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95

Information Notice No. 93­95: Storm­Related Loss of Offsite Power

Events due to Salt Buildup on Switchyard Insulators

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555

December 13, 1993

NRC INFORMATION NOTICE 93‐95: STORM‐RELATED LOSS OF OFFSITE POWER EVENTS

DUE TO SALT BUILDUP ON SWITCHYARD INSULATORS

Addressees

All holders of operating licensees or construction permits for nuclear power

reactors located close to a large body of salt water.

Purpose

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.
9312070298.

IN 93‐95

December 13, 1993

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Discussion

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 .

IN 93‐95

December 13, 1993

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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

Attachment:

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