ML20195C975

Informs That Weld 32-WD-050 Will Be Reclassified Back to GL 88-01 Category a Weld & ASME Code Section XI Insps Will Be Conducted in Next Three Insp Periods

ML20195C975
Person / Time
Site:	Nine Mile Point
Issue date:	06/01/1999
From:	Abbott R NIAGARA MOHAWK POWER CORP.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
GL-88-01, GL-88-1, NMP1L-1439, NUDOCS 9906090058
Download: ML20195C975 (2)

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NiagarahMohawk' Richard B. Abbott

• Phone: 315.349.1812 Vice Presdent Fax: 315.349.4417 NuclearEngineuring June 1, 1999 NMPIL 1439  ;

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l U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555 RE: Nine Mile Point Unit 1 Docket No. 50-220 DPR-63 l

Subject:

Analytical Evaluation of Weld 32-WD-050 Indication Gentlemen:

In a letter dated April 7,1997, Niagara Mohawk Power Corporation (NMPC) provided the analytical evaluation of an indication found at Nine Mile Point Unit 1 (NMP1) during refueling outage number (RFO) 14 inservice inspections. This indication was on weld 32-WD-050 in the reactor recirculation system piping and it measured 1.25 inches long and 0.25 inch deep. This weld had been classified as a Category "A" weld in NMPC's Generic Letter (GL) 88-01 submittal, dated March 7,1991. NMPC could not positively characterize the indication as the remnant of an original weld defect or as evidence of intergranular stress corrosion cracking (IGSCC). The evaluation concluded that irrespective of its origin, the indication met the ASME Code Section XI acceptance criteria for flaw size for at least the next two year operating cycle without requiring removal or repairs. In a letter dated April 21, 1997, NMPC informed the NRC that the NMP1 Inservice Inspection Program Plan had been revised to conservatively reclassify weld 32-WD-050 from a Category "A" weld to a Category.'

"F" weld, but if the next refueling outage examination results conclude that this indication is not an IGSCC crack, the weld would appropriately be reclassified back to Category " A."-

The NRC's Safety Evaluation (SE) dated April 30,1997, concurred that NMP1 could be safely operated for the next fuel cycle (730 days) without repair to weld 32-WD-050. The SE indicated that continued plant operation beyond that period would depend on the satisfactory evaluation of the reinspection results or implementing acceptable repairs during the next refueling outage (RFO15). The SE noted that the final flaw depth (0.485 inch) yielded by IGSCC growth rate calculations was within the ASME Code allowable flaw depth (0.787 inch). The SE also noted that based on this final flaw depth, the final flaw length was calculated as 4.7 inches. , , .

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! The RFO15 reinspection of weld 32-WD-050 has been completed. The measured length of the i indication remains 1.25 inches while its measured depth is 0.28 inch (an increase of 0.03 inch over the RFO14 measurement). The small increase in depth with no corresponding increase in l length is much less than the dimensional increases that had been predicted by the IGSCC l growth rate calculations. NMPC attributes the small increase in depth to uncertainties l

l associated with the ultrasonic examination measurement technique, and, therefore, concludes 1

that the indication is an original construction weld defect and not a flaw associated with IGSCC. Therefore, repair of weld 32-WD-050 is not required, and consistent with the NRC's SE of April 30,1997, the weld may be returned to the original GL 88-01 Category of "A."

As a conservative action, N'MPC generated additional IGSCC growth rate calculations for the duration of the next fuel cycle (730 days) using initial flaw depths of 0.28 inch (measured in RFO15) and 0.35 inch (an arbitrarily established maximum). The corresponding final flaw depths were calculated as 0.500 inch and 0.538 inch, respectively, both of which are within the ASME Code allowable flaw depth (0.787 inch).

l Weld 32-WD-050 will be reinspected in the next three inspection periods, in accordance with ASME Code Section XI, Section IWB, paragraph IWB-2420(b). The next scheduled inspection of this weld is during RFOl6 (in 2001). The non-destructive examination technique used for the Section XI weld inspections is identical to that used to detect and size IGSCC.

Therefore, the Section XI inspections will be adequate to confirm the absence ofIGSCC.

In summary, weld 32-WD-050 will be reclassified back to a GL 88-01 Category "A" weld and ASME Code Section XI inspections will be conducted in the next three inspection periods. l Very truly yours, bdk Richard B. Abbott Vice President Nuclear Engineering i

RBA/IAA/ kap xc: Mr. H. J. Miller, NRC Regional Administrator Mr. S. S. Bajwa, Section Chief PD-I, Section 1, NRR Mr. G. K. Hunegs, NRC Senior Resident Inspector

- Mr. D. S. Hood, Senior Project Manager, NRR Records Management

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