Information Notice 1997-44, Failures of Gamma Metrics Wide-Range Linear Neutron Flux Channels
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555-0001
July 1, 1997
FAILURES OF GAMMA METRICS WIDE-RANGE
LINEAR NEUTRON FLUX CHANNELS
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 inform
addressees of failures that have occurred in Gamma Metrics wide-range linear neutron flux
channels that have the potential to defeat the scram function of the channels. It is expected
that recipients will review the information for applicability to their facilities and consider action, 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.
DescriDtion of Circumstances
The non-power reactor at North Carolina State University (NCSU) has two Gamma Metrics
wide range linear neutron flux channels. One unit is used as a linear channel for power
monitoring and control and provides a high-power-level scram. The other unit is used as a
safety channel that provides a high-power-level scram.
The channels used at NCSU can be operated in two modes for ranging and two modes for
bistable scram functions. For ranging, these units can be operated (1) in an auto-ranging
mode in which the unit changes scales automatically, or (2) in a manual range-change mode
in which the reactor operator changes the range displayed on the channel to follow the
reactor power level or leaves the channel set on one range. These units can also be
operated with the bistable set (1) in the standard mode in which the scram function is present
on each range at a set percentage of range, or (2) in a smart mode in which the scram
function is present at a set percentage of range on one specific range determined by the
operator and all ranges above it. The emphasis of this information notice is on the auto- ranging and smart mode combination.
The initial problem observed by the licensee was that the linear channel unit failed to
uprange automatically with the unit in the reactor console in the auto-ranging mode. While
testing the unit in the reactor console after repair, the unit failed to uprange and exhibited
spurious range-changing while operating in the auto-ranging mode (Accession Number
9702120389). During pre-startup console testing following modification of the unit, it was
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IN 97-44 July 1, 1997 found that actuation of the rod reverse demand would cause a range change with the range
control in manual mode. During benchtop testing following repairs, the unit exhibited
spurious range changes, including oscillatory behavior (changing up one level when
requested, but then changing back to the original level). It was also observed that the unit
increased range to greater than the maximum range even though this unit has by design a
maximum range limit function.
The unit used as a safety channel exhibited spurious down ranging during reactor operation
in the manual mode with the bistable set in the standard mode.
Discussion
It is possible for a malfunction of these units to disable the scram function, which, depending
on the use of the unit, may be a high-power-level scram required by the technical
specifications (TS). For the scram to be disabled, the unit bistable would have to be in the
smart bistable mode while a spurious down ranging occurs, which places the unit on a range
without scram protection when such protection is needed. Being on the wrong range
disables the scram function because the reactor could be operated beyond the scram
setpoint power level. Operating the unit with the bistable in the standard mode with the
scram enabled on all ranges alleviates this problem.
If a spurious uprange malfunction occurs in which the range goes beyond the maximum
range limit, the scram function, if still present, will actuate with the unit bistable in the
standard mode. This result occurs because the invalid range setting forces the picoammeter
to a maximum feedback state. This maximum feedback will cause the bistable input to go full
scale for any current above 10 picoamperes. For this unit, 10 picoamperes represents either
7 or 8 decades below full power.
The fact that the unit is on an incorrect scale can be readily detected by the reactor operator
by observation of the unit display. The operator can then take whatever action is necessary
to respond to the specific situation. The impact of this type of problem is reduced by the TS
requirement for multiple high-power-evel scrams using redundant channels.
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.
Marylee M. Slosson, Acting Dire or
Division of Reactor Program Management
Office of Nuclear Reactor Regulation
Technical contact: Alexander Adams, Jr., NRR
301-415-1127 E-mail: axa@nrc.gov
Attachment: List of Recently Issued NRC Information Notices
Attachment
July 1, 1997 LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
Information
Date of
Notice No.
Subject
Issuance
Issued to
97-43
97-42
97-41
97-40
License Condition
Compliance
Management Weaknesses
Resulting in Failure
to Comply with Shipping
Requirements for Special
Nuclear Material
Potentially Undersized
Oil Coolers
Potential Nitrogen
Accumulation Resulting
from Backleakage from
Safety Injection Tanks
Inadequate 10 CFR 72.48
Safety Evaluations of
Independent Spent Fuel
Storage Installations
Level-Sensing System
Initiates Common-Mode
Failure of High-Pressure-
Injection Pumps
Retrofit to Amersham 660
Posilock Radiography
Camera to Correct Incon- sistency in 10 CFR Part 34
Compatibility
07/01/97
06/27/97
06/27/97
06/26/97
06/26/97
06/24/97
06/23/97
All holders of OLs or CPs
for nuclear power reactors
All fuel cycle conversion, enrichment, and fabrication
facilities
All holders of OLs or CPs
for boiling-water reactors
All holders of OLs or CPs
for pressurized-water
reactors
All holders of OLs or CPs
for nuclear power reactors.
All holders of licenses for
independent spent fuel
storage installations
All holders of OLs or CPs
for nuclear power reactors
All industrial radiography
licensees
97-39
97-38
96-53, Supp. 1 OL = Operating License
CP = Construction Permit
- 'July
1, 1997 found that actuation of the rod reverse demand would cause a range change with the range
control in manual mode. During benchtop testing following repairs, the unit exhibited
spurious range changes, including oscillatory behavior (changing up one level when
requested, but then changing back to the original level). It was also observed that the unit
increased range to greater than the maximum range even though this unit has by design a
maximum range limit function.
The unit used as a safety channel exhibited spurious down ranging during reactor operation
in the manual mode with the bistable set in the standard mode.
Discussion
It is possible for a malfunction of these units to disable the scram function, which, depending
on the use of the unit, may be a high-power-level scram required by the technical
specifications (TS). For the scram to be disabled, the unit bistable would have to be in the
smart bistable mode while a spurious down ranging occurs, which places the unit on a range
without scram protection when such protection is needed. Being on the wrong range
disables the scram function because the reactor could be operated beyond the scram
setpoint power level. Operating the Unit with the bistable in the standard mode with the
scram enabled on all ranges alleviates this problem.
If a spurious uprange malfunction occurs in which the range goes beyond the maximum
range limit, the scram function, if still present, will actuate with the unit bistable in the
standard mode. This result occurs because the invalid range setting forces the picoammeter
to a maximum feedback state. This maximum feedback will cause the bistable input to go full
scale for any current above 10 picoamperes. For this unit, 10 picoamperes represents either
7 or 8 decades below full power.
The fact that the unit is on an incorrect scale can be readily detected by the reactor operator
by observation of the unit display. The operator can then take whatever action is necessary
to respond to the specific situation. The impact of this type of problem is reduced by the TS
requirement for multiple high-power-evel scrams using redundant channels.
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.
original signed by S.H. Weiss for
Marylee M. Slosson, Acting Director
Division of Reactor Program Management
Office of Nuclear Reactor Regulation
Technical contact: Alexander Adams, Jr., NRR
301415-1 127 E-mail: axa~nrc.gov
Tech Editor has reviewed & concurred on 04/19197 Attachment: List of Recently Issued NRC Information Notices *See previous concurrence
To receive a copy of this document, Indicate In the box: "C" = Copy without enclosures
"E" = Copy with enclosures "N" = No copy
DOCUMENT NAME:
97-44.IN
OFFICE
Tech Contact
I
D:PDND
I
C:PECB
I
(A)D:DRPM I
NAME
A. Adams 4/18/97*
S. Weiss*
A. Chaffee*
M. Slius
V. Hodge
DATE
6/6/97
04/18/97
06/19/97
06/ j/97 &
OFCA RECORD COPY
IN 97-xx
s-~' June xx, 1997 spurious range changes, including oscillatory behavior (changing up one level when
requested, but then changing back to the original level). It was also observed that the unit
increased range to greater than the maximum range even though this unit has by design a
maximum range limit function.
The unit used as a safety channel exhibited spurious down ranging during reactor operation
in the manual mode with the bistable set in the standard mode.
Discussion
It is possible for a malfunction of these units to disable the scram function, which, depending
on the use of the unit, may be a high-power-evel scram required by the technical
specifications (TS). For the scram to be disabled, the unit bistable would have to be in the
smart bistable mode while a spurious down ranging occurs, which places the unit on a range
without scram protection when such protection is needed. Being on the wrong range
disables the scram function because the reactor could be operated beyond the scram
setpoint power level. Operating the unit with the bistable in the standard mode with the
scram enabled on all ranges alleviates this problem.
If a spurious uprange malfunction occurs In which the range goes beyond the maximum
range limit, the scram function, if still present, will actuate with the unit bistable In the
standard mode. This result occurs because the invalid range setting forces the picoammeter
to a maximum feedback state. This maximum feedback will cause the bistable input to go full
scale for any current above 10 picoamperes. For this unit, 10 picoamperes represents either
7 or 8 decades below full power.
The fact that the unit is on an incorrect scale can be readily detected by the reactor operator
by observation of the unit display. The operator can then take whatever action is necessary
to respond to the specific situation. The impact of this type of problem Is reduced by the TS
requirement for multiple high-power-level scrams using redundant channels.
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.
Marylee M. Slosson, Acting Director
Division of Reactor Program Management
Office of Nuclear Reactor Regulation
Technical contact: Alexander Adams, Jr., NRR
301-415-1127 E-mail: axa@nrc.gov
Attachment: List of Recently Issued NRC Information Notices *See previous concurrence
To receive a copy of this document, Indicate In the box: "C" = Copy without enclosures
"E" = Copy with enclosures "N" = No copy
OFFICE
Tech Contact
I
D:PDND
I
A
(A)D:DRPM
NAME
A. Adams 4/18/97*
S. Weiss*
V C
e
M. Slosson
DATE
6/6/97
04/18/97
106/14 /97
06/ /97 OFFICIAL RECORD COPY
I
/
4tk
417/11
IN 97-x
E.>
June xm"97 spurious range changes, including oscillatory behavior (changing up one level when
requested, but then changing back to the original level). It was also observed that the unit
increased range to greater than the maximum range even though this unit has by design a
maximum range limit function.
The unit used as a safety channel exhibited spurious down ranging during reactor operation
in the manual mode with the bistable set in the standard mode.
Discussion
It is possible for a malfunction of these units to disable the scram function, which, depending
on the use of the unit, may be a high-power-level scram required by the technical
specifications (TS). For the scram to be disabled, the unit bistable would have to be in the
smart bistable mode while a spurious down ranging occurs, which places the unit on a range
without scram protection when such protection is needed. Being on the wrong range
disables the scram function because the reactor could be operated beyond the scram
setpoint power level. Operating the unit with the bistable in the standard mode with the
scram enabled on all ranges alleviates this problem.
If a spurious uprange malfunction occurs in which the range goes beyond the maximum
range limit, the scram function, if still present, will actuate with the unit bistable in the
standard mode. This result occurs because the invalid range setting forces the picoammeter
to a maximum feedback state. This maximum feedback will cause the bistable input to go full
scale for any current above 10 picoamperes. For this unit, 10 picoamperes represents either
seven or eight decades below full power.
The fact that the unit is on an incorrect scale can be readily detected by the reactor operator
by observation of the unit display. The operator can then take whatever action is necessary
to respond to the specific situation. The impact of this type of problem is reduced by the TS
requirement for multiple high-power-level scrams using redundant channels.
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.
Marylee M. Slosson, Acting Director
Division of Reactor Program Management
Office of Nuclear Reactor Regulation
Technical contact:
Alexander Adams, Jr., NRR
(301) 415-1127 E-nail: axa@nrc.gov
Attachment: List of Recently Issued NRC Information Notices
- See previous concurrence
To receive a copy of this document, Indicate In the box: "C" = Copy without enclosures
"E" = Copy with enclosures "N" = No copy
OFFICE
Tech Contact
I
D:PDND
I
C:PECB
I
(A)D:DRPM
NAME
A. Adams 4/18/97*
S. Weiss*
IA. Chaffee
M. Slosson
V. HodgeII
DATE
6/6/97
04/18/97
06/ /97
06/ /97 l
OFFICI
IN 97-xx
V
,~
)LaWxx, 1997 jA spurious range changes, including oscillatory behavior (changing up one level when
requested, but then changing back to the original level). It was also observed that
unit
increased range to greater than the maximum range even though this unit has b
design a
maximum range limit function.
The unit used as a safety channel exhibited spurious down ranging duri
reactor operation
in the manual mode with the bistable set in the standard mode.
Discussion
It is possible for a malfunction of these units to disable the s
m function, which, depending
on the use of the unit, may be a high-power-level scram reuired by the technical
specifications (TS). For the scram to be disabled, the u
bistable would have to be in the
smart bistable mode while a spurious down ranging oi
rs, which places the unit on a range
without scram protection when such protection is ne ed.
Being on the wrong range
disables the scram function because the reactor co d be operated beyond the scram
setpoint power level. Operating the unit with the istable in the standard mode with the
scram enabled on all ranges alleviates this pro m.
If a spurious uprange malfunction occurs In
ich the range goes beyond the maximum
range limit, the scram function, If still preseet, will actuate with the unit bistable In the
standard mode. This resuit occurs beca
e the invalid range setting forces the picoammeter
to a maximum feedback state. This ma imum feedback will cause the bistable input to go full
scale for any current above 10 picoa
res. For this unit, 10 picoamperes represents either
seven or eight decades below full po
er.
The fact that the unit is on an in
ect scale can be readily detected by the reactor operator
by observation of the unit displa
The operator can then take whatever action is necessary
to respond to the specific situa on. The impact of this type of problem is reduced by the TS
requirement for multiple high- ower-level scrams using redundant channels.
This information notice re
ires no specific action or written response. If you have any
questions about the info
ation in this notice, please contact the technical contact listed
below.
Marylee M. Slosson, Acting Director
Division of Reactor Program Management
Office of Nuclear Reactor Regulation
Technical cont
Alexander Adams, Jr., NRR
(301) 415-1127 E-mail: axa@nrc.gov
Attachmen
List of Recently Issued NRC Information Notices
To receive a copy of this document, Indicate In the box: "C" = Copy without enclosures
"E" = Copy with enclosures "N" = No copy
OFFICE
Tech Contact
I
D:PDND
I
C:PECB
I
D:DRPM
I
INAME
A. Adams 4/I8/97*
S. Weiss*
A. Chaffee
T. Martin
V. Hodge
u
- 104 DATE
06/ /97
04/18/97
06/ /97
06/ /97 mFIILREODCP
IN 97-xx
May xx, 1997 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.
Marylee M. Slosson, Acting Director
Division of Reactor Program Management
Office of Nuclear Reactor Regulation
TECHNICAL
CONTACT
- Alexander Adams, Jr., NRR
(301) 415-1127 E-mail: axa@nrc.gov
Attachment:
List of Recently Issued NRC Information Notices
To receive a copy of this document, Indicate In the box: "C" = Copy without enclosures
"E" = Copy with enclosures "N" = No copy
OFFICE
Tech Contact
I
D:PDND
I
C:PECB
I
D:DRPM
NAME
A. Adams 4/18/97*
S. Weiss*
IA.
Chaffee
T. Martin
V. Hodge
I
DATE
05/ /97
04/18/97
105/ /97
05/ /97
OFFICIAL RECORD COPY
-
vIN
97-xx
April xx, 1997 The unit used as a safety channel exhibited spurious down ranging during reactor operation
in the manual mode with the bistable set in the "standard" mode.
Discussion
It is possible for a malfunction of these units to disable the scram function, which, depending
on the use of the unit, may be a high-power-level scram required by the technical
specifications (TS). For the scram to be disabled, the unit bistable would have to be in the
"smart" mode while a spurious down ranging occurs, which places the unit on a range without
scram protection when such protection is needed. Being on the wrong range disables the
scram function because the reactor could be operated beyond the scram setpoint power
level. Operating the unit with the bistable in the "standard" mode with the scram enabled on
all ranges alleviates this problem.
If a spurious uprange malfunction occurs in which the range goes beyond the maximum
range limit, the scram function, if still present, will not actuate at the proper setpoint even with
the unit bistable in the "standard" mode. This result occurs because the scram is set for a
percentage of the range on all ranges, which will be above the scram setpoint when it is
beyond the maximum range. Licensees should be aware of this type of behavior. The
impact of this type of problem is reduced by the TS requirement for multiple high-power-level
scrams using redundant channels. The possibility of a problem Is further reduced if the
redundant channels are also diverse.
The fact that the unit is on an incorrect scale can be readily detected by the reactor operator
by observation of the unit display. The operator can then take whatever action is necessary
to respond to the specific situation.
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.
Thomas T. Martin, Director
Division of Reactor Program Management
Office of Nuclear Reactor Regulation
TECHNICAL
CONTACT
- Alexander Adams, Jr., NRR
(301) 415-1127 E-mail: axa@nrc.gov
Attachment: List of Recently Issued NRC Information Notices
DOCUMENT NAME: G:WVERN\\INGM
To receive a copy of this document, Indicate In the box: "C' - Copy without enclosures "F
Copy with enclosures "N' - No copy
OFFICE ITech Contact
D:PDND
C:PECB
D:DRPM
NAME
A. Adams
S. Weiss
A. Chaffee
T. Martin
V. Hodge
.
DATE
04/ /97
04/18/97
04/ /97 '
04/ /97 OFIILCR-P
- 3 -
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.
Thomas T. Martin, Director
Division of Reactor Program Management
Office of Nuclear Reactor Regulation
TECHNICAL
CONTACT
Alexander Adams, Jr., NRR
(301) 415-1127 E-mail: axa@nrc.gov
Attachment:
List of Recently Issued NRC Information Notices
TECH ED
BCalure
04 /9/97 SWelss
DOCUMENT
PDN'Y J
q/
7 PECB
/ /97 RECORD COPY
NAME: G:\\SECY\\ADAMS\\INGM
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4//6/97 DRPM: D
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