05000416/LER-2008-001, Regarding Manual Reactor Scram Due to Loss of Main Electrical Output Transformer Cooling

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Regarding Manual Reactor Scram Due to Loss of Main Electrical Output Transformer Cooling
ML080700702
Person / Time
Site: Grand Gulf Entergy icon.png
Issue date: 03/10/2008
From: Larson M
Entergy Operations
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
GNRO-2008/00008 LER 08-001-00
Download: ML080700702 (6)
v • d • e


LER-2008-001, Regarding Manual Reactor Scram Due to Loss of Main Electrical Output Transformer Cooling
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
10 CFR 50.73(b)(5)
LER closed by
IR 05000416/2008004 (17 October 2008)
4162008001R00 - NRC Website
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text

-=::::-Entergy GNRO-2008/00008 March 10,2008 Entergy Operations, Inc.

P.O. 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 2008-001 Manual Reactor SCRAM Due to Loss of Main Electrical Output Transformer Cooling Grand Gulf Nuclear Station, Unit 1 Docket No. 50-416 License No. NPF-29

Dear Sir or Madam:

Attached is Licensee Event Report (LER) 2008-001-00 which is a final report.

This letter does not contain any commitments.

Yours truly, Michael J. Larson Acting-Manager, Licensing MJL

attachment:

cc:

LER 2008-001-00 (See Next Page)

-=::::-Entergy GNRO-2008/00008 March 10,2008 Entergy Operations, Inc.

P.O. 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 2008-001 Manual Reactor SCRAM Due to Loss of Main Electrical Output Transformer Cooling Grand Gulf Nuclear Station, Unit 1 Docket No. 50-416 License No. NPF-29

Dear Sir or Madam:

Attached is Licensee Event Report (LER) 2008-001-00 which is a final report.

This letter does not contain any commitments.

Yours truly, Michael J. Larson Acting-Manager, Licensing MJL

attachment:

cc:

LER 2008-001-00 (See Next Page)

-=::::-Entergy GNRO-2008/00008 March 10,2008 Entergy Operations, Inc.

P.O. 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 2008-001 Manual Reactor SCRAM Due to Loss of Main Electrical Output Transformer Cooling Grand Gulf Nuclear Station, Unit 1 Docket No. 50-416 License No. NPF-29

Dear Sir or Madam:

Attached is Licensee Event Report (LER) 2008-001-00 which is a final report.

This letter does not contain any commitments.

Yours truly, Michael J. Larson Acting-Manager, Licensing MJL

attachment:

cc:

LER 2008-001-00 (See Next Page)

GNRO-2008/00008 March 10,2008 cc:

NRC Senior Resident Inspector Grand Gulf Nuclear Station Port Gibson, MS 39150 U. S. Nuclear Regulatory Commission AnN: 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. Jack Donohew, NRRlDORL (w/2)

AnN: ADDRESSEE ONLY ATTN: U. S. Postal Delivery Address Only Mail Stop OWFN/8 G14 Washington, DC 20555-0001 GNRO-2008/00008 March 10,2008 cc:

NRC Senior Resident Inspector Grand Gulf Nuclear Station Port Gibson, MS 39150 U. S. Nuclear Regulatory Commission AnN: 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. Jack Donohew, NRRlDORL (w/2)

AnN: ADDRESSEE ONLY ATTN: U. S. Postal Delivery Address Only Mail Stop OWFN/8 G14 Washington, DC 20555-0001 GNRO-2008/00008 March 10,2008 cc:

NRC Senior Resident Inspector Grand Gulf Nuclear Station Port Gibson, MS 39150 U. S. Nuclear Regulatory Commission AnN: 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. Jack Donohew, NRRlDORL (w/2)

AnN: ADDRESSEE ONLY ATTN: U. S. Postal Delivery Address Only Mail Stop OWFN/8 G14 Washington, DC 20555-0001

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION (9-2007)

LICENSEE EVENT REPORT (LER)

(See reverse for required number of digits/characters for each block)

APPROVED BY OMB: NO. 3150-0104 EXPIRES: 08/31/2010

, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

1. FACILITY NAME Grand Gulf Nuclear Station, Unit 1
2. DOCKET NUMBER 05000 416
3. PAGE 1 OF 4
4. TITLE Manual Reactor SCRAM Due to Loss of Main Electrical Output Transformer Cooling
5. EVENT DATE
6. LER NUMBER
7. REPORT DATE
8. OTHER FACILITIES INVOLVED MONTH DAY YEAR YEAR SEQUENTIAL NUMBER REV NO.

MONTH DAY YEAR FACILITY NAME N/A DOCKET NUMBER N/A 01 12 2008 2008 - 001 - 00 03 10 2008 FACILITY NAME N/A DOCKET NUMBER N/A

9. OPERATING MODE 1
10. POWER LEVEL 099
11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR§: (Check all that apply) 20.2201(b) 20.2203(a)(3)(i) 50.73(a)(2)(i)(C) 50.73(a)(2)(vii) 20.2201(d) 20.2203(a)(3)(ii) 50.73(a)(2)(ii)(A) 50.73(a)(2)(viii)(A) 20.2203(a)(1) 20.2203(a)(4) 50.73(a)(2)(ii)(B) 50.73(a)(2)(viii)(B) 20.2203(a)(2)(i) 50.36(c)(1)(i)(A) 50.73(a)(2)(iii) 50.73(a)(2)(ix)(A) 20.2203(a)(2)(ii) 50.36(c)(1)(ii)(A) 50.73(a)(2)(iv)(A) 50.73(a)(2)(x) 20.2203(a)(2)(iii) 50.36(c)(2) 50.73(a)(2)(v)(A) 73.71(a)(4) 20.2203(a)(2)(iv) 50.46(a)(3)(ii) 50.73(a)(2)(v)(B) 73.71(a)(5) 20.2203(a)(2)(v) 50.73(a)(2)(i)(A) 50.73(a)(2)(v)(C)

OTHER 20.2203(a)(2)(vi) 50.73(a)(2)(i)(B) 50.73(a)(2)(v)(D)

Specify in Abstract below or in NRC Form 366A

12. LICENSEE CONTACT FOR THIS LER FACILITY NAME Grand Gulf Nuclear Station - Michael J. Larson, Licensing Engineer TELEPHONE NUMBER (Include Area Code) 601-437-6685CAUSE SYSTEM COMPONENT MANU-FACTURER REPORTABLE TO EPIX

CAUSE

SYSTEM COMPONENT MANU-FACTURER REPORTABLE TO EPIX X

EL XFMR ABB Y

MONTH DAY YEAR

14. SUPPLEMENTAL REPORT EXPECTED YES (If yes, complete 15. EXPECTED SUBMISSION DATE)

NO

15. EXPECTED SUBMISSION DATE ABSTRACT (Limit to 1400 spaces, i.e., approximately 15 single-spaced typewritten lines)

On January 12, 2008, at 1626 hours0.0188 days <br />0.452 hours <br />0.00269 weeks <br />6.18693e-4 months <br /> a manual reactor scram was initiated from 99 percent power due to loss of cooling to the Main Transformers. After the scram reactor water level decreased to Level 2 (-41.6 inches) and Reactor Core Isolation Cooling initiated. 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 the loss of cooling to the Main Transformers caused by loss of Auxiliary Power to the Main Transformer cooling system. Inspection of the complete circuit for Main Transformer Auxiliary Power showed that the B phase power cables were found to be burned in two at the transfer switch panel. The cause of the B phase power cable failure is attributed to failure of an electrical compression connection on a lug connection. This particular cable and connection has been inservice since plant start-up. Potential root causes were determined to be use of a compression connection for high current applications versus the preferred crimp type connection and an inadequate preventive maintenance strategy to provide early detection. Corrective actions included an inspection of the power panel and replacement of all damaged cabling.

NRC FORM 366 (9-2007)(9-2007)

LICENSEE EVENT REPORT (LER)

1. FACILITY NAME
2. DOCKET
6. LER NUMBER
3. PAGE YEAR SEQUENTIAL NUMBER REV NO.

Grand Gulf Nuclear Station, Unit 1 05000416 2008

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00 2

of 4

A. REPORTABLE OCCURRENCE On January 12, 2008, at 1626 hours0.0188 days <br />0.452 hours <br />0.00269 weeks <br />6.18693e-4 months <br /> Grand Gulf Nuclear Station initiated a manual reactor scram from 99 percent power due loss of cooling to the Main Transformers [EL XFMR]. After the scram reactor water level decreased to Level 2 (-41.6 inches) and Reactor Core Isolation Cooling (RCIC) initiated. The following occurrences were considered reportable:

3/4 Manual Actuation of Reactor Protection System (RPS) [JC] Manual Scram (Reference:

10CFR50.73(a)(2)(iv) (A) & (B)(1))

3/4 Reactor Core Isolation Cooling (RClC) [BN] automatic initiation and injection on Reactor Vessel Water Level - Low Low, Level 2 into the reactor. (Reference: 10CFR50.73(a)(2)(iv) (A) & (B)(5))

Notification was made to the NRCs 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) - Any event or condition that resulted in manual or automatic actuation of any of the systems listed in paragraph (a)(2)(iv)(B) of this section.

B.

INITIAL CONDITIONS At the time of the event, the reactor was in OPERATIONAL MODE 1 with reactor power at approximately 99 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 January 12, 2008, at 1558, Main Transformer trouble alarms were received for all three in-service transformers. Investigation revealed a malfunction had occurred on the B phase Auxiliary Power Supply (panel 1SMT1) to the Main Transformer Auxiliaries. Operations and Electrical personnel were dispatched to the transformers. The A Transformer was found with no cooler groups running. The B and C Transformers were found with only partial cooler groups running. Subsequently, all cooling groups stopped for the B and C Transformers. Further investigation in the field indicated that power to the transformer cooling systems could not be restored.

Because there was a loss of cooling to the Main Transformers, a manual SCRAM was initiated at 1626 followed by a Main Turbine trip at 1627. After the scram reactor level decreased due to shrinkage to Level 2

(-41.6 inches) and Reactor Core Isolation Cooling initiated. Operators manually tripped Reactor Feed Pump Turbine (RFPT) B. Reactor Pressure Vessel (RPV) water level increased to a maximum of +60 inches resulting in a RCIC shutdown on Level 8 (+53.5 inches) and a RFPT A trip on Level 9 (+56 inches).

Operations returned RFPT A to startup level control and placed RCIC in the normal standby lineup. The scram was reset at 1636. The normal heat sink (main condenser) remained available and no Main Steam Safety Relief Valves (MSRV) actuations occurred during the event. All control rods fully inserted and all safety systems functioned as designed and responded properly. This was NOT a SCRAM with complications. (9-2007)

LICENSEE EVENT REPORT (LER)

1. FACILITY NAME
2. DOCKET
6. LER NUMBER
3. PAGE YEAR SEQUENTIAL NUMBER REV NO.

Grand Gulf Nuclear Station, Unit 1 05000416 2008

-- 001 --

00 3

of 4

D.

CAUSE of OCCURRENCE The cause of this event was the loss of cooling to the Main Transformers caused by loss of Auxiliary power to the Main Transformer cooling system. Inspection of the complete circuit for Main Transformer Auxiliary Power showed that the B phase power cables were found to be burned in two in panel 1SMT1 (transfer switch panel). The cause of the B phase power cable failure is attributed to failure of an electrical compression connection on a lug connection; the connection was manufactured by BURNDY, Model No.

D1281. The root cause of the power cable failure could not be conclusively determined by the initial investigation. This particular cable and connection has been inservice since plant start-up. One potential root cause was determined to be use of a compression connection for high current applications versus the preferred crimp type connection. Another potential root cause was there was an inadequate preventive maintenance strategy to provide early detection. Figure 1 provides a picture of the failed connection.

E.

CORRECTIVE ACTIONS

Immediate Corrective Actions - Completed inspection of the 1SMT1 Transfer Switch Panel. All damaged cabling has been replaced. Inspection results indicate that no damage occurred to the affected transformers and all equipment responses were as designed and expected.

Long Term Corrective Actions - Condition Report GGN-2008-00174 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 safety systems responded as designed in this event.

Reactor Core Isolation Cooling initiated at Level 2 (-41.6 inches). No Emergency Core Cooling System (ECCS) initiations occurred. 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.

This condition 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.

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. 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 001 00 4

of 4

Figure 1 - As Found Condition

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