United States Nuclear Regulatory Commission - Protecting People and the Environment

ACCESSION #: 9906230324


06/13/1999 U.S. Nuclear Regulatory Commission Operations Center Event Report Page 1
General Information or Other (PAR) Event 35844
Rep Org: ROSEMOUNT NUCLEAR INSTRUMENTS, INC. Notification Date / Time: 06/18/1999 13:02 (EDT)
Supplier: ROSEMOUNT NUCLEAR INSTRUMENTS, INC Event Date / Time: 06/18/1999 (CDT)
Last Modification: 06/18/1999
Region: 3 Docket #:
City: EDEN PRAIRIE Agreement State: No
County: License #:
State: MN
NRC Notified by: GERRY HANSON Notifications: VERN HODGE (via fax) NRR
HQ Ops Officer: BOB STRANSKY
Emergency Class: NON EMERGENCY
10 CFR Section: 21.21 UNSPECIFIED PARAGRAPH
10 CFR PART 21 REPORT REGARDING POTENTIAL NEED FOR CAPACITOR REPLACEMENT IN SPECIFIC TRIP/CALIBRATION SYSTEMS

The following is text of a letter submitted to the NRC Operations Center via facsimile:

"The purpose of this letter is to inform you that a specific capacitor C25 used in Rosemount Trip/Calibration Systems may require replacement. This affects all Rosemount Model 510DU Trip Units (obsolete since 1987) and certain Rosemount Model 710DU Trip Units.

"Prior to 1987, there were 10 confirmed random failures of C25 capacitors used in slave and master trip unit circuit boards. In 1987, a number of tests were run on sample capacitors in an attempt to duplicate the failure modes. It was found that unless the capacitors were exposed to temperatures and voltages in excess of normal operating conditions, no failures were induced. However, introduction of a contaminant such as moisture could possibly cause this type of failure. As a precautionary measure, a component change was instituted on the C25 capacitor beginning with manufacturer date code 8630. This change featured an enhanced moisture seal. No confirmed failures of the post 8630 date code C25 capacitor have been identified. However, Rosemount Nuclear Instruments. Inc. is sending this letter to affected utilities to remind users that the model 710 and 510 trip units with pre-8630 date code C25 capacitors could be susceptible to this condition. Failure of the C25 capacitor can cause a low resistance condition between the power supply input and chassis ground. This low resistance can allow overcurrent conditions to cause failure of the affected unit.

"A letter [enclosed in facsimile] was issued by Rosemount Nuclear Instruments Inc. to the Scram Frequency Reduction (SFR) Committee of the BWR Owners' Group in response to a BWROG request for information [enclosed in facsimile], documenting the change which had been made in 1987. Since that time, there have been five additional confirmed C25 failures and fourteen additional failures possibly related to the C25 capacitor. Again, all of these failures occurred in units with C25 capacitors that had date codes of pre-8630. The total number of model 510 and 710 trip units shipped with the pre-8630 date code capacitors was 18,164. We believe that recent failures may warrant further examination of your 510DU/710DU systems to determine whether replacement of the pre-8630 date code capacitors is warranted."

Rosemount Nuclear Instruments Rosemount Nuclear Instruments. Inc.
12001 Technology Drive
Eden Prairie, MN 55344 USA
Tel 1(612)820-8252
Fax 1(612)828-8280
18 June 1999
To: Rosemount Model 510 and 710 Master Trip Unit Users
From: Rosemount Nuclear Instruments Inc. Marketing Group
Subject: Update on pre 1987 C25 capacitor performance
References:
1. Rosemount Letter dated 20 October 1987 to BWROG-SFR
2. BWROG-8756 dated 8 October 1987

The purpose of this letter is to inform you that a specific capacitor C25 used in Rosemount Trip/Calibration Systems may require replacement. This affects all Rosemount Model 510DU Trip Units (obsolete since 1987) and certain Rosemount Model 710DU Trip Units.

Prior to 1987, there were 10 confirmed random failures of C25 capacitors used in slave and master trip unit circuit boards. In 1987, a number of tests were run on sample capacitors in an attempt to duplicate the failure modes. It was found that unless the capacitors were exposed to temperatures and voltages in excess of normal operating conditions. no failures were induced. However, introduction of a contaminant such as moisture could possibly cause this type of failure. As a precautionary Measure, a component change was instituted on the C-25 capacitor beginning with manufacturer date code 8630. This change featured an enhanced moisture seal. No confirmed failures of the post 8630 date code C25 capacitor have been identified. However, Rosemount Nuclear Instruments, Inc. is sending this letter to affected utilities to remind users that the model 710 and 510 trip units with pre-8630 date code C25 capacitors could be susceptible to this condition. Failure of the C25 capacitor can cause a low resistance condition between the power supply input and chassis ground. This low resistance can allow over-current conditions to cause failure of the affected unit.

A letter (reference 1) was issued by Rosemount Nuclear Instruments Inc. to the Scram Frequency Reduction (SFR) Committee of the BWR Owners' Group in response to a BWROG request for information (reference 2), documenting the change which had been made in 1987. Since that time, there have been 5 additional confirmed C25 failures and fourteen additional failures possibly related to the C25 capacitor. Again, all of these failures occurred in units with C25 capacitors that had date codes of pre-8630. The total number of model 510 and 710 trip units shipped with the pre-8630 date code capacitors was 18,164. We believe that recent failures may warrant further examination of your 510DU/710DU systems to determine whether replacement of the pre-8630 date code capacitors is warranted.

In anticipation that affected utilities may wish to rework existing 510/710 units, Rosemount Nuclear Instruments, Inc. is preparing a repair/rework procedure to be made available at no charge.

FISHER-ROSEMOUNT

If you have any further questions, please contact any of the following individuals:

Jerry Edwards at (612) 828-3951
Gerard Hanson at (612) 828-3480
Mike Dougherty at (612) 828-5626.

Sincerely,

Gerard Hanson
Senior Marketing Engineer
Rosemount Nuclear Instruments, Inc.

FISHER-ROSEMOUNT

Reference 1
Rosemount Letter dated 20 October 1987
To BWROG-SFR

ROSEMOUNT INC.
12001 Technology Drive
Eden Prairie, MN 55344 U.S.A.
(612) 941-5560
TWX: 4310012 or 4310024
FAX: (612) 628-3088

October 20, 1987

R. E. Coon, Chairman
Rosemount

BWR Owner's Group SFR
c/o Commonwealth Edison co.
Room 34 FN East
P.O. Box 767
Chicago, IL

Reference: BWROG-8756

Dear Mr. Coon,

It was a pleasure hearing from you in the above referenced letter. Rosemount is very interested in working with your group on any concerns that may arise. In this case Rosemount is aware of the issue concerning the C25 capacitor which our internal returned goods tracking system pointed out.

After being raised as a concern Rosemount completed extensive evaluation testing earlier this year and concluded the following:

1. There is no [illegible print] relationship on the capacitors in question.
2. We have been unable to duplicate the failure mode without subjecting the capacitors to environmental parameters such as voltages and temperatures in excess of what they should see in normal operation.
3. Introduction of a contaminant such as moisture into the capacitor along with the excess environmental parameters could cause this type of failure.

We have instituted a component change to an upgraded component. This new component incorporates an enhanced seal against contamination and thus is more reliable. This change was instituted in May 1987. No reports of failures of the new capacitors have been reported.

We are very interested in establishing communication between Rosemount and BWR Owners Group on any topics of mutual concern. Please feel free to or have any of your group call me at (612) 828-3285 with questions or concerns.

Sincerely,

Jane Sandstrom
Sr. Marketing Engineer

Reference 2

BWROG-8756 dated 8 October 1987

Robert F. Janecek, Chairman
BWR OWNERS' GROUP
(312) 294-3971

c/o COMMONWEALTH EDISON COMPANY o Rm 34 FN East o P.O. Box 767 o Chicago, IL 60690

BWROG-8756

October 8, 1987

Ms. Jane Sandstrom
Sr. Marketing Engineer
Rosemount, Inc.
12001 Technology Drive
Eden Prairie, MN 55344

Dear Ms. Sandstrom;

The Boiling Water-Reactor Owners' Group (BWROG) Scram Frequency Reduction (SFR) Maintenance Committee is composed of Maintenance Supervisors from 23 of the domestic BWR utilities. The I&C section of this Committee is very active in pursuing the actions needed by the utilities to reduce their number of scrams.

A number of the BWR utilities have experienced capacitor failures (shorts) on the Model 710 analog trip card and a few of these utilities have experienced fires as a result of these capacitor failures (specifically, the power input capacitor, C25). These capacitor failures are viewed as a generic maintenance problem that needs your assistance to help reduce the scram frequency of the plant. We would appreciate your consideration of this matter. Specifically, we are interested in:

  • Is this an issue which has already been identified by Rosemount, and, if so, do you have any proposed solutions for it.

  • Are you willing to work with the BWROG on this issue.

Suggestions made by Committee members are.:

1. Upgrade the capacitor(s) in question.
a. Use a higher working voltage rating; i.e., >/= 100 VDC
b. Use a different, more reliable capacitor
2. Alter the circuit to protect the circuit from a potential fire when this capacitor fails (shorts).
3. Redesign the circuit to eliminate the potential for a fire as a result of a component failure.


BWROG-8756

October 8, 1987

Page 2

Our Committee has a large number of active participants and provides an excellent forum to address this topic. If I can be of further assistance, please call me at (315) 349-2427 or call our Program Manager, Rick Hill (GE), at (408) 925-5388.

Thanking you in advance for your effort.

Sincerely,

R. E. Coon, Chairman
BWROG SFR
Maintenance Committee

/na

cc: R. F. Janecek, BWROG Chairman
D. N. Grace, BWROG Vice Chairman
BWROG Primary Representatives
H. Wyckoff, EPRI
W. S. Green, INPO
H. Huston, NUMARC


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