Information Notice No. 85-25:Consideration of Thermal Conditions in the Design and Installation of Supports for Diesel Generator Exhaust Silencers
SSINS No.: 6835
IN 85-25
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, DC 20555
April 2, 1985
Information Notice No. 85-25: CONSIDERATION OF THERMAL CONDITIONS IN THE
DESIGN AND INSTALLATION OF SUPPORTS FOR
DIESEL GENERATOR EXHAUST SILENCERS
Addressees:
All nuclear power reactor facilities holding an operating license (OL) or a
construction permit (CP).
Purpose:
This information notice is provided to alert recipients of a potentially
significant problem pertaining to the effects of thermal conditions on
supports for diesel generator exhaust silencers. It is expected that recip-
ients will review the information for applicability to their facilities and
consider actions, if appropriate, to preclude a similar problem occurring at
their facilities. However, suggestions contained in this information notice
do not constitute NRC requirements; therefore, no specific action or written
response is required.
Description of Circumstances:
Seabrook - An NRC regional inspection (50-443/84-02 and 50-443/84-04) iden-
tified cracks in the concrete supports for the diesel generator exhaust
silencers that were manufactured by Riley-Beard, Incorporated. Further
investigation by the licensee determined that the set of concrete pedestals
supporting the exhaust silencer tank for one of the diesel generators
cracked during operational testing. The cracking was caused by thermal
expansion, which had not been accounted for in the pedestal base plate
design of the steel support saddles of the exhaust silencers. These support
saddles experi-enced temperatures in excess of 200F and expanded more
than the anchor bolt clearances allowed at the base plate. Significant
restraining forces developed in the anchor bolts and in the concrete
pedestals where the anchor bolts were set. In addition, temperatures above
200F, which were higher than the maximum recommended sustained
temperature of the concrete, were reached near the top portion of the
concrete pedestal.
River Bend - The NRC Construction Appraisal Team (CAT) inspection at the
River Bend Nuclear Power Station found that the exhaust silencers for the
Transamerica Delaval, Inc. diesel generators were installed without any
sliding connection for thermal expansion. Investigation by the architect/
engineer found that the manufacturer's installation drawing was incorrect.
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IN 85-25
April 2, 1985
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Shearon Harris - At the Shearon Harris Nuclear Power Station, the NRC CAT
inspectors found that the diesel generator exhaust silencers, manufactured
by American Air Filter Company, had grout in and around the slotted sections
of the base plates. These sections were designed to be clear to allow for
movement caused by thermal expansion. In addition, the concrete support pad
under the sliding attachment for one of the exhaust silencers was sloped in
such a fashion as to cause the attachment to wedge itself tight as expansion
occurred.
Braidwood - At the Braidwood Nuclear Power Station, the applicant identified
cracked concrete pedestals of the diesel generator exhaust silencers
manufactured by Riley-Beard, Incorporated. The architect/engineer determined
that the original design did not properly account for thermal expansion.
During the Braidwood NRC CAT inspection, the CAT inspectors also noticed
that the bolted connections of the sliding ends of the exhaust silencers may
have been too tight to permit movement for thermal expansion. Corrective
action required modifying the sliding joints of the exhaust silencers.
Discussion:
The deficiencies described above show that there was inadequate
consideration of thermal conditions in the supports for exhaust silencers at
four nuclear plant sites. Generally, thermal conditions of the diesel
generator exhaust silencers were not adequately accounted for in either the
design or installation requirements for the component concrete pedestals and
sliding joints. As a result, in two cases the forces created by expansion
when the exhaust silencers reached operating temperatures caused damage to
the concrete pedestals.
If left as they are, the cracked foundations for the exhaust silencers may
not be able to support imposed loads in a seismic event. Failure of the
exhaust silencers could reduce the capacity of the diesel generators.
Similar problems may exist with other mechanical equipment that operates at
elevated temperatures and that is supported by concrete pedestals with slid-
ing connections.
No specific action or written response is required by this information
notice. If you need additional information about this matter, please contact
the Regional Administrator of the appropriate NRC regional office or this
office.
Edward L. Jordan, Director
Division of Emergency Preparedness
and Engineering Response
Office of Inspection and Enforcement
Technical Contact: John Nemoto, IE
(301) 492-7557
Attachment: List of Recently Issued IE Information Notices
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