Information Notice No. 94-04: Digital Integrated Circuit Sockets with Intermittent Contact

                                 UNITED STATES
                         NUCLEAR REGULATORY COMMISSION
                     OFFICE OF NUCLEAR REACTOR REGULATION
                            WASHINGTON, D.C.  20555

                               January 14, 1994


NRC INFORMATION NOTICE 94-04:  DIGITAL INTEGRATED CIRCUIT SOCKETS WITH
                               INTERMITTENT CONTACT


Addressees

All NRC licensees except licensed operators.

Purpose

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information
notice to alert addressees to a potential problem involving socket connectors
used for digital integrated circuits manufactured by Augat, Inc.   It is
expected that recipients will review the information for applicability to
their facilities and consider actions, as appropriate, to avoid similar
problems.  However, suggestions contained in this information notice are not
NRC requirements; therefore, no specific action or written response is
required.

Description of Circumstances

During April 1993, at the D. C. Cook Nuclear Plant, the licensee observed
intermittent failures of various process control units during testing.  The
internal monitoring system for a control unit would detect a problem and shut
the instrument down (i.e., cause its outputs to reduce to zero and remain in
an audible alarm state).  The NRC learned about this recurrent problem during
an analog-to-digital process instrumentation inspection at this site (NRC
Inspection Report 50-315/93-18; 50-316/93-18).  Subsequent to a July 1, 1993,
meeting between the licensee and the control unit manufacturer, Asea Brown
Boveri-Kent-Taylor (ABB-Kent-Taylor), the problem was isolated to the sockets
for the integrated circuits.  Deficiencies in the sockets resulted in
intermittent contacts between the integrated circuits and the sockets, thus
interrupting signal processing.  These sockets, which are manufactured by
Augat, Inc., are made in various grades and one of the lower grade sockets was
being used.  Augat, Inc. is an international supplier of interconnection
systems for the computer, automotive, and telecommunications industries.
These sockets were produced in large numbers and some may be in use in nuclear
as well as non-nuclear applications where their failure could either initiate
a transient or interfere with response to a transient.

The process control units (Taylor MOD 30) were built as commercial-grade
equipment in 1989 but were not delivered to the licensee until 1992, and were
not shipped to the site until the Spring of 1993.  The original purchase order
included both safety-related units and nonsafety-related units.  Asea Brown
Boveri-Combustion Engineering (ABB-CE) was supposed to qualify the equipment

9401100143.

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designated for safety-related use before the safety-related equipment was
released and shipped to the D.C. Cook plant.  For reasons unrelated to the
socket deficiencies, the contract was amended to exclude safety-related
equipment.  However, the nonsafety-related equipment will be used in the AMSAC
[ATWS (anticipated transients without scram) Mitigation System Actuation
Circuitry].

The licensee informed ABB-CE of this potential generic product deficiency in
an August 20, 1993, letter.  Followup in September 1993 revealed that the
manufacturer believes it has not sold any Taylor MOD 30 instruments to nuclear
power plants for use in safety-related applications.

Discussion

In the D. C. Cook application, the sockets are located on an internal
component identified as a "digital board."  There are 7 sockets per digital
board; 5 of the sockets are 28-pin sockets and are being used for programmed
PROMs (Programmable Read Only Memories), one 20-pin socket is being used for a
programmed logic array integrated circuit, and one 40-pin socket is being used
for a single-chip microprocessor unit.  The 520 instruments contain a total of
more than 3500 sockets.

Subsequent discussions with the licensee concerning the generic nature of the
deficiency produced additional information.  The 20-, 28-, and 40-pin sockets
had the following respective Augat part numbers:  520-AG12D-ES, 528-AG12D-ES,
540-AG12D-ES.  The "ES" suffix indicates that a socket is an Economy Series
socket.  Augat, Inc. introduced this series in 1985 to provide a less
expensive version of its traditional machined contact.  The contact portion of
the ES socket is produced by a stamping process rather than by a machining
process.  The stamped ES sockets were first used in Taylor MOD 30 equipment in
1988.  In February 1991, the control unit manufacturer, ABB-Kent-Taylor,
changed back to the machined version after producing approximately 7,000-
10,000 instruments with the ES sockets.  Tests performed in July 1993
confirmed that the withdrawal force for the ES stamped contact sockets was
considerably less than for the machined contact sockets.  Both of these
sockets had a tin-lead inner contact.  The ES sockets are being replaced with
machined contact 520-AG12D, 528-AG12D, and 540-AG12D sockets.

Some Augat, Inc. ES sockets have exhibited a relatively high incidence of
intermittent failure.  The failure rate among the 256 Taylor MOD 30
instruments tested was determined to be approximately 15 percent through
July 1993.  It appears that the use of a tin-lead inner contact, the stamping
method of manufacture, and the length of time an instrument sits de-energized
may serve in combination to permit or create oxidation on the contacts.
However, the root cause of the intermittent contact between the integrated
circuit and its socket has not been determined.  ABB-Kent-Taylor believes that
the delay between shipment and construction, while the units sat de-energized,
may have been a contributing factor in the failure.  If this is the case,
instruments stored as spare parts (which would also be de-energized) could be
similarly affected..

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A recent design review of an analog-to-digital upgrade for the reactor
protection system at a foreign plant revealed that the integrated circuit
socket specified was the type discussed above; i.e., it was manufactured by
Augat, Inc. and was the ES type.  The contact design is being reevaluated.

This information notice requires no specific action or written response.  If
you have any questions about the information in this notice, please contact
one of the technical contacts listed below or the appropriate Office of
Nuclear Reactor Regulation project manager.

                                    /S/'D BY BKGRIMES

                                    Brian K. Grimes, Director
                                    Division of Operating Reactor Support
                                    Office of Nuclear Reactor Regulation

Technical contacts:  Edward R. Schweibinz, RIII
                     (708) 829-9712

                     Vern Hodge, NRR
                     (301) 504-1861

Attachment:
List of Recently Issued NRC Information