ML20205H135

Safety Evaluation Re Insps for & Repairs of Igscc.Facility Can Be Safely Operated for One 18-month Fuel Cycle in Present Configuration

ML20205H135
Person / Time
Site:	Quad Cities
Issue date:	03/23/1987
From:	Office of Nuclear Reactor Regulation
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ML20205H123	List: ML20205H118 ML20205H135
References
NUDOCS 8703310635
Download: ML20205H135 (5)

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1. o UNITED STATES

! 1 NUCLEAR REGULATORY COMMISSION

$ $ WASHINGTON, D. C. 20555

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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATING TO INSPECTIONS FOR AND REPAIRS OF INTERGRANULAR STRESS CORROSION CRACKING OUAD CITIES NUCLEAR POWER STATION, UNIT 2 COMMONWEALTH EDIS0N COMPANY (CECO)

DOCKET N0.: 50-265

1.0 INTRODUCTION

During the current Quad Cities Unit 2 refueling outage, a total of 127 welds susceptible to intergranular stress corrosion cracking (IGSCC) were ultrason-ically inspected. Those inspected welds included 99 stainless steel piping welds, 2 recirculation safe end welds, 2 jet pump instrumentation nozzle penetration welds,14 overlay repaired welds and 10. unrepaired piping welds.

The details of the inspected welds in terms of systems and pipe sizes'are provided in Table 1.

The results of the inspection showed that crack-like indications were observed in five additional recirculation welds (3-12" and 2-28" welds). Of the five flawed welds reported in this outage, four welds were overlay repaired and one 28-inch weld (02BD-F8) was left in as-is condition. The licensee (CECO) provided a fracture mechanics analysis to justify continued service of weld 02BD-F8 for one fuel cycle without overlay repair. During this outage, all 14 weld overlays applied in the previous refueling outages were upgraded to full structural thickness. Of the 10 flawed welds left in as-is condition fran previous inspection; two welds were overlay repaired because additional axial flaws were found; two welds were determined to be not cracked; and the other six welds did not show any significant changes in flaw sizes from the previous examinations.

2.0 DISCUSSION The staff has reviewed the licensee's submittals including the inspection results, NUTECH's flaw evaluations and overlay designs to support the continued operation of Quad Cities Unit 2 for one 18-month fuel cycle in its present configurations. The details of the review follows:

Scope of Inspection:

The licensee indicated that all the large diameter (212") piping welds in the recirculation system were inspected during this outage, because crack-like indications were found in the samples of previously unflawed recirculation piping welds. The inspection sample was expanded twice from the initial 67 welds to a final sample of 127 welds. Except for the large diameter recirculation piping welds, approximately 20% of the welds in each pipe size were inspected. The current inspection also inspected i

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all the overlay repaired welds and flawed welds not repaired in the <

previous outages. The licensee's sample expansion method did not completely meet the guidelines in Generic Letter 84-11; however, considering that all the IGSCC susceptible welds were inspected during the previous two refueling outages and that a large number of those welds were mitigated ,

with induction heating stress improvement (IHSI), we conclude that the scope of the current inspection performed during this outage is acceptable.

Ultrasonic Examination:

The licensee reported that the ultrasonic examinations were performed by EPRI qualified General Electric personnel, and the evaluations of indications, review of data package and final acceptance of indications were made by qualified CECO UT personnel. In the examination of the weld overlays, the surfaces were conditioned and the EPRI NDE Center developed guidelines +

were followed.

The NRC Region III inspectors have selectively reviewed the ultrasonic examination procedures and data, and held discussion with examiners regarding the nondestructive examinations performed during this outage.

NRC Region III concluded in their inspection reports (50-254/86019 and 50-265-86014 dated January 30,1987) that the nondestructive examinations were performed by qualified personnel and that no violations of NRC requirements were identified.

Five new welds were found flawed during this outage. The worst circum-ferential flaws were reported in a 28-inch safe end-to-elbow weld 02BS-F2 (recirculation suction line) with a total length of 15 inches and a maximum depth of 73% through wall. A small pinhole leak was found in a 12-inch safe end-to-pipe rise weld (02K-S3). All five new flawed welds were examined in 1983 cutage after IHSI, with geometric indications reported in three of the 5 welds in the 1983 inspection. The licensee

! contended that these crack-like indications were present in 1983 but were missed since the 1983 examiners were not as skillful or experienced as the 1

1986 requalified examiners in IGSCC detection. Since some question exists -

i regarding when the cracking occurred and there is a lack cf service experience l with IHSI mitigated welds we require that the licensee reinspect all the IHSI l treated welds over the next two refueling cycles.

l Unrepaired Welds:

A total of seven flawed welds,six previously unrepaired welds and one new flawed weld, were left in as-is condition. The current inspection results have shown that the flaw sizes in the six previously unrepaired welds did not change significantly in length or depth from that reported in the previous l

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outages. Justification for continued service of these six welds was based on previously performed fracture mechanics evaluation. Two welds (28S-F14 and 285-S12) which were previously identified as cracked were determined not to be.

cracked because the UT indications were identified as root geometry. Since some uncertainty exists regarding these two welds they should continue to be inspected. Of the five welds found cracked during this outage, only one weld (02BD-F8) was not repaired. Weld 02BD-F8 is a 28-inch valve to elbow weldlin the recirculation pump discharge piping. Circumferential cracking was observed on the elbow side with a combined length of 4 1/2 inches and a maximum depth of 15% through wall. NUTECH performed the flawed pipe analysis for the licensee in accordance with ASME B&PV Code and NRC requirements. The results of NUTECH's evaluation showed that weld 02BD-F8 did not require weld overlay repair. The ifcensee also reported that all unrepaired welds were successfully treated with IHSI. The staff agrees with the licensee's conclusion that these seven unrepaired welds can be safely operated for one 18-month fuel cycle because the flaws in those welds are shallow (6 22% wall thickness) and are not expected to grow beyond the Code allowable limits in one fuel cycle.

Weld Overlay Repairs:

During the current refueling outage, a total of six new wefds were reinforced with weld overlays; four were currently identified as flawed welds, and two were previously unrepaired welds which now require repair because additional axial flaws were found by the current inspection. In addition, all weld overlays (14) repaired in previous outages were upgraded to neet the requirements for full structural design and were ground to facilitate llT inspections.

NUTECH designed the weld overlays for the licensee. We do not completely I agree with NUTECH's design of full structural overlay because the minimum design wall thickness instead of the actual pipe wall thickness was used in the evaluation. However, based on the reported as-built overlay thicknesses, all overlays except weld 02A-S10 qualify as full structural or standard designed overlays.

Weld 02A-S10 (22-inch end cap) was overlay repaired during this outage becausc additional axial flaws were found. During the overlay repair, nine " steam-blow-outs" were observed in the first four layers. All

" steam-blow-outs" were reported to be repaired by standard practices including excavation and seal weld, and followed by liquid penetrant examination. A total overlay thickness of 0.48-inch (7 layers) was applied to weld 02A-S10. After completion of overlay repair, UT exam-inations, using both manual and automatic modes were performed. One circumferential and eight axial flaws were found in the weld overlay metal. BasedontheaverageUTmeasurements(bothmanualandautomatic),

the minimum thickness of the overlay over the circumferential flaw was reported to be 0.33 inch. NUTECH's evaluation indicated that this thickness l

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met the minimum thickness required for a full structural overlay. However, the staff considered NUTECH's overlay evaluation for weld 02A-S10 not conservative because the actual wall thickness and the flawed portion of the overlay were neglected in calculating the minimum thickness of the full structural overlay.- Since the overlay thickness of weld 02A-510 does not completely meet the staff's criteria for full structural or standard overlay design, we have determined that the subject repaired weld is acceptable for

. limited service of one 18-month fuel cycle. For service beyond one fuel cycle, additional mitigation should he applied to this weld. The staff strongly recommends the replacement of weld 02A-S10 since the tensile residual stresses in the weld metal are expected to promote growth of the deep flaws that are present.

3.0 CONCLUSION

Based on our review of the licensee's submittals, we conclude that Quad Cities Unit 2 can be safely operated for one* 18-month fuel cycle in the present configuration.

Principal Contributor: .W. Koo Dated: March 23, 1987 l

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4 Table 1.

Quad Cities Unit #2 Summary of 1986 IGSCC Inspection Results

. Total Number of Number Number overlay of of repaired unrepaired Welds System Size Total Welds Welds Examined Recirculation 83' 85' 86' 83' 85' 86' -t Risers 12" 44 4 3 3 2 0 0 44 Header 22" 22 0 0 2(1) (1) 0 0 22 ,

Outlets 28" 30 4 1 1 4(2) 0 1 30 ,

SE (Thermal Sleeve 12" 10 0 0 0 0 0 0 2  ;

LPCI 16" 32 0 0 0 0 0 0 6 SDC 20" 18 1 1 'O O O O 5 CS 10" 27 0 0 0 0 0 0 5 HS/RWCU 6" 13 0 0 0 0 0 0 4 RECIRC/CRD HS/HV 4" 34 0 0 0 0 0 0 7 JPI 10 0 0 0 0 0 0 2 Total Number of Welds 240 (9 + 5 + 6) = 20 (6 + 0 + 1) = 7 127 l Notes: (1) Two 22-inch end cap welds found cracked in 1983 were overlay repaired during this outage i because additional axial flaws were observed.

(2) Two 28 inch welds reported to show crack-like indications in 1983 were determined to be not cracked during this outage.

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