05000237/LER-2009-005, Regarding Recirculation Drain Line Pressure Boundary Leakage
| ML100191794 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 12/22/2009 |
| From: | Hanley T Exelon Corp, Exelon Generation Co, Exelon Nuclear |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| SVPLTR # 09-0066 LER 09-005-00 | |
| Download: ML100191794 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 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 |
| 2372009005R00 - NRC Website | |
text
Exelt n Exelon Generation Company, LLC www.exeloncorp.com Nuclear Dresden Nuclear Power Station 6500 North Dresden Road Morris, IL 60450-9765 10 CFR 50.73 SVPLTR # 09-0066 December 22, 2009 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Dresden Nuclear Power Station, Unit 2 Renewed Facility Operating License No. DPR-19 NRC Docket No. 50-237
Subject:
Licensee Event Report 237/2009-005-00, "Unit 2 Reactor Recirculation Drain Line Pressure Boundary Leakage" Enclosed is Licensee Event Report 237/2009-005-00, "Unit 2 Reactor Recirculation Drain Line Pressure Boundary Leakage," for Dresden Nuclear Power Station, Unit 2. This event is being reported in accordance with 10 CFR 50.73(a)(2)(ii)(A), "Any event or condition that resulted in the condition of the nuclear power plant, including its principal safety barriers, being seriously degraded."
There are no regulatory commitments contained in this submittal.
Should you have any questions concerning this letter, please contact Ms. Marri Marchionda at (815) 416-2800.
Respectfully, Tim Haly Site Vice President Dresden Nuclear Power Station Enclosure cc:
Regional Administrator - NRC Region III NRC Senior Resident Inspector - Dresden Nuclear Power Station
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 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, LICENSEE EVENT REPORT (LER)
Washington, DC 20555-0001, or by internet e-mail to infocollects@nrc.gov, and to 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 (See reverse for required number of number, the NRC may not conduct or sponsor, and a person is not required to respond digits/characters for each block) to, the information collection.
- 13. PAGE Dresden Nuclear Power Station, Unit 2 05000237 1 OF 4
- 4. TITLE Unit 2 Reactor Recirculation Drain Line Pressure Boundary Leakage
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED FACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR NUMBER REV MONTH DAY YEAR N/A N/A FACILITY NAME DOCKET NUMBER 11 03 2009 2009 005 00 12 22 2009 N/A N/A
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply)
[] 20.2201(b)
El 20.2203(a)(3)(i)
[I 50.73(a)(2)(i)(C)
El 50.73(a)(2)(vii) 5 [1 20.2201(d)
El 20.2203(a)(3)(ii) 0 50.73(a)(2)(ii)(A)
El 50.73(a)(2)(viii)(A) 0l 20.2203(a)(1)
El 20.2203(a)(4)
[] 50.73(a)(2)(ii)(B)
E] 50.73(a)(2)(viii)(B)
EI 20.2203(a)(2)(i) 0l 50.36(c)(1)(i)(A)
E] 50.73(a)(2)(iii)
Cl 50.73(a)(2)(ix)(A)
- 10. POWER LEVEL E] 20.2203(a)(2)(ii)
[I 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) 0l 50.36(c)(2)
El 50.73(a)(2)(v)(A)
El 73.71(a)(4) 000 El 20.2203(a)(2)(iv)
El 50.46(a)(3)(ii)
El 50.73(a)(2)(v)(B)
El 73.71(a)(5)
[] 20.2203(a)(2)(v)
El 50.73(a)(2)(i)(A)
El 50.73(a)(2)(v)(C)
El OTHER E] 20.2203(a)(2)(vi)
El 50.73(a)(2)(i)(B)
El 50.73(a)(2)(v)(D)
Specify in Abstract below or in C.
Cause of Event
Based on the examination of the failed component, two indications were identified. The larger circumferential indication extended 150 degrees. The through-wall portion extended approximately 85 degrees. The second indication was smaller and was not through-wall. Observing the fracture radial markings, the larger indication initiated from the outer diameter of the pipe. Microscopic examination revealed the cracking propagated in a non-branching transgranular manner, which was indicative of fatigue. The smaller indication initiated from the toe of the coupling weld.
The angled nature of the cracking near the origin indicated that the pipe was subjected to cyclic torsional loads, which would be consistent with cantilever loading induced by the weight of the two downstream valves. Likely causes of the cyclic loading include a known period when the 2B Reactor Recirculation pump experienced higher than normal vibrations or possibly a periodic resonance condition associated with intermediate pump operating speeds.
The 2-0202-5B Recirculation Pump Discharge Valve above seat drain line is connected to the top of the bonnet of the valve, which is located approximately 3 feet from the discharge nozzle of the 2B Reactor Recirculation pump. During pump operation the discharge piping experiences flow induced vibration from the high velocity fluid, pump impeller vane pass frequency, and vibration from the operating pump. The 2B Recirculation pump began experiencing increased vibrations in late 2005, 2006 and 2007, which resulted in Recirculation pump seal leaks. This was caused by degradation in the pump hydrostatic bearing, resulting in axial shuttling and increased axial vibrations.
A review of the weld size from the failure report indicates that, while the weld meets minimum code requirements for a socket weld in this configuration, the proportions are such that it is susceptible to weld toe fatigue failure when subjected to a high vibration environment. Additionally, this type of geometry, with two welds nearly touching, is a stress intensifier. This configuration is seen as a contributing cause as it created a point of stress intensification.
D.
Safety Analysis
Reactor makeup capability was not affected and was available to provide adequate flow to compensate for the leaking drain line. Emergency Core Cooling Systems were operable and capable of performing their intended safety functions during the time that the leak existed. Therefore, the safety significance of this event is minimal due to the health and safety of the public not being compromised.
Corrective Actions
The 2B Reactor Recirculation pump internals were replaced in 2007 which reduced the amount of vibration associated with pump operation.
The leaking above seat drain line was cut and capped. This arrangement results in a vibration tolerant configuration.
Non-destructive examinations were conducted on welds in the below seat drains for the 2-0202-5A and 2-0202-5B valves. No additional indications were identified.
A walkdown of Unit 2 Recirculation system accessible small bore piping connections confirmed that no other close weld geometry existed.
A walkdown of Unit 2 Recirculation system accessible small bore piping confirmed that no other unsupported cantilever connections exist.
A walkdown of Unit 3 Recirculation system accessible small bore piping connections is scheduled to be performed to ensure that no other close weld geometry exist.
A walkdown of Unit 3 Recirculation system accessible small bore piping is scheduled to be performed to ensure that no other unsupported cantilever connections exist.
F.
Previous Occurrences
A review of DNPS Licensee Event Reports (LERs) was performed and the following events were identified.
Licensee Event Report 249/2002-003-00, "Reactor Recirculation Loop A Sensing Line Socket Weld Vibration Fatigue Failure"
" Licensee Event Report 249/2002-006-00, "Reactor Recirculation Loop A Sensing Line Socket Weld Vibration Fatigue Failure" G.
Component Failure Data
N/APRINTED ON RECYCLED PAPERPRINTED ON RECYCLED PAPER