ML13094A191

Meeting Handout - Results of Fall 2012 Inspection

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: ML13094A181 ML13094A191 ML13094A193 ML13095A347
References
TAC ME9534
Download: ML13094A191 (16)

Text

St. Lucie (PSL) Unit 2 Steam Generators Results of Fall 2012 Inspection p

Nuclear Regulatory g y Commission ((NRC)) /

Florida Power and Light (FPL) Meeting Rudy R d Gil March 14, 2013

Discussion Topics

• Steam Generator (SG) Design

• SG Inspection History

• Previous Inspection Results Summary

• Root Cause Evaluation Overview

• Numbers of Indications and Tubes Affected

• Wear Rate Progression

• Depth Distributions

• O Operational ti l Assessment A t (OA) Results R lt Summary S

• Conclusion 2

The St. Lucie Unit 2 Replacement SGs are Areva Model 86/19TI recirculating units - Installed in 2007 STEAM GENERATOR (SG) DESIGN

• Each of the two SGs has 8999 t b tubes

• The SGs have seven horizontal supports that incorporate the broached design and the tubes are in a triangular pitch configuration

• 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 y Treated Alloy 690 3

Inspection After Each of the First Three Cycles SG INSPECTION HISTORY

• SGs replaced in 2007 at End-of-Cycle (EOC) -16 outage

• 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 p in 2012 at EOC-19 outage g

- Selected rotating probe inspections were performed each outage Top-of-tubesheet p locations in p periphery p y tubes for both hot/cold legs g

Special interest and flaw profiling

- 4th in-service inspection p p planned for 2014 at EOC-20 will also include 100% bobbin and selected rotating coil exams 4

Higher than expected wear identified after the first cycle of operation (CY-17).

PREVIOUS INSPECTION RESULTS

SUMMARY

• The EOC-17 inspection (performed after the first cycle of 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

- No tubes plugged for indications >40% Through-Wall

- 13 tubes plugged to address uncertainty

- The Th OA calculated l l t d a Probability P b bilit off B Burstt (POB) off 2.4%

2 4% for f the th 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 (Cont.)

t)

• The EOC-18 inspection results show that wear rates 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 77.2%

2% to 1 1.3%

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; 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 (Cont.))

• The EOC-19 inspection results show the wear rates continue to attenuate

- 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 g y issues identified*

- Seven tubes plugged in SG A for indications sized at 40%

- No tubes plugged for indications >40% Through-Wall in SG B

- Additional Additi l tubes t b plugged l d based b d on d deterministic t i i ti review i

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 16, 2012

• Based on Structural Integrity Performance Criteria 7

Industry Operating Experience Applied to St. Lucie PREVIOUS INSPECTION RESULTS

SUMMARY

(Cont (Cont.))

• SONGS Operating Experience (OE) was applied to the 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

• The root cause investigated a full range of potential contributors

- Design g p process

- Manufacturing process

- Materials and associated tolerances

- Potential P t ti l operational ti l effects ff t 9

Cause of the tube wear is understood ROOT CAUSE EVALUATION OVERVIEW (Cont (Cont.))

• The conclusion of the root cause was that the U-tubes were not effectively supported during the tubing installation process

- Tube bundle was allowed to sag, causing slight deformation of the AVBs AVBs, which in turn closed the tube tube-to-AVB 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 No changes h iin overall ll conclusions l i identified id tifi d based b d 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.

Avg Upper Avg.

Avg Upper Avg.

Avg Upper Growth 95th Growth 95th Growth 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 12

In SG A, ~87% of the indications are below 25% wear DEPTH DISTRIBUTIONS AVB Wear Indication Depth Distribution PSL-2 SGA Sep-2012 3500 Previously-Reported Indications 3000 Newly-Reported Indications 2500 2000 1500 Numb ber of Indications s

1000 500 0

10- 15- 20- 25- 30- 35- 40- 50- >=60

<5% 5-9%

14% 19% 24% 29% 34% 39% 49% 59%  %

Previously-Reported Indications 163 1795 1174 860 670 483 313 119 7 0 0 Newly-Reported Indications 4 1354 328 59 141Estimated 13 Bobbin 2 Depth 0

(%TW) 0 0 0 Note: %TW = % Through-Wall 13

In SG B, ~97% of the indications are below 25% wear DEPTH DISTRIBUTIONS ((Cont.))

AVB Wear Indication Depth Distribution PSL-2 SGB Sep-2012 3500 Previously-Reported Indications 3000 Newly-Reported Indications 2500 2000 1500 Numb ber of Indications s

1000 500 0

10- 15- 20- 25- 30- 35- 40- 50- >=60

<5% 5-9%

14% 19% 24% 29% 34% 39% 49% 59%  %

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 Estimated Bobbin Depth (%TW)

Note: %TW = % Through-Wall 14

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 length, POB is 1 1.5%

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

- 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 months total cycle length 15

Inspections continue to show that the wear rate is attenuating CONCLUSION

• Three 100% inspections have now been completed

• No tube integrity issues have been identified

• No tube-to-tube wear has been identified

• 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