ML20195C960
| ML20195C960 | |
| Person / Time | |
|---|---|
| Site: | Nine Mile Point  |
| Issue date: | 05/28/1999 |
| From: | Abbott R NIAGARA MOHAWK POWER CORP. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GL-94-03, GL-94-3, NMP1L-1438, NUDOCS 9906090054 | |
| Download: ML20195C960 (2) | |
Text
4 NiagarahMohawk'
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Richard 8. Abbott Phone 315 3491812 Vice President Fas 315 349 4417 ivaclear Engineenna
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M9y 28,1999 NMPIL 1438 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555 RE:
Nine Mile Point Unit 1 Docket No. 50-220 DPR-63
Subject:
Generic Letter 94-03, 7ntemmnular Stress Cormsion Cmcking of Core Shmuds in Boiling Water Reactors, 'SupplementalIrzformation Regarding Requestfor Appmval Under the Pmvision of10CFR5ti.55a(a)(3)(i)for Modification of the Four Stabiliter Assemblies (11e Rods)for Nine Mile Point Unit 1 (NMP1)
Gentlemen:
By letter dated May 21,1999, Niagara Mohawk Power Corpe atin (NMPC) requested Staff approval of a proposed modification to each of the four tie rods pursuant to i
10CFR50.55a(a)(3)(i). As stated in that letter, the modification replaces the design function of u
the failed cap screw and other cap screws that have the potential for future failure in the upper spring. NMPC also stated that it was continuing to evaluate the extent of condition of the failed cap screw beyond the upper spring and would provide the final extent of condition evaluation by May 28,1999. The purpose of this letter is to provide the final extent of condition evaluation.
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1 A detailed review of all threaded fasteners in the shroud repair indicated that there were no other threaded fasteners that had excessively stressed dissimilar metal connections. A detailed review was performed for X-750 threaded fasteners for the effects of thermal expansion, applied torque and/or stresses due to friction from the tie rod contacts on the vessel and the shroud walls during heatup and cooldown. This review indicated that no other X-750 threaded
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fasteners had an applied stress intensity factor under sustained stress greater than a K value m
of 20 to 30 ksi/in, which is considered to be the stress corrosion threshold value applicable to X-750 threaded fasteners. Accordingly, even if a crack is postulated at the root of the thread, J'
Intergranular Stress Corrosion Cracking crack growth is not expected.
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g NMPC has determined that the torquing process was properly controlled during initial h
f assembly of the tie rods and provides reasonable assurance that the stress corrosion threshold d
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f value for X-750 thrc9 ed fasteners was not exceeded.
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Page 2 Based on this evaluation, NMPC continues to conclude, as stated in our letter dated May 21, 1999, that no additional modi 5 cations are needed other than those indicated in our letter.
Accordingly, NMPC continues to conclude that the proposed modification provides an acceptable level of quality and safety. Approval of the proposed alternative is requested prior to June 8,1999, which is the currently scheduled startup date of NMPl.
Very truly yours, Richard B. Abbott Vice President - Nuclear Engineering RBA/KWK/ 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 l
.