United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No.80-21 – Anchorage and Support of Safety-Related Electrical Equipment

                                                          SSINS No.: 6870  
                                                          Accession No.    
                                                          8005050050 

                                UNITED STATES
                       NUCLEAR REGULATORY COMMISSION 
                    OFFICE OF INSPECTION AND ENFORCEMENT 
                           WASHINGTON, D.C. 20555
                                     
                               May 16, 1980  

                                           Information Notice No. 80-21 

ANCHORAGE AND SUPPORT OF SAFETY-RELATED ELECTRICAL EQUIPMENT 

Description of Circumstances: 

Seismic design evaluations in connection with the NRC Systematic Evaluation 
Program (SEP) have indicated a potential safety deficiency in the anchorage 
and support of safety-related electrical equipment. This subject was 
highlighted for more in-depth evaluation after site visits to several 
facilities. The site reviews indicated that equipment was supported in a 
non-uniform manner. In some cases, design modifications were required to 
render acceptable seismic design margins. The deficiencies in anchorage and 
support may be due to the fact that earlier engineering design criteria did 
not require rigorous analyses. 

Letters were issued in January 1980 to the SEP plants which requested a 
review of the anchorage of safety-related electrical equipment. The findings
from the reviews at Haddam Neck, Big Rock Point, Dresden 2, Oyster Creek, 
and Palisades identified various safety-related electrical equipment that 
did not have positive anchorage. The reviews at other SEP plants are 
continuing. A summary is provided below of those items so far identified. 

     Station Service Transformers       Motor Control Centers 
          (4160 V - 480V)               Cable Trays 
     DC to AC Inverters                 Computer 
     Emergency Diesel Generator         Control Panels - MG Set 
          Room Heater                                  - Air Compressor
     Batteries - Emergency Diesel                      - Control Room 
                    Generator           Instrument Rack 
               - Diesel Fire Pump       Battery Room Main Breaker and 
               - Station                     Distribution Panel 
     Station Battery Rack 

A related item has been identified at Comanche Peak (under construction) in 
which the welds to the floor supports for the main control panels were found
to be undersized and improperly spaced. Also, the SEP reviewers observed 
that non-seismic Category I ancillary items (dolleys, gas bottles, block and
tackle gear, ductwork, etc.) may be located such that they could potentially
dislodge, impact, and damage safety related equipment during an earthquake. 

The type of anchorage systems utilized in the SEP plants and their expected 
capacities vary widely. For example, high uncertainty exists relative to the
capacity of non-engineered tack welds and attachments that rely on 
frictional clamping forces. In some cases, equipment has been found free 
standing with no means of positive lateral support. (Friction being the only 
lateral load 
.

Information Notice No. 80-21                              May 16, 1980  
                                                             Page 2 of 2   

carrying mechanism). Most often, heavier equipment is anchored using (1) 
tack welds to steel angles embedded in concrete; (2) clips that rely on 
frictional resistance; (3) concrete embedded anchor bolts; or (4) external 
braced frames.  Lighter equipment housed in cabinets or attached to panels 
or racks has been anchored using (1) bolts; (2) sheet metal screws; (3) tack 
welds; and (4) braced racks. 

The potential concern is that certain pieces of equipment may not have 
adequate levels of seismic resistance capability due to limited anchorage 
capacity. The potential problems relate to overturning and/or sliding of 
large equipment and gross movement or unacceptable forces on smaller 
attached equipment that may render it inoperable during an earthquake. For 
certain large battery racks, this judgment is supported by analysis that 
predict unacceptable seismic behavior. 

Section 3.10 of the Standard Review Plan provides acceptance criteria for 
the seismic qualification of Category I electrical equipment. These criteria
include IEEE Std. 344, "Guide for Seismic Qualification of Class 1E 
Electrical Equipment for Nuclear Power Generating Stations", first issued in
1971. Facilities designed before about 1971 without benefit of such design 
and testing criteria may have some anchorage deficiencies. 

The NRC staff is continuing to evaluate this issue on the SEP plants as part
of the seismic review in the SEP. Remedial actions have been planned for the
affected plants. 

This Information Notice is provided as notification of a possibly 
significant matter. It is expected that recipients will review the 
information for possible applicability to their facilities. No specific 
action or response is requested at this time. If NRC evaluations so 
indicate, additional actions may be requested or required. If you have any 
questions regarding this matter, please contact the Director of the 
appropriate NRC Regional Office. 

Page Last Reviewed/Updated Tuesday, November 12, 2013