05000374/LER-2017-001, Regarding Manual Reactor Scram Due to Turbine-Generator Run-Back Caused by Stem-Disc Separation in Stator Water Cooling Heat Exchanger Inlet Valve
| ML17083A122 | |
| Person / Time | |
|---|---|
| Site: | LaSalle  |
| Issue date: | 03/24/2017 |
| From: | Vinyard H Exelon Generation Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| RA17-030 LER 17-001-00 | |
| Download: ML17083A122 (4) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation 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)(ix)(A) 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)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(i) |
| 3742017001R00 - NRC Website | |
text
x l Generation RA17-030 March 24, 2017 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 LaSalle County Station, Unit 2 Renewed Facility Operating License No. NPF-18 NRG Docket No. 50-374 LaSalle County Station 2601 North 21 51 Road Marseilles, IL 61341 815-415-2000 Telephone www.exeloncorp.com 10 CFR 50.73
Subject:
Licensee Event Report 2017-001-00, Manual Reactor Scram due to Turbine-Generator Run-Back Caused by Stem-Disc Separation in Stator Water Cooling Heat Exchanger Inlet Valve In accordance with 10 CFR 50.73(a)(2)(iv)(A), Exelon Generation Company, LLC (EGG) is submitting Licensee Event Report (LER) Number 2017-001-00 for LaSalle County Station, Unit 2.
There are no regulatory commitments in this letter. Should you have any questions concerning this report, please contact Mr. Guy V. Ford, Jr., Regulatory Assurance Manager, at (815) 415-2800.
~y~
Harold T. Vinyard Plant Manager LaSalle County Station
Enclosure:
Licensee Event Report cc:
Regional Administrator-NRG Region Ill NRG Senior Resident Inspector - LaSalle County Station
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150*0104 EXPIRES: 10/31/2018 (06*2016)
Estimated burden per response ta 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 led back ta industry.
9 LICENSEE EVENT REPORT (LER)
Send comments regarding burden estimate ta the FOIA, Privacy and Information Collections
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- ~j Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail (See Page 2 for required number of digits/characters for each block) to lnfocollects.Resource@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 (See NUREG-1022, R.3 for instruction and guidance for completing this form means used to impose an information collection does not display a currenUy valid OMB control httQ://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3l) number, the NRG may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 3. PAGE LaSalle County Station, Unit 2 05000374 1 OF 3
- 4. TITLE Manual Reactor Scram due to Turbine-Generator Run-Back Caused by Stem-Disc Separation in Stator Water Cooling Heat Exchanger Inlet Valve
- 5. EVENT DATE
- 6. LEA NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED I
SEQUENTIAL I REV FACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR NUMBER NO.
MONTH DAY YEAR NA NA FACILITY NAME DOCKET NUMBER 01 23 2017 2017 - 001
- - 00 03 24 2017 NA NA
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITIED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: {Check all that apply)
D 20.2201 (bl D 20.2203(a)(3)(il D 50.73(a)(2)(ii)(A) 0 50.73(a)(2)(viii)(A) 1 D 20.2201 (dl D 20.2203(a)(3)(iil D 50.73(a)(2)(ii)(B)
D 50.73(a)(2)(viii)(B)
D 20.2203(a)(1 l D 20.2203(a)(4l D so.13(a)(2)(m)
D 50.73(a)(2)(ix)(A)
D 20.2203(a)(2)(il D 50.36(c)(1 )(i)(A) 1:8] 50. 73(a)(2)(iv)(A)
D 50.73(a)(2)(x)
- 10. POWER LEVEL D 20.2203(a)(2)(iil D 50.36(c)(1 )(ii)(A)
D 50.73(a)(2)(v)(A)
D 13.11(a)(4l D 20.2203(a)(2)(mJ D so.3s(c)(2)
D 50.73(a)(2)(v)(B)
D 13_11 (a)(s)
D 20.2203(a)(2)(iv)
D so.46(a)(3)(iil D 50.73(a)(2)(v)(C)
D 13.77(a)(1J 99 D 20.2203(a)(2)(v)
D 50.73(a)(2)(i)(A)
D 50.73(a)(2)(v)(D)
D 13.11(a)(2)(il D 20.2203(a)(2)(vi)
D 50.73(a)(2)(i)(B)
D 50.73(a)(2)(vii)
D 13.11(a)(2)(iil D 50.73(a)(2)(i)(C)
D OTHER Specify in Abstract below or in SEQUENTIAL NUMBER 001 REV NO.
00 In this event, the digital EHC {DEHC) system detected the conditions for generator run-back {two-of-two low pressure switches closed) and initiated a run-back. During a run-back, after a 15-second delay the DEHC system is designed to reduce the load reference at 30 percent per minute from the normal full power load reference of 105 percent. This caused the control valves to close, which caused the reactor pressure to rise and the bypass valves to open. Approximately 54 seconds after the run-back was initiated, a manual scram was inserted, which reduced reactor pressure and allowed the bypass valves to close. The DEHC system functioned as expected.
CORRECTIVE ACTIONS
Initial investigation found evidence that limited cooling water flow to the generator existed, and testing of all valves in the normal flow-path from the 'B' GC pump and the 'A' heat exchanger to the pressure control valve indicated that the most likely cause was plugging in the 'A' heat exchanger. An extent of condition review was performed for the opposite unit's GC system and associated valves and controllers. A review of GC heat exchanger preventative maintenance for both units indicated all tasks were current, with no outstanding corrective work orders. Additionally, a review of corrective work orders on the GC valves at LaSalle indicated they were related to leak-by issues and not tube plugging.
Additional inspections of the GC system were performed during the scheduled refueling outage in order to ascertain a more definitive cause. These inspections determined the cause of the GC system failure was stem-disc separation in the 'A' GC heat exchanger inlet valve 2GC-V08. The valve was repaired during the refueling outage, which restored the system. The extent of condition applied to the 'B' train GC heat exchanger inlet valve 2GC-V09, which was disassembled and inspected as part of the troubleshooting plan, due to its operation under similar conditions. Similarly, the GC heat exchanger outlet valves were inspected
{2GC-Y11) or replaced (2GC-V10). Unit 1 GC heat exchanger inlet and outlet valves are scheduled for the next Unit 1 refueling outage for stem-disc replacements.
PREVIOUS OCCURRENCES
A review of LaSalle Station Licensee Event Reports for the past three years, related to reactor trips, identified instances where a reactor manual or automatic scram was inserted; however, no previous occurrences related directly to turbine controls or the GC system operation at LaSalle Station were identified. Valve stem-disc separation issues have occurred at LaSalle Station, including the following event.
LER 374-2014-001-00:
On August 5, 2014, Unit 2 automatically scrammed from 100 percent power on high neutron flux, followed by a Group I containment isolation. Troubleshooting of the 2C Main Steam Isolation Valve {MSIV) determined that the valve stem-disc had separated from the stem, which allowed the main disc to drop into the main steam's flow-path. The cause of the stem-disc separation on the 2C MSIV was fretting wear attributable to marginal design. The root cause of the event was a legacy decision made in 2008 deferring installation of a manufacturer upgrade that would have prevented the failure. Corrective actions included installing the upgrade on all MSIVs on both units, and reviewing previous deferral decisions made using the same decision-making process.
COMPONENT FAILURE DATA
Manufacturer: Crane [C665] I Aloyco [A200]
Device: 90-Degree Angle, Globe, 6-lnch [Model 336-8-SP]
Component ID: Crane Part Number PN 31196 Page_3_ of _3_