05000498/LER-2007-001, Regarding Turbine-Driven Auxiliary Feedwater Pump Failed to Start During Surveillance Testing
| ML071230108 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 04/26/2007 |
| From: | Coates K South Texas |
| To: | Document Control Desk, Plant Licensing Branch III-2 |
| References | |
| G25, NOC-AE-07002151 LER 07-001-00 | |
| Download: ML071230108 (7) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 4982007001R00 - NRC Website | |
text
Nuclear Operating Company South Texas Project Electrc GencratinS Station PO. Box 289 Wadsworth, Texas 77483 A
April 26, 2007 NOC-AE-07002151 File No.: G25 10 CFR 50.73 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 1-07-001 Turbine-Driven Auxiliary Feedwater Pump Failed to Start During Surveillance Testing Pursuant to 10 CFR 50.73, the STP Nuclear Operating Company (STPNOC) submits the attached Unit 1 Licensee Event Report 1-07-001 to address an incident in which the turbine-driven auxiliary feedwater pump failed to start during surveillance testing.
The Unit 1 turbine-driven auxiliary feedwater pump failed to start during surveillance testing on December 12, 2006. The pump was returned to operability on December 14 within the 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> allowed by Technical Specifications.
Subsequent review determined that the cause of the failure to start originated during the previous surveillance test.
As a result, the pump is considered to have been inoperable from November 16, 2006, to December 14, exceeding the allowed outage time of 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. Consequently, this condition is reportable under 10 CFR 50.73(a)(2)(i)(B) for operation or condition prohibited by Technical Specifications.
This event did not have an adverse effect on the health and safety of the public.
There are no commitments in this letter. Corrective measures will be processed in accordance with the STP Corrective Action Program.
If there are any questions on this submittal, please contact either P. L. Walker at (361) 972-8392 or me at (361) 972-8902.
Ken L. Coates Plant General Manager PLW
Attachment:
LER 1-07-001, Turbine-Driven Auxiliary Feedwater Pump Failed to Start During Surveillance Testing STI: 32148231
NOC-AE-07002151 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 Richard A. Ratliff Bureau of Radiation Control Texas Department of Health 1100 West 4 9 th Street Austin, TX 78756-3189 Senior Resident Inspector U. S. Nuclear Regulatory Commission P. 0. Box 289, Mail Code: MN1 16 Wadsworth, TX 77483 C. M. Canady City of Austin Electric Utility Department 721 Barton Springs Road Austin, TX 78704 A. H. Gutterman, Esquire Morgan, Lewis & Bockius LLP Mohan Thadani U. S. Nuclear Regulatory Commission Thad Hill Christine Jacobs Eddy Daniels Marty Ryan NRG South Texas LP J. J. Nesrsta R. K. Temple Kevin Polio E. Alarcon City Public Service C. Kirksey City of Austin Jon C. Wood Cox Smith Matthews
Abstract
On December 12, 2006, the Unit 1 turbine-driven auxiliary feedwater pump failed to start during a surveillance test. It had previously passed surveillance testing on November 16, 2006. A motor-operated valve controlling steam flow to the turbine did not open. Subsequent review determined that the cause of the failure to start originated during the previous surveillance test. As a result, the pump is considered to have been inoperable from November 16, 2006, to December 14, 2006.
Technical Specification 3.7.1.2.b requires that, with the turbine-driven auxiliary feedwater pump inoperable, it is to be restored to operability within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> or the unit is to be in hot standby within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in hot shutdown in the following 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />. Because this pump was inoperable longer than allowed under the Technical Specifications without entering the appropriate action statements, this event is reportable pursuant to 10 CFR 50.73(a)(2)(i)(B).
The closed motor-operated steam inlet valve was found with the valve actuator in the open position.
Subsequent review determined that the latching mechanism had not been fully engaged. The root causes were determined to be inadequate maintenance instructions and a latching mechanism that was not easily set correctly. For corrective actions, maintenance instructions will be revised and determination will be made if modification of the latching mechanism is feasible.
Only Unit 1 was affected. This event resulted in no personnel injuries, no offsite radiological releases, and no damage to other safety-related equipment.
(If more space is required, use additional copies of SUMMARY OF THE EVENT On December 12, 2006 at 1046 hours0.0121 days <br />0.291 hours <br />0.00173 weeks <br />3.98003e-4 months <br />, a surveillance test of Unit 1 TDAFW pump 14 was performed.
However, when the Control Room Operator attempted to open the steam flow control valve for steam flow to the turbine, the valve did not open, and the TDAFW pump did not start.
Plant personnel were stationed at the TDAFW pump for the surveillance run and test equipment was installed to collect turbine start-up data. As part of the pre-start procedure requirements, the turbine was verified to be properly set-up for the surveillance test including visual inspection of the latch-up lever and trip hook engagement. Visual inspection of the latch-up lever and trip hook found that the two faces were not fully engaged, but the condition was deemed to meet minimum interface requirements documented by previous engineering assessment.
After the attempted start, it was determined that, based on information from the personnel stationed at the pump and the fact that the test equipment did not record any movement of the governor valve or speed indication from the turbine, steam had not been supplied to the turbine. The pump was declared inoperable.
Examination revealed that the trip and throttle valve latch-up lever at the valve actuator had disengaged from the trip hook and the steam flow control valve had remained closed.
Items susceptible to wear and degradation were inspected, including the latch-up lever and trip hook mating surfaces. The mating surfaces showed no wear, but were found to be coated with a layer of grease that was more than the vendor-recommended light coating. The excess grease was removed and a light coating applied. The rod end (ball joint) assembly located at the turbine end of the overspeed mechanical trip linkage was suspect based on the fault tree review and was replaced. Inspection of the replaced part found no degradation that would have affected the operation of the assembly or mechanical trip linkage.
(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)
IV. CAUSE OF THE EVENT
Two factors were identified as being root causes because they both contributed to the event:
- 1. Inadequate maintenance instructions; and
- 2. The design of the trip and throttle valve linkage leaves no margin for variability.
V. CORRECTIVE ACTIONS
- 1. Enhanced detail / guidance for adjusting / setting latch-up lever and trip hook interface gap and impact space has been included in maintenance procedures. The enhanced impact space set-up instructions will be incorporated into the training materials to include how to optimize the impact space setting, applicable lessons learned and operating experience. Currently certified personnel will be retrained.
- 2. An evaluation will be performed to determine if a modification to the linkage will improve its reliability. If this modification is not feasible, additional actions will be assessed to address the configuration of the latching mechanism.
- 3. An operator aid has been developed to assist plant operators in determining that the latch-up lever and trip hook linkage is properly latched.
- 4. The requirement for 75% latch-up lever and trip hook interface has been reviewed, and is consistent with the vendor manual for generic applications of this type of valve.
VI. PREVIOUS SIMILAR EVENTS
Over the preceding five years, there have been no reportable events involving the TDAFW pump due to similar linkage misalignment.