ML19317D614

Rept on Internals Handling Fixture Problem, Prepared for Util

ML19317D614
Person / Time
Site:	Oconee
Issue date:	09/20/1974
From:	BABCOCK & WILCOX CO.
To:
Shared Package
ML19317D611	List: ML19317D610 ML19317D614
References
NUDOCS 7912060853
Download: ML19317D614 (2)

Text

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REP"T ON INTE?SAI.S F.AND?.ING FIXTT/~ ?RO3I.D!

. b nis repdre is being made pursuant to 10 CFR 50.55(e) on significant deficiencies to docu=ent the generic investigation of the significant deficiency in the design of the internals handling fixture spherical nut retaining device. /

Tdentification of Problen ,

IJuring the preparation for plenum assembly removal from the reactor vessel at "DiI-1,, it was noticed that the spherical nut was not secured to the threaded rod and could becone unthreaded. The set screws on the three asse=blics were found to be either missing, loose, or the wrong length.

Annivsis A design review by B&W engineering has found that the set screw concept of preventing the spherical nuts from rotating relative to the threaded rods (i.e.. beco=e unthreaded) is inadequate in the original design. The spherical nuts could be unthreaded during the adjusting procedure,1 caving inadequate thread engage:aent to support the weight of the internals. Shoudl the threads shear off, the resulting drop of the internals from as little as 6 inches height could result in fuel damage. Drops'from greater heights could also result in damage to the internals dnd the reactor vessel.

Evaluation With the inadequate method of capture between the spherical nut and the threaded -

rod, t.bere would be no assurance that the proper thread engagement would always be made. A s=all drop of about 7 inches could cause fuel assembly damage which would adversely affect the safety of the internals handling operation. This design deficiency is considered to be a significant deficiency pursuant to 10 CER 3D.65 (e).

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All affseted plants have been notified of the proble=. Thera ~has been no fcil-

• 1 ure of the interna.., handling fir.ure and, thus, nu da= age or adverse effect

. 'on safety res".1 ting fro = this deficiency. '

Corrective k rions i

1) On THI-1, the probic= vas resolved by a fie}d modification. Tnis modificatior consisted of drilling a hole in the threaded rod to ensure capture by the set screw and staking of the set screw to ensure that the set screws would not back out. , .

2) A redesign of the capture device has been i=ple=ented on other contracts.

This design revision consists of attaching a plant to the bottom of the threaded rod which vill not allow the spherical nut to unthread.

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- Letter from Duke Power Cortpany, A. C. Thies, dated September 20, 1974 - 50-269, 50-270 and 50-287 DISTRIBUTION:

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