ML20236J815
| ML20236J815 | |
| Person / Time | |
|---|---|
| Site: | FitzPatrick  |
| Issue date: | 07/30/1987 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20236J798 | List: |
| References | |
| NUDOCS 8708060292 | |
| Download: ML20236J815 (4) | |
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p atto UNITED STATES e-'
NUCLEAR REGULATORY COMMISSION I
o WASHINGTON, D. C. 20555 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATING TO INSPECTIONS FOR AND REPAIRS OF IGSCC JAMES A. FITZPATRICK NUCLEAR POWER PLANT POWER AUTHORITY OF THE STATE OF NEW YORK
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DOCKET N0. 50-333 INTRODUCTION During the Reload 7/ Cycle 8 refueling outage, a total of 48 welds susceptible to intergranular stress corrosion cracking (IGSCC) were ultrasonically inspected. The inspection sample included eight Inconel-182 buttered nozzle-to-safe end welds, six overlay repaired welds, and six unrepaired piping welds.
The results of the inspection showed that crack-like indications were observed l
in three core spray welds. These three welds were reinforced with weld overlays.
Ten recirculation piping welds with previous indications were also inspected.
Five of those welds were confirmed to have IGSCC and two other welds were con-servatively evaluated as containing IGSCC.
These seven welds were justified for k
continued service without repair by a fracture mechanics evaluation.
The licensee 1
plans to implement hydrogen water chemistry in the fall of 1987 to further mitigate IGSCC. To ensure timely detection of unidentified leakage, the licensee also plans to implement augmented leakage surveillance in accordance with the requirements of Generic Letter 84-11, Attachment 1.
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l EVALUATION The staff has reviewed the licensee's submittals dated March 10 and April 9,1987.
Contained in these submittals are the inspection results, flaw evaluations, and overlay designs to support the continued operation of FitzPatrick for one 18-month fuel cycle in its present configuration.
The details of the review follow:
Scope of Inspection:
The licensee's initial inspection sample of 42 welds was patterned after the 1
draft NUREG-0313. Revision 2 as issued for public comment, with some exceptions for category C, D and G welds.
The inspection schedule for category C, D and G welds was lengthened by a factor of two, because the licensee took credit for hydrogen water chemistry, and because of the concern for high radiation exposure to inspection personnel. Although we do not agree with those exceptions 8708060292 870730 DR ADOCK 0500 3
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(hydrogen water chemistry has not yet been implemented), we find that the licensee's initial sample size is consistent with that required by Generic j
L Letter 84-11 and, therefore, is acceptable.
The inspection sample was expanded j
from the initial 4? welds to 48 welds because crack-like indications were found in two core spray welds (category D) and data interpretation differences were noted in four category C and E welds.
8 Six welds in the residual heat removal (PHR) system were scheduled to be
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inspected by the MINAC technioue (high eneray radiographic inspection) because l
the configuration of these weMs prevented normal ultrasonic inspection.
After i
inspecting several welds, the MINAC process was abandoned because the quality I
of the radiographic films produced was not acceptable for interpretation.
j Instead, these welds were inspected by dye penetrant, and were not included in the final count of the inspected welds.
The licensee indicated that a new procedure (MINAC or automated UT) will be developed to inspect these six welds during the next (1988) refueling outage.
We conclude that the scope of the inspection performed during the Reload 7/ Cycle 8 refueling outage is acceptable.
Ultrasonic Examination:
i The licensee reported that the detection of IGSCC was performed by EBASCO
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using manual techniques and by Independent Testing Labs (ITL) using automated l
P-scan. All IGSCC indications were sized by two EPRI-qualified inspectors i
from EBASCO and General Electric.
I The overlays of six previously repaired welds were inspected by qualified personnel using EPRI NDE Center procedures.
Prior to inspection, the overlay surfaces were mechanically, finished to enhance inspectability.
No indications i
were found in these welds. Because of the high radiation environment (8 person-i rem), the overlays of the three core spray welds repaired during this outage were not surface finished, and were inspected for bonding only. The licensee indicated that the core spray piping, including the three repaired welds, is scheduled for replacement during the next refueling outage.
In view of the j
favorable industry experience with weld overlay repairs, we consider this one.
time deviation in overlay inspection acceptable.
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Ten recirculation piping welds (12-4, 12-17, 12-61, 12-81, 28-48, 28-53, 28-56, 28-57,28-112 and 28-113) with previous indications were reinspected i
during this outage.
In 1984, seven of these welds (12-17, 12-61, 12-81, 1
28-48, 28-56, 28-57 and 28-113) were initially reported by EBASCO to have l
relevant indications. After further evaluation by a second contractor, KWU (Kraftwerk Union), the indications in welds 12-61, 12-81, 28-56 and 28-57 were determined to be tool marks, fusion line indications, or root geometry.
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1985, only welds 12-4, 28-53 and 28-112 were confirmed to contain IGSCC.
Reinspection of the above ten welds confirmed that five of the welds (12-61, i
28-48, 28-53, 28-56 and 28-113) were cracked.
The indications in these five j
welds were not significantly changed from previous examinations, with the exception of crack lengths in welds 28-53 and 28-113.
The apparent increase in flaw lengths was attributed to the use of improved inspection techniques during the Reload 7/ Cycle 8 outage and was not the result of crack growth.
The licensee indicated that eight of the ten welds (except welds 12-57 and 12-81) i will be reinspected during the next refueling outage.
However, in view of the widely known uncertainties in the discrimination of the UT indications, the staff
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recommends that all ten welds be reinspected during the next refueling outage.
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i Piping Replacement:
During the Reload 7/ Cycle 8 refteling outage, portions of piping in the recirculation, RHR and RWCU systems were replaced.
The recirculation bypass lines were removed and capped. The cap material was 304L and the 304 weld-o-let was cladded internally with 304L weld metal with ferrite number (FN1 greater than 8.
The suction piping in the RHR and RWCU systens was replaced with carbon steel mate-ial, and the 304 piping was clad with 308L i
weld metal (FN>8) when welded t: carbon steel piping.
The carbon steel piping and applied weld cladding of 304L and 308L are resistant to stress j
corrosion cracking, and are acceptable.
Flaw Evaluation:
Structural Integrity Associates (SIA) performed the flaw evaluation for the licensee on seven recirculation welds (12-4, 12-61, 28-48, 28-53, 28-56,28-112 and 28-113) conservatively identified as containing IGSCC indications.
These welds were all previously treated with induction heating stress improvement (IHSI). The evaluation was performed for the post-IHSI condition, and indicated essentially no crack growth in these seven welds.
For welds 28-53 and 28-113, an additional flaw evaluation was performed for the as-welded condition because the flaw lengths in these welds exceeded 10% of the circumference. The final flaw size at the end of 40,000 hours0 days <br />0 hours <br />0 weeks <br />0 months <br /> (about 4.5 years) was calculated to be about 43% of wall in depth, shich is acceptable according to IWB 3600 of the ASME Section XI Code.
Therefore, we conclude that the seven unrepaired welds can be safely operated for at least one 18-i month fuel cycle.
Weld Overlay Repairs:
Three core spray welds (493, 496 and 495) were found to be cracked and were overlay repaired.
The overlays for welds 493 and 496, which contained circum-ferential cracks, were designed using SIA's computer program PC-Crack to meet the standard weld overlay design as defined in the' draft NUREG-0313, Revision 2, Weld 495 contained four axial flaws, and its overlay was designed as a leak barrier consisting of only two overlay layers.
The design thicknesses for these welds did not include the first weld layer that passed the dye penetrant inspection.
The length of the overlay was designed to provide adequate structural reinforcement and to allow adequate ultrasonic inspection.
The licensee reported that all as-built overlay thicknesses and lengths exceeded the design values.
Six previously repaired overlays were surface finished prior to reinspection.
The overlay thicknesses (not including the first acceptable layer) were measured after surface finish, and were evaluated in accordance with the draft NUREG-0313, Revision 2.
The results of the evaluation showed that the thickness of each surface-finished overlay met the requirements of standard overlay design.
We conclude that the six previous overlays and three new overlays are acceptable for continued service for at least one 18-month fuel cycle.
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4 CONCLUSION l
Based on our review of the licensee's submittals, we conclude that the FitzPatrick plant can be safely operated for one 18-month fuel cycle in its i
present configuration, with the assurance that the integrity of the reactor coolant pressure boundary will be maintained.
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