05000374/LER-2003-001, Manual Scram Due to Lowering Reactor Water Level as a Result of a Trip of the 2B Condensate/Condensate Booster Pump
| ML030770655 | |
| Person / Time | |
|---|---|
| Site: | LaSalle  |
| Issue date: | 03/11/2003 |
| From: | Landahl S Exelon Generation Co, Exelon Nuclear |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LER 03-001-00 | |
| Download: ML030770655 (4) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv), System Actuation |
| 3742003001R00 - NRC Website | |
text
ExeIenM Exelon Generation Company, LLC www exeloncorp corn Nuclear LaSalle County Station 2601 North 21" Road Marseilles, IL 61341-9757 March 11, 2003 10 CFR 50.73 United States Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555 LaSalle County Station, Unit 2 Facility Operating License No. NPF-18 NRC Docket No. 50-374
Subject:
Licensee Event Report In accordance with 10 CFR 50.73(a)(2)(iv), Exelon Generation Company, (EGC), LLC, is submitting Licensee Event Report Number 03-001-00, Docket No. 050-374.
Should you have any questions concerning this letter, please contact Mr. Glen Kaegi, Regulatory Assurance Manager, at (815) 415-2800.
Respectfully, Susan R. Landahl Plant Manager LaSalle County Station Attachments Licensee Event Report cc:
Regional Administrator - NRC Region IlIl NRC Senior Resident Inspector - LaSalle County Station
Abstract
On January 10, 2003, at 1156, Unit 2 was manually scrammed in anticipation of an automatic scram due to decreasing reactor water level.
The event was initiated by a trip of the 2B Condensate/Condensate Booster (CD/CB) pump on instantaneous overcurrent.
The electrical perturbation, along with a latent failed level switch on the heater drain tank, caused the 2A and 2C Heater Drain pumps to trip. This resulted in a low suction pressure trip of both Turbine Driven Reactor Feed Pumps.
When the Operators could not maintain reactor water level, a manual scram was inserted. Reactor water level was restored using the Motor Driven Reactor Feed Pump following the scram.
The cause of the trip of the 2B CD/CB pump was a broken lug on the 6.9 kV cable connection to the B phase of the motor.
Corrective actions include repairing the termination such that stresses on the connection are limited, and inspecting the terminations to other large motors.
The safety significance of this event was minimal.
All control rods fully inserted and all systems responded as expected to the scram.
The Emergency Core Cooling Systems were not challenged.
NRC FORM 366 (7-2001)
(If more space is required, use additional copies of (If more space is required, use additional copies of NRC Form 366A)
The root cause of this event was an inadequate original installation, in that the field fit up of the lead box resulted in a vibration-induced fracture and failure of the 'B' phase motor cable lug on the 2B CD/CB pump.
The routing of the cable into the motor termination box placed additional weight and stresses on the cable lug (i.e., the weight of the cable conductors and tension due to cable bends).
The cause of the trip of the 2A and 2C HD pumps was a failure in the two out of two logic circuit, in which a failed heater drain tank level switch caused one relay in the logic to be in the tripped condition.
This relay failure, when combined with the reduced voltage experienced during the 2B CD/CB motor overcurrent, resulted in the completion of the second part of the logic, which tripped the 2A and 2C HD pumps.
The failed level switch was corrected as part of the troubleshooting and recovery efforts to return the unit to service.
D.
SAFETY ANALYSIS
The safety significance of this event was minimal.
All control rods fully inserted and all systems responded as expected to the scram.
The Emergency Core Cooling Systems were not challenged.
The loss of a CD/CB pump or reactor feed water flow is an analyzed event.
The likelihood of a severe accident does not increase as a result of this event.
E.
CORRECTIVE ACTIONS
Corrective Actions:
- 1. Large cable routings will be reviewed and terminations in junction boxes attached to large motors will be inspected (AT# 139037-25, 26).
- 2. The lug failure will be reviewed to determine applicability to other Exelon stations (AT# 139037-28).
- 3. Engineering will evaluate if a typical motor fault will cause a loss of loads on station busses, and recommend possible changes to prevent loss of loads (AT# 139037-23).
- 4. A review will be performed to identify and evaluate plant systems for latent failures that could potentially affect plant production (AT# 139037-21).
Corrective Action to Prevent Recurrence:
- 5. The 2B CD/CB motor terminations will be repaired to ensure that stresses on the lugs are minimized (AT# 139037-19).
F.
PREVIOUS OCCURRENCES
On July 24, 1996, the CD/CB pump 2CDOlPB auto tripped.
Investigation found that overcurrent relay 2551-AP115 was tripped at Bus 252.
Inspection of the 2B CD/CB pump found that the 'A' phase motor pigtail had burned off at the lug.
A new 3/0 3/8" hole lug was attached and the lugs for the 'B' and 'C' phase motor leads were also replaced.
The repair was performed under WO 9607053501.
The cause of the problem was identified in the work order as an improperly installed and sized lug.
This was a different cause than the scram on January 10, 2003.
G.
COMPONENT FAILURE DATA
Penn-Union, Connector, Lug, 4/0 Cable, Part No. BBLU-4/OD