ML17266A402

Draft Final Deficiency Rept Re Missed Nondestructive Exam in Mfg of Control Element Drive Mechanism Motor Housing Initially Reported 801124.Event Not Reportable Under 10CFR50.55e as Substantial Safety Hazard Not Anticipated

ML17266A402
Person / Time
Site:	Saint Lucie
Issue date:	12/23/1980
From:	Robert E. Uhrig FLORIDA POWER & LIGHT CO.
To:	James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
References
10CDR-50.55E, 10CFR-050.55E, 10CFR-50.55E, DEFE-801223, L-80-416, NUDOCS 8102250614
Download: ML17266A402 (6)

Text

I P.O. BOX 529100 MIAMI,FL33152.

FLORIDA POWER & LIGHT COMPANY December 23, 1980 L-80-416 Mr. James P. O'Reilly Director, Region II Office of Inspection and Enforcement U..S.. Nuclear Regulatory Commission 101 Marietta Street, Suite 3100 Georgia 30303 'tlanta,

Dear Nr. O'Reilly:

Re: St. Lucie Unit 2,

, Docket No. 50-389 CEDM Motor Housin NDE Attached is a draft of the, final response to the NRC on the subject 10 CFR 50.55(e) item reported on November 24, 1980.

Very tr yours, obert E. Uhrig

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Vice President Advanced Systems 5.Technology REU/TCG/ah Attachment cc: Harold F. Reis, Esquire i

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Combustion Engineering (C-E) notified Florida Power & Light (FPL) of a missed ASME Section III final non-destructive examination (NDE) step in the manufacture of the Control Element Drive Mechanism (CEDM) Motor Housings used at St. Lucie Unit 2.

The material on which the examination was not performed is part of the Lower Pressure Housing, fabricated of quenched and tempered Type 403 ferritic stainless steel. Use of this material is covered by Code Cases 1334 (now N-2) and also by Case 1337. (N-4). The material as received by C-E. had already been subjected to the ultrasonic (volumetric) and Surface (MT) examination required by the material specification.

The. quenching and tempering operations were performed by C-E at its East Windsor facility as part of the fabrication operations on the housing.

The heat treatment is followed by a machining operation which removes the sur.ace layer of material. Such parts produced to Code Case 1337 were liquid penetrant examined following heat treatment, in accordance with Code Case requirements. After a change was made to use Code Case 1334, which does not specifically cite this NDE requirement, the liquid penetrant examination was discontinued. The omission apparently resulted from the C-E personnel involved in fabrication processing not appreciating that. the requirements for examination of quenched and tempered ferritic material applied to the stainless steel fabrication process with which they were. dealing.

The ninety-one (91) CEDM Motor Housings for St. Lucie were shipped to C-'

for the required NDE and have been returned with no reportable deficiencies.

A potential concern was that quench cracks could be postulated to remain in the heat treated portion of the Lower Pressure Housing, FPL has considered this matter and concluded that omission of the non-destructive examination could not reasonably be expected to create a substantial safety hazard.

The following considerations contribute to this conclusion:

1. The materials vendor supplied material to ASME Code specifications including a 100 percent UT examination for volumetric flaws in the forged tubes and magnetic particle examination of material surfaces.

2. The heat treatment performed by C-E involved a mild quenching by air cooling which would not be expected to produce surface cracks in this type of material.

3. Both outer and inner surfaces of the tube were machined

,to remove at least 0.150 inches of material which would have removed all but the deep cracks had they been formed.

4. More than 400 housings have been previously manufactured by this procedure to Code Case 1337 and examined by dye penetrant methods without a single rejection based on code criteria.

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5. Fracture mechanics analyses show that even for full circumfer-ential cracks around the thinnest housing section there is substantial margin to failure in the, design.

In connection with the requirements of the U. S. Nuclear Regulatory Commission, 10 CFR 50.55(e) and 10 CFR 21, for reporting certain matters related to safety

'hazards in nuclear =power. plants,. Florida Power 8 Light has reviewed 'this situation and has found no expectation of a substantial safety hazard and that the situation, therefore, need not be reported as a defect under the regulation.