05000498/LER-2006-006, Re Inoperable Auxiliary Feedwater Flow Instrumentation
| ML070580139 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 02/15/2007 |
| From: | Coates K South Texas |
| To: | Document Control Desk, NRC/NRR/ADRO |
| References | |
| NOC-AE-06002098 LER 06-006-00 | |
| Download: ML070580139 (7) | |
| 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 |
| 4982006006R00 - NRC Website | |
text
Nuclear Operating Company South Texas Proect Electric Generatihn Station P0. Box 289 Wadsworth, Tcxas 77483 x x n February 15, 2007 NOC-AE-06002098 10CFR50.73 U. S. Nuclear Regulatory Commission Attention: Document Control Desk One White Flint North 11555 Rockville Pike Rockville, MD 20852-2738 South Texas Project Unit 1 Docket No. STN 50-498 Licensee Event Report 2006-06, Inoperable Auxiliary Feedwater Flow Instrumentation Pursuant to 10 CFR 50.73(a)(2)(i)(B), STP Nuclear Operating Company submits the attached Unit 1 Licensee Event Report 2006-06 regarding an inoperable channel of Auxiliary Feedwater Flow Instrumentation resulting in exceeding the allowed outage time of Technical Specification (TS) 3.3.3.6 Action 35.
This event did not have an adverse effect on the health and safety of the public.
There are no commitments contained in this event report. Resulting corrective actions will be implemented in accordance with the Corrective Action Program.
If there are any questions regarding this submittal, please contact S. M. Head at (361) 972-7136 or me at (361) 972-8902.
Ken Coates Plant General Manager awh/
Attachment: South Texas Unit 1 LER 2006-06 STI: 32103680
NOC-AE-06002098 Page 2 of 2 cc:
(paper copy)
(electronic copy)
Regional Administrator, Region IV U. S. Nuclear Regulatory Commission 611 Ryan Plaza Drive, Suite 400 Arlington, Texas 76011-8064 Senior Resident Inspector U. S. Nuclear Regulatory Commission P. O. Box 289, Mail Code: MN16 Wadsworth, TX 77483 C. M. Canady City of Austin Electric Utility Department 721 Barton Springs Road Austin, TX 78704 Richard A. Ratliff Bureau of Radiation Control Texas Department of State Health Services 1100 West 49th Street Austin, TX 78756-3189 A. H. Gutterman, Esquire Morgan, Lewis & Bockius LLP Mohan C. Thadani U. S. Nuclear Regulatory Commission Steve Winn Christine Jacobs Eddy Daniels Marty Ryan NRG South Texas LP E. Alarcon J. J. Nesrsta R. K. Temple Kevin Pollo City Public Service Jon C. Wood Cox Smith Matthews C. Kirksey City of Austin
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 06/30/2007 (6-2004)
, the NRC may not conduct or sponsor, and a person is not required to respond to, the digits/characters for each block) information collection.
- 13. PAGE South Texas, Unit 1 05000498 1 OF 5
- 4. TITLE TS 3.3.3.6 Action 35 Allowed Outage Time Exceeded
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED MONTH DAY YEAR RSEQUENTIAL IREV M
H DY Y
FACILITY NAME DOCKET NUMBER MOTURYEAR SU ER E
MONTH DAY YEAR NA 05000 I
I2 17_2006_I
_I___IIFACILITY NAME DOCKET NUMBER 12 17 2006 2006 -
006 -
00 02 15 2007 NA 05000
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR§: (Check all that apply)
E] 20.2201(b)
[I 20.2203(a)(3)(i)
El 50.73(a)(2)(i)(C)
El 50.73(a)(2)(vii)
E] 20.2201(d)
El 20.2203(a)(3)(ii)
El 50.73(a)(2)(ii)(A)
El 50.73(a)(2)(viii)(A)
El 20.2203(a)(1)
El 20.2203(a)(4)
El 50.73(a)(2)(ii)(B)
El 50.73(a)(2)(viii)(B)
El 20.2203(a)(2)(i)
El 50.36(c)(1)(i)(A)
El 50.73(a)(2)(iii)
[I 50.73(a)(2)(ix)(A)
- 10. POWER LEVEL El 20.2203(a)(2)(ii)
El 50.36(c)(1)(ii)(A)
El 50.73(a)(2)(iv)(A)
El 50.73(a)(2)(x)
El 20.2203(a)(2)(iii)
El 50.36(c)(2)
El 50.73(a)(2)(v)(A)
El 73.71(a)(4)
El 20.2203(a)(2)(iv)
El 50.46(a)(3)(ii)
El 50.73(a)(2)(v)(B)
El 73.71(a)(5) 100 El 20.2203(a)(2)(v)
[] 50.73(a)(2)(i)(A)
El 50.73(a)(2)(v)(C)
[E OTHER El 20.2203(a)(2)(vi) 0 50.73(a)(2)(i)(B)
El 50.73(a)(2)(v)(D)
Specify in Abstract below or in SUMMARY OF THE EVENT, INCLUDING DATES AND APPROXIMATE TIMES At 0945 on December 15, 2006 with Unit 1 at 100% power, D train distribution panel 1202 (DP1 202) generated a voltage transient that resulted in the loss of multiple loads due to fuses clearing and damage to the connected loads. The transient was indicated by ground fault and inverter trouble alarms in the control room. However, following the transient, inverter 1202 was found to be operating normally. An Engineering evaluation determined the inverter was degraded but operable. The loads listed in Section II.C below were lost from the inverter.
The Operators responded appropriately to the electrical transient and its effects. The Operators were temporarily required to take manual control of pressurizer level and Steam Generator (SG) 1D and SG 1C level.
The most limiting TS actions were due to the inoperable AFW Flow indication with a 72-hour shutdown action required by TS 3.7.1.2 ACTION b and a 48-hour shutdown action required by TS 3.3.3.6 ACTION 35. STPNOC determined that restoration of the QDPS Auxiliary Processing Cabinet (APC) D2 and the AFW flow instrumentation channel would likely require replacement of EEPROM chips that were not available on site. Consequently, STPNOC determined that the function could not be restored prior to the expiration of the allowed outage time. In a teleconference on December 17, 2006, STPNOC requested enforcement discretion to extend the allowed outage time to 2145 on December 18, 2006. NRC granted the enforcement discretion at 0839 on December 17, 2006.
STPNOC found that two of three EEPROM chips located on a QDPS CPU circuit board had been damaged due to the electrical transient. STP replaced the damaged EEPROMs and affected downstream circuit boards. QDPS Cabinet D2 and the
(If more space is required, use additional copies of (if more space is required, use additional copies of (If more space is required, use additional copies of NRC Form 366A) (17)
A detailed assessment is provided in STPNOC's documentation of the enforcement discretion request dated December 18, 2006 (NOC-AE-06002095, ML063620440).
The NRC approved the request as described in Notice of Enforcement Discretion for South Texas Project Nuclear Operating Company Regarding South Texas Project, Unit 1 [ ML063540518, TAC NO. MD3829, NOED NO. 06-4-002].
IV.
CAUSE OF THE EVENT
The electrical transient that initiated the event was caused by the failure of the C805 capacitor.
V.
CORRECTIVE ACTIONS
STPNOC replaced the damaged EEPROMs and affected downstream circuit boards.
The affected capacitor bank was replaced on December 20, 2006 with a bank that was x-rayed prior to installation to confirm acceptability.
The corresponding capacitor banks for the inverters on the other channels will be replaced as needed. Capacitor banks to be used for replacement will be x-rayed prior to installation to confirm manufacturing flaws like the one that caused the subject capacitor failure are not present.
STPNOC has focused the corrective action on the capacitor failure cause as described above. However, STPNOC will evaluate the need for design improvements to protect the loads downstream of the inverter by October 31, 2007.
STPNOC submitted a TS change application prior to the event that proposes to change the allowed outage time for the AFW Flow indication channel from 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> to 30 days (ML062830032). STPNOC anticipates NRC approval of this application later this year. The proposed new allowed outage time would have provided adequate time to restore the affected AFW Flow channel to operable status and precluded the TS violation that made the event reportable.
VI.
PREVIOUS SIMILAR EVENTS
A similar event occurred at STP in December 2005. The initiating cause of the event was a failed capacitor in the same inverter. STPNOC performed a failure analysis of that capacitor and determined that an internal lead in the capacitor had shorted to ground. STPNOC notified the inverter vendor (Ametek) and the capacitor vendor (Aerovox) of our findings.
Aerovox subsequently notified STPNOC that changes had recently been made in their manufacturing process to reduce the potential for internal faults. STPNOC replaced all capacitors in all Unit 1 Ametek inverters with newly designed capacitors in the October 2006 refueling outage. The December 2005 event did not result in damage to the EEPROMs because the input line surge suppressor protected the EEPROMS.