05000237/LER-2009-001, Regarding Common Mode Failure of Reactor Building Isolation Dampers
| ML091060742 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 04/07/2009 |
| From: | Hanley T Exelon Generation Co, Exelon Nuclear |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| SVPLTR 09-0015 LER 09-001-00 | |
| Download: ML091060742 (6) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(i) 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 |
| 2372009001R00 - NRC Website | |
text
Exelkn Exelon Generation Company, LLC www.exeloncorp.com Dresden Nuclear Power Station Nuclear 65oo North Dresden Road Morris, IL 60450-9765 10 CFR 50.73 SVPLTR # 09-0015 April 7, 2009 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Dresden Nuclear Power Station, Units 2 and 3 Renewed Facility Operating License No. DPR-19 and DPR-25 NRC Docket Nos. 50-237 and 50-249
Subject:
Licensee Event Report 237/2009-001-00, "Common Mode Failure of Reactor Building Isolation Dampers" Enclosed is Licensee Event Report 237/2009-001-00, "Common Mode Failure of Reactor Building Isolation Dampers" for Dresden Nuclear Power Station. This event is being reported in accordance with 10 CFR 50.73(a)(2)(v)(C), "Any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to control the release of radioactive material;" 10 CFR 50.73(a)(2)(vii), common cause inoperability of independent trains or channels; and 10 CFR 50.73(a)(2)(i)(B), operation or condition prohibited by the plant's Technical Specifications. There are no regulatory commitments contained in this submittal.
Should you have any questions concerning this report, please contact Mr. Stephen Taylor, Regulatory Assurance Manager, at (815) 416-2800.
Respectfully, Tim Hanley Site Vice President Dresden Nuclear Power Station Enclosure cc:
Regional Administrator - NRC Region III NRC Senior Resident Inspector - Dresden Nuclear Power Station
bcc:
Officer of Nuclear Facility Safety - IEMA - DNS Director - Licensing Manager - Licensing - Clinton, Dresden, and Quad Cities Stations Regulatory Assurance Manager - Quad Cities Nuclear Power Station Midwest Document Control Desk Licensing Plant Manager - Dresden Nuclear Power Station Regulatory Assurance Manager - Dresden Nuclear Power Station LER Coordinator - Dresden Nuclear Power Station INPO Coordinator - Dresden Nuclear Power Station Regulatory Commitment Coordinator - Dresden Nuclear Power Station F. Polak - Plant Engineering J. Cox - Simulator Supervisor Dresden Regulatory Assurance, SVP File SVP Numerical File - SVPLTR #09-0015 E-MAIL: LER Completed File electronic in L:\\8360\\8301\\237\\180\\2009\\2009-001-00
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 08/31/2010 (9-2007)
, the NRC may digits/characters for each block) not conduct or sponsor, and a person is not required to respond to, the inffinrmtinn nnllp~r.tinn.
- 13. PAGE Dresden Nuclear Power Station (DNPS), Unit 2 05000237 1 OF 4
- 4. TITLE Common Mode Failure of Reactor Building Isolation Dampers
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
[
- 8. OTHER FACILITIES INVOLVED M
DAY Y
R FACILITY DOCKET NUMBER MONTH DAY YEAR YEAR NUMBER NO.
MONTH DAY YEAR DNPS Unit 3 05000249 FACILITY NAME DOCKET NUMBER 10 09 2008 2009 - 001 -
00 04 07 2009 [N/A N/A
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply)
[1 20.2201(b)
El 20.2203(a)(3)(i)
[] 50.73(a)(2)(i)(C) 0 50.73(a)(2)(vii)
[1E 20.2201(d)
El 20.2203(a)(3)(ii)
El 50.73(a)(2)(ii)(A)
El 50.73(a)(2)(viii)(A)
El 20.2203(a)(1)
El 20.2203(a)(4)
El 50.73(a)(2)(ii)(B)
El 50.73(a)(2)(viii)(B) 20.2203(a)(2)(i)
El 50.36(c)(1)(i)(A)
[I 50.73(a)(2)(iii)
[I 50.73(a)(2)(ix)(A)
- 10. POWER LEVEL [I 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)
[I 20.2203(a)(2)(iii)
El 50.36(c)(2)
El 50.73(a)(2)(v)(A)
El 73.71 (a)(4) 100 El 20.2203(a)(2)(iv)
El 50.46(a)(3)(ii)
El 50.73(a)(2)(v)(B)
[1 73.71 (a)(5)
[I 20.2203(a)(2)(v)
[I 50.73(a)(2)(i)(A) 0 50.73(a)(2)(v)(C)
[E OTHER El 20.2203(a)(2)(vi)
ED 50.73(a)(2)(i)(B)
El 50.73(a)(2)(v)(D)
Specify in Abstract below or in the plant, the RBV System Manager did not believe it was necessary to drive resolution of the potential common mode failure mechanism on a more timely basis.
Subsequent IRs generated for the failures in 2008 and 2009 did not identify the existence of a potential common mode failure mechanism and the individuals involved in the review of the IRs failed to recognize the possibility of the common mode failure mechanism as the secondary containment function was never lost.
A second contributing cause of the RBV damper solenoid valve failures is attributed to ineffective system performance monitoring. A review of the RBV damper quarterly surveillance closure times identified all RBV dampers, which ultimately failed, exhibited high closure times during the previous quarterly surveillance(s). Although Engineering was trending the surveillance results, an IR was not generated to document the adverse trend.
D.
Safety Analysis
The RBV system is designed with Secondary Containment Isolation Valves to isolate the Reactor Building from the atmosphere via the RBV system ducts. Two isolation dampers are in series on the supply and exhaust ductwork of each unit. The inlet and outlet isolation dampers are normally open during system operation. Closure of one damper in both the inlet and outlet satisfies the secondary containment isolation requirements.
These RBV isolation dampers are required to automatically close when a Secondary Containment Isolation signal is present. The RBV isolation dampers are required to stoke from full-open to full-closed within 60 seconds of the closed signal. All RBV isolation dampers rely on the same model solenoid valve to close and perform their safety related function to control the release of radioactive material and mitigate the consequences of an accident.
In 2005 through 2007, several RBV isolation dampers failed the required closure time both at DNPS and another Exelon facility. Failure analyses by Exelon and the solenoid vendor (VERSA) in 2007 identified a potential common mode failure mechanism of solenoid valve sticking due to inadequate lubrication of the internal parts. This previously identified RBV damper common mode failure mechanism of solenoid valve sticking due to inadequate lubrication of the internal parts could have prevented the fulfillment of the safety function.
For these events, RBV dampers failed to close and perform the secondary containment isolation design function due to the solenoid valve sticking. The consequence of a single isolation damper failure is minimized by the in-series isolation damper closure to maintain secondary containment integrity. Closure of one inlet damper and one outlet damper satisfies the full isolation requirements.
For all solenoid damper failure events, at least one in-series isolation damper closed per design.
Therefore, secondary containment integrity was maintained.
Therefore, the consequences of this event had minimal impact on the health and safety of the public and reactor safety.
E.
Corrective Actions
Replacement of all RBV isolation damper solenoid valves with an upgraded model was completed in January 2009.
A corrective action to be taken is to reinforce the procedural requirement to generate a new IR if a previously identified condition has deteriorated to the point the operability or reportability is affected to all Engineering personnel. In addition, a new IR shall be generated when new information is obtained for an on-going condition. The new IR shall summarize the entire condition to allow proper operability and reportability assessment.
In addition, a Training Case Study of these events shall be presented to the Engineering and Operations organizations and senior management.
F.
Previous Occurrences
A review of DNPS Licensee Event Reports (LERs) for the last three years did identified one LER associated with previous failures of components that resulted in untimely reporting.
LER 237/2006-003-00, "Unit 2 Reactor Steam Dome Pressure-Low Permissive Switch Determined To Have Been Historically Inoperable," identified an issue of repeat failures of a permissive switch that was not previously evaluated. In this case, the RBV system monitoring plan did not formally monitor the RBV damper closure times.
G.
Component Failure Data
EPIX Numbers 834, 836 and 845.PRINTED ON RECYCLED PAPERPRINTED ON RECYCLED PAPER