ML11216A244

0523 - R504P - Westinghouse Advanced Technology - 07.3 - Water Hammer at San Onofre

ML11216A244
Person / Time
Site:	San Onofre
Issue date:	12/12/2008
From:	NRC/HR/ADHRTD/RTTB-PWR
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Download: ML11216A244 (26)

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Water Hammer at San Onofre 1 Section 7.3 What is Water Hammer?A pressure transient which creates fluid shock waves in piping systems due to changesinfluidvelocityorpressure 2 changes in fluid velocity or pressure.

Learning Objective 1Describe three types of water hammer and their causes.

3 Learning Objective 2 Describe corrective actions that were taken to prevent previoussteamgenerator 4 previous steam generator water hammer problems.

Learning Objective 3Describe the damage caused by the water hammer event atSanOnofreNuclear 5 at San Onofre Nuclear Generating Station Unit 1 (SONGS-1).

Learning Objective 4Describe how multiple check valve failures contributed to theinitiationofthewater 6 the initiation of the water hammer at SONGS-1.

Learning Objective 5Discuss how check valve testing required by the American Society of Mechanical EngineersBoilerandPressure 7 Engineers Boiler and Pressure Vessel code could haveprevented the SONGS-1 water

hammer incident.

Types of Water Hammer(Section 7.3.2)*Classical water hammer*Condensation induced water hammer 8 hammer*Steam Generator water hammer Classical Water Hammer Boom!9Generally a shock wave created by a moving fluid column suddenly stopping. Usually accompanied by

noise.

Classical Water Hammer -Common Causes Boom!10Failure to properly fill and vent system before establishing flow.Sudden valve closure.

Condensation-induced Water HammerBegins w/ a long horizontal steam filled pipe being filled by relatively cool water (AFW).

11As the cool water begins to fill the pipe, the steam is condensed and waves are

formed.

Condensation-induced Water HammerAs the water level & waves increase, a volume of steam can be trapped, where it will condense rapidly.

12 The collapsing steam pockets

create localized low pressure

areas.Slugs of water accelerate towards the low pressure areas.

Condensation-induced Water Hammer Boom!13 The collapsing steam pockets create localized low pressure

areas.Slugs of water accelerate towards the low pressure areas.

S/G Water Hammer is condensation-induced water hammer in a feedwater line.Causes are generally the same.14Damage is generally in S/G feedring and its supports, the FW nozzle, and FW piping

snubbers & supports.

3 Modifications to prevent water hammer. (Section 7.3.1) 15 1) Installing J-tubes to prevent draining feedring.

3 Modifications to prevent water hammer. (continued)

2) Shorten Horizontal runs of FW piping adjacent to S/Gs.

163) Limit AFW flow to avoid rapid refill of horizontal runs of FW piping.

SGsSONGS -1 Water Hammer (Sections 7.3.3 & 7.3.4)East MFP 17 AFWWest MFP SGsEast MFPE-MFP lost due to Aux Transformer problem.

18 AFWWest MFPMFP Check ValveMFP Check Valve As Found SGsEast MFP Check valve downstream of FRV was leaking too.

19 AFWWest MFPFRV Check Valve As Found SGs Boom!East MFP Operators closed FWIS valves.

20 AFWWest MFP Consequence / Damage (Section 7.3.5)*Cracked feedwater pipe.*Several damaged pipe supports 21 supports.*Several damaged valves.

CAUSESFailure of 5 safety related check valves.Inadequatecheck 22 Inadequate check valve testing.

Questions 23 24 Fig. 7.3-13 MFP Discharge Check Valve Fully Assembled 25 Fig. 7.3-13 MFP Discharge Check Valve As Found Fig. 7.3-12 Check Valve Downstream of FRV As 26 Found