Information Notice 1993-27, Level Instrumentation Inaccuracies Observed During Normal Plant Depressurization: Difference between revisions

From kanterella
Jump to navigation Jump to search
(Created page by program invented by StriderTol)
(StriderTol Bot change)
 
(One intermediate revision by the same user not shown)
Line 14: Line 14:
| page count = 8
| page count = 8
}}
}}
{{#Wiki_filter:UNITED STATES NUCLEAR REGULATORY
{{#Wiki_filter:UNITED STATES


COMMISSION
===NUCLEAR REGULATORY COMMISSION===
OFFICE OF NUCLEAR REACTOR REGULATION


===OFFICE OF NUCLEAR REACTOR REGULATION===
WASHINGTON, D.C.
WASHINGTON, D.C. 20555 April 8, 1993 NRC INFORMATION


NOTICE 93-27: LEVEL INSTRUMENTATION
20555


INACCURACIES
===April 8, 1993===
NRC INFORMATION NOTICE 93-27:


===OBSERVED DURING NORMAL PLANT DEPRESSURIZATION===
===LEVEL INSTRUMENTATION INACCURACIES OBSERVED===
DURING NORMAL PLANT DEPRESSURIZATION


==Addressees==
==Addressees==
All holders of operating
All holders of operating licenses or construction permits for nuclear power


licenses or construction
reactors.
 
permits for nuclear power reactors.


==Purpose==
==Purpose==
The U.S. Nuclear Regulatory
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information


Commission (NRC) is issuing this information
notice to alert addressees to inaccuracies in reactor vessel level indication


notice to alert addressees
that occurred during a normal depressurization of the reactor coolant system


to inaccuracies
at the Washington Nuclear Plant Unit 2 (WNP-2) and to the fact that errors in


in reactor vessel level indication
level indication may result in a failure to automatically isolate the residual


that occurred during a normal depressurization
heat removal (RHR) system under certain conditions. It is expected that


of the reactor coolant system at the Washington
recipients will review the information for applicability to their facilities


Nuclear Plant Unit 2 (WNP-2) and to the fact that errors in level indication
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.


may result in a failure to automatically
===Background===
As discussed in NRC Information Notice 92-54, "Level Instrumentation


isolate the residual heat removal (RHR) system under certain conditions.
Inaccuracies Caused by Rapid Depressurization," and Generic Letter 92-04,
"Resolution of the Issues Related to Reactor Vessel Water Level


It is expected that recipients
Instrumentation in BWRs Pursuant to 10 CFR 50.54(f)," noncondensible gas may


will review the information
become dissolved in the reference leg of water level instrumentation and lead


for applicability
to false indications of high level after a rapid depressurization event.


to their facilities
Reactor vessel level indication signals are important because these signals


and consider actions, as appropriate, to avoid similar problems.
are used for actuating automatic safety systems and for guidance to operators


However, suggestions
during and after an event. While Information Notice 92-54 dealt with


contained
potential consequences of rapid system depressurization, this information


in this information
notice discusses level indication errors that may occur during normal plant


notice are not NRC requirements;
cooldown and depressurization.
therefore, no specific action or written response is required.Background


As discussed
==Description of Circumstances==
On January 21, i993, during a plant cooldown following a reactor scram at


in NRC Information
WNP-2, "notching" of the level indication was observed on at least two of four


Notice 92-54, "Level Instrumentation
channels of the reactor vessel narrow range level instrumentation.


Inaccuracies
"Notching


Caused by Rapid Depressurization," and Generic Letter 92-04,"Resolution
is a momentary increase in indicated water level. This increase occurs when a


of the Issues Related to Reactor Vessel Water Level Instrumentation
gas bubble moves through a vertical portion of the reference leg and causes a


in BWRs Pursuant to 10 CFR 50.54(f)," noncondensible
temporary decrease in the static head in the reference leg.


gas may become dissolved
===The notching at===
9304020319 PD9Z


in the reference
X


leg of water level instrumentation
3 MoC


and lead to false indications
J


of high level after a rapid depressurization
3pzu


event.Reactor vessel level indication
13 oqat


signals are important
P-
o'itv k


because these signals are used for actuating
IN 93-27 April 8, 1993 WNP-2 was first observed on channel NC" at a pressure of approximately


automatic
827 kPa (120 psig].


safety systems and for guidance to operators during and after an event. While Information
===Channel IBS experienced notching starting at===
approximately 350 kPa [50 psig]. At these pressures, the level error was on


Notice 92-54 dealt with potential
the order of 10 to 18 centimeters (4 to 7 inches] and persisted for


consequences
approximately one minute.


of rapid system depressurization, this information
Beginning at a pressure of approximately 240 kPa [35 psig], the level


notice discusses
indication from channel IC' became erratic and, as the plant continued to


level indication
depressurize, an 81-centimeter (32-inch] level indication error occurred.


errors that may occur during normal plant cooldown and depressurization.
This depressurization was coincident with the initiation of the shutdown


Description
cooling system.


of Circumstances
The 81-centimeter [32-inch] level error was sustained and was


On January 21, i993, during a plant cooldown following
gradually recovered over a period of two hours.


a reactor scram at WNP-2, "notching" of the level indication
===The licensee postulated that===
this large error in level indication was caused by gas released in the


was observed on at least two of four channels of the reactor vessel narrow range level instrumentation. "Notching is a momentary
reference leg displacing approximately 40 percent of the water volume.


increase in indicated
The


water level. This increase occurs when a gas bubble moves through a vertical portion of the reference
licensee also postulated that the slow recovery of correct level indication


leg and causes a temporary
was a result of the time needed for steam to condense in the condensate


decrease in the static head in the reference
chamber and refill the reference leg. The licensee inspected the IC"
reference leg and discovered leakage through reference leg fittings. This


leg. The notching at 9304020319 PD9Z X 3 MoC J 3pzu 13 oqat P- o'itv k
leakage may have been a contributing factor for an increased accumulation of


IN 93-27 April 8, 1993 WNP-2 was first observed on channel NC" at a pressure of approximately
dissolved noncondensible gas in that reference leg.


827 kPa (120 psig]. Channel IBS experienced
The licensee determined that the type of errors observed in level indication


notching starting at approximately
during this event could result in a failure to automatically isolate a leak in


350 kPa [50 psig]. At these pressures, the level error was on the order of 10 to 18 centimeters
the RHR system during shutdown cooling. The design basis for WNP-2 includes a


(4 to 7 inches] and persisted
postulated leak in the RHR system piping outside containment while the plant


for approximately
Is in the shutdown cooling mode.


one minute.Beginning
===For this event, the shutdown cooling suctlon===
valves are assumed to automatically isolate on a low reactor vessel water


at a pressure of approximately
level signal to mitigate the consequences of the event.


240 kPa [35 psig], the level indication
For the January 21,
1993 plant cooldown, the licensee concluded that, with the observed errors in


from channel IC' became erratic and, as the plant continued
level indication, the shutdown cooling suction valves may not have


to depressurize, an 81-centimeter
automatically isolated the RHR system on low reactor vessel water level as;
designed. The licensee has implemented compensatory measures for future plant


(32-inch]
cooldowns to ensure that a leak that occurs in the RHR system during shutdown
level indication


error occurred.This depressurization
cooling operation would be isolated promptly. These measures include touring


was coincident
the associated RHR pump room hourly during shutdown cooling and backfilling


with the initiation
the water level instrument reference legs after entry into mode 3 (hot


of the shutdown cooling system. The 81-centimeter
shutdown). The licensee is also evaluating measures to minimize leakage from


[32-inch]
the IC' reference leg.
level error was sustained


and was gradually
Discussion


recovered
The event described above is different than events previously reported because


over a period of two hours. The licensee postulated
of the large magnitude and sustained duration (as opposed to momentary


that this large error in level indication
notching) of the level error that occurred during normal plant cooldown. A


was caused by gas released in the reference
large sustained level error is of concern because of the potential for


leg displacing
complicating long-term operator actions.


approximately
===In addition, the scenario of a===
postulated leak in the RHR system evaluated by WNP-2 suggests that some safety


40 percent of the water volume. The licensee also postulated
systems may not automatically actuate should an event occur while the reactor


that the slow recovery of correct level indication
is in a reduced pressure condition. Generic Letter 92-04 requested, in part, that licensees determine the impact of potential level indication errors on


was a result of the time needed for steam to condense in the condensate
IN 93-27 April 8, 1993 automatic safety system response during licensing basis transients and


chamber and refill the reference
accidents.


leg. The licensee inspected
The information in this notice indicates that sustained level


the IC" reference
instrument inaccuracies can occur during a normal reactor depressurization.


leg and discovered
Therefore, events occurring during low pressure conditions may also be


leakage through reference
complicated by level indication errors.


leg fittings.
This information notice requires no specific action or written response. If


This leakage may have been a contributing
you have any questions about the information in this notice, please contact


factor for an increased
the technical contact listed below or the appropriate Office of Nuclear


accumulation
Reactor Regulation (NRR) project manager.


of dissolved
===Brian K. Grimes, Director===
Division of Operational Events Assessment


noncondensible
===Office of Nuclear Reactor Regulation===
Technical contact:


gas in that reference
===Amy Cubbage, NRR===
(301) 504-2875 Attachment:


leg.The licensee determined
===List of Recently Issued NRC Information Notices===


that the type of errors observed in level indication
Attachnent


during this event could result in a failure to automatically
IN 93-27


isolate a leak in the RHR system during shutdown cooling. The design basis for WNP-2 includes a postulated
===April 8, 1993===
Pge I of I


leak in the RHR system piping outside containment
ME0
a- dc


while the plant Is in the shutdown cooling mode. For this event, the shutdown cooling suctlon valves are assumed to automatically
===LIST OF RECENTLY ISSUED===
HRC INFORMATION NOTICES


isolate on a low reactor vessel water level signal to mitigate the consequences
inroruauon


of the event. For the January 21, 1993 plant cooldown, the licensee concluded
Inforuti0n


that, with the observed errors in level indication, the shutdown cooling suction valves may not have automatically
Notice No.


isolated the RHR system on low reactor vessel water level as;designed.
93-26
)
93-25
93-24
93-23
93-22
93-21 Subject


The licensee has implemented
===Grease Solidification===
Causes Molded Case


compensatory
===Circuit Breaker===
Failure to Close


measures for future plant cooldowns
===Electrical fenetration===
Assembly Degradation


to ensure that a leak that occurs in the RHR system during shutdown cooling operation
===Distribution of===
Revision 7 of NUREG-1021,
*Operator Licensing


would be isolated promptly.
Examiner Standards'


These measures include touring the associated
===Veschler Instruments===
Model 252 Switchboard


RHR pump room hourly during shutdown cooling and backfilling
Meters


the water level instrument
Tripping of Ilockner- toeller Molded-Case


reference
===Circuit Breakers due to===
Support Level Failure


legs after entry into mode 3 (hot shutdown).
===Sumary of NRC Staff===
Observations Compiled


The licensee is also evaluating
'during Engineering Audits


measures to minimize leakage from the IC' reference
or Inspections of Licen- see Erosion/Corrosion


leg.Discussion
Programs


The event described
===Thermal Fatigue Cracking===
of Feedwater Piping to


above is different
===Stem Generators===
Slab Hopper Bulging


than events previously
Portable Moisture-Density


reported because of the large magnitude
===Gauge User Responsibilities===
during Field Operations


and sustained
u te OT


duration (as opposed to momentary notching)
Issuance
of the level error that occurred during normal plant cooldown.


A large sustained
Issued to


level error is of concern because of the potential
04/07/93


for complicating
===All holders of OLs or CPs===
for nuclear power reactors.


long-term
04/01/93


operator actions. In addition, the scenario of a postulated
===All holders of OLs or Cps===
for nuclear power reactors.


leak in the RHR system evaluated
03/31/93


by WNP-2 suggests that some safety systems may not automatically
===All holders of operator and===
senior operator licenses at


actuate should an event occur while the reactor is in a reduced pressure condition.
nuclear power reactors.


Generic Letter 92-04 requested, in part, that licensees
03/31/93


determine
===All holders of OLs or CPs===
for nuclear power reactors.


the impact of potential
03/26/93


level indication
===All holders of Ots or CPs===
for nuclear power reactors.


errors on
03/25/93


IN 93-27 April 8, 1993 automatic
===All holders of Ots or CPs===
for light water nuclear


safety system response during licensing
power reactors.


basis transients
93-20
)
93-19
93-18
03/24/93


and accidents.
===All holdefs of Os or CPs===
for PFRs supplied by


The information
===Westinghouse or Combustion===
Engineering.


in this notice indicates
03/17/92


that sustained
===All nuclear fuel cycle===
licensees.


level instrument
03/10/93


inaccuracies
===All U.S. Nuclear Regulatory===
Couuission licensees that


can occur during a normal reactor depressurization.
possess moisture-density


Therefore, events occurring
gauges.


during low pressure conditions
2
° _
clo


may also be complicated
co o


by level indication
001 c2 o


errors.This information
II


notice requires no specific action or written response.
2 u


If you have any questions
z


about the information
J qq


in this notice, please contact the technical
:3
00
a.


contact listed below or the appropriate
LwU)
:)4 aL.


Office of Nuclear Reactor Regulation (NRR) project manager.Brian K. Grimes, Director Division of Operational
OL - Operating License


===Events Assessment===
CP
Office of Nuclear Reactor Regulation


Technical
* Construction Permit


contact: Amy Cubbage, NRR (301) 504-2875 Attachment:
IN 93-27 April 8, 1993 automatic safety system response during licensing basis transients and
List of Recently Issued NRC Information


Notices
accidents. The information in this notice indicates that sustained level


Attachnent
instrument inaccuracies can occur during a normal reactor depressurization.


IN 93-27 April 8, 1993 Pge I of I ME0 a-dc LIST OF RECENTLY ISSUED HRC INFORMATION
Therefore, events occurring during low pressure conditions may also be


===NOTICES inroruauon===
complicated by level indication errors.
Inforuti0n


Notice No.93-26)93-25 93-24 93-23 93-22 93-21 Subject Grease Solidification
This information notice requires no specific action or written response.


Causes Molded Case Circuit Breaker Failure to Close Electrical
If


fenetration
you have any questions about the information in this notice, please contact


===Assembly Degradation===
the technical contact listed below or the appropriate Office of Nuclear
Distribution


of Revision 7 of NUREG-1021,*Operator
Reactor Regulation (NRR) project manager.


Licensing Examiner Standards'
===Original signed by===
Brian K. Grime:


===Veschler Instruments===
===Brian K. Grimes, Director===
Model 252 Switchboard
Division of Operational Events Assessment


Meters Tripping of Ilockner-toeller Molded-Case
===Office of Nuclear Reactor Regulation===
Technical contact:


Circuit Breakers due to Support Level Failure Sumary of NRC Staff Observations
===Amy Cubbage, NRR===
(301) 504-2875 Attachment:


Compiled'during Engineering
===List of Recently Issued NRC Information Notices===
*See previous concurrence


Audits or Inspections
*OGCB:DORS:NRR


of Licen-see Erosion/Corrosion
===JLBirmingham===
 
04/01/93
Programs Thermal Fatigue Cracking of Feedwater
*SRXB:DSSA:NRR
 
===Piping to Stem Generators===
Slab Hopper Bulging Portable Moisture-Density
 
===Gauge User Responsibilities===
during Field Operations
 
u te OT Issuance Issued to 04/07/93 All holders of OLs or CPs for nuclear power reactors.04/01/93 All holders of OLs or Cps for nuclear power reactors.03/31/93 All holders of operator and senior operator licenses at nuclear power reactors.03/31/93 All holders of OLs or CPs for nuclear power reactors.03/26/93 All holders of Ots or CPs for nuclear power reactors.03/25/93 All holders of Ots or CPs for light water nuclear power reactors.93-20)93-19 93-18 03/24/93 All holdefs of Os or CPs for PFRs supplied by Westinghouse


or Combustion
ACubbage


Engineering.
03/19/93
*C/OGCB:DORS:NRR


03/17/92 All nuclear fuel cycle licensees.
GHMarcus


03/10/93 All U.S. Nuclear Regulatory
04/01/93
*C/SRXB:DSSA:NRR


Couuission
RJones


licensees
03/26/93
*TECH:ED


that possess moisture-density
RSanders


gauges.2° _clo co o 001 c 2 o II 2 u z J qq:3 0 0 a.LwU):)4 aL.OL -Operating
03/18/93
*D/DSSA:NRR


License CP
AThadani


* Construction
03/26/93 Document name: 93-27.IN


Permit
IN 93-XX


IN 93-27 April 8, 1993 automatic
March XX, 1993 errors on automatic safety system response during licensing basis transients
 
safety system response during licensing
 
basis transients


and accidents.
and accidents.


The information
The information in this notice indicates that sustained level


in this notice indicates
instrument inaccuracies can occur during a normal reactor depressurization.


that sustained
Therefore, events occurring during low pressure conditions may also be


level instrument
complicated by level indication errors.


inaccuracies
This information notice requires no specific action or written response.


can occur during a normal reactor depressurization.
If


Therefore, events occurring
you have any questions about the information in this notice, please contact


during low pressure conditions
(one of) the technical contact(s) listed below or the appropriate Office of


may also be complicated
Nuclear Reactor Regulation (NRR) project manager.


by level indication
===Brian K. Grimes, Director===
Division of Operational Events Assessment


errors.This information
===Office of Nuclear Reactor Regulation===
Technical contact:


notice requires no specific action or written response.
===Amy Cubbage, NRR===
(301) 504-2875 Attachment:


If you have any questions
===List of Recently Issued NRC Information Notices===
*See previous c


about the information
OGCB:DORS:NRR
 
in this notice, please contact the technical
 
contact listed below or the appropriate
 
Office of Nuclear Reactor Regulation (NRR) project manager.Original signed by Brian K. Grime: Brian K. Grimes, Director Division of Operational
 
===Events Assessment===
Office of Nuclear Reactor Regulation
 
Technical
 
contact: Amy Cubbage, NRR (301) 504-2875 Attachment:
List of Recently Issued NRC Information
 
Notices*See previous concurrence
 
*OGCB:DORS:NRR


===JLBirmingham===
===JLBirmingham===
04/01/93*SRXB:DSSA:NRR
03"'
3 gY.Z-
*SRXB:DSSA:NRR


ACubbage 03/19/93*C/OGCB:DORS:NRR
ACubbage


GHMarcus 04/01/93*C/SRXB:DSSA:NRR
03/19/93 concurrence


RJones 03/26/93*TECH:ED RSanders 03/18/93*D/DSSA:NRR
C/OGCB:DORS:NRR


AThadani 03/26/93 Document name: 93-27.IN
GHMarcusas


IN 93-XX March XX, 1993 errors on automatic
°f 1 /93C tW


safety system response during licensing
*C/SRXB:DSSA:NRR


basis transients
RJones


and accidents.
03/26/93 D/DORS:NRR


The information
BKGrimesrMk


in this notice indicates
03/ /931'
*D/DSSA:NRR


that sustained
AThadani


level instrument
03/26/93
*TECH:ED


inaccuracies
RSanders


can occur during a normal reactor depressurization.
03/18/93 Document name:
RVLEVEL.IN


Therefore, events occurring
\\
I


during low pressure conditions
This information notice requires no specific action or written response.


may also be complicated
If


by level indication
you have any questions regarding the information in this notice, please


errors.This information
contact the technical contact listed below or the appropriate Office of


notice requires no specific action or written response.
Nuclear Reactor Regulation (NRR) project manager.


If you have any questions
===Brian K. Grimes, Director===
Division of Operating Reactor Support


about the information
===Office of Nuclear Reactor Regulation===
Technical contact:


in this notice, please contact (one of) the technical
===Amy Cubbage, NRR===
(301) 504-2875 Attachment: List of Recently Issued NRC Information Notices


contact(s)
Document name:
listed below or the appropriate
RVLEVEL.IN


Office of Nuclear Reactor Regulation (NRR) project manager.Brian K. Grimes, Director Division of Operational
*SEE PREVIOUS CONCURRENCE


===Events Assessment===
OGCB:DORS:NRR
Office of Nuclear Reactor Regulation


Technical
C/OGCB:DORS:NRR


contact: Amy Cubbage, NRR (301) 504-2875 Attachment:
D/DORS:NRR
List of Recently Issued NRC Information


Notices*See previous c OGCB:DORS:NRR
JLBirmingham


===JLBirmingham===
GHMarcus
03"' 3 gY.Z-*SRXB:DSSA:NRR


ACubbage 03/19/93 concurrence
BKGrimes


C/OGCB:DORS:NRR
03//903/
93
03
/93
*SRXB:DSSA:NRR


GHMarcusas
B:DSSA:NR &
D/DSSA:NR


°f 1 /93C tW*C/SRXB:DSSA:NRR
ACubbage


RJones 03/26/93 D/DORS:NRR
RJ nes


BKGrimesrMk
Thadani


03/ /931'*D/DSSA:NRR
03/ /93
0 t;/
/93
03 X/931
*TECHED:ADM


AThadani 03/26/93*TECH:ED RSanders 03/18/93 Document name: RVLEVEL.IN
RSanders


\ I This information
03/ /93


notice requires no specific action or written response.
IN 93-XX


If you have any questions
March XX, 1993 This information notice requires no specific action or written response. If


regarding
you have any questions regarding the information in this notice, please


the information
contact the technical contact listed below or the appropriate Office of


in this notice, please contact the technical
Nuclear Reactor Regulation (NRR) project manager.


contact listed below or the appropriate
===Brian K. Grimes, Director===
Division of Operating Reactor Support


Office of Nuclear Reactor Regulation (NRR) project manager.Brian K. Grimes, Director Division of Operating
===Office of Nuclear Reactor Regulation===
Technical contact:


===Reactor Support Office of Nuclear Reactor Regulation===
===Amy Cubbage, NRR===
Technical
(301) 504-2875 Attachment: List of Recently Issued NRC Information Notices


contact: Amy Cubbage, NRR (301) 504-2875 Attachment:
Document name:
List of Recently Issued NRC Information
 
Notices Document name: RVLEVEL.IN
 
*SEE PREVIOUS CONCURRENCE


===INFONOT2.RVL===
OGCB:DORS:NRR
OGCB:DORS:NRR


C/OGCB:DORS:NRR
===JLBirmingham===
03/ /93 C/OGCB: DORS:NRR


D/DORS:NRR
GHMarcus


JLBirmingham
03/ /93
0/DORS:NRR


GHMarcus BKGrimes 03//903/ 93 03 /93*SRXB:DSSA:NRR
BKGrimes


B:DSSA:NR
03/ /93 TECHED LADM


& D/DSSA:NR ACubbage RJ nes Thadani 03/ /93 0 t;/ /93 03 X/931*TECHED:ADM
JMain


RSanders 03/ /93 IN 93-XX March XX, 1993 This information
03/8 /93 SRXB:DSSA~:NlRR


notice requires no specific action or written response.
ACubbagqAtf-~
 
03/lcj/93 C/SRXB:DSSA:NRR
If you have any questions
 
regarding
 
the information
 
in this notice, please contact the technical
 
contact 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


contact: Amy Cubbage, NRR (301) 504-2875 Attachment:
RJones
List of Recently Issued NRC Information


Notices Document name: INFONOT2.RVL
03/ /93 D/DSSA:NRR
 
OGCB:DORS:NRR
 
===JLBirmingham===
03/ /93 C/OGCB: DORS:NRR GHMarcus 03/ /93 0/DORS:NRR
 
BKGrimes 03/ /93 TECHED LADM JMain 03/8 /93 SRXB:DSSA~:NlRR
 
ACubbagqAtf-~
03/lcj/93 C/SRXB:DSSA:NRR


RJones 03/ /93 D/DSSA:NRR
AThadani


AThadani 03/ /93}}
03/ /93}}


{{Information notice-Nav}}
{{Information notice-Nav}}

Latest revision as of 10:45, 16 January 2025

Level Instrumentation Inaccuracies Observed During Normal Plant Depressurization
ML031080007
Person / Time
Site: Beaver Valley, Millstone, Hatch, Monticello, Calvert Cliffs, Dresden, Davis Besse, Peach Bottom, Browns Ferry, Salem, Oconee, Mcguire, Nine Mile Point, Palisades, Palo Verde, Perry, Indian Point, Fermi, Kewaunee, Catawba, Harris, Wolf Creek, Saint Lucie, Point Beach, Oyster Creek, Watts Bar, Hope Creek, Grand Gulf, Cooper, Sequoyah, Byron, Pilgrim, Arkansas Nuclear, Braidwood, Susquehanna, Summer, Prairie Island, Columbia, Seabrook, Brunswick, Surry, Limerick, North Anna, Turkey Point, River Bend, Vermont Yankee, Crystal River, Haddam Neck, Ginna, Diablo Canyon, Callaway, Vogtle, Waterford, Duane Arnold, Farley, Robinson, Clinton, South Texas, San Onofre, Cook, Comanche Peak, Yankee Rowe, Maine Yankee, Quad Cities, Humboldt Bay, La Crosse, Big Rock Point, Rancho Seco, Zion, Midland, Bellefonte, Fort Calhoun, FitzPatrick, McGuire, LaSalle, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant, Crane  Entergy icon.png
Issue date: 04/08/1993
From: Grimes B
Office of Nuclear Reactor Regulation
To:
References
IN-93-027, NUDOCS 9304020319
Download: ML031080007 (8)
v • d • e


UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C.

20555

April 8, 1993

NRC INFORMATION NOTICE 93-27:

LEVEL INSTRUMENTATION INACCURACIES OBSERVED

DURING NORMAL PLANT DEPRESSURIZATION

Addressees

All holders of operating licenses or construction permits for nuclear power

reactors.

Purpose

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information

notice to alert addressees to inaccuracies in reactor vessel level indication

that occurred during a normal depressurization of the reactor coolant system

at the Washington Nuclear Plant Unit 2 (WNP-2) and to the fact that errors in

level indication may result in a failure to automatically isolate the residual

heat removal (RHR) system under certain conditions. 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.

Background

As discussed in NRC Information Notice 92-54, "Level Instrumentation

Inaccuracies Caused by Rapid Depressurization," and Generic Letter 92-04,

"Resolution of the Issues Related to Reactor Vessel Water Level

Instrumentation in BWRs Pursuant to 10 CFR 50.54(f)," noncondensible gas may

become dissolved in the reference leg of water level instrumentation and lead

to false indications of high level after a rapid depressurization event.

Reactor vessel level indication signals are important because these signals

are used for actuating automatic safety systems and for guidance to operators

during and after an event. While Information Notice 92-54 dealt with

potential consequences of rapid system depressurization, this information

notice discusses level indication errors that may occur during normal plant

cooldown and depressurization.

Description of Circumstances

On January 21, i993, during a plant cooldown following a reactor scram at

WNP-2, "notching" of the level indication was observed on at least two of four

channels of the reactor vessel narrow range level instrumentation.

"Notching

is a momentary increase in indicated water level. This increase occurs when a

gas bubble moves through a vertical portion of the reference leg and causes a

temporary decrease in the static head in the reference leg.

The notching at

9304020319 PD9Z

X

3 MoC

J

3pzu

13 oqat

P-

o'itv k

IN 93-27 April 8, 1993 WNP-2 was first observed on channel NC" at a pressure of approximately

827 kPa (120 psig].

Channel IBS experienced notching starting at

approximately 350 kPa [50 psig]. At these pressures, the level error was on

the order of 10 to 18 centimeters (4 to 7 inches] and persisted for

approximately one minute.

Beginning at a pressure of approximately 240 kPa [35 psig], the level

indication from channel IC' became erratic and, as the plant continued to

depressurize, an 81-centimeter (32-inch] level indication error occurred.

This depressurization was coincident with the initiation of the shutdown

cooling system.

The 81-centimeter [32-inch] level error was sustained and was

gradually recovered over a period of two hours.

The licensee postulated that

this large error in level indication was caused by gas released in the

reference leg displacing approximately 40 percent of the water volume.

The

licensee also postulated that the slow recovery of correct level indication

was a result of the time needed for steam to condense in the condensate

chamber and refill the reference leg. The licensee inspected the IC"

reference leg and discovered leakage through reference leg fittings. This

leakage may have been a contributing factor for an increased accumulation of

dissolved noncondensible gas in that reference leg.

The licensee determined that the type of errors observed in level indication

during this event could result in a failure to automatically isolate a leak in

the RHR system during shutdown cooling. The design basis for WNP-2 includes a

postulated leak in the RHR system piping outside containment while the plant

Is in the shutdown cooling mode.

For this event, the shutdown cooling suctlon

valves are assumed to automatically isolate on a low reactor vessel water

level signal to mitigate the consequences of the event.

For the January 21,

1993 plant cooldown, the licensee concluded that, with the observed errors in

level indication, the shutdown cooling suction valves may not have

automatically isolated the RHR system on low reactor vessel water level as;

designed. The licensee has implemented compensatory measures for future plant

cooldowns to ensure that a leak that occurs in the RHR system during shutdown

cooling operation would be isolated promptly. These measures include touring

the associated RHR pump room hourly during shutdown cooling and backfilling

the water level instrument reference legs after entry into mode 3 (hot

shutdown). The licensee is also evaluating measures to minimize leakage from

the IC' reference leg.

Discussion

The event described above is different than events previously reported because

of the large magnitude and sustained duration (as opposed to momentary

notching) of the level error that occurred during normal plant cooldown. A

large sustained level error is of concern because of the potential for

complicating long-term operator actions.

In addition, the scenario of a

postulated leak in the RHR system evaluated by WNP-2 suggests that some safety

systems may not automatically actuate should an event occur while the reactor

is in a reduced pressure condition. Generic Letter 92-04 requested, in part, that licensees determine the impact of potential level indication errors on

IN 93-27 April 8, 1993 automatic safety system response during licensing basis transients and

accidents.

The information in this notice indicates that sustained level

instrument inaccuracies can occur during a normal reactor depressurization.

Therefore, events occurring during low pressure conditions may also be

complicated by level indication errors.

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 Office of Nuclear

Reactor Regulation (NRR) project manager.

Brian K. Grimes, Director

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Technical contact:

Amy Cubbage, NRR

(301) 504-2875 Attachment:

List of Recently Issued NRC Information Notices

Attachnent

IN 93-27

April 8, 1993

Pge I of I

ME0

a- dc

LIST OF RECENTLY ISSUED

HRC INFORMATION NOTICES

inroruauon

Inforuti0n

Notice No.

93-26

)

93-25

93-24

93-23

93-22

93-21 Subject

Grease Solidification

Causes Molded Case

Circuit Breaker

Failure to Close

Electrical fenetration

Assembly Degradation

Distribution of

Revision 7 of NUREG-1021,

  • Operator Licensing

Examiner Standards'

Veschler Instruments

Model 252 Switchboard

Meters

Tripping of Ilockner- toeller Molded-Case

Circuit Breakers due to

Support Level Failure

Sumary of NRC Staff

Observations Compiled

'during Engineering Audits

or Inspections of Licen- see Erosion/Corrosion

Programs

Thermal Fatigue Cracking

of Feedwater Piping to

Stem Generators

Slab Hopper Bulging

Portable Moisture-Density

Gauge User Responsibilities

during Field Operations

u te OT

Issuance

Issued to

04/07/93

All holders of OLs or CPs

for nuclear power reactors.

04/01/93

All holders of OLs or Cps

for nuclear power reactors.

03/31/93

All holders of operator and

senior operator licenses at

nuclear power reactors.

03/31/93

All holders of OLs or CPs

for nuclear power reactors.

03/26/93

All holders of Ots or CPs

for nuclear power reactors.

03/25/93

All holders of Ots or CPs

for light water nuclear

power reactors.

93-20

)

93-19

93-18

03/24/93

All holdefs of Os or CPs

for PFRs supplied by

Westinghouse or Combustion

Engineering.

03/17/92

All nuclear fuel cycle

licensees.

03/10/93

All U.S. Nuclear Regulatory

Couuission licensees that

possess moisture-density

gauges.

2

° _

clo

co o

001 c2 o

II

2 u

z

J qq

3

00

a.

LwU)

)4 aL.

OL - Operating License

CP

  • Construction Permit

IN 93-27 April 8, 1993 automatic safety system response during licensing basis transients and

accidents. The information in this notice indicates that sustained level

instrument inaccuracies can occur during a normal reactor depressurization.

Therefore, events occurring during low pressure conditions may also be

complicated by level indication errors.

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 Office of Nuclear

Reactor Regulation (NRR) project manager.

Original signed by

Brian K. Grime:

Brian K. Grimes, Director

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Technical contact:

Amy Cubbage, NRR

(301) 504-2875 Attachment:

List of Recently Issued NRC Information Notices

  • See previous concurrence
  • OGCB:DORS:NRR

JLBirmingham

04/01/93

  • SRXB:DSSA:NRR

ACubbage

03/19/93

  • C/OGCB:DORS:NRR

GHMarcus

04/01/93

  • C/SRXB:DSSA:NRR

RJones

03/26/93

  • TECH:ED

RSanders

03/18/93

  • D/DSSA:NRR

AThadani

03/26/93 Document name: 93-27.IN

IN 93-XX

March XX, 1993 errors on automatic safety system response during licensing basis transients

and accidents.

The information in this notice indicates that sustained level

instrument inaccuracies can occur during a normal reactor depressurization.

Therefore, events occurring during low pressure conditions may also be

complicated by level indication errors.

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 contact(s) listed below or the appropriate Office of

Nuclear Reactor Regulation (NRR) project manager.

Brian K. Grimes, Director

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Technical contact:

Amy Cubbage, NRR

(301) 504-2875 Attachment:

List of Recently Issued NRC Information Notices

  • See previous c

OGCB:DORS:NRR

JLBirmingham

03"'

3 gY.Z-

  • SRXB:DSSA:NRR

ACubbage

03/19/93 concurrence

C/OGCB:DORS:NRR

GHMarcusas

°f 1 /93C tW

  • C/SRXB:DSSA:NRR

RJones

03/26/93 D/DORS:NRR

BKGrimesrMk

03/ /931'

  • D/DSSA:NRR

AThadani

03/26/93

  • TECH:ED

RSanders

03/18/93 Document name:

RVLEVEL.IN

\\

I

This information notice requires no specific action or written response.

If

you have any questions regarding the information in this notice, please

contact the technical contact 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 contact:

Amy Cubbage, NRR

(301) 504-2875 Attachment: List of Recently Issued NRC Information Notices

Document name:

RVLEVEL.IN

  • SEE PREVIOUS CONCURRENCE

OGCB:DORS:NRR

C/OGCB:DORS:NRR

D/DORS:NRR

JLBirmingham

GHMarcus

BKGrimes

03//903/

93

03

/93

  • SRXB:DSSA:NRR

B:DSSA:NR &

D/DSSA:NR

ACubbage

RJ nes

Thadani

03/ /93

0 t;/

/93

03 X/931

  • TECHED:ADM

RSanders

03/ /93

IN 93-XX

March XX, 1993 This information notice requires no specific action or written response. If

you have any questions regarding the information in this notice, please

contact the technical contact 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 contact:

Amy Cubbage, NRR

(301) 504-2875 Attachment: List of Recently Issued NRC Information Notices

Document name:

INFONOT2.RVL

OGCB:DORS:NRR

JLBirmingham

03/ /93 C/OGCB: DORS:NRR

GHMarcus

03/ /93

0/DORS:NRR

BKGrimes

03/ /93 TECHED LADM

JMain

03/8 /93 SRXB:DSSA~:NlRR

ACubbagqAtf-~

03/lcj/93 C/SRXB:DSSA:NRR

RJones

03/ /93 D/DSSA:NRR

AThadani

03/ /93


Retrieved from "https://kanterella.com/w/index.php?title=Information_Notice_1993-27,_Level_Instrumentation_Inaccuracies_Observed_During_Normal_Plant_Depressurization&oldid=5422533"