ML20155G774
| ML20155G774 | |
| Person / Time | |
|---|---|
| Site: | Vermont Yankee File:NorthStar Vermont Yankee icon.png |
| Issue date: | 05/05/1986 |
| From: | Murphy W VERMONT YANKEE NUCLEAR POWER CORP. |
| To: | Muller D Office of Nuclear Reactor Regulation |
| References | |
| FVY-86-36, IEIN-84-41, NUDOCS 8605070124 | |
| Download: ML20155G774 (22) | |
Text
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o VERMONT YANKEE NUCLEAR POWER CORPORATION FVY 86-36 RD S. Box 169, Ferry Road, Brattleboro, VT 05301
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ENGINEERING OFFICE 1671 WORCESTER ROAD FR AMINGHAM, MASSACHUSETTS 01701 May 5, 1986 U.S. Nuclear Regulatory Commission Washington, D.C.
20555 Attn:
Office of Nuclear Reactor Regulation Mr. Daniel R. Muller, Director BWR Project Directorate #2 Division of Licensing
References:
a)
License No. DPR-28 (Docket No. 50-271) b)
Letter, USNRC to All BWR Facilities, IE Information Notice 84-41, dated 6/1/84 c)
Letter, VYNPC to USNRC, FVY 83-50, dated 6/3/83 d)
Letter, VYNPC to USNRC, FVY 84-93, dated 7/30/84
Dear Sir:
Subject:
Core Spray Nozzle Weld Overlay During ultrasonic inspections of the core spray nozzle weld butter per-formed in accordance with our commitment relative to I&E Notice 84-41, Reference b), weld defects indicative of intergranular stress corrosion cracking (IGSCC) were detected. Vermont Yankee initiated a conference call with the NRC on April 28, 1986 to notify the NRC of these indications and present the NRC with our initial assessment and action plan.
In response to the staff's request made during this conference call, we hereby provide Vermont Yankee's proposed repair / design parameters to address and remedy the inspection findings.
Background
In 1984, IGSCC was detected in the Iconel 182 weld butter on several reac-tor pressure vessel nozzles at a domestic reactor.
This cracking was discovered when the nozzle safe ends were removed as part of a recirculation pipe replace-ment program. The cracking at that reactor was observed by liquid penetrant examination of the inside surface of the nozzle. Since the cracking was actually in the weld metal, standard ultrasonic techniques were not able to detect the cracking.
The nuclear industry funded a development program by the Electric Power Research Institute (EPRI) to develop special ultrasonic (UT) techniques for inspecting the Iconel 182 nozzle weld butter. Vermont Yankee committed to per-form an inspection when the technique became available, hD 0 0124 860505
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VERMONT YANKEE NUCLEAR POWEH COMPORATION U.S. Nuclear Regulatory Commission May 5, 1986 Page 2 The metallurgical geometry of the core spray nozzle safe end at Vermont Yankee is shown in Figure 1.
The Iconel 182 nozzle butter is the area showing the indication of IGSCC. A description of the inspection methodology and the inspection results is contained in Appendix A.
Repair Methodoloay The repair approach will be to apply a weld overlay similar to those applied at Vermont Yankee in 1983 and 1984 [ References c) and d)].
The application of these overlays is slightly different since previous overlays were applied over stainless steel base metal.
For the core spray nozzles, the base metals are low alloy steel on the nozzle side of the weld and Iconel 600 on the safe end side of the weld.
The presence of the low alloy steel requires that specialized weld processes be developed. The repair approach will be an extension of the pressure vessel repair procedure described in ASME Code Case N-432.
The first step is to apply a weld overlay of 0.125 inches minimum thickness over the low alloy steel nozzle.
This will be done with the nozzle drained and preheated to between 300* to 400*F.
This will be accomplished in approximately three to four layers in the so-called " butter-temper" process to ensure any embrittlement caused by the first weld layer is tempered by the subsequent layers. The 0.125 inch minimum thickness is selected to ensure sufficient thickness so that the application of the actual overlay does not affect the nozzle base metal. Typical weld parameters are shown in Appendix B (these are for information only; the actual weld parameters will be developed by mockup testing at Vermont Yankee).
Following completion of this process, the actual weld overlay is applied.
The overlay is designed for a minimum five-year lifetime. The overlay design is in compliance with the ASME Code,Section XI, Subsection IWB-3640 and draft NUREG 0313, Revision 2.
The overlay is a full structural overlay; no credit is taken for the thickness of the butter-temper layers. The details of the design are included in Appendix C.
Following installation, the overlay will be inspected in accordance with the current EPRI/NRC weld overlay inspection criteria, as would apply to Iconel, using personnel qualified at the EPRI NDE Center.
' Repair Qualification All procedures and welders will be qualified in accordance with the appropriate ASME Code requirements.
In addition, in order to verify the effec-tiveness of.the low alloy steel butter temper process, micro-hardness readings will be taken on the mockup before welding, following the first layers, and following the complete butter-temper process to demonstrate the tempering of any possible embrittlement.
In addition, Charpy V-notch tests will be conducted to demonstrate proper recovery of toughness.
VERMONT YANKEE NUCLEAR POWER CORPORATION U.S. Nuclear Regulatory Commission May 5, 1986 Page 3 Schedule of Performance Mockup development is currently underway with actual repair scheduled to begin the week of May 25, 1986.
In addition to the special weld procedure, development of a safe end/ nozzle / vessel shell plate mockup has been established for personnel training.
In accordance with the provisions of 10 CFR 170.12, an application fee of
$150.00 is enclosed.
In order to maintain our 1986 startup schedule, your immediate attention to this matter is requested. We are willing to meet with you and your staff at your earliest convenience, if necessary.
Very truly yours, VERMONT YANKEE NUCLEAR POWER CORPORATION 1
M Warren P. Murphy Vice President and Manager of Operat, s
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4 APPENDIX A The Vermont Yankee N5 nozzle reducer to safe-end welds (stainless to Inconel), the Inconel safe-end threaded regions, and the Inconel safe-end to nozzle welds were examined during the 1985-1986 refueling outage. Examinations. included liquid penetrant and ultrasonics; both manual and P-scan. The reducer to safe-end welds and the safe-end threaded region showed no indications interpreted to be defects.
The safe-end to nozzle weld including the nozzle but-tering showed linear indications during the 0.0. surface liquid penetrant examination. The NSB weld contained 37 indi-vidual linear indications located approximately.060 inches out-board of the nozzle in the Inconel butter spread circum-ferentially around the nozzle 0.D.
Of the indications noted, two individual indications were rejectable to Section XI and one additional grouping exceeded the criteria when evaluated in accordance with IWA 3400-1.
The NSA nozzle was similarly indicated though the indica-tions were not as numerous.
The indications are short, tight linear indications both grouped and random. They are both parallel and skewed with respect to the nozzle butter interface.
Both welds were examined ultrasonically using P-scan and manual techniques intended for use with multiple Inconel weld layers P-scan showed three closely spaced indications in the circumferential direction (parallel with weld longitudinal axis) on the NSB nozzle. The N5A nozzle showed no circum-ferential indications. Manual axial examination of NSB shoced seven axial indications with a concentration of indications at the circumferentially indicated area. N5A showed seven ran-domly spaced axial indications.
Some correlation appears to exist with respect to axial flaw location and 0.0. Liquid Penetrant indications.
Connection between the 0.D. Liquid Penetrant indications and the axial U.T. has not been confirmed or disproven.
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APPENDIX B WELD OVERLAY PARAMETER INFORMATION PRELIMINARY
---Preheat nozzle to 350*F - hold for 4 hour4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> LAYER 1 PARAMETERS o
Current:
120 Amps:
1/3 of time 210 Amps:
2/3 cf time o
Voltage:
11 Volts o
No oscillation o
Wire size 0.035" diameter Sandvik ER NI CR-3 wire o
Torch angle 90*
3 o
Shield gas: Welding Grade Argon at 30 ft / hour o
Wire feed:
o 30 inches / minute - 1/3 of the time o
43 inches / minute - 2/3 of the time o
Travel speed:
8.5 inches / minute o
Bead overlap was 50%
o Preheat and interpass 300*F to 400*F during entire layer o
Double down welding o
Heat input of 14,000 J/ inch LAYER 2 PARAMETERS o
Current:
140 Amps:
1/3 of time 230 Amps:
2/3 of time j
o Voltage:
11 Volts o
No oscillation o
Wire size:
0.035 inch diameter o
Torch angle - 90*
3 o
Shield gas: Argon @ 30ft / hour o
Wire Feed o
51 inches / minute:
1/3 of time i
o 63 inches / minute:
2/3 of time I
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Travel speed:
7 inches / minute j
o Bead and interpass temperature 300*F to 400*F i
I o
Heat input:
19,000 J/ inch o
Double down welding o
Bead Overlap was 50%
LAYER 3 PARAMETERS o
Current:
160 Amps:
1/3 of time 250 Amps: 2/3 of time o
Voltage:
11 Volts o
Oscillation: 0.156 inches o
0.2 second excursion o
Pulse synchronization o
0.4 second dwell on each side of bead o
Wire size:
0.035 inch o
Torus angle:
as Layer 1 o
Shield gas:
as Layer 1 o
Wire feed:
o 56 inches / minute:
1/3 of time o
69 inches / minute:
2/3 of time o
Bead overlap:
50%
o Heat input:
24,000 J/ inch o
Preheat and interpass temperature o
300*F to 400*F FOLLOWING THIRD LAYER o
Hold preheat until postheat Post heat -- 450*F to 500*F Hold three hours and slow cool Fill with tap water o
used 3 gpm flow Complete overlay with o
second layer weld parameters EXCEPT i
o Preheat and interpass temperatures are 70*F to 110*F i
o Can use orbital welding procedure or continue double down l
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PRELIMINARY REPAIR OF IGSCC FLAWS IN THE CORE SPRAY SAFE-END TO N022LE WELDS AT VERMONT YANKEE NUCLEAR POWER PL ANT
1.0 REFERENCES
1.1. General Electric Compeng Design Certification DC23A4322, " Reactor Vessel - Core Spray Safe End", for Vermont Yankee, August 12,1985.
1.2. General Electric Company Stress Report 23A4904," Core Spray Nozzle,
for Reactor System - Vermont Yankee, December 13,1985.
1.3 Electric Power Research Institute Research Project EPRI 1566-1,
' Stress Corrosion Cracking of Alloys 600 and 690 and Competible Weld Metals in BWR Environments", Prepared by Southwest Research Institute, Second Interim Report, June,1984.
2.0 PURPOSE Flows believed to be due to IGSCC were identified in the inconel butter on the core sprey safe end to nozzle weld at Vermont Yonkee.The flows were detected by ultrasonic and dye penetrent methods.
The purpose of this calculation is to document the design of a weld overley repeir et this location which will provide adequate safety mergin et the repelred location for e period of et least 5 years.
l Weld overleys applied to steinless steel piping ere typically applied using 308L weld metel.This meterial has been sho.wn to be highly resistent to IGSCC propogelion. Flows generally arrest et the overley boundary. Weld material for repelr of flowed Inconel piping is not generally immune to IGSCC propogetion, however. The observed flows et Vermont Yankee are in inconel 182 weld meterial, for exemple. Consequently, weld overley design using inconel weld meterial must include ellowance for continued crack growth.
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This calculation presents e design for weld overley repeir of the observed flows based upon the requirements of ASME Section XI, peregraph IWB-3641, and upon location-specific stress information f rom ref erences 1.1 &l.2. For the purpose of overley design, the flows were assumed to be through the existing pipe well, and to extend 360* circumferentially. The resulting overley design was then evolueted for the possibility of degradetion due to continued crack propagetion. It is demonstrated that the integrity of the design overleg will not be reduced below Code levels for et leest the design life of 5 years, when the beneficiel effects of overley application on the residual stress distribution are included in the evaluation.
3.0 STRESS DETERMINATION in accordance with the requirements of Section XI, only primary membrane and primary bending stresses were considered in the overley design. The values of these components were taken from reference 1.2.
OVERLAY DESIGN STRESS = Pm + P = 8513 psi.
b It is also necessary to demonstrate that the overley thickness is not reduced below acceptable level during the life of the repair (5 years) due to IGSCC crack growth in the inconel overley meterial. For the crack 9rowth calculations, thermal expension is included in the stress sum above.
CRACK GROWTH STRESS = Pm + P + THERMAL = 15088 psi.
b 4.0 WELD OVERLAY DESIGN For the purpose of weld overley design, the pipe well thickness was taken as 0.939, as shown in reference 1.2.The required minimum length of the V
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overley is then L = 1.5 x /Rt, where R = outside redius of pipe = 6.72" t = well thickness = 0.939' so L = 3.77" At least 0.75 x /Rt of the length must be on each side of any flow to provide adequate reinforcement. Since observed flows are in the butter, en additionallength of 1 is included to account for the width of the weld crown.The final overley length is therefore L = 4.7T, rounded to 5.0" This length should be centered on the Y 91d Center-line.
The weld overleg required thickness best d upon Section XI was determined using the program pc-CRACK.The pc-CRACK calculations are etteched to this package.The required thickness is 0.34". This thickness is in addition to the thickness required by Code for a temper bead, es shown in figure 1.
5.0 WELD OVERLAY RESIDUAL STRESS DISTRIBLITIONS Application of a weld overley es indicated in figure 1 has been shown by I
finite element onelysis to produce residual stress distributions through the pipe well es shown in figure 2. In both the exiel and circumferential directions, these distributions are highly compressive near the ID of the component, and become tensile near the outer surface of the overleg.These distributions cre used in the crack growth calculations which are necessery to demonstrate that on inconel weld overley on the core sprog Prepared by/dete
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l safe end to nozzle weld will not be degraded below the design limit due to crack growth during the design life of the repeir.
6.0 STRESS INTENSITY CALCULATIONS The residue 1 stress distributions in figure 2 were input to the program pc-CRACK. Using these distributions together with Vermont Yankee geometry information, the program was then used to calculate stress intensity as a function of crack depth. A similar calculation was performed assuming on opplied stress of 15.088 ksi, factored by the ratio of the pipe well thickness to the overley repaired thickness.That is, APPLIED STRESS = 15.088 X (PIPE WALL /(PIPE WALL +0VERLAY)
The results of these calculations are shown in figure 3. In this figure, stress intensity is plotted egoinst crack depth into the composite (ptpe +
overleg) well for e 0.5" total thickness overleg. Note that the figure demonstrates that the net stress intensity (Kapplied + Kresidual) remains negative well beyond the flew depth corresponding to the original pipe well thickness.This demonstrates that no IGSCC crack growth would be enticipated for this weld overleg design.
7.0 CRACK GROWTH CALCULATIONS l
l Inconel 82 and 182 behave similarly to stainless steel with regard to IGSCC. Some of the available date on inconel IGSCC crack growth rties is l
presented in figure 4 (reference 1.3), which also presents stainless steel date. A crack growth correlation which bounds the eyeilable date is i
de/dt = 1.078 x 10-0 2.26 K
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de/dt is in units of inches / hour K is the stress intensity in units of ksi-/ inches Crack growth calculations were performed assuming en initial crack which was through the original pipe well.The residual stresses, epplied stresses, and crack growth correlation described above were input to e l
pc-CRACK celculation. As discussed in the previous section, the combined stress intensity K is negative for flow depths greater then the original well thickness. Review cf the crack growth correlation above leeds to e prediction of no growth due to IGSCC over the life of the repelr.The integrity of the overleg is not expected to be degraded during this period.
8.0 CONCLUSION
The overley design in figure 1 meets the requirements of Section XI.
Analysis shows that e through well flew would be errested by the residuel stress benefits of the weld overley application. Because of the uncertainty associated with flew definition,it is recommended that re-inspection and re-evoluetton of the repairs be performed efter I cycle of operation, to confirm the acceptebility of the repairs for subsequent cycles.
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INCONEL 182 SUTTER FLAW LOCAT10N A
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WELD OVERLAY DESIGN VERMONT YANKEE CORE SPRAY l
NOTES:
- 1. 0YER ALL VELD OVERL AY DESIGN THICKESS E O.50*.
- 2. VELD E AT WPUT TO ele APPLED W TE SEQUENCE SHOVN l
N ACCORDANCE VITH PARAFTTERS GNEN N TE LETTER FROM l
A.J. GI AfefUZZi TO J0Wi HOFFM AN, D ATED APRIL 11,1 %6 ( AJG-86-025). VELD SEQUENCE l
TO BE PERFORf4D M ACCORD ANCE VITH AJG-06-025, OR ALTERN ATlYELY, W ACCORD ANCE VITH TE LETTER D ATED M AY 1,1986 ( AJG-96-031, S AK CORRESPOPOENTS).
DESIGN NUMBER: YAEC-05-01 REVISION: 1 DATE: 5-2-66 PREPARED BY/DATF j [-2-W[g jf-2-kh REVIEWED BY/DATF na l
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pc-CRACI (C) COFYRIGHT 1984 19E6 9
STRUCTURAL INTEGRITY ASSOCIATES. INC.
SAN JOSE, CA (406)976-8000 VERSION 1.1 WELD OVERLAY SITING EVALUATION WELD OVERLAY SIZING FOR CIRCUMF. CRACK, WROUGHT / CAST STAINLESS VERMONTYANKEE CORE SPRAY WELD OVERLAY WALL THICKNESS =
0.9390 MEMBRANE STRESS = 3662.3000 BENDING STRESS =
4851.0000 STRESS RATIO =
0.4921 ALLOWABLE STRESS =173OO.OOOO FLOW STRESS =51900.OOOO L/ CIRCUM O.00 0.10 0.20 0.30 0.40 0.50 FINAL A/T O.7500 0.7500 0.7500 0.7500 0.7500 0.7373 OVERLAY THICKNESS 0.3130 0.3130 0.3130 0.3130 0.3130 0.3346 END OF pc-CRACK l
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SAN JOSE, CA (405)978-8200 VERSION 1.3 LINEAR ELAFTIC FRACTURE MFCHANICE EsLLUAT]ON VERMONT YANKEE CORE SPRAY : RESIDUAL AND FACTORED APPLIED STRESSES CRACK MODEL: CIRCUMFERENTIAL CRACK IN CYLINDER (T/R=0.1)
WALL THICKNESS =
1.4400 STRESS COEFFICIENTS CASE ID CO C1 C2 C3 VY144DL
-13.6306
-112.8590 214.8675
-70.7868 VYCGAPL 9.7810 0.0000 0.0000 0.0000 CRACK ------------------------STRESS INTENSITY FACTOR-----------------------
DEPTH CASE CASE VY144DL VYCGAPL O.0230
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-6.98 4.15 0.0691
-9.25 5.10 0.0922
-11.44 5.92 0.1152
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-15.67 7.31 0.1613
-17.83 7.97 0.1843
-19.99 8.62 0.2074
-22.14 9.25 0.2304
-24.26 9.86 0.2534
-26.35 10.46 0.2765
-28.41 11.05 0.2995
-30.49 11.66 0.3226
-32.61 12.29 0.3456
-34.68 12.93 0.3686
-36.71 13.56 0.3917
-38.67 14.20 0.4147
-40.58 14.83 O.4378
-42.47 15.50 0.4608
-44.48 16.28
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-48.26 17.86 0.5299
-50.02 18.66 0.5530
-51.69 19.47 0.5760
-53.25 20.28 0.5990
-54.86 21.16 0.6221
-56.36 22.04 0.6451
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-63.42 27.67 0.7834
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-65.77 30.79 0.8525
-66.26 31.86 0.8755
-66.49 32.98 0.8986
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-66.17 35.33 0.9446
-65.72 36.53 0.9677
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-63.29 40.23 1.0368
-62.53 41.59 1.0598
-61.52 42.98 1.0829
-60.27 44.37 1.1059
-58.76 45.78 1.1290
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