ML20149H184
| ML20149H184 | |
| Person / Time | |
|---|---|
| Site: | Peach Bottom  |
| Issue date: | 11/07/1994 |
| From: | Hunger G PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GL-94-03, GL-94-3, NUDOCS 9411180161 | |
| Download: ML20149H184 (33) | |
Text
l station Support Deper'msnt ]'
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' PECO ENERGY Nuclear Group Headquarters 965 Chesterbrook Boulevard )
Wayne, PA 19087 5691 November 7,1994 Docket No. 50-277.
License No. DPR-44 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555 >
Subject:
Peach Bottom Atomic Power Station, Unit 2 Supplemental Response to Generic Letter 94-03 Summary of Core Shroud Inspection Results
Dear Sir:
In our letters from G. A. Hunger, Jr. (PECO Energy Company) to U. S. Nuclear Regulatory Commission (USNRC), dated August 24,1994, September 9,1994 and September 26,1994, PECO Energy Company provided inspection plans for the Peach Bottom Atomic Power Station (PBAPS), Unit 2 core shroud. These plans were submitted in accordance with Reporting Requirements 1 and 2 of Generic Letter (GL) 94-03, "intergranular Stress Corrosion Cracking of Core Shrouds in Boilhg Water Reactors." A preliminary summary of the inspection results and a preliminary evaluation of the results were provided in a letter dated October 17,1994.
The purpose of this letter is to provide the final summary report, as requested by Reporting Regt,lrement 3, of the GL in summary, the overall results of the inspection revealed a minimum amount of flaws. Less than 5% of the examined weld length was found to contain flaws. The evaluation of the results was performed following the approach outlined in the "BWR Core Shroud Inspection and Flaw Evaluation Guidelines," GENE-523-113-8094, dated September 1994. This evaluation, based on the examination data, concludes that there is a substantial margin for each of these welds under conservative, bounding conditions to allow for continued operation of PBAPS, Unit 2.
If you have any questions, please contact us.
Very truly yours, e .
G. A. Hunger, Jr.,
Director - Licensing Attachment, Affidavit ,
cc: T. T. Martin, Administrator, Region I, USNRC W. L Schmidt, USNRC Senior Resident inspector, PBAPS g,,
A v V 04 "b \
9411180161 DR 941107 i ADDCK 05000277 i PDR i
, - - _ - ____ _ _ _ __ - _ O
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COMMONWEALTH OF PENNSYLVANIA ss.
COUNTY OF CHESTER W. H. Smith, Ill, being first duly sworn, deposes and says:
That he is Vice President of PECO Energy Company; that he has read the enclosed response to Generic Letter 9443 dated July 25,1994, for Peach Bottom Facility Operating License DPR-44 and knows the contents thereof; and that the statements and matters set forth therein are true and correct to the best of his knowledge, information and belief.
V ,
Vice President l
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l Subscribed and sworn to before me this r(4)"
i day of #N' # h 1994.
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Notary Public Norana: soar
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l PECO ENERGY COMPANY PEACH BOTTOM ATOMIC POWER STATION UNIT 2 REACTOR PRESSURE VESSEL CORE SHROUD INSPECTIONS FINAL REPORT 2R10, October 1994 Docket No. 50-277 In September and October of 1994, during the tenth refueling outage of Peach Bottom Atomic Power Station (PBAPS), Unit 2, the core shroud structure was comprehensively inspected. These inspections were conducted to determine the condition of the shroud welds, relative to the potential for existence of Intergranular Stress Corrosion Cracking (IGSCC). The effort satisfied the commitment made for PBAPS, Unit 2, in the PECO Energy responses to NRC Generic Letter 94-03, included in PECO Energy letters dated 8/24/94,9/9/94, and 9/26/94. The inspections were conducted in accordance with the guidance provided by the Boiling Water Reactor Vessel and Internals Project (BWR-VlP), as presented in the "BWR Core Shroud Inspection and Flaw Evaluation Guidelines", GENE-523-113-0894, dated September 1994 (Reference 1).
The following describes the overall inspection effort and summarizes the results of this effort.
Further, additional plans to assure continued core shroud integrity are presented.
BACKGROUND:
The PBAPS, Unit 2 shroud was fabricated by Rotterdam Drydock Co. LTD., Rotterdam, Holland.
The product forms used for this fabrication included 2" thick ASTM A240, Type 304 stainless steel plate (for shroud cylinders), and ASTM A182, Grade F304 seamless, stainless steel rolled forgings (rings). The plate materials contain relatively hi0h carbon contents (.059% to .062%), while the ring forgings contain lower carbon contents (.028% to .035%). The product forms where joined using the submerged arc welding process. The weld filler metal used was ASTM A371 Type Er308, with low carbon content. Welds H-1 through H-6 were welded from both surf aces, using a double bevel weld prep. 'Neid H-7 was welded from the inside surf ace of the shroud using a single bevel weld prep and a backing ring. The H-7 weld was made at the PBAPS site, and it attached the pref abricated shroud structure to the Reactor Pressure Vessel. This weld is a dissimilar metal weld (304 stainless to Alloy 600). The filler metal used for this weld was ASTM B 304, Type ERNiCr-3 (Alloy 82). The process used for this joint was the Shielded Metal Arc Welding process. Attachment 1 includes a drawing which depicts the shroud configuration, weld locations, and materials of fabrication.
The PBAPS, Unit 2 shroud has been in service since July 1974. During the first decade of hot operation, PBAPS, Unit 2 operated with relatively high primary water conductivity. Unit 2's arithmetic mean conductivity actually exceeded 1.0 pS/cm during the first few years of operation.
Subsequently, conductivity values were steadily decreased to below current EPRI guidelines.1992 and 1993 values were actually less than 0.1 pS/cm. The effects of such early water chemistry history on the susceptibility of the shroud welds to IGSCC are addressed in Reference 1.
The above described factors place the PBAPS, Unit 2 shroud into inspection Category C, as defined by Reference 1. This category has a high potential for some amount of shroud cracking, and, therefore, comprehensive inspections of welds H-1 through H-7 is recommended.
Page 1 of 4
PECO ENERGY COMPANY
, PEACH BOTTOM ATOMIC POWER STATION UNIT 2 REACTOR PRESSURE VESSEL CORE SHROUD INSPECTIONS -
FINAL REPORT 2R10, October 1994 :
I Docket No. 50-277 INSPECTIONS:
The scope of the core shroud inspections included all of the shroud circumferential welds (e.g. H-1 through H-7). The method used for inspection of these circumferential welds was Ultrasonic Testing (UT), performed from the outside surface of the shroud, using the General Electric Company's SM ART 2000 data acquisition system and the General Electric Company's OD Tracker and Suction Cup Scanners. The extent of the planned inspections included all portions of the circumferential welds which were accessible for the above described equipment. This scope and extent of planned ,
inspections was identified in PECO Energy's second response to Generic Letter 94-03, dated September 9,1994, and clarified during subsequent communications with the NRC.
The UT scanning was accomplished using three transducers. These transducers included 45' shear wave, 60' longitudinal wave, and creeping wave units. The transducers scanned each Heat ,
Affected Zone (HAZ) of the accessible lengths of each weld. The creeping wave transducer was
- not used on the H-3 weld inspection, due to equipment f ailure. The creeping wave transducer was used to enable better near-surface detection capabilities, primarily on the ring side HAZ of welds H-1, H-2, H-5, and H-6. On the plata side HAZ of the welds, the 45' shear wave transducer j typically was able to achieve a full V sound transmission, enabling near-surface detection with this transducer.
The purpose of the shroud inspections was to assess the condition of the shroud circumferential welds so that the integrity of the shroud structure could be quantitatively or qualitatively demonstrated. Additionally, the inspection results will be used to establish a baseline of this condition for comparison to future inspection results. This baseline data and subsequent inspection results will also be used to develop schedules for future shroud inspections, evaluations, or repairs.
The extent of shroud weld inspections performed during 2R10 include:
33% of the length of Weld H-1, distributed over 66% of the weld circumference. 230" 84% of the length of Weld H-2, 583" 88% of the length of Weld H-3, 574" 89% of the length of Weld H-4, 580" 83% of the length of Weld H-5, 540" ;
10% of the length of Weld H-6, plus an additional 13% performed visually. 148" 09% of the length of Weld H-7. 59" Subtotal 2714" x 2 (HAZ per weld)
Total 5428" The extent of these weld inspections is graphically depicted on the attached weld maps, Figures 1.1 through 1.7 (Attachment 2).
Page 2 of 4
l
. . j PECO ENERGY COMPANY PEACH BOTTOM ATOMIC POWER STATION UNIT 2 REACTOR PRESSURE VESSEL CORE SHROUD INSPECTIONS FINAL REPORT 2R10, October 1994 Docket No. 50-277 RESULTS: j A sufficient length of welds H-2, H-3, H-4, and H-5 was inspected to quantifiably demonstrate the condition and, therefore, the structural integrity of these welds. For welds H-1, H-6, and H-7, a limited amount of weld length was inspected, due to accessibility for inspection equipment. In these cases, the welds received a qualitative evaluation of their structural integrity. This qualitative approach is identified and discussed in Reference 1.
Some indications were found on welds H-1, H-3, H-4, H-5, and H-6, No indications were found on [
welds H-2 and H-7. Tables 1,1 through 1.7 provide data on the as-found indications, and are included as Attachment 3.
Because the H-6 weld had limited UT inspection, both in extent and distribution, and because one i indication was identified, an additional scope of inspections was implemented for this weld. This additional scope included an enhanced visual inspection (VT-1) of all remaining accessible areas ,
of this weld from the OD. These areas included the spaces between the ten sets of jet pumps. The {
weld was cleaned before the inspections.
EVALUATIONS:
l For welds which were accessible for a comprehensive inspection, all as-found indications were .
assumed to be through wall. Therefore, depth sizing of the indications was not utilized. Additionally, i the weld lengths which were not inspected, due to inaccessibility, were also assumed to be through wall indications. -
For welds which had limited accessibility, the conditions found within the inspected weld length were extrapolated over the areas of the weld which were inaccessible for inspection. This extrapolated condition was then evaluated for structural integrity. For welds H-1, and H-6, the ;
evaluation assumed that the entire circumference of the weld had an indication equal in size (i.e. t depth) to the deepest indication actually found on the weld by the inspections. The remaining ;
safety margin was then calculated. Since no indications were found on weld H-7, calculations were i developed to determine the maximum initial indication size (assuming a 360* length), which could '
be tolerated. This information was then used for qualitative comparison to the as-found conditions. >
Inspection results, for welds which received a comprehensive inspection, were initially compared !
to a screening criteria, which had been developed prior to the inspections. If the results of the ;
inspection indicated that sufficient unflawed material existed in the correct locations around the weld circumference, the results were considered acceptable. For welds which received a limited inspection, and for comprehensive inspection results which did not meet the original screening criteria, a detailed evaluation was performed. Ultimately, a detailed evaluation was performed for all welds, to determine the margin of safety for each weld (see Table 3 and 4 in Attachment 4). ,
The detailed evaluations were performed by Structurat integrity Associates (SI). These evaluations used the guidance provided in the evaluation portion of Reference 1. The as-found indication lengths were adjusted for upper bound crack growth, NDE uncertainty, and proximity factors. The I Page 3 of 4
. _ . ..A -
, PECO ENERGY COMPANY PEACH BOTTOM ATOMIC POWER STATION i UNIT 2 REACTOR PRESSURE VESSEL CORE SHROUD INSPECTIONS
- FINAL REPORT j 2R10, October 1994 !
Docket No. 50-277 resultant indication lengths (as-evaluated indications) were then used to calculate the amount of safety margin remaining in the subject weld, using the limit load methodology. Additionally, for Welds H-3 and H-4, the Linear Elastic Fracture Mechanics (LEFM) technique was used, due to the extent of neutron exposure received at these weld locations. The safety factors were calculated .
against the most limiting design basis loading conditions, derived f rom the General Electric Nuclear . [
Energy Screening Criteria Document (Reference 2) and the PBAPS, Unit 2 UFSAR. The loadings also considered Power Rerate conditions. ,
The as-evaluated indication lengths are graphically depicted on the attached weld maps, Figures 1.1 through 1.7, (Attachment 2). !
A more detailed discussion of the evaluations, including factors utilized for crack growth and NDE I uncertainties, is contained in the Structural integrity Associates' final report No. SIR-94-111, Rev.0, included as Attachment 4. :
CONCLUSIONS: l A 10CFR50.59 determination and safety evaluation has been developed and reviewed by the Plant Operations Review Committee (PORC). The conclusion of this evaluation indicates that no l unreviewed safety questions exist as a result of the shroud inspection findings.
The results of the inspections and evaluations conclude that the condition of the PBAPS, Unit 2 !
shroud, projected through the next, two-year operating cycle, will support the required safety margins, specified in the ASME Code and reinforced by the BWR-VIP recommendations.
Additionally, the results of these UT inspections substantiate the assumptions made for Unit 2, ,
during the PBAPS, Unit 3 shroud visual inspections, and the Safety Analysis developed in responsa to Generic Letter 94-03.
The extent of the shroud inspections provide a comprehensive baseline for comparison to future inspections. In accordance with Reference 1, welds H-1, H-6, and H-7 require reevaluation and/or reexamination during the next refueling outage (2R11). Welds H-2, H-3, H-4, and H-5 require reevaluation and/or reexamination during the following refueling outage (2R12).
The results of the UT inspection of the two access hole cover welds revealed no indications.
PECO Energy will continue to follow the developments of the BWR-VIP guidance documents, and will evaluate their applicability to the PBAPS Site.
REFERENCES:
- 1. BWR Core Shroud inspection and Flaw Evaluation Guidelines, GENE-523-113-0894, September, 1994.
- 2. Evaluation and Screening Criteria for the Peach Bottom Unit 2 Shroud, GENE-523-176-1293, December 13,1993.
Page 4 of 4
4 l
l PECO ENERGY COMPANY PEACH BOTTOM ATOMIC POWER STATION UNIT 2 REACTOR PRESSURE VESSEL CORE SHROUD INSPECTIONS FINAL REPORT 2R10, October 1994 Docket 140 . 50-277 ATTACHMENT 1 ;
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REACTOR PRESSURE VESSEL CORE SHROUD INSPECDONS - !
FINAL REPORT- t 2R10, October 1994 Docket No. 50-277 ATTACHMENT 1 REACTOR PRESSURE VESSEL - SHROUD PEACH BOTTOM ATOMIC POWER STATION UNIT 2 & 3 DRYER / SEPARATOR SUPPORT RING WELD NO. !
$1 ITEM 7 A182-F 304 0.035 % C V1 V2 H1 f ITEM 5 A240 TP. 304 0.062 %, CI (MAX)
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g gCORE PLATE SUPPORT RING ffrj$dITEM 13 A182-F 304 0.030 % C (UNI' 2) 0.035 % C (UNIT 3) ,
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FINAL REPORT 2R10, October 1994 Docket No. 50-277 ATTACHMENT 2 l i
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2R10 LEGEN0:
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BETWEEN H-1 8 H-2 BETwEEN H-1 & H-2 UPPER HEAT AFFECTE0 ZONE LOWER HEAT AFFECTE0 ZONE WELD LENGTH TOTAL INSPECTED PERCENT OF TOTAL WELD SHROUD CIRCUMFERENCE WELD LENGTH WELO LENGTH NUMBER 0.0.( I NC H E S ) 0.0.( I N C H E S ) ( I NCHES) INSPECTED H -1 UPPER 220" 691.2" 230" 33%
H-1 LOWER 220" 891.2" 230" 33%
LEGEND:
2R10 PBAPS UNI T 2 I I = S ATISFACTORY -
INSPECTION CORE SHROUD INSPECTION i==i = u N I NS PE C T E D WELO MAP FOR WELO N o. H-2 AS FOUND M = INDICATIONS 0
FI GURE NO.1.2 0' Q = AS EV ALUATED INDICATIONS
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UPPER HEAT AFFECTED ZONE LOWER HEAT AFFECTED ZONE WELD LENGTH TOTAL INSPECTED PERCENT OF TOTAL WELD SHROUD CIRCUMFERENCE WELD LENGTH WELD LENGTH NUMBER 0.0.( I NCH E S ) 0.0.( I NCH E S ) (INCHES) INSPECTED H-2 UPPER 220" 691.2" 583" 84%
H-2 LOWER 220" 691.2" 583" 84%
LEGEND:
2R10 t = INDICATION #
PBAPS UNIT ~2 1 I = S ATISF ACTORY CORE SHROUD INSPECTION INSPECTION ml = UNINSPECTED WELD MAP FOR WELO N o. H-3 = AS FOUND FIGURE N O . 1.3 INDICATIONS O' 0* E = AS EVALUATED INDICATIONS ~
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/-E _=T .: i.~ ; 4 3 180' I80' UPPER HEAT AFFECTED ZONE LOWER HEAT AFFECTED ZONE WELO LENOTH TOTAL INSPECTED PERCENT OF TOTAL WELD SHROUD CIRCUMFERENCE WELO LENGTH WELD LENGTH NUMBER 0.0.( I NCHE S ) 0.0.( I N CHE S ) (INCHES) INSPECTED H-3 UPPER 207" 651" 574" 88%
H-3 LOWER 207" 651" 574" 88%
LEGEND:
2RIO * = INDICATION #
PBAPS UNI T 2 I I = SATISFACTORY CORE SHROUD INSPECTION INSPECTION J = UNINSPECTED WELD MAP FOR WELD No. H-4 i FIGURE N O . 1.4 " " $No!c"8 IONS O' 0* M = AS EV ALU ATED.
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H-4 LOWER 207" 851" 580" BS%
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l 180' 180' UPPER HEAT AFFECTED ZONE LOWER HEAT AFFECTED ZONE WELO LENGTH TOT AL INSPECTED PERCENT OF TOTAL WELO SHROUD CIRCUMFERENCE WELD LENGTH WELD LENGTH NUMBER 0.0.f I NCHES) 0.0.( I NC H E S ) ( I NCHES) INSPECTED H-5 UPPER 207" G51" 540" 83%
H-5 LOWER 207" 651" 540" 83%
LEGENO:
2R10 t = INDIC ATION #
PBAPS UNI T 2 i i = S ATISFACTORY CORE SHROUD INSPECTION INSPECTION l i = UNINSPECTED WELD MAP FOR WELD N o. H-6 k * ( M = AS FOUND '
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$ m' I B O' 5". '* O m '. d O' UPPER HEAT AFFECTED ZONE LOWER HEAT AFFECTED ZONE WELD LENGTH TOTAL INSPECTED PERCENT OF TOTAL WELD SHROUD CIRCUMFERENCE WELD LENGTH WELD LENGTH NUMBER 0.0.( I NCH ES ) 0.0.( I NCH E S ) (INCHES) INSPECTED H-6 UPPER 201" 631.5" G4" U T, 84" vi 10% UT,13% VT H-6 LOWER 201" 631.5" 64" UT, 8 4" VT 10% UT,13% V T
L GEND:
2R10 PBAPS UNI T 2 I i = SATISFACTORY I NSPECT I ON CORE SHROUD INSPECTION lEsl = UNINSPECTED WELO MAP FOR WELD N o. H-7 M = AS FOUND .
INDICATIONS g' g ,, , FIGURE N O . 1.7 g' .
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UPPER HEAT AFFECTED ZONE LOWER HEAT AFFECTED ZONE WELO LENETH TOTAL INSPECTED PERCENT OF TOTAL WELD SHROUD CI RCUMFERENCE WELO LENGTH WELD LENGTH NUMBER 0.0.( I NCHE S ) 0.0.( I NCHE S ) ( I NCHES) INSPECTED H-7 UPPER 201" G 31.5" 59" 9%
H-7 LOWER 201" 831.5" 59" 9%
l PECO ENERGY COMPANY PEACH BOTTOM ATOMIC POWER STAilON UNIT 2 REACTOR PRESSURE VESSEL CORE SHROUD INSPECTIONS-FINAL REPORT 2R10, October 1994 Docket No. 50-277 ATTACHMENT 3 t
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PECO ENERGY COMPANY .
PEACH BOTTOM ATOMIC POWER STATION UNIT 2
SUMMARY
OF CORE SHROUD EXAMINATION RESULTS 2R10 TABLE 1.1 Weld No. H1 Azimuth Location Indication # Surface Weld Side Length
- Depth Rernarks Start Stop 1 ID Lower 12.87* 15.02* 4.13" .48' Detected by 45'S/60*RL 2 ID Lower 20.09' 21.40* 2.52' .61" Detected by 45*S/60*RL _
3 ID Lower 27.81* 29.63* 3.50' .55' Detected by 45*S/60*RL 4 ID Lower 38.22* 38.33' O.21" .31 " Detected by 45*S/60*RL 5 ID Lower 42.59' 45.02* 4.67" .63* Detected by 45'S/60*RL 6 ID Lower 57.59' 59.52' 3.71* .54" Detected by 45'S/60*RL 7 ID Lower 73.36' 75.83* 4.75" .74' Detected by 45*S/60*RL 8 ID Lower 80.92* 83.11' 4.21" .71* Detected by 45'S/60*RL 9 ID Lower 320.20' 321.41" 2.33' .54" Detected by 45'S/60*RL 10 ID Lower 327.59' 328.90* 2.52' .35" Detected by 45'S/60*RL 11 ID Lower 330.11* 330.83* 1.38' .41" Detected by 45*S/60*RL l
,
- Indication Length - As developed on outside surface of shroud. (Using 1.923*/Deg.)
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PECO ENERGY COMPANY -
PEACH BOTTOM ATOMIC POWER STATION UNIT 2 -
SUMMARY
OF CORE SHROUD EXAMINATION RESULTS 2R10 TABLE 1.2 Weld No. H2 Azimuth Location Indication # Surface Weld Side Length
- Depth Remarks Start Stop NO INDICATIONS FOUND
- Indication Length - As developed on outside surface of shroud. (Using 1.923"/Deg.)
PECO ENERGY COMPANY ,
PEACH BOTTOM ATOMIC POWER STATION UNIT 2
SUMMARY
OF CORE SHROUD EXAMINATION RESULTS 2R10 Weld No. H3 TABLE 1.3 Aximuth Location Indication # Surface Weld Side Length
- Depth Remarks Start Stop Lower 8.34' **
1 ID 9.33* 1.79" Detected by 45'S/60*RL 2 ID Lower 11.37* 14.78* ** Detected by 45'S/60*RL 6.16" 3 ID Lower 41.04* 41. 0* 1.19" Detected by 45'S/60*RL 4 Lower **
ID 70.32* 72.46* 3.87" Detected by 45*S/60*RL Lower **
5 ID 73.63* 75.24* 2.91" Detected by 45'S/60*RL 6 Lower **
ID 79.75* 81.20* 2.62" Detected by 45'S/60*RL T
7 ID Lower 82.40' 83.61* 2.19" 3etected by 45*S/60*RL ID Lower **
8 102.47* 106.32' 6.96" Detected by 45'S/60*RL 9 ID Lower 118.30' **
114.28* 7.27" Detected by 45'S/60*RL ID Lower **
10 120.79* 123.25* 4.45" Detected by 45*S/60*RL 11 ID Lower 142.76* 144.41* 2.98* Detected by 45'S/60*RL ID Lower **
12 148.96* 150.70" 3.14" Detected by 45*S/60*RL ID Lower **
13 151.89* 154.04* 3.89" Detected by 45'S/60*RL '
14 ID Lower 159.49' ** Detected by 45*S/60*RL 160.31* 1.48" Lower **
I 15 ID 190.65* 194.18' 6.38" Detected by 45'S/60*RL ID Lower **
16 239.18* 244.02* 8.75" Detected by 45'S/60*RL ID Lower **
17 255.65* 255.98* 0.60" Detected by 45*S/60*RL ID Lower **
l 18 256.17* 256.65* 0.87* Detected by 45'S/60*RL ID Lower **
19 344.11* 344.65* 0.98" Detected by 45*S/60*RL
- Indication Length - As developed on outside surface of shroud. (Jsing 1.807'/Dega ** Depth sizing not performed 1
PECO ENERGY COMPANY -
PEACH BOTTOM ATOMIC POWER STATION-UNIT 2 .
SUMMARY
OF CORE SHROUD EXAMINATION RESULTS 2R10 TABLE 1.4
! Weld No. H4 Azirnuth Location Indication # Surface Weld Side Length
- Depth Remarks Start Stop Upper **
{ 1 OD 21.30* 21.91* 1.10" Detected by creeping wave UT only.
2 OD Lower 66.96* 67.24' ** Detected by creeping wave UT only.
O.51"
,w OD Upper 138.37* 138 81* ** Detected by creeping wave UT only.
0.80" g_ 3_
S Upper **
4 ID 146.78* 149.97* 5.76" .
Detected by 45'S/60*RL 5 OD Lower 151.88* 152.27' O.70* Detected by creeping wave UT only.
OD Lower 153.32* **
6, 153.81* 0.89* Detected by creeping wave UT only.
7 OD Upper 193.70* 194.03* 0.60" Detected by creeping wave UT only.
8 OD Upper 197.22* 197.83* 1.10" Detected by creeping wave UT only.
4
- Indication Length - As developed on outside surface of shroud. (Using 1.807*/Deg.) ** Depth sizing not performed
. g 1
. ,. = - , _ , .. . _ , _ , .--,. ,. _ . = - -..- _.. - . - . - _ - . _ - . _ . _ _ . . _ . . . _ , . . , . _ . - , . . . - . . - . _ - . . - - - - . . - . . - _ _ . . . . - . . - - . . . . . - _ .,
PECO ENERGY COMPANY -
PEACH BOTTOM ATOMIC POWER STATION UNIT 2
SUMMARY
OF CORE SHROUD EXAMINATION RESULTS 2R10 TABLE 1.5 Weld No. H5 Azimuth Location Indication #- Surface Weld Side Length
- Indication Length - As developed on outside surface of shroud. (Using 1.807*/Deg.) ** Depth sizing not performed l
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PECO ENERGY COMPANY .
PEACH BOTTOM ATOMIC POWER STATION UNIT 2
SUMMARY
OF CORE SHROUD EXAMINATION RESULTS 2R10 TABLE 1.6 Weld No. H6 Azimuth Location Indication # Surface '" eld Side Length
- Depth Remarks 1 ID Upper 10,90* 13.60* 4.73* .45' Detected by 45*S/60*RL
- Indication Length - As developed on outside surface of shroud. (Using 1.75"/Deg.)
,, _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ . -_._m_ _ _ _ _ _ .
PECO ENERGY COMPANY -
PEACH BOTTOM ATOMIC POWER STATION UNIT 2 -
SUMMARY
OF CORE SHROUD EXAMINATION RESULTS 2R10 TABLE 1.7 Weld NO. HZ , _
m Azimuth Location Indication # Surface Weld Side Length
- Depth Remarks Start Stop NO INDICATIONS FOUND
- Indication Length - As developed on outside surface of shroud. (Using 1.754"/Deg )
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PECO ENERGY COMPANY PEACH BOTTOM ATOMIC POWFR STATION UNIT 2 REACTOR PRESSURE VESSEL CORE S 1ROUD INSPECTIONS FINAL REPORT 2R10, October 1994 Docket No. 50-277 ATTACHMENT 4 l
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Structural Integrity Associates, Inc.
3315 Almaden Expressway suite 24 san Jose,CA 951181557 October 14,1994 Phone: 408-978 8200 Far 408-978-8964 RAM-94-333 SIR-94-111, Rev. O Mr. Vijay M. Nilekani PECO Energy Company 965 Chesterbrook Blvd.,63C-9 Wayne, PA 19087-5691
Subject:
Evaluation of Peach Bottom, Unit 2 Shroud Indications
Dear Vijay:
StructuralIntegrity Associates (SI) has performed an evaluation of the flaw indications found during the inspection of circumferential welds H1, H2, H3, H4, H5, H6, and H7 at Peach Bottom, Unit 2, in order to determine the structural margin in each of these welds. The evaluation performed and documented herein was designed to evaluate operation without repair of these welds for an additional 24-month operating cycle for welds H1, H6, and H7, and for two additional 24-month operating cycles for welds H2, H3, H4 and H5. The evaluations were performed following the approach used in the BWR Vessel and Internals Project (VIP) evaluation guidelines [1] and the GE screening criteria [2] developed for Peach Bottom, Unit 2, based on limit load and linear elastic fracture mechanics (LEFM) techniques. The following sections of this letter report describe the methodology used to evaluate each weld, and the resulting safety margins.
Inspection and Evaluation Methodology The inspection and evaluation approach employed at Peach Bottom, Unit 2 provides the necessary information for determination of the allowable flaw lengths, including the appropriate amount for crack growth and nondestructive examination detectibility uncertainties, for all observed flaws. Ultrasonic testing (UT) techniques were utilized which provided complete through-thickness determination of any observed indications. Due to accessibility limitations, the extent of examination of these welds varied. In me.it cases, sufficient weld length was adequately interrogated to quantifiably demonstrate the condition, and hence the structuralintegrity of the weld. However,in some cases, the extent of weld length accessible for exa,mination was limited. In these cases, the results of the examinations were extrapolated over the portions of the weld which were not exan:fr.ed, thus resulting in a qualitative evaluation of the condition and structuralintegrity of the weld.
Because both quantitative and qualitative assessments have been performed, evaluation methodologies will be addressed separately with respect to structural integrity evaluation.
In compliance with the evaluation guidelines [1], evaluation for two cycles of operation is
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Mr. Vijay M. Nilekani October 14,1994 Page 2 RAM-94-333/ SIR-94-111, Rev. O considered for those welds which can support a quantitative assessment (welds H2, H3, H4, and H5), and one cycle of operation is considered for those welds in which only a qualitative assessment was performed (welds H1, H6, and H7). For purposes of this evaluation, one cycle of operation is assumed to be two years in length, at 110% of current rated pown and 110% of rated core flow.
Acceptance Criteria The core shroud is a core support structure which provides lateral support for the fuel. The applicable codes, standards and classifications for the core shroud are as follows:
The core shroud is classified as a safety-related component.
The core shroud is not an ASME Code,Section III component. However, the original design is in accordance with the intent of Section III of the ASME Code.
The evaluation of the core shroud was performed in accordance with the requirements of the BWR VIP's evaluation guidelines [1].
Flaw Evaluation Results Follow;ng completion of the inspection of the H1, H2, H3, H4, H5, H6, and H7 welds, flaw analyses were performed to demonstrate that the structural margins identified in the evaluation guidelines were maintained for the actual flaw configurations which were identified. (It should be noted that welds H2 and H7 have no reported indications.) The flaw analyses were performed using limit load as the failure criterion for each of the welds.
For the quantitative assessment, the evaluation performed here takes into account the distribution of uncracked material around the circumference of the shroud. In addition, the H3 and H4 welds, which are the most highly irradiated, were also evaluated using LEFM fracture methodology to be consistent with the evaluation guidelines [1]. For those welds, v hich could only be qualitatively assessed due to access limitations (welds H1 and H6), a different approach was utilized. The maximum flaw depth observed was assumed to be continuous for 360 of the shroud circumference. Because welds H1 and H6 are in areas of less radiation (< 3 x 102 n/cm ), only limit load techniques were utilized. In addition, an allowable flaw depth for weld H7 was determined using the same methodology.
Substantial conservatistus were built into the flaw evaluation to account for the weld area examined, the weld area which was not examined, evaluation guidelines' detection and sizing uncertainties, through-the-thickness (radial) crack growth and circumferential crack growth, and the evaluation guidelines flaw proximity criteria as applied to adjacent flaws. The speci5c consenatisms utilized in this evaluation are as follows:
f StructuralIntegrity Associates. Inc.
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Mr. Vijay M. Nilekani October 14,1994 Page 3 RAM-94-333/ SIR-94-111, Rev. 0
- 1. A bounding crack growth rate (5x104 inches / hour) [1, 2] through-wall and around the circumference was applied to the cracks detected. For the circumferential crack growth, two cycles were utilized for the structural rnargin assessment.
- 2. For the quantitative assessment, all inspected regions which are identified as cracked are treated as through-wall cracks and assumed to grow by 1.6 inches at each end during the next two operating cycles.
- 3. Per the evaluation guidelines, twice the shroud thickness, or 4 inches, was added to each end of identified indications.
- 4. For the quantitative assessment, all areas not mspected are assumed to be cracked through-wall. These areas are also increased in length by the crack growth and uncertainty factors described above.
- 5. For the qualitative assessment, identified flaws are increased in depth by 0.3 inches to account for UT sizing uncertainties, and 0.8 inches for one cycle of crack growth. This is in compliance with the evaluation guidelines.
- 6. For the qualitative assessment, the deepest identified flaw is assumed to be 360 in circumferential length.
- 7. ASME Code,Section XI proximity rules for adjacent flaws were applied.
- 8. ASME Code,Section XI pressure boundary safety margins were applied to these evaluations even though the core shroud is not a primary pressure boundary.
The conservative assumptions described above were applied to each of the horizontal welds examined in this report. Table 1 presents the membrane and bending stresses which were used for the limit load analyses for each of the welds identified in the table, and for the LEFM analyses performed for welds H3 and H4. One notes from Table 1 that the highest stresses are observed at the H7 weld, and the lowest stresses occur at the H1 weld location.
The limit load analysis was performed for all welds evaluated in this study, the H1, H2, H3, H4, H5, H6, and H7 welds, and LEFM was also performed for the H3 and H4 welds.
Because the Fauhed Condition factor-of-safety is half the Upset Condition factor-of-safety, it is clear that the loading condition which governs the analysis for welds above the core plate is the Faulted Condition, with the Upset Condition governing welds H6 and H7.
Table 2 presents the results of the ultrasonic examination for each of the horizontal welds j quantitatively evaluated in this report. For welds H1 and H6, which are qualitatively assessed due to examination accessibility limitations, the maximum detected flaw depth is increased by 0.3 inches for detection uncertainty, and 0.8 inches for one cycle of crack growth. The postulated resulting 360 circumferential flaws which were analyzed are 1.84 f Structural Integrity Associates, Inc.
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Mr. Vijay M. Nilekani October 14,1994 Page 4 RAM-94-333/ SIR-94-111, Rev. 0 1
inches deep for weld H1, and 1.55 inches deep for weld H6. Using the same methodology, it war determined that the H7 weld could satisfy acceptance criteria with an initial 0.8 inch i deep flaw. '
The results of the limit load analysis for each of the horizontal welds examined is presented in Table 3, based upon the stresses reported in Table 1, and the examination results reported in Table 2. One observes from this table that the factors-of-safety for the Faulted Condition for welds H1, H2, H3, H4, and H5 range from 5.4 for weld H1 'o 40.2 for weld H2. This compares to an ASME Code minimum factor-of-safety of 1.4 specified for pressure boundary components imder faulted loading conditions. For weld H6, the reported factor-of-safety for Upset Conditions is 14.0, with an allowable of 2.8. One should note that the conservatisms utilized in this study are as described previously in this section.
Finally, an evaluation of the H3 and H4 welds was performed using the LEFM methodology to determine the applied stress intensity factor resulting from the conservatively estimated cracking combined with the bounding loading condition (the Faulted Condition) for these weld locations. The results of this analysis demonstrate that the 150 ksi-(in)m toughness which is presented in the evaluation guidelines i:] as the acceptable fracture toughness for this material under irradiation embrittled conditions is met. Table 4 illustrates that the ASME Code minimum factor-of-safety of 1.4 has been met under this loading condition for the flaws present at welds H3 and H4.
Summary Based upon a review of the examination data for circumferential welds H1, H2, H3, H4, H5, H6, and H7, there is substantial margin for each of these welds under conservative, bounding conditions to allow for continued operation for a minimum of one additional 24-month operating cycle for welds H1, H6 and H7, and two additional cycles for welds H2, H3, H4 and H5. The analyses performed included limit load analyser under bounding design basis conditions, and LEFM for the postulated highest fluence welds. The quantitative evaluations were performed with the assumption that all regions uninspected were cracked through-wall, and that any cracking observed was cracked through-wall. Additionally, all areas assumed to be cracked were grown (at each end) at the bounding crack growth rate of 5x104 inches / hour for two cycles, and increased in length by 4 inches (for a total increase of 5.6 inches at each end). The qualitative evaluations were performed with a 0.3 inch sizing uncertainty and 0.8 inches for one cycle of crack growth. ASME Code safety margins were used, and were significantly exceeded in all cases for the specified operating period.
Very truly yours,
/
R. A. Mattson, P.E.
Associate attachments f Structural Integrity Associates, Inc.
Mr. Vijay M.' Nilekani October 14,1994 Page 5 RAM-94-333/ SIR-94-111, Rev. O References
GENE-523-113-0894. September 1994.
- 2. GE Nuclear Energy," Evaluation ar,d Screening Criteria for the Peach Bottom Unit-2 Shroud", Report Number GENE-523-176-1293, December 13, 1993.
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Table 1 Membrane / Bending Stresses j l
i Shroud Stresses 2 Weld Location Membrane Bending j Upset Faulted Upset Faulted H1 0.38 ksi 0.88 ksi 0.09 ksi 0.18 ksi H2 0.38 ksi 0.88 ksi 0.12 ksi 0.23 ksi H3 0.36 ksi 0.83 ksi 0.14 ksi 0.27 ksi H4 0.36 ksi 0.83 ksi 0.27 ksi 0.55 ksi H5 0.36 ksi 0.83 ksi 0.42 ksi 0.84 ksi H6 0.62 ksi 1.10 ksi 0.46 ksi 0.91 ksi H7 0.62 ksi 1.10 ksi 0.56 ksi 1.11 ksi NOTE: 1. Because the Faulted Cendition factor-of-safety is half the Upset Condition factor-of-safety,it is clear that the Faulted Condition governs for welds H1 through H5, and the Upset Condition governs for welds H6 and H7.
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) StructuralIntegrity Associates. Inc.
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Table 2 UT Examination Results Used for Quantitative Analyses Weld Unflawed Material for Analyses Total Unflawed Location Material H2 11.37 -154.31 , 191.37 -333.31 537"/79 %
H3 17.94o 37.88 , 44.86 -67.16 ,
342"/54 %
86.77 -99.31 , 126.41 -139.60 ,
197.34 -236.02 , 247.18o 252.49 ,
259.81 -340.95 H4 12.15 -18.14o, 25.07o i3.80 ,
449"/70 %
70.40 -135.21 , 156.97 -160.53 ,
200.99 -341.03 H5 12.15 -117.57 , 125.15o 153.53 ,
474"/74 %
199.65 -333.53o l NOTES: 1. All reported indications have been assumed through-wall and increased in length by 5.6 inches (2T + 2CG) at each end.
- 2. All areas not inspected are assumed to be cracked through-wall, and j extended in length by 5.6 inches (2T + 2CG) at each end. I i
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l Attachment to RAM-94-333/ SIR-94-111 Structural Integrity Associates, Inc.
. Table 3 Limit Load Factors-of-Safety Weld Location Factors-of-Safety .2 2
HI 5.4 H2 40.2 H3 26.3 H4 27.3 H5 24.2 H6 14.0 H7 3.13 NOTES: 1. The Faulted Condition governs for welds H1, H2, H3, H4, and H5, with an allowable factor-of-safety of 1.4.
- 2. The Upset Condition governs for welds H6 and H7, with an utowable factor-of-safety of 2.8.
- 3. Based upon an assumed initial flaw depth of 0.8 inches.
Table 4 LFFM Factors-of-Safety Weld Location Factors-of-Safety 2 H3 3.6 H4 2.S NOTE: 1. The Faulted Condition governs. with an allowable factor-of-safety of 1.4.
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Structural Integrity Associates. Inc. _
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