05000499/LER-2011-001, For South Texas, Unit 2, Regarding Exceeding ESF Bus Voltage Technical Specification Surveillance Acceptance Criteria
| ML11255A193 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 09/06/2011 |
| From: | Peter L South Texas |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NOC-AE-11002725, STI: 32925927 LER 11-001-00 | |
| Download: ML11255A193 (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 |
| 4992011001R00 - NRC Website | |
text
Nuclear Operating Company South Teas Project Electric Generating Station PO Box 289 Wadsworth. Texas 77483 September 6, 2011 NOC-AE-1 1002725 File No.: G25 10 CFR 50.73 STI: 32925927 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 2-2011 -001 Exceeding ESF Bus Voltage Technical Specification Surveillance Acceptance Criteria Pursuant to 10 CFR 50.73, STP Nuclear Operating Company (STPNOC) submits the attached Unit 2 Licensee Event Report (LER) 2-2011-001 regarding a condition when Class 1E 4.16 kV ESF Bus E2B exceeded the surveillance acceptance criteria longer than allowed by the associated Technical Specification Limiting Condition of Operation.
This condition is considered reportable under 10 CFR 50.73(a)(2)(i)(B), as an operation or condition prohibited by South Texas Project Technical Specifications.
This event did not have an adverse effect on the health and safety of the public.
There are no commitments contained in this LER. Corrective actions will be implemented in accordance with the STP Corrective Action Program.
If there are any questions on this submittal, please contact either Joe Loya at (361) 972-8005 or me at (361) 972-7158.
L. W. Peter Plant General Manager JAL Attachment: LER 2-2011-001
NOC-AE-1 1002725 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 Balwant K. Singal Senior Project Manager U.S. Nuclear Regulatory Commission One White Flint North (MS 8B13) 11555 Rockville Pike Rockville, MD 20852 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 Balwant K. Singal U. S. Nuclear Regulatory Commission John Ragan Catherine Callaway Jim von Suskil NRG South Texas LP Ed Alarcon Kevin Polio Richard Pena City Public Service Peter Nemeth Crain Caton & James, P.C.
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 OMB: NO. 3150-0104 EXPIRES: 10/31/2013 (10-2010)
, 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 0
05000499 1OF 4
- 4. TITLE Exceeding ESF Bus Voltage Technical Specification Surveillance Acceptance Criteria
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED MONTH DAY YEAR YEAR SEQUENTIAL REV MONTH DAY I YEAR FACILITY NAME DOCKET NUMBER NUMBER NO.
2011 N/A 1 N/A 05 05 2011 2011 001 0
09 06
/2011 N/A N/A
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 1 OCFR§: (Check all that apply) 1E 20.2201(b)
El 20.2203(a)(3)(i)
[E 50.73(a)(2)(i)(C)
I]
50.73(a)(2)(vii)
El 20.2201(d)
El 20.2203(a)(3)(ii)
E] 50.73(a)(2)(ii)(A)
El 50.73(a)(2)(viii)(A)
__ 20.2203(a)(1)
El 20.2203(a)(4)
El 50.73(a)(2)(ii)(B)
El 50.73(a)(2)(viii)(B)
- 10. POWER LEVEL 20.2203(a)(2)(i)
El 50.36(c)(1)(i)(A)
[-
50.73(a)(2)(iii)
El 50.73(a)(2)(ix)(A) 100%
El 20.2203(a)(2)(ii)
E] 50.36(c)(1)(ii)(A)
[E 50.73(a)(2)(iv)(A)
[E 50.73(a)(2)(x)
E] 20.2203(a)(2)(iii)
[]
50.36(c)(2)
El 50.73(a)(2)(v)(A)
El 73.71 (a)(4)
E] 20.2203(a)(2)(iv)
El 50.46(a)(3)(ii)
El 50.73(a)(2)(v)(B)
El 73.71 (a)(5)
El 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)
[
50.73(a)(2)(i)(B)
El 50.73(a)(2)(v)(D)
Specify in Abstract below or in NRC Form 366A
- 12. LICENSEE CONTACT FOR THIS LER FACILITY NAME TELEPHONE NUMBER (Include Area Code)
Joe Loya, Licensing Engineer 361-972-8005r2 YES (if yes, complete 15. EXPECTED SUBMISSION DATE)
ABSTRACT (Limit to 1400 spaces, i.e., approximately 15 single-spaced typewritten lines)
On May 14, Class 1 E 4.16 kV Bus E2B was declared inoperable due to load center (LC) voltage being greater than Engineering Safety Features (ESF) Power Availability surveillance procedure acceptance criteria. Per the Integrated Computer System (ICS), Class 1 E 4.16 kV ESF Bus E2B was inoperable longer than allowed by Technical Specifications. The associated ESF buses were inoperable longer than allowed by Technical Specifications. Therefore, this condition is reportable as a condition prohibited by Technical Specifications.
The Root Causes are: 1) the range of voltage allowed by the bandwidth of the Load Tap Changers (LTC) on the Unit Auxiliary Transformer and the ESF B Transformers was not conservatively modeled; 2) The Failure Modes and Effects Analysis (FMEA) for the ESF Transformer LTC was inadequate; and 3)Management oversight did not have a method to identify, classify, control and monitor highly complex modifications.
The associated corrective actions are as follows: 1) Develop and issue an electrical design calculation methodology guideline or procedure; 2) Develop and issue a guideline or a procedure for completing a Failure Modes and Effects Analysis and 3) Define complex modifications in the design change procedure including defining the requirements for management oversight over providing adequate resources, development of project schedules, and ensuring site involvement in reviews of project documents.
There were no personnel injuries, no offsite radiological releases, and no damage to safety-related equipment associated with this condition. This condition did not have an adverse effect on the health and safety of the public.
NRC FORM 366 (10-2010)
SUMMARY OF THE EVENT On May 14, 2011, during the weekly performance of the Engineered Safety Features (ESF) power availability surveillance, B Train 480 Volt ESF Load Centers (LC) E2B1 and E2B2 were found with local indication for voltage at 520 Volts which exceeds the surveillance acceptance criterion of a maximum allowed bus voltage of 506 volts.
Based on the failed surveillance, the Class 1 E 4160V Bus 2B was declared INOPERABLE at 21:32.
The following Technical Specification action statements were entered:
TS 3.8.3.1 action a was entered requiring re-energizing the associated bus within 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> or apply the requirements of the Configuration Risk Management Program (CRMP) or be in at least HOT STANDBY in the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in COLD SHUTDOWN within the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />.
TS 3.8.1.1 ACTION a was entered which requires demonstration of the OPERABILITY of the remaining A.C. sources by performing Surveillance Requirement 4.8.1.9.1.a within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> and at least once per 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> thereafter, within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> restore the offsite circuit to OPERABLE status or apply the requirements of the CRMP, or be in at least HOT SHUTDOWN within the next 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> and in COLD SHUTDOWN within the following 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.
On 05/15/11 13:26, the ESF Transformer 2B Load Tap Changer was placed in manual per plant procedures and lowered bus voltage.
On 05/15/11 15:21, the 4160 V BUS E2B was declared OPERABLE after adjusting both 4160 V E2B voltage and 480 V LC E2B voltage to within specified bands. TS 3.8.3.1 action a and TS 3.8.1.1 action a were exited including the requirements of the CRMP.
FORM 366 (10-2010)LICENSEE EVENT REPORT (LER)
U.S. NUCLEAR REGULATORY COMMISSION CONTINUATION SHEET
- 1. FACILITY NAME
- 2. DOCKET
- 6. LER NUMBER
- 3. PAGE
- - YEAR4 SEQUENTIAL REV. NO
' NUMBER 3O South Texas Unit 2 05000499 NUMBER 3 OF4 2011 001 00 Per Integrated Computer System (ICS) data, Class1 E 4160 V ESF Bus E2B downstream 480 Volt Load Center Buses E2B1 and E2B2 were inoperable from approximately 06:15 on May 5 to approximately 06:15 on May 7 and from approximately 09:00 on May 8 to approximately 13:30 on May 15.
Since there is firm evidence that the associated ESF buses were inoperable longer than the allowed Technical Specification action statement duration of eight hours including the 6 hour6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> requirement to be in HOT STANDBY, this is considered a condition prohibited by the plant's Technical Specifications.
E.
METHOD OF DISCOVERY
The over-voltage condition was discovered by reviewing the local voltage indicators during the weekly performance of ESF Power Availability surveillance.
I1. EVENT-DRIVEN INFORMATION A.
SAFETY SYSTEMS THAT RESPONDED N/A B.
DURATION OF SAFETY SYSTEM INOPERABILITY
Per the ICS, Class 1 E 4.16 kV ESF Bus E2B and downstream 480 Volt Load Center Buses E2B1 and E2B2 were inoperable from approximately:
06:15 on May 5 to approximately 06:15 on May 7 09:00 on May 8 to approximately 13:30 on May 15 C.
SAFETY CONSEQUENCES AND IMPLICATIONS OF THE EVENT Per engineering evaluation, there is reasonable assurance that the condition would not have prevented the affected safety-related switchgear and associated loads from performing their safety functions. Therefore, any increase in Core Damage Frequency or Large Early Release Frequency was insignificant. Consequently, there is no adverse effect on the health and safety of the public.
Ill. CAUSE OF THE EVENT
- 1. The range of voltage values allowed by the bandwidth of the Load Tap Changers (LTC) on the Unit Auxiliary Transformer and the ESF B Transformers was not conservatively modeled. An electrical set-point methodology for modeling LTCs did not exist at STP resulting in knowledge-based task performance by the user and reviewer. Program inputs/assumptions used in the computerized Electrical Transient Analyzer Program (ETAP) Calculation are not clear and were not adequately documented which impeded the capability to review the calculation.
- 2. Failure Modes and Effects Analysis (FMEA) for the ESF transformer LTC did not accurately identify the severity of all failure effects, and did not conclude that the method of failure detection was inadequate. An adequate FMEA would have identified the need for instrumentation and alarms. Full understanding of the potential failure modes would have identified the potential voltage range in which the LTC could fail and would have determined the voltage limits on the 480V bus could be exceeded.
FORM 366 (10-2010)LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET U.S. NUCLEAR REGULATORY COMMISSION I
- 3. Management oversight did not have a method to identify, classify, control and monitor complex modifications.
IV. CORRECTIVE ACTIONS
A. Root Cause 1:
a. Develop and issue an electrical design calculation methodology guideline or procedure for EC calculations EC-5000, EC-5001, EC-5002, EC-5008, and EC-5036.
b. Provide Training on the requirements/availability of the electrical design calculation methodology guidance and the requirements of the calculation pre-job brief.
B. Root Cause 2:
a. Develop and issue a guideline or a procedure for completing a Failure Modes and Effects Analysis using INPO and industry best practices.
b. Provide Training on the completion of FMEA documentation using the guideline or procedure developed in correction action (IV.B.a).
C. Root Cause 3:
a. To identify modifications that require the management oversight, develop and implement a definition for complex modifications in the design change package procedure including defining the requirements for management oversight which may include adequate resources, development of project schedules and site involvement in the rigorous reviews of project documents.
b. Provide training for design engineering and staff augmented contract engineers on the Plant Investment Plan Guidelines for modifications that are complex or meet the definition of a complex modification.
V. PREVIOUS SIMILAR EVENTS
There have been no similar reportable events at STP within the last three years.
VI. ADDITIONAL INFORMATION
N/A FORM 366 (10-2010)