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| number = ML20059G090 | | number = ML20059G090 | ||
| issue date = 10/27/1993 | | issue date = 10/27/1993 | ||
| title = Evaluation & Screening Criteria for Peach Bottom Unit-3 Shroud Indications | | title = Evaluation & Screening Criteria for Peach Bottom Unit-3 Shroud Indications | ||
| author name = Herrera M, Mehta H, Ranganath S | | author name = Herrera M, Mehta H, Ranganath S | ||
| author affiliation = PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC | | author affiliation = PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC | ||
| Line 140: | Line 140: | ||
P.2 CCT IS '93 tE:ZFi1 GE EtR TEOfiOLCGY , | P.2 CCT IS '93 tE:ZFi1 GE EtR TEOfiOLCGY , | ||
GENuckap Ewy GENE-333-141.]093 1.1 Background Indications have been observed in the shrouds of three plants to date (including Peach Bottom Unit-3). Cracking was observed in a BWR/4 located outside the United States in 1990. The cracking was confined to the heat affected zone (HAZ) of a circumferential-weld. | GENuckap Ewy GENE-333-141.]093 | ||
===1.1 Background=== | |||
Indications have been observed in the shrouds of three plants to date (including Peach Bottom Unit-3). Cracking was observed in a BWR/4 located outside the United States in 1990. The cracking was confined to the heat affected zone (HAZ) of a circumferential-weld. | |||
In 1993, the second occurrence of cracking in a shroud was reported. Cracking was observed on the inside surface (ID) of the top guide support ring near the H3 weld. The cracking was approximately 360* around the circumference, in the weld heat affected zone (HA2), in a material with carbon content of 0.06%. The fluence was estimated as 1.8x1020 nyt (E>1Mev). | In 1993, the second occurrence of cracking in a shroud was reported. Cracking was observed on the inside surface (ID) of the top guide support ring near the H3 weld. The cracking was approximately 360* around the circumference, in the weld heat affected zone (HA2), in a material with carbon content of 0.06%. The fluence was estimated as 1.8x1020 nyt (E>1Mev). | ||
t In addition to the H3 weld HAZ cracking, indications were visually observed at the H1, H2, H4, H5 (shroud cylinder) and, H6a weld HAZ (at core plate support ring). l i | t In addition to the H3 weld HAZ cracking, indications were visually observed at the H1, H2, H4, H5 (shroud cylinder) and, H6a weld HAZ (at core plate support ring). l i | ||
Latest revision as of 08:49, 2 June 2023
| ML20059G090 | |
| Person / Time | |
|---|---|
| Site: | Peach Bottom  |
| Issue date: | 10/27/1993 |
| From: | Marisa Herrera, Mehta H, Ranganath S PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC |
| To: | |
| Shared Package | |
| ML20059G078 | List: |
| References | |
| GENE-523-141-10, GENE-523-141-1093, NUDOCS 9311050283 | |
| Download: ML20059G090 (70) | |
Text
{{#Wiki_filter:.; i GENE-523-141-1093 DRF 137-0010-6 i { i Evaluation and Screening Criteria for the , Peach Bottom Unit-3 Shroud Indications t j.
}
l October 27,1993 l Prepared by. / f I i Marcos L. Herrera, Principal Engineer Structural Mechanics Project. ; i U ! Dr. Hardayal Mehta, Principal Engineer :
> Structural Mechanics Projects [
Approved By: b i Dr. Sampath Ranganath, Manager Structural Mechanics Projects GE Nuclear Energy San Jose, CA l0A' 2889 ubyg, ? !' PDR , ku
IMPORTANTNOTICE REGARDING CONTENTS OF THIS REPORT i f Please Read Carefully The only undertakings of the General Electric Company (GE) respecting information in this document are contained in the contract between Philadelphia Electric Co. and GE, and nothing containedin this document shall be construed as changing the contract. The use of this information by anyone other than PECo, orfor any pur;>ose other than thatfor which it is intended under such contract is not authori:ed; and with respect to any unauthori:ed use, GE makes no representation or warranty, and assumes no liability as to the completeness, accuracy, or usefulness of the information contained in this document, or that its use may not infringe privately ownedrights. L k l i i
W l r l Table of Contents : i l i i EXECUTIVE
SUMMARY
iv -;
1.0 INTRODUCTION
.. .. . . . . . .. . .. .1 i i 1.1 Background . . .. . . . .. . .. . . . . . .3 j 1.2 Screening Criteria.. . .. . . . .. . .. .. . .3 j 1.3 References . . . . . . . . . . . . . . . . .. . . . .. . .. . 6 ! i 2.0 FABRICATION HISTORY . . . . . .. . .. .. . 11 ! 3.0 CHEMISTRY AND FLUENCE CONSIDERATIONS... . .. ... .. . . . . .. . 23 3.1 Water Chemistry History.. . . . . . . . . . . . . ... . .23 . 3.2 Fluence Considerations.. . . . . . . . . . . . .25 ! 3.3 References . .. . .. .. .. . . . . . . .. .. . 26 'l' t 4.0 IN-VESSEL VISUAL INSPECTION... . .. . . . . . . . . .36 l 5.0 FLAW EVALUATION . .. .. . . . .. . . . . . . . . . .39 -j 5.1 Structural Analysis.. . . .. . . . .. . . . . . . . . 39 l 5.2 Allowable Through-Wall Flaws. .... .. . . . . . . . 43 - ,- l 5.3 Screening Criteria.. . . . . . . . . . . . .. . 46 5.4 Summary of Screening Criteria.. . . . . . . . . . . .. .48 q 5.5 Application of Screening Criteria.. .. . . .. . . 49 : 5.6 References .. . . . .. . . . . . . . . . . . . .50 l i 6.0
SUMMARY
AND CONCLUSIONS. .. . . .. . .57 . i k APPENDIX A DETERMINATION OF THE EFFECTIVE FLAW LENGTH .! i i
'l i
-i
i GENaclear FrerKY GLVE-583-141-1093 r EXECUTIVE
SUMMARY
Indications have been observed in the Peach Bottom Unit 3 core shroud. Indications were seen during in-vessel visual inspection (IVVI) of the various shroud welds as recommended by GE SIL 572, Rev.1. Results showed that both circumferential and axial i indications were present at the H3 and H4 welds. H3 corresponds to the weld between the top guide support ring and core shroud cylinder, and the H4 weld is located at approximately the mid-height of the fuel. In addition, circumferential indications were i observed in the shroud plate associated with a vertical weld. The lengths of the indications associated with the vertical welds were short (E2.5" max.) compared to those associated with the horizontal welds. This evaluation was performed to disposition the indications by demonstrating that the , structural integrity of the shroud is maintained for the next fuel cycle (two year cycle with , power rerate conditions). In addition, the report documents material, water chemistry and fluence information which are additional variables which may have contributed to the shroud condition. f The primary focus of this report is to demonstrate that even with several conservatisms in the evaluation, the structural integrity of the shroud is mainteined during a limiting event. This was performed by developing conservative screening criteria, assuming throughwall indications, which can determine the acceptability of the flaws based solely on the IVVI results. The assumption of through-wallindications removes any uncertainty regarding sizing and the need to further characterize the indications. By meeting the screening criteria, the ASME Code Section XI safety margins are satisfied. , The screening criteria use both linear clastic fracture mechanics (LEni) and limit load concepts to determine acceptable through-wall indication lengths. The limiting flaw length ; based on either LEni or limit load was used for the screening criteria. l The screening criteria also use the ASME Code Section XI criteria for combining flaws { based on the proximity ofindications. In addition, a second method for including the l interaction between neighboring indication tips was considered for the LEB1 allowable flaw size calculation. The resulting effective flaw lengths were compared against the screening criteria to determine if the structural integrity of the shroud was maintained. ! 1 iv I
}
GENuclear Energ GESTS $33-1411093 Based on the results of the application of the screening criteria to the observed indications, , it is concluded that the structural integrity of the shroud is maintained for the next fuel cycle. All effective indication lengths were shown to be less than the allowable flaw size. t t I i' 4 i t i V
l ctsauarura - ccvt.m. man ;
!r
1.0 INTRODUCTION
The objective of this repon is to document the conditions found on the Peach Bottom Unit-3 shroud, and evaluate these conditions based on GE SIL 572, Rev.1 (Reference l-
- 1) recommendations, in order to validate the structural margins of the shroud.
Recently, in-vessel visual inspection (IVVI) of the Peach Bottom Unit-3 shroud revealed l indications in the inside surface heat affected zones (HAZ) at weld locations H3 and H4. l Figure 1-1 is a schematic illustrating the general locations of the shroud welds in Unit-3. Ficures 1-2 and 1-3 are the shroud maps which show the locations where indications were found. Figure 1-4 is a plan view which indicates the locations referred to in Figures 1-2 , and 1-3. Figure 1-2 shows the inside surface shroud map and Figure 1-3 shows the , i outside surface shroud map. Horizontal and vertical indications were seen associated with , the H3 and H4 welds. Circumferential indications were also observed associated with one of the vertical welds (V3). However, these indications were relatively short compared to those associated with the horizontal welds. 3 In addition to the H3 and H4 welds, IVVI of the HI, H2, H5, H6. H7 and H8 welds was , performed on the outside surface. Only a few shon indications.were c5 served on the , outside surface ofH1 and H4. It should also be noted that the area adjacent to the H9 weld was visually inspected as part of the access hole cover inspection (AHC) at this f i outage. The inspection did not reveal any indications. Additional detail of the IVVI j results is presented in Section 4.0. i I GE SIL 572, Rev.1, provides the following recommendations based on the observed indications and evaluations performed to date: l I Plant Fabrication and Operational History I w Review plants fabrication and operational histories for the core shroud, including the
- meterials of construction.
Non-Destructive Examination Actions t Visual examinations of accessible areas should be performed on the shroud ID and OD surface at the next scheduled refueling outage for all plants with Type 304 stainless steel l l shrouds with six or more years of power operation, and for all plants with L-grade 2 1 l
GENuclear Energy GENE-H3-1411093 i eight or more years of power operation. These examinations should be performed with an enhanced VT-1 system or a qualified UT examination from the outer surface. , 1 Ifindications are not observed, examination should be performed at every second refueling i outage. Ifindications are observed, the shroud should be examined and lengths measured t during each refueling outage. The SIL also provides a recommended examination j process. i Destructive Testing : A boat or core sample may be necessary depending on the results of the examination. l 1 i Structural Marcin Analysis , Perform a structural margin analysis using the results from the NDE, and, if performed, the destmetive analysis. If numerous indications are observed, the need for corrective I action can be assessed using cumulative flaw length structural margin criteria. f J T Corrective Action ! ^ Based on the results of the structural margin evaluation, determine if continued operation j isjustified for another cycle without repair. If cracking is found and sufficient structural ! margin remains, examine the shroud during each subsequent refueling outage. l This report provides the pertinent information required to demonstrate that continued i operation of Peach Bottom Unit-3 isjustified based on the SIL recommendations noted ; above. Specifically, the report presents the following information: l t
. Fabrication history of the shroud. !
. Water Chemistry and Fluence Considerations t
' . In-Vessel VisualInspection
. StructuralMargin Analysis ;
. Screening Criteria for Application to IVVI results.
1 it is noted that the loads used in this evaluation correspond to those for power rerate. A
> two-year operating cycle was used in the determination of crack growth.
l 2 I l
P.2 CCT IS '93 tE:ZFi1 GE EtR TEOfiOLCGY , GENuckap Ewy GENE-333-141.]093
1.1 Background
Indications have been observed in the shrouds of three plants to date (including Peach Bottom Unit-3). Cracking was observed in a BWR/4 located outside the United States in 1990. The cracking was confined to the heat affected zone (HAZ) of a circumferential-weld. In 1993, the second occurrence of cracking in a shroud was reported. Cracking was observed on the inside surface (ID) of the top guide support ring near the H3 weld. The cracking was approximately 360* around the circumference, in the weld heat affected zone (HA2), in a material with carbon content of 0.06%. The fluence was estimated as 1.8x1020 nyt (E>1Mev). t In addition to the H3 weld HAZ cracking, indications were visually observed at the H1, H2, H4, H5 (shroud cylinder) and, H6a weld HAZ (at core plate support ring). l i Indications were seen mostly on the inner surface at H3, H4 and H5. Indications were seen on the outer surface at the HI, H2 and H6 welds. 1.2 Scrooning Criteria ; IVVI provides the length characterization of any present indications. Given that non-destructive examination (NDE) of every visually detected indication could be difficult and l time consuming, a method of screening indications for subsequent evaluation is required. : This report presents such a screening critenon. l; The guiding parameter used for the selection of the indications for further evaluation is the allowable through-wall flaw size, which already includes the safety factors. If all of the ; visually detected indications are assumed to be through-wall, then the longest flaws, or combination of flaws, would have the limiting margin against the allowable through-wall flaw size. In reality, the indications are likely not through-wall, and therefore, the criteria l and methods presented in this report are conservative. The result of this procedure will be the determination of the effective flaw lengths wluch will be used to compare against the allowable flaw size and sdection ofindications for more detailed evaluation. The determination of effective flawlength is based on ASNE Code, Section XI, Subarticle IWA-3300 (1986 Edition) proximity criteria. These criteria 3
i GENcelear Energy GENE-523.H11993 , 1 I 1 provide the basis for the combination of neighboring indications depending on vadous i geometric dimensions. Crack growth over a subsequent two year operating and power ! rerate cycle is factored into the cdteria. This is conservative since power rerate will not be in effect dudng the next fuel cycle. The proximity mies described here also conservatively assume that there is interaction between two perpendicular flaws. It is assumed that circumferential and axial indications could increase the effective flaw length depending on the unflawed distance between them. ; - This effective circumferential flaw length must be compared against the allowable , circumferential flaw length. The axial flaw would be compared against the cllowable axial flaw length. Flaws are considered in the same plane if the perpendicular distance between the planes is 4" or less. Any flaws which lie at an angle to the horizontal plane should be separated into a circumferential and axial component. These components can then be used separately in l the determination of effective flew lengths. The selection ofindications for further investigation can be performed by evaluating the resulting effective flaw lengths. Indications with effective flaw lengths greater than the allowable flaw sizes would require further characterization by NDE or more detailed analysis. The procedure described here is conservative since all of the indications are assumed through-wall and are being compared against the allowable through-wall flaw size. t The report covers the limiting stresses for all the shroud welds (H1 through H8 welds). Therefore, the screening criteria developed here cover all shroud weld indications. .A list ! of conservatisms used in this evaluation is summadzed in Table 1-1. i i-t i i l I 4
JA e " f n P.3 , C$'T 15' 'E 12:EF 1 GE BG TECHTOL%Y GENaclear Eurg GENE-Jal 1411093 Table 1-1 Conservatisms Included In Screening Evaluation i
- 1. All surface indications were assumed to be through-wall for analysis.
- 2. The highest stress computed for any single location was used for alllocations.
- 3. The highest seismic moment computed for any single location, as applicable, was used for corresponding locations. ,
4 The bounding crack growth estimated for the next fuel cycle was included in flaw lengths used for evaluation.
- 5. ASSE Code primary pressure boundary safety margins were applied even though the shroud is not a primary pressure boundary.
- 6. AShE Code, Section XI proximity rules were applied.
- 7. A proximity rule to account for perpendicular flaws was applied, although not '
required by Section XI.
- 8. An additional proximity rule which accounts for fracture mechanics interaction between adjacent flaws was used.
- 9. Fracture toughness measured for similar materials having a higher fluence was used.
- 10. Both LEFM and limit load analysis were applied, even though LEFM underestimates allowable flaw size for austenitic materials and is not required per AShE Code Section XI procedures.
t
- 11. The screening criteria limit one fourth of a!!owable circumferential flaws to any arbitrary 90 sector. ,
- 12. Allindications are assumed to be grouped together for the limit load calculation and no credit is taken for the spacing between indications. {
- 13. Power rerate conditions were used although it will not be in effect during the next ;
fuel cycle. l 5 i
GE%T,323141.jops , GENr. clear Energy-1.3 References ! l
- 1. GE Services Information Letter (SIL) 572, Rev.1, October,1993 ,
[ t h e t i P P 8 t I E
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GEVFs523141-o993 , GENuclear En"l7 , Shroud Head Flange H1 , f fl/ Top Guide Suppen Ring k///) H3 4 H4
/ H5 Core Plate Suppon Ring [/((g H6 ,
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/ RPV Shroud Suppen Cylinder d
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II:57FM GE EJ TECM ELO_Y P.4 MT EB 'E.: GENuc! ct Enery GENE 523 RI-1093 2.0 FABRICATION HISTORY I This section describes the fabrication history of the Peach Bottom Unit-3 shroud. Of key interest is the material composition and any activities which could have possibly , contributed to the increase ofintergranular stress corrosion cracking (IGSCC) susceptibility. Quality assurance records received from the vessel vendor (Rotterdam) were examined in detaif to determine the appropriate information. Table 21 shows the material data for the Unit-3 shroud. The part numbers are identified in the schematic shown as part of Table 2-1. Also shown in the table is the number of , pieces for each part, material designation, heat numbers, and carbon content. Figure 2-1 shows the assembly of the shroud. All welds are identified including venical and horizontal welds. Figure 2-2 through 2-9 show the details of the shroud welds as l
!abeled in Figure 2-1.
l The upper, central and lower rings (part numbers 1,3 and 6) are austenitic stainless steel ' seamless rolled forging. The materialis ASTM A182 - F304. The heat treatment of these rings consisted of heating to 1100"C, holding for 6 hours, followed by water quenching to , below 100 C. The carbon content of the rings ranges from 0.03% to 0.035% max. . Hardness measurements upon completion of solution heat treatment and rough machining of the rings ranged from Brinell Hardness of 137 to 153. Each cylinder is made of 2 plate segments formed and welded to drawing requirements. ' Plate materialis austenitic stainless steel made to ASTM A240, Type 304 specifications. The carbon content of the plate material ranges from 0.057% to 0.062% max. The hardness of the plate materir.1 ranges from Brinell Hardness of 137 to 155 f All welding was performed by submerged arc-welding except H7. The procedure and welder qualification was performed to ASME Section IX requirements. The filler metal met ASTM A-371 Type ER-30S requirements with required carbon content of 0.08% max. The weldedjoints did not use backing strips but utilized 3 to 4 hand weld passes. Weld prep surfaces of the base metal were prepared by machining. The backside of the groove welding was prepared by grinding or gouging followed by liquid penetrant R inspection. Final surfaces of the welds were inspected by liquid penetrant examination. 11 l l J
P,5 CCT ES '93 12 57Ft1 C-E DE TECHF'LCC" GENuc!rar Eneety GEN &5231411093 i The H7 weld was performed using metalinert gas with Alloy 82 wire. In addition,100% ultrasonic examination of weld H7 was performed. Based on GE Quality Assurance records received from Rotterdam, no abnormal fabrication history was found. General practice during assembly and shipment of the of , the shroud, bracing, temporary welds, and supports are used to help in meeting thejoining l of the various components and to meet geometric tolerances. Although there is no record documentation of these practices, it is likely that they were present during fabrication. These actions resuh in a local effect on materia! behavior and stress. For example, the welding of temporary pads would result in a local area of weld residual stress and perhaps some grinding (cold work). If these local cFects contribute to SCC, it is likely that the cracking would be oflesser concern than cracks near the horizontal welds. 1 k i i 1 [ 12 l
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i I gggy yyy. GENE-523-Hi-1093 l i 3.0 CHEMISTRY AND FLUENCE CONSIDERATIONS I 3.1 Water Chemistry History j i For the first decade of hot operation, Peach Bottom Unit-3 operated with relatively high primary water conductivity. As can be seen in Figure 3-1, Unit-3's arithmetic mean conductivity actually exceeded 1.0 pS/cm in 1976 and 1977. The arithmetic mean conductivity was very high and exceeded 0.4 pS/cm through 1986. Subsequently, conductivity values steadily decreased, and was <0.1 pS/cm (0.089 pS/cm) during 1992 f i and 1993. These last two year's conductivity values are considered world class performance. i The high conductivity during the first half oflife was partly due to leaking condensers and resin change out problems. However, besides the high early life steady state conductivity, ! there was also one relatively severe transient experienced at Unit-3 as presented in Table r 3-1, a summary of BWR fleet severe transients through about 1983. As can be seen in Table 3-1, Unit-3 suffered at least one power resin intrusion (Incident Rank 13) during j which the conductivity reached 23.6 pS/cm due to possible condensate demineralizer resin intrusion. This intrusion type ofincident results in the injection of sulfate into the RPV. : Since IGSCC initiation and propagation in sensitized austenitic stainless steel and nickel l base alloys are controlled by the rate of cathodic reduction of species such as dissolved oxygen, hydrogen peroxide and/or various oxyanions, then the additional presence of a detrimental oxyanion, such as sulfate, would increase the cathodic current and thus accelerate anodic dissolution at the crack tip, i.e., IGSCC (Reference 3-1). l l 3.1.1 Effects ofImpurities on IGSCC An example of the effects of sulfate / conductivity on crack initiation in uncreviced material l is presented in Figure 3-2. It is clear that an increase in sulfate / conductivity results m an j acceleration in crack initiation as measured by the constant extension rate test (CERT) l (References 3-1 through 3-4). A specific Peach Bottom example of acceleration in crack l propagation rate (creviced) with sulfate is shown in Figure 3-3. Figure 3-3 displays June 1986 (not included in Table 3-1) Unit-3 on-line crack monitoring data for sensitized Type 304 stainless steel. The results clearly illustrate the change in crack growth observed after two closely linked water chemistry transients of 4-5 pS/cm, i.e., increases in water 23 i l
.---_ . . _ - _ _ _ _A
GENaclear Enerv GENE-523.H11993 ' conductivity due to intrusions of demineralizer resin material (Reference 3-5). This figure demonstrates the dramatic increase in crack growth rate (2X) with conductivity. Similar ; on-line crack monitoring results with sulfate have also been documented in the laboratory, Figure 3-4 (Reference 3-6). Other anions such as chloride, carbonate, etc. have similar e kinetic effects on IGSCC initiation and propagation (References 3-7 and 3-8). This high conductivity crack initiation and propagation acceleration factor is consistent j with the relatively high incidence ofIGSCC observed at Unit-3 in creviced Alloy 600 shroud head bolts (15 of 25 bolts examined cracked) and access hole covers. No cracking of these two components has been identined in Unit-2. Both units have suffered IGSCC of creviced safe ends. Additional documentation on the strong correlation ofIGSCC i susceptibility with actual BWR plant water chemistry history for creviced B%11 I components has been published (Reference 3-9). 3.1.2 IGSCC Modeling ; Finally, the effect of conductivity on crack propagation has also been quantified at the GE Research and Development Center based on a "first principles" model of crack advance ; known as the film rupture / slip dissolution model(Reference 3-10). Predictions from the film mpture/ slip dissolution model, PLEDGE (Plant Life Extension Diagnosis by GE), l have been extensively compared with laboratory and field data and has provided validation l of the technique. For example, PLEDGE predicts the crack growth rate in stainless steel i and low alloy steel within a factor of approximately two for a 70% statistical confidence ; I
- over a range in observed crack growth rate of more than six orders of magnitude.
! Likewise, it provides a very reasonable mean value and can accurately bound the observed l > crack growth rate in stainless steel piping and other components. Aside from piping i predictions, PLEDGE has been successfully used for on-line crack growth monitoring data, safe ends (avoiding mid-cycle plant shutdowns), non-sensitized (stabilized) stainless a
steels and reactor internals such as the core shroud, top guide, access hole cover and in- ; core monitor housing. The PLEDGE model ofIGSCC and more recently IASCC (Reference 3-11) indicates the strong effect of conductivity on crack growth rate and by inference crack initiation. Figure 3-5 presents a schematic estimation ofUnit-3 crack growth rates as a function of conductivity using PLEDGE. Crack growth rates based on actual conductivity averages J for the first ten years (0.752 S/cm) were compared to those averages for the last two 24
CCT E3 '93 12:558 'iE El TNM'IY I GENucleuEwg GEYE-321-1413093 I years. The electrochemical potentials (ECPs) were graphically estimated between 0 and 100 mV[SHE). As no:ed in Figure 3-5, a factor of approximately twenty decrease in crack growth rate is obtained with the unit's decrease in conductivity. Thus, crack growth ! i over the past few years has been signincantly reduced by proper control ofwater i chemistry. ' 3.2 Fluence Considerations An important parameter which helps in the evaluation of the cracking mechanism is fluence. The fluence is the time integrated flux at a particular location Shroud peak ; fluence was calculated by multiplying peak flux at the shroud location by the effective full l power seconds of operation. The peak fluence in the Unit-3 shroud at the end of the next 2 fuel cyde will be approximately 7.9x1020 n/cm (E>1Mev). Typically, the fluence varies with shroud azimuthallocation and elevation. i i Ahhough peak shroud flux may vary significantly from cycle to cycle, available flux results are generally limited to one operating cycle per plant due to substantial resource ; requirements for vessel flux analysis. Shroud fluence estimates were therefore calculated based on the assumption that flux remains constant throughout the life of the plant. Further evaluation would be needed to quantify the uncertainty associated with this assumption. However, the method of determining fluence is considered to be suf5cient to obtain an estimate of the overall condition of the material with respect to irradiation j I ' - effects. The impact ofirradiation on core materials including crack growth rates has been studied and is discussed in References 3 11 and 3-12. l i i I 25
r GENaclar Energ GENE-523-141-1093 4 3.3 References 3-1 W.J. Shack, et al, " Environmentally Assisted Cracking in Light Water Reactors: . Semiannual Report April - September 1985," NUREG/CR-4667, ANL-86-31, June 1986. 3-2 W.J. Shack, et al, " Environmentally Assisted Cracking in Light Water Reactors: Annual Report October 1983 - September 1984," NUREG/CR-4287, ANL-85-33, , June 1985. 3-3 L.G. Ljungberg, D. Cubicciotti and M. Trolle, " Effects ofImpurities on the IGSCC of Stainless Steel in High Temperature Water," Corrosion, Vol. 44, No. 2, February 1988. 3-4 W.E. Ruther, W. K. Soppet and T. F. Kassner, "Effect of Temperature and Ionic Impurities at Very Low Concentrations on Stress Corrosion Cracking of Type 304 Stainless Steel," paper 102 presented at Corrosion 85, Boston, MA, NACE, March 1985, published in Corrosion, Vol. 44, No. I1, November 1988. 3-5 D.A. Hale and C. G. Diehl, "Real Time Monitoring of Environmental Crack Growth in BWRs", paper 455 presented at Corrosion 88, St. Louis, MO, NACE, March 1988. 3-6 B.M. Gordon, Corrosion and Corrosion Controlin BWRs, NEDE-30637, p. 6-22, December 1984. l 3-7 R.B. Davis and M. E. Indig, "The Effect of Aqueous Impurities on the Stress l Corrosion Cracking of Austenitic Stainless Steelin High Temperature Water," paper : 128 presented at Corrosion 83, Anaheim, CA, NACE, April 1983. l 3-8 P.L. Andresen, "A Mechanism for the Effects oflonic Impurities on SCC of : Austenitic Iron and Nickel Base Alloys in High Temperature Water," paper 101 l presented at Corrosion 85, Boston, MA, NACE, March 1985 4 3-9 K.S. Brown and G. M. Gordon, " Effects of BWR Coolant Chemistry on the , i Propensity for IGSCC Initiation and Growth in Creviced Reactor Intemals Components," paper presented at the Third Int. Symp. of Erwironmental Degradation of Materials in Nuclear Power Systems-Water Reactors, Traverse City, MI, August 1987, published in proceedings of same, TMS-AIME, Warrendale, PA,1988. 4 3-10 F.P. Ford et al, " Prediction and Control of Stress Corrosion Cracking in the Sensitized Stainless Steel / Water System," paper 352 presented at Corrosion 85, Boston, MA, NACE, March 1985. l 4 , 26 i
P.7' CCT E9 '93 12:5EF1 C-E BE TECritG 06/ f GLVE.533-1411003 GENuctw Energy i 3.3 References (cont'd) t 3-11 P.L. Andresen and F. P. Ford, "Modeling ofIrradiation Effects on Stress Corrosion Cracking Growth Rates," paper 497 presented at Corrosion 89, New Orleans, LA, I NACE, April 1989. ! 3-12 P.L. Andresen, F P. Ford, and A.M. Murphy, " State of Knowledge of Radiation Effects on Environmental Cracking in Light Water Reactor Core Materials," Proceedings of the Fourth International Conference on Environmental Degradation of Materials in Nuclear Power Systems - Water Reactors, Jekyl Island, GA, August 1989, NACE,1990 i a [ i a 1 27 i I
gg57,333,j4g,ygy; GENahar % I i Table 3-1 Severe Water Chemistry Transients in BWRS
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49 7 45 5.0 5: 8 78:227 ORGANIC INTRLSI;9 VI A C0h0E45A?E SYSTES EP81 NP 4134 77 i 5; 4.3 49 48 8 76 221 5.;18ECTE0 RESIN INTRUSION E41 %8 4134 65 l 51 K 4.1 5.1 80 8 741015 RVCU RESIN INTRus!CN EsRI we 4134 56 l 52 At 3.3 5.4 50 P 770125 IMPRCDER RINSE OF CONDENSATE OEMIN EPRI NP 4134 58 { 53 C 3.3 5.2 38 P 750309 POSSIBLE RESIN INTRUSICN EPRI =P 4134 59 3.2 ; 810715 RvCU RE51N INTRUSION E*R1 kP 4134 88 ; 54 8 3.2 4.7 495 P 780131 RESIN INTRU510N EPR! MP 4134 73 55 5 3.0 5.5 96 8 750902 SUSPECTED RESIN INTRUSION EPRI 48 4134 El 56 8 2.9 5.4 50 P 751125 PROBABLE RWCU RE51N INTRU510N EPRI MP 4134 52 57 8 . 2.8 5.2 65
- 770912 IMPROPER RINSE OF CONOENSATE DEMIK EPRI NP 4134 71 l 58 T 27 7.6 P 750526 RESIN INTRUSICN EPRI mP 4134 60 f
59 8 2.3 P 80C824 09GANIC INTRUSICN EPRI NP 4134 83 60 7 l 2.2 5.5 50 P 790108 $U5PECTED ORGANICS IN CONDENSATE STORAGE EPRI NP 4134 78 j 61 i 1.8 5.4 355 P 781208 CCNCENSATE DEMIN RE51N INTRU510N EPRI NP 4134 76 ; 62 Y 14 5.6 83 P 741125 VALvlNG ERROR OtRlWG RE51N TRANSFER EPRI NP 4134 58 63 AC 1.4 8.1 38 P 780112 CONDENSATE DEMIN RES!N INTRUSION EPRI NP 4134 72 + 54 M ' 65 AJ 1.4 P 750906 $USPECTED FLOC / FILTER A10/$tRFACT FROM RAD VASTE JM5 OC 930717 99 1.1 5.6 3: P 770225 5USPECTED RE51N INTRUSION EPRI NP 4134 59 l 66 0 1.1 8.8 72 P 780511 CONDENSATE DEMIN RE51N INTRUSION EPRI NP 4134 75 67 H I.0 P 811030 GYLCOL INTRUSION VIA RA0 WASTE EPRI *P 4134 90 [ 68 W 1.0 P 810622 CIL INTRUSION INTO NOTWELL EPRI NP 4134 87 l 69 PEACH BOTTOM 2 PCMT 82LOACI 4 i 70 A5 725 P 711113 HIGH FEE 0 WATER CONDUCTIVITT 540 P 780129 PCMT 82 LOA 01 33 71 8 1200 P 7607D8 CONDENSATE ST5 TEM MOMENTARILY BYPASSED PCMT BZLDA01 24 72 8 600 P 750103 RWCU OUT OF SERVICE PCMT 82 LOA 01 16 ; 73 AR [ 74 8 541.0 3.5 87000 5 790426 COOLING WATER INGRESS FROM RM RPV H2O TO HOTVELL PCMT 82LCA01 43 5 740801 ACIO INTO RPV FROM DEM!N STORAGE TANK PCMT 82LDA01 - 12 ;
, 75 8 423.0 3.2 5 760519 PCMT 82 LOA 01 22 f 76 H 140.0 PCMT 82LDA01 26 77 7 45.9 3.8 zu 5 781103 TORUS WATER PUMPED INTO RPY PRIOR TO STARTUP PCMT 82LDA01 23 {
78 8 13.3 1600 5 760520 ' 5 780801 LEAK IN R$ (AT E1CMNGER PCM T 82LDA01 36 ' 19 A 13.0 5 770917 RWCU OUT OF SERVICE PC M T 82LDA01 29 ! 80 8 12.9 i 5 800815 PCMT 82LDA01 47 l 81 T 12.1 PCMT 82 LOA 01 9 ! 82 AL 11.8 5 730603 RWCU OUT OF SERVICE I 5 800822 PCM T 82LDA01 48 83 8 11.2 5 601219 PCMT 82LDA01 51 i 84 0 11.2 l EPRI W 4134 91 85 F 10.5 5 820427 P0551tLE ORGAalt INTRUSION ' EPRI NP 4134 37 56 8 10.5 5.8 140 $ 780023 RWCU RE51N INTRU510R PCMT 82LDA01 18 j 87 H 20.3 5 750405 RWCU OUT OF SERV!CE PCMT 82LD401 5 88 AS 10.0 730 5 720604 OEPLETED RWCU DEMIR EPRI W 4134 55 f 89 0 5.0 5.5 60 5 740429 Con 0ERSATE DEula RE51R INTRU510R EPRI W 4134 97 l 90 AA 4.5 5.2 220 $ 830505 ORGAsic INTRU510R VIA RADWA5TE 91 8 4.2 5.3 600 5 781110 ORGAalC INTRU510E VIA ConDER5 ATE. DECon OCTER/DILS PCMf " EPRI W 4134 93 1 92 AP 1.0 5 820900 GYLCOL IETRU510R VIA RAmeASTE 29 4 i
)
GENE-5331411093 GENuclear Energy l Table'3-1 Severe Water Chemistry Transients in BWRS j l
%AA >A2 '*/07/93 COND. CH. C1, 80w OATE OATA ]
4A*( PLANT us/cm min go ry .- CC= EMTS ggggarggg p;gg7
- 7.
33 E 700 5 800305 PChai 22 LOA 01 A5 _A r ,* 13:0 5 73:325 C %:E45EE LEA (, t;%:E%5 ATE BYPASSEO. twtu Out 'CLRT B2 LOA 01 41 35 0 5:0 5 B 1:17 PCbET 82 LOA 01 50
- 5
~ A; '83 5 77:309
~ DC&RT 82 LOA 01 27 5 13:213 GYLCOL INTO RA0 BASTE. OETECTED PRIOR TO COND STOR EPRI mP 413A 95 37 (
1200 5 790315 CONOENSER LE AK. C0h0ENSATE OEPLETED. CI Into CST PCLAT 82 LOA 01 A0 38 T pC&RT 22 LOA 01 31 , pp 3 B00 5 771205 Rwtu OUT OF SERV!CE NOTE. SWR 5 3AhKED IN THE FOLLOVING GROER:
- 1. PCVER (P) OR SHUTOCVM (5)
I
- 2. 00m0VCTiv!TY CTHER NOTES: * = RESIN BEADS P80 VIDE LONG TERM LOV pH t
i e H + i t 30 i f
Arithmetic Mean Conductivity a Peach Bottom 3 I l Conductivity, pS/cm 1.4 - 1.2 - Peach Bottom 3 all years = 0.536 3 0.8 @
\
0.6 -
\
0.4 - n 0.2 - u_A f i i t t i .l. _.J 1 1 90 92 94 3 74 76 78- 80 82 84 86 88 Fuel year $l l Figure 3-1: Peach llottom 3 Arithmetic Mean Conductivity
Effect of Concentration and Conductivity S on IGSCC Initiation - FS Type 304 I Acceleration Factor { 5 O ANL Data V EPRI Data 4-- / } k
,/
Q/ 0 U t 3 - O y- V 2 - O Conductivity (pS/cm)
.. n.
.. n,. 7
, . ,. .,. . ; . 7r, rrn , i i r rrrrr e
, , ,,, rr; , , , i 10 i i,,,,,,,
10000 E 10 0 1000 to 1 Sulfate (ppb) l Crack initiation data based on CERT FS Type 304 Figure 3-2 Effect of Concentration and Conductivity on IGSCC Initiation
Peach Bottom 3 Response to June 1986 m Water Chemistry Transient >- I ' 19.16 Crack length, mm f Resin Resin Intrusion 2 Intrusion-1 - 19.14 - ..
..:2,..-
Y.. 19.12 -
~
2..-
.f ' d a /d t = 1.09 mm/ y U ,
,,' da/d t = 0.55 mm/y 19.08 -
c 19.06 h 2300 2400 2500 2600 2700 2800 g 210 0 2200 .:. - Hours t 5 Figure 3-3 Peach Bottom 3 llesponse to June 1986 Water Chemistry Transient _.__.._..__._..m__._.________.___.___________m. -
.~ m , ~_- . . , , . . . , , , , ,..e ,-o, - -., .,-.,,.,,..,,.m ....r ,,__,,-,_...,w,,_ , , , . . - . . , , , ,
MM.
!!! sCL 1 CO N ST A NT L O A D - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
20.8 : - 0.82 g
- 1.0 pSICM
- Ne2SO4 Q
< 0.1 pS /cm ,,
I i
<0 I pS/cm 0 45 pS/cm Na2SO4 -
O 5 pS/cm z 0.01 O 20.5 - ; it E 2 $ = Z
- z <
4 er m
. .a t-0.80 -- u 20.3 -
2
-- - 20 PP8 0XYGEN----
~
p --- -200 PPD OXYGEN - -- -- 0.79 ! --
- --- - 200 PPB OXYGEN -< -
20.1 - 19.8 - 0.78 - I w : A ~ 19.8 - 0.77 :-
~
* ~
d 10.3 - 0.76 p -- 0.1-0 03' pM/h 1.5 pM/h 1.1 pM/h (80' pin th) 0.09 pM/h 14.1-1.2' vb.th)
- 145 pin./hl 13.8 plo./h) 19.0 - 0.75 ,
o
- M I ' ' ' ' ' ' '
M P ' ' ' ' ' ' ' ' ' ' 1500 2000 2500 { 18.8 - 0.74 1000 t 0 500 :. Houns 'NO COMPLI ANCE UNLOADING @ Crack Length Versus Time, Sensi!Ized Type-304 Stainless Steel 286*C Oxygenated Figure 3-4 Water Environment, K = 28.6-30.5 MPadhi(26-28 ksi JIN)
e GENE PLEDGE Model Prediction for ~ Peach Bottom 3 Type 304 Crack Growth (it
^
% 10 0 . m V _.-.
K Early Life Operation s O mv zs , g --
- a. 1000 -
-100 mV 3 3 g Current I actor or improvement Operation I~20
- - - - ~ - - -
100 g .- g ._ b 10 .- u 3 o D d 5 1 0.6 0.8 1.2 $ 0 0.2 0.4 1 Conductivity, pS/cm $ PLEDGE: 15 C/cm2, 25ksi/in Estimated CGRs for ECP 0-100 mVlSHEl Figure 3-5 GENE Pledge Model Prediction for Peach Bottom 3 Type 304 Crack Growth w.-__ . -
t GE Naclear Energy GENE-523.Hi-H93 ' i 4.0 IN-VESSEL VISUAL INSPECTION j i This section summarizes the IVVI results of the Peach Bottom Unit-3 core shroud. IVVI of welds HI through H8 were performed during this outage. The IVVI included both
't inside surface and outside surface examination. Figures 1-2 shows the indications associated with the H3 and H4 welds. Only a few short indications were observed on the j j
outside surface of H1 and H4. Circumferential indications were observed on the inside surface associated with vertical weld V3 (See Figure 1-2). It should also be noted that the I area adjacent to the H9 weld was visually inspected as part of access hole evver (AHC) inspection at this outage. The inspection did not reveal any indications. The H9 weld in , the vicinity of the access hole cover is considered a higher stressed location and therefore I these IVVI results are considered to provide a reasonable assessment of the overall i condition of the entire H9 weld. 5 All indications associated with the H3 weld inside surface were in the HAZ of the shroud : t cylinder. No indications were found in the ring. The indications near H3 were all . circumferentially oriented. As can be seen in Figure 1-2, most of the indication length is ; located between the azimuth of 146* and 360 ; t i The indications observed at the H4 inside surface HAZ were a mixture of circumferential and axial indications as shown in Figure 1-2. i T Circumferential indications were observed emanating from the V3 weld on the inside i i i surface. Eight indications were observed grouped together with a spacing of approximately 2" between indications. All other IVVI vertical scans found no indications. 4 . On the outside surface a limited number of short indications were observed associated ,
. /
with H1 and H4. t i t Table 4-1 is the IVVI plan which indicates the original planned inspections. Due to the l observation ofindications at H3 and H4, the inspection scope was expanded and is also j described in Table 4-1. A summary of the IVVI results is shown in Table 4-2. See Figure : 1-2,1-3 and 1-4 for further details. l l i 36 l
F.6-OCT ES '92 12:E::t1 C-E IWR TECH:OhiY GENuctearEnergy GENE 583.M11M3 Table 4-1 Peach Bottom Unit 3 Core Shroud Exam Plan (3R09) i ORIGINAL PLAN (Prior to issuance of SIL 572) l
- 1. Perform sample examination "ID" at (8) celllocations of the "H3" and "H4" welds. l i
- 2. Perform sample examination "OD" at (8) locations in the high flux areas l
at welds "H1, "H2", and "H5" EXPANDED PLAN (Following identincation ofindications on the "H3" and "H4") ;
- 1. Perform 100% examination of the "H3" and "H4" welds from the ID.
- 2. Perform 100% examination of accessible areas of the "H4" weld from the OD.
- 3. Perform examinations of the "H3" weld, OD", where cracks were not .
identified from the "ID"
- 4. Perform an examination of the "H3" weld "OD", including significant l corTesponding areas of cracking identified on "ID". ;
- 5. Perform a sample examination on the "OD", at (8) locations of the "H6" weld. .
- 6. Perform a sample examination of the "OD" at (2) locations of the "H7" t and "HS" welds
- 7. Perform an examination of(l) vertical weld between the "H3" and "H4" !
t weld. 8, Perform a sample examination of the plate to include: (1) 8" area at the vertical weld. (1) 8" area between "H3" and "H4" welds. (1) 2" area between "H3" and "H4" welds. NOTE: Consideration was given to high neutron flux, stress, and repair areas for selection of the sample locations i 37
i GENuclear Deergy GENE-523-141-1993 Table 4-2 , Summary ofIVVI Indications 1 Weld Inside Surface Indications Outside Surface Indications I l ~ HI N/A 1 short vertical ; i H2 N/A None i H3 Circumferentialin Shroud None l Cylinder HAZ i H4 Circumferentialand Axial 2 shon venical ; i H5 N/A None j ! H6 N/A None l H7 N/A None H8 N/A None i V3 s enc <+ unam _
. ~ -
wwnn N/A i . PLATE None N/A : l l I i ! r I I 4 [ f , ? i e ?, ! i I l; 38 t
P. 9 C{T Es '93 oD oN M GE ES TECH 8 OLOGY gg.g g,, car.s83-m-un 5.0 FLAW EVALUATION This section provides the flaw evaluation and application of the screening criteria to the Peach Bottom Unit-3 indications. Included in this section is the structural analysis, allowable flaw size determination, and screening criteria. 5.1 Structural Analysis This section describes the details and the results of the struemral analysis performed to determine the allowable flaw lengths. The structural analysis consists of two steps: the ; determination of axid and circumferential stress magnitudes in the shroud, and the calculation of the allowable flaw lengths. Both the fracture mechanics (LEFhi) and limit load methods are used in the calculation of allowable flew lengths. 5.1.1 Applied Loads and Calculated Stresses The applied loads on the shroud consist ofintemal differential pressure, weight and , seismic. The seisnic loads consist of a horizontal shear force at the top of the shroud and l an ovenurning bending moment. The shear force produces a shear stress ofinsignificant j magnitude, and is not considered. The bending moment stress at a shroud cross-section , varies as a function ofits vertical distance from the top of the shroud. Because of the , inherent ductility of the material, residua! stresses and other secondary stresses do not affect structural margin. Thus, they need not be considered in the analysis. l , The magnitudes of the applied loads were obtained from the seismic stress analysis and . system information reports. The nominal shroud radius and thickness (2.0 in.) were used to calculate the stresses from the applied loads. The stresses are essentially based on the strength of materials formulas. Since the bending stress due to seismic shear force varies with the elevation of a location, two conservative values of this stress were calculated: one l applicable to shroud sections above the core plate (H1, H2, H3, H4, and H5) and the other for sections below the core plate (H6, H7 and HS). Figure 5-1 shows the weld j designation and relative locations in the shroud. ; l 1 39
GENmlear Energy GENE-533-1411093 , t Table 5-1 show;s the calculated seismic stress magnitudes for both the upset (Design ; Earthquake - DE) and faulted conditions (Maximum Credible Earthquake - hiCE). The appropriate pressure differences for the uoset and faulted conditions are shown in Table 5-2. Table 5-1 Seismic Axial Stresses at Shroud Welds Weld hiCE Stress (ksi) hioment s Designation (ft-kips) AfCE DE H1 1104.7 0.18 0.08 H2 1438.6 0.23 0.11 H3 1479.1 0.27 0.13 H4 2995.8 0.54 0.24 HS 4583.8 0.83 0.37 , H6 4679.7 0.90 0.40 H7 5697.6 1.10 0.49 H8 6749.7 1.30 0.58 i Table 5-2 Pressure DifTerences Pressure Differences (psi) __ Component Faulted Condition , Upset Condition Shroud Head and 32.9 14.12 Upper Shroud Core Plate Support Ring 54.8 35.68 and Lower Shroud 4
- The structural analysis for the indications uses two methods; linear elastic fracture mechanics (LEFhi) and limit load analysis. Both the limit load and the LEFM methods ,
- were used in determining the allowable flaw sizes in the shroud. Since the limit load is concerned with the gross failure of the section, the allowable flaw length based on this ,
approach may be used for comparison with the sum of the lengths of all the flaws at a cross-section. On the other hand, the LEFhi approach considers the flaw tip fracture ; toughness and thus, the allowable flaw length based on this approach may be used for , comparison with the largest effective flaw length at a cross-section. The technical , approach for the two methods is described below. I 40 i
GENcdear Energ GENE-583-141-1093 5.1.2 FractureMechanics Analysis The shroud material (austenitic stainless steel)is inherently ductile and it can be argued that the structural integrity analysis can be performed entirely on the basis oflimit load. In fact, J-R curve measurements (Figure 5-2) made on a core shroud sample taken from an overseas plant having higher fluence (8x1020 n/cm2) showed stable crack extension and ductile faiW. The AShE Code recognizes this fact in using only limit load techniques in Section Xi,3ubsubarticle IWB-3640 analysis. Nevertheless, a conservative fracture mechanics evaluation was performed using an equivalent Kjc corresponding to the ; material IJ c. The Kjc for the overseas plant shroud was approximately 150 ksidin. Use of this equivalence is conservative since: 1 i) The calculated fluence for Peach Bottom Unit-3 is lower than that for the overseas , plant from which J-R curves were obtained. ) ii) The J-R curves show J m ax values well above the Jlc, confirming that there is load ! capability well beyond crack initiation (See Figure 5-2). Using the AShE Code safety factor of 3, which is applicable for normal and upset l conditions of pressure boundary components, the allowable K el value becomes 50 ksiVin. f l For faulted conditions the allowable KIc is 107 ksiVin using the AShE Code safety factor of 42. For the analysis presented here, the LEFM analysis is confined to the H4 weld and above. The fluence corresponding to welds at and below the core plate elevation is an order of magnitude lower and the associated fracture toughness is comparable to that of the unirradiated material. For those locations, limit load analysis is used. An additional consideration that applies only to the fracture mechanics analysis is the question, "When is a flaw independent of an adjacent flaw?" The AShE Code proximity rule considers how flaws can link up and become a single flaw as a result of proximity. However, even when two flaws are separated by a ligament that exceeds the criterion, they may not be considered totally independent of each other. That is, the flaw tip stress intensity factor may be affected by the presence of the adjacent flaw. This can be accounted for by using the finite width correction factor for a flaw in a fini:e plate. For a through-wall flaw in an " infinite" plate, the stress intensity factor is: K = c4(xa) 41
i assuiarraru __ctst sss-m ms "; i For a finite plate, the K value is higher as determined by the finite width correction factor, f F. In this screening evaluation it is assumed that the plate is " infinite" if the correction f factor F is less than 1.1. As seen in Figure 5-3, if the width of the plate exceeds 2.5L1 (or j a/b less than 0.4), then there would be no interaction due to plate end edge effects. If this j same condition is applied to two neighboring flaws, then there will be no interaction . between the two indications if the tips are at least 0.75(L1+L2) apart. If the distance j between indications is greater than 0.75(Ll+L2), then they are consider ed as two separate ; flaws. However, if they are closer, for the purpose of fracture analysis, the equivalent flaw j length is the sum of the two individual flaws. 1 I 5.1.3 Limit Load Analysis q 1 A through-wall circumferential flaw was assumed in this calculation. Limit load ] calculations were conducted using the approach outlined in Subsubarticle IWB-3640 and l Appendix C of Section XI of the AShiE Code. The flow stress was taken as 3S m . The Sm value for the shroud material (Type 304 stainless steel)is 16.9 ksi at the nonnal j operating temperature of 550 F. i Safety factors similar to that used in the AShfE Code (2.8 for normal and upset and 1.4 j for emergency and faulted) were used in the analysis. The highest seismic stress was used ! for the limit load calculations and is shown in Table 5-1. Similarly, the highest axial ; pressure stress corresponding to the lower shroud was used. Thus, the analytical results are applicable for all welds since limiting values are used. 1 t
?
e I t I i
'l 1
i 42 { i i
t i GENeclear Ecergy GENE-523.H1-1093 j i 5.2 Allowable Through Wall Flaws ; Y Allowable through-wall flaw sizes were determined using both fracture mechanics and ; I limit load techniques for both circumferential and axial flaws. It should be emphasized that the allowable through-wall flaws are based on many conservative assumptions and are ! intended for use only in the screening criteda. hfore detailed analysis can be performed to l justify larger flaws (both through-wall or pan through when measured flaw depths are : available). However, since the intent of the screening criteria is to determine when additional evaluation or NDE characterization is needed, a conservative bounding approach is utilized. 5.2.1 Allowable Through-Wall Circumferential Flaw Size Both the LEFhi and limit load methods were used to evaluate the allowable through-wall flaws. Above the core plate, LEFM and limit load analysis methods were used. Since this is a screening criteria, single allowable flaw size criteria (limiting location) was used for all weld locations. It should be noted that the H7 and H8 welds involve Alloy 600 which has higher Sm values and therefore has higher limit load capability. Fracture Mechanics Analysis l The total axial pressure and seismic stress corresponding to the upset condition is 0.6i ksi, and 1.39 ksi for the faulted condition. Using the ASME Code safety factors for fracture ; analysis, the faulted condition is limiting. To determine the allowable flaw size based on LEFM methods, the consenatively : estimated irradiated material fracture toughness K cI value of150 ksiVin was used. Applying a safety factor of 1.4 for the faulted condition, the allowable KI of 107 ksiVin was obtained. The allowable flaw size was calculated using the following equation: i K I= Gm *o*4(na) : where Gm is a curvature correction factor as defined in Figure 5-4 (Reference 5-1), o is l
~
the axial stress, and 'a' is the half flaw length. The allowable through-wall circumferential ! flaw length (2a) was determined as s 344 inches. 1 43
i GENuclear Energy GE.%583141.jpg3 i Limit Load Analysis t A through-wall circumferential flaw was assumed in this calculation. The limit load f calculations were conducted using the approach outlined in Subsubarticle IWB-3640 and l Appendix C of Section XI of the ASME Code. The flow stress was taken as 3Sm. The -{ Sm value for the shroud material is 16.9 ksi at the normal operating temperature of } 550 F. i The stresses for the limit load analysis for the upset condition consisted of an axial force j stress of 0.71 ksi, and a bending moment stress of 0.49 ksi. F Similarly for the faulted condition, the axial force stress was 1.21 ksi, and the bending , t moment stress was 1.1 ksi. The allowable flaw length was approximately 430 in. including : the ASME Code, Section XI safety factors. ; i 5.2.2 Allowable Axial Flaw Size
\
t
+
Fracture Mechanics Analysis J The allowable axial flaw size is governed entirely by the pressure hoop stress. Similar to the circumferential flaw case, the allowable axial flaw size was detennined assuming a through-wall flaw. For a through-wall flaw oflength 2a in the shroud, the applied stress j i intensity factor is given by: i K = M
- ch
- 44a) ]
where M is the curvature correction factor. M is given by: j i M = Gm + Gb (Figure 5-5, from Reference 5-1) In the above expression, the allowable flaw length 2a can be determined by equating the I calculated K to the fracture toughness divided by the safety factor of 3. The hoop stress is 1.85 ksi and .ne allowable K = 150/3 (where 150 ksiVin represents a conservative estimate of the material toughness and 3 is the safety factor). i The allowable flaw length was conservatively determined to be 2a = 59 in. l
)
44 i t
GENcelear Energ GEVE 523 Hi-10H
.r Limit Load l
An alternate approach to determining the allowable flaw size is to use limit load j techniques. The allowable flaw length is given by the equation: oh
- Of/ (M1
- SF) 4
?
is a curvature correction factor (which is a function of the flaw length where M1 (Reference 5-2)), or= 3Sm is the flow stress, SF is the safety factor of 2.8 for upset j conditions, and ch = the hoop stress corresponding to the upset AP of 35.68 psi. The l allowable flaw length based on the limit analysis is 200 in. which exceeds that determined by LEFM. Thus, the allowable axial through-wa!! flaw length is 59 in. i t s
?
?
i 6 i i h l 5 i L l 45 I i
l GENaclear FarD' GENE-333-141-1M3 I 5.3 Screening Criteria ' i The determination of the allowable through-wall flaws has been described in Section 5.2. l The objective was to use the allowable flaw size as the basis for the screening criteria. ; Since the screening rules represent the first step in the evaluation, they are by definition .j conservative. If the criteria are exceeded, the option of doing funher detailed evaluation j or performing additional NDE remains. The effective flaw lengths (Llefr, L2 eft, etc.) l determined by combining indications using the proximity and interaction rules, are used in f the comparison with the allowable flaw sizes. The determination of effective flaw sizes ; are discussed in detail in Appendix A. The allowable through-wall flaws were: [ i e Circumferential Flaws
- 344 in. using LEFM t
- 430 in. using limit load 3 i
~
- Axial Flaws ;
- 59 in. using LEFM
- 200 in. using limit load A conservative approach in developing the screening rule is to include both the LEFM and limit load analysis. For axial flaws, the allowable flaw length based on the LEFM controls, and the screening limit is 59 in. !
For circumferential flaws the fracture mechanics based limit for a single flaw is 344 in. This in itselfis not sufficient since there could be several flaws (each less than 344 in.) in a 4 circumferential plane that cumulatively add up to greater than 430 in. (the allowable circumferential flaw size based on limit load analysis). Thus, the cumulative flaw length should be less than 430 inches. While this fully assures the ASME Code margins, an j additional conservatism is included in the screening. This states that the cumulative r
.I i
flaw length cannot be more than 430/4 = 107.5 in. in any 90 degree sector of the shroud. This is a conservative restriction that assures that long continuous flaws are not -l admissible. With the provision that :.he cumulative flaw length cannot exceed 107.5 m. m i any 90 sector of the shroud, this criterion becomes more limiting than the fracture mechanics limit of 344 in. The approach used here for the 107.5 inch limit for circumferential flaws is to assume a template with a moving window equal to the 90 l sector. The cumulative length of flaws that appear in the window should be less than ; I 46 i
,1 I
GENaclear Energy GENE-523-141-1093 107.5 in. A similar restriction based on limit loads is not needed for axial flaws since they _ are associated only with circumferential welds and are unlikely to be aligned in the same l plane. It should be noted that when considering LEFM based evaluations, the crack interaction l criteria described in Appendix A, must be applied in comparing against the allowable l lengths. For example, the adjacent flaws where the spacing S is less than 0.75 (L1 ef r+ j L2efd, the length L=Llefr+ L2 eft si used for comparison with the LEFM based ! allowable flaw length. i f b 4 d o u I I 47
t GENcntear Energ GENE-323141-1093 , l 5.4 Summary of Screening Criteria The screening criteria is schematically shown in Figure 5-6. The first step is to map the , flaw indications observed by IVVI. Next the proximity rules are applied to the flaw map to develop etTective flaw lengths (Appendix A provides the details for determining effective lengths). The results of the effective flaw lengths are also mapped. : For axial flaws located in a vertical plane, two neighboring flaws must be summed if S < l 0.75(L1 eff+L2 efr). If the longest resulting flaw is less than 59 inches, then the screening limit is met for axial flaws. I For circumferential flaws, all flaws are summed in any 90 sector using a template. The l i total flaw length in the 90 window must be less then 107.5 inches to meet the screening criteria. The next step is the LEFM based comparison using the interaction criteria. If - l j S <0.75 (L1 efr+L2 ef r), then the length L = L1efr+ L2eftshould be compared with the LEFM limit of 344 in for circumferential flaws. 4 ! [ i r i j l l a 48
9
?
GENuclear Enero GENE-3D.m.m3 5,5 Application of Screening Criteria f The screening criteria was used to evaluate the indications found by IVVI. The stmetural , integrity of the core shroud is assured if the screening criteria is met for all of the indications. All axial effective indication lengths are significantly less than the allowable flaw size based either on LEFM or limit load methods. Thus the axial indications seen by IVVI are acceptable per the screening criteria developed for Unit-3. i The effective indication lengths were determined for all of the circumferential indications as shown in Figure I-2. The calculation took into consideration the detailed geometrie information such as each indications length, the azimuth of each crack tip and the spacing i between indication planes in order to properly determine the effective length. The resulting effective indication lengths were then compared against the allowable indication length. Since all effective indication lengths satisfy the screening criteria, the structural integrity of the Unit-3 shroud is assured for the next two year cycle with power rerate conditions.
.}
l l 4 i 49
i GENuclear Energy GEhTs533-141 1093 5.6 References , 5-1. Rooke, D.P. and Cartwright, D.1, . Compendium of Stress Intensity Factors," The ; Hillingdon Press (1976). j 1 5-2. Ranganath, S., Mehta, H.S. and Norris, D.M., " Structural Evaluation of Flaws in l Power Plant Piping," ASME PVP Volume No. 94 (1984). j i 1 i i i i I, i I i A 1 1 1 50 l l
i GEST 583141-0993 GENuclear Enerv Shroud Head Flange H1 L'N Top Guide Support Ring k///) 4 H2 H3 s/c - H4 h fu - Core Plate Support Ring [j[/ H6 s S' 4 H7 H8
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Shroud Support Plate
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- act 29 ogg : ci:imm e atyssnI41IN3 IWI Y
y,cp A;l Flow Indicctions I Y Proximity Rules - Mcp Effective flow !.engths Circumferentic (Figure 2-4) Flows g
/wict Ficus 4No Sum of Flows in cny 900 5ecter<107.5" -
t Yes ; No f.<0.75(L1cif +Qff ;
, for AdJccent Fiews? g, lf 5<0.75(L1ef f + L2,f f l Fer Adjocent Ficwa7 j L=Lieff Of U eff Yes '
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Continued Operation m Justified Figure 5-6 SCHEMATIC OF SCREENING CRITERIA 56 l l
. I
GENuclear Energy GENE-523-141-1993 6.0
SUMMARY
AND CONCLUSIONS , r An evaluation of the indications in the Peach Bottom Unit-3 core shroud has been performed to demonstrate that the structural integrity of the shroud is assured for the next two year cycle. In addition, the report documents material, water chemistry and fluence information which provides additional insight to the shroud condition. The primary focus of this report was to demonstrate that even with several conservatisms in the evaluation, the structural integrity of the shroud is maintained dudng a limiting event. This was performed by developing a screening criteria, assuming throughwall indications, which can determine the acceptability of the flaws based solely on the IVVI ; results. The assumption of through-wall indications removes any uncertainty regarding sizing and the need to further characterize the indications. By meeting the screening criteda, the ASME Code Section XI safety margins are satisfied. The screening criteria uses both linear elastic fracture mechanics (LEFM) and limit load concepts to determine acceptable through-wall indication lengths. The limiting flaw length I based on either LEFM or limit load was used for the screening criteria. The screening criteria also uses the ASME Code Section XI criteria for combining flaws based on the proximity ofindications. In addition, a second method for including the interaction between neighboring indication tips was considered for the LEFM allowable flaw size calculation. The resulting efTective flaw lengths were compared against the , screening criteria to determine if the structural integrity of the shroud was maintained. ' Based on the results of the application of the screening criteria to the observed indications, , it is concluded that the structural integrity of the shroud is maintained for the next fuel l cycle. All effective indication lengths were shown to be less than the allowable flaw size. l l a l 57
)
I
t GE Nutear Eurgy GENE-533-14 -0993 APPENDIX A ' DETERMINATION OF TIIE EFFECTIVE FLAW LENGTH > The effective flaw lengths are based on ASME Code, Section XI proximity criteria as , presented in Subarticle IWA-3300. The procedure addresses both circumferential and , axial flaws. Indications are considered to be in the same plane if the perpendicular distance between the planes is less than 4" (2 times the shroud thickness). All flaws are l considered to be through-wall. Therefore, indications on the inside and outside surface 1 should be treated as if they are on the same surface. When two indications are close to each other, rules are established to combine them based on proximity. These rules are ! described here. A.1 Proximity Rules : The flaw combination methodology used here is similar to the ASME Code, Section XI proximity rules concerning neighboring indications. Under the rules, if two surface indications are in the same plane (perpendicular distance between flaw planes <4") and are within two times the depth of the deepest indication, then the two indications must be considered as one indication. In Figure A-1, two adjacent flaws L1 and L2 are separated by a ligament S. Crack growth > would cause the tips to be closer. Assuming a conservative crack growth rate of 5x10-5 in/hr, crack extension at each tip is 0.8 in. for 16,000 hours or one fuel cycle. Therefore, combining the crack growth and proximity criteria, the flaws are assumed to be close enough to be considered as one continuous flaw if the ligcment is less than (2 x 0.8 + 2 x
, I shroud thickness). For a shroud thickness of 2.0 in., this bounding ligament is 5.6 in.
Thus, if the ligament is less than 5.6 inches, the effective length is (Ll+L2+S+1.6"). Note l tbt the addition of 1.6 in. is to include crack growth at the other (non-adjacent) end of each tigw (See Figure A-2). If the ligament is geater than 5.6 in., then the effective flaw length is determined by adding the projected tip prowth to each end of the flaw. For this example, Ll e g= L1 + 1.6", and L2eg= L2 + 1.6" A similar approach is used to combine ikws when a circumferential flaw is close to an ' axial flaw (See Figure A-3). If the ligament between the flaws is less than 4.8 inches, then P A-1
a GENcclear Energ GENE-523-Hi-0993 i i the effective flaw length for the circumferential flaw is Lefr= L1+S+0.8" (the bounding ligament for these cases). If the ligament is greater than 4.8 in., then the flaws are treated separately. , After the circumferential and axial flaws have been combined per the above criteria, a map of the effective flaws in the shroud can be made, and the effective flaw length can be used for subsequent fracture mechanics analysis. In order to demonstrate the proximity criteria, three examples are shown in Table A-1 and described below. Table A-1 Flaw Combinations Considered in Proximity Criteria i Circumferential Flaw Axial Flaw , Case A Yes No Yes Yes B 9 No Yes C 1 A.1.1 Case A: Circumferential Flaw - No Arial Crack This case applies when two circumferential indications are considered. Figure A-2a shows this condition. If the distance between the two surface flaw tips is less than 5 6", the l indications must be combined such that the effective length is (See Figure A-2b): L efr= L1 + S + L2 + 1.6" i where: L1 = length of first circumferential indication , L2 = length of second circumferential indication S = distance between two indications l 1
]
1 l l I A-2 l i
GENucleu Ency GENE.3D.in-0993 i i If the distance i>etween the two tips is greater than 5.6", the effective flaw lengths are (See 4 Figure A-2c): l l Lleff = L1 + 16" ; L2eg= L2 + 1.6" A.I.2 Case B: Circumferential Flaw - Axial Flaw This case applies when both a circumferential and an axial flaw are being considered. Figure A-3a demonstrates this condition. For this case, only growth of the circumferential ; flaw is considered. If the distance between the circumferential indication tip and the axial l indication is less than 4.8", then the effective circumferential flaw length is (See Figure A- i 3b): i Leg = L1 + S + 0.8" where: L1 = length of circumferential indication distance between the circumferential tip and ; S= axial flaw. J and the effective axial length is (Figure A-3b): Leg = L2 + 1.6" where: L2 = length of axialindication ! 1 l If the distance between the circumferentialindication tip to the axial indication is greater than 4.8", then the flaws are not combined (See Figure A-3c) and the effective lengths are:
)
Ll g= e L1 + 1.6" (for circumferential flaw) L2eg= L2 + 1.6" (for axial flaw) i 1 1 A.I.3 Case C: No Circumferential Flaw- Arial Flaw This case applies to when only axial flaws are being considered. The effective length is determined in a manner similar to that used for case A for circumferential flaws. 1 A-3
i l i GENuclear Energ GLVE-523-H1-0993 I
\
A.2 Application of EITective Flaw Length Criteria The application of the effective length criteria is applied to two adjacent indications at a l time. Figure A-4 is a schematic which illustrates the process. For example, using the 0 ; i azimuth as the starting location for a circumferential weld or plane, the general procedure would be as follows:
. Moving in the positive azimuthal direction, the first indication encountered is '
indication 1.
. The next indication is indication 2.
. Apply proximity rules to the pair ofindications (indications 1 and 2). Combine the ,
flaws if necessary (Ll+L2+S). Old indication 2 becomes new indication 1.
. Continue along positive azimuthal direction until the next indication is '
encountered. This becomes new indication 2.
. Apply proximity rules to new indications 1 and 2.
. Continue proximity rule evaluation until all indications along the subject weld or plane have been considered.
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=li l Figure A APPLICATION OF PROXIMITY PROCEDURE TO NElGHBORING CIRCUMFERENTIAL FLAWS
. A-6 i
5 i __ GENF,533 14j. opp) GENadeer Eurgy f g ? Raws Assamed Through. cts r A' s As-Founc
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i Figure A APPLICATION OF PROX 1MITY PROCEDURE TO NE!GHBORING AXIAL AND CIRCUMFERENTIAL FLAWS A-7 l
GENedear Energy GENE.323141-0993 Stcri ct Tneta =0 Move in + Theto Direction , I Y i= 1 r Y First Flow is R o w i i i Y Next Rcw is Acw i+ 1 Y Perform Effective Lengtn Calculation Y Combine Rows if Necessary To Determirie Effective Length i=i+1 If now i+1 = Row i d i No Lost Row? Yes
+ Done I
Fi9 ure A 4 - PROCESS FOR DETERMINING EFFECTIVE CIRCUMFERENTIAL Fl.AW LENGTH i A-8 4 1}}