05000341/LER-2013-004, Regarding Condition Prohibited by Technical Specifications for 480 Volt Bus Inoperable Due to Failed Voltage Regulator
| ML14171A435 | |
| Person / Time | |
|---|---|
| Site: | Fermi  |
| Issue date: | 06/20/2014 |
| From: | Conner J DTE Energy |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NRC-14-0046 LER 13-004-00 | |
| Download: ML14171A435 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 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 |
| 3412013004R00 - NRC Website | |
text
J. Todd Conner Site Vice President DTE Energy Company 6400 N. Dixie Highway, Newport, MI 48166 Tel: 734.586.4849 Fax: 734.586.5295 Email: connerj@dteenergy.com DTE Energy-June 20, 2014 10 CFR 50.73 NRC-14-0046 U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington D C 20555-0001
Reference:
Fermi 2 NRC Docket No. 50-341 NRC License No. NPF-43
Subject:
Licensee Event Report (LER) No. 2013-004 Pursuant to 10 CFR 50.73 (a)(2)(i)(B), DTE Electric Company is submitting LER No.
2013-004, Condition Prohibited by Technical Specifications for 480 Volt Bus Inoperable Due to Failed Voltage Regulator.
No commitments are being made in this LER.
Should you have any questions or require additional information, please contact Mr.
Zackary W. Rad of my staff at (734) 586-5076.
Sincerely, Enclosure cc:
NRC Project Manager NRC Resident Office Reactor Projects Chief, Branch 5, Region III Regional Administrator, Region III Michigan Public Service Commission Regulated Energy Division (kindschl@michigan.gov)
Enclosure to NRC-14-0046 Fermi 2 NRC Docket No. 50-341 Operating License No. NPF-43 LER 2013-004, Condition Prohibited by Technical Specifications for 480 Volt Bus Inoperable Due to Failed Voltage Regulator
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 01131/2017 (02-2014)
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 />.
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 Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by LICENSEE EVENT REPORT (LER) internet 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 Fermi 2 05000 341 1 OF 3
- 4. TITLE Condition Prohibited by Technical Specifications for 480 Volt Bus Inoperable Due to Failed Voltage Regulator
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED MONTH DAY YEAR YEAR SEQUENTIAL REV MONTH DAY YEAR FACILITY NAME DOCKET NUMBER NUBR NO.
05000 FACILITY NAME DOCKET NUMBER 12 14 2013 2013 -
004 00 06 20 2014 05000
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply)
Q 20.2201(b) 20.2203(a)(3)(i) 50.73(a)(2)(i)(C) 50.73(a)(2)(vii)
Q 20.2201(d) 20.2203(a)(3)(ii) 50.73(a)(2)(ii)(A) 50.73(a)(2)(viii)(A)
Q 20.2203(a)(1) 20.2203(a)(4) 50.73(a)(2)(ii)(B) 50.73(a)(2)(viii)(B)
Q 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 Q
20.2203(a)(2)(ii) 50.36(c)(1)(ii)(A) 50.73(a)(2)(iv)(A) 50.73(a)(2)(x)
Q 20.2203(a)(2)(iii) 50.36(c)(2) 50.73(a)(2)(v)(A) 73.71(a)(4) 100 20.2203(a)(2)(iv) 50.46(a)(3)(ii) 50.73(a)(2)(v)(B) 73.71(a)(5) 20.2203(a)(2)(v) 50.73(a)(2)(i)(A) 50.73(a)(2)(v)(C)
OTHER 20.2203(a)(2)(vi)
/
50.73(a)(2)(i)(B) 50.73(a)(2)(v)(D)
Sp in A act below or in
- 12. LICENSEE CONTACT FOR THIS LER LICENSEE CONTACT TELEPHONE NUMBER (include Area Code)
David G. Coseo - Supervisor, Nuclear Compliance (734) 586-4273CAUSE SYSTEM COMPONENT FACTURER REPORTABLE
CAUSE
SYSTEM COMPONENT AURER REPORTABLE B
EC RG G080 Y
- 14. SUPPLEMENTAL REPORT EXPECTED
- 15. EXPECTED MONTH DAY YEAR YES (If yes, complete 15. EXPECTED SUBMISSION DATE)
/
NO SUBMISSION I
DATE ABSTRACT (Limit to 1400 spaces, i.e., approximately 15 single-spaced typewritten lines)
On April 21, 2014, an Engineering past operability evaluation of the electrical 72E Bus Voltage Regulator determined that the AC power distribution bus would have been inoperable under degraded grid voltage conditions during a design basis accident. After reviewing weekly voltage readings from December 2013, it was concluded the 72E Bus Voltage Regulator had stopped functioning between December 14, 2013 and December 21, 2013, while the plant was in Mode 1. Limiting Condition for Operation 3.8.7 for the loss of one 480V bus required completion time was exceeded and is reportable under 10 CFR 50.73(a)(2)(i)(B) as an operation or condition which was prohibited by the plant's Technical Specifications.
Inspection of the 72E Bus Voltage Regulator revealed significant wear on the worm gear assemblies. This wear was found on all three worm assemblies and contributed to looseness and excess movement causing binding to occur. Binding caused the drive motors to draw a higher current and overheat, leading to motor failure. After replacing all worn and degraded parts, the voltage regulator was reassembled and satisfactorily passed post maintenance testing.
NRC FORM 366 (02-2014)
Initial Plant Conditions
Mode 1
Reactor Power 100 percent Description of the Event:
On April 21, 2014, an Engineering past operability evaluation of the electrical 72E Bus Voltage Regulator determined that the AC power distribution bus would not have performed its safety function under degraded grid voltage conditions during a design basis accident. The failure to enter the Limiting Condition for Operation 3.8.7 for the loss of one 480V bus within the required completion time is reportable under 10 CFR 50.73(a)(2)(i)(B) as an operation or condition which was prohibited by the plant's Technical Specifications.
During Refueling Outage 16, with the plant in Mode 5, on February 16, 2014, voltage on the 72E bus [BU] was found to be above 128 Volts AC. The expected value and set point for the 72E voltage regulator [RG] is approximately 120 Volts AC. Attempts to manually lower the voltage by Operations and Electrical Maintenance were unsuccessful. Engineering analysis was performed and determined the high voltage condition of the 72E Bus was satisfactory to support the loads necessary for Mode 5 and the addition of loads required for Mode 5 were not expected to draw the voltage down to invalidate the analysis. The regulator was returned to automatic control and an emergent issues team was formed to resolve the problem.
The emergent issues team inspected the 72E Bus Voltage Regulator, drive motors and gear assemblies. The team gathered all necessary parts to replace any failed or worn components, and reassembled accordingly. After being reassembled, the 72E Bus Voltage Regulator performed satisfactorily in Post Maintenance Testing.
A review of the weekly voltage readings taken in December 2013 suggests the 72E voltage regulator had stopped functioning properly between December 14, 2013 and December 21, 2013, prior to Refueling Outage 16 while in Mode 1. Therefore, between December 14, 2013, and February 10, 2014, the required actions and completion times for Limiting Condition for Operations 3.8.7, Electrical Distribution Systems while Operating [EC] while in Mode 1, were not met.
Under degraded voltage conditions, voltage requirements demand the 72E voltage regulator should be in its maximum position to mitigate a design-basis accident. With the regulator held at the as-found nominal position, the 72E Bus would have an unacceptable reduction in voltage to its supported loads. Therefore, the as-found position of the regulator in its nominal position would not sufficiently support the safety related electrical equipment (motor operated valves, battery chargers, etc.) under degraded voltage conditions during design basis accident mitigation.
The timeliness in discovery of the failed condition of the 72E regulator can be attributed to the configuration of the upstream step down transformers and voltage acceptance criteria. During Engineering analysis, it was demonstrated that the voltages coming from Transformer 65 and the Bus 72E transformer [XFMR] can mask a 72E regulator failure.
Significant Safety Consequences and Implications
The purpose of Technical Specification 3.8.7 is to ensure the availability of AC and DC electrical power for the systems required to shut down the reactor and maintain it in a safe condition after an anticipated operational occurrence or a postulated Design Basis Accident. AC and DC electrical power is required for Engineered Safety Features to function during any analyzed accident with a loss of off site power, neither of which occurred coincident with this event. Maintaining the required Division 1 and 2 AC and DC electrical power distribution subsystems Operable ensures redundancy of the Engineered Safety Features is not defeated such that a single failure within any system or within the electrical power distribution subsystems will not prevent the safe shutdown of the reactor.
While the 72E Bus was in a degraded condition that would not support the required Division 2 switchgear [SWGR] loads during a Mode 1 Design Basis Accident concurrent with a degraded grid condition, buses 65F/72F, 64B/72B and 64C/72C were fully functional to operate the necessary required loads, mitigating a risk to Nuclear Safety.
Cause of the Event
During the inspection of the 72E voltage regulator, the gear boxes and worm assemblies were disassembled and inspected. Significant wear was found on the worm gear shafts and on the worm bushings in the keyed/slotted area that engages with the worm. This wear was found on all three worm assemblies and contributed to looseness and excess movement causing binding to occur. Binding caused the drive motors to draw a higher current and overheat, leading to motor failure.
Corrective Actions
The failed drive motors were replaced, worn worm assembly parts were either replaced with new parts from stock, or fabricated off site to satisfactorily complete the refurbishment and reinstatement of the 72E Bus Voltage Regulator.
Each of the other three General Electric Inductrol type Voltage Regulators of the same design as the 72E Bus Regulator did not experience high bus voltages, and are in proper working order.
Additional Information
A.
Failed Component: Bus Voltage Regulator Function: Regulate the voltage at the 480 Volt AC Bus by automatically adjusting upon system fluctuations.
Manufacturer: General Electric Inductrol Model Number: 5KCP16KG21A Failure Cause: Overheated drive motors