05000352/LER-2002-003, Scram Due to Actuation of Main Thrust Bearing Wear Detector

Scram Due to Actuation of Main Thrust Bearing Wear Detector

ML022050042
Person / Time
Site:	Limerick
Issue date:	07/18/2002
From:	Levis W Exelon Nuclear
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
LER 02-003-00
Download: ML022050042 (5)

LER-2002-003, Scram Due to Actuation of Main Thrust Bearing Wear Detector

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(ix)(A) 10 CFR 50.73(a)(2)(iii) 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), Loss of Safety Function
3522002003R00 - NRC Website

text

Exekon.

Exelon Nuclear www.exeloncorp.com Nuclear Limerick Generating Station P.O. Box 2300 Sanatoga, PA 19464 1 OCFR50.73 July 18, 2002 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Limerick Generating Station, Unit 1 Facility Operating License Nos. NPF-39 NRC Docket Nos. 50-352 Subject: LER 1-02-003, Unit 1 Scram due to Actuation of Main Turbine Thrust Bearing Wear Detector This Licensee Event Report (LER) addresses an actuation of the Unit 1 main turbine thrust bearing wear detector that resulted in a main turbine trip and reactor scram.

Report Number:

1-02-003 Revision:

00 Event Date:

May 19, 2002 Discovered Date:

May 19, 2002 Report Date:

July 18, 2002 This LER is being submitted pursuant to the requirements of 1 OCFR50.73(a)(2)(iv)(A).

If you have any questions or require additional information, please do not hesitate to contact us.

Sincerely, William Levis Vice President - Limerick cc: H. J. Miller, Administrator Region I, USNRC A. L. Burritt, USNRC Senior Resident Inspector, LGS V

r1

NRC FORM 366 U.S. NUCLEAR REGULATORY APPROVED BY OMB NO. 3150-0104 EXPIRES 6-30-2001 (1-2001)

COMMISSION

, the NRC may not conduct or sponsor, and a digits/characters for each block) person is not required to respond to, the information collection.

FACILITY NAME (I)

DOCKET NUMBER (2)

PAGE (3)

Limerick Generating Station, Unit 1 05000 352 1 OF 4

TITLE (4)

Scram due to Actuation of Main Thrust Bearing Wear Detector EVENT DATE (5)

LER NUMBER (6)

REPORT DATE (7)

OTHER FACILITIES INVOLVED (8)

MO DAY YEAR YEAR SEQUENTIAL REV MO DAY YEAR FACILITY NAME DOCKET NUMBER NUMBER NO 05 19 2002 2002 003 00 07 18 2002 OPERATING 1

THIS REPORT IS SUBMITTID PURESUANT TO '

HE REQUIREMENTS OF 10 CFR §: (Check all that apply) (11)

MODE (9) 20.2201(b) 20.2203(a)(3)(ii) 50.73(a)(2)(ii)(B) 50.73(a)(2)(ix)(A)

POWER 1 00 20.2201(d) 20.2203(a)(4) 50.73(a)(2)(iii) 50.73(a)(2)(x)

LEVEL (10) 20.2203(a)(1) 50.36(c)(1)(i)(A)

X 50.73(a)(2)(iv)(A) 73.71(a)(4) 20.2203(aX(2X2i) 50.36(c)(1)(ii)(A) 50.73(a)(2)(v)(A) 73.7 1 (a)(5) 20.2203(a)(2)(ii) 50.36(c)(2) 50.73(a)(2)(v)(B3)

OTHER (If more space is required, use additional copies of NRC Forn 366A) (17)

Unit Conditions Prior to the Event Unit 1 was in Operational Condition (OPCON) 1 (Power Operation) at approximately 94% power. There were no structures, systems or components out of service that contributed to this event.

Description of the Event On May 18, 2002, at 22:12 hours, power was reduced to 94% to perform main turbine (EIIS:TRB) control valve (TCV), stop valve (TSV), and combined intermediate valve (CIV) (EIIS:SHV) testing. The Main Turbine Control Valve Exercise & RPS Channel Functional Test (ST-6-001 -765-1) was completed without incident.

The TSV portion of the Main Turbine CIV, Stop Valve RPS & EOC-RPT Channel Functional Test was also completed without incident.

During the CIV portion of the test, specifically during closure of CIV-2 at 00:54 hours on May 19, 2002, an actuation of the main turbine thrust bearing wear detector (TBWD) (EIIS:DET) occurred. The actuation of the TBWD resulted in a main turbine trip. The subsequent closure of the TSVs at greater than 30% power caused an actuation of the reactor protection system (RPS) which resulted in a reactor scram as designed.

All controls rods inserted as designed.

Reactor pressure peaked at approximately 1122 psig by the upset range instrumentation and was controlled by the main turbine bypass valves (BPV). The lowest main steam relief valve (MSRV) setpoint of 1170 psig was not exceeded; therefore, no actuation of MSRVs occurred.

Reactor narrow range level dropped to approximately -7 inches and the Group 2 RHR isolation occurred as designed at +12.5 inches. Reactor level subsequently increased to approximately +57 inches resulting in high-level trip of the reactor feed pumps (RFP) and High Pressure Coolant Injection (HPCI) at +54 inches.

The Main Turbine also received a high-level trip signal but had been previously tripped by the TBWD actuation. The discharge valve for the 1 A RFP would not close from the Main Control Room control switch due to a defective contactor in the motor control center (MCC) and was closed using the MOV local hand-wheel. The 1 A RFP was reset and used to control reactor level.

Following plant restart it was determined that the feedwater level control master controller setpoint setdown feature did not actuate as designed due to a lifted lead restoration error that occurred during the prior refueling outage (1 R09) in March 2002. The failure of this feature contributed to the high level trip of the RFPTs following the scram. The setpoint setdown feature has been scheduled for repair during the next outage opportunity.

In addition, the 1A & 1 B Reactor Recirc pump M-G sets tripped as designed during the fast-transfer of the 13kV Unit Auxiliary buses and the RPT-EOC trip actuated due to closure of the TSVs above 30% power.

This event involved an actuation of the RPS system when the reactor was critical and a valid actuation of the RPS system. The 4-hour ENS notification required by 10CFR50.72(b)(2)(iv)(B) and the 8-hour ENS notification required by 10CFR50.72(b)(3)(iv)(A) were completed on May 19, 2002 at 03:33 hours (Event#

38927).

This event involved an automatic actuation of the reactor protection system. Therefore, this LER is being submitted pursuant to the requirements of 1 OCFR50.73(a)(2)(iv)(A).

(If more space is required, use additional copies ofI (Ifmore space is required, use additional copies of NRC Form 366A) (17)

The Unit 1 main turbine thrust bearing assembly will be inspected during the next refueling outage or outage opportunity of sufficient duration.

Previous Similar Occurrences There were no previous occurrences of actuation of the TBWD.