05000461/LER-2017-010-02, Division 1 Transformer Failure Leads to Instrument Air Isolation to Containment Requiring a Manual Reactor Scram: Difference between revisions

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{{Adams
#REDIRECT [[05000461/LER-2017-010-01, Division 1 Transformer Failure Leads to Instrument Air Isolation to Containment Requiring a Manual Reactor Scram]]
| number = ML19022A264
| issue date = 01/17/2019
| title = Division 1 Transformer Failure Leads to Instrument Air Isolation to Containment Requiring a Manual Reactor Scram
| author name = Stoner T
| author affiliation = Exelon Generation Co, LLC
| addressee name =
| addressee affiliation = NRC/Document Control Desk, NRC/NRR
| docket = 05000461
| license number = NPF-062
| contact person =
| case reference number = U-604466
| document report number = LER 2017-010-02
| document type = Letter, Licensee Event Report (LER)
| page count = 5
}}
{{LER
| Title = Division 1 Transformer Failure Leads to Instrument Air Isolation to Containment Requiring a Manual Reactor Scram
| Plant =
| Reporting criterion = 10 CFR 50.73(a)(2)(ii)(A), 10 CFR 50.73(a)(2)(viii)(A), 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), 10 CFR 50.73(a)(2)(x), 10 CFR 50.73(a)(2)(v)(A), 10 CFR 50.73(a)(2)(v)(B), 10 CFR 50.73(a)(2)(v), 10 CFR 50.73(a)(2)(i)(A), 10 CFR 50.73(a)(2)(i)(B), 10 CFR 50.73(a)(2)(vii), 10 CFR 50.73(a)(2)(i), 10 CFR 50.73(a)(2)(ii)(B)
| Power level =
| Mode =
| Docket = 05000461
| LER year = 2017
| LER number = 10
| LER revision = 2
| Event date =
| Report date =
| ENS =
| abstract =
}}
 
=text=
{{#Wiki_filter:Clinton Power Station 8401 Power Road Clinton, IL 61727 U-604466 January 17, 20.19 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555-0001 Clinton Power Station, Unit 1 Facility Operating License No. NPF-62 NRC Docket No. 50-461 Subject: Licensee Event Report 2017-010-02 10 CFR 50.73 SRRS 5A.108 Enclosed is Licensee Event Report (LER) 2017-010-02: Division 1 Transformer Failure Leads to Instrument Air Isolation to Containment Requiring a Manual Reactor Scram. This is a supplemental report to LER 2017-010-01 submitted to the NRC on August 3, 2018. The updated information in the LER is denoted by revision bars located in the right-hand margin. 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,
~
Theodore R. Stoner Site Vice President Clinton Power Station kp/lam
 
==Attachment:==
License Event Report 2017-010-02 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 (04-2018)
, the NRC 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 Division 1 Transformer Failure Leads to Instrument Air Isolation to Containment Requiring a Manual Reactor Scram
: 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 12 09 2017 2017 -
010 02 01 18 19 05000
: 9. Operating Mode
: 11. This Report is Submitted Pursuant to the Requirements of 1 O CFR §: (Check all that apply)
D 20.2201(b)
D 20.2203(a)(3)(i)
D 50.73(a)(2)(ii)(A)
D 50.73(a)(2)(viii)(A)
D 20.2201(d)
D 20.2203(a)(3)(ii)
~ 50. 73(a)(2)(ii)(B)
D 50.73(a)(2)(viii)(B) 1 D
D 20.2203(a)(4J D
D 20.2203(a)(1) 50.73(a)(2)(iii) 50.73(a)(2)(ix)(A)
D 20.2203(a)(2)(i)
D 50.36( c )( 1 )(i)(A)
~ 50.73(a)(2)(iv)(A)
D 50.73(a)(2)(x) 1 o. Power Level D 20.2203(a)(2)(ii)
D 50.36(c)(1 )(ii)(A)
D 50.73(a)(2)(v)(A)
D 73.71 (a)(4)
D 20.2203(a)(2)(iii)
D 50.36(c)(2)
D 50.73(a)(2)(v)(B)
D 73.71 (a)(5)
D 20.2203(a)(2)(iv)
D 5o.46(a)(3)(iiJ
~ 50.73(a)(2)(v)(C)
D 73.77(a)(1) 097 D 20.2203(a)(2)(v)
D 50.73(a)(2)(i)(A)
~ 50.73(a)(2)(v)(D)
D 73.77(a)(2)(i)
D 20.2203(a)(2)(vi)
D 50.73(a)(2)(i)(B)
D 50.73(a)(2)(vii) tJ 73.77(a)(2)(ii)
Li;:\\*** :1~::: *. r **
*****.t.:iJ
,.;,:.. ;d;Y.'-'**
D 50.73(a)(2)(i)(C)
D Other (Specify in Abstract below or in SEQUENTIAL NUMBER 010 REV NO.
02 This event is reportable under 1 O CFR 50.73(a)(2)(iv)(A) as a manual actuation of the Reactor Protection System (RPS), 1 O CFR 50.73(a){2)(v)(C) as a condition that could have prevented the fulfillment of a safety function needed to control the release of radioactive material, 1 O CFR 50.73(a)(2)(v)(D) as a condition that could have prevented the fulfillment of a safety function needed to mitigate the consequences of an accident and 1 O CFR 50.73 (a)(2)(ii)(B) as an event that resulted in the plant being in an unanalyzed condition that significantly degraded plant safety.
The event described in this report is considered an unplanned scram with complications due to the loss of the Division 1 480V power.
C.
 
==Cause of the Event==
Based on analyses performed at vendor test facilities following the event, the cause of the transformer failure was determined to be excessive layer to layer design stress within the 4160V winding of a Gould Brown Boveri (GBB) dry type 4160/480V safety related transformer. This pre-existing design defect resulted in the issuance of a 1 O CFR Part 21 notification to the NRG.
D.
 
==Safety Consequences==
The trip of 4160V circuit breaker 1 AP07EJ and the failure of the 480V transformer 1 AP11 E placed the station in a potential scram condition due to loss of Instrument Air to the containment and the scram pilot air header. Manual operator actions were taken to shut down the reactor prior to an automatic scram and place the plant in a safe and stable condition. The loss of Division 1 480V power caused the Fuel
* Building Ventilation System to isolate resulting in secondary containment vacuum to rise greater than O inches water gauge and primary containment differential pressure to exceed the initial conditions assumed in the accident analysis, resulting in the plant being in an unanalyzed condition. Operators placed the Division 2*SGTS in service to restore secondary containment vacuum. Once the plant reached Mode 4, Cold Shutdown, the containment airlock was defeated to restore primary containment differential pressure to within limits. All Division 2 and Division 3 Emergency Core Cooling Systems remained operable and available throughout this event for accident mitigation if required. No plant safety limits were exceeded and no Emergency Core Cooling System actuations occurred.
E.
 
==Corrective Actions==
On December 14, 2017, the faulted transformer was replaced and the plant returned to Mode 1 operations on December 15, 2017. Safety and non-safety related Gould Brown Boveri (GBB) 4160V dry type transformers which could lead to the plant entering a forced shutdown condition or having high operational impact were replaced in the following refueling outage C1R18. Transformers were replaced with an improved design transformer which does not have layer to layer design stress in excess of the current insulation manufacturer's recommendations.
F.
Previous Similar Occurrences LER 2013-008-01 Failure of Division 1 Transformer Leads to Isolation of Instrument Air Supply to Containment, Lowering Scram Pilot Air Header Pressure, and Manual Reactor Scram On December 8, 2013 at 2026 hours with the plant in Mode 1 at 97.3 percent reactor power, operators received multiple alarms due to the trip of 4160V 1 A 1 breaker 1 AP07EJ which resulted in a loss of power to Division 1 480V unit substations 1 A and A 1. Operators were immediately dispatched and found a 4160/480V stepdown transformer A 1 (OAP05E) failed. Many Division I components lost power.
The loss of power caused an Instrument Air containment isolation. The loss of Instrument Air affected various containment loads, including the scram pilot air header, the main steam isolation valves and the reactor water cleanup system. At 2036 hours, the scram pilot air header low pressure alarm was received and in response to an anticipated automatic reactor scram, operators immediately initiated a manual reactor scram'. All control rods fully inserted into the core.
The cause of the transformer failure was a turn to turn failure of the high side windings due to insulation breakdown over time, prior to its expected end of life. An installed spare was connected to replace the failed Division 1 transformer.
 
==G. Component Failure Data==
Component Description: I-T-E Dry Type Transformer; 4160V/480V; 750KVA, Manufacturer: GOULD-BROWN-BOVERI Page _4_ of _4_
}}
 
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