ML20076F205

Final Deficiency Rept Re Undersized Power Generation Control Complex Floor Module Welds.Initially Reported on 830207. Welds Inspected & Accepted.Procedure Revised to Require Weld Leg Length Verification Using Fillet Weld Gauge

ML20076F205
Person / Time
Site:	Nine Mile Point
Issue date:	05/20/1983
From:	Manno S NIAGARA MOHAWK POWER CORP.
To:	Starostecki R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
References
10CFR-050.55E, 10CFR-50.55E, 6692, NUDOCS 8306010453
Download: ML20076F205 (3)

Text

7 M Y NIAGARA R UMOHAWK NIAGARA MOHAWK POWER CORPORATl0N/300 ERIE BouLEVARo WEST, SYRACUSE. N.Y.13202/ TELEPHONE (315) 4741511 SAMUEL F. MANNO l'lCE PRESIDENT NUCLEAR CONSTRUCTION May 20, 1983 (6692)

Mr. R. W. Starostecki, Director U.S. Nuclear Regulatory Commission Region I Division of Project and Resident Programs 631 Park Avenue King of Prussia, PA 19406 Re: Nine Mile Point Unit 2 Docket No. 50-410

Dear Mr. Starostecki:

Enclosed is a final report in accordance with 10CFR50.55(e) for the problem concerning the power generation control complex floor module welds.

This matter was reported to Mr. W. Baunack of your staff on February 7,1983.

An interim 30-day report was submitted on March 7,1983.

Very truly yours, f.

S.

Manno l

Vice President Nuclear Construction SFM/TL :ja Enclosure xc: Director of Inspection and Enforcement j

U.S. Nuclear Regulatory Comissicn l

Washington, DC 20555 Mr. R. D. Schulz, Resident Inspector i

i F306010453 830520 gDRADOCK05000 g)

NIAGARA M0flAWK P0WER C0RPORATION NINE MILE POINT - UNIT 2 DOCKET N0. 50-410 Final Report for a Problem Concerning Power Generation Control Complex Floor Module Welds Description of the Problem The problem concerns the power generator control complex floor modules supplied by General Electric (GE).

GE's typical floor section drawings specify 0.25 inch fillet welds for connecting panel support structural steel menb ers. Niagara Mohawk Power Corporation Quality Assurance has identified a number of these welds to be less than 0.25 inch.

The cause of this problem was that previous to welding the 0.25 inch fillets on the floor sections, GE was wlding panel enclosure fillets of length 0.190 inch or less. Between welding the floor sections and the panel enclosures GE failed to review the specification which called for 0.25 inch fillets on the floor sections.

In addition, GE's Inspectors, who were familiar with the panel enclosure welds and their size, did not review the specification for floor welds and thus did not question the undersized floor welds.

Analysis of Safety Implications The panel seismic loads are transmitted to the control room floor embedded steel through 0.5 inch diameter welded studs which hold the panels to the floor section steel I-beams.

In turn, these I-beams are fillet welded to cross T-beams and box beams that are welded to the embedded steel. The analysis approach compared the total weld stud cross-sectional area with the total fillet weld cross-sectional area. Although the majority of the fillet welds inspected ranged from 3/16 to 1/4 inch, numerous floor sections had 5/32 inch welds. This size was used as the worst case average available weld in the analysis (i.e., the analysis conservatively assumes that all of the structural welds in the floor section are 5/32 inch fillet welds).

Since there is a factor of 1.45 more fillet weld area (at 5/32 inch per weld) than weld stud area, the fillet weld is the strongest link in the design.

The weld stud adequacy has been verified by test and analysis performed by General Elec tric.

Since some of the structural welds had a portion of their horizontal and/or vertical legs of the fillet weld less than 5/32 inch, a calculation was performed to determine the minimum fillet weld leg size which would provide a cross-sectional area equivalent to the stud weld cross-sectional area. This minimum weld leg size was calculated to be 0.108 inches. All weld dimensions are greater than this minimum weld leg size.

This analysis shows that the existing floor section structural welds are structurally adequate.

Therefore, if this deficiency had gone undetected, it would not have adversely affected the safety of operations of Nine Mile Point Unit 2.

A Corrective Action An inspection of all accessible structural welds for the 33 floor sections was performed using a fillet weld gauge. Approximately 70% of the total number of j

structural welds were available for inspection. The results of this inspection were doctmented in General Electric Inspection Report RAG 280.

As indicated above, the undersized welds were accepted by analysis. The i

i analysis and calculation have been added to the General Electric Design Record File for Unit 2.

C These floor sections were built in the 1978-79 time frame.

In 1980, an extensive weld quality training class was.given to inspectors and welders with 4

a follow tp class in 1982.

In addition, at the time the Unit 2 floor sections were built, the procedure covering the inspections of these welds only required the welds to be visually inspec ted. The procedure currently requires the weld leg length to be j

verified (measured) using a fillet weld gauge.

f i

l a

I l

l h

l

_,