ML19220B745
| ML19220B745 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 05/20/1976 |
| From: | Arnold R Metropolitan Edison Co |
| To: | Volgenau E NRC/IE |
| References | |
| GQL-0745, GQL-745, NUDOCS 7904270290 | |
| Download: ML19220B745 (2) | |
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Di of Nuc d eactor Regulation
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U. S. Nuc i..egulatory Cocsission
'I'O Washington, D. C.
20555 Attention:
Dr. Ernst Volgenau Surject:
Three Mile Island Nuclear Station Unit No. 2 Docket No. 50-320 Faultv 'a' elds on Saf ety Related i' nit Substations
Dear Dr. Volgenau:
On April 21, 1976, Mr. L. Narrev of your office was verbally notified of a situation which Metropolitan Edison Company considered to be reportable in accordance with the requirements of 10 CFR 50.55(e).
This letter constitutes the required thirty day follow-up letter.
Description
'4hile connecting the flexible cables frc= the load break switch cabinets to the bus bars frem the high side of the transformer in a GE supplied unit substation, a transition piece welded to the aluminum bus bar in the unit substation broke off. The transition piece is a short flat alitninum bar which overlaps the high side bus bar by about one inch and is attached to the bus bar by a fillet veld. The other end of the transition plate is bolted to the flexible conductor frem the load break switch. An ernmination of the broken weld showed the veld to be extremely porous with insufficient throat size.
It appeared that the weld was made at too lcw a te=peratu*.
A representative from GE was called to the site and an examination of similar joints was conducted on all unit substations. A s1=ilar condition existed throughout nest units including safeguards units.
In most cases, the GE representative was able to snap off the transition plates by hand. Additionally, the GE representative indicated
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that the weld is the current carrying medium between plates.
790427023o 82 W4 F4at b
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,To:
Dr. E. Volgenau Analvsis of Safety I=clications Four of the unit substations exhibiting this condition are safety related. Had this faulty weld re=ained undetected, it is possible that a weld would have failed under load causing the less of power and control of those safety related loads supplied downstream of the 4160V to 400V transfor er.
It is unlikely that a weld in a redundant unit substation would fail simultaneously so the redundant safety related components would be available to safely shut-down the reactor. For this reason, this incident would not have co= promised the health and safety of the public or the plant staff.
Corrective Action The above condition was documented on a site deviation report.
General Electric has supplied a weld repair procedure and instructions for reattaching the transition plates to the bus bars to provide for proper attach =ent and eliminate recurrence of the proble=. Repair work is now in progress under the direction of a General Electric Field Represen-tative.
It is asti=ated that the repairs should be conpleted by June 1, 1976. Docu=entation a0sociated with the repair activities will be available at the site for your inspection.
Very truly yours, 4
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R. C. Arnold Vice President F.CA:rk File: 62.10C0.1010 02.0016.CC03.0C53 82 025