ML20214Q385

Safety Evaluation Re Insp & Repair of Reactor Coolant Piping Sys

ML20214Q385
Person / Time
Site:	Quad Cities
Issue date:	11/17/1986
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20214Q367	List: ML20214Q364 ML20214Q385
References
NUDOCS 8612050139
Download: ML20214Q385 (4)

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4, , S SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATING TO INSPECTION AND REPAIR OF REACTOR COOLANT PIPING SYSTEMS COMMONWEALTH EDISON COMPANY OUAD CITIES NUCLEAR p0WER STATION, UNIT 1 ,

DOCKET NO. 50-254

1.0 INTRODUCTION

During the Quad Cities Unit 1 Spring 1986 refueling outage, a total of 58 Intergranular Stress Corrosion Cracking (IGSCC) susceptible stainless steel welds in the reactor coolant piping systems were ultrasonically inspected. Three weld overlay repaired welds (12-inch recirculation pipe to elbow), three Inconel buttered recirculation nozzle-to-safe-end welds (1 28-inch and 2 12-inch) and a cracked recirculation weld 02BS-59 (28-inch) not repaired in last refueling outage were among the welds inspected. The licensee's (Commonwealth Edison Company, Ceco) original sample size for inspection was 54 welds. As a result of NRC's recommendation, four additional 28-inch recirculation welds were added to the inspection sample.

2.0 DISCUSSION 2.1 Ultrasonic Examination Ultrasonic examinations for IGSCC were performed by qualified ultrasonic testing (UT) personnel from General Electric Company (GE) for the licensee.

The examiners performing IGSCC detection and discrimination were requalified at Electric Power Research Institute (EPRI), Nondestructive Examination (NDE) Center. The crack depth was determined by using dp drop and crack tip diffraction techniques and the SLIC-40 transducer. Final review of reported indications was performed by qualified CECO level III UT examiners.

For inspecting overlay repaired welds, the overlay surface was machined to a finish of 125 rms and the EPRI recommended techniques were used.

2.2 Inspection Results The inspection performed during this refueling outage did not identify any new cracked weld. The crack growth in the unrepaired weld 02BS-59 was reported to be not significant. However, some minor circumferential cracking was observed in the elbow side of this weld during this inspection, wnereas during 1984 inspection, most of these indications were evaluated as ID geometry or slags. The licensee attributed the discrepancies of the inspection results in this unrepaired weld due to the use of enhanced transducer and better trained examiners in the current inspection. As discussed below, this weld was evaluated for justification of continued operation without repair for another 18-month fuel cycle by a fracture mechanics evaluation, e612050139 861117 PDR ADOCK 05000254' O PDRi.

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l The inspection results of the three overlay repaired welds indicated l that no circumferential cracks were observed in the weld overlays or in i the outer half thickness of the original pipe wall, however, several j axial indications were found in the dilution zone of the weld metal and i base metal interface. ,Most of these axial indications were reported to be associated with steam blow out repairs. The licensee attributed the finding of new axial indications in this cutage due to better pre-paration of the overlay surface of the repaired welds. .

2.3 Fracture Mechanics Evaluation NUTECH perfomed the fracture mechanics evaluation of the cracked recirculation 28-inch weld 02SB-S9 for the licensee. The crack growth evaluation was based on the use of a total sustaining stress of 8105 psi including a weld overlay shrinkage stress of 900 psi, a crack depth of 24% of the pipe wall thickness and the post-induction. heat stress improve-ment (IHSI) residual stress distribution. The calculated final crack size at the end of a 1300-h'our period is well within the allowable of ASME Code Section XI Table 3641-5 for flux valds as well as the NRC acceptance criteria in Generic letter 84-11. Therefore, theilicensee concluded that weld 01BS-S9 was acceptable for continued operation without repair for another 18-month fuel cycle.

2.4 Weld Overlay Desing NUTECH upgraded the overlay designs of'three welds (02C-24, 02J-S4 and 02K-S3) inspected during this outage to full structural overlays because the thickness of these overlays were reduced as a result of surface preparation for ultrasonic inspection.

NUTECH also re-evaluated the adequacies in overlay repairs of the other 13 repaired welds not inspected during this outage. The results of NUTECH's re-evaluction indicated that the as-built overlay thickness ,

in those repaired welds meets the ASME Code Section XI and Generic Letter 84-11 requirements.

2.5 NRC Region III Input 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 report (50-254/85030) that the nondestructive examinations were performed by qualified personnel and that no violations of NRC requirements were identified.

3.0 ,E_ VALUATION _

We have reviewed the licensee's submittals to support the continued  ;

operation of Quad Cities Unit 1 for an 18-month fuel cycle in its l present configuration. i

3.1 Scope of Inspection Except for the inspection of the IHSI treated 12-inch recirculation riser welds, the percentage of welds inspected in each pipe size meets the ,

Eguidelines in Generic letter 84-11. The licensee followed the guidelines in NUREG-1061 for inspecting the IHSI treated 12-inch recirculation riser welds; a total of two such welds were inspected. NRC staff considers the licensee's inspection of the IHSI treated recirculation riser welds during this outage acceptable because all of the subject welds were UT inspected af ter IHSI treatment during the previous refueling outage.

In the proposed NUREG-0313. Revision 2, all IHSI treated welds are recommended to be 100% re-inspected within three and one-third years subsequent to the post-IHSI inspection. Recently, many IHSI treated welds were reported to be cracked in Pe~ach Bottom Unit 3. These welds were reported to be not cracked in the post-IHSI inspections. Therefore, the licensee should consider inspecting more of those IHSI treated welds during the next refueling outage.

!' 3.2 Unrepaired Weld 01BS-S9 NUTECH's fracture mechanics evaluation took credit for the favorable post-IHSI residual stress distribution. In view of the new crack-like indications found in the elbow side of this weld after IHSI treatment, NRC staff considers NUTECH's method of evaluation not very conservative.

NRC staff has performed an independent crack growth evaluation based on an as-welded ' residual stress. distribution and a maximum crack depth of 24%

of the pipe wall thickness. The result of the evaluation indicated that the final crack depth (42% of the pipe wall thickness) at the end of an 18-month period is well within the ASME Code allowable for the flux welds. Therefore, NRC staff concludes that the unrepaired weld 02BS-S9 can be safely operated for another 18-month fuel cycle.

3.3 Repaired Weld 02BS-S12 Both welds 02BS-S9 and 02BS-512 were found crachc-d during the previous refueling outage. The flaws in weld 02BS-512 were removed by core drilling and the holes were repaired by installing half-couplings. In.

view of the finding of new crack indications in weld 02BS-59 during 1986 refueling outage, NRC staff recommends that 02BS-512 be inspected during the next refueling outage to ensure that no cracks were missed during previous inspections and that no new cracks have developed.

3.4 Overlay "epaired Welds No new weld was overlay repaired during the outage. Three of the sixteen -

previously repaired welds containing circumferential flaws over 10% of the pipe circumference were inspected during the outage. The overlays of j these three welds were upgraded to full structural overlays to accommodate l

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the reduced overlay thickness due to surface conditioning for inspection.

the upgraded overlay thickness is thicker than the original thickness.

Of the 13 repaired welds not inspected in this outage, 7 contained only axial flaws and 6 contained both axial and circumferential flaws. NUTECH's overlay design evaluation has shown that the as-built overlay thickness of each of the 16 repaired welds meets the ASME Code requirements and the staff acceptance criteria. Therefore, based on the inspection results of the 3 repaired welds and the adequate overlay reinforcement of each repaired weld, as denonstrated by NUTECH's evaluation, NRC staff concludes that all 16 overlay repaired welds can be safety operated for one more 18-month fuel cycle.

4.0 CONCLUSION

Based on our review of the licensee's submittal, NRC staff concludes that the IGSCC inspection performed during the 1986 refueling outage provides assurance that Quad Cities Unit 1 can be safely operated in its present configuration for an 18-month fuel cycle.

i Nevertheless, NRC staff is still concerned ~with long term growth of small cracks that may be present which have not been detected during these inspections. Therefore, plans for inspection and/or modification of the recirculation and any other service sensitive austenitic stainless steel piping systems operating above 200*F should be submitted for our review at least 3 months before the start of the next refueling outage.

Principal Contributor: W. Koo, T. Rotella Dated: November 17, 1986.

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