Information Notice 1991-29, Deficiencies Identifie During Electrical Distribution System Functional Inspections
4 A
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C.
20555
April 15, 1991
NRC INFORMATION NOTICE NO. 91-29:
DEFICIENCIES IDENTIFIED DURING ELECTRICAL
DISTRIBUTION SYSTEM FUNCTIONAL INSPECTIONS
Addressees
All holders of operating licenses or construction permits for nuclear power
reactors.
Purpose
This information notice is intended to alert addressees to deficiencies identi- fied during recently performed electrical distribution system functional
inspections (EDSFIs).
It is expected that recipients will review the informa- tion for applicability to their facilities and consider actions, as appropri- ate, to avoid similar problems.
However, suggestions contained in this
information notice do not constitute NRC requirements; therefore, no specific
action or written response is required.
Description of Circumstances
During multidisciplinary inspections, the U.S. Nuclear Regulatory Commission
(NRC) has identified many deficiencies related to tWeelectrical distribution
system. To address these deficiencies, the NRC has developed an inspection to
specifically evaluate the electrical distribution system. During the last
year, the NRC completed eight EDSFIs, performing at least one in each of the
five NRC geographical regions. During these inspections, the staff found
several common deficiencies in the licensees' programs and in the electrical
distribution systems as designed and configured at each plant. These deficien- cies included inadequate ac voltages at the 480 Vac and 120 Vac distribution
levels, inadequate procedures to test circuit breakers, and inadequate determi- nations and evaluations of setpoints.
Discussion:
Inadequate Voltage
During inspections conducted at the San Onofre Nuclear Generating Station
(Inspection Reports 50-361/89-200 and 50-362/89-200), the Susquehanna Steam
Electric Station (Inspection Reports 50-387/90-200 and 50-388/90-200), and the
9104090124
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IN 91-29 April 15, 1991 Waterford Steam Electric Station (Inspection Report 50-382/90-23), the staff
found that, under certain conditions, the voltage available at the safety buses
would be inadequate to Operate safety-related loads and associated equipment.
These conditions could occur when the plan~t's electrical distribution systems
were being supplied from an offsite grid that had become degraded but that
continued to supply voltages that remained above the setpoints at which the
degraded grid relays would be activated.
At San Onofre, the numerous voltage drops throughout the system could cause the
voltage to 120 Vaciontactors to drop below the-voltage range for which these
contactors were certified as acceptable by their manufacturers.
To resolve
this problem the licensee has performed testing that established a lower
acceptable voltage range for this equipment.
At Susquehanna, the degraded grid relay setpoint'was'set at 84 percent on the
4160 Yac buses.
Th'i's setpoint could have allowed inadequate voltage to be
-delivered to numerous safety-related loads at both the 480 Vac and 120 Vac
levels. The licensee calculated that setpoints'of at least 93 percent would be
required to ensure adequate voTtage to all safety-related equipment. To
resolve this problem, the lice'isee has raised the setpoints of the degraded
grid relays and has initiated a modification to install 120 Vac regulating
transformers.
At the Waterford nuclear plant, the degraded grid relays were set at
87.5 percent'as sensed on the'4160 Vac buses. :Although this setting was found
to be marginally adequate-'for-equipment connected to the 4160 Vac buses, the
setting was too low to ensure that adequate v6ltage would'be maintained at the
480 Vac and 120 Vac levels. The licensee is 6e4aluating solutions to this
problem and has instituted a procedure- to manually'separate from the grid if
the voltage falls to unacceptable levels but remains above the relay setpoints.
The function of the degraded grid relays is to en'sure that adequate voltage is
available tooperate all Class lE loads at all distribution levels.
In order
to ensure-that all required' Class E 'loads will remain operable during degraded
voltage conditions, some licensees are currently'reanalyzing the basis for the
degraded grid relay setpoints. The new analyses consider all required Class 1E
loads and include the assumption that the voltage on the buses being sensed by
these relays can remain at a level just above the relay setpoints.
Inadequate Circuit Breaker Testing Procedures
During recent EDSFIs ahd previously on other NRC inspections, the staff identi- fied repetitive deficiencies in licensees' programs to test circuit breakers.
These deficiencies included inadequate procedures, inadequate test acceptance
criteria, inadequate test equipment, and inadequate control of testing. At the
Susquehanna plant (Inspection Reports 50-387/90-200 and 50-388/90-200), the
staff found that the licensee was testing dc molded case circuit breakers with
a procedure written for testing ac breakers. The licensee had not established
specific acceptance criteria for the dc breakers.
IN 91-29 April 15, 1991 At the Shearon Harris Nuclear Power Plant (Inspection Report 50-400/90-200),
the staff identified that the licensee was.testing molded case circuit breakers
against National Electrical Manufacturers Association (NEMA),acceptance crite- ria, which were less stringent than the manufacturer's time-current curves for
these breakers. In addition, the staff identified that the licensee was
testing 480 V air circuit breakers with test equipment that applied a test
signal (secondary injection) to the solid state trip units in the circuit
breakers.
Although this method adequately verified that the trip units func- tioned properly, it did not verify that the breaker's current transformer
functioned properly or that the wiring and connectors were adequate between the
current transformer and the solid state trip units. Other licensees have
performed testing by primary current injection or by individually checking each
component of the circuit breaker, including the wiring and connectors to
demonstrate that the circuit breaker functions properly.
Inadequate Determinations and Evaluations of Setpoints
Many of the findings identified during recent EDSFIs were related to inadequate
setpoint determinations. Useful guidance for determining setpoints is provided
by Instrument Society of America Standard 67.04-1982, "Setpoints for Nuclear
Safety-Related Instrumentation used in Nuclear Power Plants," which the NRC
staff has endorsed by Regulatory Guide 1.105 Revision 2 -
1986, "Instrument
Setpoints for Safety-Related Systems." This guidance applies both to process
instrumentation and, in part, to certain relays that perform a safety function.
Some licensees have operated equipment outside of acceptable limits because
they did not determine proper setpoints and did not evaluate and account for
instrument drift. Operating the equipment under these conditions could
compromise the safety functions of the equipment. The staff has identified
these circumstances primarily for those instruments in which the licensee has
determined the setpoints as opposed to those instruments for which the
setpoints were determined by the architect/engineer or the nuclear safety
system supplier. Those setpoints not contained in the plant technical specifi- cations were also more frequently found to be deficient. During recent EDSFIs, the staff identified deficiencies in setpoints for diesel day tank level
indicators, diesel air start compressor controllers and alarms, inverter low
voltage shutdown circuitry, degraded grid relays, and diesel overcurrent
relays.
In addition to identifying deficiencies in the setpoints themselves, the NRC
has determined that not all the licensees are typically verifying that the
magnitude of instrument drift that was assumed in the original setpoint calcu- lation coincides with the magnitude of drift observed in the plant. Some
licensees have corrected this deficiency by verifying the magnitude of instru- ment drift by trending, (comparing "as found" calibration data to previous "as
left" data). This is particularly important for the degraded grid relay
setpoints, which often require very tight calibration tolerance bands, and for
which very low drift values are often assumed.
v- IN 91-29 April 15, 1991 This information notice requires no specific action or written response. If
you have any questions about the information in this notice, please contact the
technical contact listed below or the appropriate NRR project manager.
Charles E. Rossi, eirector
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contact:
Jeffrey B. Jacobson, NRR
(301) 492-0996 Attachment: List of Recently Issued NRC Information Notices
i
Attachment 1
April 15, 1991 LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
Information
Date of
Notice No.
Subject
Issuance
Issued to
91-28
91-27
89-90,
Supp. 1
91-26
91-25
91-24
91-23
Cracking in Feedwater
System Piping
Incorrect Rotation of
Positive Displacement Pump
Pressurizer Safety Valve
Lift Setpoint Shift
Potential Nonconservative
Errors in the Working Format
Hansen-Roach Cross-Section
Set Provided with The Keno
and Scale Codes
Commercial-Grade Structural
Framing Components Supplied
As Nuclear Safety-Related
Equipment
Recent Operating Experience
Involving Reactor Operation
Without A Licensed Reactor
Operator or Senior Reactor
Operator Present in the
Control Room
Accidental Radiation Over- exposures to Personnel Due to
Industrial Radiography Acces- sory Equipment Malfunctions
04/15/91
All holders of OLs or
CPs for pressurized
water reactors (PWRs).
04/10/91
All holders of OLs or
CPs for nuclear power
reactors.
04/10/91
All holders of OLs or
CPs for nuclear power
reactors.
04/02/91
All fuel cycle licensees
and other licensees, in- cluding all holders of
operating licenses for
nuclear power reactors, who use physics codes to
support criticality
safety in the use of
fissile material.
04/01/91
All holders of OLs or
CPs for nuclear power
reactors.
03/26/91
All holders of OLs or
CPs for nuclear power, test, and research re- actors, and all Part 55 licensed operators.
03/26/91
All Nuclear Regulatory
Commission (NRC) licens- ees authorized to use
sealed sources for indus- trial radiography.
OL = Operating License
CP = Construction Permit
IN 91-29 April 15, 1991 This information notice requires no specific action or written response. If
you have any questions about the information in this notice, please contact the
technical contact listed below or the appropriate NRR project manager.
O6ginal agen& by
Charles E. Ross!
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contact:
Jeffrey B. Jacobson, NRR
(301) 492-0996 Attachment:
List of Recently Issued NRC Information Notices
- SEE PREVIOUS
PCWen
04/
/91
CONCURRENCES
- C/OGCB:DOEA:NRR*RPB:ADM
- C/SICB:DST:NRR
CHBerlinger
TechEd
SNewberry
04/08/91
03/20/91
03/18/91
- RSIB:DRIS:NRR *SC/RSIB:DRIS:NRR*C/RSIB:DRIS:NRR
JBJacobson:bt
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WDLanning
02/08/91
02/08/91
02/19/91
- C/SELB:DST:NRR
FRosa
03/18/91
- D/DRIS:NRR
BKGrimes
02/27/91
- - I
IN 91-XX
April xx, 1991 This information notice requires no specific action or written response. If
you have any questions about the information in this notice, please contact the
technical contact listed below or the appropriate NRR project manager.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contact:
Jeffrey B. Jacobson, NRR
(301) 492-0996
List of Recently Issued NRC Information Notices
Attachment:
- SEE PREVIOUS CONCURRENCES
- C/SICB:DST:NRR
D/DOEA:NRR
C/OGCB:DO
T*RPB:Ad
SNewBerry
CERossi Y-
CHBerling rjw TechEd
04/ /91
04/8/91
03/20/91
03/18/91
,c
CB:DOEA:NRR *RSIB:DRIS:NRR *SC/RSIB:DRIS:NRR*C/RSIB:DRISNRR
4CvPvWen
JBJacobson:bt
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WMLanning
04/cl/91
02/08/91
02/08/91
02/19/91
- C/SELB:DST:NRR
FRosa
03/18/91
- D/DRIS:NRR
BKGrimes
02/27/91
IN 91-XX
March xx, 1991 Inadequate Determinations and Evaluations of Setpoints
Many of the findings identified during recent EDSFIs related to inadequate
setpoint determinations. Useful guidance for determining setpoints is provided
by Instrument Society of America Standard 67.04-1982, "Setpoints for Nuclear
Safety-Related Instrumentation used in Nuclear Power Plants," which the NRC
staff has endorsed by Regulatory Guide 1.105 Revision 2 - 1986, "Instrument
Setpoints for Safety-Related Systems." This guidance applies both to process
instrumentation and, in part, to certain relays that perform a safety function.
Licensees have operated equipment outside of acceptable limits because they did
not determine proper setpoints and did not evaluate and account for instrument
drifts. Operating the equipment under these conditions could compromise the
safety functions of the equipment. The staff has identified these circum- stances primarily for those instruments in which the licensee has determined
the setpoints as opposed to those instruments for which the setpoints were
determined by the architect/engineer or the nuclear safety system supplier.
Those setpoints not contained in the plant technical specifications were also
more frequently found to be deficient. During recent EDSFIs, the staff
identified deficiencies in setpoints for diesel day tank level indicators, diesel air start compressor controllers and alarms, inverter low voltage
shutdown circuitry, degraded grid relays, and diesel overcurrent relays.
In addition to identifying deficiencies in the setpoints themselves, the NRC
has determined that licensees are not typically verifying that the magnitude
of instrument drift that was assumed in the original setpoint calculation
coincides with the magnitude of drift observed in the plant.
Licensee can
verify the magnitude of instrument drift by trending, (comparing 'as found"
calibration data to previous 'as left" data). This is particularly important
for the degraded grid relay setpoints, which often require very tight calibra- tion tolerance bands, and for which very low drift values are often assumed.
This information notice requires no specific action or written response. If
you have any questions about the information in this notice, please contact the
technical contact listed below or the appropriate NRR project manager.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contact:
Jeffrey B. Jacobson, NRR
(301) 492-0996 Attachment:
RPB:ADM
TechEd* imJa
03/20/91 P
RSIB:DRIS
JBdacobson*:t
02/08/91
List of Recently Issued NRC Information Notices
C:OGCB:UOEA
D:DOEA
- See previous c
CHBerlinger
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1 03/l/91
03/ /91 oncurrence
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03/18/91
-
IN 91-XX
January xx, 1991 Inadequate Setpoint Determinations and Evaluations
Many of the findings identified during recent EDSFIs were related to inadequate
setpoint determinations. In order to properly determine an appropriate
instrument setpoint, all associated inaccuracies and tolerances must be
accounted for. Useful guidance for determining setpoints is provided by ISA
67.04-1982, "Setpoints for Nuclear Safety-Related Instrumentation used in
Nuclear Power Plants' which has been endorsed by Regulatory Guide 1.105 Revision 2 - 1986, "Instrument Setpoints for Safety Related Systems". This
guidance is applicable not Just for instrumentation but is also applicable for
certain relays and other control oriented pieces of equipment.
The setpoint problem has been identified primarily with those instruments in
which the licensee has determined the setpoints as opposed to those setpoints
determined by the NSSS vendor. Those setpoints not contained in the plant
technical specifications are also likely to be suspect. During recent EDSFIs, deficiencies in setpoints related to diesel day tank level indicators, diesel
air start compressor controllers and alarms, invertor low voltage shutdown
circuitry, degraded grid relays, and diesel overcurrent relays have been
identified.
In addition to the deficiencies identified in the setpoints themselves, the NRC
has determined that licensees are not typically verifying that the magnitude of
setpoint drift that was assumed in the original setpoint calculation is indeed
correct. This verification can be performed by trending, i.e., by comparing
"as found" calibration data to previous "as left" data. This is particularly
important for the degraded grid setpoints where very tight calibration
tolerance bands are often required and where very low drift values are often
assumed. Failure to evaluate and account for instrument drifts has led to the
operation of equipment outside of acceptable limits which could compromise the
safety functions of the equipment.
This information notice requires no specific action or written response. If
you have any questions about the information in this notice, please contact the
technical contact listed below or the appropriate NRR project manager.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contact:
Jeffrey B. Jacobson, NRR
(301) 492-0996 Attachment:
List of Recently Issued NRC Information Notices
- See previous concurrence
RPB:ADM
C:OGCB:DOEA
D:DOEA
TechEd
CHBerlinger
CERossi
02/ /91
02/ /91
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IN 91-XX
January xx, 1991 Inadequate Setpoint Determinations and Evaluations
Many of the findings identified during recent EDSFIs were related to inadequate
setpoint determinations. In order to properly determine an appropriate
instrument setpoint, all associated inaccuracies and tolerances must be
accounted for. Guidance for setpoint determinations is given in ANSI Standard
S67.04-1988, 'Setpoints for Nuclear Safety-Related Instrumentation." This
guidance is applicable not Just for instrumentation but is also applicable for
certain relays and other control oriented pieces of equipment.
The setpoint problem is most prevalent for those instruments in which the
licensee has determined the setpoints as opposed to those setpoints determined
by the NSSS vendor. Those setpoints not contained in the plant technical
specifications are also likely to be suspect. During recent EDSFIs, defi- ciencies in setpoints related to diesel day tank level indicators, diesel air
start compressor controllers and alarms, invertor low voltage shutdown
circuitry, degraded grid relays, and diesel overcurrent relays have been
identified.
In addition to the deficiencies identified in the setpoints themselves, the NRC
has determined that licensees are not typically verifying that the magnitude of
setpoint drift that was assumed in the original setpoint calculation is indeed
correct. This verification can be performed by trending, i.e., by comparing
"as found" calibration data to previous "as left" data. This is particularly
important for the degraded grid rely setpoints where very tight calibration
tolerance bands are often required and where very low drift values are often
assumed. Failure to evaluate and account for instrument drifts has led to the
operation of equipment outside of acceptable limits which could compromise the
safety functions of the equipment.
This information notice requires no specific action or written response. If
you have any questions about the information in this notice, please contact the
technical contact listed below or the appropriate NRR project manager.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contact:
Jeffrey B. Jacobson, NRR
(301) 492-0996 Attachment: List of Recently Issued NRC Information Notices
RPB:ADM
C:OGCB:DOEA
D:DOEA
TechEd
CHBerlinger
CERossi
02/ /91
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