Information Notice No. 93-95: Storm-Related Loss of Offsite Power Events due to Salt Buildup on Switchyard Insulators

                                 UNITED STATES
                         NUCLEAR REGULATORY COMMISSION
                            WASHINGTON, D.C. 20555

                               December 13, 1993



All holders of operating licensees or construction permits for nuclear power
reactors located close to a large body of salt water.


The U.S. Nuclear Regulatory Commission (NRC) is issuing this information
notice to alert addressees to the potential for loss of offsite power due to 
salt contamination of switchyard insulators.  It is expected that recipients
will review the information for applicability to their facilities and consider
actions, as appropriate, to avoid similar problems.  However, no specific
action or written response is required.

Description of Circumstances

On March 17, 1993, the Florida Power Corporation Crystal River Unit 3
experienced a loss of the 230 kV switchyard (normal offsite power to safety-
related busses) when a light rain caused arcing across salt-laden 230 kV
insulators and opened breakers in the switchyard.  At the time, the unit was
in cold shutdown during a maintenance outage.  The "A" emergency diesel
generator was used to power safety-related loads including shutdown cooling
until the 230 kV switchyard was restored.  The "B" emergency diesel generator
was unavailable due to maintenance.  The 500 kV switchyard supplied nonvital
loads throughout the event.

On March 16 through 18, 1993, Carolina Power and Light Company's Brunswick
Units 1 and 2 experienced a loss of the 230 kV switchyards (all offsite power)
when light rain caused arcing across salt-laden insulators and opened breakers
in the switchyard.  At the time, both units were in cold shutdown during an
extended outage.  Emergency diesel generators were used to power safety-
related loads including shutdown cooling until the offsite power was restored.

Since 1982, the Boston Edison Company Pilgrim station has also experienced
several loss of offsite power events when heavy ocean storms deposited salt on
the 345 kV switchyard causing the insulators to arc to ground. 


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Intense and unusual storms on March 13 and 14, 1993, produced high tides and
high winds (average of 80 to 97 kilometers/hour high winds [50 to 60
miles/hour], with gusts up to 160 kilometers/hour [100 miles/hour] blowing
ashore from the ocean i.e., Gulf of Mexico and Atlantic Ocean.  These storms
caused an unusual buildup of salt on the switchyard insulators at 
Crystal River Unit 3 and Brunswick Units 1 and 2.  The storms were unusual in
that they included high winds but little or no precipitation.  As a result,
salt from ocean spray built up on the switchyard insulators and was not washed
away by rain.  

Days later, light rain increased the electrical conductivity of the salt,
resulting in arcing across the insulators at both sites.  To remove the salt
from the insulators, Florida Power Corporation and Carolina Power and Light
Company deenergized the affected switchyards, washed the insulators with high
pressure demineralized water, then returned the switchyards to service.  The
washing stopped the electrical arcing across the insulators.  

The 500 kV switchyard for Crystal River Unit 3 is located adjacent to the  
230 kV switchyard.  It was relatively unaffected.  The 500 kV switchyard is
used for main generator output when Unit 3 is operating and is used for an
alternate source of offsite power (i.e., backfeeding of nonvital loads) during
Unit 3 outages.  The 500 kV switchyard experienced less arcing across the
insulators than the 230 kV switchyard and no tripped breakers.  As a
precautionary measure, the licensee also deenergized and washed the 500 kV
switchyard insulators.  Factors that may have reduced the storm inpact on the
500 kV switchyard included location (farther away from the shore) and higher
insulation level (the 500 kV insulators were designed for up to 700 kV
operation while the 230 kV insulators were designed for up to 242 kV
operation).  In addition, the licensee observed that, of the two types of  
230 kV insulators installed, the newer post type had less arcing than the
older cap and pin type.    

Licensee followup action in response to these events, to improve the future
performance of non-safety switchyard equipment, included:  investigating
available salt buildup monitoring systems, evaluating insulator washing
methods/capabilities, considering the use of room temperature vulcanized (RTV)
silicon rubber coatings, installing newer metal oxide gapless surge arrestors
to replace older silicon carbide gap type surge arrestors, and replacing
cellon-treated wood transmission towers.  

The 345 kV switchyard insulators at Pilgrim were coated with RTV silicon
rubber (Sylgard) in 1987.  It was expected that the RTV coating, when applied
in 1987, would be effective for a period of 15 years.  However, actual
experience at Pilgrim indicates that the coating is effective for a much .

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shorter period of time.  Consequently, the insulators at Pilgrim were cleaned
and coated with RTV again during the spring 1993 refueling outage.  As a long-
term option, the licensee is considering a replacement of the existing 345 kV
switchyard with a modern compactly designed switchyard which would be more
resistant to the coastal environment.     

These events illustrate the significance of maintaining reliable offsite and
onsite power sources during outages as well as during operation.

This information notice requires no specific action or written response.  If
you have any questions about the information in this notice, please contact
one of the technical contacts listed below or the appropriate Office of
Nuclear Regulation (NRR) project manager.

                                    /s/'d by BKGrimes

                                    Brian K. Grimes, Director
                                    Division of Operating Reactor Support
                                    Office of Nuclear Reactor Regulation

Technical contacts:  R. Schin, RII           P. Fillion, RII
                     (404) 331-5561          (404) 331-7288

                     P. Holmes-Ray, RII      P. Kang, NRR
                     (904) 795-7677          (301) 504-2779

                     R. Prevatte, RII
                     (919) 457-9531

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