05000499/LER-2009-001, Regarding Essential Chiller 22A Trip on Low Oil Pressure
| ML092650188 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 09/14/2009 |
| From: | Peter L South Texas |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NOC-AE-09002462 LER 09-001-00 | |
| Download: ML092650188 (6) | |
| 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 |
| 4992009001R00 - NRC Website | |
text
Nuclear Operating Company South Texas Project Electric Generating Station PO Box 289 Wadsworth. Texas 77483 September 14, 2009 NOC-AE-09002462 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 2 Docket No. STN 50-499 Licensee Event Report 2-2009-001 Essential Chiller 22A Trip on Low Oil Pressure Pursuant to 10 CFR 50.73, the STP Nuclear Operating Company (STPNOC) submits the attached Unit 2 Licensee Event Report 2-2009-001 as a result of the determination that Essential Chiller 22A had been inoperable longer than the time allowed by Technical Specifications. This condition is reportable under 10 CFR 50.73(a)(2)(i)(B).
This event did not have an adverse effect on the health and safety of the public.
There are no commitments contained in this Licensee Event Report. Corrective actions will be processed in accordance with the STP Corrective Action Program.
If there are any questions on this submittal, please contact either J. R. Morris at (361) 972-8652 or me at (361) 972-7158.
L. W. Peter Plant General Manager JRM Attachment: LER 2-2009-01, Essential Chiller 22A Trip on Low Oil Pressure STI: 32534415
NOC-AE-09002462 Page 2 of 2 cc:
(paper copy)
(electronic copy)
Regional Administrator, Region IV U. S. Nuclear Regulatory Commission 612 East Lamar Blvd, Suite 400 Arlington, Texas 76011-4125 Mohan C. Thadani Senior Project Manager U.S. Nuclear Regulatory Commission One White Flint North (MS 8B1A) 11555 Rockville Pike Rockville, MD 20852 Senior Resident Inspector U. S. Nuclear Regulatory Commission P. O. Box 289, Mail Code: MNl16 Wadsworth, TX 77483 U. S. Nuclear Regulatory Commission Attention: Document Control Desk One White Flint North 11555 Rockville Pike Rockville, MD 20852 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 C. Thadani U. S. Nuclear Regulatory Commission Kevin Howell Catherine Callaway Jim von Suskil NRG South Texas LP Ed Alarcon J. J. Nesrsta R. K. Temple Kevin Pollo City Public Service Jon C. Wood Cox Smith Matthews C. Mele City of Austin Richard A. Ratliff Texas Department of State Health Services Alice Rogers Texas Department of State Health Services
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 08/31/2010 (9"2007)
, the NRC may digits/characters for each block) not conduct or sponsor, and a person is not required to respond to, the information collection.
- 3. PAGE South Texas Unit 2 05000499 1 OF 4
- 4. TITLE Essential Chiller 22A Trip on Low Oil Pressure
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED FAcILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR SEQUENTIAL REV MONTH DAY YEAR I
NA NUMBER NO.
N/A FACILITY NAME DOCKET NUMBER 07 09 2009 2009 - 001 00 09 14 2009 N/A
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR§: (Check all that apply)
.[ 20.2201(b)
El 20.2203(a)(3)(i)
Dl 50.73(a)(2)(i)(C)
El 50.73(a)(2)(vii) 1 El 20.2201(d) 0l 20.2203(a)(3)(ii)
[3 50.73(a)(2)(ii)(A)
[I 50.73(a)(2)(viii)(A)
[I 20.2203(a)(1)
[3 20.2203(a)(4)
[3 50.73(a)(2)(ii)(B)
El 50.73(a)(2)(viii)(B)
[3 20.2203(a)(2)(i)
[I 50.36(c)(1)(i)(A)
E3 50.73(a)(2)(iii)
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- 10. POWER LEVEL 0l 20.2203(a)(2)(ii)
El 50.36(c)(1)(ii)(A)
[I 50.73(a)(2)(iv)(A)
El 50.73(a)(2)(x)
El 20.2203(a)(2)(iii) 0l 50.36(c)(2) 0l 50.73(a)(2)(v)(A)
El 73.71 (a)(4)
El 20.2203(a)(2)(iv)
El 50.46(a)(3)(ii)
[3 50.73(a)(2)(v)(B)
El 73.71(a)(5) 100 E] 20.2203(a)(2)(v)
El 50.73(a)(2)(i)(A)
El 50.73(a)(2)(v)(C)
El OTHER El 20.2203(a)(2)(vi) x 50.73(a)(2)(i)(B)
El 50.73(a)(2)(v)(D)
Specify in Abstract below or in SUMMARY OF THE EVENT On July 9, 2009, Unit 2 was in Mode 1. At 11:21, Essential Chiller 22A tripped due to low oil pressure approximately 105 seconds into its startup sequence. Prior to the event, Essential Chiller 22A had been idle for over 14 days. Station personnel were present during the start attempt. Chiller parameters were observed and a stopwatch was used to correlate chiller parameters such as lube oil pressure with known startup sequence actions such as the opening of the equalizing valve.
During the prelube portion of the startup cycle, the oil pressure was noted to be approximately 36 psig. When the compressor started approximately 30 seconds later, the oil supply pressure dropped to 16 psig and then started to recover to about 24 psig. At the point where the lube oil equalizing solenoid valve is timed to open (i.e., at approximately 105 seconds after the Control Room started the chiller), the oil supply pressure was observed to rapidly drop past 8 psig and the chiller tripped. The trip setpoint for low oil pressure occurs when the pressure differential between the lube oil supply and the compressor suction vacuum is less than 15 psid so the trip occurred approximately when expected.
Following the Essential Chiller 22A trip, a second start was attempted at 11:53. The observed oil pressures remained higher this time and the chiller started successfully. Despite the successful start on the second attempt, Chiller 22A was declared inoperable pending resolution of any material conditions associated with the chiller..
Subsequent investigation determined that there were no material conditions or degraded components associated with this event. However, it was determined that the Essential Chillers are sensitive to long idle conditions, especially during warmer weather conditions and a maximum idle time limit of 6 days was imposed on all Essential Chillers. Because Essential Chiller 22A had been idle for greater than 14 days prior to the event, and Engineering concluded that low pressure trips of the type experienced could occur after 6 days, the 22A Essential Chiller was considered to be inoperable for lonaer than the action times permitted in
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III. CAUSE OF THE EVENT
The root cause of the Essential Chiller 22A trip on low oil pressure was refrigerant saturation in the lube oil due to a long idle period prior to the attempted start.
IV. CORRECTIVE ACTIONS
A 6-day idle time maximum has been implemented for all Essential Chillers.
Purge and equalizing solenoid valve timing changes have been implemented on all Essential Chillers, which are expected to mitigate the effects of refrigerant saturation. Startup lube oil pressure profile data will be collected and evaluated, and if supported by the data, the idle time restrictions will be relaxed or removed. If not supported by the data, appropriate idle time restrictions will be implemented. (Expected completion 11/16/2009)
V. PREVIOUS SIMILAR EVENTS
Essential Chiller 12A (Unit 1) tripped on low oil pressure twice in 2007 and twice in 2008. Prior to this event, Chiller 22A had not experienced a trip due to low oil pressure, and other than Chiller 12A, none of the other essential chillers had tripped on low oil pressure since 2003.
VI. ADDITIONAL INFORMATION
In addition to the Essential Chiller 22A trip on low oil pressure, there have been several other issues with Essential Chillers in 2009 that challenged chiller reliability. An Essential Chiller Task Force has been established to evaluate current station practices and industry experience to make recommendations to improve the reliability of the Essential Chillers.