Information Notice 1991-29, Deficiencies Identifie During Electrical Distribution System Functional Inspections: Difference between revisions
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| issue date = 04/15/1991 | | issue date = 04/15/1991 | ||
| title = Deficiencies Identifie During Electrical Distribution System Functional Inspections | | title = Deficiencies Identifie During Electrical Distribution System Functional Inspections | ||
| author name = Rossi C | | author name = Rossi C | ||
| author affiliation = NRC/NRR | | author affiliation = NRC/NRR | ||
| addressee name = | | addressee name = | ||
Revision as of 04:48, 14 July 2019
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
' J 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 IN 91-29 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 04/ fI9 OGC :DOEA: RR 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
EVImbro 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
EVImbro 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
CERossi 1 03/l/91 03/ /91 oncurrence
bt SC:RSIB:DRIS
EVImbro*02/08/91 C:RSIB:DRIS
WDLanning*
02/19/91 D:DRIS BKGrimes*02/27/91 C:SELB:DST
FRosa*03/18/91 C:SICB:DST
SNewberry*
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 02/ /91 Xrt" RSIB:DRIS
SC:RSIB:DRIS
C: S C:S C:SI JBJacobson*:bt
EVImbro* WD ng mes FRoV-rW SNe rry 02/08/91 02/08/91 024 7/91 02/t7/91 "- / 91O/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. 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 02/ /91 02/ /91 RSIB: SC:RX RIS C:RSIB:DRIS
D:DRIS C:SELB:DST
C:SICB:DST
JBJac 6n:bt EVIm 'J>' WDLanning
BKGrimes FRosa SNewberry 020 A' 02/djz1 02/ /91 02/ /91 02/ /91 02/ /91