent with the EPitt database used for the supporting voltage correlations, it should be noted that the majority of the pullei tubes currently included in the %" tube pulled tube database have been retnoved from the Doel 4 plant, which also utilized Model E steam generators of a design similar to STP Unit 2, including the use of 405 SS drilled hole TSPs, Any other type of tube degradation or any other kication in the tube bundle other than the TSPs shall continue to be evaluated in accordance with existing STP Unit 2 Technical Specifications. The observation of circumferential cracks, or primary water stress corrosion cracking associated with TSP indications, or ODSCC beyond the TSP thickness will be reported to the NitC prior to return to power.
The voltage based repair criteria will not be applied at the following tube to TSP intersections of the steam generator tube bundle:
1.
Elecations where tubes with decradation could substantially deform or collaps durme 1mstulate[LQG + SSE loading. Conservative analysis results summarized in Appendix A indicate that no intersections meet the criteria for exclusion based on permanent i
deformation exceeding 0.030" during the combined LOCA + SSE event. Appendix A provides a summary of the tube collapse determination methodology. llounding LOCA rarefaction wave loadings for the surge line and accumulator line breaks and STP Unit 2 seismic input data were used to perform the analyses outlined in Appendix A. The resulting loads on the TSPs are compared to data from a TSP crush test program to ultimately 1
determine the susceptibility to tube deformation greater than the 0.030" limit and to defme the list of excluded intersections. The NitC Staff has concluded that STP Unit 2 is in compliance with GDC 4, and that therefore, the probability of a rupture of the primary reactor coolant piping and surge line is extremely low. The dynamic effects of postulated pipe ruptures are therefore eliminated from the design basis. The technical support document for the Unit I voltage based plugging criteria application (approved by the NitC 5
l SG-98-01-004 staf0 sites the use ofleak before break (Lillt) application to exclude large break loadings.
The analysis performed by Westinghouse uses bounding LOCA inputs for the surge line and accumulator line breaks. The LOCA loadings used conservatively bound all of the small break hications and sizes.
The tube exclusion analysis methodology employed by Westinghouse has been shown to be quite conservative. The NitC has permitted the use of small break combined event loadings for voltage based repair criteria evaluation for another plant with D i steam generators (iteference 8) as well as for South Texas Unit 1.
2.
ALiule TSP interactions with dent slenals exceedine 5.0 (bobbin) volts. Any indications confirmed by itPC will be plugged or repaired (sleeved).
3.
At tube TSP intersections where mixed residuals could mask a 1.0 volt bobbin volt ODSCC indicatiori. Any indications confirmed by itPC will be plugged or repaired (sleeved).
4.
At tube TSP intersections where comwr deposits interfere with bobbin volt siunals. Any indications confirmed by itPC (or equivalent, i.e., + Point) will be plugged or epaired. No occurrence of copper deposits at a TSP intersection has been found for any Westinghouse SG for which the AltC has been applied.
5.
At tube intersections in which the tube material is not consistent with_the.cnTr.atix necented database. A total af 15 tubes in SG D at STP Unit 2 use thermally treated Alloy 600 tube material and these tube locations are identified in Table 2. For NDE, structural and leakage considerations, the responses of thermally treated and mill annealed tubing is expected to be similar. For conservatism, and since no corrosion degradation in thermally treated Alloy 600 tubing has been evidenced, or confirmed by tube pulls, the tubes listed in Table 2
- vill be excluded from application of the criteria. The thermally treated tubes in Table 2 are expected to be less susceptible to stress corrosion cracking than mill annealed tubes.
Table 2 South Texas Unit 2 SG D Tubes Excluded from Application of the Voltage liased llepair Criteria due to Use of Thermally Trented Alloy 600 Tube Material It13 C01 1t14 CGI 1115 CO2 1116 C62 It13 062 1114 C62 It15 C03 It16 C63 1113 C63 1114 CG3 1115 C64 lt13 C64 1114 C64 it15 C65 11la C65 6
4 SG 98-01-004 4
3.0 GL 95-05 Section 2: TUHE INTEGRITY EVALUATION l
4 There are three principal engineering analyses that shall be performed during each 1.0 volt I
repair process at STP Unit 2:
)
i Prediction of SG bobbin voltage population distribution at end of next cycle, n.
b.
Calculation of SG tubo leakage during a postulated steam line break (SLil),
Calculation of SG tube burst probability during a postulated SLil.
c.
The latest approved EPHI database (3/t inch diameter tubing) utilizing NHC approved data i
exclusion criteria will be applied in the voltage correlations (burst, probability ofleakage, SLil -
leak rate) used for the leak rate, burst probability and upper voltage repair limit calculations.
The NHC approved industry protocol for updating the database will be followed by STPNOC.
- The methodology to be applied by STPNOC at STP Unit 2 for the performance of these analyses, I
including correlations which relate bobbin voltage amplitudes, free span burst pressure, probability ofleakage and associated leak rates is documented in Reference 2 and is consistent with the methodology of Attachment 1, Section 2 of GL 05 05. The NHC approved revisions to Heference 2 or equivalent methodology reports will be implemented, in addition, the upper voltage repair limit used to repair bobbin indications independent of HPC confirmation will be determined at each outage based on the guidance of Section 2.n.2 of GL 05 05.
For example purposes, the EOC 5 bobbin signals are projected to EOC 0 (the current cycle) conditions using this methodology. At EOC 5,100% of the tubes in all four steam generators were inspected using the bobbin probe. As a less than 100% bobbin inspection was performed at
-EOC 1, growth values for DSis inspected at EOC 3 but not EOC 4 were adjusted based on the estimated operating cycle lengths of Cycle 1 and Cycle 5 to develop Cycle 5 growths for these indications (see Figure 1). Using this growth projection,- the limiting conditional tube burst
. probability at EOC 0, assuming the criteria were applied at EOC 5, was found for SG A and determined to be 1.00 x 101, which is well below the GL 05 05 reporting limit of 1.0 x 10 8. The example case BOC 0 (assuming no tubes were plugged and assuming the criteria were applied at EOC 5) and EOC 0 bobbin voltage distributions for all 4 steam generators assuming a POD of O.0 are provided in Figures 2a thru 2d. All tubes were assumed to have been left in service since j
the bobbin voltages were allless than the upper voltage repair limit. The low conditional burst
(
probability calculated in the example using a POD of 0.0 should not be used to reduce the 3
importance of the applicability of POPCD,it only shows that the occurrence of ODSCC at TSPs at STP Unit 2 is in its' carly stages.
i 7
SG 98-01-004 SLil Tabe Leak ILite The calculated maximum allowable tube leak rate for STP Unit 2 during a postulated main steam line break (SLil) event shall not exceed 5.0 gpm in the faulted loop (calculated at room temperature conditions). This value was established for the STP Unit I voltage based repair criteria implementation and applies to both Units. The 5.0 gpm leak rate valut in the faulted loop (with leakage in the intact k> ops equal to the Technical Speci0 cation normal operation leakage limit of 150 gpd) will not result in either control room dose exceeding the ODC 19 limit or the off site dose exceeding 10% of the 10 CFit 100 guidelines for accident initiated iodine spiking or off site dose exceeding the 10 CFit 100 guidelines for preaccident iodine spiking, and therefore is consistent with the STP Unit 2 licensing basis, ifit is determined during the operating cycle that this leakage limit might be exceeded, the reporting requirements of Section 0.a.1 will be followed. The calculated lenkrate limit and maximum allowable leakrate values for STP Unit 2 are specified as room temperature values, therefore, these values are compared using a consistent set of reference conditions.
Consistent with the guidance of Section 2.c, the STP Unit 2 SLilleak rate analysis performed prior to returning the SGs to service may be performed based on the projected next EOC voltage distribution or the actual measured distribution at a given outage. The method selected at a given outage will be based on outage schedule constraints, particularly the ability to complete the growth rate analysis prior to restart. Leak rate analysis for STP Unit 2 will be performed for a limiting primary to secondary pressure differential of 2407 psig, which represents the pressurizer POltV setpoint of 2335 psig plus 3% accumulation effects. The NitC staff has concluded that the STP Unit 2 pressurizer POllVs and associated block valves will be available during postulated accident or transient event recovery, and therefore can be relied upon to control llCS pressure during accident or transient recovery, Using the EOC 5 voltage distributions for the STP Unit 2 SGs, projected EOC 0 SLilleak rates were simulated assuming no tubes were plugged at EOC 5 since all of the bobbin voltages were less than the upper voltage repair limit. Using a POD of 0.6, the limiting leak rate is found to be 0.0130 gpm in SG A (room temperature conditions). The simulated leak rates, burst probabilities and largest simulated indication voltages are provided in Table 3. These simulations are exceptionally conservative since G99 of the 1050 total TSP indications were plugged at EOC 5, and the simulation of SLilleakage was done at a pressure differential of 2500 psig, whereas availability of pressurizer POllVs and block valves will permit the ItCS to be controlled to a maximum of 2335 psig (plus 3% accumulation) during recovery from a postulated SLil event. Also contained in Table 3 are the simulation results for SG A (largest growth) and SG II (largest number 1100 G indications) using actual 110C G voltage distributions, which include the plugging effects.
8 i
U
SG-98-01-004 Table 3 STP Unit 2 EOC 6 Leak Itate and llurst Probability Simulation Results Assuming No Tubes Plugged at EOC 6 80
!*ak Itate (gpm) llurst probabihty 1,argest Simulated Ind. Voltage A
0.0139 1.09 x 10 4 2.50 11 0.0055 8.98 x 10 8 2.50 0
0.0012 0.05 x 10 4 1.90
~
D 0.0013 2.37 x 10 4 t.80 STP Unit 2 EOC 61 cak Hate and llurst Probability Simulation Results
~
Using Actual 1100 6 Voltage Distribution A
0.0002 4.9 x 10 4 230 11 0.0027 2.0 x 10 4 2.30 Note: leak Itate and burst probabihty based on SLil AP of 2500 psig. Conservative for STP Unit 2 due to POltV availability during Stil recovery limits AP to 2335 psig + 3% accumulation.
The offsite dose calculations have been performed consistent with GL 95 05 recommendations and other analyses previously approved by the NitC related to the GL 95 05 plugging criteria.
The SLilleak rate limit for Unit 2 is consistent with the Unit I limit. The analysis of SLH cffects upon the reactor core, fuel, and DNillt potential described in the South Texas UFSAll indicates no DNil occurs for any rupture assuming the most reactive assembly is stuck in the fully withdrawn position for the SLB cvent.
Pressurizer PORY Availability Per Section % AA of the South Texas Units 1 and 2 Tech Specs, LCO 3.1 A requires that both pressurizer PORVs and their associated block valves shall be OPEllABLE during Modes 1,2, and 3. Action statements are included in the Technical Specifications which limit PoltV inoperability to a maximum of I hour.
Unlike most other PWits, the South Texas 1 and 2 PoltVs and block valves can be relied upon to function during transient or accident recovery conditions. The South Texas PORVs and block valves are safety class 1 valves and within the scope of a quality assurance program in compliance with 10 CFR 50, Appendix H. The South Texas 1 and 2 PORVs are solenoid operated, Class IE powered, and are seismically and environmentally qualified. The pilot valve which causes activation of the PORY is operated by a 125 VDC solenoid powered by battery backed vital switchgear EIA11. The AC supply for the switchgear is ESF diesel backed. The South Texas I and 2 solenoid operated PORVs and block valves are included in the ISI program covered by Subsection IWV of Section XI of the ASME Code. The PORV block valves are included in the South Texas expanded MOV test program. By design, the operability of the 9
l SG 08 01001
)
l POllVs is not based on the automatic control function. Inoperability of the POllVs automatic function during manual operation does not result in inoperability of the POltVs manual operation. The South Texas 1 and 2 Technical Specificatt ns incorporate the recommendations provided in Enclosure A and Enclosure 11 of GL 90-00, thereby resolving Generic lasues 70 and 91.
The NltC Staff has concluded in SElt Amendment No. 55 to NPF 70 (Unit 1) and Sell Amendment No.11 to NPF 80 (Unit 2), that the POltVs and their associated block valves satisfy Generne issues 70 and 91.
As the South Texas pressurizer POltVs and bh>ck valves can be relied upon during transient and accident recovery conditions, operator action will result in itCS pressure being maintained well below the POltV setpoint. The maximum S1.11 pressure differential for burst and leakage analyses is then 2107 psig based on the pressurizer POltV setpoint of 2335 peig plug 3%
measurement uncertainty allowance.
Voltage Dependent Probability of Prior Cycle Detection (POPCD)
Section 2.b.1 of GL 95 05 includes a bobbin coil probability of detection (POD) of 0.0. This POD value is considered exceptionally conservative, especially for larger voltage indications. G1,95-05 states that an alternative POD function can be used, if one becomes available, and is aubsequently approved by the NltC. NitC approvalis requested to apply the EPill voltage dependent POD described in Iteference G.
With a constant POD, as recommended by GL 95 05, an additional percer.tage of an indication is included in the itPC distribution for leal and burst analyses for each detected indication. Large voltage, POD driven indications are included in the 800 distributions even if repaired and these indications contribute significantly to the projected leak rates and tube burst probabilities.
Since the AltC experience data indicate that POD approaches unity above about 2.5 to 3,5 volts, the larger voltage POD driven indications are unsubstantiated in the analysis above a few volts, and represent a large portion of the projected SLilleak rate and conditional burst probability.
For AllC applications, the important indications are those that could significantly contribute to EOC leak or burst probability. These significant indications can be expected to be detected by bobbin and confirmed by ItPC. Thus, the population ofinterest for APC POD assessments is the EOCn itPC confirmed indications that were detected or not detected at the EOCna inspection.
EOCn is the end of the just completed operating cycle and EOCna is the end of the previous opgrating cycle. This POD definition accounts for undetected indications, indications below the detection threshold and new indications. Consequently, there is no need to modify the associated POD values or otherwise account for new indications. Using the information provided 10
SG-08-01-004 in Heference 0, it is concluded that a large (15 inspections of 8 plants) AltC field experience database is available and has been applied to develop a voltage dependent POD. The recommended POD, based on the lower 95% confidence limit of the data, is low er than the NitC recommended POD value of 0.0 below about 0.5 volts, increases to 0.9 at 1.2 volts, and approaches unity at 2.5 to 3.5 volts. Flaw population growth increases the need to apply a voltage dependent POD to reduce the number of high voltage " phantom" indications included in the leak and burst analysis as a result of applying a constant POD of 0.0.
Application of Unconfirmed Indications in HOC Distribution
- 01. 95 05, Section 2.b.1 provides an option for applying a fraction of unconfiimed (ItPC NDD) indientions in the 1100 voltage distribution. NitC approval for applying a fractional representation of the itPC NDDs in the S1.11 leak rate projection has been approved at Beaver Valley Unit 1. Currently, a sufficient database for itPC NDDs does not exist for South Texas 2.
A subsequent update submittal may be presented by STPNOC once sufficient data has been collected to include a fractional tepresentation of the ItPC NDDs into the SLB leak rate projection. This data will compare the ItPC NDDs left in service at EOCoa and EOCo.
Inspection data from other plants indicates that typically about 50% of the ItPC NDDs progress to detectable HPC indications from one cycle to the next, compared to the GL 95 05 guidance which includes all itPC NDDs in the S1.11 leak rate projection.
Voltage Growth Due to Defect Progression The more conservative growth rate of the previous two cycles shall be used for the projection of bobbin voltage distribution during the next operating cycle, consistent with Section 2.b.2(2) of Gl,95 05 and existing practice (Heference 2). Iloth 1100 and corresponding EOC bobbin indications at a tube TSP intersection are necessary to specify a growth data point. Growth data from both cycles may be combined if necessary to obtain at least 200 data points in the distribution, otherwise industry data will be used, if > 200 indications are available on a per SG hasis, the more limiting of SG specific or all SG combined growth will be used. Negative growth rGes shall not be used in growth rate distributions used to make voltage projections although they shall be used in establishing average growth for determining the upper voltage repair limit of 2.a.2 and 2.a.3.
Using the 1997 (EOC 5) inspection data and conservatively allotting G5% of the total growth to Cycle 5 for indications not inspected at EOC 4, the 95% cumulative probability growth rate at EOC 5 is 0.2 la volts. This adjustment is conservative compared to the ratio of the estimated Cycle 4 and Cycle 5 lengths used for this example,475 EFPD and 450 EFPD, respectively. The actual EFPDs for Cycle 4 and 5 may vney by a few days from these example values. The average absolute growth (for the entire cycle) for this distribution is 0,136 volts. A histogram plot of the 11
- __ _A
SG-98-01-004 EOC 5 bobbin voltage growth rates is provided in Figure 1. This 6gure is a representation of the growth trends at South Texas Unit 2. On an EPPY basis, the 95% and average growths are 0.107 and 0.110 volts, respectively, if the two cycle growths for indications not inspected at EOC 4 are adjusted baned on the ratio of Cycle 5 length divided by the combined Cycle 4 + Cycle 5 length, the 95% and average absolute growths are 0.222 volts, and 0.120 volts, respectively. On an EFpY basis, the 95% and average growths (adjusted by cycle length) are 0.190 volts and 0.10 volts, iespectively.
Comparison of Bohhin Voltages for 405 SS and Carbon Steel TSP Material-GL 05 05 defines applicability of the voltage based repair limits to drilled hole carbon steel TSPs. South Texas Unit 2 has drilled hole 405 SS TSPs, This section addresses the influence of the TSP on the voltage response of Daws to demonstrate applicability of the voltage based repair limits to 405 SS TSPe.
The EPill database approved by the NHC for application to the voltage based repair limits include data from Plant E 4 (Doel 4) which is a blodel E steam generator, nearly identical to STP Unit 2, with drilled hole 405 SS TSPs. There are 21 Plant E 4 data points fairly uniformly distributed from 0.2 to 15,7 volts in the burst correlation and 11 data points from 0,02 to 10.2 volts in the leak rate correlation. These data points are compared with data from other EPIll database domestic pulled tubes em model boiler specimens with carbon steel TSPs in Figures 3 and 4. The Plant E 4 data span the regression fit to the data and demonstrato consistency with the other data from SGs with carbon steel TSPs. Therefore, the Plant E 4 data support application of the voltage based repair criteria to STP Unit 2 with stainless steel TSPs.
An assessment of the influence of the TSP material on voltage measurements can also be obtained by comparing voltages for machined flaws such as the AShlE holes and axial EDhl slots. Bobbin voltages were normalized to 2.75 volts for the 550/130kHz mix on the 20% AShlE holes with no TSP, which is the GL 05 05 voltage normalization. Separate voltage normalizations were made after mixing on a carbon steel TSP and on a 405 stainless steel TSP. The carbon steel mix was then used to measure voltages for the AShlE holes and axial slots with a carbon steel TSP over the flaws. The same measurements were made using the stainless steel mix and n stainless steel TSP. A comparison of the voltage measurements for the machined flaws is given in Table 4. The agreement for the two TSP materials is good for the axial slots with the only significant difference in that the stainless steel TSP voltage for the 60% slot is about 10% lower 12
SG 98-01-004 than the carbon steel TSP while the 40%,80% and 100% slot voltages agree within about 1%. For the ASME holes, the stainless steel TSP voltages are about 510% higher for the 20% and G0% holes while agreement is within 1% for the 100% hole. The reasonable agreement for the ASME holes and axial slots between carbon steel and stainless steel TSPs supports the good agreement found for the EPill database shown in Figures 3 and
- 4. The data base used in Figures 3 and 4 includos pulled tubo data from 13yron 1 and Ilraidwood 1 which has not yet been officially recognized in the AllC data base by the NitC. Use of this data base results in a structurallimit voltage of 4.79 volts for a AP of 3G57 psi as opposed to a structurallimit voltage of 4.70 volts for a AP of 3057 psi using the currently approved data base. Overall, it is concluded that the voltage based repair limits can be applied to SGs with drilled hole stainless steel TSPs as well as the more common drilled hole carbon steel TSPs. The major contribution of the Plant E 4 data to the EPill database for burst and leakage support the application to both stainless and carbon steel TSPs.
Table 4. Comparison of Voltage Hesponses for Carbon and Stainless Steel TSPsm Carbon Steel TSP and Stainless Steel TSP and Carbon Steel Support Stainless Steel Support Mix Mix Flaw Volts Flaw Volts ASME Drilled llolo Flaws 20%
2.24 2.40 JO%
4.05 4.24 100%
5.03 5.01 Axial Slots 40%
0.45 0.45 60%
1.45 1.28 80%
3.38 3.40 100%
44.18 44.57 Notes:
- 1. Bobbin voltages normalirmi to 2.75 volts on the 20% ASME holes with no tsp for the 550/130 kilz mix wiOi separato normalizations for the carbon steel and stainless steel mixes.
(
13
SG-98 01-004 Figure 3: Burst Pressure vs Bobbin Amplitude 3/4" x 0.043" Alloy 600 MA SG Tubes (Nov.1997 Database )
12.0 e
o Domestic Pulled Tubes. CS TSPs 10.0 ;,N a
.______a
.Sm Data Regression (Mean) o
.o m
80
,X a
a
95% Prediction @ LTL
~s
.o
. ' N, _ P _ __L
_ o....
._._.._____a__.-._____
_. +. _. _...__ _ _-.__.
oo
~~
a a
.a E
60
'.'s, Ou yu
~~
e
__1-(
._6 d_
O.!
...__.._;_,.__...;._......___1.__..
1 o a y-3.657 ksi
-q j
j h,
. _ _ _ _ _ _ _. _ _ _ _ _ _ _ _ _ _ ~ _ ~ _
e a e
._ 2.560 ksi _ __2_._
s-
' ~ ~,
a _ y_._ _
._.._.._..u..____.._.._t._.._._.._ A, 2.0
[
t
'~~
- _ -. i.2 ~ ' _..- -.
s n
.- 4.79 V 12.3 V
~
i 0.0
~;
t 0.1 1.0 10.0 100.0 Bobbin Amplitude (Volts) 14
SG-98-01-004 Figure 4: SLB Leak Rate vs. Bobbin Amplitude 3/4" x 0.043" Alloy 600 SG Tubes @ G50 F, AP = 2560 psi (Nov.1997 Database)
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SG 98-01-004 Clarifications to GL 95-05 Section 2, Tube Integrity Evaluation Calculation of conditional burst probability and SLil leak rate will be performed using a voltage dependent probability of detection, referred to as probability of prior cycle detection, or POPCD, as opposed to a constant probability of detection of 0.0. The POPCD reference curve will be that defined in Addendum 1 to EPHI NP.7480 L, or later updates that reDect the latest combined industry response for both 7/8" OD and 3/4" OD SG tubing. The use of POPCD in SLIIleakrate and conditional burst probability assessments represents a reasonable and logical approach to realistic EOC population projections.
Establishment of Upper Veltage Hepair Limits (
) for TSP and FDH Intersections The voltage structural limit is the voltage from the burst pressure. bobbin voltage carrelation, at the 95% prediction interval curve reduced to account for lower tolerance limit material properties at 050 degrees F. The voltage structurallimit must be adjusted for Daw growth during an operating interval and to account for NDE uncertainty. The upper voltage repair 1
limit, b, is determined from the following equation:
= V.i. Ver. h where Ver represents the growth allowance and h represents the allowance for potential sources of error, including analyst variabihty. The structurallimit voltage is taken from the latest NHC approved database (currently contained in Iteference 6). For TSP intersections, the structural limit voltago is generally established based on a pressure loading of 1.43 times the bounding SLil pressure differential of 2500 pai, or 3001 psi, since the proximity of the TSP prevents burst during normal operating conditions. Specifically for STP Unit 2, pressurizer PORVs and block valves will be available and can be relied upon to operato during accident recovery conditions, and the applicable faulted condition AP becomes 1,43 times 2407 paid (where the value 2407 paid represents PORV actuation setpoint of 233', psig in the faulted loop plus 3% uncertainty due to accumulation), or 3442 paid, The term paid represents a differential pressure from atmo3pheric, and is therefore conaistent with the gauge pressure. Based on the operational characteristics of the STP Unit 2 PORVs, a 3% uncertainty allowance is considered conservative. The increased tube to FDB gap does not provide sufficient constraint such that burst will not occur within the FDB. Therefore, the FDB voltage structural limit is established using a pressure loading of 3 times the normal operating pressure differential across the SG tubes. The current maximum SG tube AP for STP Unit 2 is approximately 1210 psid, and the limiting 3AP value is therefore 3030 psi. For analysis purposes and to take into account future tube plugging effects upon steam pressure output, a 3AP value of 3076 pai will be used. For a limiting faulted conditions AP of value of 3442 psid the value of V.i for the TSP is defined to be 16 i
- m. m
--,-m,--
f SG-98-01-004 5.45 volts and for the limiting 3AP value of 3075 paid, W for the FD!)is defined to be 4.47 volts.
The calculation of the structurallimit voltages was performed using regression coef6cients corresponding to the latest NitC approved data base for %" tubing, which includes the original 01,95 05 data base updated using South Texas 1 pulled tube data points. Using the above equation, with values for h of 20% of u and W of 00% of
, b for the TSP and FDll are established to be 3.03 volts and 2.48 volts, respectively. As the criteria will be implemented at the beginning of Cycle 7, the growth allowance applied must be representative of the projected Cycle 7 operating length, or approximately 329 days. Therefore, the growth allowance applied for Cycle 7 to establish b is determined to be the limiting Cycle 5 growth of 60% times the ratio of Cycle 7 to Cycle 5 lengths (329 days /439 days), or 45% Using this growth allowance and %
allowance of 20%, b for the TSP and FDit are ultimately established to be 3.30 volts and 2.71 volts, respectively.
llobbin voltage growth analyses were performed for the EOC 5 indications which met the criteria for growth analysis. From Tables 5 and G it is seen that the 110C voltages are quite low, and therefore small growths represent large percentage voltage growths, and may be a cause of the apparent large percentage volta?e growth rates seen in Steam Generators A and C. Of the *otal 703 growth indications,694 had 1100 5 bobbin voltages less than 0.75 volts.1100 5 voltages for indications not inspected at EOC 4 were developed by adjusting the EOC 3 to EOC 5 growth based on the Cycle 4 and Cycle 5 EFPD values. The growth for Cycle 5 for these indications was adjusted by the ratio of the approximated Cycle 5 EFPD to the combined Cycle 4 plus Cycle 5 EPPD value, or 450 EPPD / 925 EFPD = 0.4865. The 1100 5 voltage was then determined by subtracting this adjusted growth value from the EOC 5 bobbin voltage. Of the 703 total growth indications,442 had to be adjusted by this methodology. If the growth indication population is segregated at 0.5 volts as opposed to 0.75 volts, it is seen in Table 6 that 024 of the 703 total growth indications had a 1100 5 bobbin voltage less than 0.5 volts.
17
SG-98-01-004 Table 5 South Texas Unit 2 Average Voltage Growth During Cycle St < 0.75, t 0.75 Volts HOC Voltage llange Number of Avg. Voltage Avg. Voltage Growth I'ercent Gr>wth Indications 1100 $
Cycle 5 EFI'Y Cycle 5 EFPY Composite of All Steam Generators Entire Voltage -
703 0.31 0.12 0.10-39%
32%-
Itange Vboc < 0.75 volts GD1 0.31 0.12 0.10 30%
32%
Yboc 2 0,75 volta 9
0.00 0.23 0.19 26 %
21%
Steam Generator A Entire Voltage 144 0.35 0.21 0.17 00%
49%
llange Vboc < 0.75 volts 141 0.34 0.20 0.10 59%
47%
Yboc 2 0.75 volta 3
0.80 0.41 0.33 51%
41%
Steam Generator 11 Entire Voltage 195 0.33 0.07 0.00 21%
18 %
llange Yboc < 0.75 volta 192 0.32 0.07 0.06 22 %
10%
Yboe 2 0.75 volta 3
0.96 0.34 0.28 35%
20%
Steam Oenerator C Entire Voltage 189 0.30 0.14 0.12 47%
40%
llange Vboc < 0.75 volta 187 0.29 0.14 0.12 48%
41%
Yboc 2 0.75 volts 2
0.82 0.05 0.04 6%
5%
Steam Oener stor D Entire Voltage 175 0.29 0.07 0,00 24% -
21%
llange -
Yboc < 0.75 volta 174 0.28 0.07 0.00 25%
21%
Yboc 2 0.75 volts 1
1.01 0.11 0.09 11%
9%
18 s
SG-98-01-004 Table 6 South Texas Unit 2 Average Valtage Growth During Cycle 5: < 0.5, > 0.5 Volts 1100 Voltage llange Number of Avg. Voltage Avg. Voltage Growth I'ercent Orowth Indications 11005 Cycle 6 EFPY Cycle 5 EFI'Y Composite of All Steam Generators Entire Voltage 703 0.31 0.12 0.10 39%
32 %
llange Vboc < 0.5 volts 624 0.28 0.11 0.09 39%
32%
Yboc 2 0.5 volts 79 0.00 0.18 0.14 30%
23%
Steam Generator A Entire Voltage 144 0.35 0.21 0.17 60%
49%
llange Vboc < 0.5 volts 120 0.30 0.18 0.15 60%
$0%
Yboe 2 0.5 volta 24 0.6I l
0.32 -
0.26 52%
43%
Steam Generator D Entire Voltare 195 0.33 0.07 0.00 21%
18%
llange Vboc < 0.5 volta 171 0.29 0.07 0.06 21%
21%
Yboc 2 0.5 volta 24 0.59 0.10 0.08 17 %
14 %
Steam Generator C Entire Voltage 189 0.30 0.14 0 12 47%
40%
llange Yboc c 0.5 volts 168 0.26 0.14 0.12 51%
46%
Yboe 2 0.5 volts 21 0.60 0.15 0.12 25%
20%
Steam Generator D Entire Voltage 175 0.29 0.07 0.06 24%
21%
l llange Vboc < 0.5 volts 165 0.27 0.07 0.06 26%
22%
Yboc 2 0.5 volts 10 0.00 0.09 0.07 15%
12%
19
SG 98 01-004 4.0 01,95 05 Section 3: INSPECTION CRITERIA -
All SG tubes will be inspected with the bobbin coil during each normally scheduled refueling outage at STP Unit 2. The inspection will include all hot leg tube to TSP intersections and all cold leg tube to TSP intersections down to the lowest cold leg TSP with identified ODSCC. Data acquisition and anal (sis will be performed to provide consistent methodology as that described G14 95 05, as updated by the clarifications listed below, which include use of the updated probe wear guidelines and new probe acceptability guidelines. The supplementary guidance of Section 3 of Gis 95 05 will be applied with the clarifications noted below. Any indication with bobbin.
voltage exceeding 1.0 volts shall be inspected with a rotating pancake coil (RPC) or equivalent, and shall be repaired if the bobbin indication is confirmed as a flaw by RPC. Any indication will be plugged or repaired regardless of any RPC inspection results, if the bobbin voltage exceeds the upper voltage repair limit as obtained per Section 2.a.2 of OL 95 05. For STP Unit 2, specific upper voltage repair limits are separately developed for both TSP and FDilintersections.
Clarifications to Section 3, inspection Criteria 1.
In a letter dated January 23,1990, the Nuclear Energy Instituto provided a methodology for meeting the new probe variability criteria in OL 95 05 Section 3.c.2. The NRC requested additional information in a letter dated February 9,1999 from Ilrain Sheron to Alex Marion of NEI, Initial NRC concurrence of this methodology was provided in a letter from Mr.
Ilrian Sheron to Alex Marion of NEl, dated March 18,1990. Additionalindustry information was provided in a NEl letter dated October 10,1990, which dealt with test data for probes manufactured by Westinghouse and Zetec. Ilriefly summarized, this methodology requires, in part, that the primary frequency and mix frequency voltage response of a new probe be compared to the nominal response determined by the vendor to ensure that the new probe is within i 10% of the nominal response for both the primary and mix channels.
In a letter from 11rian Sheron to Dave Modeen of NEl, the NRC determined that NEl has provided sufficient information in response to the NRC staff request in the February 9,1990 biter. STPNOC will follow the guidance provided in the NRC letter dated March 18,1990 as supplemented by the test data contained in the NEl letter dated October 10,1990.
2.
In a letter dated January 23,1990, the Nuclear Energy Institute provided an alternative to the probe wear criteria in GL 95 05. NRC concurrence of this methodology was provided in a letter from Mr. lirain Sheron to Mr. Alex Marion of NEl, dated February 9,1996. Briefly summarized, this alternative to the GL 95 05 probe wear criteria requires that when a probe does not pass the probe wear check (15%), all tube locations inspected with the worn probe having detected indications with amplitudes greater than or equal to 75% of the repair voltage liinit (i.e.,1.0 volt for 3/4" OD tubes) will be reinspected with a new 20
SG 98-01-004 l
neceptable probe. STPNOC will follow the guidance provided in the NHC letter dated February 9,1900.
3.
GL 05 05 (llackground, Page 3 of 7) permits use of alternates to the rotating pancake coil for H1'O inspections. Currently, the + Point probe is considered by the industry as an acceptable alternative to HPC. STPNOC will utilize the + Point probe for TSP indication confirmation at EOC 0 and + Point or equivalent probe at later inspections.
Section 4:
TUHE HEMOVAL AND EXAMINATIONffESTING The STP Unit 2 program for tube removal and examination will comply with the guidance of Section 4 of GL 05 05. Currently, no tubes have been removed from STP Unit 2. Consistent with the Section 4 recommendations of GL 05 05, upon the initialimplementation of voltage based repair criteria, a minimum of four hot leg TSP intersections will be removed from STP Unit 2.
Section 5:
LEAKAGE The Technical Specification operational leakage limit, LCO 3.4.0.2.c, addressing steam generator tube leakage, has been changed to 150 gpd in any SG. This Tech Spec change was initiated for Unit 2 when the laser welded sleeving process was licensed. SG tubes with known leaks will be repaired prior to returning the SGs to service, consistent with GL 05 05.
Section 6:
HEPORTING HEQUIREMENTS STPN00 will comply with the reporting requirements of Section G of GL 05 05.
21
SG-98-01-004 ItEFEltENCES 1.
NitC Generic letter 95 05:" Voltage Innsed Criteria for Westinghouse Steam Generator Tubes Affected by Outside Diameter Stress Corrosion Cracking," August 3,1995 2.
Westinghouse WCAP 11277, Itevision 1, "S1.11 Iscak Itate and Tube llurst Probability Analysis hiethods for ODSCC at TSP Intersections " December 1990 3.
NitC letter from lirian Sheron (Nitit) to Alex Marion of NEl dated February 9,1990 1.
NEl letter from Alex Marion to lirian Sheron of NIta (Nitit) dated January 23,1990 5.
NEl letter from Alex Marion to lirian Sheron of NitC (Nitit) dated October 10,1990 6.
EPlti iteport NP.7180 L Addendum 1," Steam Generator Tubing Outside Diameter Stress Corrosion Cracking at Tube Support Plates Database for Alternate llepair 1.imits,1990 D::tabase Update", November 1990 7.
EPill Tit 101788 It, "PWit Primary to Secondary Irak Guidelines," November 1997 8.
NltC letter from llamin 11. Assa, Project Manager, Nltit, to Commonwealth Edison Co.,
" Safety Evaluation llegarding lenk llefore llreak Analysis Ilyron Station, Units 1 and 2, and liraidwood Station Units 1 and 2", dated October 25,1990 9.
NitC letter from lirain Sheron to David Modeen of NEl, dated July 29,1997
- 10. NSD E SGDA 98 0011," Identification ofinput Information Used for Development of S0 98 Ol 001",1/20/08 *
- 11. IIL&P letter ST ilL-AE 3059, *ltesponse to Generic 1,etter 90 00," 12/21/90
- 12. lit,&P letter St llL-AE 3042," Prop'osed Amendment to the Unit I and Unit 2 Technical Specifications Lt.1 and 01.9.3,12/21/90
- 13. South Texas Project Updated Final Safety Analysis Iteport Internal Westinghouse lleference used for preparation of this evaluation, not to be submitted to NllC.
22 l
i
SG-98-01-004 Figure 1 Bobbin Voltsy Grmvth History-South Texas 1 All SGs Combined South Texas 2 EOC 5 Growth History: All SGs 390 1
09 300 08 IN 07 >
e
. 8 5
j 06 N
.g 2m g ___.._
]
'g EEMNoini 5
- mw
$ 150
.o 04 3 E
E 3
m 03 1
02 50 0.1 0
O
-0 2
-0.1 0
01 0.2 03 04 05 06 07 08 09 Bobbin Voltage Growth (volts bins) 23
SG-98-01-004 Assuming the Voltage Based Plugging n we i
d t E C 5 and ing a POD of 0.G. No Tubes Plugged South Texas 2 SG A Voltage Distribution 45 40 35 30
, _ 2s 20 iS 10 5
E a m.
0 A
E E
E E
E E
E E
Bosbin v$ltagekbin)
A
~
~
24
~.
I SG-9S-01-004 Figue 2b 4
Projected EOC G Bobbin Voltage Distribution i
Assuming the Voltage Bewd Plugging Criteria were Applied at EOC 5, and Using a POD of 0.6. No Tubes Plugged l
1 5 outh Texas 2 SG B Voltage Distribution 120 j
i 100 j MEOC5
)
MEOC 6 l i
E 80
[
E h
I 5
60
.i 40 L----_
L.E 20 t
0 f
b
.2 E 2 $ $ $ ) S $
h 5 E N
o o o o o
o
.l Bobbin Voltage (bins)
-_..,.,__.-.____..._._,....__.,.._.._m.
1 i
25
- -.~.._....
l t
j SG-98-01-004 l
Mpmh Projected EOC 6 Bobbin Voltage Distribution Assuming the Voltage Based Plugging Criteria were Applied at EOC 5, and Using a POD of 0.G. No Tubes Plugged South Texas 2 SG C Voltage Distribution l
90 I
l 80 l
70
'E l
NEOC5 60
=
50 I
E 40 tg 30 20 E
to 1
0 i
5 5
2 5
2 0
3 E
3 U
)
~
]
Bobbin Voltago (bins) 4 i
l i
26 i
V W km 1
SG-98-01-004 Figure 2d
, Projected EOC G Bobbin Voltage Distribution Assuming the Voltage Based Plugging Criteria were Applied at EOC 5, and Using a POD of 0.6, No Tubes Plugged I
S o u th T exa s 2 S G D Vs.ita g e Distribu tio n 120 1
a, 100
-u--
- ~
MEOC5 j
EEOC 6 p.
e 0
l 5
f 60 o
40 20 E
a '-
0 2
2 S
5 5
E S
5 U
U S
3 I
E E
I
~
Bobbin Voltage (bins)
~. - -
27
l SG-98-01-004 Appendix A Analysis Methodology Used for Performance of Tube Exclusion Analysis for Application of Voltage Based Repair Criteria:
South Texas Unit 2 i
28
SG-98-01-004 Appendix A Analysis Methodology Used for Performance of Tube Exclusion Analysis for Application of Voltage Based Repair Criteria:
Discussion of Analysis Relative to application of the voltage based plugging criteria and integration with other plant conditions, the most limiting accident condition is a combined seismic safo shutdown earthquake (SSE) plus loss of coolant accident (LOCA). For the combined I.OCA + SSE event, the potential exists for yielding of the tube support plate in the vicinity of the wedge groups, accompanied by deformation of the tubes and subsequent loss of ficw area and possible in leakage due to opening of axial cracks. The wedges are as their name implies, wedge shaped steel components which are used to provide radial contact between the TSP and wrapper at multiple locations around the periphery of the TSP.
Combined Plate Loads Seismic loads result from motion of the ground during an earthquake. The SSE excitation of the steam generator is defined in the form of acceleration response spectra at the steam generator supports. To perform the analysis, the response spectra are converted into acceleration time history input. Acceleration time histories for the nonlinear analysis are synthesized from El Centro Earthquake motions, using a frequency suppression / raising technique, such that the resulting spectrum in each of the axes closely envelopes the original specified spectrum. The resulting time histories are then simultaneously applied at each steam generator support. For the South Texas 2 tube exclusion analysis, results of a response spectra seismic analysis for South Texas taken from Westinghouse Report WNET-150, "Model E2 Stress Report Plant Specific Seismic Analysis South Texas Nuclear Power Plant Units 1 and 2" were used to develop non-linear plate loads. A factor of 3 was applied to the response spectra values to establish the non-linear plate loads. The bounding plate load was applied to all plates.
Leak before break of the primary loop piping has been approved by the NRC for South Texas 2. In Reference 8, the NRC indicates the acceptability of the use of small break loadings for such analyses when LBB has been approved. The LOCA hydraulic forcing functions used for the South Texas 2 analysis are taken from a thermal / hydraulic j
29
SG-98-01-004 analysis of a Model D5 steam generator, and are considered conservative for the South Texas 2 SGs. To validate the use of the D5 LOCA rarefaction loads for South Texas 2, the hot to cold leg pressure drops across the U bends were compared for the D5 and E steam generators for a large break, surge line break, and accumulator line break. This comparison indicates that the large break AP for the Model E SG was approximately 1%
greater than the D5 AP, while the D5 APs for the surge line and accumulator line breaks were greater than the Model E APs. Although larger in shell diameter than a D5 So, the tube bundle geometries between the D5 and E SGs are considered very similar and the D5 results can therefore be applied to the South Texas 2 Model E SGs. A comparison of the time history characteristics for the surge line ard accumulator ?ine breaks was performed for the D5 and E SGs, indicating good agreement between the two, further substantiating the use of the D5 results. For South Texas 2, the surge line and accumulator line break inputs for the D5 SG were used and are considered bounding f
since the surge and accumulator line breaks represent a limiting transient for the RHR line bre;. Therefore, the LOCA input forcing functions used for South Texas 2 are conservative based on the acceptance of the LBB methodology at South Texas and use of the larger surge and accumulator line break inputs. LOCA loads are developed as a result of transient flow, and temperature and pressure fluctuations following a postulated pipe break. As a result of a LOCA event, the steam generator tubing is subjected to primary fluid rarefaction wave loadings and steam generator shaking loads due to the coolant loop motion. LOCA shaking loads are considered insignificant for the bounding LOC / Sads used, therefore, the rarefaction wave loading provides the only significant contributing loadings with respect to tube deformation.
The LOCA and SSE load are combined using a square root of the sum of the squares technique. In reacting the load among the various wedge groups, a cosine distribution is assumed among the wedges that are loaded. Typically, only half of the wedge groups are loaded at any given time. In determining the 1%4 distribution for seismic and LOCA loads, the directionality of the load is considered. LOCA loads are uni directional, in that they only act in the plane of the U bend. Seismic loads on the other hand are random, and can act in any direction. Calculations are performed to determine load factc a for the various plates, grouping the TSP by commonality of their wedge group locations. The load factors are not a function of the wedge group size, only oflocation. Applying these load factors, overall TSP load for each of the wedge groups are determined.
30
SG-98-01-004 Tube Defumation in estimating the number of deformed tubes, the results of TSP crush tests for Model D steam generators are used. The applicability of using the hiodel D tests is based on a comparison of Model D and Model E plate geometries, summarized in Table A 1 Based on the comparison of these geometric parameters, the Model D test piece is judged applicable to the Model E plate. The deformation criteria for establishing a tube as being susceptible to in leakage has been previously established for similar analyses to be 0.030" diametrical. It has been previously judged that deformation of this level will not result in significant in leakage. Using the crush test data, a correlation is developed between clastic plate load and the number of tubes that would have a deformation of 0.030" or greater. This correlation is used to approximate the number of affected tubes. For the South Texas 2 analysis, TSP material certifications were available which showed the actual TSP material property values were greater than the ASME Code minimum values.
These actual material property values were used in the analysis. In order to account for the thicker Model E top plate, top plate loads were scaled downward by the ratio of the top plate thickness to the actual test plate thickness. To account for the higher yield strength of the South Texas 2 plates, the yield point of the plates is scaled upwards. Once yielding begins, the plates were assumed to follow the same inelastic slope as the test plates.
The applied combined loadings were then compared to the expected load to cause permanent deformation of the South Texas 2 TSPs and fmm this comparison, it was determined that the South Texas 2 TSPs will not experience deformation such that the tubes in the wedge regions will experience a diameter deformation of greater than 0.030".
Therefore, no tubes are to be excluded from application of the criteria due to a collapse potential.
Compariscn of Tube Support Plate Hole Patterns Model D vs. Model E Parameter Test Plate (Model D)
Model E Tube Hole Diameter 0.7735" 0.776" Flow Hole Diameter 0.5075" 0.5075" Tube Pitch 1.0625" 1.08" Plate Rim Thickness 0.432" 1.26" Plate Yield Strength 35.7 Ksi 54.9 Ksi 31
- _ _ _ _ _