05000416/LER-2008-005, Regarding Automatic Reactor Scram Due to Turbine Control Valve Fast Closure Caused by an Electrical Generator Trip
| ML083510826 | |
| Person / Time | |
|---|---|
| Site: | Grand Gulf  |
| Issue date: | 12/15/2008 |
| From: | Larson M Entergy Operations |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| GNRO-2008/00075 LER 08-005-00 | |
| Download: ML083510826 (5) | |
| 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)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(b)(5) |
| 4162008005R00 - NRC Website | |
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-===-Entergy GNRO-2008/00075 December 15, 2008 Entergy Operations, Inc.
PO Box 756 Port Gibson, MS 39150 Tel 601 437 2800 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001
SUbject:
LER 2008-005 Automatic Reactor Scram Due to Turbine Control Valve Fast Closure Caused by an Electrical Generator Trip Grand Gulf Nuclear Station, Unit 1 Docket No. 50-416 License No. NPF-29
Dear Sir or Madam:
Attached is Licensee Event Report (LER) 2008-005-00 which is a final report.
This letter does not contain any commitments.
Yours truly, Michael J. Larson Acting-Manager, Licensing MJL
attachment:
cc:
LER 2008-005-00 (See Next Page)
GNRO-2008/00075 Page 2 cc:
NRC Senior Resident Inspector Grand Gulf Nuclear Station Port Gibson, MS 39150 u. S. Nuclear Regulatory Commission ATTN: Mr. Elmo E. Collins (w/a)
Regional Administrator, Region IV 611 Ryan Plaza Drive, Suite 400 Arlington, TX 76011-4005 U. S. Nuclear Regulatory Commission ATTN: Mr. Carl F. Lyon, NRRlADROIDORL (w/2)
ATIN: ADDRESSEE ONLY ATIN: U. S. Postal Delivery Address Only Mail Stop OWFN/8 81 Washington, DC 20555-0001
GNRO-2008/00075 NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: 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.
- 1. FACILITY NAME 2, DOCKET NUMBER
- 13. PAGE Grand Gulf Nuclear Station, Unit 1 05000416 1 OF 3
- 4. TITLE Automatic Reactor Scram Due to Turbine Control Valve Fast Closure Caused by an Electrical Generator Trip
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED SEQUENTIAL REV FACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR NUMBER NO.
MONTH DAY YEAR N/A N/A FACILITY NAME DOCKET NUMBER 10 26 2008 2008
- - 005 - 00 12 15 2008 N/A N/A
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITIED PURSUANT TO THE REQUIREMENTS OF 10 CFR§: (Check all that apply) o 20.2201(b) o 20.2203(a)(3)(i) o 50.73(a)(2)(i)(C) o 50.73(a)(2)(vii) 1 o 20.2201 (d) o 20.2203(a)(3)(ii) o 50.73(a)(2)(ii)(A) o 50.73(a)(2)(viii)(A) o 20.2203(a)(1) o 20.2203(a)(4) o 50.73(a)(2)(ii)(B) o 50.73(a)(2)(viii)(B) o 20.2203(a)(2)(i) o 50.36(c)(1 )(i)(A) o 50.73(a)(2)(iii) o 50.73(a)(2)(ix)(A)
- 10. POWER LEVEL o 20.2203(a)(2)(ii) o 50.36(c)(1)(ii)(A)
[8J 50.73(a)(2)(iv)(A) o 50.73(a)(2)(x) o 20.2203(a)(2)(iii) o 50.36(c)(2) o 50.73(a)(2)(v)(A) o 73.71 (a)(4) 050 o 20.2203(a)(2)(iv) o 50.46(a)(3)(ii) o 50.73(a)(2)(v)(B) o 73.71(a)(5) o 20.2203(a)(2)(v) o 50.73(a)(2)(i)(A) o 50 73(a)(2)(v)(C) o OTHER o 20.2203(a)(2)(vi) o 50.73(a)(2)(i)(B) o 50 73(a)(2)(v)(D)
Specify in Abstract below or in NRC Form 366A
- 12. LICENSEE CONTACT FOR THIS LER FACILITY NAME I~ELEPHONE NUMBER (Include Area Code)
Grand Gulf Nuclear Station - Michael J. Larson. Actina Licensina Manaaer 601-437-6685CAUSE SYSTEM COMPONENT MANU-REPORTABLE
CAUSE
SYSTEM COMPONENT MANU-REPORTABLE FACTURER TO EPIX FACTURER TO EPIX E
EL EC SIEMENS y
- 14. SUPPLEMENTAL REPORT EXPECTED
[8J NO DATE
~BSTRACT(Umit to 1400 spaces, i.e., approximately 15 single-spaced typewritten lines)
On October 26, 2008 at 1125, Grand Gulf Nuclear Station was in Mode 1 operating at approximately 50 percent power when an automatic reactor scram was initiated by the Reactor Protection System (RPS) on detection of fast closure of the Turbine Control Valves (TCVs). After the scram reactor water level decreased to -2.67 inches and was maintained with the reactor feedwater system. There were no inoperable structures, systems, or components at the start of the event that contributed to the event. The normal heat sink (main condenser) remained available and no Main Steam Safety Relief Valves actuations occurred during the event. All control rods fully inserted and all safety systems functioned as designed and responded properly.
The cause of this event was due to the Main Generator Thyristor Voltage Regulator (TVR transferring from automatic control to manual control resulting in an unexpected under excited condition which tripped the main generator which then caused a fast closure of the TCV. It was determined that the TVR card manual reference setter was not tracking the automatic reference setter due to a defective manual reference setter motor operated potentiometer (MOP).
The root cause of this event was determined to be lack of a preventive maintenance (PM) strategy for the TVR control system to ensure reliability of the voltage control circuits NRC FORM 366 (9-2007)U.S. NUCLEAR REGULATORY COMMISSION (9-2007)
LICENSEE EVENT REPORT (LER)
- 1. FACILITY NAME
- 2. DOCKET
- 6. LER NUMBER
- 3. PAGE I SEQUENTIAL I REV YEAR NUMBER NO.
Grand Gulf Nuclear Station Unit 1 05000416 2008 005 -
00 2
of 3
A. REPORTABLE OCCURRENCE On October 26, 2008 at 1125, Grand Gulf Nuclear Station was in Mode 1 operating at approximately 50 -
percent power when an automatic reactor scram was initiated by the Reactor Protection System (RPS)
[JC] on detection of fast closure of the Main Turbine Control Valves (TCVs). After the scram reactor water level decreased to - 2.67 inches and was maintained with the reactor feedwater system [SJ]. The following occurrences were considered reportable:
~
Automatic actuation of Reactor Protection System (RPS) [JC]Automatic Scram (Reference:
10CFR50.73(a)(2)(iv) (A) & (B)(1)
Notification was made to the NRC's Emergency Notification System (ENS) reporting this condition pursuant to 10CFR50.72(b)(2)(iv)(B) and 10CFR50.72(b)(3)(iv)(A) and this event is reported under 50.73(a)(2)(iv)(A).
B.
INITIAL CONDITIONS At the time of the event, the reactor was in OPERATIONAL MODE 1 with reactor power at approximately 50 percent. There were no additional inoperable structures, systems, or components at the start of the event that contributed to the event.
C.
DESCRIPTION OF OCCURRENCE On October 26, 2008 at 1125 hours0.013 days <br />0.313 hours <br />0.00186 weeks <br />4.280625e-4 months <br />, Grand Gulf Nuclear Station was in Mode 1 operating at approximately 50 percent power when a reactor scram was initiated by the Reactor Protection System (RPS) on detection of fast closure of the Main Turbine Control Valves (TCVs). The fast closure of the TCVs was the result of a Main Generator [TB] trip caused by a generator loss of field condition. The loss of field occurred when the Thyristor Voltage Regulator (TVR) transferred from automatic to a failed manual controller.
After the scram reactor level decreased due to shrinkage to a level of - 2.67 inches. Water level in the Reactor Pressure Vessel (RPV) was maintained by Reactor Feed Pump Turbine (RFPT) "An using startup level control. Since reactor feedwater was available, this was not a SCRAM with complications.
The normal heat sink (main condenser) remained available after the scram.
All control rods fully inserted to position 00. All safety systems performed as designed, there were no Emergency Core Cooling System (ECCS) [BJ, BO] actuations, no vessel isolation (Main Steam Isolation Valves remained open), and no Safety/Relief Valves (SRVs) lifted. There were no radiological or industrial safety impacts as a result of this scram.U.S. NUCLEAR REGULATORY COMMISSION (9-2007)
LICENSEE EVENT REPORT (LER)
- 1. FACILITY NAME
- 2. DOCKET
- 6. LER NUMBER
- 3. PAGE I SEQUENTIAL I REV YEAR NUMBER NO.
Grand Gulf Nuclear Station Unit 1 05000416 2008 ODS --
DO 3
of 3
D.
CAUSE~OCCURRENCE The cause of this event was due to the Main Generator Thyristor Voltage Regulator ( TVR ) transferring from automatic control to manual control resulting in an unexpected under excited condition which tripped the main generator. It was determined that the TVR card manual reference setter was not tracking the automatic reference setter due to a defective manual reference setter motor operated potentiometer (MOP).
The root cause of this event was determined to be lack of a preventive maintenance (PM) strategy for the TVR control system to ensure reliability of the voltage control circuits.
E.
CORRECTIVE ACTIONS
Immediate Corrective Actions - The manual reference setter motor operated potentiometer for the TVR was replaced and verified to operate properly.
Long Term Corrective Actions - Condition Report GGN-2008-6241 was written and will address any additional actions.
F.
SAFETY ASSESSMENT
Immediate actions performed by the Operations staff were adequate and appropriate in placing and maintaining the reactor in safe shutdown condition. No margin of safety was affected or encroached. All control rods fully inserted to position 00. All safety systems performed as designed, there were no Emergency Core Cooling System (ECCS) actuations, no vessel isolation (MSIV's remained open), and no Safety/Relief Valves (SRVs) lifted. There were no radiological or industrial safety impacts as a result of this scram.
The Group 2 and 3 Primary Containment Isolation initiated at Level 3 (+11.4 inches), however no valves changed position because these valves were already in the normal isolated position. The Group 2 and 3 isolations were for valves in the same system (Residual Heat Removal).
No damage occurred as a result of the turbine trip and all equipment responses were as designed and expected.
This event did not prevent the fulfillment of a safety function therefore there were no safety system functional failures. Based on the discussion provided, the health and safety of the public was not compromised by this event.SQOF G.
ADDITIONAL INFORMATION
Previous Similar Events - Pursuant to 10CFR50.73(b)(5) this issue is considered an infrequent event.
There has not been any occurrence of the same underlying concern in the past two years at Grand Gulf Nuclear Station.