1. Feedwater System Reliability Users Group 2015 Meeting San Antonio James Alston – South Texas Project Rob Frazee – South Texas Project Frank Todd – True North Consulting, LLC Ken Porter – True North Consulting, LLC STP Feedwater Pipe Erosion and Nozzle Replacement Options

2. Feedwater Pipe Erosion Discovery of Pipe Wall Thinning Erosion of the main feedwater piping in the area of the CrossFlow Transducers Discovered in December 2013 LER submitted January 2014 For Overpower Event – Withdrawn After Evaluation Compensatory Actions Revised pipe wall thickness values inserted in flow computer Compensate for change in flow area Mitigate any possible overpower condition

3. Feedwater Pipe Erosion Assumption ◦ Erosion Occurred Slowly Over Time ◦ Any Power Change Would Also Occur Over Time Methodology Analysis Would Have To Include Data From Multiple Cycles To Pick-up Suspected Change In Indicated RX Power

4. Feedwater Pipe Erosion Three Evaluation Methods Chosen ◦ MW Output Vs CW Temperature (Multiple Cycles)  Assumes Steady Operation From Cycle To Cycle  Assumes No Other Significant TP Events ◦ True North Power Predictor  Utilizes A “Best Estimate Statistical Analysis” Method  Assumes Valid Baseline Data Is Available ◦ Analysis Of HP Turbine Parameters Over Time  Assumes Good Operation

5. Feedwater Pipe Erosion Unit 1 – MW Output Vs CW Temperature Chart

6. Feedwater Pipe Erosion Significant Issues In Unit 1 Data Data Not Available Prior To Cycle 12 Cycles 12-13 Combined (Prior To LP Turbine Retrofit) Cycle 15 Data Split To Show Impact of Extraction Steam Bellows Failure Cycle 17 Data A Clear Outlier ◦ Problem With MW Transducer During Cycle Cycle 18 Htr 15c Extraction Line Issue Cycle 18 Significant Reduction In Plant Output When New Pipe Wall Thickness Value Inserted In January 2014

7. Feedwater Pipe Erosion Unit 2 – MW Output Vs CW Temperature Chart

8. Feedwater Pipe Erosion Significant Issues In Unit 2 Data Data Not Available Prior To Cycle 10 Cycles 10-12 Combined (Prior To LP Turbine Retrofit) Cycle 14 Data Split To Show Impact of Extraction Steam Bellows Failure Cycle 17 Significant Reduction In Plant Output When New Pipe Wall Thickness Value Inserted

9. Feedwater Pipe Erosion Unit 1– Predicted RX Power Vs Time

10. Feedwater Pipe Erosion Unit 2– Predicted RX Power Vs Time

11. Feedwater Pipe Erosion PAA (Polyacrylic Acid) Injection Evaluation ◦ Unit 1 Began Injection In Cycle 16 (Dec. 2010) ◦ Unit 2 Began Injection In Cycle 15 (Feb 2011) No Evidence That PAA Injection Caused A Change In Flow Measurement

12. Feedwater Pipe Erosion Unit 1 Plant Parameter Evaluation

13. Feedwater Pipe Erosion Unit 2 Plant Parameter Evaluation

14. Feedwater Pipe Erosion Unit 1 Average Calculated CrossFlow CF Vs Time Unit 2 Average Calculated CrossFlow CF Vs Time

15. Feedwater Pipe Erosion 15

16. Feedwater Pipe Erosion Conclusions No Overpower Event Despite Erosion Suspect Change In Pipe Wall Roughness Resulted In Flow Profile Change

17. Flow Nozzle Replacement Original Meter Design ◦ Nom. pipe size = 18.00 in. ◦ Pipe I.D. = 15.250 in. ◦ Nozzle throat I.D. = 8.0063 in. ◦ Ref. Temp. = 68 Deg. F ◦ Carbon steel pipe ◦ Stainless steel nozzle and downstream portion of recovery cone ◦ Carbon steel end of recovery cone ◦ Angle of divergence of recovery cone (from centerline) = 6 Deg. 30 Min. ◦ Three tap sets, 120 Deg. apart. ◦ Upstream taps have stainless steel tube inserts with 0.25” I.D. ◦ Throat taps are 0.25” I.D. and connected to outside pipe taps by internal tubing. 17

18. Flow Nozzle Replacement Original Meter Design 18

19. Flow Nozzle Replacement Modified for inspection port and flanges 19

20. Flow Nozzle Replacement Difficult Access 20 Piping plan view of the area around the feedwater flow nozzles. The feedwater flow nozzles are wedged in below some larger piping. Part of the meter runs are also located above the diesel generating room.

21. Flow Nozzle Replacement Sample Isometric of Flow Nozzle 21

22. Nozzle Error Modes 22 Upstream fouling or erosion – roughness & diameter effects Upstream erosion around tap Leaking throat tap Nozzle fouling– roughness effects Drain hole erosion Failure of nozzle attachment point Throat Tap irregularities

23. Flow Nozzle Replacement Upstream Tap Condition – Possible Effects 23 Possible higher pressure measurement on the upstream tap due to pipe diameter change and localized turbulence could result in a higher dp measurement at a given flow rate. Plant data indicates that the overall effect was in the conservative direction.

24. Flow Nozzle Replacement Flow Comparison 24

25. Flow Nozzle Replacement Flow Comparison 25

26. Feedwater Nozzle Replacement Proposed Design Options ◦ Removable PTC 6 Nozzle/Recovery Cone Insert ◦ Welded-in Flow Nozzle/Recovery Cone Meter Tube ◦ Flanged Low Head Loss Nozzle Meter Tube Other Options Considered ◦ Universal Venturi Tube ◦ ASME Classical Venturi ◦ High Head Recovery Meter Tube 26

27. Feedwater Nozzle Replacement Proposed Design- Removable PTC 6 Nozzle/Recovery Cone Insert 27

28. Feedwater Nozzle Replacement ◦ Welded-in Flow Nozzle/Recovery Cone Meter Tube or Flanged Low Head Loss Nozzle Meter Tube (similar design but shorter length) 28

29. Feedwater Nozzle Replacement 29 DesignCostUncertainty Removable PTC 6 Nozzle/Recovery Cone 60 -100K plus calibration 0.2% to 0.3% (meets almost all ASME Specs) Welded-in Flow Nozzle/Recovery Cone180K plus calibration 0.2% to 0.3% (meets all ASME Specs) Low Head Loss Meter Tube94K plus calibration 0.5% (does not meet all ASME Specs)

30. Feedwater Nozzle Replacement 30 Selected Replacement Nozzle – Triad ASME PTC-6 LHL Flow Meter Tube