Seabrook Station Condenser Tube Leaks. Jim Johnson Seabrook Station FSRUG 2017

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1 Seabrook Station Condenser Tube Leaks Jim Johnson Seabrook Station FSRUG

2 Seabrook Condenser Tube Leaks Seabrook Condenser and Circulating Water Design 4 Loop Westinghouse PWR, 1296 MWe Generation Site was intended for 2 Units, only 1 Completed. Cooling water North Atlantic Ocean Tunnels (~3 miles) run from site to ocean for intake and discharge of cooling water. North Atlantic is great source of cooling water, maximum temperature ~65F for a few hours a summer, average sustained high temperature is about ~55F. Foster Wheeler Condenser 3 Interconnected Shells, Two Pass (bundles) in each Shell. Designed and constructed for Cu-Ni tubes Converted to Titanium tubes before any tubes were installed Support spacing was too long, installed lots of stakes, piano wire, and micarta bracing before plant start up. Condenser Tube Protection is Steam Generator Protection Condenser and Steam Generator Health are Plant Enterprise Risk 2

3 Seabrook Condenser Tube Leaks Circulating Water System 3

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5 Seabrook Condenser Tube Leaks Tube leaks on A and C waterboxes were discovered before plant startup Small tube leak on CO-E-27-C, North Bundle, caused by tube stake wear. Located by ECT. May 2002 B Waterbox, Leakage past a plug in a plugged tube. Plug was removed for waterbox coating. Tube was removed from tube sheet and same size plug was re-installed. This was very difficult to find; open waterbox with vacuum in condenser would draw plug in, CW flow would move plug around. These two events were caused by human error. 5

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7 Seabrook Condenser Tube Leaks History of Tube Leaks 2002 Event was a challenge to locate resulted in a review of unlikely leak paths. Leak at tube sheet, condenser, and waterbox mechanical joint Tube sheet leak at tube, below, coating. Tube sheet Conductivity Trough 7

8 Seabrook Condenser Tube Leaks History of Tube Leaks 6/5/2008 CO-E-27-C, Rapid increase in Sodium Levels Operating at full power with HD condenser dump valve full open for 60 hours. Downpower to 30% to repair. Tube in discharge of HD dump pitted. ~36 Hours to find and repair while at 30% to 50% power. Human Error or Equipment Error? Risk of running with HD dump open was known to engineering, Risk was not recognized by station Uprate had increased HD dump flow HD pump work was planned for one shift, but lasted much longer Less time on dump might have allowed pitting on tube to be identified and fixed before failure. 8

9 Heater Drain Tube Failure from Heater Drain Dump Flow

10 Spring 2015 Tube Leak Steam Generator Sodium Trends - Hotwell Trends Spike when shifting water box priming pumps Real indication on SG Sodium Levels. One hotwell instrument was out of service. Investigation finds nothing Second Minor Spike no corresponding event SG Sodium Levels Remain Elevated, need higher blowdown flow rates to maintain normal levels Hotwell Sodium instruments vs. hotwell or trough conductivity? Sodium much more sensitive at low levels. Suspect leak - A Condenser Wood flour injection Maximum blowdown flow for several months to maintain acceptable sodium levels most being dumped overboard Plan for outage work How to find leak at about 0.1 gallons per day? 10

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12 Finding Low Level Leak Overall Success Isolated waterbox a couple days early (reduced power) to allow time for Helium testing with full vacuum. Used various size boxes to attempt to get a leak region. Could get a repeat hit in one area of air removal section. Questionable on repeat hits of single tubes. Hits were much slower and lower than normal almost noise. Used Helium Testing, Dimple Plugs, and Eddy Current Testing Dimple plugs 2 more hits, then positive He (at below normal criteria) on these tubes Later realized dimple plugs need careful technique, stoppers or plugs on opposite end can trap air in tube, can pinch dimple plug if pushed too far in. Many False Positives Fall 2015 Planned Outage How Long for Results? Tube Leak Who can Touch? Work Order Steps, Procedural Compliance. 12

13 General area He hit Specific tube He hits ECT >90% wall loss 13

14 Fall 2015 Refueling Outage Extent of Condition Added ECT scope to include most of Air Removal section on other 5 tube bundles. No other issues noted. Tube that had failed was confirmed with array probe could see tube was moving mid-span and contacting three adjacent tubes. No ECT on failed tube since 100% baseline before plant startup. ECT scope was based on likely areas of damage and repeat on sample tube to see if an trend was occurring. About 10% of tubes were tested each refueling outage. Final results first equipment related failure, direct cause was movement of tube, reason for movement is unknown. Tube has not been pulled. 14

15 Post Outage Winter Another Tube Leak? Shortly after Outage Spikes in Condenser and SG Sodium Increased Blowdown Flow Needed Wood flour back on line 1/17/2016 Downpower to 700MWe to Remove A Waterbox from Service (82 hours to repair) SG Soduim \\sbksa10\sc_a1961_v \\sbksa10\sc_a4744_v \\sbksa10\sc_a4745_v 2.5 \\sbksa10\sc_a4746_v \\sbksa10\sc_a4751_v \\sbksa10\sc_a4781_v \\sbksa10\sc_a4782_v \\sbksa10\sc_a4783_v \\sbksa10\sc_a4784_v \\sbksa10\sc_a4785_v \\sbksa10\sc_a4786_v \\sbksa10\sc_b8241_v \\sbksa10\sc_b8242_v 1 \\sbksa10\sc_b8243_v \\sbksa10\sc_b8244_v \\sbksa10\sc_b8245_v \\sbksa10\sc_b8246_v \\sbksa10\sc_d5106_v 0.5 \\sbksa10\sc_d5108_v \\sbksa10\sc_d5110_v \\sbksa10\sc_a0082_v \\sbksa10\sc_a0022_v /12/ :38:18 AM days STM GEN A BLOWDOWN SODIUM CONDENSER 27C NORTH SODIUM CONDENSER 27C SOUTH SODIUM CONDENSER 27B NORTH SODIUM CONDENSER 27B SOUTH SODIUM CONDENSER 27A NORTH SODIUM CONDENSER 27A SOUTH SODIUM 1/23/2016 4:19:36 PM 15

16 Post Outage Tube Leak Tube Leak Found Used dimple plugs (on-site) to locate leak. Started installing in tube sheet at bottom and worked up. More tubes than dimple plugs. Technique is important Found Leak in A North bundle. Tube was inspected by ECT last outage Tube had a history of abnormalities sometimes noted Fleet had white paper instructions, but not incorporated into site work plans. With more information we might have detected this wall loss and plugged before leak. 16

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18 Known Defect? Extent of Condition Seabrook had been inspecting same tubes every outage 10% of tubes based on high risk location and a few general area Based on Updated ECT Screening Criteria there were many more suspect tubes based on existing ECT traces Many tubes were unknown no ECT data Rest of Cycle and Next Outage Digital Turbine Controls Related Trip allowed entry into all three waterboxes to plug 12 high risk tubes. 1 Spike in Sodium Levels Wood flour injection for a couple weeks Next Outage (4/1/2017) 100% Tube Cleaning (First time cleaning) 100% ECT on non-plugged tubes Future Increase ECT scope to get every tube in 10 years, ~18% of tube Remove and replace rubber plugs 18

19 Where do We Stand? 2 Equipment Related Tube Failures in Less than 1 Year Past History 3 tube failures, not directly equipment failures Titanium tubes Installation scratches and dings show up as failures after about years of operation? Are we going to see lots of tubes with potential issues when doing 100% ECT? When do we care how many we plug? Two recent failures Just bad luck? Second failure is in a likely location for bump damage Neither tube has been pulled (yet) or visually inspected. Long term low level leakage? SG Sodium levels tend to increase if SG blowdown is less than normal (60 gpm) years ago this didn t happen. What should we expect for future? 19