ML093090256
| ML093090256 | |
| Person / Time | |
|---|---|
| Site: | Cook  |
| Issue date: | 11/02/2009 |
| From: | Jensen J American Electric Power Co |
| To: | NRC/RGN-III |
| References | |
| Download: ML093090256 (27) | |
Text
Joe Jensen Senior Vice President and Chief Nuclear Officer D.C. Cook Nuclear Plant American Electric Power Nuclear Regulatory Commission Presentation November 2, 2009 Unit 1 Cook Nuclear Plant Turbine Event Status Report
2
Opening Remarks - Joe Jensen, Senior Vice President and Chief Nuclear Officer
Unit 1 Event & Damage Summary - Larry Weber, Site Vice President
Root Cause - Ray Hruby, Site Services Vice President
Initiating Event
Equipment Root Cause
Recertification Report
Corrective Actions
Current Repair Status - Larry Weber
Modifications
Repairs Completed
Lower Exhaust Hood Details
Repairs Remaining
Rotor Support Testing
Restart Readiness - Larry Weber
Readiness Validation, Testing and Start-up
Closing Remarks and Questions - Joe Jensen Agenda
3 Event Description
On Saturday, September 20, 2008 at 2005 hours0.0232 days <br />0.557 hours <br />0.00332 weeks <br />7.629025e-4 months <br />, the control room experienced simultaneous high-high vibration readings on all main turbine bearings with severe vibration and rumbling felt coming from outside the control room.
The reactor operator manually tripped the reactor within 5 seconds, all control rods fully inserted, and major systems functioned as designed (Good operator response).
Turbine generator went from 1800 RPM to 0 RPM in less than 2 minutes.
4 Event Description
A main generator fire was caused by a failure of the hydrogen seal.
The shift manager initiated the Emergency Plan based on the fire in the protected area.
The fire was extinguished at 2028 hours0.0235 days <br />0.563 hours <br />0.00335 weeks <br />7.71654e-4 months <br />.
The Technical Support Center was functional at 2113 hours0.0245 days <br />0.587 hours <br />0.00349 weeks <br />8.039965e-4 months <br />.
The Unusual Event was terminated on Sunday, September 21, 2008 at 0409 hours0.00473 days <br />0.114 hours <br />6.762566e-4 weeks <br />1.556245e-4 months <br />.
5 Event Description Unit 1 Main Turbine-Generator Overview GE High Pressure Turbine GE Generator Siemens Low Pressure Turbines (3)
6 Damage Summary Excellent Response to Event-No Injuries Fire damage to main generator/exciter housing Turbine damage Piping insulation damage Visible concrete damage around turbine Oil spills Damaged hangers and supports on various pipe systems
7 Damage Summary LP turbine exhaust hoods LP turbine exhaust hoods display evidence of blade impact All blades were contained within turbine hoods Bearing housings were displaced
8 Damage Summary
Turbine shafts No coast down or turning gear operation Significant shaft scoring Bearing damage evident at all 12 main bearing locations
9 Damage Summary - Fire
Fire due to failure of generator hydrogen seal
Fire brigade responded and extinguished fire within 23 minutes
Excellent local fire department assistance
10 Damage Summary - Fire
The Fire Water System experienced complications including a breach of the piping on the West side of the plant, draining of the South Fire Water Tank and failure of the East Diesel Fire Pump.
The NRC sent a fire protection inspector to the site on September 21, 2008, to launch a Special Inspection Team (SIT).
The on-site NRC resident inspectors and SIT inspectors monitored activities associated with full restoration of the site-wide fire protection system and conducted an investigation into the causes of both the turbine failure and the fire suppression system failure.
A number of enhancements were identified and entered into the Corrective Action Program.
11 Initiating Event
Blade #40 on LP turbine B, turbine side (LP B TS) is liberated due to high cycle fatigue
Blade #56 on LP B TS also exhibited high cycle fatigue and is liberated during the event
Blade #189 on LP turbine C TS also exhibited high cycle fatigue and is liberated during the event
Blades #29 and #64 on LP B TS fracture in overload during the event
The loss of 5 L-0 blades creates a severe unbalance condition on the rotor
The high vibration of the unbalanced turbine causes extensive damage to connected systems.
12 Initiating Event LP B and LP C Blade Failures
13 Equipment Root Cause A Blade-Rotor System Design Which Failed to Provide Adequate Stress Margin in at Least Three L-0 Blades Findings:
Blade vibrations Indications of non-uniform loading in root engagement Normal electrical grid variations correlate to fracture beach marks
LPB Blade #40 Fracture Surface Distinctive Zones and Beach Marks
15 Recertification Report Single comprehensive document Revision 0 provided to the NRC Complete discussion of:
Damage to the turbine system Repairs performed Technical basis for restart Revision 1 will be approved prior to applying steam to the turbine
16 Corrective Actions Interim repaired LP turbines without L-0 blades Replace LP turbines with proven design in 2011 Design to be validated by a third party review Additional turbine monitoring instrumentation
17 Current Repair Status Design Modifications L-0 blades removed from LP turbines and baffle plates installed to mimic turbine pressure drop LP rotor - #3 disc reshaped to address rotordynamic resonance Exhaust hood and bearing housing stiffening struts installed to move shaft resonant speed away from operating speed.
Several other minor changes in dimensions and materials were made
18 Current Repair Status Repairs Complete
HP & LP turbine rotors repaired
HP turbine inlet and outlet piping reconnected to turbine shell
LP exhaust hood upper and lower seating surface repairs complete**
Generator rotor installed
Exciter installed
HP turbine - front and mid-standards complete
LP turbines - Repaired sole plates, concrete and foundation bolts
Repaired foundation plates and ready to grout
Support Systems being operated and flushed
- See next 5 slides for a description of the significance of the lower exhaust hood repair effort
19 Lower Exhaust Hood (LEH)
Cone extension pushed down during the event Caused vertical surfaces to push outward
20 Initial Inspection of LEHs Initial damage assessment:
Structural supports and struts damaged Cone extension have moved Grout cracking and foundation bolts damaged LEHs required extensive repairs and are now complete Cracked welds
21 Lifting LEHs Struts and supports Lift system Issue on first lift attempt:
Sole plates between hoods were welded, due to event, to bottom of LEH feet. Had to be cut without effecting hood supports.
Hood feet Sole plate Cut
22 Inspection after Lift
Sole plates welded to bottom of LEH feet causing damage to feet, requires machining
Cone extensions have pushed vertical wall on north and south ends
Large number of welds inside the cones had to be repair and stressed relieved.
Upper hood Scope expansion:
- 1) Number of welds
- 2) Lift hoods additional 2 for machining
- 3) Machining feet and verticals Major challenges:
1)
Hood movement during repairs 2)
Access to welds
23 Repairs after LEHs Set
100% NDE on welds revealed more repair then expected.
Weld build-up on horizontal cone section and bolt holes.
Machining on horizontal cones
Installation of strut modification
Weld buildup and machining on horizontal surfaces for UEH and LEH fit.
Lower exhaust hood alignment to centerline
Weld buildup for boring operations Challenges:
Never been done Volume of welding in small area Stress relieve of cones during welding and hood movement due to welding
24 Current Repair Status Repairs Remaining Lower inner casing installation Main turbine lube oil system cleanup Main generator seal oil system cleanup Main condenser eddy current testing, repair and cleanup Cleanup of all secondary system heat exchangers Replace and setup turbine digital control system and Turbine supervisory instruments
25 Rotor Support Testing Rotor is supported by foundation, bearings, and oil film Testing will verify that adequate support exists Shaker testing allows for selective identification of natural resonances Concrete foundation adequacy has been verified by initial testing Bearing cone testing is in progress Total shaft support testing will follow later in the testing program
26 Restart Readiness Validation, Testing & Start-up
Validation Recertification Report Independent assessment by MPR Associates System Affirmations
Testing Baffle plate bump test Rotor support bump and shaker testing Laser alignment checks of rotor bearings Support system performance monitoring
Start-up
3 hour3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> ramp from 10% to 29% power (400 minute minimum heat soak) 10 hour1.157407e-4 days <br />0.00278 hours <br />1.653439e-5 weeks <br />3.805e-6 months <br /> ramp from 29% to 68% power (200 minute minimum heat soak)
8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> ramp from 68% to 100% power Online torsional monitoring and shaft vibration monitoring
27 Closing Remarks and Questions
Overall Major physical event to the Cook plant Major emotional event to Cook employees and stakeholders Repair effort is unprecedented in nuclear industry (biggest insurance claim ever)
The Cook teams immediate and long term response to the event were recognized by the industry as very good
Unit 2 has continued to safely operate
Nuclear safety culture has remained strong (October 2009 USA Assessment)
The Cook team is a stronger, smarter, more agile team as a result of the event.
Questions?