ML20092M418
| ML20092M418 | |
| Person / Time | |
|---|---|
| Site: | Nine Mile Point  |
| Issue date: | 06/15/1984 |
| From: | Mangan C NIAGARA MOHAWK POWER CORP. |
| To: | Starostecki R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| References | |
| NMP2L-0085, NMP2L-85, NUDOCS 8407020234 | |
| Download: ML20092M418 (2) | |
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M V NIAGARA R UMOHAWK NIAGARA MOHAWK POWER CORPORATION /300 ERIE BOULEVARD WEST. SYRACUSE. N Y.13202/ TELEPHONE (315) 474-1511 f
l r
I P
June 15,1984 (NMP2L 0085) l 1
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Mr. R.L W. Staros tecki, Director U.S. Nuclear Regulatory Commission Region I Division of Project and Resident Programs l
631 Park Avenue
- King of Prussia, PA 19406 g
Re: Nine Mile Point Unit 2 i
Docket No. 50-410
Dear Mr.'Starostecki:
Enclosed is a final report for the problem concerning mechanical snubbers supplied by Pacific Scientific Company. This problem was reported via a telecon_ to R. Gallo of your staff on November 17, 1983. An interim, report was submitted via our letter dated December 16, 1983.
Very truly yours, C. V. Mangan i
l Vice President
' Nuclear Engineering'& Licensing i-a r-TL:ja Enclosure xc: Director of-Inspection and Enforcement -
U.S; Nuclear Regulatory Commis'; ion
' Washington, DC.20555.
R. A.: Gram, Resident Inspector 8407020234 840615 PDR ADOCK 05000410
'S PDR 71 f
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NIAGARA M0 HAWK POWER CORPORATION NINE MILE POINT UNIT 2 DOCKET N0. 50-110 Final Report for a Problem-Concerning Mechanical Snubbers c
Description of the Problem
'The problem concerns the mechanical snubbers si
,l'.d by Pacific Scientific
_ Company and was identified by the vendor to St.
& Webster Engineering t
. Corporation via letter dated September 21, 1983. The vendor informed Stone &
Webster Engineering Corporation that during testing of mechanical snubber
!Model PSA-1, at another plant, four of the seven snubbers tested revealed a broken capstan spring tang. The details of testing and cause of failure at
~this plant.are not known. The capstan springs are manufactured for Pacific-Scientific Company by a spring manufacturer. Pacific Scientific has indicated
- that'the problem pertains to only mechanical snubber models PSA-1 and PSA-3
'with certain serial numbers. The broken springs were sent by the vendor for an independent metallurgical examination.
iThe metallurgical examination' report notes that some of the tangs of the capstan! springs submitted for analysis exhibited cracks (microcracks) in the
. bend radius.. The report concludes that the cracks ~are formed during silver plating and are a-result of high residual stress in the formed radius of the tang coupled with hydrogen generated during the cleaning and plating operation combining to~ produce hydrogen-induced cracking. The springs that crack as a
' result of the plating' operating have all been made by one manufacturer. A second manufacturer.who makes the same springs has no+ experienced the cracking problem although they are plated by the same endor. The report also notes-that'in the springs in which the tangs cracked, the tangs were formed
-after_the springs had been aged at 900*F whereas, in the case of the other spring vendor, the tangs were formed prior,to age hardening at 900*F.
~
Pacific Scientific has since performed additio9al testing of capstan springs
'which contained microcracks.
Based on these tests and independent metallurgical' evaluation, Pacific Scientific has concluded that those
' mechanical snubbers which contain the subject capstan springs meet the requirements of Pacific Tcientific Design Specification DR1319 because these springs with microcracks, sustained the designed cyclic loads during testing.
However, the corrective actions outlined below are being/will be taken.
Analysis of Safety Implications As-a result of'the Pacific-Scientific Company's conclusion that the subject capstan springs meet.the requirements of its design specification, a
. deficiency does not exist. As a result, this condition does not meet the criteria for reportability under 10CFR50.55(e).
! Corrective Action
. Suspected snubbers have been' returned to the vendor for examination. The vendor is required ~to replace any snubbers if springs are found to contain microcracks. The corrected snubbers will be returned to the Nine Mile Point
-Unit 2 site by' September 1, 1984.
.-