ML20214A557

Safety Evaluation Re Insp & Repair of Reactor Coolant Piping Sys & Supporting Return to Operation for Next Operating Cycle

ML20214A557
Person / Time
Site:	Oyster Creek
Issue date:	11/14/1986
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20214A538	List: ML20214A537 ML20214A557
References
NUDOCS 8611200137
Download: ML20214A557 (3)

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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGUL'ATION RELATING TO INSPECTION AND REPAIR OF REACTOR COOLANT PIPING SYSTEMS GPU NUCLEAR CORPORATION JERSEY CENTRAL POWER & LIGHT COMPANY OYSTER CREEK NUCLEAR GENERATING STATION DOCKET N0.: 50-219

1.0 INTRODUCTION

During the current Oyster Creek Cycle 11 refueling (Cycle 11R) outage, a total of 151 stainless steel butt welds which were susceptible to inter-granular stress corrosion cracking (IGSCC) and 18 overlay repaired welds in the Recirculation, Shutdown Coolir.g, Reactor Water Cleanup, Core Spray and Isolation Condenser systems were ultrasonically inspected. Crack-like indications were found in three recirculation welds (26-inch diameter, NG-C-9A, NG-C-17 and NG-C-23) and an Isolation Condenser weld (12-inch diameter, NE-1-27) in the steam supply line outside the drywell. Weld overlay repairs were applied on welds NG-C-17, NG-C-23 and NE-1-27. Weld NG-C-9A was justified by GPU Nuclear (the licensee) for continued service without repair by fracture mechanics evaluations.

In addition, 64 recirculation welds including the unrepaired weld NG-C-9A were successfully treated with induction-heating-stress improvertent (IHSI).

2.0 EVALUATION We have reviewed the licensee's submittal dated October 3,1986, on the results' from the inspection program of the stainless steel piping during the Cycle 11R outage. This submittal included the inspection results and weld overlay designs to support the continued operation of Oyster Creek Nuclear Generating Station for the next 18-month fuel cycle in its present configuration with the weld overlay repairs.

2.1 S_ cope of Inspection Based on the information provided by the licensee on the sampling base and inspection history of each IGSCC susceptible piping system, we find the initial sample plan for inspection in accordance with Generic letter 84-11 which requires a minimum of 72 welds including 20 class 2 isolation condenser welds.

The licensee has inspected a total of 151 welds which is more than double that of the required minimum initial sample size. Furthermore, all IHSI treated welds and overlay repaired welds were ultrasonically inspected. Therefore, we have determined that the inspection scope performed during the current outage met the sampling and sample expansion guidelines in Generic letter 84-11, 8611200137 861114 R ADOCK 0500 9

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2.2 Ultrasonic Examination The licensee reported that the ultrasonic test (UT) examination and data evaluation were performed by UT personnel from General Electric Company (GE) and the licensee, who were qualified at the Electric Power Research Institute (EPRI) Non Destructive Examination (NDE) Center including requalification for IGSCC detection. In examining the overlay repaired welds, the overlay surfaces were conditioned procedures to EPRIBoth and techniques. requirements manual andand inspected by(using EPRI developedGE-sm automated used for IGSCC detection, however, only manual UT was used for flaw sizing.

The inspection results reported that crack-like indications were found in three recirculation welds and an isolation condenser weld. No 'IGSCC indications were found in the 18 repaired overlays and outer 25% of the original pipe wall.

The NRC Region I inspectors have selectively reviewed the ultrasonic examina-tion procedures and data, and held discussions with cognizant licensee personnel regarding the NDE performed during this outage. Region I concluded in its two inspection reports (50-219/86-19 dated 8/1/86 and 50-219/86-23 dated 9/5/86) that the NDE were performed by qualified personnel using the latest recognized techniques and equipment.

2.3 Weld Overlay Designs Two recirculation welds (NG-C-17 and NG-C-23) and an isolation condenser weld (NE-1-27) located outside the drywell were weld overlay repaired during this outage. A full structure overlay, was designed for each repaired weld in accordance with the requirements of American Society of Mechanical Engineers (ASME) Code,Section XI, IWB-3462 assuming a 360 degrees throughwall crack.

The overlays were deposited by the automated GTAW process with 308L stainless steel bar wire. Liquid penetrant examination was performed on the original pipe surface and the final overlay surface. The designed minimum overlay thickness included the thickness of the first layer that passed the ferrite ,

test. We find the minimum overlay thickness designed for the three repaired I welds allowed a maximum flaw depth up to 77% of the total thickness (overlay +

pipe wall), which exceeded the maximum Code allowable flaw depth of 75% of wall-thickness. The maximum allowable flaw depth of 75% of the wall thickness in ASME Code IWB-3641 tables is artificially determined and its purpose is to provide additional margin against leakage or failure when deep flaws are present. However, the average as-built overlay thickness of those repaired welds is reported to be thicker than the designed minimum overlay thickness.

Therefore, the thickness of all three repaired overlays met the ASME Code requirements including the maximum flaw depth limit as discussed above.

2.4 Unrepaired Weld NG-C-9A Recirculation weld NG-C-9A was reported to contain a circumferential flaw indication with a maximum flaw depth of 18% of the wall thickness and 2.2 inches in length. This weld was treated with IHSI. The licensee performed a fracture mechanics evaluation of this weld, which considered post-IHSI residual stress pattern. The evaluation result showed that this weld was acceptable for continued service without repair at least for one 18-month fuel cycle because the final flaw depth at the end of the evaluation period would not exceed the allowable flaw depth for flux welds in ASME Code,Section XI IWB-3640.

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As the reported flaw indication in this weld is short and shallow, we expect the IHSI treatment performed on this weld to be effective in prohibiting further crack growth and initiation.

3.0 CONCLUSION

Based on the evaluation of the above information, we conclude that Oyster Creek can safely return to operation for the next 18-month fuel cycle in its present configuration with the weld overlay repairs. Because the staff is concerned with long term growth of small cracks that may be present but were not detected during these inspections, we have requested,the licensee to submit its plans for inspection and/or modification of the recirculation and any other service sensitive austenitic stainless steel piping systems operating over 200"F. This is to be submitted for our review at least 3 months before the .

start of the next refueling (Cycle 12R) outage.

4.0 REFERENCES

1. Letter from R. F. Wilson (GPUN) to J. A. Zwolinski (NRC), Response to Generic Letter 84-11, dated October 3, 1986.

2. NRC Region I Inspection Reports No. 50-219/86-19 and 50-219/86-23, dated August 1 and September 5, 1986, respectively.

Principal Contributor: W. Koo Dated: IKHf 14 566 i

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