05000261/LER-2010-005, Regarding Emergency Diesel Generator Inoperable Due to Inverter Failure
| ML102380104 | |
| Person / Time | |
|---|---|
| Site: | Robinson  |
| Issue date: | 08/23/2010 |
| From: | Saunders W Progress Energy Carolinas |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| RNP-RA-10-0074 LER 10-005-00 | |
| Download: ML102380104 (6) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 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)(viii)(A) 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)(iv)(A), System Actuation 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 |
| 2612010005R00 - NRC Website | |
text
& Progress Energy Serial: RNP-RA/10-0074 AUG 2 3 2010 Attn: Document Control Desk United States Nuclear Regulatory Commission Washington, DC 20555-0001 H. B. ROBINSON STEAM ELECTRIC PLANT, UNIT NO. 2 DOCKET NO. 50-261/LICENSE NO. DPR-23 LICENSEE EVENT REPORT NO. 2010-005-00 EMERGENCY DIESEL GENERATOR INOPERABLE DUE TO INVERTER FAILURE Ladies and Gentlemen:
The attached Licensee Event Report is submitted in accordance with the requirements of 10 CFR 50.73. Should you have any questions regarding this matter, please contact Mr. C. A. Castell at (843) 857-1626.
Sincerely, W. Scott Saunders Plant General Manager H. B. Robinson Steam Electric Plant, Unit No. 2 WSS/ahv Attachment C:
L. A. Reyes, NRC, Region II T. J. Orf, NRC, NRR NRC Resident Inspector Progress Energy Carolinas, Inc.
Robinson Nuclear Plant 3581 West Entrance Road H-artsville, SC 29550
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES 08/31/2010 (9-2007)
Estimated burden per response to comply with this mandatory collection request: 80 hours9.259259e-4 days <br />0.0222 hours <br />1.322751e-4 weeks <br />3.044e-5 months <br />. Reported lessons learned are incorporated into the licensing process and LICENSEE EVENT REPORT (LER) 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, (See reverse for required number of Washington, DC 20555-0001, or by internet e-mail to infocollects@nrc.gov, and to digits/characters for each block) the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202, (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 I respond to. the information collection.
- 3. PAGE H. B. Robinson Steam Electric Plant, Unit No. 2 05000261 1 OF 5
- 4. TITLE Emergency Diesel Generator Inoperable Due To Inverter Failure
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED I
FACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR SEQUENTIAL REV NUMBER NO MONTH DAY YEAR 05000 FACILITY NAME DOCKET NUMBER 06 24 2010 2010-005 00 08 23 2010 05000
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply)
- 9. OPERATING MODE E]
20.2201(b)
El 20.2203(a)(3)(i)
El 50.73(a)(2)(i)(C)
F1 50.73(a)(2)(vii)
El 20.2201(d)
El 20.2203(a)(3)(ii)
El 50.73(a)(2)(ii)(A)
El 50.73(a)(2)(viii)(A) 5 El 20.2203(a)(1)
El 20.2203(a)(4)
El 50.73(a)(2)(ii)(B)
El 50.73(a)(2)(viii)(B)
El 20.2203(a)(2)(i)
El 50.36(c)(1)(i)(A)
El 50.73(a)(2)(iii)
El 50.73(a)(2)(ix)(A)
- 10. POWER LEVEL El 20.2203(a)(2)(ii)
El 50.36(c)(1)(ii)(A)
El 50.73(a)(2)(iv)(A)
El 50.73(a)(2)(x)
El 20.2203(a)(2)(iii)
El 50.36(c)(2)
El 50.73(a)(2)(v)(A)
EJ 73.71(a)(4) 0%
E]
20.2203(a)(2)(iv)
El 50.46(a)(3)(ii)
El 50.73(a)(2)(v)(B)
El 73.71(a)(5)
El 20.2203(a)(2)(v)
El 50.73(a)(2)(i)(A)
El 50.73(a)(2)(v)(C)
E]
OTHER Specify in Abstract below El 20.2203(a)(2)(vi)
El 50.73(a)(2)(i)(B) z 50.73(a)(2)(v)(D) or in TS LCO 3.4.8, Condition B, was exited at 1451 hours0.0168 days <br />0.403 hours <br />0.0024 weeks <br />5.521055e-4 months <br /> on June 24, 2010, after restoration of IB-3 using the alternate power supply. TS LCO 3.8.2, Condition B, and LCO 3.8.8, Condition A, were exited on June 27, 2010 at 1109 hours0.0128 days <br />0.308 hours <br />0.00183 weeks <br />4.219745e-4 months <br />, after restoring operability of Inverter B.
I1. CAUSE OF EVENT The cause of the loss of Inverter B was determined to be that the slew rate (the rate in which the inverter output changes to match the sync source) had deteriorated on Inverter B sync board. The deterioration was due to age degradation.
The sync board was not replaced in 2004 along with other internal components as scheduled due to an evaluation that had to be performed on the replacement sync board for compatibility. Replacement was not rescheduled appropriately due to the work order being incorrectly statused as completed satisfactory. Procedure, ADM-NGGC-01 04, "Work Management Process," does not explicitly define "complete" when closing Preventive Maintenance work orders. Therefore, the work order was closed as completed even though the entire scope had not been completed. A follow-up work order was not initiated and this allowed the component to exceed its end-of-life expectance.
II1. ANALYSIS OF EVENT This event was investigated in accordance with the HBRSEP, Unit No. 2, Corrective Action Program (CAP) and documented in Significant Adverse Nuclear Condition Report 406834. This reportable event associated with the significant adverse condition investigation was reviewed by the Plant Nuclear Safety Committee on August 18, 2010.
In this event, EDG B was capable of automatically starting and providing power to the associated emergency bus. The automatic loading of the blackout sequence loads was inoperable due to the loss of IB-3. Therefore, manual starting of the required loads would have been required if an actual loss of power had occurred. The service water pumps are needed to maintain cooling water flow to the EDG.
Operator action would have been required to restore service water via the control room in accordance with procedure, AOP-020, "Loss of Residual Heat Removal." AOP-020 is a direct entry procedure for a loss of Residual Heat Removal and includes steps to restore service water. The operators validated the procedural guidance based on conditions similar to the event and it was concluded that it would take approximately 25 minutes to restore the required components that would normally be started via the 'B' Train Blackout Sequencer. The EDG can operate without service water under station blackout loads for approximately 40 minutes.
In addition, the loss of power supply to IB-3 resulted in reduced RHR flow to approximately 2,700 gpm caused by valve HCV-758, RHR Heat Exchanger Outlet Flow to Cold Legs, failing closed. The operators took appropriate actions as directed by procedure AOP-020. The power supply to HIC-758 (RHR Heat Exchanger Flow Controller) was restored after power was restored to IB-3 by use of an alternate power supply. During the period while HCV-758 was closed and control of FCV-605 was lost,
RHR temperature rose from 93.5 degrees Fahrenheit to 96.9 degrees Fahrenheit, which is consistent with the reduction in flow caused by the closure of HCV-758.
During this event, RHR flow reduced from approximately 3,450 gpm to approximately 2,700 gpm due to the loss of Instrument Bus 3. RHR flow remained approximately 2,700 gpm until 1450 hours0.0168 days <br />0.403 hours <br />0.0024 weeks <br />5.51725e-4 months <br /> on June 24, 2010. During this time, no charging pumps were in operation; therefore there was no boron dilution source to the Reactor Coolant System (RCS) [AB]. Additionally, the measured RCS boron concentration was 2,226 parts per million (ppm). Updated Final Safety Analysis Report (UFSAR),
Section 15.4.6, "Chemical and Volume Control System Malfunction That Results in A Decrease in The Boron Concentration in The Reactor Coolant," describes a boron dilution event. The UFSAR event in Mode 5 states that if the RHR flowrate is below 2,800 gpm operators must take action to restore it above 2,800 gpm. The flowrate is to ensure "perfect mixing" as assumed in the analysis. The analysis further assumes all three charging pumps are in operation and delivering 250.5 gpm of primary water and a starting RCS boron concentration of 1,782.1 ppm. With no dilution source present and a significantly higher initial RCS boron concentration, the reduced RHR flow exhibited in this event did not violate the boron dilution analysis as described in UFSAR.
IV. CORRECTIVE ACTIONS
Completed Corrective Actions:
Power was restored to IB-3 by use of an alternate power supply.
Inverter B was repaired and restored to operable status at 0803 hours0.00929 days <br />0.223 hours <br />0.00133 weeks <br />3.055415e-4 months <br /> on June 27, 2010.
Planned Corrective Actions
Procedure, ADM-NGGC-0104, "Work Management Process," is scheduled to be revised by May 31, 2011, to clarify guidance for partial Preventive Maintenance Work Order completion and the associated technical documentation requirements.
In the interim, guidance will be provided to personnel regarding the completion and coding of partially performed or not performed Preventive Maintenance work orders. The significance of incomplete work orders will be highlighted to ensure work orders are processed in accordance with procedure, ADM-NGGC-0104. This action is scheduled to be completed by September 7, 2010.
V. ADDITIONAL INFORMATION
Previous Similar Events:
License Event Reports (LERs) for HBRSEP, Unit No. 2, were reviewed from the past 10 years. The following event was identified as being similar to the event described in this LER:
LER 2010-002-00, Plant Trip Due to Electrical Fault. This event involved a loss of power to Instrument Bus 3 for approximately two minutes due to the loss of Inverter B. The cause of the loss and restoration of Inverter B was indeterminate, but the failure mechanism is currently considered to be unrelated to the event described in this LER.