ML18058B902

Part 21 Rept Re Potential Defect in Vicor Corp mini-mod Dc/ DC Converter Modules.Deficiency Identified During Failure Analysis of Subj Modules While in Svc at Palisades in Apr 1993.Affected Dc/Dc Converter Modules at Plant Replaced

ML18058B902
Person / Time
Site:	Palisades
Issue date:	07/01/1993
From:	Toelle S ASEA BROWN BOVERI, INC.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
REF-PT21-93 LD-93-107, NUDOCS 9307070324
Download: ML18058B902 (7)

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July 1, 1993 LD-93-107 Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555

Subject:

10 CFR Part 21 Report on Vicor Corporation Mini-Mod DC/DC Converter Modules

Dear Sir:

Pursuant to the requirements of 10 CFR Part 21, the purpose of this letter is to notify the Nuclear Regulatory Commission of a potential defect in certain DC/DC Converter modules manufactured by Vicor Corporation during 1991 and supplied by ABB Combustion Engineering (ABB-CE) to Consumers Power Company's Palisades Plant in the Reactor Protective System (RPS) power supply drawers.

Certain DC/DC Converter modules manufactured by Vicor Corporation during a 4-week period in 1991 contained a capacitor which was deficient in being unusually susceptible to in-service failure.

Several models of DC/DC Converters are used in the Palisades Plant Reactor Protective system, and in-service failures were observed in one model (two occurrences). As a result of an evaluation, it was concluded that a similar failure in a different model converter might disable a single channel of the four logic channels of the reactor trip system for a particular trip *function. Should a simultaneous, similar failure of this converter for the same trip function occur in three of the.four channels, and should none of the failures be detected by routin~ testing, the Reactor Protective System would be degraded from its design bases. Hence it was concluded that a potential "defect" as defined in 10 CFR Part 21 existed. The component which contains this potential defect is the Vicor Mini-Mod DC/DC Converter module, model VI-J62-IY, in the RPS

+/-15vdc Bistable Power Supply.

The deficient capacitor was identified during failure analysis of two Vicor Mini-Mod DC/DC Converter modules, model VI-J5L-IX, which failed in the RPS +28vdc Matrix Power Supply while in service at the Palisades Plant in April 1993. The failu~e analysis indicates that an electrical short in a surface mounted ceramic capacitor caused the DC/DC Converter modules to fail. The two failed DC/DC Converters were manufactured during the twenty-third week of 1991 (date code 9123).

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ABB Combustion Engineering Nuclear Power ;ff!(

1000 Prospect Hill Road Telephone (203) 688-1911 Post Office Box 500 Fax (203) 285-9512 Windsor, Connecticut 06095-0500 Telex 99297 COMBEN WSOR

U.S. Nuclear Regu~ry Commission LD-93-107

• Jul¥ 1, 1993 Page 2 Vicor has concluded that the failures are a result of a batch lot problem with the capacitor potentially affecting DC/DC - Converter-modules with date codes between, and including, 9121 and 9124. A review of Vicor records identified two non-nuclear customers that have experienced an additional six failures of the same capacitor in modules manufactured with a date code of 9123.

This same type and model capacitor is used throughout the VI-JOO Mini-Mod family of DC/DC Converters, which potentially affects two other DC/DC Converter modules used in the Palisades RPS power supplies. The additional DC/DC Converter modules affected. are models VI-J61-IZ, used in the RPS +12vdc Test Power Supply, and VI-J62-IY, used in the RPS +/-15vdc Bistable Power Supply. While there*

have not been any identified VI-J61-IZ or VI-J62-IY module failures to date in the Palisades RPS, there is insufficient information to conclusively limit the problem to the +28vdc power supplies.

Arizona Public Service Company's Palo Verde Nuclear Generating Station Units 1, 2, and 3 use Vicor power supplies in the Diverse.

Auxilic;try Feedwater Actuation System. These power supplies, however, are not the same type or model and are therefore not expected to be subject to the same failure mechanism. Vicor has also verified that the capacitor used in the Palisades power supply modules is not used in the Palo Verde power supplies.

Because of the potential operational problems associated with the deficient DC/DC Converters, ABB-CE began and, on June 13, 1993, completed the replacement of all affected DC/DC Converter* modules in the Palisades Plant.

The enclosure summarizes the information ~vailable to us at this time. If you have any questions, please contact me at (203) 285-5213.

Very truly yours, s

s.

fJ.-dL A. Toelle Manager Nuclear Licensing llj/lw

Enclosure:

As Stated

En~sure to LD-93-107 W Page 1 of 5*

-- - - (i) Name and address of the individua;L or individuals informing the comniission*. - -*------= .:-

Steven A. Toelle Manager, Nuclear Licensing AB~ Combustion Engineering Nuclear Services 1000 Prospect Hill Road Windsor, .

CT 06095 (ii) Identi~ication of the facility, the activity, or the basic component supplied for such facility or such activity within the_ United States which fafls to comply or contains

• a defect *.

Vicor Coiporation'Mini-Mod DC/DC c6nverter modules, model VI-J62-IY with date codes between, and including, 9l21 and 9124/ used in the +/-15vdc Bistable Power Supplies in the Palisades Plant Reactor Protective System power* supply drawer.

,(iii) -Identification of the firm const~ucting the fac;ility ~r supplying the basic compo~ent which fails* to comply or c6ntains a defect.

C-E purchased the ~ubject component from:

Vicor Corporat~on 23 Frontage-Road Andover, MA 01810 (iv) Nature of .the .defect or failure to comply and the safety hazard which is created or could.-be created by such defect or failure to comply. *

• The defect involves a potential failure mode of the Vicor model VI-J62-IY DC/DC Converter module as described below.

The deficiency in certain Vicor DC/DC Converter modules was*

identified during the failure analysis of two Vicor DC/DC Converter-modules, model VI-J5L-IX, which failed while in service at the Palisades Plant in April 1993. The failure analysis indiqates that an electrical short in a surf ace mounted ceramtc C55 capacitor caused the DC/DC Converter module to fail. The 'C55 capacitor is an integral component in the module's rectification system that provides the

E~osure to LD-93-107

,, Page 2 of 5 power supply voltage for the LM358 error amplifier. The C55 failure removed the power supply reference voltage from the error amplifier, which resulted in a high unregulated output voltage level from the DC/DC Converter modules that caused both of them to fail.

Vicor's failure analysis revealed that the capacitor short.ed due to cracks on its surf ace. Vicor has concluded that the failures are a result of a batch lot problem with the capacitor potentially affecting DC/DC Converter modules with date codes between, and inc"luding, 9121 and 9124.

During their analysis, Vicor identified that poor soldering or insufficient application of the protective coating over the component prior to encapsulation may have also contributed to the failure of the capacitor.

The two failed DC/DC Converters were manufactured during the twenty-third week of 1991 (date code 9123). A review of Vicor records identified two other non-nuclear customers that together have experienced a total of six C55 capacitor failures in the .DC/DC Converter modules manufactured with a date code of 9123.

This same type and model capacitor is used throughout the VI-JOO Mini-Mod family of DC/DC Converters which affects two othe~ DC/DC Converter modules used in the Palisades RPS power supplies. The additional DC/DC Converter modules affected are models VI-J61-IZ and VI-J62-IY. However, there have not been any identified VI-J61-IZ or VI-J62-IY

• module failures to date in the Palisades RPS.

Model VI-J5L-IX DC/DC Converter (two failures observed)

The Vicor DC/DC Converter module, model VI-J5L-IX, is used in the RPS +28vdc Matrix Power Supply (C-E part number 43555). It provides power to maintain the Matrix Trip Relay coils energized in the 2/4 Coincidence Logic Matrix.

The relay coil remains energized when no 2/4 Coincidence Logic Matrix trip condition exists and the relay coil is de-energized, interrupting the path, when a 2/4 trip condition occurs. A maximum unregulated output voltage of

+56vdc could result from the failure of the C55 capacitor in this system. A voltage of this magnitude would not inhibit a valid trip condition because the Matrix Power Supply voltage does not control the 2/4 Coincidence Logic Matrix channel trip relays. However, a voltage of this magnitude may cause a plant trip if the high voltage is allowed to exist until it burns out the Matrix Trip Relay coils and they open. The two failures of this DC/DC Converter module at Palisades did not result in plant trips because the condition was detected before the coils burned out.

En~sure to LD-93-107 Page 3 of 5 Model VI~J62-IY DC/DC Converter (no failures observed)

The Vicor DC/DC Converter module, model VI-J62-IY, is used in each of the individual RPS +/-15vdc Bistable Power Supplies (C-E part number 43553), twelve (12) per channel.

It provides separate logic power to each of the twelve (12)

Bistable Trip Modules. The Bistable Trip Module controls the 2/4 Coincidence Logic Matrix channel trip relays, which are internal to each trip module. The channel trip relays are de-energized opening the associated 2/4 Coincidence Logic Matrix contacts when a channel trip condition exists to interrupt the Matrix Trip Relay coil power path. . A maximum unregulated output voltage of +28vdc could result from the failure of the* C55 capacitor in this system. A voltage of this magnitude would cause considerable damage to the Bistable Trip Module ;most likely resulting in a channel trip for that function in the respective 2/4 Coincidence Logic Matrices. There is a potential for a voltage of this magnitude to damage its associated Bistable Trip Module and mai~tain the channel trip relays in an energized condition. This would inhibit a trip in only one trip channel. However, a *single +/-15vdc Bistable Power Supply failure would not prevent the RPS from performing its protective function because each Bistable Trip Module is powered ,from an independent +/-15vdc Bistable Power Supply. Should a simultaneous, similar failure of this converter for the same trip function occur in three of the four channels, and should none of the failures be detected by routine testing, the Reactor Protective System would be degraded from its design bases.

Model VI-J61-IZ DC/DC Converter (no failures observed)

The Vicor DC/DC Converter module, model VI-J61-IZ, is used in the RPS +12vdc Test Power Supply (C-E part number 43554). It provides test signals to one Bistable Trip Unit at a time during RPS maintena~ce or surveillance activities. The Test Power Supply is isolated from the Bistable Trip Units by the Meter Output Select Switch located on the RPS Power Supply Drawer Assembly. A maximum unregulated output voltage of +28vdc could result from the failure of the C55 capacitor in this system. A voltage of this magnitude would not inhibit a valid trip condition during maintenance or surveillance as the Bistable under test would be placed in Trip Channel Bypass.

(v) The date on which the information of such defect or failure to comply was obtained.

Initial evaluation of the deficiency was begun on May 12, 1993. The deficiency was assessed to be limited to the

Enami.sure to LD-93-107 W Page 4 of 5 model VI-J5L--IX module used in the +28vdc Matrix Power Supply which was evaluated not to be a safety issue; New

• information became available to ABB-CE on June 2, 1993, which extended the potential deficiency to two other models of DC/DC converters used in the Palisades RPS.

(vi) In the case of a basic component which contains a defect or fails to comply, the number and location of all such components in use at, supplied for, or being supplied for one or more facilities or activities subject to the regulations in this part.

The following Vicor model VI-J62-IY DC/DC Converter modules with date codes between, and including 9121 and 9124 were in the Palisades RPS Power Supply drawers and spare inventory.

Channel Module Type A ~ ~ .Q Spares Total VI-J62-I~ (+/-15v~c) 19 11 15 4 0 49 For information, the locations of the other model modules with the same date codes were:.

VI-J5L-IX (+28vdc) 3 2 3 3 1 12 VI-J61-IZ (+12vdc) 1 0 1 1 0' 3 Arizona Public Service Company's Palo Verde Nuclear Generating Station Units 1, 2, and 3 also use Vicor power supplies in the Diverse Auxiliary Feedwater Actuation System. These power supplies, however, are not the same type or model and are therefore not expected to be subject to the same failure mechanism. Vicor has also verified that the capacitor used in the Palisades power supply modules is not used in the Palo Verde power supplies.

(vii) The corrective action which has been, is being, or will be taken; the name of the individual or organization responsible for the action; and the length of time that bas been or will be taken to complete the action.

On June 13, 1993, ABB-CE completed the replacement of all affected DC/DC Converter modules supplied to the Palisades Plant.

. E~sure to LD-93-107

' Page 5 of 5 (viii) Any advise related to the defect or failure to comply about the facility, activity, or basic component that has been, is being, or will be given to purchasers or licensees.

All potentially affected DC/DC Converter modules supplied to the Palisades Plant have been replaced.