United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 92-77: Questionable Selection and Review To Determine Suitability of Electropneumatic Relays for Certain Applications

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

                               November 17, 1992


NRC INFORMATION NOTICE 92-77:  QUESTIONABLE SELECTION AND REVIEW TO DETERMINE  
                               SUITABILITY OF ELECTROPNEUMATIC RELAYS FOR 
                               CERTAIN APPLICATIONS


Addressees

All holders of operating licenses or construction permits for nuclear power
reactors.

Purpose

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information
notice to alert licensees to problems that could develop as a result of 
inadequate selection and review for the suitability of application of
electropneumatic relays in certain safety-related load sequencer applications.
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

On November 21, 1989, the NRC found a problem with the use of Amerace
Corporation (Amerace) Agastat commercial time-delay 7000 series relays by the
Carolina Power and Light Company (the licensee) in its load sequencer panels
at the H.B. Robinson Steam Electric Plant (Robinson).  The NRC documented its
findings in Inspection Report 50-261/89-25.  In an accident, these sequencers
provide electrical signals to connect emergency loads in steps to either the
offsite or onsite emergency power source.  The licensee assumed in the
accident analysis for Robinson that load blocks are energized within a +/- 2
second operating band.  The NRC inspectors reviewed the plant's previous
performance history for the Agastat relay applications and found that the
relays had failed to consistently meet the +/- 2 second operating band assumed
in Robinson's accident analysis.  The licensee subsequently determined that
the actual operating band could allow pump motor starts to unintentionally
overlap.  In an accident, this could result in the emergency bus voltage being
reduced below the setpoint of the degraded voltage relay, thereby interrupting
the connection of emergency loads to the preferred power source.  This concern
prompted the licensee to replace the 7000 series relays with Agastat solid
state DSC series digital timers.




9211100421.

                                                            IN 92-77
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                                                            Page 2 of 3


On July 29 - August 30, 1991, the NRC conducted an electrical distribution
system functional inspection (EDSFI) at the North Anna Power Station.  The NRC
found test results indicating the time-delay drift of certain Agastat Class 1E
qualified E7000 and commercial 7000 series relays in its EDG load sequencer
panels had been outside allowable parameters.  The NRC documented its findings
in Inspection Report 50-338, 339/91-17.  The North Anna technical
specifications require that the load sequencers be tested every 18 months and
specifies the allowed parameters of starting times of vital loads.  The
results of load sequencer time-delay tests conducted between March 1987 and
July 1991 indicated that numerous time-delay setpoints had drifted outside
their allowed technical specification values during the 18-month surveillance
interval.  The Virginia Electric and Power Company (the licensee) conducted an
engineering safety review to determine the effect of these time-delay
setpoints being outside their technical specification allowed values.  The
licensee determined that the loads could have been successfully sequenced and
that the EDG safety function would not have been adversely affected.  After
the inspection, the licensee submitted licensee event reports 50-339/92-04 and
50-338/92-05 in which it was reported that the time-delay setpoints of its EDG
load sequencers continued to drift.  The licensee committed to perform an
engineering evaluation to determine the cause of the timer setpoint drift, and
the long term resolution.

During an EDSFI on June 8 - July 10, 1992, at the Joseph M. Farley Nuclear
Plant (Farley), the inspection team noted numerous instances in which the EDG
load sequencers failed surveillance tests because of problems with the
application of Agastat E7000 series time-delay relays.  The NRC documented its
findings in Inspection Report 50-348, 364/92-17.  Farley replaced the relays
for the EDG load sequencers between late 1990 and early 1991 because the
relays were approaching their projected qualified end of life (10 years).  The
NRC inspectors found that the time-delay intervals prescribed by the Farley
technical specifications were not met in four of the first six EDG sequencer
tests performed after the relays were replaced.  Testing after the event
suggested a generic problem with using the Agastat relays in load sequencer
time-delay applications because the repeat accuracy tolerance of the relay was
equal to the setpoint drift tolerance as reflected in the technical
specifications.  Consequently, there was no margin for calibration error.

Discussion

The NRC staff reviewed the Amerace electropneumatic relay catalogs and found
that the Agastat Class 1E qualified E7000 series relays have a stated "repeat
accuracy at any fixed temperature of +/- 10% of setting," whereas, the Amerace
commercial grade relay catalog for Agastat 7000 series commercial grade relays
have a stated repeat accuracy range between +/- 5% and +/- 15%, based upon
relay configuration, time-delay duration, and the fixed temperature at
calibration.  Amerace stated that temperature changes in the panel may
influence time-delay drift..

                                                            IN 92-77
                                                            November 17, 1992
                                                            Page 3 of 3


If time-delay relays are outside the required technical specification
parameters, they could cause equipment to start early, simultaneously, or
late.  These conditions may cause the overloading of the EDGs, resulting in
emergency bus voltage and frequency to drop to the point where the loads may
be disconnected by undervoltage protection devices.  If load connection is
delayed, the emergency safety feature equipment may not operate within the
time assumed in the accident analysis.  Criterion III, "Design Control," of
Appendix B to Part 50 of Title 10 of the Code Of Federal Regulations, 
(10 CFR Part 50), states, in part, that "[m]easures shall also be established
for the selection and review for suitability of application of materials,
parts, equipment, and processes that are essential to the safety-related
functions of the structures, systems and components."

This information notice requires no specific action or written response.  If
you have any questions about this matter, please contact the technical contact
listed below or the appropriate Nuclear Reactor Regulation (NRR) project
manager.


                                       ORIGINAL SIGNED BY


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

Technical contact:  Lee A. Keller, Region II
                    (803) 345-5683

                    Joseph J. Petrosino, NRR
                    (301) 504-2979

Attachment:  
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