ML20138Q111
| ML20138Q111 | |
| Person / Time | |
|---|---|
| Site: | Peach Bottom  |
| Issue date: | 12/20/1985 |
| From: | Daltroff S PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC |
| To: | M Uller D, Muller D Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML20138Q114 | List: |
| References | |
| GL-84-11, IEB-83-02, IEB-83-2, NUDOCS 8512270055 | |
| Download: ML20138Q111 (6) | |
Text
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PHILADELPHIA ELECTRIC COMPANY 23O1 MARKET STREET P.O. BOX 8699 PHILADELPHIA. PA.19101 (215) B41-5001 SHIELDS L. D ALTROFF ELECTm C Pm c on December 20, 1985 Docket No. 50-278 J
Mr. Daniel R. Muller, Director BWR Project Directorate #2 Division of Boiling Water Reactor Licensing U.S. Nuclear Regulatory Commission Washington, D.C.
20555
SUBJECT:
Peach Bottom Atornic Power Station Unit 3 Justification for Continued Operation Following In-Service Inspection and Repairs of Non-Conforming Austenitic Stainless Steel Piping Welds
REFERENCE:
(1)
Letter, S. L.
Daltroff, PECo, to J.
F. Stolz, USNRC, dated December 14, 1984 (2)
Letter, S. L.
Daltroff, PECo, to gg[
BWR - L/BC's TECH SUPPORT g,
p.
Stolz, USNRC, dated October 11, 1985 EB (LTAW) l)
Letter, S. L.
Daltroff, PECo, to PSB (L. HULMAN)
J.
F.
Stolz, USNRC, dated November 15, 1985 EICSB (SRINIVASAN) l}
Let ter, S. L.
Daltroff, PECo, to J.
F.
Stolz, USNRC, dated November 27, 1985 F
VAS 0)
Dear Mr. Muller:
This letter transmits an evaluation of the Peach Bottom Unit 3 Recirculation and Residual Heat Removal system crack indications.
The evaluation jus ti fies an additio".al eighteen months of continued operation.
The evaluation is provided in the attached document titled, " Weld Overlay Desigrf and Analysis fo r the Indications in the Peach Bottom Unit 3 Recirculation and Residual Heat Removal System" (Attachment 1).
Peach Bottom Unit 3 was removed from service on July 14, 1985 for a refueling and pipe weld inspection outage and is expected to return to service January 10, 1986.
The weld inspections have been completed in response to Generic Letter 84-11, " Inspections of BWR Stainles s Steel Piping", dated April 19, 1984.- The scope of the welds exam ined is as described in to the reference (1 ) letter.
Og egg 22;ggg gig 2,g, gl g G
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r Mr. Daniel R. Muller December 20, 1985 Page 2 The inspection identified eighteen pipe welds on the Recirculation System with crack indications, of which thirteen have been subsequently repaired by weld overlay methods.
Twelve pipe welds were found to exhibit crack indications on the Residual Heat Removal System.
Five of those welds were repaired with weld overlays.
Tables 1 and 2 of Attachment 1 summarize the
~isposition of these welds.
d The evaluation provides the technical basis for (1) the acceptability of indications not requiring repairs, (2) designing weld overlays for indications that require repair, and (3) determining the ef fect of the weld overlay shrinkage on the system.
The analyses are in compliance with the requirements of the ASME Code Section XI and Generic Letter 84-11.
The results verify that all of ~the repaired and unrepaired welds are acceptable for at least an additional eighteen months of continued operation.
Further, an in-house safety evaluation has been prepared (Attachment. 2) concerning the Unit 3 weld inspection program.
If you have any questions or require additional in fo rma tion, please do not hesitate to contact us.
Very truly yo_urs,
/ )
/7
~ %/
}"f IP y
Attachme nts cc:
Dr.
T.
E. Murley, Administrator, Region I, USNRC T.
P. Johnson, Resident Site Inspector
s
- Docket No. 5 0-278 December, 1985 ATTACHMENT 2 Safety Evaluation for the Operation of Peach Bottom Atomic
SUBJECT:
Power Station Unit No. 3 for at Least 18 Months.
I NTRODUCTION During 'the Peach Bottom Unit 3 outage which began on July 14, 1985, Philadelphia Electric Company, through contracts with General-Electric Company (GE) and Southwest Research Institute
. (SwRI), pe rformed ultrasonic examinations of welds in the recirculation and residual heat removal (RHR) sys tems.
These examinations were performed as required by USNRC Generic Letter 84 -11, NUREG 0313, and the ASME Boiler and Pressure Vessel Code Section XI ten-year inservice ' inspection program.
A total' of one-hundred and thirty-two (13 2) welds h1 IGSCC susceptible material were examined with the result that IGSCC cracking 'was' detected in forty (40) welds in which it had not been previously-detected.
Thirty (30) of these were butt welds
' in the recirculation and RHR systems and ten (10) were thermal sleeve attachment welds on the recirculation inlet safe ends.
Included in the one-hundred and thirty-two (132) welds examined were five (5) RHR system welds and two (2) jet pump instrumentation penetration welds which were weld f averlay repaired in 1983 and 1984 respectively.
These examinations determined-that the overlays were sound and that the IGSCC cracks had not grown since their repairs.
These seven (7) ' welds are not included in the current total of forty (40) welds with cracking.
Philadelphia Electric Company contracted GE to analyze the welds with indications arVI to make : recommendations.
Using. acceptance criteria from Generic Letter 84-11 and the ASME Code Secticn XI, GE determined that twenty-two (22) welds could be operated without repair for a minimum of eighteen (18) months.
These included twelve (12) butt welds - seven (7) RHR and five (5)
Recirculation - and the ten (10) Recirculation inlet saf e end thermal sleeve attachment welds.
The remaining eighteen (18) butt welds were recommended for ove rlay repair.
These included five (5) RHR welds and thirteen (13) Recirculation welds.
GE provided designs fo r full structural ove rlays which met the requirements of Generic letter 84-11 and provided the ASME code safety margins.
The overlays were completed.by welders qualified to procedures developed by GE
ATTACHMENT 2 Docket No. 50-278 Page 2 in concurrence with the on-site representative of the Hartford Steam-Boiler Inspection and Insurance Company.
DISCUSSION A.
Examination The ultrasonic examination procedures used in dhe detection of the crack-like indications had been demonstrated to be capable of finding IGSCC cracking at the EPRI NDE Center in Charlotte,. N rth Carolina.
The technicians participating in o
the examination were-qualified as being able to detect service induced IGSCC by an actual demonstration using cracked specime ns in accordance with NRC IE Bulletin 83-02 and Generic Letter 84-11.
All indications were verified by an independent examiner.
GE ve rif ied the SwRI findings and vice versa.
All sizing was performed by examiners qualified in sizing at the EPRI NDE Center.
B. - Analysis Fracture Mechanics Analysis was performed by GE in accordance with Section XI, Appendix X of the ASME Code.
For all welds to be operated without repair, the calculated growth 'was less than the limit for net section collapse with a safety factor of 3.0 and was also less than 2/3 of the limit for depth and length-provided in the ASME Code Section XI, paragraph IWB-3640.
In addition, calculated crack sizes in pipe butt welds were less than the allowable flaw size proposed in Section XI, Table IWB-3641-5.
The analysis was conservative in that the crack depth assumed was the peak depth measured by ultrasonic examination.
In all cases the crack growth af ter 18 months of operation was calculated to be less than the above criteria.
All butt welds to be operated without repair except welds 2-AS-8 'and 2-BD-12 also met the criteria for length and depth set forth in Generic Letter 84-11.
PECo. has committed to performing a mid-cycle examination of these two (2) welds which do not meet the criteria.
Additional information is available in PECo correspondence to the NRC dated November 15, 1985.
Crack growth calculations for the ten (10) recirculation inlet safe end thermal sleeve attachment welds also demonstrate that they can be operated without repair for at least eighteen (18) months.
However, because many of these cracks exceed the limits for length and depth set forth in Gene ric Letter 84-11, PECo. has also committed to a mid-cycle inspection of the two (2) most severely cracked safe-ends.
ATTACHMENT 2 Docket No. 50-278 Page 3 Additional information is available in PECo correspondence to the NRC dated November 27, 1985.
C.
Repairs The overlay designs used to repair the eighteen (18) RHR and recirculation butt welds are conservative since they were designed to accommodate a hypothetical through-wall crack, 360 degrees in circumference.
The ove rlay welds as applied are full structural overlays and meet all the requirements of NRC Generic Letter 84-11.
The welding procedures and welders used to perform the weld ove rlays were qualified to procedures which meet the requirements of the ASME Code Section III, 1983 Edition including the Summer 1983 Addenda.
The welding procedures required adequate cooling water inside the pipe which produced compressive stresses on the inside diameter.
Crack propagation into the weld metal is not likely to occur by IGSCC since the high ferrite weld material is not susceptible to IGSCC.
Additional conservatism was built into the overlay repairs in that no credit for thickness was taken until acceptable ferrite readings were achieved.
This meant that at least one (1) laye r of weld mate rial (and in some cases two (2) ) was applied before credit for thickness was take n.
Inspection of the completed ove rlays included visual, liquid penetrant, and ultrasonic to verify the soundness of the overlay.
CONCLUSION It is concluded, based on Ehe considerations discussed above, that:
1.
The Unit 3 ultrasonic examination was conducted by personnel trained in the detection and sizing of IGSCC cracking and qualified by ultrasonic technique demonstration at the EPRI NDE Center in Charlotte, North Carolina, in acco rd ance wi th I. E.
Bulletin 83-02 and NRC Generic Letter 84-11.
The procedures and instrumentation used in this examination have been proven capable of detecting and characterizing intergranular stress corrosion cracking with a high level of certainty.
2.
The Fracture Mechanics Analysis perfo rmed on the crack indications and the applied ove rlay temporary repairs possess an inherent safety factor of three (3) and provide full structural margins in accordance with NRC Generic Letter 84-11.
ATTACHMENT 2 Docket No. 50-278 Page 4 3.
The overwhelming laboratory and indus try experience to date has shown that if piping af fected by IGSCC should fail, such failure would result in leak before break.
It can be concluded that Pea 6h Bottom Atomic Power Station Unit 3 can operate at f ull powe r fo r at least eighteen (18) months with reasonable assurance that the health and safety of the public will not be endangered.
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