tva watts bar nuclear plant dog bone seal failure ...fsrug.org/presentations2016/26.pdfdog bone seal...
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TVA Watts Bar Nuclear PlantDog Bone Seal Failure, Installation,
and Inspection
Presented by: Billy SharpPresented to: FSRUG
January 28, 20161
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Dog Bone Seal Failure
• Watts Bar
– 2 unit, 4 Loop Westinghouse PWR.
– TVA designed Secondary Side
– Ingersol Rand Main Condenser
• WBN1 was manually tripped at 10:32 a.m. on 02/21/15 in anticipation of an automatic turbine and reactor trip due to low condenser vacuum.
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Dog Bone Seal FailureMain Condenser Design
Failure of C Zone Dog Bone Seal
3 Cascading Condenser Zones27,410 115ft-long Tubes
NormalVacuum Exhaust
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Dog Bone Seal Failure
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Horizontal Tear along the clamping bar
Vertical Tear along the vulcanized splice
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Dog Bone Seal Failure
Splice Transition to seal
Outside deterioration of the seal
Internal deterioration of the seal
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Dog Bone Water Seal
• In-service for the life of the failed seal
• Interior Durometerreadings were normal.
• Recommended to only use for air in-leakage troubleshooting.
• Water seal is shut off for new seal
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Dog Bone Water Seal
Water inside seal
Water Seal Side
Condenser Side
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Dog Bone Seal Clamps
Seal, Clamp, Shield Side View
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Clamping bar design is to hold on the bulb of the seal. Minimal pressure should be on the belt center.
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Dog Bone Seal Splice Thickness
• C Zone Splice • B Zone Splice • A Zone Splice
A Zone Thickness not
measured during failure analysis
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Dog Bone Seal Splice
• Single steps instead of multistep
• Prepared ends do not meet.
Splice Transition to seal
Failed Seal
Splice
New Seal
Splice
First Cut Second Cut
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After Vulcanization
Dog Bone Seal Splice
Original Seal Cap Strip Replacement Seal Cap Strip
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Indicates insufficient compression during vulcanization
Smooth transition between cap strip and seal surface
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Dog Bone Seal Inspections
• Visual Inspections of splice and locations on each wall each refueling outage– Cracks
– Blisters
– Delamination
– Bulging
• Durometer deadings of 4 walls and splice each refueling outage
• Future: Microwave scanning of splice inspecting for voids.
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Dog Bone Seal
Questions???12