05000324/LER-2008-001, Regarding Automatic Reactor Scram Due to Turbine Power/Load Unbalance Actuation
| ML083090389 | |
| Person / Time | |
|---|---|
| Site: | Brunswick  |
| Issue date: | 10/23/2008 |
| From: | Wills E Progress Energy Carolinas |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| BSEP 08-0138 LER 08-001-00 | |
| Download: ML083090389 (7) | |
| 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)(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 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3242008001R00 - NRC Website | |
text
Progress Energy OCT 2 3 2008 SERIAL: BSEP 08-0138 10 CFR 50.73 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001
Subject:
Brunswick Steam Electric Plant, Unit No. 2 Docket No. 50-324/License No. DPR-62 Licensee Event Report 2-2008-001 Ladies and Gentlemen:
In accordance with the Code of Federal Regulations, Title 10, Part 50.73, Carolina Power
& Light Company, now doing business as Progress Energy Carolinas, Inc., submits the enclosed Licensee Event Report. This report fulfills the requirement for a written report within sixty (60) days of a reportable occurrence.
Please refer any questions regarding this submittal to Mr. Gene Atkinson, Supervisor -
Licensing/Regulatory Programs, at (910) 457-2056.
Sincerely, Edward L. Wills, Jr.
Plant General Manager Brunswick Steam Electric Plant LJG/ljg
Enclosure:
Licensee Event Report Progress Energy Carolinas, Inc.
Brunswick Nuclear Plant PO Box 10429 Southport, NC 28461
Document Control Desk BSEP 08-0138 / Page 2 cc (with enclosure):
U. S. Nuclear Regulatory Commission, Region II ATTN: Mr. Luis A. Reyes, Regional Administrator Sam Nunn Atlanta Federal Center 61 Forsyth Street, SW, Suite 23T85 Atlanta, GA 30303-8931 U. S. Nuclear Regulatory Commission ATTN: Mr. Joseph D. Austin, NRC Senior Resident Inspector 8470 River Road Southport, NC 28461-8869 U. S. Nuclear Regulatory Commission ATTN: Mrs. Farideh E. Saba (Mail Stop OWFN 8G9A) (Electronic Copy Only) 11555 Rockville Pike Rockville, MD 20852-2738 Chair - North Carolina Utilities Commission P.O. Box 29510 Raleigh, NC 27626-0510
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB NO. 3150-0104 EXPIRES 08/31/2010 (9-2007)
, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 3. PAGE Brunswick Steam Electric Plant (BSEP), Unit 2 05000324 1 OF 5
- 4. TITLE Automatic Reactor Scram Due to Turbine Power/Load Unbalance Actuation
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED MONTH DAY YEAR YEAR I SEQUENTIAL REV IFACILITY NAME DOCKET AUMBER NUMBER NO MONTHDAYYEAR_05000 FACILITY NAME DOCKET NUMBER 08 30 2008 2008 -- 001 00 10 23 2008 05000
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check one or more)
El 20.2201(b)
El 20.2203(a)(3)(i)
F-50.73(a)(2)(i)(C)
El 50.73(a)(2)(vii)
Dl 20.2201(d)
El 20.2203(a)(3)(ii)
El 50.73(a)(2)(ii)(A)
El 50.73(a)(2)(viii)(A)
E3 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)
El 50.73(a)(2)(ix)(A)
- 10. POWER LEVEL El 20.2203(a)(2)(ii)
El 50.36(c)(1)(ii)(A) 0 50.73(a)(2)(iv)(A)
El 50.73(a)(2)(x) 100 El 20.2203(a)(2)(iii)
El 50.36(c)(2)
[3 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)
E] 73.71(a)(5)
El 20.2203(a)(2)(v)
[1 50.73(a)(2)(i)(A)
El 50.73(a)(2)(v)(C)
El OTHER Specify in Abstract below El 20.2203(a)(2)(vi)
El 50.73(a)(2)(i)(B)
El 50.73(a)(2)(v)(D) or in (i.e., load) for rapid reductions when power level derived from first stage High Pressure Turbine pressure is greater than 40%. The rate sensitive PLU circuit and relays have a two-fold purpose:
" To initiate Control Valve closure under load rejection conditions that might lead to a rapid acceleration and turbine overspeed.
" To prevent any valve action under stable fault conditions which are self-clearing within a reasonable amount of time.
Load signal is provided to the PLU via the Electro-Hydraulic Control (EHC) [IT] cabinet which is connected to the Generator and Transformer relaying and metering control circuit. This circuit is supplied by two 25,OOOA to 5A current transformers on the "A" and "C" phases of the Main Generator outputs.
The most probable initiating event of the scram was the introduction of a short onto the Generator's current monitoring circuit during post-modification testing for an Engineering Change (i.e., EC 68642) that installed a new digital fault recorder to provide dynamic disturbance monitoring capability. The testing was being performed by a Transmission Maintenance technician working in a relay house in the switchyard.
The new recorder was connected to various inputs sources, including the Generator and Transformer Relaying and Metering control circuits, via a shorting type test device. This test device has a series of knife switches used to isolate the recorder from the main circuit. In the case of the Generator and Transformer Relaying and Metering control circuits, the test device shorted the main circuit in order to maintain its continuity, and provided for opening of the leads to the recorder. It also provided test terminals for communication with the recorder. This test device has 10 channels, two of which are part of the "A" phase current circuit and two of which are part of the "C" phase current circuit.
The actual short appears to have occurred while a test plug was being removed from the test device mentioned above during a brief time period when the plug was still electrically in contact with the test switch but the switch was not electrically isolated from the main circuit. This allowed an unidentified path to ground, via the test equipment, and resulted in a current transient of sufficient magnitude to actuate the PLU protective device within the EHC cabinet.
The PLU properly responded to the sensed Generator current changes and the EHC system responded to the PLU actuations as designed. Troubleshooting activities, including physical testing and visual inspections of the current transducers, test switch, and test plug, found no obvious problems. Continuity and meggering checks were performed on the A, B, and C phase circuits and no grounds were found. The troubleshooting concluded without finding a definitive source of the current transient.
EVENT CAUSE
No root cause was able to be determined for this event. The select cause of this event was the lack of adequate work controls for transmission maintenance activities due to an inaccurate perception of risk.
The PLU actuation and subsequent scram were the result of a current transient on the Generator and Transformer relaying and metering control circuit introduced during post-modification testing for EC 68642.
Implementation of EC 68642 was undertaken without fully understanding the potential consequences of the work. As a result, adequate work controls for transmission maintenance activities were not established.
SAFETY ASSESSMENT
The safety significance of this condition is considered minimal. The plant is designed for this type of event and responded as expected for this condition. Safety system actuations functioned as designed and Operations personnel responded appropriately in accordance with procedures.
CORRECTIVE ACTIONS
The following corrective actions to prevent recurrence will be taken.
" NGGM-IA-0003, "Transmission Interface Agreement for Operation, Maintenance, and Engineering Activities at Nuclear Plants," will be revised, or other procedural controls will be established, to strengthen work control of transmission maintenance activities. This action is currently scheduled to be completed by December 15, 2008.
" OAP-025, "BNP Integrated Scheduling," will be revised to include responsibility to evaluate risk associated with work involving critical shared transmission components providing BSEP support functions, and to strengthen work control of transmission maintenance activities. This action is currently scheduled to be completed by December 15, 2008.
Additional corrective actions include the following.
" Develop standards for test blocks used by Transmission personnel, and implement in the field. This action is currently scheduled to be completed by March 15, 2009.
" Perform training needs analysis for Design Engineering to assess training on how to perform Risk Assessments in accordance with EGR-NGGC-001 1, "Engineering Product Quality." This action is currently scheduled to be completed by December 15, 2008.
PREVIOUS SIMILAR EVENTS
A review of LERs and corrective action program condition reports for the past three years identified the following similar event.
0 Nuclear Condition Report (NCR) 270475 documents an invalid Unit 1 Primary Containment Isolation System (PCIS) Group 1 actuation which occurred on March 15, 2008 (i.e., Event Notification 44213). This event occurred as a result of switchyard work associated with EC 63842 to replace the main generator output breakers 22A and 22B. However, the root cause of this event was determined to be a lack of effectiveness of prior actions taken to prevent Group I isolations during shutdown conditions. As such, the corrective action to prevent recurrence could not reasonably have been expected to prevent occurrence of the event reported in this LER.
COMMITMENTS
No regulatory commitments are contained in this report.