05000282/LER-2008-002, Regarding Inadvertent Reactor Trip Caused by Failed Controller During Reactor Protection System Testing

Regarding Inadvertent Reactor Trip Caused by Failed Controller During Reactor Protection System Testing

ML082730897
Person / Time
Site:	Prairie Island
Issue date:	09/29/2008
From:	Wadley M Northern States Power Co, Xcel Energy
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
L-PI-08-076 LER 08-002-00
Download: ML082730897 (6)

LER-2008-002, Regarding Inadvertent Reactor Trip Caused by Failed Controller During Reactor Protection System Testing

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(1) 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(v), Loss of Safety Function
2822008002R00 - NRC Website

text

September 29, 2008 L-PI-08-076 10 CFR 50.73 U S Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Prairie Island Nuclear Generating Plant Unit 1 Docket 50-282 License No. DPR-42 LER 1-08-02, Inadvertent Reactor Trip Caused by Failed Controller During Reactor Protection System Testing Licensee Event Report (LER) 1-08-02 for this event is attached. Northern States Power Company, a Minnesota corporation (NSPM), notified the NRC of this event as required by 10 CFR 50.72(b)(2)(iv)(B) on July 31St, 2008. Please contact us if you require additional information related to this event.

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

' //., /d71d )J(;

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,/ t f h[ [, 4.k Michael D. Wadley

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Site Vice President 3

Prairie Island Nuclear Generating Plant 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 171 7 Wakonade Drive East Welch, Minnesota 55089-9642 Telephone: 651.388.1 121

ENCLOSURE LICENSEE EVENT REPORT 1-08-02 4 Pages Follow

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

LICENSEE EVENT REPORT (LER)

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

1. FACILITY NAME Pralrle Island Nuclear Generating Plant, Unit 1 APPROVED BY OMB NO 3150-0104 EXPIRES 08/31/2010 Estimated burden per response to comply w~th 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 rndustry Send comments regard~ng burden estlmate to the Records and FOIAlPr~vacy S e ~ ~ c e Branch (T-5 F52), U S Nuclear Regulatory Commlss~on, Washlngton, DC 20555-0001, or by Internet e-mall to ~nfocollects@nrc gov, and to the Desk Officer, Office of lnformatlon and Regulatory Affalrs, NEOB-10202, (3150-0066), Office of Management and Budget, Washington, DC 20503 If a means used to lmpose an lnformatlon collect~on does not dlsplay a currently valld OMB control number, the NRC may not conduct or sponsor, and a person IS not requlred to respond to, the ~nforrnat~on collectlon

2. DOCKET NUMBER 05000282

4. TITLE Inadvertent Reactor Tr~p Caused by Failed Controller During Reactor Protection System Testing

3. PAGE 1 of4

5. EVENT DATE MONTH 07

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

11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR 5: (Check all that apply)

[7 20 2201(b) 20 2203(a)(3)(i) 50 73(a)(2)(1)(C) 50 73(a)(2)(vll) 20 2201(d) 20 2203(a)(3)(11) 50 73(a)(2)(11)(A) 50 73(a)(2)(v111)(A) 20 2203(a)(l) 20 2203(a)(4) 50 73(a)(2)(11)(6)

[7 50 73(a)(2)(v111)(B) 20 2203(a)(2)(1) 50 36(c)(l )(I)(A)

[7 50 73(a)(2)(111)

[7 50 73(a)(2)(1x)(A)

[7 20 2203(a)(2)(11)

[7 50 36(c)(l)(11)(A) 50 73(a)(2)(1v)(A) 50 73(a)(2)(x) 20 2203(a)(2)(111) 50 36(c)(2) 50 73(a)(2)(v)(A) 73 71 (a)(4)

[7 20 2203(a)(2)(1v) 50 46(a)(3)(11) 50 73(a)(2)(v)(B) 73 71 (a)(5) 20 2203(a)(2)(~)

50 73(a)(2)(l)(A) 50 73(a)(Z)(v)(C)

OTHER i

20 2203(a)(2)(vl) 50.73(a)(2)(1)(B)

Spec~fy ~n Abstract below or ~n

12. LICENSEE CONTACT FOR THlS LER

9. OPERATING MODE Mode 1

10. POWER LEVEL 100 DAY 31 YEAR TELEPHONE NUMBER (Include Area Code) 651.388.1 121 YEAR 2008

7. REPORT DATE 2008 - 002 - 00 SEQUENTIAL NUMBER

8. OTHER FACILITIES INVOLVED MONTH 09 REV NO FACILITY NAME FACILITY NAME DOCKET NUMBER DOCKET NUMBER DAY 29 REPORTABLE TO EPlX YEAR YEAR 2008 ABSTRACT (L~mrt to 1400 spaces, I e, approxrmately 15 smgle-spaced typewritten Ilnes)

On July 31, 2008, Prairie Island Nuclear Generating Plant (PINGP), Unit 1 was operating at 100 percent power. At 0817 CDT during performance of the quarterly analog protection functional test, Unit 1 reactor tripped. At the time of the trip the yellow channel over-temperature delta T (OT delta T) bistables were in the tripped condition as directed by the testing procedure when a red channel OT delta T reactor trip signal was generated due to a failed controller. The red channel OT delta T setpoint was not expected to be challenged nor was a reactor trip expected at any point during yellow channel OT delta T analog testing.

All automat~c actions for a reactor trip occurred as required with two exceptions: The Unit 1 turbine-driven auxiliary feedwater pump (1 1 TDAFWP) auto started as designed, but tripped 42 seconds later on low discharge pressure (see LER 1-08-03); and a Unit 1 Turbine 2 Reheat Stop Valve indicated intermediate vice closed due to a fault with the position indication. Operator response and recovery actions were as expected.

The reactor trip was caused by a failed F delta Q proportional controller, which was subsequently replaced.

Planned corrective actions include replacement of all similar controllers.

NRC FORM 366 (9-2007)

MANU-FA CTURER

CAUSE

X

14. SUPPLEMENTAL REPORT EXPECTED O NO 0

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

SYSTEM J C COMPONENT IMOD REPORTABLE TO EPIX Y

MANU-FACTURER F180 DAY

15. EXPECTED SUBMISSION DATE

CAUSE

MONTH SYSTEM COMPONENT

EVENT DESCRIPTION LICENSEE EVENT REPORT (LER)

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

CONTINUATION SHEET On July 31, 2008, 0817 CDT, Prairie Island Nuclear Generating Plant (PINGP), Unit 1 was operating at 100 percent power when the reactor tripped on an over-temperature delta T (OT delta T) reactor trip signal from the reactor protection system1.

At the time of the event, instrumentation and control personnel were performing the quarterly analog reactor protection functional test on the yellow channel when the red channel OT delta T bistable was actuated. Subsequent troubleshooting and root cause investigation determined that the red channel bistable actuation was caused by the failure of a Foxboro H-line (model 62H-2E-0) F delta Q controlle? in the OT delta T circuit. The controller output failed high causing the OT delta T setpoint to drop below the actual delta T parameter thus causing a red channel reactor trip signal. The red channel OT delta T reactor trip signal combined with the yellow channel OT delta T bistables being in test (trip) as directed by the surveillance procedure completed the 2 out of 4 coincidence logic required to initiate a reactor trip. During the performance of yellow channel OT delta T analog testing, the red channel OT delta T setpoint was not expected to be challenged nor was a reactor trip expected at any point.

3. PAGE 2 o f 4

1. FACILITY NAME Prairie Island Nuclear Generating Plant Unit 1 All automatic actions for a reactor trip occurred as required with the following exceptions:

Subsequent to the trip, the Unit 1 turbine-driven auxiliary feedwater pump (1 1 TDAFWP) auto started as designed, but tripped 42 seconds later on low discharge pressure. And a Unit 1 Turbine 2 Reheat Stop Valve indicated intermediate vice closed. However, physical inspection verified that this valve was indeed closed and that the intermediate indication was caused due to a failed switch rod (linkage) that actuates a proximity switch to indicate valve position. Operator response and recovery actions for the reactor trip were completed as expected.

EVENT ANALYSIS

2. DOCKET NUMBER 05000282 A reactor trip is required to be reported per 10 CFR 50.73(a)(2)(iv)(A). The reactor trip by itself did not result in a condition that could have prevented the fulfillment of a safety function per 10 CFR 50.73(a)(2)(v). Issues associated with the 11 TDAFWP are addressed in LER 1-08-03. The erroneous indication for the Unit 1 Turbine 2 Reheat Stop Valve is not directly related to the reactor trip and was repaired under the site's corrective action program on 08/02/2008.

6. LER NUMBER YEAR SEQUENTIAL REV NUMBER NO 2008 -

002

- 00 1

2 Ells System Code: JC Ells Component Identifier: IMOD

SAFETY SIGNIFICANCE LICENSEE EVENT REPORT (LER)

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

CONTINUATION SHEET The OT delta T trip along with the overpower delta T trip is designed to keep the departure from nuclear boiling ratio (DNBR) greater than the limit for slow reactivity additions. This event was due to an equipment failure and not related to a reactivity addition. With the exception of the 11 TDAFWP trip and a Unit 1 Turbine 2 Reheat Stop Valve position indication, all systems performed as expected to the reactor trip signal and operators responded and recovered as expected. Thus, this event did not affect the health and safety of the public and the safety significance of this event is considered minimal.

CAUSE

3. PAGE 3 o f 4 The equipment root cause for the failure of the F delta Q controller is attributed to the random failure of varactor diode (CRI) located inside the controller. Although this controller was refurbished in 1985, only the capacitors were routinely replaced as part of refurbishments. Therefore, CR1 was not replaced as part of the 1985 refurbishment.

6. LER NUMBER YEAR SEQUENTIAL REV NUMBER NO 2008 -

002

- 00

1. FACILITY NAME Prairie Island Nuclear Generating Plant Unit 1 The organizational cause was found to be the inadequate prioritization by the site in the creation of a preventive maintenance strategy for the analog components within the reactor protection and control system.

2. DOCKET NUMBER 05000282

CORRECTIVE ACTION

Immediate corrective action:

1. Replaced the failed F delta Q proportional controller.

Planned corrective actions include:

1. Replacement or refurbishment of all F delta Q proportional controllers.

2. Implement an improved preventive maintenance strategy for the Foxboro H-Line components of the reactor protection and control system.

3. Implement a Life Cycle Management Plan for the reactor protection and control system. This will ensure timely preventative replacement of the Foxboro H-Line components.

PREVIOUS SIMILAR EVENTS LICENSEE EVENT REPORT (LER)

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

CONTINUATION SHEET LER 2-07-01 describes a reactor trip due to the failure of an MG-6 style relay in the safety injection system3 and LER 1-06-01 describes a reactor trip due to a ground caused by degraded motor insulation in one of the condensate system4 pumps.

Although both of these events describe reactor trips due to equipment related issues, the MG-6 style relay failure was due to high contact resistance while the ground caused by degraded motor insulation was an age related failure. Both of the previous LERs include preventive maintenance in the corrective actions. LER 1-06-01 included an action to institute a large motor program that would not prevent the event of this LER. LER 2-07-01 included an action to implement preventive maintenance strategy for all critical equipment. This action was completed in February of 2008, but some improvements were made apparent by the event of this LER (see Corrective Action discussion, above).

3. PAGE 4 o f 4 Ells System Code: BQ 4 Ells System Code: SD

6. LER NUMBER YEAR SEQUENTIAL REV NUMBER NO 2008 -

002

- 00

1. FACILITY NAME Prairie Island Nuclear Generating Plant Unit 1

2. DOCKET NUMBER 05000282