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)

Text

Water Hammer at San Onofre Section 7.3 1

What is Water Hammer?

A pressure transient which creates fluid shock waves in piping systems due to changes in fluid velocity or pressure.

pressure 2

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 water hammer problems.

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Learning Objective 3 Describe the damage caused by the water hammer event 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 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 Vessel code could have prevented 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

• Steam Generator water hammer 8

Classical Water Hammer Boom!

Generally a shock wave created by a moving fluid column suddenly stopping. Usually accompanied by noise.

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Classical Water Hammer -

Common Causes Boom!

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).

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.

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!

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.

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)

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.

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

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SONGS -1 Water Hammer (Sections 7.3.3 & 7.3.4)

East MFP SGs West MFP AFW 17

E-MFP lost due to Aux Transformer problem.

East MFP SGs West MFP AFW MFP Check Valve MFP Check Valve As Found 18

Check valve downstream of FRV was leaking too.

East MFP SGs West MFP AFW FRV Check Valve As Found 19

Operators closed FWIS valves.

Boom!

East MFP SGs West MFP AFW 20

Consequence / Damage (Section 7.3.5)

• Cracked feedwater pipe.

• Several damaged pipe supports supports.

• Several damaged valves.

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CAUSES Failure of 5 safety related check valves.

Inadequate check valve testing.

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Questions 23

Fig. 7.3-13 MFP Discharge Check Valve Fully Assembled 24

Fig. 7.3-13 MFP Discharge Check Valve As Found 25

Fig. 7.3-12 Check Valve Downstream of FRV As Found 26