05000250/LER-2004-007, Regarding Manual Reactor Trip Due to Generator Exciter Turbine Cooling Water Leak

Regarding Manual Reactor Trip Due to Generator Exciter Turbine Cooling Water Leak

ML050630263
Person / Time
Site:	Turkey Point  (DPR-031)
Issue date:	02/25/2005
From:	Jones T Florida Power & Light Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
L-2005-049 LER 04-007-00
Download: ML050630263 (6)

LER-2004-007, Regarding Manual Reactor Trip Due to Generator Exciter Turbine Cooling Water Leak

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(iv)(B)(6) 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) 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)(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 10 CFR 50.73(a)(2)(iv)(B), System Actuation
2502004007R00 - NRC Website

text

FPL FEB 2 5 2005 10 CFR § 50.73 L-2005-049 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D. C. 20555 Re:

Turkey Point Unit 3 Docket No. 50-250 Reportable Event: 2004-007-00 Date of Event: December 28, 2004 Manual Reactor Trip Due to Generator Exciter Turbine Cooling Water Leak The attached Licensee Event Report 250/2004-007-00 is being submitted pursuant to the requirements of 10 CFR 50.73(a)(2)(iv)(A) and 10 CFR 50.73(a)(2)(iv)(B)(6) to provide notification of the subject event.

If there are any questions, please call Mr. Walter Parker at (305) 246-6632.

Very truly yours, Terry 0. Jones Vice President Turkey Point Nuclear Plant Attachment cc:

Regional Administrator, USNRC, Region II Senior Resident Inspector, USNRC, Turkey Point Nuclear Plant an FPL Group company

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- k NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 06/30/2007 (6-204)Estmate budenperresponse to cornply with this mandatory collection request

52) hours Reported essons learned are incorporated Into the licensing process and fed back to Industry. Send comments regarding burden estimate to the Records and FOIA/Privacy Service Branch (T-5 F52), U.S. Nuclear Regulatory Commission, LICENSEE EVENT REPORT (LER)

Washington, DC 20555-0001, or by Intemet e-mail to Infocollects~nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, NEOB-1 0202, (3150-0104). Office of Management and Budget, Washington, DC 20503. If a means used to impose an Information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person Is not required to respond to, the Information collection.

3. PAGE Turkey Point Unit 3 05000250 1 OF 5

4. TITLE Manual Reactor Trip Due to Main Generator Exciter Turbine Cooling Water Leak

5. EVENT DATE

6. LER NUMBER

7. REPORT DATE

8. OTHER FACILITIES INVOLVED SEQUENTIAL REV FACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR NUMBENI NO.

MONTH DAY YEAR FACILITY NAME DOCKET NUMBER 12 28 2004 2004 -

007 - 00 02 25 2005

9. OPERATING MODE

11. THIS REPORT IS SUBMITED PURSUANT TO THE REQUIREMENTS OF 10 CFR§: (Check allthat apply) 0 20.2201(b) a 20.2203(a)(3)(i) 0 50.73(a)(2)(i)(C)

E 50.73(a)(2)(vii) 1l 20.2201(d) 0 20.2203(a)(3)(ii) 0 50.73(a)(2)(ii)(A)

El 50.73(a)(2)(vii0i(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) 03 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 LEVELE0 20.2203(a)(2)(ii) 0 50.36(c)(1)(ii)(A) 0 50.73(a)(2)(iv)(A) a 50.73(a)(2)(x) 0l 20.2203(a)(2)(iii) 0 50.36(c)(2) 0 50.73(a)(2)(v)(A) 0 73.71 (a)(4) 0 20.2203(a)(2)(iv) 0 50.46(a)(3)(ii) 0 50.73(a)(2)(v)(B)

El 73.71(a)(5) 70 E 20.2203(a)(2)(v) 0 50.73(a)(2)(i)(A) 0 50.73(a)(2)(v)(C)

E OTHER O 20.2203(a)(2)(vi) 0 50.73(a)(2)(i)(B) 0 50.73(a)(2)(v)(D)

Specify In Abstract below or in NRC Form 366A

12. UCENSEE CONTACT FOR THIS LER NAME TELEPHONE NUMBER (Include Area Code)

Stavroula Mihalakea - Licensing Engineer 305-246-6454

13. COMPLETE ONE UNE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT

CAUSE

SYSTEM COMPONENT MANU-REPORTABLE

CAUSE

SYSTEM COMPONENT MANU-REPORTABLE I

T FACT'URER TO EPIX 1CMO FACTURER TO EPIX B

TL EXCl

14. SUPPLEMENTAL REPORT EXPECTED

15. EXPECTED MONTH DAY YEAR SUBMISSION x YES (if yes, complete 15. EXPECTED SUBMISSION DATE)

[El NO DATE 7

30 2005~

ABSTRACT (Umit to 1400 spaces, Le., approximately 15 single-spaced typewritten lines)

On December 28, 2004 at 22:46 Turkey Point Unit 3 reactor was manually tripped from 70% power following a fast load reduction from 100%. The load reduction was initiated when it was recognized that the Turbine Plant Cooling Water (TPCW) leakage exceeded the makeup capability to the TPCW surge tank. The reactor trip was initiated following the discovery of water in the Turkey Point Unit 3 Main Generator exciter housing.

The apparent cause of the exciter TPCW air cooler leak was found to be a failed gasket at the joint between the cooler channel head and the air cooler assembly. The preliminary root cause of the cooler failure is determined to be poor workmanship on the part of the refurbishment vendor. Immediate corrective actions included the identification and repair of the TPCW leak source and drying of electrical components. Although parts of the 3B 4160 Volt safety related switchgear enclosure at the lower elevation were wetted due to water intrusion through the conduit penetrations in the overhead, the bus remained energized throughout the event.

All plant parameters remained within the design envelope for this type of transient. All plant safety systems functioned as designed and there were no adverse effects on the operating crew's ability to safely shutdown the reactor and stabilize the plant. The health and safety of the public was not challenged nor adversely affected by this event.

NRC FORM 368(6.2004)

PRINTED ON RECYCLED PAPER NRC FORM 366 (6-2004)

PRINTED ON RECYCLED PAPER

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,!U.S. NUCLEAR REGULATORY COMMISSION I-2001)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITY NAME (1)

NUMBER (2)

LER NUMBER (6)

PAGE (3)

Tk PEoiSEQUENTIAL REVISION YER NUMBER NUMB3ER Turkey Point Unit 3 05000250 Page 2of 5 2004

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- 00 TEXT (If more space Is required, use additional copies of NRC Form 366A) (17)

DESCRIPTION OF THE EVENT On December 28, 2004, Turkey Point Unit 3 was operating at 100% power. At 22:17, the operating crew received a Turbine Plant Cooling Water (TPCW) [KB] Annunciator I 5/5, "TPCW Surge Tank HiILo level," alerting them to a low level in the TPCW surge tank [KB:SPP:TK]. At 22:20, Annunciator E8/3 "Generator Field Brush Contact Fail/Ground" was actuated. The crew entered the Off-Normal Operating Procedure 3-ONOP-008 "TPCW Malfunction" and established makeup to the TPCW surge tank. The TPCW surge tank level continued to decrease, indicating that the leakage was beyond the automatic makeup capability. While the operating crew was investigating the source of the TPCW leak, they estimated that approximately 90 gpm makeup water was being supplied to the TPCW system to maintain the surge tank level. The control room dispatched the Field Supervisor to investigate the leak. At 22:35, the operating crew entered the 0-ONOP-100, "Fast Load Reduction," to perform a reduction in load. The Field Supervisor reported a major water leak had occurred within the Unit 3 Main Generator exciter housing. At 22:46, the Turkey Point Unit 3 reactor was manually tripped from 70% power. At 22:50, the Field Supervisor isolated the TPCW water supply to the Unit 3 Main Generator exciter air cooler piping [TL:EXC:CLR]. Residual water from the exciter housing entered through conduit floor seals onto 3B 4160 Volt (3B 4kV) safety related switchgear enclosure [EB], located directly beneath the exciter housing.

Engineering performed a walkdown on 12/29/04 at approximately 0145 hours0.00168 days <br />0.0403 hours <br />2.397487e-4 weeks <br />5.51725e-5 months <br /> to investigate, evaluate and address issues related to the water intrusion into 3B 4kV switchgear room. Subsequently, it was concluded that the 3B 4kV switchgear remained operable throughout the event and did not experience any AC grounds.

With the manual reactor trip, the operating crew entered 3-EOP-E-0, "Reactor Trip or Safety Injection",

and verified that the reactor and turbine were tripped and safety injection was not required. All control rods inserted fully. Auxiliary Feedwater actuated automatically as expected and operated normally following the reactor trip. The operation of Turkey Point Unit 4 was unaffected by this event.

BACKGROUND The exciter assembly is cooled by a closed air system and water cooled heat exchanger. The heat exchanger is a shell and tube type with spiral fins around tubes. There are four coolers (A-D) on the top of the exciter assembly components. Cooling water is supplied by the TPCW system to the exciter air coolers and makes multiple passes as it flows through the tubes of the heat exchanger. The air within the exciter is a closed system with a fan forcing air circulation through the coolers inside the exciter housing.

ANALYSIS OF THE EVENT

Subsequent to the reactor trip, the TPCW piping inside the exciter was inspected. Inspections of the inlet and exciter air cooler reversing chambers revealed evidence of a failed gasket on the top south air cooler (Cooler C) reversing chamber. Detailed inspections of the C Cooler found a notable gap between the sealing surface of the reversing chamber and the cooler tube sheet. The force applied on the rubber gasket led to the extrusion of the gasket material resulting in the TPCW leak.

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' s Z-U.S. NUCLEAR REGULATORY COMMISSION l-2001)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITY NAME (1)

NUMBER 2 LER NUMBER (6)

PAGE (3)

Tk SEQUENTIAL REVISION Turkey Point Unit 3 05000250

~

UBR Page 3 of 5 2004-007-00 TEXT (If more space Is required, use additional copies of NRC Form 366A) (17)

All Unit 3 exciter air cooler inlet and reversing chamber gaskets were replaced with suitable gaskets. Unit 4 exciter air coolers have not yet been examined for similar deficiencies due to restricted access during operation. These will be evaluated during the upcoming Turkey Point Unit 4 refueling outage in Spring of 2005.

The electrical components in the exciter housing were inspected and there was no visual evidence of damage by arcing. A visual examination of the exciter skid was conducted. The inspection revealed standing water in the bottom of the exciter housing. There was evidence of a flow path for water from the gaps in the penetration seals around conduit penetrating the bottom of the exciter housing. This was the apparent leak path for water to enter the Unit 3B 4kV switchgear room.

Water from the exciter housing was forced past sealed conduits into the 3B 4kV switchgear room.

Although, the conduits are sealed with fire/moisture barriers, these conduits are located in the positive pressure section of the exciter. There are zones of positive and negative pressure inside the exciter housing caused by forced air circulation. The positive pressure allowed some quantity of water to pass through the conduit seals and drip down onto the 3B 4kV switchgear enclosure. The existing seals [SEAL] in the exciter minimized the water intrusion. Some shrinkage of the seals was noted due to age degradation. The conduits penetrate into the ceiling of the 3B 4kV switchgear room above breaker cubicles 3AB 13, 14, and

15. Most of the water was accumulated in the walkway areas. Some water was visible on the top of the enclosure between breakers 3AB08 through 3AB16 and in some associated relay cases.

Operations conservatively secured the following operating loads that were associated with breakers 3AB08 through 3AB 16: 3B Component Cooling Water Pump [CC:P], the 3B Intake Cooling Water Pump [BS:P],

the 3B Turbine Cooling Water Pump[KB:P], and the 3B 1 Circulating Water Pump. Additionally, the 3B Residual Heat Removal (RHR) Pump [BP:P] was declared out of service due to the RHR pump motor overload and pump trip alarm that were received as a result of water in associated alarm relays mounted within the front part of the switchgear enclosure.

Investigation determined that there were no AC grounds or shorts caused by the water other than the annunciator alarms. The 3B RHR pump was not in operation at the time of the event and its motor supply breaker remained open throughout the event. Based on the inspection results of the cubicle and breaker followed by the successful start and stop of the 3B RHR pump, it was determined that the 3B RHR pump was not adversely affected by the water from the exciter TPCW water leak. The 3B RHR pump was subsequently placed back in service.

The 3B 4kV switchgear remained energized throughout the event. Testing and evaluation of the alarms received for the 3B 4kV switchgear determined that it was only the alarm contacts and relays that were affected by the water and causes of the alarm indications did not prevent the 3B 4kV switchgear from performing its design safety functions. The switchgear room was dried within the first few hours following the event. The annunciators cleared following the isolation of the TPCW leak and the drying of the switchgear alarm relays.

NNRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION (7-2001)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITY NAME (1)

CNUMBER (2)

T LER NUMBER (6)

PAGE (3)

!-YEAR SEQUENTIAL REVISION Turkey Point Unit 3 05000250 24 NUMER NUMER Page 4 of 5 TEXT (If more space Is required, use additional copies of NRC Form 366A) (17)

CAUSE OF THE EVENT

The preliminary root cause of the Unit 3 exciter cooler failure was determined to be poor workmanship on the part of the refurbishment vendor.

REPORTABILITY

A review of the reporting requirements of 10 CFR 50.72 and 10 CFR 50.73 and NRC guidance provided in NUREG-1022, Revision 2, Event Reporting Guidelines 10 CFR 50.72 and 10 CFR 50.73, was performed for the subject condition. As a result of this review, the condition is reportable as described below.

10CFR50.73(a)(2)(iv)(A) states that the licensee shall report any event or condition that resulted in a manual or automatic actuation of any of the systems listed in 10CFR50.73(a)(2)(iv)(B). This event is reportable in accordance with 10 CFR 50.73(a)(iv)(B)(1), actuation of the Reactor Protection System (RPS) since Unit 3 was manually tripped in response to TPCW air cooler leak in the exciter housing.

The event is also reportable in accordance with 10 CFR 50.73 (a)(2)(iv)(A), due to AFW system actuation (10 CFR 50.73(a)(2)(iv)(B)(6)). In addition, in accordance with 10CFR 50.72(b)(2)(iv)(B), a report was made to the NRC for the manual reactor trip and 10CFR 50.72(b)(3)(iv)(A) for valid AFW system actuation on December 28, 2004, at 23:51 hours, recorded as event number: 41298.

ANALYSIS OF SAFETY SIGNIFICANCE For this manual reactor trip, the initial conditions were well within the assumed conditions for the postulated Loss of External Electrical Load event analyzed in the Updated Final Safety Analysis Report (UFSAR). The plant was operating at 70% power with automatic Reactor Coolant System (RCS) [AB]

pressure control. A 70% loss of load resulted when the turbine was tripped by the manual reactor trip.

The nuclear power, pressurizer pressure, pressurizer water volume, RCS average temperature, RCS inlet temperature, and the steam generator pressure trends for this trip compared conservatively to the trends provided in the UFSAR. All plant parameters remained within the design envelope for this type of transient. There were no safety systems out of service prior to the event. There were no Risk Significant components out of service prior to the event. All plant systems functioned as designed and there were no adverse effects on the operating crew's ability to safely shutdown the reactor and stabilize the plant.

The UFSAR minimum and maximum values were not exceeded during this event. No unexplained aspects of this transient were noted when compared to the UFSAR. The integrity of the core was maintained by the reactor protection system and the health and safety of the public was not compromised.U.S. NUCLEAR REGULATORY COMMISSION (7-2001)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITY NAME (1)

DOCKET LER NUMBER (6)

PAGE (3)

N U M B E R (2)

YEAR SEQUENTIAL REVISION Turkey Point Unit 3 05000250 NUMBER NUMBER Page 5 of 5 200T -

007 s 00 TEXT (if more space Is required, use additional copies of NRC Form 366A) (1 7)-

CORRECTIVE ACTIONS

1. The affected Unit 3 Main Generator exciter equipment was disassembled, dried out, reassembled and successfully tested.

2. The Unit 4 Main Generator exciter air cooler gaskets will be inspected for similar deficiencies during the next refueling outage in spring of 2005.

3. The conduit seals in the Unit 4 Main Generator exciter housing will be inspected and repaired if needed during next refueling outage in spring of 2005.

4. Determination of Long Term corrective actions to address root cause have not yet been completed.

They will be provided in a supplement to this LER.

ADDITIONAL INFORMATION

EIIS Codes are shown in the format [EUS SYSTEM: IEEE system identifier, component function identifier, second component function identifier (if appropriate)].

SIMILAR EVENTS

A data base search for the past 3 years found no similar events.