05000461/LER-2012-002
| Clinton Power Station | |
| Event date: | 03-01-2012 |
|---|---|
| Report date: | 11-27-2012 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat |
| 4612012002R00 - NRC Website | |
PLANT AND SYSTEM IDENTIFICATION
General Electric -- Boiling Water Reactor, 3473 Megawatts Thermal Rated Core Power Energy Industry Identification System (EIIS) codes are identified in test as [XX].
EVENT IDENTIFICATION
Division 1 Emergency Diesel Generator Supply Air Damper Failure.
A. Plant Operating Conditions Before the Event
Unit: 1 Discovery Date: 3/1/2012 Discovery Time: 1215 hours0.0141 days <br />0.338 hours <br />0.00201 weeks <br />4.623075e-4 months <br /> CST Mode: 1 Mode Name: Power Operation Reactor Power: 97 percent B.DESCRIPTION OF EVENT On March 1, 2012, at 1212 hours0.014 days <br />0.337 hours <br />0.002 weeks <br />4.61166e-4 months <br />, Clinton Power Station (CPS) Operations started the Division 1 Emergency Diesel Generator (EDG) for monthly surveillance testing per procedure CPS No. 9080.01, "Diesel Generator 1A Operability - Manual and Quick Start Operability." At 1215, Operators in the Division 1 EDG room reported a lack of expected air flow in the room and that the doors [DR] between the EDG rooms did not have the typical high differential pressure (d/p) across them. The EDG Room 1A supply air fan [FAN][VJ], 1VDO1CA, automatically started as expected, as evidenced by Main Control Room (MCR) and field indications. In addition, Engineering noted the fan room door bowing inward slightly due to high d/p.
At 1300 hours0.015 days <br />0.361 hours <br />0.00215 weeks <br />4.9465e-4 months <br />, the Shift Manager directed the Division 1 EDG and 1VDO1CA to be secured.
With the EDG room fan secured, investigation found the supply air 1VDO1YA damper [DMP] to hydramotor 1TZVD001A coupling [CPLG] disconnected, which resulted in the supply air damper remaining in the closed position even when the supply air fan started.
Initially, this event was found during surveillance testing and a review of relevant information (e.g., equipment history and cause of failure) determined the event was considered not reportable based on lack of evidence that the condition existed prior to the monthly surveillance test. However, this position was challenged and based on a review of industry information, the event has been determined to be reportable.
The Division 1 EDG was previously run for a monthly surveillance test on January 25, 2012 with no problems noted. This date is the last date for which there is firm evidence that the supply air damper for the Division 1 EDG would have been operable had a demand occurred. The first start demand after this date was March 1, 2012, the date of discovery. Since the time span between January 25, 2012 and March 1, 2012 (36 days) is longer than Technical Specifications (TS) allow, this event is being reported as any operation or condition which was prohibited by the plant's TS per 10 CFR 50.73(a)(2)(i)(B).
Between the performances of the monthly surveillance tests on the Division 1 EDG, the Division 2 EDG was run on February 8, 2012 for a monthly surveillance test and was inoperable during prestart checks and during the time the EDG output breaker control switch was in Pull-To-Lock position. Since the Division 2 EDG was inoperable during portions of the time the Division 1 EDG was inoperable, (i.e., approximately fifteen hours), this event is also being reported as a condition that could have prevented the fulfillment of a safety function per 10 CFR 50.73(a)(2)(v)(B).
NR FORCM 366A (10-2010)
C. CAUSE OF EVENT
Hydramotor 1TZVD001A (model NH91), which controls the 1VD01YA damper, was last replaced per Work Order (WO) 1220488 on September 29, 2010. At the time of replacement the workers did not identify either deficiencies or discrepant conditions on the old hydramotor coupling or on the as-left coupling installation (i.e., loose lock nut or stripped threads).
The Apparent Cause Evaluation performed on the event determined the cause was failure to ensure the lock nut on the coupling was sufficiently tightened during the previous hydramotor replacement because of a lack of quantitative procedural guidance.
D. SAFETY CONSEQUENCES
There were no actual nuclear, radiological or industrial safety significant consequences related to this event. This event resulted in the loss of EDG Room Ventilation, due to the 1VDO1YA damper hydramotor 1TZVD001A coupling becoming disconnected, which resulted in the supply air damper remaining in the closed position. Engineering has determined that an Operator would have a sufficient amount of time, approximately 109 minutes, to perform simple actions to restore a ventilation flow path before high temperatures would be expected that could exceed the room maximum design temperature:
This event was determined to be of very low safety significance during a detailed quantitative Significance Determination Process review since the delta core damage frequency and delta large early release frequency were both determined to be negligible based upon crediting operator recovery actions to restore EDG room ventilation.
E. CORRECTIVE ACTIONS
CPS Procedure 8452.04, "AH91/NH91 Hydramotor Actuator Maintenance", has been revised to include supervisory oversight on the assembly of the lock nut and coupling and allow the use of an engineered adhesive (i.e., Loctite®) for coupling lock nuts.
F. PREVIOUS OCCURRENCES
A review for previous occurrences did not identify similar events at CPS.
G. COMPONENT FAILURE DATA
Manufacturer � Nomenclature � Manufacturer Model Number Pacific Air Products � Hydramotor � SL-100-5600 NR FORCM 366A (10-2010)