05000306/LER-2008-002, Manual Reactor Trip During Low Power Physics Testing

Manual Reactor Trip During Low Power Physics Testing

ML083570572
Person / Time
Site:	Prairie Island
Issue date:	12/19/2008
From:	Wadley M Xcel Energy
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
L-PI-08-099 LER 08-002-00
Download: ML083570572 (5)

LER-2008-002, Manual Reactor Trip During Low Power Physics Testing

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(iv)(A), System Actuation
3062008002R00 - NRC Website

text

'@ Xcel Energym December 19,2008 L-PI-08-099 10 CFR 50.73 U S Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Prairie Island Nuclear Generating Plant Unit 2 Docket 50-306 License No. DPR-60 LER 2-08-02, Unit 2 Manual Reactor Trip during Low Power Physics Testinq Northern States Power Company, a Minnesota corporation (NSPM) herewith encloses Licensee Event Report (LER) 2-08-02. The LER describes a condition where Prairie Island Nuclear Generating Plant (PINGP) Unit 2 was manually tripped due to a rod control urgent failure alarm and failure of one group of rods to move inward as expected. This occurred during the reactor physics testing portion of startup following PINGP's twenty-fifth, Unit 2 refueling outage (2R25). NSPM notified the NRC of this event as required by 10 CFR 50.72.(b)(2)(iv)(B) on October 30, 2008. Please contact us if you require additional information related to this event.

Summaw of Commitments This letter contains no new commitments and no changes to existing commitments.

Michael D. Wadley Site Vice President Q

Prairie Island Nuclear Generating lant Northern States Power Company - Minnesota Enclosure cc:

Administrator, Region Ill, USNRC Project Manager, Prairie Island, USNRC Resident Inspector, Prairie Island, USNRC Department of Commerce, State of Minnesota 1717 Wakonade Drive East Welch, Minnesota 55089-9642 Telephone: 651.388.1 121

ENCLOSURE LICENSEE EVENT REPORT 2-08-02 3 Pages Follow

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

LICENSEE EVENT REPORT (LER)

(See reverse for requlred number of d~g~tslcharacters for each block)

I FACILITY NAME Pra~r~e Island Nuclear Generating Plant Unit 2 APPROVED BY OMB NO 3150-0104 EXPIRES 08/31/2010 Estimated burden per response to comply wlth thls mandatory collectlon request 80 hours9.259259e-4 days <br />0.0222 hours <br />1.322751e-4 weeks <br />3.044e-5 months <br /> Reported lessons learned are Incorporated Into the llcenslng process and fed back to Industry Send comments regarding burden estlmate to the Records and FOINPrlvacy Sewlce Branch (T-5 F52) U S Nuclear Regulatory Commlsslon, Washlngton, DC 20555-0001, or by Internet e-mall to lnfocollects@nrc gov, and to the Desk Officer, Offlce of lnformatlon and Regulatory Affalrs, NEOB-10202, (3150-0066), Office of Management and Budget, Washington, DC 20503 If a means used to ~mpose an lnformatlon collect~on does not dlsplay a currently valld OMB control number, the NRC may not conduct or sponsor and a person 1s not requlred to respond to, the lnformat~on collectlon

2. DOCKET NUMBER 05000306

4. TITLE Un~t 2 Manual Reactor Tr~p dur~ng Low Power Physics Test~ng.

3. PAGE 1 of3

5. EVENT DATE MONTH 10

6. LER NUMBER NAME Jorge L O'Farr~ll, Licensing Engineer

11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR 5: (Check all that apply) 20 2201(b) 20 2203(a)(3)(1) 50 73(a)(2)(1)(C) 50 73(a)(2)(vll) 20 2201(d)

Cj 20 2203(a)(3)(11)

Cj 50 73(a)(2)(11)(A) 50 73(a)(2)(v111)(A) 20 2203(a)(I) 20 2203(a)(4) 50 73(a)(2)(11)(B) 50 73(a)(2)(v111)(B) 20 2203(a)(2)(1) 50 36(c)(l )(I)(A) 50 73(a)(2)(111) 50 73(a)(2)(1x)(A)

Cj 20 2203(a)(2)(11)

Cj 50 36(c)(l)(11)(A) 50 73(a)(2)(1v)(A)

Cj 50 73(a)(2)(x)

Cj 20 2203(a)(2)(111)

Cj 50 36(c)(2)

Cj 50 73(a)(2)(v)(A)

Cj 73 71 (a)(4)

Cj 20 2203(a)(2)(1v)

Cj 50 46(a)(3)(11)

Cj 50 73(a)(2)(v)(B)

Cj 73 71 (a)(5) 20 2203(a)(2)(v)

Cj 50 73(a)(2)(1)(A) 50 73(a)(2)(v)(C)

OTHER Cj 20 2203(a)(2)(v1)

Cj 50 73(a)(2)(1)(B) 50 73(a)(2)(v)(D)

Spec~fy In Abstract below or In NRC F w

366A

12. LICENSEE CONTACT FOR THIS LER

9. OPERATING MODE Mode 2

10. POWER LEVEL 00 1 DAY 30 YEAR TELEPHONE NUMBER (Include Area Code) 651.388.1 121 YEAR 2008

7. REPORT DATE 2008 - 002 - 00 SEQUENTIAL NUMBER MONTH 12

8. OTHER FACILITIES INVOLVED REV NO FACILITY NAME FACILITY NAME DAY 19 DOCKET NUMBER DOCKET NUMBER

CAUSE

X YEAR 2008 MANU-FA CTURER REPORTABLE TO EPIX SYSTEM AA YEAR

14. SUPPLEMENTAL REPORT EXPECTED 0 YES (If yes, complete 15. EXPECTED SUBMISSION DATE).

O NO ABSTRACT (Llmrt to 1400 spaces, I e, approx~mately 15 s~ngle-spaced typewritten Ilnes)

On October 30, 2008, at 1414 CDT during reactor physics testing following a Unit 2 outage, Prairie Island Nuclear Generating Plant (PINGP) Unit 2 was just above the point of adding heat (POAH) when an urgent fallure alarm was received while moving Bank A control rods inward. It was noted that Group 1 control rods in Power Cablnet 21AC unexpectedly stopped moving while Group 2 control rods in Power Cabinet 22AC continued inward rod motion. Operators stopped Group 2 control rods and initiated a manual reactor trip. All systems operated as expected following the trip and operator response and recovery actions were as expected.

Subsequent troubleshooting identified that a Phase C fuse in the 21AC Moveable Gripper bus duct disconnect swltch had blown. Troubleshooting also identified that the blown fuse was not fault related and likely due to a random failure. All 21AC moveable gripper bus duct disconnect switch fuses were replaced on October 31St, 2008 at approximately 0031 CDT thereby restoring full functionality of bank A control rods. In addition, all of the moveable gripper bus duct disconnect-switch fuses for the other two power cabinets (22AC and 21 BD) in Unit 2 were replaced to ensure that the extent of condition was corrected.

Reactor startup and physics testing were resumed on October 31, 2008 at 11 15 and Unit 2 reactor was returned to crltlcality on October 31, 2008 at 131 1 CDT.

NRC FORM 366 (9-2007)

COMPONENT F U

15. EXPECTED SUBMISSION DATE

CAUSE

MANU-FACTURER S156 MONTH SYSTEM REPORTABLE TO EPlX Y

DAY COMPONENT

EVENT DESCRIPTION

On October 30, 2008 PlNGP was in the process of a Unit 2 reactor startup following a scheduled refueling outage. The reactor was critical and was slightly above the POAH when at 1414 CDT a rod control system' urgent failure alarm was received. At this point, PlNGP operators were performing reactor physics testing for control rod bank A, which required both rod control groups 1 and 2 to be inserted. When the urgent failure alarm was received, operators noted that group 1 stopped moving while group 2 continued inward motion. Operators immediately stopped group 2 control rods and based on plant conditions at the time, operations personnel initiated a manual reactor trip of PlNGP Unit 2.

The manual trip was initiated since power was decreasing with low power conditions present. All control rods fully inserted as expected and all operator actions were as expected for the reactor trip. The event is being reported as required by 10 CFR 50.73(a)(2)(iv)(A) due to the manual actuation of the reactor protection system. LICENSEE EVENT REPORT (LER)

U.S. NUCLEAR REGULATORY COMMISSION (9-2007)

CONTINUATION SHEET

EVENT ANALYSIS

One of the Reactor Protection system2 design functions is to prevent or suppress conditions that could result in exceeding acceptable fuel damage limits by opening the reactor trip breakers and allowing all control rods to fall inward. This rapid insertion of rods creates negative reactivity which causes a rapid reactivity shutdown. When operators manually tripped the reactor, all control rods fully inserted as expected. Therefore, the reactor protection system operated as designed and there was no loss of safety function per 10 CFR 73(a)(2)(v).

SAFETY SIGNIFICANCE

The reactor protection system is designed so that reactor shutdown with rods is completely independent of the normal rod control functions since the reactor trip breakers completely interrupt power to the rod latching mechanisms regardless of existing control signals. When operators manually initiated the reactor trip, all control rods fully inserted as expected. For these reasons this event was of low safety

3. PAGE 2 of 3 significance.

6. LER NUMBER YEAR SEQUENTIAL REV NUMBER NO 2008 -

002

- 00 I. FACILITY NAME Prairie Island Nuclear Generating Plant Unit 2

CAUSE

It was not known at the time of the trip, but subsequent troubleshooting isolated the cause of the rod

2. DOCKET NUMBER 05000306 control urgent failure alarm and failure of control bank A group 1 rods to insert to a phase C fuse failure in the 21AC power cabinet moveable gripper bus duct disconnect switch. This fuse provides power to the moveable gripper assemblies in power cabinet 21AC. Troubleshooting was unable to determine a fault that would cause the fuse to blow and the apparent cause was determined to be a random fuse failure.

CORRECTIVE ACTION

The blown fuse along with all of the moveable gripper bus duct disconnect-switch fuses for each power cabinet was replaced on Unit 2. This restored the full functionality of Unit 2 control rods.

Troubleshooting and repairs were completed on October 31, 2008 at approximately 0031 CDT. At 11 15 CDT, PlNGP resumed Unit 2 startup and the reactor was successfully restored to criticality on October 31, 2008, at 131 1 CDT.

1 EEllS Component Identifier: AA 2 EEllS Component Identifier: JC

In order to correct the extent of condition, a preventative maintenance program to replace all of the bus duct fuses in both PlNGP Unit 1 and Unit 2 every 10 years will be implemented. In addition, all of the bus duct fuses for Unit 1 will be replaced during the next refueling outage. LICENSEE EVENT REPORT (LER)

U.S. NUCLEAR REGULATORY COMMlsSlON (9-2007)

CONTINUATION SHEET

PREVIOUS SIMILAR EVENTS

Three reactor trip events were found under LER 1-06-01, LER 2-07-01, and LER 1-08-02. LER 1-06-01 describes a manual reactor trip initiated due to a ground in a condensate pump, LER 2-07-01 was an automatic reactor trip caused by a failed safety injection relay, and LER 1-08-02 was an automatic reactor trip caused by a failed reactor protection controller during testing.

I.

FACILITY NAME Prairie Island Nuclear Generating Plant Unit 2 Although similar in that they all describe reactor trips related to equipment problems, they are not significant with regard to the subject event because each equipment problem was significantly different.

2. DOCKET NUMBER 05000306

6. LER NUMBER YEAR SEQUENTIAL REV NUMBER NO 2008 -

002

- 00

3. PAGE 3 of 3