ML13094A191
| ML13094A191 | |
| Person / Time | |
|---|---|
| Site: | Saint Lucie  |
| Issue date: | 03/14/2013 |
| From: | Gil R Florida Power & Light Co |
| To: | Division of Operating Reactor Licensing |
| Rodriguez R NRR/DORL/LPL2-2 | |
| Shared Package | |
| ML13094A174 | List: |
| References | |
| TAC ME9534 | |
| Download: ML13094A191 (16) | |
Text
St. Lucie (PSL) Unit 2 Steam Generators Results of Fall 2012 Inspection p
Nuclear Regulatory Commission (NRC) /
g y
(
)
Florida Power and Light (FPL) Meeting R d Gil Rudy Gil March 14, 2013
Discussion Topics Steam Generator (SG) Design SG Inspection History Previous Inspection Results Summary Previous Inspection Results Summary Root Cause Evaluation Overview Numbers of Indications and Tubes Affected Wear Rate Progression Depth Distributions O
ti l A t (OA) R lt S
Operational Assessment (OA) Results Summary Conclusion 2
The St. Lucie Unit 2 Replacement SGs are Areva Model 86/19TI recirculating units - Installed in 2007 Each of the two SGs has 8999 t b STEAM GENERATOR (SG) DESIGN tubes The SGs have seven horizontal supports that incorporate the broached design and the tubes broached 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 four sets of rectangular Anti-Vibration Bars (AVBs) installed in a V-shape The horizontal support and AVB materials are stainless steel The tubes are Thermally Treated 3
y Alloy 690
Inspection After Each of the First Three Cycles SG INSPECTION HISTORY SGs replaced in 2007 at End-of-Cycle (EOC) -16 outage SG INSPECTION HISTORY Three Inspections have been performed since replacement
- All three previous inspections were 100% bobbin inspections
- 1st in-service inspection in 2009 at EOC-17 outage
- 2nd in-service inspection in 2011 at EOC-18 outage
- 3rd in-service inspection in 2012 at EOC-19 outage p
g
- Selected rotating probe inspections were performed each outage Top-of-tubesheet locations in periphery tubes for both hot/cold legs p
p p
y g
Special interest and flaw profiling
- 4th in-service inspection planned for 2014 at EOC-20 4
p p
will also include 100% bobbin and selected rotating coil exams
Higher than expected wear identified after the first cycle of operation (CY-17).
The EOC-17 inspection (performed after the first cycle of operation of the replacement SGs) identified a number of PREVIOUS INSPECTION RESULTS
SUMMARY
operation of the replacement SGs) identified a number of tube-to-AVB wear indications
- The indications were above expectations in both the number and the depth the depth
- No tubes plugged for indications >40% Through-Wall
- 13 tubes plugged to address uncertainty Th OA l
l t d P
b bilit f B t (POB) f 2 4% f th
- The OA calculated a Probability of Burst (POB) of 2.4% for the second cycle of operation (CY-18); allowable value is 5%
5
As expected, wear rates attenuated during the second cycle of operation (CY-18)
PREVIOUS INSPECTION RESULTS
SUMMARY
(C t )
The EOC-18 inspection results show that wear rates attenuated significantly during the second cycle of PREVIOUS INSPECTION RESULTS
SUMMARY
(Cont.)
attenuated significantly during the second cycle of operation
- Average wear rates reduced from 7.9% to 3.9% per EFPY in SG A and from 7 2% to 1 3% per EFPY in SG B A and from 7.2% to 1.3% per EFPY in SG B (EFPY =Effective Full Power Years)
- At EOC-18, one tube plugged for an indication sized at 40%
Through Wall; 18 additional tubes plugged based on Through-Wall; 18 additional tubes plugged based on deterministic review
- POB for third cycle reduced to 0.07%
6
No tube integrity issues identified after third cycle of operation (CY-19)
PREVIOUS INSPECTION RESULTS
SUMMARY
(Cont )
The EOC-19 inspection results show the wear rates continue to attenuate PREVIOUS INSPECTION RESULTS
SUMMARY
(Cont.)
- Average wear rates reduced from 3.9% to 2.2% per EFPY in SG A and from 1.3% to 0.6% per EFPY in SG B
- No tube integrity issues identified*
g y
- Seven tubes plugged in SG A for indications sized at 40%
- No tubes plugged for indications >40% Through-Wall in SG B Additi l t b l
d b d
d t i i ti i
- Additional tubes plugged based on deterministic review 97 in SG A, 15 in SG B
- POB for 4th cycle calculated to be 2.5% (1.30 EFPY)
Based on planned cycle length POB is 1.5% (1.27 EFPY)
Unit went back on line on November 23, 2012 Unit reached 100% power on December 16 2012 7
- Unit reached 100% power on December 16, 2012
- Based on Structural Integrity Performance Criteria
Industry Operating Experience Applied to St. Lucie PREVIOUS INSPECTION RESULTS
SUMMARY
(Cont )
PREVIOUS INSPECTION RESULTS
SUMMARY
(Cont.)
SONGS Operating Experience (OE) was applied to the inspection inspection
- No issues were identified
- Specific analysis training was provided to St. Lucie data analysts using actual SONGS wear data 8
Root cause completed ROOT CAUSE EVALUATION OVERVIEW A comprehensive root cause evaluation was completed ROOT CAUSE EVALUATION OVERVIEW The root cause investigated a full range of potential contributors
- Design process g
p
- Manufacturing process
- Materials and associated tolerances P t ti l ti l
ff t
- Potential operational effects 9
Cause of the tube wear is understood ROOT CAUSE EVALUATION OVERVIEW (Cont )
The conclusion of the root cause was that the U-tubes were not effectively supported during the tubing ROOT CAUSE EVALUATION OVERVIEW (Cont.)
were not effectively supported during the tubing installation process
- Tube bundle was allowed to sag, causing slight deformation of the AVBs which in turn closed the tube to AVB gap the AVBs, which in turn closed the tube-to-AVB gap
- Condition caused tubes to be in constant contact with AVBs at several locations, contrary to design specification and models
- The constant contact did not permit the design gap to exist between tubes and AVBs, allowing tube wear to continue in the affected tubes/areas N
h i
ll l
i id tifi d b d
No changes in overall conclusions identified based on third cycle inspection results 10
Number of indications continued to increase, as expected NUMBERS OF INDICATIONS AND TUBES AFFECTED INSPECTION YEAR 2009 2011 2012 SG A 3700 / 1231 5862 / 1853 7485 / 2216 SG B 2155 / 814 2963 / 1125 4033 / 1529 11
Wear rate attenuation continued WEAR RATE PROGRESSION (% PER EFPY)
INSPECTION YEAR 2009 2011 2012 Avg Upper Avg Upper Avg Upper WEAR RATE PROGRESSION (% PER EFPY)
Avg.
Growth Upper 95th Avg.
Growth Upper 95th Avg.
Growth Upper 95th SG A 7.9 13.6 3.9 9.9 2.2 7.5 SG B 7.2 12.8 1.3 6.3 0.6 4.2 SG B 7.2 12.8 1.3 6.3 0.6 4.2 12
In SG A, ~87% of the indications are below 25% wear DEPTH DISTRIBUTIONS 3500 AVB Wear Indication Depth Distribution PSL-2 SGA Sep-2012 2500 3000 s
Previously-Reported Indications Newly-Reported Indications 1500 2000 ber of Indications 500 1000 Numb
<5%
5-9%
10-14%
15-19%
20-24%
25-29%
30-34%
35-39%
40-49%
50-59%
>=60 Previously-Reported Indications 163 1795 1174 860 670 483 313 119 7
0 0
0 500 13 Newly-Reported Indications 4
1354 328 141 59 13 2
0 0
0 0
Estimated Bobbin Depth (%TW)
Note: %TW = % Through-Wall
In SG B, ~97% of the indications are below 25% wear DEPTH DISTRIBUTIONS (Cont.)
3500 AVB Wear Indication Depth Distribution PSL-2 SGB Sep-2012
(
)
2500 3000 s
Previously-Reported Indications Newly-Reported Indications 1500 2000 ber of Indications 500 1000 Numb
<5%
5-9%
10-14%
15-19%
20-24%
25-29%
30-34%
35-39%
40-49%
50-59%
>=60 Previously-Reported Indications 110 1629 632 241 114 81 23 23 0
0 0
Newly-Reported Indications 7
1026 105 32 10 0
0 0
0 0
0 0
14 Estimated Bobbin Depth (%TW)
Note: %TW = % Through-Wall
OA supports full cycle operation OPERATIONAL ASSESSMENT (OA) RESULTS
SUMMARY
The OA calculated a Probability of Burst (POB) of 2.5%
for the fourth cycle of operation (CY-20); allowable value is 5%
- Second OA performed by Areva for verification of results; provides good agreement (Areva OA POB value is 2.4%)
- Based on actual planned cycle length POB is 1 5%
Based on actual planned cycle length, POB is 1.5%
Wear rate increase factor of 24% (based on Areva analysis) applied to account for effects of power-uprate Additional tubes plugged based on deterministic review Additional tubes plugged based on deterministic review
- 97 in SG A, 15 in SG B Tubes with multiple indications Tubes with high wear depth Tubes with high wear rate EOC-20 Inspection planned for next outage 15 EOC-20 Inspection planned for next outage
~ 15 months total cycle length
Inspections continue to show that the wear rate is attenuating CONCLUSION Three 100% inspections have now been completed CONCLUSION No tube integrity issues have been identified No tube-to-tube wear has been identified Average and statistical wear rate attenuation continues Average and statistical wear rate attenuation continues OA results support a full cycle operation
- Power Uprate conditions have been incorporated for Cycle 20 Next inspection planned after the current cycle of operation at EOC-20 (planned for March, 2014) 16