ML20084H554

Final Deficiency Rept Re Potential Design Deficiencies Re Fuel Handling Grapple & Malfunction of Refueling Platform Hoist Brake.Initially Reported on 740516 & 23.Grapple Rebuilt.Electromechanical Brake Power Leads Rewired

ML20084H554
Person / Time
Site:	Browns Ferry
Issue date:	07/16/1974
From:	Gilleland J TENNESSEE VALLEY AUTHORITY
To:	Knuth D US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20084H553	List: ML20084H554 ML20084H561
References
10CFR-050.55E, 10CFR-50.55E, NUDOCS 8305040622
Download: ML20084H554 (5)

Text

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.- ENNESSEE VALLEY A HOAITY  ! -

CHATTANOOGA, TENNESSEE "

37401 _

July 16, 1974 ,,,,yy ,s ,,Y

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Mr. D. F. Knuth, Director N -

Directorate of Regulatory Operations "

U.S. Atomic Energy Commission _

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Washington, DC 20545

Dear Mr. Knuth:

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BROWNS FERRY NUCLEAR PLANT UNIT 2 - POTENTIAL DESIGN DEFICIENCIES .'

INVOLVING THE FUEL HANDLING GRAPPLE AND THE MALFUNCTION OF THE -

REFUELING PLATFORM HOIST BRAKE _

y Initial reports of the subject potential deficiencies were made -

on May 16, 1974, and May 23, 1974. An interim report was submitted = '

in my letter to you dated June 20.

In compliance with paragraph 50.55(e) of 10 CFR Part 50, this is submitted as the final report of the two potential deficiencies. {j Very truly yours, i M

J. E. Gilleland ._

Assistant to the Manager of Power m

Enclosure _b CC (Enclosure): ,

Mr. Norman C. Poseley, Director _

Directorate of Regulatory Operations -

U.S. Atomic Energy Commission  ;

Regica II - Suite 818 -

230 Peachtree Street, NW.

Atlanta, Georgia 30303  ;

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. ENCLOSURE O-i BROWNS FERRY NUCLEAR PLANT UNIT 2 DEFICIENCIES OF FUEL HANDLING CRAPPLE AND REFUELING PLATFORM HOIST BRAKE Final Report This single report covers two occurrences herein identified as Deficiency 1 and Deficiency 2. On May 16, 1974, an initial report was made regarding the failure of the fuel handling grapple in Unit 2 at the Browns Ferry site

. (Deficiency 1) to W. S. Little, AEC-DRO Inspector. his report was made by M. Price and E. Hilgeman. On May 23, 1974, an initial report was made concerning the malfunction of the refueling platform hoist brake in Unit 2 at the Browns Ferry site (Deficiency 2) to W. S. Little. This report was also made by M. Price and E. Hilgeman. Rese two reports were made in compliance with paragraph 50.55(e) of 10CFR50. Our request of May 31, 1974, a to W. S. Little to incorporate these deficiencies in the same report was granted. This is the final report for the two occurrences.

Descriptions of Occurrences Deficiency 1 ,

Following the modification in the FDI 176/87000-1 to stiffen the 12-inch section of the grapple, the 10-inch section became stuck in the 12-inch section. In order to loosen the stuck section, the grapple was jarred while over the reactor vessel. The 10-inch and 7-inch sections of the grapple fell about 15 feet, impacting on the grapple stops. Some of the grapple stops broke loose and fell into the reactor vessel. No damage to the reactor vessel occurred for two reasons. First, the falling parts fell into the water contained in the reactor vessel and did not fall directly onto the surface of the reactor vessel. Second, no damage to the reactor vessel would have occurred because the falling pieces were too small to cause impact damage. The parts that fell into the reactor vessel were retrieved.

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O O 1 Deficiency 2 i

The electro-mechanical brake on the refueling platform main hoist motor was found to be inoperative.

Cguses of Deficiencies Deficiency 1 Failure of the fuel handling grapple occurred when an attempt to loosen the stuck section was made by jarring the grapple over the reactor vessel. The failure was initiated by inadequate clearances between the moving parts of the grapple.

Deficiency 2 An investigation of the inoperative brake revealed that the electric power leads to the electro-mechanical brake coil were pinched in a conduit fitting.

The pinched leads short-circuited to the conduit fitting. The coil was not -

d'maged.

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Safety Implications Deficiency 1 Safety implications related to failure of the fuel handling grapple are similar to those of the design basis accident for the refueling accident wherein a fuel assembly is dropped onto the reactor core. The result of this accident is described in Section 14.6.4 of the FSAR. The assumptions used in the design basis accident are: ,

,1. The fuel assembly is dropped from the maximum height allowed by the fuel hand 1'ing equipment.

2. The entire amount of potential energy, referenced to the top of the reactor core, is available for application to the fuel assemblics involved 1

in the accident. ,

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3. None of the energy associated with the dropped fuel assembly is absorbed by the fuel material (uranium dioxide).

It was concluded that this postulated accident would not result in any radio-logical exposures which would endanger the health and safety of the public.

Deficiency 2 The malfunction of the main hoist motor brake was not safety-related because the failure immobilized the refueling platform in a safe position. In this condition, the refueling platform could not be moved until the brake was released. However, release of the brake was not possible as long as its power source was short-circuited.

Corrective Measures

• Deficiency 1 The grapple was rebuilt using parts supplied by the General Electric Conpany and using sections taken from the Unit 3 grapple. These measures were completed prior to June 7,1974. After these measures were taken, the -

grapple functioned satisfactorily.

Deficiency 2 The power leads were rewired and the electro-mechanical brake was retested c2 May 24, 1974. It functioned satisfactorily.

'Means Taken to Prevent a Recurrence of the Deficiencies Deficiency 1 A revision has been made to the FDI (modification instruction) to assure adequate clearances and performance testing after modifying the grapple.

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f\ D U v s l Deficiency 2 l

Failure of the brake to release can not initiate an unsafe condition. Nornal electrical construction should prevent such occurrences, thus no special action is required to prevent recurrence of this deficiency, l

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