United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 97-69: Reactor Trip Breakers and Surveillance Testing of Auxiliary Contacts

                                 UNITED STATES
                         NUCLEAR REGULATORY COMMISSION
                     OFFICE OF NUCLEAR REACTOR REGULATION
                        WASHINGTON, D.C.  20555 - 0001

                              September 19, 1997


NRC INFORMATION NOTICE 97-69:  REACTOR TRIP BREAKERS AND SURVEILLANCE TESTING
                               OF AUXILIARY CONTACTS


Addressees  

All holders of operating licenses for pressurized water reactors (PWRs) except
those who have permanently ceased operations and have certified that fuel has
been permanently removed from the reactor vessel.

Purpose

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information
notice to alert addressees that three licensees have recently identified
potential problems regarding Westinghouse Type DB50 reactor trip breaker (RTB)
maintenance or surveillance testing or both.  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 September 19, 1996, with Sequoyah Unit 2 at 100 percent power, the Unit 2
"B" RTB was removed from service for routine preventive maintenance and was
replaced with a spare RTB.  After the preventive maintenance and the post-
maintenance surveillance testing was completed, the spare RTB was removed and
replaced by the refurbished RTB.  When the refurbished RTB was returned to
service, the control room operators reported an unanticipated annunciator.  An
investigation indicated a malfunction of the RTB auxiliary contacts. 
Subsequent inspection of the refurbished RTB by the licensee determined that
the linkage control to the auxiliary contacts had not been reconnected during
the breaker refurbishment activities.  As a result, the refurbished RTB had
been in service with the auxiliary contacts inoperable for approximately nine
hours, which exceeded the technical specifications limiting conditions for
operations (LCO) action time of six hours for the reactor trip system
interlock (P-4).  Inadequate post-maintenance testing permitted the RTB to be
returned to service with an inoperable P-4 interlock.  This was first reported
as an unresolved item in NRC Inspection Report (IR) 50-327/328-97-01
(Accession No. 9704010175) and later identified as a Severity Level IV
violation in IR 50-327/328-97-03 (Accession No. 9705190286).

On January 13, 1997, with Watts Bar Unit 1 operating in Mode 1 at 100 percent
power, the licensee determined that because of a misinterpretation of
technical specifications, the 


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surveillance testing requirements for the RTB auxiliary contacts, which
provide a turbine trip signal on reactor trip (P-4 interlock), were not being
performed.  On February 10, 1997, the licensee reported this in Licensee Event
Report (LER) 50-390/97-001, (Accession No. 9702180273).

On January 22, 1997, with Vogtle Unit 1 operating in Mode 1 at 100 percent
power, the licensee discovered that a portion of the RTB auxiliary contacts,
which produce the turbine trip signal on reactor trip (P-4 interlock), were
not being tested as required by technical specifications.  On February 20,
1997, the licensee reported this in LER 50-424/97-002 (Accession No.
9702240448).

Discussion

The Westinghouse Type DB50 RTB assembly has three auxiliary relays that are
mechanically connected to the breaker by linkages.  The relays are arranged in
a vertical stack.  The bottom relay is connected to the breaker by an inertia
latch linkage, with a separate linkage connecting the bottom relay to the two
upper relays.  

Bench inspection of the failed Sequoyah RTB revealed that the linkage
necessary to operate the two upper sets of auxiliary relays was not connected
which rendered the contacts associated with those two relays inoperable.  The
contacts provide a portion of the P-4 interlock.  With the reactor trip
breakers open, the interlock, among other things, causes a feedwater isolation
with low Tave and a turbine trip.  Before the refurbished RTB was installed,
the breaker had been opened and closed several times by maintenance personnel
who did not notice the disconnected linkage which was in a location that was
difficult to see.  Visual inspections of the refurbished RTB, performed with
the breaker in service, also did not reveal any discrepancies.   

The Westinghouse vendor manual contained instructions for RTB refurbishment,
including steps to test the auxiliary contacts and lubricate the linkages. 
The vendor instructions were written in sequence to first verify proper
auxiliary relay operation, then lubricate the inertia latch linkages using a
spray lubricant.  Since the use of the spray lubricant did not require
disassembly, no instructions for disassembly or reassembly were included in
the vendor procedure.  In addition, the contact verification steps, performed
before the lubrication process, were not repeated following the lubrication
steps.  The licensee's original maintenance procedure for RTB refurbishment
was prepared using these vendor recommended details and sequence.

In 1994 a problem with an inertia latch resulted in the failure of the RTB to
close on demand.  Investigation revealed that a loss of plating on the inertia
latch had subjected the parts to corrosion and had resulted in binding of the
latch linkage.  As a corrective action, the licensee revised their procedure
to add requirements to disassemble the breaker in order to inspect and
lubricate the inertia latch linkages.  At that time it was not recognized that
the linkage from the bottom relay to the two upper relays could become
disengaged when the adjacent linkage was removed for lubrication.  Therefore,
the steps necessary to verify proper .                                                            IN 97-69
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operation of the auxiliary contacts were left in the original sequence, i.e.,
they were performed before the disassembly of the linkage for lubrication. 
The procedure should have been revised to ensure proper operation of the
auxiliary contacts was verified after re-assembly.

The technical specifications require the turbine trip contacts and the
engineered safety feature actuation system contacts (P-4 interlock) of an RTB
to be operable.  Westinghouse has recommended testing the proper operation of
the P-4 contacts following breaker refurbishment or maintenance activities,
and following breaker operation.  The testing should verify that the RTB P-4
contacts are in the correct position with the breaker opened and with the
breakers closed.

Licensees may wish to review RTB surveillance and post-maintenance test
procedures to ensure adequate verification of auxiliary contact operation for
both the opened and closed breaker positions.

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.


                                         signed by

                                    Jack W. Roe, Acting Director
                                    Division of Reactor Program Management
                                    Office of Nuclear Reactor Regulation

Technical contacts:  M. C. Shannon, RII   
                     (423) 842-8001 
                     E-mail:  mxs1@nrc.gov

                     Robert D. Starkey, RII
                     (423) 842-8001
                     E-mail:  drs@nrc.gov

Attachment:  List of Recently Issued NRC Information Notices


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