ML061520412

Meeting Slides, Vogtle Unit 2, RHR Bypass Line Leaks

ML061520412
Person / Time
Site:	Vogtle
Issue date:	05/23/2006
From:	- No Known Affiliation
To:	Office of Nuclear Reactor Regulation
Shared Package
ML061520404	List: ML061520407 ML061520410 ML061520412 ML061520415
References
Download: ML061520412 (10)

Text

Vogtle Unit 2 RHR Bypass Line Leaks Root Cause Investigation May 2006

Root Cause Investigation Team Vice President-SNC President SNC Corporate Engineering-Event Engineering Event Team Leader Project Manager-SNC Corporate Engr-Root Cause Team Leader Engineer-SNC Engineer SNC Corporate Materials and Inspection Services Engineering Supv-SNC Farley Engineering Support Training Supv-SNC Vogtle Training Shift Support Supv-SNC Vogtle Operations Engineering Supv-SNC Vogtle Engineering Support Engineer-SNC Vogtle Performance Analysis Principal Engineer-SCG Maintenance Planning- Vibration Instrumentation Engineer-SCG Maintenance Planning- Vibration Instrumentation Principal Engineer-Westinghouse Systems Principal Engineer-Westinghouse Pipe Stress Senior Associate-Structural Integrity Associates Associate-Structural Integrity Associates Engineer-Bechtel-Water/Steam Hammer & Fluid Flow Expert Project Engineer-Bechtel-Pipe Design and Support Engineer-Bechtel-Pipe Design and Support

RHR Bypass Line Leak Locations 12 Vertical 3/20/06 Support 12/9/05 12 2/3/06 Horizontal 2/3/06 Supports 3/4

Weld Repair History for 2HV-8701B flow-restrictor 3/8 Flow Orifice RHR FLOW Half coupling to RHR weld in Half coupling to orifice service since original weld in service since construction Dec 2005, Location of December leak Location of March 2006 leak 1/4 Flow R Orifice H

R Weld build-ups performed during Feb 2006 to make welds comply with 2:1 weld ratio B

Y P

A S

S Orifice to coupling weld in service since October 2002 F

L O Full coupling to RHR bypass line piping in W service since Feb 2006 (weld was made as part of the replacement of RHR bypass line)

Loop 1 RHR Schematic Unit 2, Loop 1 RHR Loop Suction 500 RCS Loop Side RHR Pipe Supports 2HV8701B 255 Bonnet Leakoff line 251 Bypass Pipe Supports 2HV8701A 502 SI Secondary Check Valve 2-1204-U6-128 SI Primary Check Valve 2-1204-U6-126 RHR Pump Side SI Test Header Connection

The Theory 2HV-8701B RHR Loop Suction Line 32Hz Organ Pipe 29.5 Hz Full Full Power Power Vortex Excitation Full Bypass Line Vibration Power 251 255 Bypass line Natural Frequency 29 Hz 2-1204-U6-126 Backseat Backseat Evolution Evolution RCS 2-1204-U6-128 Depressurization Forces Flow SI HL Injection Line SI Test Header When frequencies align, resonance occurs.

7 Factors causing RHR bypass line cracks (based on measurements and observations in Feb 2006)

1. RCS Vortex Shedding Frequency across RHR nozzle at RCS

+

2. Acoustic Frequency of Loop 1 RHR piping

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3. Structural Frequency of RHR Bypass Line

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4. No Axial Support of Bypass line => Relatively flexible bypass line amplifies RHR piping movement

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5. Leaking Safety Injection Primary Check Valve

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6. Leaking AOVs in SI Test Header Line (accumulators filling up)

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7. SI Check Valve Reseat Procedure = Creates Impulse at Bypass line and 3/4 Check Valve, resulting in valve chatter and higher vibration

The factors contributing to the root causes of the cracks can be condensed into two primary causes.

1. The bypass line was flexible and not axially restrained, and

2. High vibration at power due to resonance at about 30 Hz, and 3/4 check valve chatter

Other Bypass Lines Whats different on the other RHR bypass lines that they havent cracked?

• Loop 4 of each Unit is not near a resonance condition

• SI hot leg check valve reseat not performed on Unit 1

Ongoing Actions

• Monitoring

• Investigating

• Benchmarking

• Broadness