05000271/LER-2010-001, Regarding Automatic Reactor Trip Due to Switchyard Current Transformer Problem
| ML102140401 | |
| Person / Time | |
|---|---|
| Site: | Vermont Yankee File:NorthStar Vermont Yankee icon.png |
| Issue date: | 07/26/2010 |
| From: | Michael Colomb Entergy Nuclear Operations |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| BVY 10-037 LER 10-001-00 | |
| Download: ML102140401 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation 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)(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 10 CFR 50.73(a)(2)(iv)(B), System Actuation |
| 2712010001R00 - NRC Website | |
text
"ýEnteqoy Entergy Nuclear Operations, Inc.
Vermont Yankee 320 Governor Hunt Rd.
Vernon, VT 05354 Tel 802 257 7711 Michael J. Colomb Site Vice President BVY 10-037 July 26, 2010 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001
SUBJECT:
Licensee Event Report 05000271/2010-001-00, Automatic Reactor Trip due to Switchyard Current Transformer Problem Vermont Yankee Nuclear Power Station Docket No. 50-271 License No. DPR-28
Dear Sir or Madam:
As defined by 10 CFR 50.73(a)(2)(iv)(A), we are submitting the attached Licensee Event Report, LER 05000271/2010-001-00, for a Reportable Occurrence that was discovered on May 26, 2010.
There are no new regulatory commitments contained within this correspondence.
Should you have any questions concerning this letter, please contact Mr. Robert J. Wanczyk at (802) 451-3166.
Sincerely, [MJC/RAM]
Attachment:
cc list:
LER 05000271/2010-001-00, Automatic Reactor Trip due to Switchyard Current Transformer Problem (next page)
QL,
BVY 10-037 / page 2 of 2 cc:
Region 1 Administrator U.S. Nuclear Regulatory Commission 475 Allendale Road King of Prussia, PA 19406-1415 Mr. James S. Kim, Project Manager Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, DC 20555 USNRC Resident Inspector Vermont Yankee Nuclear Power Station 320 Governor Hunt Road Vernon, VT 05354 Mr. David O'Brien, Commissioner VT Department of Public Service 112 State Street, Drawer 20 Montpelier, VT 05620-2601
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 Vermont Yankee Nuclear Power Station 05000271 1 of 3
- 4. TITLE Automatic Reactor Trip due to Switchyard Current Transformer Problem
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED I SEQUENTIAL REVISION FACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR NUMBER NUMBER MONTH
- - DAY YEAR N/A FACILITY NAME DOCKET NUMBER 05 26 2010 2010 001 00 07 26 2010 N/A
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply)
El 20.2201(b)
El 20.2203(a)(3)(i)
El 50.73(a)(2)(i)(C)
[I 50.73(a)(2)(vii)
N El 20.2201(d)
El 20.2203(a)(3)(ii)
[I 50.73(a)(2)(ii)(A)
El 50.73(a)(2)(viii)(A)
El 20.2203(a)(1)
El 20.2203(a)(4)
[I 50.73(a)(2)(ii)(B)
El 50.73(a)(2)(viii)(B)
El 20.2203(a)(2)(i)
[I 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)
[I 50.36(c)(1)(ii)(A) 0 50.73(a)(2)(iv)(A)
[1 50.73(a)(2)(x)
El 20.2203(a)(2)(iii)
[I 50.36(c)(2)
El 50.73(a)(2)(v)(A)
[1 73.71 (a)(4) 72%
El 20.2203(a)(2)(iv)
[3 50.46(a)(3)(ii)
El 50.73(a)(2)(v)(B) 73.71(a)(5)
El 20.2203(a)(2)(v)
[I 50.73(a)(2)(i)(A)
[I 50.73(a)(2)(v)(C) t~ OTHER Specify in Abstract below E] 20.2203(a)(2)(vi)
Ql 50.73(a)(2)(i)(B)
El 50.73(a)(2)(v)(D) or in (If more space is required,, use additional copies of NRC Form (366A)
Description of Event
On May 26, 2010, at approximately 1526 hours0.0177 days <br />0.424 hours <br />0.00252 weeks <br />5.80643e-4 months <br />, a generator lockout and automatic reactor trip occurred on differential current between a current transformer (CT) installed in the newly commissioned switchyard and a CT installed in the plant. During RFO 28, Vermont Yankee (VY) and the Vermont Electric Power Company (VELCO) commissioned a new 345kV switchyard [EIIS = FK].
Just prior to the trip VY was raising power following the 2010 refueling outage (RFO 28) from 72% at 1% every three minutes using the recirculation flow system [EIIS = SK]. At the time of the trip, two of three reactor feed pumps [EIIS = SK] were inservice and there were no significant equipment challenges for the control room operators. Both channels of the reactor protection system (RPS) [EIIS = JD] actuated and all control rods inserted. Following the reactor trip reactor vessel level decreased as expected causing an expected primary containment isolation system (PCIS) [EIIS = BD] groups 2, 3, 4, and 5 actuation signals. All associated valves functioned correctly. Additionally, both trains of standby gas treatment system actuated. Immediate plant actions included entering appropriate trip response procedures. The operators stabilized the plant and reset both RPS and PCIS.
This event is reportable as a licensee event report (LER) per 10CFR50.73(a)(2)(iv)(A) as an event or condition that resulted in actuation of the any of the systems listed in 10 CFR 50.73(a)(2)(iv)(B), which includes RPS and PCIS. On May 26, 2010, at approximately 1725 hours0.02 days <br />0.479 hours <br />0.00285 weeks <br />6.563625e-4 months <br /> VY completed the required NRC notification in accordance with 10CFR50.72(b)(2)(iv)(B) - RPS Actuation - Critical, and 10CFR50.72(b)(3)(iv)(A) - Valid Specific System Actuation.
Cause of Event
The direct cause of the trip was VELCO's changing of CT ratio settings within the interface between the 345kV Switchyard and not communicating the new ratio settings to VY and not receiving concurrence for the new settings from VY. This change in settings caused a differential current reading between the CT in the new switchyard and the existing CT in the plant to cause a generator lockout on differential current which caused the reactor trip.
Analysis of Event
Although the incident resulted in a trip, operators responded in accordance with established procedures and all plant systems responded as designed. This event did not impact or reduce the margin of nuclear safety and did not result in an industrial safety concern where injuries could have resulted. Further, there were no radiological safety issues associated with the trip. The safety function of the differential relay is to actuate on demand to prevent damage to large electrical components, such as the main generator or main transformer, and to isolate an electrical fault to stabilize the transmission grid. These protective functions operated as designed with the mismatch in settings.
Corrective Actions
Immediate Corrective Actions Identified and corrected the CT ratio mismatch that caused the automatic reactor shutdown and performed an extent of condition review.
(If more space is required, use additional copies of NRC Form (366A)
Ongoing Corrective Actions Revise procedures to include verification of CT ratio settings for interface relays.
Develop or enhance the process which engineering personnel control, review and approve protective relay setting calculations and application.
Establish written documentation delineating acceptance criteria for verification that the off-site power system is viable prior to re-establishing the connection to the grid following a loss of off-site power, reactor trip, or scheduled shut down.
Develop a process to control switchyard configuration management to support safe plant operation.
Previous Similar Events
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