Information Notice 1993-89, Potential Problems with BWR Level Instrumentation Backfill Modifications: Difference between revisions

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{{#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. 20555 November 26, 1993 NRC INFORMATION


NOTICE 93-89: POTENTIAL
WASHINGTON, D.C. 20555 November 26, 1993 NRC INFORMATION NOTICE 93-89:   POTENTIAL PROBLEMS WITH BWR LEVEL


PROBLEMS WITH BWR LEVEL INSTRUMENTATION
INSTRUMENTATION BACKFILL MODIFICATIONS
 
===BACKFILL MODIFICATIONS===


==Addressees==
==Addressees==
All holders of operating
All holders of operating licenses or construction permits for boiling water


licenses or construction
reactors (BWRs).
 
permits for boiling water reactors (BWRs).


==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 potential
 
problems that have been identified
 
by licensees
 
involving
 
hardware modification
 
to the reactor vessel water level instrumentation
 
system. It is expected that recipients
 
will review the information
 
for applicability
 
to their facilities
 
and consider actions, as appropriate, to avoid similar problems.
 
However, suggestions
 
contained
 
in this information
 
notice are not NRC requirements;
therefore, no specific action or written response is required.Description
 
of Circumstances
 
NRC Bulletin (NRCB) 93-03, "Resolution
 
of Issues Related to Reactor Vessel Water Level Instrumentation
 
in BWRs," issued on May 28, 1993, requested
 
that licensees
 
implement
 
hardware modifications
 
necessary


to ensure the level instrumentation
notice to alert addressees to potential problems that have been identified by


system design is of high functional
licensees involving hardware modification to the reactor vessel water level


reliability
instrumentation system. It is expected that recipients will review the


for long-term operation.
information for applicability to their facilities and consider actions, as


In response to this bulletin, all BWR licensees
appropriate, to avoid similar problems. However, suggestions contained in


with the exception of Big Rock Point, which does not use cold reference
this information notice are not NRC requirements; therefore, no specific


leg instrumentation, have either implemented
action or written response is required.


modifications
==Description of Circumstances==
NRC Bulletin (NRCB) 93-03, "Resolution of Issues Related to Reactor Vessel


or have committed
Water Level Instrumentation in BWRs," issued on May 28, 1993, requested that


to implement
licensees implement hardware modifications necessary to ensure the level


modifications.
instrumentation system design is of high functional reliability for long-term


The majority of these licensees
operation. In response to this bulletin, all BWR licensees with the exception


have decided to install a reference
of Big Rock Point, which does not use cold reference leg instrumentation, have


leg backfill system to supply a continuous
either implemented modifications or have committed to implement modifications.


flow of water from the control rod drive (CRD) hydraulic
The majority of these licensees have decided to install a reference leg


system through the reference
backfill system to supply a continuous flow of water from the control rod


legs to preclude migration of dissolved
drive (CRD) hydraulic system through the reference legs to preclude migration


noncondensible
of dissolved noncondensible gases down the legs. In August 1993, a potential


gases down the legs. In August 1993, a potential problem was found at the Susquehanna
problem was found at the Susquehanna nuclear power plant during the design of


nuclear power plant during the design of this backfill modification.
this backfill modification.


Discussion
Discussion


It was postulated
It was postulated at Susquehanna that a manual isolation valve in one of the
 
at Susquehanna
 
that a manual isolation
 
valve in one of the reference
 
legs (see Figure 1) could be closed by operator error. Closure of this valve would result in pressurization
 
of that reference
 
leg to CRD system pressure and erroneous
 
indication
 
of low reactor water level and high reactor pressure on all instrumentation
 
associated
 
with that reference
 
leg. The transient
 
resulting
 
from pressurization
 
of the most limiting reference
 
leg 9311190454
1 KE-e 93-o 93 Ill
 
K.,_ IN 93-89 November 26, 1993 includes reactor scram and opening of all safety relief valves (SRVs) due to the false high reactor pressure.
 
===The SRVs would remain open and depressurize===
the reactor until the valves are closed by operator action, or actual reactor pressure falls below approximately
 
446 kPa [50 psig] at which time the valves can no longer stay open. Reactor depressurization
 
and loss of inventory through the SRVs, in combination
 
with the false low water level signal on the affected reference
 
leg, would result in closure of the main steam isolation valves, actuation
 
of high-pressure
 
and low-pressure
 
emergency
 
core cooling system (ECCS) and containment
 
isolation.
 
Low-pressure
 
ECCS injection
 
would commence after the low-pressure
 
permissive
 
is satisfied.
 
===This permissive===
would be satisfied
 
in this scenario, allowing the low pressure ECCS injection valves to open, because only one of the pressure transmitters
 
is affected and the logic would still be satisfied.
 
A single failure could defeat this logic, however, preventing
 
all low-pressure
 
ECCS Injection.
 
The low-pressure
 
permissive
 
can be bypassed in the control room to open the injection
 
valves for all four low pressure core spray (LPCS) pumps. The Susquehanna
 
licensee has informed the NRC that it has physically
 
disabled the manual isolation valves to prevent misoperation
 
of these valves; in addition, the valves are not readily accessible


as they are located 6.1 meters [20 feet] above the floor.This event was recently analyzed for the LaSalle plant by Commonwealth
reference legs (see Figure 1) could be closed by operator error. Closure of


Edison.The analysis indicates
this valve would result in pressurization of that reference leg to CRD system


that the low-pressure
pressure and erroneous indication of low reactor water level and high reactor


permissive
pressure on all instrumentation associated with that reference leg. The


for opening the low-pressure ECCS injection
transient resulting from pressurization of the most limiting reference leg


valve would be defeated for the LaSalle design due to the false high pressure signal, thus preventing
9311190454          KE-e                                193-o                93 Ill


ECCS injection
K.,_ IN 93-89 November 26, 1993 includes reactor scram and opening of all safety relief valves (SRVs) due to


from the affected division.
the false high reactor pressure. The SRVs would remain open and depressurize


If a single failure is assumed in the relay for the low-pressure permissive
the reactor until the valves are closed by operator action, or actual reactor


on the other division, no low-pressure
pressure falls below approximately 446 kPa [50 psig] at which time the valves


ECCS injection would be available.
can no longer stay open. Reactor depressurization and loss of inventory


Because the induced plant transient
through the SRVs, in combination with the false low water level signal on the


is potentially
affected reference leg, would result in closure of the main steam isolation


so severe, LaSalle has designed its backfill modification
valves, actuation of high-pressure and low-pressure emergency core cooling


to make the injection point for the backfill system on the reactor side of the manual isolation valve and excess flow check valve, thereby precluding
system (ECCS) and containment isolation. Low-pressure ECCS injection would


the potential
commence after the low-pressure permissive is satisfied. This permissive


for pressurization
would be satisfied in this scenario, allowing the low pressure ECCS injection


of the reference
valves to open, because only one of the pressure transmitters is affected and


leg through the backfill system.Commonwealth
the logic would still be satisfied. A single failure could defeat this logic, however, preventing all low-pressure ECCS Injection. The low-pressure


Edison took a different
permissive can be bypassed in the control room to open the injection valves


design approach for its Dresden and Quad Cities plants. The backfill system design for Dresden and Quad Cities injects into the reference
for all four low pressure core spray (LPCS) pumps. The Susquehanna licensee


leg on the instrument
has informed the NRC that it has physically disabled the manual isolation


rack side of the manual isolation
valves to prevent misoperation of these valves; in addition, the valves are


valve and excess flow check valve. Additional
not readily accessible as they are located 6.1 meters [20 feet] above the


administrative
floor.


controls were developed
This event was recently analyzed for the LaSalle plant by Commonwealth Edison.


to ensure that the isolation
The analysis indicates that the low-pressure permissive for opening the low- pressure ECCS injection valve would be defeated for the LaSalle design due to


valve would not be inadvertently
the false high pressure signal, thus preventing ECCS injection from the


closed. The licensee analyzed the inadvertent
affected division. If a single failure is assumed in the relay for the low- pressure permissive on the other division, no low-pressure ECCS injection


closure of the manual isolation
would be available. Because the induced plant transient is potentially so


valve for the Dresden and Quad Cities plants and concluded that, while multiple SRVs would open, the resultant
severe, LaSalle has designed its backfill modification to make the injection


plant transient
point for the backfill system on the reactor side of the manual isolation


could be mitigated
valve and excess flow check valve, thereby precluding the potential for


by appropriate
pressurization of the reference leg through the backfill system.


operator actions. Without operator actions, the low-pressure ECCS would be available
Commonwealth Edison took a different design approach for its Dresden and


for event mitigation;
Quad Cities plants. The backfill system design for Dresden and Quad Cities
however, a single failure in the instrumentation


system could defeat the low-pressure
injects into the reference leg on the instrument rack side of the manual


permissive
isolation valve and excess flow check valve. Additional administrative


for opening the low-pressure
controls were developed to ensure that the isolation valve would not be


ECCS Injection
inadvertently closed. The licensee analyzed the inadvertent closure of the


valves and result in no low-pressure ECCS being available
manual isolation valve for the Dresden and Quad Cities plants and concluded


for this transient.
that, while multiple SRVs would open, the resultant plant transient could be


The licensee also determined
mitigated by appropriate operator actions. Without operator actions, the low- pressure ECCS would be available for event mitigation; however, a single


that this design presented
failure in the instrumentation system could defeat the low-pressure permissive


an unreviewed
for opening the low-pressure ECCS Injection valves and result in no low- pressure ECCS being available for this transient. The licensee also


safety question because it would increase the probability
determined that this design presented an unreviewed safety question because it


of a previously
would increase the probability of a previously analyzed accident, and


analyzed accident, and submitted
submitted an application to amend its license pursuant to 10 CFR 50.90. The


an application
NRC is currently reviewing the licensee submittal.


to amend its license pursuant to 10 CFR 50.90. The NRC is currently
IN 93-89 November 26, 1993 Other minor problems with the backfill system have been encountered when


reviewing
installing the system and returning the instrumentation to service after


the licensee submittal.
installation was complete. At the Perry plant, a problem occurred when the


IN 93-89 November 26, 1993 Other minor problems with the backfill system have been encountered
licensee was in the process of venting one of the instrument lines following


when installing
the installation of the modification. The job plan directed the operation of


the system and returning
the wrong valve, and instead of opening the vent valve the technician opened


the instrumentation
the isolation valve, allowing air into the reference leg. As a result, the


to service after installation
instrumentation associated with the high pressure core spray system (HPCS) was


was complete.
inoperable until it was re-filled and vented. Similar events have occurred at


At the Perry plant, a problem occurred when the licensee was in the process of venting one of the instrument
other plants due to procedural inadequacy or lack of attention to detail.


lines following the installation
===Related Generic Communications===
*    NRC Information Notice 92-54, "Level Instrumentation Inaccuracies Caused


of the modification.
by Rapid Depressurization," July 24, 1992.


The job plan directed the operation
*    Generic Letter 92-04, "Resolution of the Issues Related to Reactor


of the wrong valve, and instead of opening the vent valve the technician
Vessel Water Level Instrumentation in BWRs Pursuant to 10 CFR 50.54(f),"
      August 19, 1992.


opened the isolation
*    NRC Information Notice 93-27, 'Level Instrumentation Inaccuracies


valve, allowing air into the reference
Observed During Normal Plant Depressurization," April 8, 1993.


leg. As a result, the instrumentation
*    NRC Bulletin 93-03, Resolution of Issues Related to Reactor Vessel


associated
Water Level Instrumentation in BWRs,' May 28, 1993.


with the high pressure core spray system (HPCS) was inoperable
This information notice requires no specific action or written response.  If


until it was re-filled
you have any questions regarding the information in this notice, please


and vented. Similar events have occurred at other plants due to procedural
contact the technical contact listed below or the appropriate Office of


inadequacy
Nuclear Reactor Regulation (NRR) project manager.


or lack of attention
Brian K. Grimes, Director


to detail.Related Generic Communications
Division of Operating Reactor Support


* NRC Information
Office of Nuclear Reactor Regulation


Notice 92-54, "Level Instrumentation
Technical contact: Amy Cubbage, NRR


Inaccuracies
(301) 504-2875 Attachments:
1. Simplified Sketch of Backfill Modification


Caused by Rapid Depressurization," July 24, 1992.* Generic Letter 92-04, "Resolution
2. List of Recently Issued NRC Information Notices


of the Issues Related to Reactor Vessel Water Level Instrumentation
rfl


in BWRs Pursuant to 10 CFR 50.54(f)," August 19, 1992.* NRC Information
tO      CONDENSATE POT


Notice 93-27, 'Level Instrumentation
REACTOR VESSEL


===Inaccuracies===
(
Observed During Normal Plant Depressurization," April 8, 1993.* NRC Bulletin 93-03, Resolution
                                                        DRYWELL


of Issues Related to Reactor Vessel Water Level Instrumentation
REACTOR BLDG


in BWRs,' May 28, 1993.This information
U


notice requires no specific action or written response.
7 MANUAL


If you have any questions
L ISOLATION


regarding
C  EXCESS FLOW


the information
QA BOUNDARY                    $ CHECK VALVE


in this notice, please contact the technical
===CRD CHARGING===
WATER HEADER


contact listed below or the appropriate
REFERENCE LEG


Office of Nuclear Reactor Regulation (NRR) project manager.Brian K. Grimes, Director Division of Operating
INSTRtUm


===Reactor Support Office of Nuclear Reactor Regulation===
VARIABLE
Technical


contact: Amy Cubbage, NRR (301) 504-2875 Attachments:
LEG
1. Simplified


===Sketch of Backfill Modification===
RACK                C
2. List of Recently Issued NRC Information


Notices
e0 (
    FIGURE 1 - SIMPLIFIED SKETCH OF BACKFILL MODIFICATION


rfl tO CONDENSATE
cI-
                                                                                Ij3 ED


POT REACTOR VESSEL (QA BOUNDARY U DRYWELL REACTOR BLDG 7 MANUAL L ISOLATION C EXCESS FLOW$ CHECK VALVE REFERENCE
w,


LEG CRD CHARGING WATER HEADER INSTRtUm RACK VARIABLE LEG C FIGURE 1 -SIMPLIFIED
A4...achment 2 IN 93-89 November 26, 1993 LIST OF RECENTLY ISSUED


===SKETCH OF BACKFILL MODIFICATION===
NRC INFORMATION NOTICES
e0 (cI-Ij3 ED w, A4...achment


2 IN 93-89 November 26, 1993 LIST OF RECENTLY ISSUED NRC INFORMATION
Information                                  Date of


NOTICES Information
Notice No.            Subject                Issuance  Issued to


Date of Notice No. Subject Issuance Issued to 93-88 93-87 93-86 93-85 93-84 Status of Motor-Operated
93-88         Status of Motor-Operated       11/30/93  All holders of OLs or CPs


Valve Performance
Valve Performance Pre-                    for nuclear power reactors.


Pre-diction Program by the Electric Power Research Institute Fuse Problems with Westinghouse
diction Program by the


7300 Printed Circuit Cards Identification
Electric Power Research


of Iso-topes in the Production
Institute


and Shipment of Byproduct Material at Non-power Reactors Problems with X-Relays in DB- and DHB-Type Circuit Breakers Manu-factured by Westinghouse
93-87          Fuse Problems with             11/04/93  All holders of OLs or CPs


Determination
Westinghouse 7300                        for nuclear power reactors.


of Westing-house Reactor Coolant Pump Seal Failure 11/30/93 11/04/93 10/29/93 10/20/93 10/20/93 All holders of OLs or CPs for nuclear power reactors.All holders of OLs or CPs for nuclear power reactors.All holders of OLs or CPs for test and research reactors.All holders of OLs or CPs for nuclear power reactors.All holders of OLs or CPs for pressurized
Printed Circuit Cards


water reactors (PWRs).93-83 Potential
93-86          Identification of Iso-        10/29/93  All holders of OLs or CPs


Loss of Spent Fuel Pool Cooling Following
topes in the Production                  for test and research


A Loss of Coolant Accident (LOCA)10/07/93 All holders for boiling (BWRs).of OLs or CPs water reactors 93-82 93-81 Recent Fuel and Core Performance
and Shipment of Byproduct                reactors.


Problems in Operating
Material at Non-power


Reactors Implementation
Reactors


of Engineering
93-85          Problems with X-Relays        10/20/93  All holders of OLs or CPs


Expertise on Shift 10/12/93 10/12/93 All holders of OLs or CPs for nuclear power reactors and all NRC-approved
in DB- and DHB-Type                      for nuclear power reactors.


fuel suppliers.
Circuit Breakers Manu- factured by Westinghouse


All holders of OLs or CPs for nuclear power reactors.OL -Operating
93-84          Determination of Westing-      10/20/93  All holders of OLs or CPs


License CP -Construction
house Reactor Coolant                      for pressurized water


Permit
Pump Seal Failure                        reactors (PWRs).


IN 93-89 a-> November 26, 1993 Other minor problems with the backfill system have been encountered
93-83          Potential Loss of Spent        10/07/93  All holders of OLs or CPs


when installing
Fuel Pool Cooling                          for boiling water reactors


the system and returning
Following A Loss of                        (BWRs).


the instrumentation
Coolant Accident (LOCA)
93-82          Recent Fuel and Core          10/12/93  All holders of OLs or CPs


to service after installation
Performance Problems in                    for nuclear power reactors


was complete.
Operating Reactors                        and all NRC-approved fuel


At the Perry plant, a problem occurred when the licensee was in the process of venting one of the instrument
suppliers.


lines following the installation
93-81          Implementation of              10/12/93  All holders of OLs or CPs


of the modification.
Engineering Expertise                      for nuclear power reactors.


The Job plan directed the operation
on Shift


of the wrong valve, and instead of opening the vent valve the technician
OL - Operating License


opened the isolation
CP - Construction Permit


valve, allowing air into the reference
IN 93-89 a->    November 26, 1993 Other minor problems with the backfill system have been encountered when


leg. As a result, the instrumentation
installing the system and returning the instrumentation to service after


associated
installation was complete. At the Perry plant, a problem occurred when the


with the high pressure core spray system (HPCS) was inoperable
licensee was in the process of venting one of the instrument lines following


until it was re-filled
the installation of the modification. The Job plan directed the operation of


and vented. Similar events have occurred at other plants due to procedural
the wrong valve, and instead of opening the vent valve the technician opened


inadequacy
the isolation valve, allowing air into the reference leg. As a result, the


or lack of attention
instrumentation associated with the high pressure core spray system (HPCS) was


to detail.Related Generic Communications
inoperable until it was re-filled and vented. Similar events have occurred at


* NRC Information
other plants due to procedural inadequacy or lack of attention to detail.


Notice 92-54, "Level Instrumentation
===Related Generic Communications===
*      NRC Information Notice 92-54, "Level Instrumentation Inaccuracies Caused


Inaccuracies
by Rapid Depressurization," July 24, 1992.


Caused by Rapid Depressurization," July 24, 1992.* Generic Letter 92-04, "Resolution
*     Generic Letter 92-04, "Resolution of the Issues Related to Reactor


of the Issues Related to Reactor Vessel Water Level Instrumentation
Vessel Water Level Instrumentation in BWRs Pursuant to 10 CFR 50.54(f),"
      August 19, 1992.


in BWRs Pursuant to 10 CFR 50.54(f)," August 19, 1992.* NRC Information
*     NRC Information Notice 93-27, 'Level Instrumentation Inaccuracies


Notice 93-27, 'Level Instrumentation
Observed During Normal Plant Depressurization," April 8, 1993.


===Inaccuracies===
*     NRC Bulletin 93-03, 'Resolution of Issues Related to Reactor Vessel
Observed During Normal Plant Depressurization," April 8, 1993.* NRC Bulletin 93-03, 'Resolution


of Issues Related to Reactor Vessel Water Level Instrumentation
Water Level Instrumentation in BWRs," May 28, 1993.


in BWRs," May 28, 1993.This information
This information notice requires no specific action or written response.        If


notice requires no specific action or written response.
you have any questions regarding the information in this notice, please


If you have any questions
contact the technical contact listed below or the appropriate Office of


regarding
Nuclear Reactor Regulation (NRR) project manager.


the information
orig /s/'d by BKGrimes


in this notice, please contact the technical
Brian K. Grimes, Director


contact listed below or the appropriate
Division of Operating Reactor Support


Office of Nuclear Reactor Regulation (NRR) project manager.orig /s/'d by BKGrimes Brian K. Grimes, Director Division of Operating
Office of Nuclear Reactor Regulation


===Reactor Support Office of Nuclear Reactor Regulation===
Technical contact:    Amy Cubbage, NRR
Technical


contact: Amy Cubbage, NRR (301) 504-2875 Attachments:
(301) 504-2875 Attachments:
1. Simplified
1. Simplified Sketch of Backfill Modification


===Sketch of Backfill Modification===
2. List of Recently Issued NRC Information Notices
2. List of Recently Issued NRC Information


Notices* SEE PREVIOUS CONCURRENCE
* SEE PREVIOUS CONCURRENCE


SRXB:DSSA*  
SRXB:DSSA* OGCB:DORS* TECH ED.*       SRXB:DSSA* SRXB:DSSA* D:DSSA* OGCB:DORS*
OGCB:DORS*  
ACUBBAGE     PWEN         RSANDERS   WLYON       RJONES     ATHADANI GMARCUS
TECH ED.* SRXB:DSSA*  
SRXB:DSSA*  
D:DSSA* OGCB:DORS*
ACUBBAGE PWEN RSANDERS WLYON RJONES ATHADANI GMARCUS 1 11/16/93 11/15/93 11/16/93 11/18/93 11/20/93 11/23/93 11/2.493 DOCUMENT NAME: 93-89.IN


IN 93-xx November xx, 1993 This information
1          11/16/93      11/15/93    11/16/93    11/18/93  11/20/93  11/23/93
11/2.493 DOCUMENT NAME:    93-89.IN


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


If you have any questions
November 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


Office of Nuclear Reactor Regulation (NRR) project manager.Brian K. Grimes, Director Division of Operating
Division of Operating Reactor Support


===Reactor Support Office of Nuclear Reactor Regulation===
Office of Nuclear Reactor Regulation
Technical


Contact: Amy Cubbage, NRR (301) 504-2875 Attachments:
===Technical Contact:===
1. Simplified


===Sketch of Backfill Modification===
===Amy Cubbage, NRR===
2. List of Recently Issued NRC Information
                      (301) 504-2875 Attachments:
1. Simplified Sketch of Backfill Modification


Notices* SEE PREVIOUS CONCURRENCE
2. List of Recently Issued NRC Information Notices


SRXB:DSSA*  
* SEE PREVIOUS CONCURRENCE
OGCB:DORS*
TECH ED.*ACUBBAGE PWEN RSANDERS 11/15/93 11/16/93 11/15/93 SRXB:DSSA*
WLYON 11/16/93 SRXB:DSSA*
RJONES 11/18/93 D: DSSA*ATHADANI 11/20/93 OGCB:DORS GMARCUS At'i 11/23/93 D: DORS BGRIMES 11/ /93 DOCUMENT NAME: BWRWTLVL.WEN


instrumentation
SRXB:DSSA* OGCB:DORS* TECH ED.*      SRXB:DSSA* SRXB:DSSA* D: DSSA*  OGCB:DORS


associated
ACUBBAGE    PWEN          RSANDERS    WLYON      RJONES    ATHADANI  GMARCUS At'i


with the high pressure core spray system (HPCS) was inoperable
11/15/93    11/16/93      11/15/93    11/16/93  11/18/93    11/20/93  11/23/93 D: DORS


until it was re-filled
BGRIMES


and vented. Similar events have occurred at other plants due to procedural
11/ /93 DOCUMENT NAME:  BWRWTLVL.WEN


inadequacy
instrumentation associated with the high pressure core spray system (HPCS) was


or lack of attention
inoperable until it was re-filled and vented. Similar events have occurred at


to detail.Related Generic Communications
other plants due to procedural inadequacy or lack of attention to detail.


* NRC Information
===Related Generic Communications===
*     NRC Information Notice 92-54, "Level Instrumentation Inaccuracies Caused


Notice 92-54, "Level Instrumentation
by Rapid Depressurization," July 24, 1992.


Inaccuracies
*      Generic Letter 92-04, "Resolution of the Issues Related to Reactor


Caused by Rapid Depressurization," July 24, 1992.* Generic Letter 92-04, "Resolution
Vessel Water Level Instrumentation in BWRs Pursuant to 10 CFR 50.54(f),"
      August 19, 1992.


of the Issues Related to Reactor Vessel Water Level Instrumentation
*      NRC Information Notice 93-27, "Level Instrumentation Inaccuracies


in BWRs Pursuant to 10 CFR 50.54(f)," August 19, 1992.* NRC Information
Observed During Normal Plant Depressurization," April 8, 1993.


Notice 93-27, "Level Instrumentation
*      NRC Bulletin 93-03, "Resolution of Issues Related to Reactor Vessel


===Inaccuracies===
Water Level Instrumentation in BWRs," May 28, 1993.
Observed During Normal Plant Depressurization," April 8, 1993.* NRC Bulletin 93-03, "Resolution


of Issues Related to Reactor Vessel Water Level Instrumentation
This information notice requires no specific action or written response.    If


in BWRs," May 28, 1993.This information
you have any questions regarding the information in this notice, please


notice requires no specific action or written response.
contact the technical contact listed below or the appropriate Office of


If you have any questions
Nuclear Reactor Regulation (NRR) project manager.


regarding
Brian K. Grimes, Director


the information
Division of Operating Reactor Support


in this notice, please contact the technical
Office of Nuclear Reactor Regulation


contact listed below or the appropriate
===Technical Contact:===


Office of Nuclear Reactor Regulation (NRR) project manager.Brian K. Grimes, Director Division of Operating
===Amy Cubbage, NRR===
                        (301) 504-2875 Attachments:
1.     Simplified Sketch of Backfill Modification


===Reactor Support Office of Nuclear Reactor Regulation===
2.    List of Recently Issued NRC Information Notices
Technical


Contact: Amy Cubbage, NRR (301) 504-2875 Attachments:
EDITED BY:   R. Sanders
1. Simplified


===Sketch of Backfill Modification===
DATED:        11/15/93 SRXB:DSSA*  OGCB:DORS*  SRXB:DSSA* SRXB:DSSA* D:DSSA    OGCB:DORS  D:DORS
2. List of Recently Issued NRC Information


Notices EDITED BY: R. Sanders DATED: 11/15/93 SRXB:DSSA*
ACUBBAGE    PWEN        WLYON      RJONES    ATHAqkNI  GMARCUS    BGRIMES
OGCB:DORS*
SRXB:DSSA*
SRXB:DSSA*
D:DSSA OGCB:DORS


D:DORS ACUBBAGE PWEN WLYON RJONES ATHAqkNI GMARCUS BGRIMES 11/15/93 11/16/93 11/16/93 11/18/93 11/?V/93 11/ /93 11/ /93* SEE PREVIOUS CONCURRENCE}}
11/15/93     11/16/93   11/16/93   11/18/93   11/?V/93 11/ /93   11/ /93
* SEE PREVIOUS CONCURRENCE}}


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

Revision as of 03:23, 24 November 2019

Potential Problems with BWR Level Instrumentation Backfill Modifications
ML031070176
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: 11/26/1993
From: Grimes B
Office of Nuclear Reactor Regulation
To:
References
IN-93-089, NUDOCS 9311190454
Download: ML031070176 (8)
v • d • e


UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555 November 26, 1993 NRC INFORMATION NOTICE 93-89: POTENTIAL PROBLEMS WITH BWR LEVEL

INSTRUMENTATION BACKFILL MODIFICATIONS

Addressees

All holders of operating licenses or construction permits for boiling water

reactors (BWRs).

Purpose

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

notice to alert addressees to potential problems that have been identified by

licensees involving hardware modification to the reactor vessel water level

instrumentation system. It is expected that recipients will review the

information for applicability to their facilities and consider actions, as

appropriate, to avoid similar problems. However, suggestions contained in

this information notice are not NRC requirements; therefore, no specific

action or written response is required.

Description of Circumstances

NRC Bulletin (NRCB) 93-03, "Resolution of Issues Related to Reactor Vessel

Water Level Instrumentation in BWRs," issued on May 28, 1993, requested that

licensees implement hardware modifications necessary to ensure the level

instrumentation system design is of high functional reliability for long-term

operation. In response to this bulletin, all BWR licensees with the exception

of Big Rock Point, which does not use cold reference leg instrumentation, have

either implemented modifications or have committed to implement modifications.

The majority of these licensees have decided to install a reference leg

backfill system to supply a continuous flow of water from the control rod

drive (CRD) hydraulic system through the reference legs to preclude migration

of dissolved noncondensible gases down the legs. In August 1993, a potential

problem was found at the Susquehanna nuclear power plant during the design of

this backfill modification.

Discussion

It was postulated at Susquehanna that a manual isolation valve in one of the

reference legs (see Figure 1) could be closed by operator error. Closure of

this valve would result in pressurization of that reference leg to CRD system

pressure and erroneous indication of low reactor water level and high reactor

pressure on all instrumentation associated with that reference leg. The

transient resulting from pressurization of the most limiting reference leg

9311190454 KE-e 193-o 93 Ill

K.,_ IN 93-89 November 26, 1993 includes reactor scram and opening of all safety relief valves (SRVs) due to

the false high reactor pressure. The SRVs would remain open and depressurize

the reactor until the valves are closed by operator action, or actual reactor

pressure falls below approximately 446 kPa [50 psig] at which time the valves

can no longer stay open. Reactor depressurization and loss of inventory

through the SRVs, in combination with the false low water level signal on the

affected reference leg, would result in closure of the main steam isolation

valves, actuation of high-pressure and low-pressure emergency core cooling

system (ECCS) and containment isolation. Low-pressure ECCS injection would

commence after the low-pressure permissive is satisfied. This permissive

would be satisfied in this scenario, allowing the low pressure ECCS injection

valves to open, because only one of the pressure transmitters is affected and

the logic would still be satisfied. A single failure could defeat this logic, however, preventing all low-pressure ECCS Injection. The low-pressure

permissive can be bypassed in the control room to open the injection valves

for all four low pressure core spray (LPCS) pumps. The Susquehanna licensee

has informed the NRC that it has physically disabled the manual isolation

valves to prevent misoperation of these valves; in addition, the valves are

not readily accessible as they are located 6.1 meters [20 feet] above the

floor.

This event was recently analyzed for the LaSalle plant by Commonwealth Edison.

The analysis indicates that the low-pressure permissive for opening the low- pressure ECCS injection valve would be defeated for the LaSalle design due to

the false high pressure signal, thus preventing ECCS injection from the

affected division. If a single failure is assumed in the relay for the low- pressure permissive on the other division, no low-pressure ECCS injection

would be available. Because the induced plant transient is potentially so

severe, LaSalle has designed its backfill modification to make the injection

point for the backfill system on the reactor side of the manual isolation

valve and excess flow check valve, thereby precluding the potential for

pressurization of the reference leg through the backfill system.

Commonwealth Edison took a different design approach for its Dresden and

Quad Cities plants. The backfill system design for Dresden and Quad Cities

injects into the reference leg on the instrument rack side of the manual

isolation valve and excess flow check valve. Additional administrative

controls were developed to ensure that the isolation valve would not be

inadvertently closed. The licensee analyzed the inadvertent closure of the

manual isolation valve for the Dresden and Quad Cities plants and concluded

that, while multiple SRVs would open, the resultant plant transient could be

mitigated by appropriate operator actions. Without operator actions, the low- pressure ECCS would be available for event mitigation; however, a single

failure in the instrumentation system could defeat the low-pressure permissive

for opening the low-pressure ECCS Injection valves and result in no low- pressure ECCS being available for this transient. The licensee also

determined that this design presented an unreviewed safety question because it

would increase the probability of a previously analyzed accident, and

submitted an application to amend its license pursuant to 10 CFR 50.90. The

NRC is currently reviewing the licensee submittal.

IN 93-89 November 26, 1993 Other minor problems with the backfill system have been encountered when

installing the system and returning the instrumentation to service after

installation was complete. At the Perry plant, a problem occurred when the

licensee was in the process of venting one of the instrument lines following

the installation of the modification. The job plan directed the operation of

the wrong valve, and instead of opening the vent valve the technician opened

the isolation valve, allowing air into the reference leg. As a result, the

instrumentation associated with the high pressure core spray system (HPCS) was

inoperable until it was re-filled and vented. Similar events have occurred at

other plants due to procedural inadequacy or lack of attention to detail.

Related Generic Communications

by Rapid Depressurization," July 24, 1992.

Vessel Water Level Instrumentation in BWRs Pursuant to 10 CFR 50.54(f),"

August 19, 1992.

Observed During Normal Plant Depressurization," April 8, 1993.

Water Level Instrumentation in BWRs,' May 28, 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 Attachments:

1. Simplified Sketch of Backfill Modification

2. List of Recently Issued NRC Information Notices

rfl

tO CONDENSATE POT

REACTOR VESSEL

(

DRYWELL

REACTOR BLDG

U

7 MANUAL

L ISOLATION

C EXCESS FLOW

QA BOUNDARY $ CHECK VALVE

CRD CHARGING

WATER HEADER

REFERENCE LEG

INSTRtUm

VARIABLE

LEG

RACK C

e0 (

FIGURE 1 - SIMPLIFIED SKETCH OF BACKFILL MODIFICATION

cI-

Ij3 ED

w,

A4...achment 2 IN 93-89 November 26, 1993 LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

Information Date of

Notice No. Subject Issuance Issued to

93-88 Status of Motor-Operated 11/30/93 All holders of OLs or CPs

Valve Performance Pre- for nuclear power reactors.

diction Program by the

Electric Power Research

Institute

93-87 Fuse Problems with 11/04/93 All holders of OLs or CPs

Westinghouse 7300 for nuclear power reactors.

Printed Circuit Cards

93-86 Identification of Iso- 10/29/93 All holders of OLs or CPs

topes in the Production for test and research

and Shipment of Byproduct reactors.

Material at Non-power

Reactors

93-85 Problems with X-Relays 10/20/93 All holders of OLs or CPs

in DB- and DHB-Type for nuclear power reactors.

Circuit Breakers Manu- factured by Westinghouse

93-84 Determination of Westing- 10/20/93 All holders of OLs or CPs

house Reactor Coolant for pressurized water

Pump Seal Failure reactors (PWRs).

93-83 Potential Loss of Spent 10/07/93 All holders of OLs or CPs

Fuel Pool Cooling for boiling water reactors

Following A Loss of (BWRs).

Coolant Accident (LOCA)

93-82 Recent Fuel and Core 10/12/93 All holders of OLs or CPs

Performance Problems in for nuclear power reactors

Operating Reactors and all NRC-approved fuel

suppliers.

93-81 Implementation of 10/12/93 All holders of OLs or CPs

Engineering Expertise for nuclear power reactors.

on Shift

OL - Operating License

CP - Construction Permit

IN 93-89 a-> November 26, 1993 Other minor problems with the backfill system have been encountered when

installing the system and returning the instrumentation to service after

installation was complete. At the Perry plant, a problem occurred when the

licensee was in the process of venting one of the instrument lines following

the installation of the modification. The Job plan directed the operation of

the wrong valve, and instead of opening the vent valve the technician opened

the isolation valve, allowing air into the reference leg. As a result, the

instrumentation associated with the high pressure core spray system (HPCS) was

inoperable until it was re-filled and vented. Similar events have occurred at

other plants due to procedural inadequacy or lack of attention to detail.

Related Generic Communications

by Rapid Depressurization," July 24, 1992.

Vessel Water Level Instrumentation in BWRs Pursuant to 10 CFR 50.54(f),"

August 19, 1992.

Observed During Normal Plant Depressurization," April 8, 1993.

Water Level Instrumentation in BWRs," May 28, 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.

orig /s/'d by BKGrimes

Brian K. Grimes, Director

Division of Operating Reactor Support

Office of Nuclear Reactor Regulation

Technical contact: Amy Cubbage, NRR

(301) 504-2875 Attachments:

1. Simplified Sketch of Backfill Modification

2. List of Recently Issued NRC Information Notices

  • SEE PREVIOUS CONCURRENCE

SRXB:DSSA* OGCB:DORS* TECH ED.* SRXB:DSSA* SRXB:DSSA* D:DSSA* OGCB:DORS*

ACUBBAGE PWEN RSANDERS WLYON RJONES ATHADANI GMARCUS

1 11/16/93 11/15/93 11/16/93 11/18/93 11/20/93 11/23/93

11/2.493 DOCUMENT NAME: 93-89.IN

IN 93-xx

November 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 Attachments:

1. Simplified Sketch of Backfill Modification

2. List of Recently Issued NRC Information Notices

  • SEE PREVIOUS CONCURRENCE

SRXB:DSSA* OGCB:DORS* TECH ED.* SRXB:DSSA* SRXB:DSSA* D: DSSA* OGCB:DORS

ACUBBAGE PWEN RSANDERS WLYON RJONES ATHADANI GMARCUS At'i

11/15/93 11/16/93 11/15/93 11/16/93 11/18/93 11/20/93 11/23/93 D: DORS

BGRIMES

11/ /93 DOCUMENT NAME: BWRWTLVL.WEN

instrumentation associated with the high pressure core spray system (HPCS) was

inoperable until it was re-filled and vented. Similar events have occurred at

other plants due to procedural inadequacy or lack of attention to detail.

Related Generic Communications

by Rapid Depressurization," July 24, 1992.

Vessel Water Level Instrumentation in BWRs Pursuant to 10 CFR 50.54(f),"

August 19, 1992.

Observed During Normal Plant Depressurization," April 8, 1993.

Water Level Instrumentation in BWRs," May 28, 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 Attachments:

1. Simplified Sketch of Backfill Modification

2. List of Recently Issued NRC Information Notices

EDITED BY: R. Sanders

DATED: 11/15/93 SRXB:DSSA* OGCB:DORS* SRXB:DSSA* SRXB:DSSA* D:DSSA OGCB:DORS D:DORS

ACUBBAGE PWEN WLYON RJONES ATHAqkNI GMARCUS BGRIMES

11/15/93 11/16/93 11/16/93 11/18/93 11/?V/93 11/ /93 11/ /93

  • SEE PREVIOUS CONCURRENCE


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