Information Notice No. 95-10, Supplement 2:Potential for Loss of Automatic Engineered Safety Features Actuation

                                 UNITED STATES
                         NUCLEAR REGULATORY COMMISSION
                            WASHINGTON, D.C.  20555

                                August 11, 1995

                                             ENGINEERED SAFETY FEATURES        


All holders of operating licenses or construction permits for nuclear power


The U.S. Nuclear Regulatory Commission (NRC) is issuing this information
notice supplement to alert addressees to the changes that the licensee for the
Salem nuclear power plant has made to surveillance and maintenance practices
for the solid-state protection system (SSPS) logic matrix power supplies. 
These modifications were made in response to problems the licensee encountered
while attempting to alter an aspect of the design of the SSPS for both units. 
The modifications were being made to correct a design deficiency that had the
potential for causing the loss of the automatic actuation function of the
engineered safety features (ESF) as a result of electrical faults in non-Class
1E input signals.  It is expected that recipients will review the information
for applicability to their own facilities and will 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.


Information Notice 95-10 informed licensees of a condition that could lead to
the failure of one or both trains of the SSPS during a main steamline break in
the turbine building or during a seismic event.  The conditions were
originally reported by the licensees for the Diablo Canyon and Salem
facilities and subsequently by the licensees for the J. M. Farley, North Anna,
Sequoyah, Shearon Harris, V. C. Summer, and Watts Bar facilities.  

While attempting to correct the problematic design, the licensee for the Salem
facility encountered difficulties.  The source range high voltage block signal
was inadvertently deenergized and several SSPS power supply anomalies occurred
while performing the modification and during subsequent power supply testing
and evaluation.  Supplement 1 to Information Notice 95-10 gave details of
these difficulties.  

Description of Circumstances

On the basis of its assessment of the difficulties encountered at Salem, the
licensee has revised the maintenance and surveillance requirements for the 

9508040192.                                                            IN 95-10, Supp. 2
                                                            August 11, 1995
                                                            Page 2 of 3

SSPS power supplies.  The revised requirements incorporate vendor
recommendations and lessons learned during the recent modification and testing
of the SSPS.  The licensee is implementing the following preventive
maintenance activities to enhance the performance of the SSPS and similar
power supplies:

1.    Refurbish the SSPS Train A and B 48-V dc and 15-V dc power supplies by   
      replacing such age sensitive components as electrolytic capacitors and   
      semiconductors, as necessary, every 72 months.  Refurbishment is to
      consist of inspection of wiring, inspection of connectors (including
      solder joints), and cleaning as required.  In addition, the 48-V dc and
      15-V dc power supplies for the control board demultiplexor and the 48-V
      dc and 15-V dc power supplies for the computer demultiplexor were
      incorporated into the enhanced preventive maintenance program.

2.    Every 36 months, bench tests of all SSPS power supplies are to include   
      output power ripple checks, load tests from zero to 110 percent of full
      load, and overcurrent and overvoltage trip tests.

3.    With SSPS supplies normally loaded, perform output power ripple checks
      on logic cabinet rear terminations every 18 months in conjunction with   
      existing surveillance tests.

4.    Periodically energize replacement SSPS power supplies in inventory to    
      ensure operability.

The licensee is also reviewing the design of the SSPS general warning alarm
for possible modification.  The licensee stated that the general warning alarm
will not be received if the failure mode of the power supply is such that it
will not hold load but still maintain an acceptable in situ voltage.  This is
because the general warning circuit design is intended to initiate a general
warning alarm only upon a total loss of a power.

In addition, Westinghouse has informed its customers that resistor R28 in the
48-V dc SSPS power supply (Westinghouse part No. 2374A07G01) is undersized and
may overheat.  Westinghouse recommended changing the value of resistor R28
from 1.8K ohm, 0.5 watt +/- 5%, to 18K ohm, 0.5 watt +/- 5%.  This change is
also applicable to the control board demultiplexor and computer demultiplexor
48-V dc power supplies. 
.                                                            IN 95-10, Supp. 2
                                                            August 11, 1995
                                                            Page 3 of 3

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 (NRR) project manager.

                                    /S/'D BY DMCRUTCHFIELD

                                    Dennis M. Crutchfield, Director
                                    Division of Reactor Program Management
                                    Office of Nuclear Reactor Regulation

Technical contacts:  Cliff Doutt, NRR
                     (301) 415-2847

                     E. Nick Fields, NRR
                     (301) 415-1173

List of Recently Issued NRC Information Notices


Page Last Reviewed/Updated Thursday, March 25, 2021