ML20024J245

LER 94-006-00:on 940907,observed Receipt of Annunciator 12 Charging Pump Overload Trip.Caused by Overheated C Phase Loadside Connection at Mccb.Breaker Was Replaced & Tested. W/941006 Ltr

ML20024J245
Person / Time
Site:	Prairie Island
Issue date:	10/06/1994
From:	Richard Anderson, Hunstad A NORTHERN STATES POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-94-006-01, LER-94-6-1, NUDOCS 9410130058
Download: ML20024J245 (4)

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Northern States Power Company l Prairie Island Nuclear Generating Plant 1717 Wakonade Dr. dast Welch. Minnesota 55089 October 6, 1994 10 CFR Part 50 Section 50.73 U S Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555 PRAIRIE ISLAND NUCLEAR GENERATING PIANT Docket Nos. 50-282 License Nos. DPR-42 50-306 DPR-60 Unplanned Closu'ce of a Letdown Isolation Valve (a Containment Isolation Valve) Due to Trio of the Operatine Charrine Pump The Licensee Event Report for this occurrence is attached. In the report, we made no new NRC commitments.

Due to inadequate reporting procedures, the 4-hour ENS notification under 10 CFR 50, Section 50.72 was not made until 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> later. Reporting procedures have been revised to prevent recurrence. Please contact us if you require additional information related to this event.

jg, f )hbLC4 Roger 0 Anderson Director Licensing and Management Issues c: Regional Administrator - Region III, NRC NRR Project Manager, NRC Senior Resident Inspector, NRC Kris Sanda, State of Minnesota Attachment 1200s~

9410130058 941006 PDR S ADOCK 05000282 PDR 7 #

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NRC FORQ 356 U.S. C]) CLEAR REGULATOF T ColeelSSICJ APPROVED BY OMB NO. 3150-0104 (5 92) EXPIRES 5/31/95 I

ESTIMATED BURDEN PER RESPONSE TO COMPLY WITH 4

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LICENSEE EVENT REPORT (LER) $ARD CMMEN S REGARDING BURDEN ES TE b ,

THE INFORMATION AND RECORDS MANAGEMENT BRANCH I (MNBB 7714), U.S. NUCLEAR REGULATORY COMMISSION, (See reverse for required tunber of digits / characters for each block) , DC 20555-0001, ND TO THE RWO MANAGEMENT AND BUDGET, WASHINGTON, DC 20503.

FACILITY NAME (1) DOCKET NUMBER (2) PAGE (3)

Prairie Island Nuclear Generating Plant U1 05000 282 1 OF 3 TITLE (4) Unplanned Closure of a Containment Isolation Valve  !

EVENT DATE (5) LER NLAIBFR (6) RrPORT DATE (7) OTHER FACILITIES INVOLVED (8)

ON MONTH DAY YEAR YEAR MONTH DAY YEAR r NUMBER NUMBER

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09 07 94 94 -- 06 -- 00 10 06 94 OPERATING THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR 1: (Check one or more) (11) )

MODE (9)

N 20.402(b) 20.405(c) X 50 73(a)(2)(tv) 73.71(b) l POWER 20.405(a)(1)(1) 50.36(c)(1) 50.73(a)(2)(v) 73.71(c)

LEVEL (10) 100 20.405(a)(1)(ii) 50.36(c)(2) 50.73(a)(2)(vil) OTHER 20.405(a)(1)(111) 50.73(a)(2)(1) 50.73(a)(2)(viii)(A) (Specify in 50.73(a)(2)(li) Abstract below 20.405(a)(1)(tv) 50.73(a)(2)(vill)(B)

• 20.405(a)(1)(v) 50.73(a)(2) Wl E ~ ~ 70!73(a)(2)(x) N F rm )

LICENSEE CONTACT FOR THIS LER (12)

NAME TELEPHONE NUMBER (Include Area Code)

Arne A Hunstad 612-388-1121 l

COMPLETE ONE LINE FOR EACH CCBIPONENT FAILURE DESCRIBED IN THIS REPORT (13)

CAUSE SYSTEM COMPONENT MANUFACTURER CAUSE SYSTEM COMPONENT MANUFACTURER 0 $

s SUPPLEMENTAL REPORT EXPECTED (14) EXPECTED MONTH DAY YEAR l YES SUBMISSION l NO (If yes, complete EXPECTED SUBMISSION DATE). DATE (15)

ABSTRACT (Limit to 1400 spaces, i.e., approximately 15 single spe ed typewritten lines) (16)

On September 6, 1994, Unit 1 was operating at 100% power. At 2059, control room operators observed receipt of the annunciator "12 Charging Pump Overload Trip". Within seconds several other alarms were received (Letdown Orifice Isolation Valve - CLOSED, Low RCP Seal Injection Flow, Low RCP i Labyrinth Seal DP) as a result of the trip of No. 12 Charging Pump. Since the pump was the only charging pump operating at the time, trip of the pump caused letdown isolation; the open letdown orifice isolation valve closed.

Letdown orifice isolation valves also function as containment isolation valves. This unplanned closure of the letdown orifice isolation valve was a non-ESF actuation of dual-function equipment. The operators started No. 13 Charging Pump, restoring charging flow and reactor coolant pump seal injection flow, and within 1 minute they restored letdown. The outplant operator investigated the cause of the trip and found that the breaker for No. 12 Charging Pump had tripped. Since No. 11 and 13 Charging Pumps were

, available, no LCO was entered. i The breaker for No. 12 Charging Pump had tripped due to an overheated C l phase loadside connection at the MCCB, a connection made at the breaker. j i

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NRC FORM 366 (5 92) l

NRC FORQ .366A U.S. NUCLEAR REGULATORT COMMISSl(D APPROVED BY OMB NO. 3150-0104 (5-92) EXPIRES 5/31/95 ESilMATED BURDEN PER RESPONSE TO COMPLY WITH THIS INFORMATION COLLECTION REQUEST: 50.0 HRS.

FORWARD COMMENTS REGARDING BURDEN ESTIMATE TO LICENBEE EVENT REPORT (LER) THE INFORMATION AND RECORDS MANAGEMENT BRANCH TEXT CONTINUATION (MNBB 7714), U.S. NUCLEAR REGULATORY COMMISSION, WASHINGTON, DC 20555-0001, AND TO THE PAPERWORK REDUCTION PROJECT (3150-0104), OFFICE OF MANAGEMENT AND BUDGET, WASHINGTON, DC 20503.

FACILITY NAME (1) DOCKET NUMBE R (2) LER NUMBER (61 PAGE (3)

YEAR SEQUENTIAL REVISION Prairie Island Unit 1 NUW9ER NUMBER 05000 282 94 --

06 -- 00 TEXT (if mre space is reauired Use additional copies of hRC Form 366A) (17)

EVENT DJSCRIPTION On September 6, 1994, Unit 1 was operating at 100% power. At 2059, control room operators observed receipt of the annunciator "12 Charging Pump overload Trip". Within seconds several other alarms were received (Letdown Orifice Isolation Valve - CLOSED, Low RCP Seal Injection Flow, Low RCP Labyrinth Seal DP) as a result of the trip of No. 12 Charging Pump (EIIS

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Component Identifier P). Since the pump was the only charging pump operating 'at the"tiine, trip of the plur?p caused letdown isolation; the open letdown orifice isolation valve closed. Letdown orifice isolation valves also function as containment isolation valves. This unplanned closure of the letdown orifice isolation valve was a non-ESF actuation of dual function equipment. The operators started No. 13 Charging Pump, restoring charging flow and reactor coolant pump seal injection flow, and within 1 minute they restored letdown.

The outplant operator investigated the cause of the trip and found that the circuit breaker (EIIS Component. Identifier 52) for No. 12 Charging Pump had tripped. Since No. 11 and 13 Charging Pumps were available, no LCO was entered. A Work Request was issued to investigate and repair the cause of the breaker trip.

CAUSE OF THE EVENT The breaker for No. 12 Charging Pump tripped because of an overheated connection at the breaker's C phase MCCB. This overheating was caused by a loose terminal connection on C phase.

ANALYSIS OF THE EVENT The event is reportable pursuant to 10CFR50.73 (a) (2) (iv) since a single containment isolation valve experienced an unplanned closure.

This was a non-ESF actuation of a dual function component. The letdown orifice isolation valves are used for routine plant operation and also function as containment isolation valves. The valves are interlocked with the charging pumps; at least one charging pump must be running in order to open a valve. The pump trip caused loss of the open permissive, and the valve closed. The valves are designed for thousands of such operations; this one unplanned operation had no deleterious effect on the equipment.

The letdown orifice isolation valves were, at all times, available for their ESF function. Health and safety of the public were unaffected.

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l NRC FORM 366A U.S. NUCLEAR REGULATORY CupMISSION APPROVED B' O n No. 3150-0104 (5 92) ExF fit 5/31/95 ESTIMATED BURDEN PER RESPONSE TO COMPLY WITH THIS INFORMAfl0N COLLECTION REQUEST: 50.0 HRS. i

• FORWARD COMMENTS RECARDING BURDEN ESTIMATE To l LICENSEE EVENT REPORT (LER) THE INFORMATION AND RECORDS MANAGEMENT BRANCH I TEXT CONTINUATION (MNBB 7714), U.S. NUCLEAR REGULATORY COMMISSION, WASHINGTON, DC 20555-0001 AND TO THE PAPERWORK REDUCTION PROJECT (315IO-0104), OFFICE OF MANAGEMENT AND BUDGET, WASHINGTON, DC 20503.

FACILITY NAfE (1) DOCKET NLMBER (2) LER NLMBER (61 PAGE (3)

YEAR SEQUENTIAL REVISION l WUMBER NUMBER Prairie Island Unit 1 '

05000 282 94 --

06 -- 00 l 1 EXT (if more space is reauired use additional cooies of NRC Form 366A) (17) l CORRECTIVE ACTION A standby charging pump was started immediately and the letdown orifice isolation valve was reopened within 1 minute.

An outplant operator was sent to investigate cause of the trip.

l The bre.ake.r. was repla.ced and tested.

r neview of electrical preventive maintenance procedures was done to assure that the procedures required connections to be tightened properly.

Review of breaker maintenance history indicates that this was an isolated incident.

Electricians were cautioned on the need for proper tightening of connections after maintenance. r As other 480V breakers are periodically inspected in the preventive maintenance program, they will be checked for loose terminal connections.

FAILED COMPONENT IDENTIFICATION ,

None.

PREVIOUS SIMILAR EVENTS A previous similar event was reported as Unit 1 LER 93-09.

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