TXX-6538, Final Deficiency Rept Re Base Metal Damage on Embedded Channels.Initially Reported on 870316.Rework Activities for 6.9 Kv Switchgear Will Be Completed by 870717 for Unit 1 & 871127 for Unit 2
| ML20215K596 | |
| Person / Time | |
|---|---|
| Site: | Comanche Peak  |
| Issue date: | 06/19/1987 |
| From: | Counsil W TEXAS UTILITIES ELECTRIC CO. (TU ELECTRIC) |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| CP-87-04, CP-87-4, TXX-6538, NUDOCS 8706250385 | |
| Download: ML20215K596 (2) | |
Text
h P-Log # TXX-6538 O'
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File # 10110 i
Ref # 10CFR50.55(e)
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j 1UELECTRIC William G. Counsil Em:utive Via President U. S. Nuclear Regulatory Commission Attn:
Document Control Desk Washington, DC 20555 I
SUBJECT:
COMANCHE PEAK STEAM ELECTRIC STATION (CPSES)
DOCKET NOS. 50-445 AND 50-446 PLUG WELDING ON EMBEDDED CHANNELS j
SDAR:
CP-87-04 (FINAL REPORT)
Gentlemen:
On March 16, 1987, we verbally notified your Mr. I. Barnes of a deficiency involving base metal damage on embedded channels for one of the Unit 2, 6.9Kv switchgear installations.
Specifically, cracks have been observed in the weld made to repair grout holes in the embedded channels. We have concluded that
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this issue is reportable under the provisions of 10CFR50.55(e). The required i
information follows.
DESCRIPTION The deficiency involves cracked welds found within the embedded channels used i
for mounting one of the Unit 2, 6.9Kv emergency switchgear installations (Tag No. CP2-EPSWEA-02).
In removing seven cabinets in the unit, cracked welds were found on the channels at the point the cabinets were attached. As a l
l result of these conditions, the cabinets were not mounted per design requirements.
Nonconformance Report (NCR) CE-87-7-S was issued to document the deficiency.
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Review of the attachment detail (Desig$ Change Authorization DCA 20986) l indicated that threaded stud and attachment weld locations for equipment were coincidental with grout holes in the embedded channels.
The solution provided by the attachment detail specified adding a circular plate of the same thickness as the channel, into thc hole and welding all around with a partial penetration weld.
Subsequently, the cabinets were attached by filling a hole i
in the base of the cabinet with weld metal to the added plate.
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The cracks observed at the attachment of the cabinets followed the weld of the added plate in approximately a 2-1/2" diameter r*cle.
Since there were no forces acting to propagate the crack into the channel, the worst case would be propagation of the crack in a complete circle.
This issue hasmo technical significance since the structural integrity of the channels would not be affected.
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TXX-6538 June _19, 1987 Page 2 of 2 x
The design document, DCA 20986,' detailing the addition of the circular plate provided inappropriate weld details. The type of weld defined is a partial penetration weld with the depth of the preparation to be the thickness of the
'i base metal (tw is 3/16"). AWS Dl.1 states, for joint configuration BTC-P4, base metal thickness shall be 7/16" minimum. This condition represents a significant deficiency in design'which requires repair.
Subsequent cracking occurred because of the type of joint configuration and the increase of heat caused during the welding of the cabinets to the channel.
Failure of this connection beseen the circular plate and channel would have prevented 5 a.traint of the cabinets which could prevent the proper operation of the switchgear equipment.
SAFETY IMPLICATIONS j
The condition represents' a significant deficiency in final design as approved and released for construction. Had the condition remained uncorrected, 'i,t could have adversely affected the safety of plant operations.
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Failure of the connection between the circular plata and the chann'el could have prevented restraint of the cabinets during a ' seismic event 'and proper 1
operation of the safety related 6.9Kv switchgear.
CORRECTIVE ACTION Attachment of the cabinets in the affected areas (Plug Welds) have been prohibited per design changes which were issued to provide revised details for the installation of the switchgear.
For buses 1EA1, IEA2, and 2EA2 the DCA's are 31346, 49086, and 28985, respectively.
The DCA for bus 2EA1 will be issued after switchgear removal and engineering assessment. With the revised installation details, completion of the 6.9KV switchgear rework activities will be accomplished in accordance with the schedule described for SDAR CP 03.
The schedule for completion of activities for Unit 1 is July 17 and Unit 2 is November 27, 1987.
Very truly yours, 7VP' W. G. Counsil s
DAR/dl c - R. D. Martin, Region IV Resident Inspectors, CPSES (3) i r
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