05000461/LER-1917-009, Regarding Trip of Emergency Reserve Auxiliary Transformer Static Var Compensator Causes Positive Secondary Containment Pressure Following Voltage Transient on 138 Kv Offsite Source
| ML18008A062 | |
| Person / Time | |
|---|---|
| Site: | Clinton  |
| Issue date: | 01/04/2018 |
| From: | Stoner T Exelon Generation Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| U-604398 LER 17-009-00 | |
| Download: ML18008A062 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 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)(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)(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) |
| 4611917009R00 - NRC Website | |
text
Clinton Power Station 8401 Power Road Clinton, IL 61727 U-604398 January 4, 2018 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555-0001
Subject:
Clinton Power Station, Unit 1 Facility Operating License No. NPF-62 NRC Docket No. 50-461 Licensee Event Report 2017-009-00 Exelon Generation 10 CFR 50.73 SRRS 5A.108 Enclosed is Licensee Event Report (LER) 2017-009-00: Trip of Emergency Reserve Auxiliary Transformer Static VAR Compensator Causes Positive Secondary Containment Pressure Following Voltage Transient on 138 kV Offsite Source. This report is being submitted in accordance with the requirements of 1 O CFR 50.73.
There are no regulatory commitments contained in this report.
Should you have any questions concerning this report, please contact Mr. Dale Shelton, Regulatory Assurance Manager, at (217) 937-2800.
Respectfully,
~;:3=~::;;:::-------=~::,r Theodore R. Stoner Site Vice President Clinton Power Station KP/cac Attachment: License Event Report 2017-009-00 cc:
Regional Administrator-Region Ill NRC Senior Resident Inspector -
Clinton Power Station Office of Nuclear Facility Safety -
Illinois Emergency Management Agency
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 03/31/2020 (04-2017)
, the httQ://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/)
NRG may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 3. PAGE Clinton Power Station, Unit 1.
05000461 1 OF 4
- 4. TITLE Trip of Emergency Reserve Auxiliary Transformer Static VAR Compensator Causes Positive Secondary Containment Pressure Following Voltage Transient on 138 kV Offsite Source.
- 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 05000 FACILITY NAME DOCKET NUMBER 11 05 2017 2017 - 009 00 01 04 2018 05000
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply)
D 20.2201 (bl D
20.22os(a)(sJ(il D
50.73(a)(2)(ii)(A)
D 50.73(a)(2)(viii)(A) 1 D
20.2201 (dl D
20.22os(aJ(s)(iil D
50.73(a)(2)(ii)(B)
D 50.73(a)(2)(viii)(B)
D 20.22os(aJ(1J D
20.22os(a)(4l D
50.1s(a)(2)(iiil D
50.73(a)(2)(ix)(A)
D 20.22os(aJ(2Hil D
50.36(c)(1 )(i)(A)
D 50.73(a)(2)(iv)(A)
. D 50.73(a)(2)(x) '
- 10. POWER LEVEL D
20.22os(aJ(2Hiil D
50.36(c)(1)(ii)(A)
D 50.73(a)(2)(v)(A)
[j 73.71(a)(4)
D 20.22os(aJ(2J(iiil D
50.ss(cJ(2J D
50.73(a)(2)(v)(B)
D 1s.11 (al(5l D
20.2203(a)(2)(iv)
D 5o.4s(aJ(sJ(iil [8J 50.73(a)(2)(v)(C)
D 1s.n(a)(1J 098 D
20.2203(a)(2)(v)
D 50.73(a)(2)(i)(A)
D 50.73(a)(2)(v)(D)
D 1s.n(aJ(2J(il D
20.2203(a)(2)(vi)
D 50.73(a)(2)(i)(B)
D 50.73(a)(2)(vii)
D 1s.n(aJ(2J(iiJ D
50.73(a)(2)(i)(C)
D OTHER Specify in Abstract below or in SEQUENTIAL NUMBER 009 REV NO.
00 The Standby Gas Treatment System (VG) was manually started and SC vacuum was restored within TS limits at approximately 1242 hours0.0144 days <br />0.345 hours <br />0.00205 weeks <br />4.72581e-4 months <br />. The system actuations were addressed and plant equipment was restored to service in accordance with plant procedures. The momentary loss of power did not adversely affect the safe operation of the plant or the restoration of SC. During the investigation, Ameren reported that the Clinton feeder breaker that supplied the 138 kV line had tripped and reclosed probably due to weather. In addition, during inspection of the offsite power lines, two disconnects were found not fully seated. These disconnects were reseated and the ERAT SVC was returned to service and declared OPERABLE at 1702 hours0.0197 days <br />0.473 hours <br />0.00281 weeks <br />6.47611e-4 months <br />.
C.
Cause of the Event
The cause of the SC differential pressure becoming positive is that the circuit design of VF is not adequately robust to withstand the loss of the 138 kV feed.
D.
Safety Consequences
This event is reportable in accordance with 1 OCFR50 50.73(a)(2)(v)(C) as a condition that could have prevented fulfillment of a safety function to control the release of radioactive material because the SC was declared inoperable.
The VG system was fully operable at the time of the event and capable of performing its required safety function. Operations entered EOP-8 for SC vacuum less than -0.25 inch WG and entered TS LCO 3.6.4.1 Required Action A.1. The SC vacuum was restored to within TS limits within the completion time requirement. The SC vacuum normally is kept slightly negative relative to atmospheric pressure to prevent leakage to the atmosphere. The VF system is a non-safety ventilation system which is normally in service to maintain SC vacuum. The VG system is the safety-related system which is relied upon to perform this function following an accident. During the event, the VG system was placed in service and restored SC to operability consistent with its safety function. Therefore, the ability of the station to maintain SC vacuum in the event of an accident was never jeopardized or challenged by the VF system trip. Engineering analysis has determined that this event is not considered a safety system functional failure.
E.
Corrective Actions
A modification will be installed to prevent tripping VF during a momentary loss of power. Installation of a 138 kV Ring Bus is scheduled that is intended to improve the reliability of the radial feed of the 138 kV line.
In addition, a License Amendment Request (LAR) was submitted to the NRC on November 8, 2017 to adopt Technical Specifications Task Force (TSTF)-551, Revise Secondary Containment Surveillance Requirements, to adopt a change to the CPS TS that would eliminate the requirement to declare SC inoperable under similar transient conditions. Adoption of this LAR would have prevented this event from being reportable.
F.
Previous Similar Occurrences Licensee Event Report 2015-004-00: Trip of Emergency Reserve Auxiliary Transformer Static VAR Compensator Causes Positive Secondary Containment Pressure Following Lightning Strike on 138 kV Offsite Source.
On June 25, 2015 at 0301 CDT, the Main Control Room received numerous annunciators that indicated a trip of the ERAT Static VAR Compensator caused by a voltage transient on the 138 kV offsite source due to thunderstorms in the area. The Division 1 safety bus was manually aligned from the reserve source to its normal source.
As a result of the voltage transient, the Division 1 VF system isolation dampers closed causing a trip of VF supply and exhaust fans. Secondary Containment vacuum increased to greater than O inch WG which exceeded the TS requirement. Secondary Containment vacuum was restored within TS requirements by reopening the VF isolation dampers and restarting the VF supply and exhaust fans. The ERAT SVC was returned to service at 0457 CDT.
Licensee Event Report 2016-004-00: Trip of Emergency Reserve Auxiliary Transformer Static VAR Compensator Causes Positive Secondary Containment Pressure Following Lightning Strike on 138 kV Offsite Source On March 30, 2016, at approximately 1545 CDT, the Main Control Room received numerous annunciators that indicated a trip of the Emergency Reserve Auxiliary Transformer Static VAR Compensator caused by a voltage transient on the 138 kV supply. Technical Specification Limiting Condition for Operation 3.8.1, AC Sources-Operating, Required Action A.1 and A.2 were entered. As a result of the voltage transient, the Division 1 Fuel Building ventilation system isolation dampers closed causing a trip of VF supply and exhaust fans. With no operating VF fans, Secondary Containment vacuum rose to slightly greater than O inches water gauge which exceeded the TS requirement of greater than 0.25 inches vacuum WG.
Secondary Containment vacuum was restored within TS requirements at 1550 CDT by starting the Standby Gas Treatment System.
G.
Component Failure Data
There were no component failures associated with this event. Page _4_ of _4_