ML19319C895
| ML19319C895 | |
| Person / Time | |
|---|---|
| Site: | Crane, Crystal River  |
| Issue date: | 10/03/1974 |
| From: | BABCOCK & WILCOX CO. |
| To: | |
| Shared Package | |
| ML19319C884 | List: |
| References | |
| NUDOCS 8003040849 | |
| Download: ML19319C895 (2) | |
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..GPORT 02; -I!. i:..<l:ALS EU.7LI! C i i.~27.E.P?.03LEM y
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Tais report -is being =ade pursuant to 10 CFR 50}55(e) on significant deficiencies q
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.to docu=ent the generic investigation of-the significant deficiency in the design J
i of, the internals handling fixture spherical nut' retaining device.
T Identification o f Problem l
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During the preparation for plenus asse=bly' removal from the reactor vessel at
'IM1-1, it was noticed that the spherical nut was not secured to the threaded j
rod and could beco=a unthreaded.
The set screws on the three asse=blies were found to be either missing, loose, or the wrong length.
q Analysis A design review by B&W engineering has found that the set screw concept of
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preventing the spherical nuts fron rotating relative to~ the threaded rods J
(i.e.., beco=e unthreaded) is inadequate in the original design.
The spherical j.O R,)
nuts could be unthreaded during the adjusting procedure, leaving inadequate thread engage =ent to support the weight of the internals.
Shoudl the threads shear off, the resulting drop of the internals fro: as little as.6 inches 1
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height could result in fuel da= age.
Drops from greater heights could also
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result in damage to the internals and the reactor vessel.
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1 Evaluation l
4, With the inadequate method of capture between the spherical nut and the threaded rod, there would be no assurance that the proper thread engage =ent would cluays g
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be =ade.
A scall drop of about 7 inches could cause fuel assembly da= age which
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vould, adversely affect the safety of the internals handling operation.
This design deficiency is considered to be a significant deficiency pursuant to i.
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- ll effseted plaues hava basn notified of tha ~ proble:2.
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ure of-the internals handling fixture and, thus, no da= age or adverse effect b
on safety resulting from -this deficiency.
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Corrective M tions i
- 1) On TMI-1,' the proble: was resolved by a - field =odification.
This =odification f.
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- consisted of drilling a hols ~1n tha.. threaded rod to ensura capture by the 4
set screw and staking of the set screw to ensure that the set screws' would t.
not back out.
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- 2) A redesign of the capture device has been i=ple=ented on other contracts.
p This design revision consists of attaching a plant to the botto= of the threaded rod which will not allow the' spherical nut to unthread.
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