ML14232A067
| ML14232A067 | |
| Person / Time | |
|---|---|
| Site: | Saint Lucie  |
| Issue date: | 08/21/2014 |
| From: | Gil R Florida Power & Light Co |
| To: | Plant Licensing Branch II |
| Saba F DORL/LPL2-2 301-415-1447 | |
| References | |
| Download: ML14232A067 (10) | |
Text
St. Lucie (PSL) Unit 1 Steam Generators Results of Fall 2013 Inspection p
Nuclear Regulatory Commission (NRC) /
g y
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Florida Power and Light (FPL) Meeting R d Gil Rudy Gil August 21, 2014
Discussion Topics Steam Generator (SG) Design SG Inspection History Fall 2013 Inspection Results Fall 2013 Inspection Results Cause Evaluation Results Operational Assessment (OA) Results Summary p
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y Conclusion 2
The St. Lucie Unit 1 SGs are Babcock and Wilcox (BWI)
Replacement RSGs - Installed in 1997 Each of the two SGs has 8523 t b STEAM GENERATOR (SG) DESIGN tubes The SGs have seven horizontal supports that incorporate the lattice grid design and the tubes lattice grid design and the tubes are in a triangular pitch configuration The U-bend section of the tube The U-bend section of the tube bundle includes twelve flat fan bar supports The horizontal support and AVB The horizontal support and AVB materials are 410S stainless steel The tubes are Thermally Treated 3
y Alloy 690
Five Inspections Since Replacement SG INSPECTION HISTORY SG INSPECTION HISTORY Inspection Year Bobbin Inspection Scope No. of New Fan Bar Wear Indications Deepest Indication No. Tubes Plugged for Fan Bar Wear 1999
~50%
17 34%
11 (Preventive) 2001
~50%
2 16%
0 Skip Cycle 2004
~50%
13 32%
3 (Preventive)
Double Skip Cycles Double Skip Cycles 2008 100%
9 18%
0 Double Skip Cycle 2013 100%
215 25%
135 (Preventive)
Number of indications identified during first inspection were attributed to isolated welding manufacturing issue 4
welding manufacturing issue.
2013 Inspection Background and Results Power Uprate Conditions Implemented (~ 12% increase)
Overview
- First two cycles after fourth inspection were operated at pre-Power Uprate conditions
- The third cycle ran ~ 3 months under pre-Power Uprate conditions and 14 months under Power Uprate conditions conditions and 14 months under Power Uprate conditions.
The fifth inspection in 2013 identified 215 new fan bar wear indications.
N f
b i di ti i
t b b
dl l
ti
- New fan bar wear indications in new tube bundle locations
- The deepest new fan bar wear indication was 25%
- Pre-existing fan bar wear indications had minimal growth
- Very conservative plugging was implemented
- 135 tubes were preventatively plugged (All tubes containing fan bar wear indications) 5 (All tubes containing fan bar wear indications)
- No tube integrity concerns identified
Summary of Indications at 2013 Inspection FIRST INSPECTION AFTER POWER UPRATE 6
Summary of Indications at 2013 Inspection FIRST INSPECTION AFTER POWER UPRATE Tubesheet Map - SG A Distribution (SG B is similar) 7 Tubesheet Map SG A Distribution (SG B is similar)
A - Previous Indications, B - New Indications
Root cause completed ROOT CAUSE EVALUATION OVERVIEW A root cause evaluation was completed The root cause investigated a range of potential ROOT CAUSE EVALUATION OVERVIEW The root cause investigated a range of potential contributors and reviewed all relative industry operating experience (OE)
Cause of increased wear is attributed to operation at Cause of increased wear is attributed to operation at Power Uprate conditions
- More severe thermal-hydraulic conditions in the U-bend region of the tube bundle at Power Uprate conditions the tube bundle at Power Uprate conditions
- Random tube support clearances attributable to manufacturing tolerance distributions and operational hydraulic forces leading to some tube support locations becoming more susceptible to to some tube support locations becoming more susceptible to vibration.
No corrective actions except to monitor the wear at future scheduled inspections 8
p Wear rates are expected to attenuate based on OE
Operational Assessment Allows for Two-Cycle Run OPERATIONAL ASSESSMENT Probabilistic Operational Assessment was performed
- Confirms two-cycle run is acceptable
- 2.8% Probability of Burst for two cycles y
y Key Operational Assessment Assumptions
- The wear rate distribution is based on only the new wear detected assuming the starting depth was zero detected assuming the starting depth was zero
- No credit is taken for wear rate attenuation over future operating cycles
- The wear rate model in this analysis is depth-based and not The wear rate model in this analysis is depth based and not volume-based
- Although all tubes with wear indications were removed from service, the model incorporates the probability of wear indications having been missed due to the probability of 9
indications having been missed due to the probability of detection
Wear indications and wear rate is expected to decrease CONCLUSION New fan bar wear indications were identified after transition to Power Uprate operation CONCLUSION transition to Power Uprate operation No tubes required plugging per Technical Specifications 135 tubes were preventatively plugged No tube integrity issues were identified OA results support two full cycles of operation Number of indications & wear rates expected to decrease Number of indications & wear rates expected to decrease The OA calculated a Probability of Burst (POB) of 2.8%
for the next two cycles of operation; allowable value is 5%
5%
Next inspection planned after two cycles of operation at EOC-26 (planned for September, 2016) 10