05000389/LER-2006-001, Re Manual Reactor Trip Due to Condenser Tube Leak
| ML060870394 | |
| Person / Time | |
|---|---|
| Site: | Saint Lucie  |
| Issue date: | 03/17/2006 |
| From: | Johnston G Florida Power & Light Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| L-2006-079 LER 06-001-00 | |
| Download: ML060870394 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2)(viii)(A) 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(viii)(B) 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(ix)(A) 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(x) 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3892006001R00 - NRC Website | |
text
I FPL.
Florida Power & Light Company, 6501 S. Ocean Drive, Jensen Beach, FL 31957 March 17, 2006 L-2006-079 10 CFR § 50.73 U. S. Nuclear Regulatory Commission Attn: I)ocument Control Desk Washington, D. C. 20555 Re:
St. Lucie Unit 2 DocketNo. 50-389 Reportable Event: 2006-001-00 Date of Event: January 20, 2006 Manual Reactor Trip Due to Condenser Tube Leak The attached Licensee Event Report 2006-001 is being submitted pursuant to the requirements of 10 CFR § 50.73 to provide notification of the subject event.
Very tuly yours, Gordon L. Johnsto l
)
Acting Vice Presid St. Lucie Nuclear Plant GLJ/d]c Attachment P
an FPL Group company
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 06130/2007 (6-2004)
, the NRC may not condu:t or sponsor.
and a person is not required to respond to, the Information collection.
- 1. I-ALILI I Y NAM:
- 2. DCKET NUMBER I.AUE St. Lucie Unit 2 05000389 Page 1 of 4
- 4. JIiL1 Manual Reactor Trip Due to Condenser Tube Leak
- 5. EVENT DA-E
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVE)
"EAR YEAR NUENTRAL REvisioN MONTH DAY YEAR MONTHNUMBER MONH-AY EA 0lJ1 L
2 006 2006
-- 001 00 03 17 06
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANTTO THE REQUIREMENTS OF 10 CFR §: (Check all thal:apply) o l
20.2201(b) 0 20.2203(a)(3)(i) 0 50.73(a)(2)(i)(C) 0 50.73(a)(2)(vii) o 20.2201(d) 0 20.2203(a)(3)(ii) 0 50.73(a)(2)(ii)(A) 0 50.73(a)(2)(viii)(A) o 20.2203(a)(1) 0 20.2203(a)(4) 0 50.73(a)(2)(ii)(B) 0 50.73(a)(2)(viii)(B) o 20.2203(a)(2)(i) 0 50.36(c)(1)(i)(A) 0 50.73(a)(2)(iii) 0 50.73(a)(2)(ix)(A)
- 10. POWER LEVEL 0
20.2203(a)(2)(ii) 0 50.36(c)(1)(ii)(A)
S 50.73(a)(2)(iv)(A) 0 50.73(a)(2)(x) o00
° 20.2203(a)(2)(iii) 0 50.36(c)(2) 0 50.73(a)(2)(v)(A) 0 73.71(a)(4) o 20.2203(a)(2)(iv) 0 50.46(a)(3)(ii) 0 50.73(a)(2)(v)(B) 0 73.71(a)(5) o 20.2203(a)(2)(v) 0 50.73(a)(2)(i)(A) 0 50.73(a)(2)(v)(C) 0 OTHER Specif InAarct below or In D
20.2203(a)(2)(vi)
D 50.73(a)(2)(i)(B)
O 50.73(a)(2)(v)(D)
NRCForm 36liA
,Z.ZLLL-NbRSEE N I ACI I-UK Ilib5 LLIK NAML Donald L. Cecchett -
Licensing Engineer (772) 467 -
7155
=
On January 20, 2006, with St. Lucie Unit 2 in Mode 1 at 100 percent power, a Main Condenser high conductivity/sodium annunciator was received in the control room.
Chemistry confirmed that the high sodium level was due to seawater intrusion fron the 2B2 Main Condenser waterbox.
In accordance with the "Secondary Chemistry -
Off Normal Procedure," 2-0610030, a rapid down power was initiated.
The Shift Manager, based on Chemistry input and procedure direction, continued the down power and removed the unit from service rather than remain critical at a low power level.
All systems worked as designed and the reactor was manually tripped at approximately 25 percent power in accordarnce with plant operating procedures without incident.
All control rods fully inserted and the Steam Generator (SG) Safety Relief Valves did not actuate.
Feecdwater to the SG was supplied by the Main Feedwater (MFW) pumps during the shutdown and later transferred to the Auxiliary Feedwater (AFW) pumps.
All safe shutdown equipment operated as desicned with no equipment failures or impact to the health and safety of the public.
NNL i-IIM.jb tb-UU4)(6-2004)
U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION
- 1. FACILITY NAME St. Lucie Unit 2 TEXT (If more spa ce is required, use additional copies of NRC Form 366A, Description of the Event On January 20, 2006, with St. Lucie Unit 2 in Mode 1 at 100 percent power, annunciator G-20, "Condensate Conductivity/Sodium High" was received in the control room.
Chemistry confirmed that the high sodium level was due to seawater intrusion from the 2B2 Main Condenser waterbox.
In accordance with OP 2-0610030, "Secondary Chemistry - Off Normal Procedure,, a 1OMWe/minute down power to less than 5 percent power was initiated at 0742 in accordance with off-normal 2-ONP-22.01, "Rapid Do-n Power".
The 2B2 Circulating Water pump (EIIS:SG) was secured, and the 2B2 Main Condenser waterbox (EIIS:SG) was isolated.
The Shift Manager, based on Chemistry input and procedure direction, continued the down power and removed the unit from service.
At 0853, a brief for tripping the unit was performed and at 0856, the unit was trip~ped.
All systems worked as designed. All control rods fully inserted and the Steam Generator (SG) Safety Relief Valves did not actuate.
Feedwater to the SG was sup:plied by the Main Feedwater (MFW) pumps during the shutdown and later transferred to the Auxiliary Feedwater (AFW) pumps.
All safe shutdown equipment operated as designed with no equipment failure.
The main condenser (EIIS:SG) is classified as non-seismic, non-safety-related equipment.
The design basis for the condenser is condensation and de-aerating main steam flow exiting the low-pressure turbines.
Therefore, the identified failure of the condenser tube had no impact on the health and safety of the public and did not prevent the plant from ach2ieving a safe shutdown of the facility.
Cause oE the Event The cause of the rapid chloride and sodium level increase was a seawater 2B2 Main Condenser waterbox as a result of a condenser tube exhibiting a crack in the tube seam weld.
This type of crack is typically the result manufac:uring defect in the welded seam of the tube.
The rapid shutdown because secondary chemistry parameters reached Action Level 3 as defined Operations procedure OP-2-0610030, "Secondary Chemistry -
Off Normal".
5.3.5., for Action Level 3 requires a plant shutdown to at least Mode 2, safe operations permit, regardless of the duration of the excursion into Level 3.
leak in the longitudinal of a was reqclired in the Section as quickly as the Action
Analysis of the Event
The seawater contamination event led to the decision to trip the reactor is repo:rtable under 10 CFR 50.73(a)(2)(iv)(A) as "any event or condition resulted... in a manual reactor scram or reactor trip."
and therefore, that Review of the operating history and Eddy Current Test (ECT) data for St. Lucie Unit 1 and Unit 2 did not identify any actual failures in the past due to manufacturing weld defects. Comparison of historical ECT results of Unit 1 condenser tubes to the results found on the Unit 2 failed tube revealed an estimated twenty tubes with similar indications.
None of these indications on Unit 1 were found in the manufacturing weld of the tubes.
All Unit 1 indications were random and were preventively plugged at the time of discovery.
NRC, FORM 466A t6,1004JU.S. NUCLEAR REGULATORY COMMISSION (6&2004)
LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION
- 1. FACILITY NAME l
NUMBER
- 6. LER NUMBER
- 3. PAGE YEA EbQUENTIAL REVISIQN YEAR lSNUUMBERA NlMBERli St. Lucie Unit 2 05000389 1 N l Page 3 of 4 2006 -
001 00 TEXT (If more space is required, use additional copies of NRC Form 366A) (17)
Unit 1 and Unit 2 Main Condensers are of the same design and material, and between the Unit 1 and 2 Main Condensers, there have been more than 50 years operating experience without a previous failure of this type.
Considering the total number of condenser tubes in each unit is approximately 48,000, and the percentage of historical tube failures due to a similar cause, the probability of a near term failure would be extremely low.
Further analysis of ECT data of the surrounding tubes revealed an indicated tube wall thickness greater than nominal tube wall thickness at a point in the surrounding tubes near the failure.
The increased thickness suggests an increase in the outside diameter of adjacent tubes.
One potential cause is the failed tube was leaking for sometime and had leaked on adjacent tubes, resulting in rust/crusting of nearby tubes, thereby increasing their outside diameter and tube wall thickness.
As a conservative measure the adjacent tubes were plugged.
Considering the low number of past indications or actual tube failures similar to this event, there is a low probability of a similar event prior to the 100 percent planned ECT of the Unit 2 Main Condenser to be performed in the upcoming spring outage in 2006.
Unit 1 completed 100 percent ECT in December, 2005, and tubes were preventively plugged in accordance with FPL Engineering requirements.
Analysis of Safety Significance The Main Condenser consists of two fifty-percent capacity divided waterboxes with single pass surface condensers.
Each waterbox is connected to two separate Circulating Water inlet and outlet lines.
Cooling is provided by four Circulating Water pumps.
The condenser tubes are titanium, and the condenser tube sheets are aluminum bronze to provide corrosion resistance to the seawater environment.
The St. Lucie's Updated Final Safety Analysis (UFSAR), Section 10.4.1, states the Main Condenser serves no safety function and is classified as a non-seismic piece of equipment.
The Main Condenser's design basis is to condense 100 percent of the full load main steam flow leaving the low-pressure turbines and to de-aerate the condensate before leaving the condenser hotwell.
Given the condenser has no safety function, no safety analyses were affected.
In that the unit achieved a safe shutdown condition without any plant or equipment issues, this trip had no impact on the health and safety of the public.
Corrective Actions
The proposed corrective actions and supporting actions listed below are entered into the site Corrective Action Program.
Any changes to the proposed actions will be managed under the commitment management change program.
l.Condenser Waterbox 2B2 tube R76 T24 and the surrounding six tubes were plugged.
(Complete) 2.Addit.ional Eddy Current Testing was performed on a sample of surrounding tubes and no additional defects were noted. (Complete) 3.100 percent planned ECT of the Unit 2 Main Condenser will be performed in the upcoming spring outage, scheduled to begin 4/24/06.
NRC IFORM Jb5A (6 0UU4)U.S. NUCLEAR REGULATORY COMMISSION (6-2004)
LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION
- 1. FACILITY NAME NUMBERl
- 6. LER NUMBER
- 3. PAGE YEAR SEQUENTIAL REVISION I
NUMBER NUMBER St. Lucie Unit 2 05000389 Page 4 of 4 2006 -
001
- - 00 l
TEXA (itmore space is requiread use adaitionalcopies or Ni-ronnm 3oA) (117)
Corrective Actions (cont) 4.The failed tube in the 2B2 waterbox will be removed during second quarter refueling outage, scheduled to begin 4/24/06, and a failure analysis conducted.
Similar Events
This is the first Unit 1 or Unit 2 failure attributed to this failure mechanism.
Previous Main Condenser ECT sampling has revealed unexpected inside wall diamete::
indications of tubes in non-impact zones.
Some of the indications were more than 90 percent through wall.
All tubes identified were preventively plugged.
Failed Component Main Condenser Tube N
FORIKM 366v5A tI2004)