05000261/LER-2009-003

LER-2009-003, Manual Reactor Trip Due to Failure of 'A' Steam Generator Level Module

Docket Number
Event date:	11-06-2009
Report date:	01-05-2010
Reporting criterion:	10 CFR 50.73(a)(2)(iv)(B), System Actuation 10 CFR 50.73(a)(2)(iv)(A), System Actuation
2612009003R00 - NRC Website

I. DESCRIPTION OF EVENT

At 2203 hours0.0255 days <br />0.612 hours <br />0.00364 weeks <br />8.382415e-4 months <br /> EST on November 6, 2009, with H. B. Robinson Steam Electric Plant (HBRSEP), Unit No. 2, operating at approximately 100% power, control room operators responded to alarms received for steam flow greater than feed flow and level deviation on 'A' Steam Generator (SG) [EIIS System:Component AB:SG]. Feed Regulating Valve [JB:FCV] FCV-478 for 'A' SG indicated closed with controller demand of 0 percent. Control room operators attempted to manually open FCV-478 in accordance with AOP-010, "Main Feedwater/Condensate Malfunction." During this time, an increase in feed flow was noted. The 'A' SG level continued to lower to approximately 35 percent. The reactor was manually tripped at 2203 as the trip setpoint of 30 percent was approaching.

The control room operators entered the appropriate post-trip procedures. The auxiliary feedwater system [BA] initiated during the event, as expected. Intermediate Range Nuclear Instrument System Detector [IG:DET], N-35, was noted to be spiking causing the power above Intermediate Range Neutron Flux, P-6 interlock, status light to come on periodically. The spiking on N-35 was attributed to a faulty power supply and was later replaced on November 8, 2009, prior to unit start up.

II. CAUSE OF EVENT

The cause of this event was determined to be due to a vendor design error that resulted in premature part failure in the power supply for the Feed Regulating Control Loop FC-478E. A causal factor that contributed to this event was a lack of documentation regarding design issues with the Ensign' Power Supply-Revision 3 by the vendor.

III. ANALYSIS OF EVENT

The condition described in this Licensee Event Report is reportable under 10 CFR 50.73(a)(2)(iv)(A), any event or condition that resulted in manual or automatic actuation of any of the systems listed in 10 CFR 50.73(a)(2)(iv)(B).

This event was investigated using the HBRSEP, Unit No. 2, Corrective Action Program (CAP) and documented in Significant Adverse Nuclear Condition Report 364853. The significant adverse condition investigation associated with this reportable event was reviewed by the Plant Nuclear Safety Committee on December 22, 2009. The investigation determined that failure of the FC-478E summator power supply was due to a vendor design error that resulted in premature part failure in the power supply.

During the investigation, the extent of condition was evaluated for all modules with Ensigns' Power Supplies-Revision 3. There were 88 modules identified at HBRSEP, Unit No. 2. Of these 88, 78 are currently in operation. There are 10 modules where a failure in the power supply could cause a plant transient or loss of control function. In addition, there are 34 modules where a failure in the power supply could cause the plant to be placed in a 12 trip condition. / The remaining modules are for alarm and indication only.

The safety significance of this event is considered very low. The plant responded as designed and the operating crew manually tripped the reactor in response to the condition they observed.

The auxiliary feedwater system initiated during the event, as expected. Therefore, this event posed negligible adverse safety consequences for the public or plant personnel.

IV. CORRECTIVE ACTIONS

Completed Corrective Actions:

• FC-478E summator power supply was replaced with an Ensign's Power Supply-Revision 4.

Revision 4 does not contain the same capacitors in Revision 3 that caused the premature failure of the power supply. The channel was tested and restored to normal operation at 1752 hours0.0203 days <br />0.487 hours <br />0.0029 weeks <br />6.66636e-4 months <br /> EDT on November 7, 2009.

• Identified and located all HBRSEP, Unit No. 2, modules with Ensign's Power Supplies- Revision 3 installed.

• Placed stock quantities of NUS modules and modules being prepared for installation that contain Ensign' Power Supplies-Revision 3 "on-hold" to be returned to the vendor for replacement of the power supply.

Planned Corrective Actions:

• Replace modules in applications that have an Ensign' Power Supply-Revision 3 where a blown fuse failure could result in a potential transient, loss of control function, or put the plant in a half trip condition. The module replacements are targeted for completion during the next refueling outage, which is currently scheduled to begin on April 17, 2010.

V. ADDITIONAL INFORMATION

Failed Component Information:

The failed power supply was an Ensign's Power Supply-Revision 3 contained in a Halliburton summator, Model Number MTH-800-05/05/05/05-07-08.

Previous Similar Events:

Licensee Event Reports (LERs) for HBRSEP, Unit No. 2, were reviewed from the past 10 years. No events were identified that were similar to the event described in this LER.