1. TVA Sequoyah and Watts Bar Nuclear Plants
Feedwater Control System Upgrades – Lessons Learned
Scott Gladney
Digital Upgrade Program Manager
1/23/13

2. Key Project Goals Replace obsolete Foxboro H-Line components
Continued K1 Relay issues
Limited Replacement Controllers/Modules
Reduce single point vulnerabilities (~40/unit)
Multiple unit trips due to K1/Local Remote select switch issues
Original design relied on single power feeds for critical components
Ease Operator Burden
Improve automatic control capability at low power
Automate feedwater valve transfer (SQN)
Auto Balance feedpumps during second pump start
Reduce operator actions during instrument malfunctions

3. Project History - Sequoyah
Project to replace NSSS and BOP controls is started
2002 – Original project cancelled due to engineering budget and schedule issues
Fall 2007 – Feedwater Controls portion of the Project is restarted
09/08 – Unit 1 Factory Acceptance Test
11/08 - Unit 1 Installation delayed from R16 to R17 due to Procedures
02/09 – Unit 2 Factory Acceptance Test
11/09 - U2R16 - Unit 2 Feedwater Controls Installation
11/10 – U1R17 - Unit 1 Feedwater Controls Installation

4. Project History – Watts Bar
Fall 2007 – Feedwater Controls and Boric Acid Blend Controls Replacement Project is started in conjunction with Sequoyah
07/09 – Unit 1 Project Cancelled
03/10 – U1R10, original scheduled installation
10/10 – Unit 1 Project resurrected, up-scoped due to WBN2
01/12 – All DCS but FW removed from U1R11 Outage
04/12 – Unit 1 Factory Acceptance Test
11/12 – U1R11 - Unit 1 Feedwater Controls Installation
04/14 – U1R12 - Scheduled remainder of DCS install (Major BOP/NSSS Control)

5. System Enhancements
Replaced selector switch driven Feed/Steam Flow channel selection with software average and failure detection
Removed ~40 single point failure vulnerabilities per unit such as hand stations, power supplies, inputs, etc.
All new system power comes from diverse sources
Redundant output cards used for critical control functions
Channel segregation used to protect inputs on hardware failure
Automated operator critical functions such as valve transfer (Sequoyah) and placing second main feed pump in service
Enabled full automatic control from startup to full power (2% to 100% power at Sequoyah).

6. System Acceptance Testing
Factory Acceptance Testing
Medium Fidelity Simulated Model
Failure Mode Testing
Network Broadcast Storm
Power failure (including transmitter input and power supply)
Component Failures
Parameter updates (block reset)
EMI/RFI Testing
Performed in-house at a TVA lab
Used to validate results from Foxboro and 3rd parties
No changes required due to this testing
Development system
Used for Engineering Code testing
Used for OPS procedure development
Used for Maintenance procedure development
Software Review
Complete review of software settings
Function testing to ensure analyzed timing still valid

7. Simulator Testing Additional Validation Testing performed on simulator
Used to validate system response
Controller tuning developed separately based on existing analog tuning settings and empirical models
Used to test failure modes and system response
Eagle Rack Failure/Lockup
Transmitter/Instrument Failures
Loss of Power Supply(s)
Design Enhancement due to lessons learned
Previously unknown plant design issue on loss of Vital Instrument Power Board locking a turbine runback in

8. Implementation Issues
Simulator
U2 installed first, U1 referenced simulator
Malfunctions had to be recreated, new ones developed
Training
Generic training vs. specific training
Generic Training for everyone vs. Maintenance Experts
Procedures
FW Controls affected hundreds of procedures across Maintenance, Engineering and Operations
Understaffing of procedure writers delayed implementation one cycle at Sequoyah
Significant changes to Operations Abnormal Operating procedures and General Operating Procedures
Materials
Large modification with lots of parts suppliers, track to ensure all parts are ordered and on-site
Bench calibrate items like transmitters, valve positioners, etc before the outage
Quantity of piece parts required due to retrofitting in old cabinets

9. Implementation Issues (cont.)
Challenges
Remaining rack analog hardware in-service during rack modifications
Re-use of existing racks at Sequoyah
Extensive Control Board Modifications
Poorly documented or labeled internal cabinet wiring in original plant cabinets

10. System Testing Outage Testing Startup Testing
Loop tests integrated with normal outage activities
Hardware calibration verification done pre-installation
Testing performed parallel to installation
Startup Testing
Intentional Process upsets to validate tuning
Main Feed Pump Output Step Change
Feedwater Flow Step Change
Steam Generator Level Setpoint Step Change
Monitoring of normal startup transients

11. Post Implementation Issues
All Problems are because of the DCS
The new controls will be initially blamed for plant problems till proven otherwise
Different characteristic response isn’t necessarily bad
New or enhanced monitoring capability
Legacy issues will come to the surface as “new” problems
Valve Setup
Measurement problems
Feedpump/Heater oscillations
Establish Performance Requirements beforehand
Specific Issues
Sequoyah Unit 2 Thermal Power Oscillation
Initially blamed on DFW modification
Sequoyah Unit 1 Reactor Trip
Missed PMT of Steam Dump Controller (relocated old analog controller)
Watts Bar Unit 1 Down Power
I/P transducer issues on Main Feedwater Reg Valves

12. Lessons Learned Dedicated Team Simulator testing invaluable
A dedicated team for the project needs to be selected early and turnover kept as low as possible throughout the project
Includes Maintenance, Ops, Engineering, and Training.
Simulator testing invaluable
Great for proof of concept, training, experimental tuning, etc
Do NOT tune the plant system to the simulator and expect it to be perfect
Utilize new racks if possible
Create a highly integrated schedule (Mods, Maintenance, Testing, Ops)
Material Verification
Place hands on parts well prior to outage
Establish holding area for project parts

13. Future Plans
Complete moving the NSSS/BOP Critical Control Functions into DCS
Pressurizer Pressure and Level
CVCS Volume Control
Boric Acid Blending
Steam Dumps and Atmospheric Reliefs
Automatic Rod Control module
Upgrade Main Feed Pump turbine controls
Main Feed Reg Valve positioner upgrade

14. Any Questions?