ML20245G771

Untraceable Molded Case Circuit Breakers Installed in Safety-Related Application, Safety Evaluation 265

ML20245G771
Person / Time
Site:	Prairie Island
Issue date:	04/28/1989
From:	Mccloskey S, Mendele D, Silverberg T NORTHERN STATES POWER CO.
To:
Shared Package
ML20245G738	List: ML20245G734 ML20245G771 ML20245L263 ML20245L289
References
265, NUDOCS 8906290258
Download: ML20245G771 (10)

Text

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[ ' ' PINGP 279, R:.v. 6 SAFETY EVALUATION "

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Rdtention: Lifa (NON-MODIFICATION)

SE No. M -

Addendum l.

Page 1 of l All Safety Evaluations for safety related changes and tests other than Modifications SHALL be submitted on this form.

TITLE: UNTRACEABLE MOLDED CASE CIRCUIT BREAKERS INSTALLED IN SAFETY RELATED APPLICATIO)

1. DESCRIPTION (Attach additional sheets as necessary)

SEE ATTACHED

2. YES l[l TECHNICAL SPECIFICATION / LICENSE AMENDMENT OR UNREVIEWED NO l_Tl SAFETY QUESTION

a. Amendment Request Transmittal DATE:

b. Authorizing Letter Received DATE:

PREPARED BY: W DATE: 9/Je/B9 REVIEWED BY: - " ~

3 / DATE: Y/2f/87

%.w, OPERATIONS COMMITTEE REVIEW:

DATE: 9/2r/f9 APPROVED BY: L M fedj h DATE: Mk,I!I9

/

. SUPTT ING & D PROT.

Technical Support Training Supervisor DATE:

COPY TO:

SAFETY AUDIT COMMITTEE REVIEW DATE:

(For Technical Specification / License Amendments or Unreviewed Safety Questions the SAC SHALL review the change prior to implementation).

IBM k $j62902see90620 s G ADOCK 050002B2 PNu m_m.______

Rsv. 6 (Beck) SE No. eUkdbdb

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INDEX to FUTURE NEEDS ')

YES l NO .

l . ,

I l ly l Drawing Revision Request ....................DRR #

l lf l New Drawing Request . . . . . . . . . . . . . . . . . .........NDR #

l L / l Drawing Deletion Request ....................DDR #

l Lx ! Construction File Submittal .................CFS.#

l 'x l Technical Manual Addition ...................TAF #

l l4 Technical Manual Deletion ...................TDF #

l lx Technical Manual Revision ...................TRF #

l j x New or Revised Specifications .............. SPEC #

l l x Technical Specifications Changes ........Amndmnt #

l l x l USAR / FSAR Changes ................... Submitted # ~

l Al 10CFR 50.59 Report Summary . . . . . . . . . . /. Submitted #  !

l xl Fire Hazards Analysis ................. Submitted # _

l <l Safe Shutdown Analysis ................ Submitted #

lxl Appendix R Submittals ................. Submitted #

l lA l NRC Submittal Review .................. Submitted #

l lA l Operating Procedures or Changes ......... Updated #

l l l ......................SP lac_l Surveillance #v l Maintenance Procedures .......................PM l t l ASME Section XI Program (ISI/IST) ..... Submitted 9 Procedures #

l .)

l lx l Data Files ..................................CFN #

l l x l Modification Training Request ......... Submitted #

l l xl Installation Procedures ...................WR/WRA

..................WR/WRA l l xl Pre-Op Test Procedures l l v l Operational Test ProcedQres ..............WR/WRA #

l l xl Purchase Orders ..............................PO l l xl Spare Parts ............................. Ordered #

l l yl HOLDS .......................................... #

l l rs[ Other Organizations ................... Contacted #

Name:

l l s l OTHER Future Needs:

The above applicable Future Needs have been completed and/or submitted. -

Responsible Engineer: d 2 Date: IWM  !

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d SAFETY EVALUATION- N Mb b UNTRACEABLE MOLDED CASE CIRCUIT BREAKERS INSTALLED IN SAFETY-RELATED APPLICATIONS

,f' TABLE OF CONTENTS

SUMMARY

AND CONCLUSIONS-DETAILED ANALYSIS OF'#12-INVERTER -

I. #12' Instrument Bus Inverter

'II. ' Traceability Search III. Installation and Work History DISPOSITION OF OTHER' UNTRACEABLE CIRCUIT BREAKERS

1. Unit Two-Circuit Breaker 226-33 l 'II. Unit One Pressurizer Heater Alternate Power Circuit Breaker

'III.' Unit One'#11 Battery Charger and Unit Two Feedwater Isolation Valve Circuit Breakers IV. Unit One-Steam' Generator Blowdown Motor Valve Circuit' Breaker

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PROCUREMENT OF REPLACEMENTS

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SUMMARY

AND CONCLUSIONS 1

The purpose of this evaluation is to : Justify continued operation of Prairie Island Units 1 and 2. ,

With the issue of NRC lE.Bulletin 88-10, concern was raised over the traceability of molded case circuit breakers (MCCBs) in-safety-related applications.- This bulletin instructed utilities to ensure MCCB's'with safety-related applications (whether procured safety-related or commercial grade) could be properly traced to the circuit breaker manufacturer (CBM). Prairie Island's letter to'the NRC dated March 31, 1989, identified six MCCBs. installed in safety-related applications not properly traceable to the CBM. This document details Prairie Island's disposition of these untraceable MCCBs.

In summary, of the six breakers, two have been replaced with traceable Ch\ 1 MCCBs, one has been evaluated as in a non-safety related application, one has been removed from use during plant operation by procedural control tags, one was replaced previously by a used breaker addressed by safety evaluation SE #252, and one has been analyzed to ensure that its failure would not affect the safety of the plant. A detailed analysis of this last breaker

(#12 Instrument Bus Inverter) is outlined below.

As is shown below, failure of the #12 Instrument Bus Inverter AC output breaker will not impact the safety function of the instrument power system it supplies. Due to the integral static transfer switch, should the breaker open prematurely or experience a downstream fault, power will shift to the alternate source without loss of instrumentation. This equipment has been proven by Prairie Island operational experience during instrument power system transients. Therefore, the six untraceable MCCBs do not create the possibility for an accident or malfunction of a different type than evaluated previously in the USAR or any subsequent commitments.

They do not increase the probability of occurrence of an accident or malfunction of equipment important to safety previously analyzed in the USAR or subsequent commitments.

They do not increase the consequences of any accident or malfunction of equipment important to safety previously analyzed

'in tbe USAR or subsequent commitments. <

They do not reduce the margin of safety as defined in the basis for any Technical Specification.

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ANALYSIS OF 12 INVERTER There are many mechanisms that can cause a breaker to fail. This l evaluation does not examine how a breaker fails, but looks at the  !

f l effects of a failed breaker. There are basically two effects from a failed breaker: .

1) It opens prematurely (no electrical fault downstream of breaker)

2) It opens late or not at all (fault downstream of breaker or l it is the source of the fault)

If it opens prematurely, the individual load is lost. If it is delayed, it is assumed that the upstream breaker is actuated. This causes the inverter to be de-energized.

If the fault is located internal to the breaker, then the effect is the same as the case where the fault is downstream of the breaker and the breaker does not open on a fault.

The instrumentation inverter is actually an uninterruptable power supply whose output is fed to a Static Transfer Switch (see Figure 1). If the circuit breaker opens prematurely, the Static Transfer Switch automatically transfers the load to the alternate 120VAC source which is generated from the 480VAC source that supplies the inverter, through an alternate AC source breaker.

This operation is completely automatic. An annunciator will notify operators that the inverter has been bypassed, either automatically, indicating inverter trouble, or manually when the unit is being tested or maintained. This prevents any breaker malfunction from going unnoticed.

Should a fault occur and the breaker fail to open, the upstream breaker (CBl) will open and cause the static transfer switch to switch as before.

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Pega 5 j In the unlikely occurrence that the entire #12 inverter is lost due to a failure of the CB2 breaker, plant safety will not be affected. This is because the inverter provides power to only one of four plant instrumentation channels (channel A). Technical Specification 3.5 allows continuous operation of the plant with the remaining three channels (maintaining a degree of redundancy of two). Thus, plant safety will not be diminished by loss of the inverter. Further, as Figure 2 shows, an alternate power supply to the #12 inverter loads is possible by manual alignment of I power to panel 112 from panel 117 (permitted by tech. specification 3.7), thus restoring the instrumentation.

In the extremely unlikely occurrence of the concurrent malfunction of the #12 inverter output breaker and a loss of all AC power, plant safety would still be assured, since this is essentially the same scenario as loss of the inverter. Again, technical specification 3.5 allows operation of the plant with the three remaining instrumentation panels.

In the summary, the following possible occurrences and the safety analysis are:

OCCURRENCE SAFETY ANALYSIS SAFETY CONCERN Breaker opens prematurely Inverter power switches NO to alternate Breaker fails to open Upstream breaker provides N0 on fault protection Breaker causes entire Operation without one NO inverter panel failure channel permitted by

. Technical Specification, manual transfer to

' alternate power (per tech. spec. 3.7)

Breaker failure prevents Operation without one NO transfer during loss of channel permitted by all AC technical specification 3.5 Thus, the failure of the #12 inverter output breaker will not adversely impact the ability to safely operate the plant. l l

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TRACEABILITY SEARCH )

1 The #12 inverter AC voltage output breaker is a Westinghouse model l QC 2100 MCCB. The only independent documentation indicating the ]

source of the MCCB is a packing list, recording the shipment of 1 the breaker from We tinghouse Electric Supply Co. in St. Paul, MN. 1 This is insufficient documentation to completely verify traceability per the requirements of the 88-10 bulletin. However, there is no evidence at this time that this breaker was not a I

l fully operative and legitimate MCCB at the time of delivery.

l INSTALLATION AND WORK HISTORY Upon installation of this MCCB in September of 1986, a thorough test for operability and proper tripping was performed. Since that time no abnormal occurrences are known to be associated with this circuit breaker.

DISPOSITION OF OTHER UNTRACEABLE CIRCUIT BREAKERS I. Unit Two Circuit Breaker 226-33, G.E. Model THED 136015 WL (breaker to motor for valve MV-32235-RHR Letdown Valve to CVCS)

Since establishing traceability or replacement with a qualified spare was not possible at this time, this breaker was procedurally removed from service during plant operation.

This motor valve is required to provide a pressure source for the purification function when the plant is at low pressure during startup and shutdown. Efforts are ongoing to procure a qualified spare to replace this circuit breaker.

II. Unit One Pressurizer Heater Alternate Power - Bus 180/MCC 1R1 G.E. Model THED 136070 WL.

Further research indicated that this circuit breaker does not have a safety-related function. No further action or analysis is necessary.

III. Unit One Battery Charger and Unit Two Feedwater Isolation Valve Motor Circuit Breakers - G.E. Model THED 136050 WL.

For the Unit Two FW isolation valve, a qualified, traceable replacement circuit breaker was on hand at Prairie Island for this application. Breaker replacement for the feedwater isolation valve motor circuit breaker has occurred (WR #M3292).

No further action or analysis is required.

Further research indicated that the Unit One #11 Battery Charger breaker has been replaced by a THEF model evaluated previously in Safety Evaluation #252, dated 11/11/88. No further action is required.

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IV. Unit One Steam Generator Blowdown Motor Valve G.E. Model THED 136030 WL Circuit Breaker.

A qualified, traceable replacement circuit breaker was on hand at. Prairie I,sland.. This breaker was replaced by the qualified spare (WR #N3609 EBQ) and no further actions or analysis is required.

PROCUREMENT OF REPLACEMENTS Negotiations are ongoing to procure fully qualified, traceable replacement circuit breakers for these applications. Once obtained, these circuit breakers will be installed as necessary to replace untraceable breakers as the plant operating schedule permits. Long lead times for these items make accurate prediction of replacement dates impossible.

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