05000461/LER-2006-001, Regarding Failure to Tighten Terminal Screw Causes Turbine/Generator Trip and Reactor Scram
| ML061450317 | |
| Person / Time | |
|---|---|
| Site: | Clinton  |
| Issue date: | 05/17/2006 |
| From: | Bryan Hanson AmerGen Energy Co, Exelon Corp |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| U-603771 LER 06-001-00 | |
| Download: ML061450317 (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) 10 CFR 50.73(a)(2)(viii)(A) 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 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)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 4612006001R00 - NRC Website | |
text
AmerGen SM An Exelon Company Clinton Power Station R. R. 3, Box 228 Clinton, IL 61727 10 CFR 50.73 SRRS 5A.108 U-603771 May 17, 2006 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 2006-001-00 Enclosed is Licensee Event Report (LER) No. 2006-001-00: Failure to Ti hten Terminal Screw Causes Turbine/Generator TriD and Reactor Scram. This report is being submitted in accordance with the requirements of 10CFR50.73.
Should you have any questions concerning this report, please contact Mr. Ronald Frantz, Sr.
Regulatory Specialist, at (217)-937-2813.
Respectfully, Site Vice President Clinton Power Station RSF/blf
Enclosures:
Licensee Event Report 2006-001-00 Summary of Commitments cc:
Regional Administrator - NRC Region IlIl NRC Senior Resident Inspector - Clinton-Power Station Office of Nuclear Facility Safety - IEMA Division of Nuclear Safety leIIa7
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 06/30/2007 6Estimated burden per response to comply with this mandatory collection request: 50 hours5.787037e-4 days <br />0.0139 hours <br />8.267196e-5 weeks <br />1.9025e-5 months <br />. Reported lessons learned are incorporated into the licensing process and fed back to Industry. Send comments regarding burden estimate to the Records and FOIAIPrnvacy Service Branch (T-5 F52), U.S.
LICENSEEV EVRENT REPORT(LER)
Nuclear Regulatory Commission, Washington, DC 20555-00, or byn Ee-mail to Infocollectsnnrc.gov, and to the Desk Officer, Office of Information Budgandegutory Aff(airs, NE B-1020 (3150-0104), Office of Management and Budgt, ashngtn, C 2503 Ifa mansused to impose an information (See reverse for required number of tollect iondoesdisplaye a
currentlol number, the NRC may digits/characters for each block) not conduct or sponsor, and a person Is not required to respond to, the
- 3. PAGE Clinton Power Station 05000 461 1 OF 3
- 4. TITLE Failure to Tighten Terminal Screw Causes Turbine/Generator Trip and Reactor Scram
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE S. OTHER FACILfl1ES INVOLVED MONTH DAY YEAR YE AR NUMBER NO. MONTH DAY YEAR None DOCETNUBE FACILITY NAME DOCKET NUMBER 03 20 2006 2006 -
001 00 05 1 7 2006 None 05000
.OPERATING IMODE I11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR§: (Check all that apply) o 20.2201(b) 0 20.2203(a)(3)(1
)
0 50.73(a)(2)(i)(C) 0 50.73(a)(2)(vii) 0 20.2201(d) 0 20.2203(a)(3)(i1) 0 50.73(a)(2)(1i)(A) 0 50.73(a)(2)(viii)(A) o 20.2203(a)(1) 0 20.2203(a)(4) 0 50.73(a)(2)(ii)(B) 0 50.73(a)(2)(viiI)(B) 0 l 20.2203(a)(2)(i
)
0 5
0.36(c)(1)(i)(A) 0 50.73(a)(2)(iii) 0 50.73(a)(2)(ix)(A)
- 10. POWER LEVEL [I 20.2203(a)(2)(ii
)
0 50.36(c)(1)(ii)(A) 0 50.73(a)(2)(iv)(A)
El 50.73(a)(2)(x) o 20.2203(a)(2)(lii) 0 50.36(c)(2) 0 50.73(a)(2)(v)(A) 0 73.71(a)(4) o6 20.2203(a)(2)(iv) 0 50.46(a)(3)(iI 0
50.73(a)(2)(v)(B) 0 73.71 (a)(5) 096 3 20.2203(a)(2)(v) 0 50.73(a)(2)(')(A) 0 50.73(a)(2)(v)(C) 0 OTHER o3 20.2203(a)(2)(vi) 0 50.73(a)(2)(i)(B) 0 50.73(a)(2)(v)(D)
Specify In Abstract below
___or In NRr Form 'WA
- 12. ICENSEE CONTACT FOR THIS LER NAME TELEPHONE NUMBER (Indude Area Code)
. J. Kowalski, Plant Engineering (217) 937-2818CAUSE SYSTEM COMPONENT MANU-REPORTABLE
CAUSE
SYSTEM COMPONENT MANU_
REPORTABLE FACTURER TO EPIX
=FACTURER TOEPIX
- 14. SUPPLEMENTAL REPORT EXPECTED
- 15. EXPECTED MONTH DAY YEAR SUBMISSION 0 YES (If yes, complete 15. EXPECTED SUBMISSION DATE) 0 NO DATE ABSTRACT (LUmit to 1400 spaces, ie.,
approximately 15 single-spaced typewritten lines)
On 3/20/06, at about 0450 hours0.00521 days <br />0.125 hours <br />7.440476e-4 weeks <br />1.71225e-4 months <br /> with the plant at about 96 percent power, an open circuit in the C phase neutral Current Transformer (CT) of the Main Generator output caused the Generator Differential Overcurrent 87-Gl relay to trip due to a sensed current imbalance. Actuation of the 87-G1 relay resulted in a Generator Trip / Lockout and an automatic Turbine Electro Hydraulic Control (EHC) trip. The Turbine EHC trip caused a Turbine Control Valve fast closure and a Reactor Protection System signal for the automatic scram. A loose terminal screw on the CT lead wire caused the open circuit, resulting in high resistance and overheating that melted the wire. The cause of this event was inadequate workmanship that occurred during Generator High-Potential testing, as a result of a process weakness. The inadequate workmanship most likely occurred during the eighth refueling outage. Terminal screws at the C phase CT were most likely loosened to install test leads and not adequately retightened following removal of the test leads, resulting in a failure of the wire termination. Corrective action includes adding process controls to ensure that lifted and landed leads will be adequately tightened in the future.
NRC FRM 36(6-004)PRINTED ON RECYCLED PAPER NRC FORM 366 (6-2OD4)
PRINTED ON RECYCLED PAPER
"C.
(If more space is required, use additional copies of (If more space is required, use additional copies of NRC Form 366A) (17)
Issue Report 468357 was initiated to perform a root cause evaluation of the reactor scram and to identify corrective action.
No automatic or manually initiated safety system responses were necessary to place the plant in a safe and stable condition. No other inoperable equipment or components directly affected this event.
CAUSE OF EVENT
The cause of this event was inadequate workmanship that occurred during Generator High-Potential testing, as a result of a process weakness. The inadequate workmanship most likely occurred during the eighth refueling outage. Terminal screws were most likely loosened to install test leads, and following removal of the test leads, the terminal screw was not adequately retightened, resulting in a failure of the wire termination.
SAFETY ANALYSIS
This event is reportable under the provisions of 1 OCFR50.73(a)(2)(iv)(A) as an event that resulted in an automatic reactor scram while the reactor was critical.
The response and behavior of the plant and operator performance during this event were compared to the Generator Load Rejection transient discussed in Chapter 15 of the Updated Safety Analysis Report and the General Electric Transient Safety Analysis Report and were determined to be within those analyses. This event posed no challenges to fission product barriers. All systems responded as required for an event without bypass valve failure.
No safety system functional failures occurred during this event.
CORRECTIVE ACTION
Process controls are being added to ensure that lifted and landed leads will be adequately tightened in the future. The quality control checklist of the contractor will be revised to include controls similar to those used in the Clinton Power Station procedure for Wire Removal/Jumper Installation, including a step to perform a pre-job brief on the requirements. (468357-19)
The other Main Generator CT connections have been verified to be tight.
Technicians removed the CT from the neutral bus bar under a temporary modification due to concerns that the CT may have been stressed and could fail. A replacement CT was not available.
PREVIOUS OCCURRENCES
None
COMPONENT FAILURE DATA
Manufacturer Nomenclature Manufacturer Model Number Serial Number None NHI, rUCMM 366A (I ZIU1 )
SUMMARY OF COMMITMENTS The following table identifies commitments made in this document. (Any other actions discussed in the submittal represent intended or planned actions. They are described to the NRC for the NRC's information and are not regulatory commitments.)
COMMITMENT TYPE
COMMITMENT
ONE-TIME ACTION Programmatic (Yes/No)
(Yes/No)
This document has no regulatory
commitments