water hammer at san onofre · 2012-12-05 · condensation-induced water hammer as the water level...
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Water Hammer at San Onofre
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Section 7.3
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What is Water Hammer?
A pressure transient which creates fluid shock waves in piping systems due to changes in fluid velocity or pressure
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changes in fluid velocity or pressure.
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Learning Objective 1
Describe three types of water hammer and their causes.
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Learning Objective 2
Describe corrective actions that were taken to prevent previous steam generator
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previous steam generator water hammer problems.
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Learning Objective 3
Describe the damage caused by the water hammer event at San Onofre Nuclear
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at San Onofre Nuclear Generating Station Unit 1 (SONGS-1).
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Learning Objective 4
Describe how multiple check valve failures contributed to the initiation of the water
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the initiation of the water hammer at SONGS-1.
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Learning Objective 5
Discuss how check valve testing required by the American Society of Mechanical Engineers Boiler and Pressure
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Engineers Boiler and Pressure Vessel code could haveprevented the SONGS-1 water hammer incident.
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Types of Water Hammer(Section 7.3.2)
• Classical water hammer
• Condensation induced water hammer
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hammer
• Steam Generator water hammer
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Classical Water Hammer
Boom!
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Generally a shock wave created by a moving fluid column suddenly stopping. Usually accompanied by noise.
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Classical Water Hammer -
Common CausesBoom!
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Failure to properly fill and vent system before establishing flow.
Sudden valve closure.
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Condensation-induced Water Hammer
Begins w/ a long horizontal steam filled pipe being filled by relatively cool water (AFW).
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As the cool water begins to fill the pipe, the steam is condensed and waves are formed.
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Condensation-induced Water Hammer
As the water level & waves increase, a volume of steam can be trapped, where it will condense rapidly.
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The collapsing steam pockets create localized low pressure areas.
Slugs of water accelerate towards the low pressure areas.
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Condensation-induced Water Hammer
Boom!
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The collapsing steam pockets create localized low pressure areas.
Slugs of water accelerate towards the low pressure areas.
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S/G Water Hammer is condensation-induced
water hammer in a feedwater line.
Causes are generally the same.
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Damage is generally in S/G feedring and its supports, the FW nozzle, and FW piping snubbers & supports.
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3 Modifications to prevent water hammer.
(Section 7.3.1)
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1) Installing J-tubes to prevent draining feedring.
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3 Modifications to prevent water hammer.
(continued)2) Shorten Horizontal runs of FW piping adjacent to S/Gs.
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3) Limit AFW flow to avoid rapid refill of horizontal runs of FW piping.
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SGs
SONGS –1 Water Hammer (Sections 7.3.3 & 7.3.4)
East MFP
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AFWWest MFP
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SGs
East MFP
E-MFP lost due to Aux Transformer problem.
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AFWWest MFP
MFP Check Valve MFP Check Valve As Found
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SGs
East MFP
Check valve downstream of FRV was leaking too.
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AFWWest MFP
FRV Check Valve As Found
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SGs
Boom!East MFP
Operators closed FWIS valves.
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AFWWest MFP
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Consequence / Damage(Section 7.3.5)
• Cracked feedwater pipe.
• Several damaged pipe supports
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supports.
• Several damaged valves.
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CAUSES
Failure of 5 safety related check valves.
Inadequate check
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Inadequate check valve testing.
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Questions
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Fig. 7.3-13 MFP Discharge Check Valve Fully Assembled
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Fig. 7.3-13 MFP Discharge Check Valve As Found
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Fig. 7.3-12 Check Valve Downstream
of FRV As
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Found