ML061520412
| ML061520412 | |
| Person / Time | |
|---|---|
| Site: | Vogtle  |
| Issue date: | 05/23/2006 |
| From: | - No Known Affiliation |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML061520404 | List: |
| References | |
| Download: ML061520412 (10) | |
Text
Vogtle Unit 2 Vogtle Unit 2 RHR Bypass Line Leaks RHR Bypass Line Leaks Root Cause Investigation Root Cause Investigation May 2006 May 2006
Root Cause Investigation Team Root Cause Investigation Team Vice President Vice President-SNC Corporate Engineering SNC Corporate Engineering-Event Team Leader Event Team Leader Project Manager-SNC Corporate Engr-Root Cause Team Leader Engineer Engineer-SNC Corporate Materials and Inspection Services 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
2/3/06 2/3/06 12/9/05 3/4 12 12 Vertical Support Horizontal Supports 3/20/06 RHR Bypass Line Leak Locations RHR Bypass Line Leak Locations
Weld Repair History for 2HV Weld Repair History for 2HV--8701B 8701B flow flow--restrictor restrictor Half coupling to RHR weld in service since original construction Weld build-ups performed during Feb 2006 to make welds comply with 2:1 weld ratio Orifice to coupling weld in service since October 2002 Full coupling to RHR bypass line piping in service since Feb 2006 (weld was made as part of the replacement of RHR bypass line)
Location of March 2006 leak RHR FLOW R
H R
B Y
P A
S S
F L
O W
3/8 Flow Orifice 1/4 Flow Orifice Half coupling to orifice weld in service since Dec 2005, Location of December leak
Loop 1 RHR Schematic Loop 1 RHR Schematic 502 500 2HV8701B 251 255 Bonnet Leakoff line Bypass Pipe Supports RHR Pipe Supports Unit 2, Loop 1 RHR Loop Suction RHR Pump Side RCS Loop Side SI Primary Check Valve 2-1204-U6-126 SI Secondary Check Valve 2-1204-U6-128 2HV8701A SI Test Header Connection
The Theory The Theory Depressurization Forces 2-1204-U6-126 2HV-8701B RHR Loop Suction Line RCS Flow 32Hz Full Power 29.5 Hz Full Power 251 255 SI HL Injection Line Vortex Excitation Organ Pipe Bypass Line Vibration Backseat Evolution Backseat Evolution Bypass line Natural Frequency 29 Hz Full Power When frequencies align, resonance occurs.
7 Factors causing RHR bypass line cracks (based on measurements and observations in Feb 2006)
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- 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
+
- 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 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 Ongoing Actions
- Monitoring Monitoring
- Investigating Investigating
- Benchmarking Benchmarking
- Broadness Broadness