Information Notice 1993-78, Inoperable Safety Systems at a Non-Power Reactor
S
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C.
20555
October 4, 1993
NRC INFORMATION NOTICE 93-78: INOPERABLE SAFETY SYSTEMS AT A NON-POWER
REACTOR
Addressees
All holders of operating licenses or construction permits for test and
research reactors.
Purpose
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information
notice to alert addressees to a problem which resulted in inoperable safety
systems at a non-power reactor.
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 April 28, 1993, after a number of spurious scrams had occurred, the
licensee for the University of Virginia Research Reactor shut down the reactor
and began troubleshooting activities to determine the cause of the problem.
The reactor had been experiencing spurious scrams for some time and the
licensee had concluded that the scrams were not caused by'electrical
transients or line noise.
The licensee suspected the reactor-scram logic to
be the cause of the scrams.
The reactor scram logic consists of two trains
that cause power to different magnets to be cut off on receiptIof a scram
signal. This in turn releases control rods and shuts down the'reactor.
While
investigating the problem, the senior reactor operator (SRO) interchanged
components of the scram logic system between the two trains.
Among these
components were solid-state relays and mixer-drivers (M/Ds) which act as a.
28-channel "OR" gate in the scram logic.
After consulting the facility safety
analysis report and visually inspecting the exterior of the components, the
SRO assumed that the interchanged components were identical.
However, the
M/Ds had been internally modified in the 1970s to tie unused inputs together
and were no longer identical.
After the M/Ds had been exchanged and no spurious scram signals were received
for 30 minutes, the reactor administrator and the SRO started the reactor.
Neither the reactor administrator nor the SRO recognized that the
troubleshooting activities-were actually a maintenance or modification
function and that testing to verify the operability of the reactor scram
system was required before the reactor was restarted.
9309290007 R
No.'De, qs o7r
73l
IN 93-78 October 4, 1993 After operating for approximately 5k hours, the reactor was shut down by
driving the rods into the core. With three of the four control rods seated, licensee personnel then introduced a scram signal into the reactor
electronics using the intermediate range channel switch.
However, the
electronics did not generate a scram signal as expected.
The licensee
investigated and found that the M/Ds were not internally identical as
described above.
Further investigation showed that the following scram
signals were inoperable:
the two power level scrams, intermediate range
period scram, primary coolant low flow scram, loss of power to the primary
pump scram, intermediate channel range switch scram, and key switch scram.
The licensee returned the M/Ds to their original positions and tested the
reactor to ensure that the reactor electronics had not been damaged.
To prevent a recurrence of this problem, the licensee made the following
changes:
(1) revised the facility standard operating procedures (SOPs) to
clearly define maintenance and troubleshooting activities, (2) added a
checklist to the SOPs to specifically control maintenance activities, and
(3) added a checklist to the SOPs to verify the operability of the reactor
safety systems after an unplanned reactor scram.
Other changes were also made
to the SOPs to ensure management control over maintenance.
The licensee checked the reactor electronics against the schematics and found
that changes had been made to console modules that were not reflected in the
schematics. The licensee found two instances where externally identical
components were internally different and therefore not interchangeable. After
completing this check, the licensee labeled the modules that had been modified
to clearly indicate that they were unique and not interchangeable.
Discussion
The circumstances described above demonstrate the importance of recognizing
and controlling maintenance and modification actions.
Clearly defining
maintenance activities in facility procedures and providing training to
personnel can be effective methods for controlling such activities.
Also
important to reactor safety is updating schematics of reactor electronics to
reflect modifications to safety systems.
Performing testing of the affected
safety systems after activities of the type described above may prevent the
occurrence of similar events.
IN 93-78 October 4, 1993 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.
orig /s/'d by AEChaffee/for
Brian K. Grimes, Director
Division of Operating Reactor Support
Office of Nuclear Reactor Regulation
Technical contacts:
A. Adams, Jr., NRR
(301) 504-1127
C. Bassett, RII
(404) 331-5570
Attachment:
List of Recently Issued NRC Information Notices
- See previous concurrence
ONDD:LA*
ONDD:PM*
RII*
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7/30/93
7/30/93
8/03/93 TECH ED.*
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9/07/93
OFFICIAL RECORD COPY
DOCUMENT NAME:
93-78.IN
j
IN 93- September
Page 3 of
, 1993 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.
Brian K. Grimes, Director
Division of Operating Reactor Support
Office of Nuclear Reactor Regulation
Technical contacts:
A. Adams, Jr.,
(301) 504-1127 NRR
C. Bassett, RII
(404) 331-5570
Attachment:
List of Recently Issued NRC Information Notices
- See previous concurrence
ONDD:LA*
ONDD:PM*
RII*
EHylton
AAdams:dmj
CBassett
7/30/93
7/30/93
8/03/93 TECH ED.*
MMejac
7/29/93 C/ONDD*
SWeiss
8/03/93 C/OGCB*
GHMarcus
9/07/93 BGrimes~I(
9 X /93'
OGCB:DORS*
JBirmingham
9/07/93
OFFICIAL RECORD COPY
DOCUMENT NAME: MNTNCIN.JLB
IN 93-xx
September xx, 1993
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.
Brian K. Grimes, Director
Division of Operating Reactor Support
Office of Nuclear Reactor Regulation
Technical contacts:
A. Adams, Jr, NRR
(301) 504-1127
C. Bassett, RII
(404) 331-5570
Attachment:
List of Recently Issued NRC Information Notices
- See previous concurrence
ONDD:LA*
ONDD:PM*
RII*
EHylton
AAdams:dmj
CBassett
7/30/93
7/30/93
8/03/93 TECH ED.*
KMejac
7/29/93 C/ONDD
SWeiss
8/03/93 C/OGe
GHMa9 s
9/ ? /93 D/DORS
BGrimes
9l /93 OGCB:DORS
JBirminghgm
9 / 7 /9 P zwc
OFFICIAL RECORD COPY
DOCUMENT NAME: MNTNCIN.JLB
K
s~IN
93- (Date) problem was corrected by returning the M/Ds to their original position.
The
reactor was tested to ensure that the reactor electronics had not been
damaged.
The UVRR staff has instituted a number of corrective actions to prevent a
recurrence of this problem.
Facility standard operating procedures (SOPs)
have been revised to clearly define maintenance and troubleshooting, a new
checklist to control maintenance has been developed and added to the SOPs, a
new checklist to be followed after an unplanned reactor scram to verify
operability of the reactor safety systems has been added to the SOPs, and
other changes have been made to the SOPs to increase management control over
maintenance. The reactor electronics have been checked against schematics, and the schematics have been updated when necessary. The licensee found that
various changes had been made to console modules that were not reflected in
the schematics. The reactor console was checked for other externally
identical components that were internally different and not interchangeable.
Two instances of this type were identified.
Modules in the console were
clearly labeled to indicate if any modifications were made and if they were
unique and not interchangeable. A sign was added to the reactor console
reminding operators that modules in the console were not interchangeable.
Discussion
This problem emphasizes the importance of recognizing and controlling
maintenance functions at NPRs. What constitutes maintenance should be clearly
defined in the facility procedures and understood by the staff.
The
operability of safety systems should be verified every time maintenance is
performed on a system.
Also important is having clear, up-to-date schematics of reactor electronics
and procedures that ensure that they will be consulted during maintenance.
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.
Brian K. Grimes, Director
Division of Operating Reactor Support
Office of Nuclear Reactor Regulation
Technical contacts: A. Adams, Jr.
(301) 504-1127 C. Bassett
(404) 331-5570
DISTRIBUTION:
Attachment:
Central File
GMarcus
List of Recently Issued NRC Information Notices
BGrimes
AAdams
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EHylton
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DOCUMENT NAME: A:IN2.AA (ONDD DOCUMENTS DISK)
i.-2 IN 93- (Date) pump scram, intermediate channel range switch scram and key switch scram were
found to Oe inoperable.
This problem was corrected by returning the M/Ds to
their orininal position. The reactor was tested to ensure that no damage
occurred to the reactor electronics.
The UVRR staff Was instituted a number of corrective actions to prevent
reoccurrence of
is problem.
Facility Standard Operating Procedures (SOPs)
have been revised o clearly define maintenance and troubleshooting, a new
checklist to contro maintenance has been developed and added to the SOPs, a
new checklist to be
llowed after an unplanned reactor scram to verify
operability of the rea tor safety systems has been added to the SOPs, and
other changes have been ade to the SOPs to increase management control over
maintenance. The reacto electronics have been checked against schematics and
schematics updated when ne essary. The licensee found that various changes
had been made to console mo les that were not reflected in the schematics.
The reactor console was revie ed for other externally identical components
that were internally different nd not interchangeable.
Two instances of this
type were identified.
Modules
the console were clearly labeled to indicate
if any modifications were made an if they were unique and not
interchangeable. A sign was added o the reactor console reminding operators
that modules in the console were not nterchangeable.
Discussion
This problem emphasizes the importance o
ecognizing and controlling
maintenance functions at NPRs. What const utes maintenance should be clearly
defined in the facility procedures and unde tood by the staff.
The
operability of safety systems should be veri ed every time that maintenance
is performed on a system.
Also important is having clear, up-to-date schema ics of reactor electronics
and procedures that ensure that they will be consu ted during maintenance.
This information notice requires no specific action
written response.
If
you have any questions about the information in this
tice, please contact
the technical contact listed below or the appropriate
fice of Nuclear
Reactor Regulation (NRR) project manager.
Brian K. Grimes, Directo
Division of Operating Rea tor Support
Office of Nuclear Reactor
gulation
Technical contacts: A. Adams, Jr.
DISTRIBUTION:
(301) 504-1127 Central File
GMarcus
C. Bassett
BGrimes
AAdams
(404) 331-5570
SWeiss
ylton
Attachment:
List of Recently Issued NRC Information Notices
ONDD:LA
ONDD:PM
TECH ED.
OGCB:BC
ONDD:D
DORS:DD
EHylton
AAdams:dmJ
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GMarcus
SWeiss
BGrimes
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/93
/
/93
' /aj/93
/
/93
1 /93
/
/93
OFFICIAL RECORD COPY
DOCUMENT NAME: A:IN2.AA (ONDD DOCUMENTS DISK)
KJ
IN 93-78 October 4, 1993 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.
Brian K. Grimes, Director
Division of Operating Reactor Support
Office of Nuclear Reactor Regulation
Technical contacts: A. Adams, Jr., NRR
(301) 504-1127
C. Bassett, RII
(404) 331-5570
Attachment:
List of Recently Issued NRC Information Notices
N-
AttachJ
IN 93- 7r
October 4, 1993
Page I of I
LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
Information
Date of
Notice No.
Subject
Issuance
Issued to
93-77 Human Errors that Result
10/04/93
All nuclear fuel cycle
in Inadvertent Transfers
licensees.
of Special Nuclear
Material at Fuel Cycle
Facilities
93-76 Inadequate Control of
09/21/93
All holders of OLs or CPs
Paint and Cleaners for
for nuclear power reactors.
Safety-Related Equipment
93-75 Spurious Tripping of
09/17/93
All holders of OLs or CPs
Low-Voltage Power Circuit
for nuclear power reactors.
Breakers with GE RMS-9
Digital Trip Units
93-74 High Temperatures Reduce
09/16/93
All holders of OLs or CPs
Limitorque AC Motor
for nuclear power reactors.
Operator Torque
93-73 Criminal Prosecution of
09/15/93 All NRC licensees.
Nuclear Suppliers for
Wrongdoing
93-72 Observations from Recent
09/14/93
All holders of OLs or CPs
Shutdown Risk and Outage
for nuclear power reactors.
Management Pilot Team
Inspections
93-71 Fire at Chernobyl Unit.2
09/13/93
All holders of OLs or CPs
for nuclear power reactors.
93-70
Degradation of Boraflex
09/10/93
All holders of OLs or CPs
Neutron Absorber Coupons
for nuclear power reactors.
93-69 Radiography Events at
09/02/93
All holders of OLs or CPs
Operating Power Reactors
for nuclear power reactors
and all radiography
licensees.
OL - Operating License
- Construction Permit
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