05000461/LER-2013-008, Regarding Failure of Division I Transformer Leads to Isolation of Instrument Air Supply to Containment, Lowering Scram Pilot Air Header Pressure, and Manual Reactor Scram
| ML14049A283 | |
| Person / Time | |
|---|---|
| Site: | Clinton  |
| Issue date: | 02/03/2014 |
| From: | Taber B Exelon Generation Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| U-604156 LER 13-008-00 | |
| Download: ML14049A283 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 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 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 4612013008R00 - NRC Website | |
text
A Exelon Generation.
Clinton Power Station 8401 Power Road Clinton, IL 61727 U-604156 February 3, 2014 10 CFR 50.73 SRRS 5A.108 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 2013-008-00 Enclosed is Licensee Event Report (LER) No. 2013-008-00: Failure of Division 1 Transformer Leads to Isolation of Instrument Air Supply to Containment, Lowering Scram Pilot Air Header Pressure, and Manual Reactor Scram. This report is being submitted in accordance with the requirements of 10 CFR 50.73.
There are no regulatory commitments contained in this report.
Should you have any questions concerning this report, please contact Mr. Jeffrey E. Cunningham, Acting Regulatory Assurance Manager, at (217)-937-3160.
Respectfully, B. Keith Taber Site Vice President Clinton Power Station RSF/blf
Enclosure:
Licensee Event Report 2013-008-00 cc:
Regional Administrator - NRC Region III NRC Senior Resident In ector - Clinton PowrS0to
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 01/3112017 (01-2014)
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 />.
4,1 f Reported lessons learned are incorporated into the licensing process and fed back to industry.
Send comments regarding burden estimate to the FOIA, Privacy and Information Collections IC S
EBranch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by LICENSEE EVENT REPORT (LER intemet e-mail to Infocollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and (See Page 2 for required number of 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 digits/characters for each block) control number, 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 05000 461 1 OF 4
- 4. TITLE Failure of Division I Transformer Leads to Isolation of Instrument Air Supply to Containment, Lowering Scram Pilot Air Header Pressure, and Manual Reactor Scram
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED MSEQUENTIAL REV FACILITY NAME DOCKET NUMBER YEAR YEAR NUMBER NO, MONTH DAY YEAR 05000 FACILITY NAME DOCKET NUMBER 12 08 2013 2013 008 00 02 03 2014 05000
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply)
[] 20.2201(b)
F] 20.2203(a)(3)(i)
El 50.73(a)(2)(i)(C)
F] 50.73(a)(2)(vii) 1] 20.2201(d)
F] 20.2203(a)(3)(ii) 50.73(a)(2)(ii)(A)
[
50.73(a)(2)(viii)(A)
E] 20.2203(a)(1)
[
20.2203(a)(4) 50.73(a)(2)(ii)(B)
[j 50.73(a)(2)(viii)(B) 20.2203(a)(2)(i)
[
50.36(c)(1)(i)(A) 50.73(a)(2)(iii)
[
50.73(a)(2)(ix)(A)
- 10. POWER LEVEL LI 20.2203(a)(2)(ii)
[]
50.36(c)(1)(ii)(A) 50.73(a)(2)(iv)(A)
[
50.73(a)(2)(x)
LI 20.2203(a)(2)(iii)
[
50.36(c)(2)
LI 50.73(a)(2)(v)(A) 73.71(a)(4) 097 LI 20.2203(a)(2)(iv)
[
50.46(a)(3)(ii) 50.73(a)(2)(v)(B) 73.71(a)(5)
E] 20.2203(a)(2)(v)
[
50.73(a)(2)(i)(A) 50.73(a)(2)(v)(C)
[]
OTHER El 20.2203(a)(2)(vi)
[] 50.73(a)(2)(i)(B)
(7 50.73(a)(2)(v)(D)
Specfy in Abstract below or in
PLANT AND SYSTEM IDENTIFICATION
General Electric -- Boiling Water Reactor, 3473 Megawatts Thermal Rated Core Power Energy Industry Identification System (EIIS) codes are identified in text as [XX].
EVENT IDENTIFICATION Failure of Division 1 Transformer Leads to Isolation of Instrument Air Supply to Containment, Lowering Scram Pilot Air Header Pressure, and Manual Reactor Scram
A. Plant Operating Conditions Before the Event
Unit: 1 Event Date: 12/8/2013 Event Time: 2036 hours0.0236 days <br />0.566 hours <br />0.00337 weeks <br />7.74698e-4 months <br /> CST Mode: 1 Mode Name: POWER OPERATION Reactor Power: 97.3 percent
B. DESCRIPTION OF EVENT
On 12/8/2013 at 2026 hours0.0234 days <br />0.563 hours <br />0.00335 weeks <br />7.70893e-4 months <br />, with the plant in Mode 1 (Power Operation) at 97.3 percent reactor power, multiple alarms [ALM] were received in the Main Control Room (MCR) due to the trip of 4160 volt [EB] 1 Al breaker [BKRI 1 AP07EJ which resulted in a loss of power to Division 1 480 volt unit substations 1 A [ED] and Al. Area operators were immediately dispatched to investigate the trip of the breaker. Many Division 1 components lost power. Operators entered the action requirements for numerous Technical Specification Limiting Conditions for Operation. Major impacts to the station as discussed in this report include: loss of Instrument Air (IA) [LE] supply to Containment loads, affecting the Control Rod Drive system (CRD) [AAI, main steam isolation valves (MSIVs) [ISV] [SB], and the Reactor Water Cleanup system (RWCU)
[CE] ; loss of Secondary Containment [VG] differential pressure; loss of Low Pressure Core Spray system (LPCS) [BM]
capability; and loss of Residual Heat Removal (RHR) [BN] Train A capability.
Operators in the MCR noted the loss of power caused IA containment isolation valves to close so operators began monitoring the control rod drive (CRD) scram pilot air header pressure for potential of control rods [ROD] to drift due to the loss of air. At 2035 hours0.0236 days <br />0.565 hours <br />0.00336 weeks <br />7.743175e-4 months <br />, the MCR received an alarm for Rod Control and Information System inoperable due to the loss of power to the Division 1 Rod Action Control System (RACS). The loss of instrument air affected various other containment loads, including the MSIVs and the RWCU system.
At 2036 hours0.0236 days <br />0.566 hours <br />0.00337 weeks <br />7.74698e-4 months <br />, when the pre-established scram pilot air header low pressure alarm limit was reached, operators immediately placed the reactor mode switch [HS] into the shutdown position, initiating a manual reactor scram. At 2037 hours0.0236 days <br />0.566 hours <br />0.00337 weeks <br />7.750785e-4 months <br />, reactor pressure vessel water level dropped to the low reactor water Level 3 setpoint (normal result of a scram from high power) and operators entered Emergency Operating Procedure (EOP) -1, Reactor Pressure Vessel (RPV) Control. At 2042 hours0.0236 days <br />0.567 hours <br />0.00338 weeks <br />7.76981e-4 months <br />, operators verified all control rods fully inserted into the core using the Division 2 RACS.
At 2037 hours0.0236 days <br />0.566 hours <br />0.00337 weeks <br />7.750785e-4 months <br />, normally closed Group 2 (Residual Heat Removal (RHR) [BO]), Group 3 (RHR), and Group 20 (miscellaneous systems) containment isolation valves received signals to close as expected and operators subsequently verified the valves were closed.
At 2043 hours0.0236 days <br />0.568 hours <br />0.00338 weeks <br />7.773615e-4 months <br />, operators manually initiated the standby gas treatment system (SGTS) [BH] to restore Secondary Containment differential pressure that became positive when the Fuel Building ventilation system isolated due to the loss of 480 volt power.
At 2052 hours0.0238 days <br />0.57 hours <br />0.00339 weeks <br />7.80786e-4 months <br />, a report from the field indicated that the 480 volt Unit Sub A 4160/480 volt stepdown transformer [XFMRI OAP05E2 was the source of the fault that caused the trip of the 4160 volt breaker 1 AP07EJ. A subsequent visual inspection of the transformer identified damage to the A and B phase windings.
At 2114 hours0.0245 days <br />0.587 hours <br />0.0035 weeks <br />8.04377e-4 months <br />, operators manually opened the outboard instrument air containment isolation valve 1 IA01 2A in accordance with the loss of power off-normal procedure to restore the instrument air supply to the containment.
At 0121 hours0.0014 days <br />0.0336 hours <br />2.000661e-4 weeks <br />4.60405e-5 months <br /> on 12/9/13, the plant was in a stable condition and operators exited EOP-1.
RPV pressure control was maintained using main steam line drains to the main condenser [COND] and RPV water level control was maintained using condensate I condensate booster systems [SDI and the CRD system.
This event is reportable under the provisions of: 10 CFR 50.73(a)(2)(iv)(A) due to the unplanned actuations of the Reactor Protection System [JC] (RPS) and containment isolation valves; 10 CFR 50.73(a)(2)(v)(C) due a loss of normal ventilation and differential pressure to Secondary Containment; and 10 CFR 50.73(a)(2)(v)(D) as a result of the loss of Division 1 480 volt power causing the loss of accident mitigation abilities of the LPCS system. Event Notification 49617 was made to the NRC on 12/9/13 at 0015 hours1.736111e-4 days <br />0.00417 hours <br />2.480159e-5 weeks <br />5.7075e-6 months <br /> Central Standard Time.
This event was entered into the Clinton Power Station corrective action program under Issue Report 1594407.
C. CAUSE OF EVENT
A definitive root cause cannot be determined for this event at this time. The cause of the OAP05E2 transformer failure cannot be identified until it can be removed from its installed location in the plant and a failure analysis is completed.
The transformer vendor was contacted to assist in determining the most likely cause for the failure. Photographs of the failed transformer were provided to the vendor. The vendor compared these photographs to photographs of other failed transformers and indicated that based on their visual assessment, the most probable cause of the OAP05E2 transformer failure is a turn to turn failure of the high side windings due to insulation breakdown over time.
Since a primary cause (root cause) cannot be identified at this time, a Special Plant Condition (SPC) action has been created to track the transformer removal and vendor failure analysis.
The OAP05E2 transformer was installed in 1980 with a 40 year life expectancy (2020). The transformer failed seven years prior to its expected end of life. Based on the vendor's dry transformer performance history, the failure of OAPO5E2 transformer is considered a low probability event within the expected 40 year life cycle.
D. SAFETY CONSEQUENCES
The failure of OAPO5E2 transformer and subsequent trip of 4160 volt circuit breaker 1 AP07EJ placed the station in a potential scram condition due to loss of instrument air to the containment and 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 480 volt power caused the Fuel Building Ventilation System to isolate resulting in positive secondary containment pressure. Operators placed the Division 2 SGTS in service to restore secondary containment negative pressure. All Division 2 and Division 3 Emergency Core Cooling Systems remained operable and available throughout this event for accident mitigation if needed. No plant safety limits were exceeded and no Emergency Core Cooling System actuations occurred.
E. CORRECTIVE ACTIONS
An Engineering Change document was developed to utilize the spare OAP05E7 transformer. Maintenance personnel performed necessary work to transfer leads, cables, conduit, etc. from the OAP05E2 transformer to the OAPO5E7 transformer. The OAP05E7 transformer was energized and the station restored Division 1 to service and restarted the unit.
F. PREVIOUS OCCURRENCES
CPS experienced one other dry type transformer failure on 2/3/1996. This transformer was a non-safety radiological waste building transformer and its fault was non-consequential. Conditions (transformer load and cycling due to cold outside temperatures) were the most likely cause of the 2/3/1996 transformer failure. A transformer autopsy was determined to be cost prohibitive and a definitive cause of the 2/3/1996 transformer failure was not identified. The 12/8/2013 failure was reviewed and determined to be unlike the 2/3/1996 failure.
G. COMPONENT FAILURE DATA
Component Description: I-T-E Dry Type Transformer; 4160V/480V; 750KVA Manufacturer: GOULD-BROWN-BOVERI Model: VU-9 Year Built: 1980