Information Notice 1989-51, Potential Loss of Required Shutdown Margin During Refueling Operations
-
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION.
WASHINGTON, D.C.
20555
May 31, 1989
NRC INFORMATION NOTICE NO. 89-51:
POTENTIAL LOSS OF REQUIRED SHUTDOWN
MARGIN DURING REFUELING OPERATIONS
Addressees
All holders of operating licenses or construction permits for nuclear power
reactors.
Purpose
This information notice Is being'provided to alert addressees to the potential
loss of required shutdown margin during the movement and placement of highly
reactive fuel during refueling operations.
It is expected that recipients will
review the information for applicability to their facilities and consider
actions, as approprlate,-to avoid similar problems. However, suggestions
contained in this information notice do not constitute NRC requirements;
therefore, no specific action or written response is required.
Description of Circumstances
Baltimore Gas-and-Electric Company (BG&E) submitted a10 CFR Part 21 report
to the NRC on. March 15, 1989, regarding the potential loss of shutdown margin
during refueling operations at its Calvert Cliffs Nuclear Power Plant, Units 1 and 2. BG&E reported that it had increased the fuel enrichment during the last
several fuel cycles. In the current cycle, 4.3 weight percent U-235 fuel was
loaded into the core.
During a review of NRC Information Notice No. 88-21,
"Inadvertent Criticality Events at Oskarshamn and U.S. Nuclear Power Plants,"
BG&E discovered that the Calvert Cliffs refueling procedures allowed the
placement of fuel assemblies in-intermediate positions during core alterations.
In addition, BG&E determined that the potential existed for placing several
fresh 4.3 weight percent reload assemblies together and losing some of the
required 5 percent shutdown margin. Calculations also showed that under
extreme conditions an inadvertent criticality could occur if a number of highly
reactive assemblies were grouped together and no credit was taken for control
rods or burnable poisons.
BG&E has revised the Calvert Cliffs refueling procedures to ensure that fuel
assemblies will not be placed in intermediate positions during core alterations
without first verifying their potential reactivity. The revised procedures
allow fuel to be positioned only in intermediate core locations that will
contain fuel of equal or greater reactivity in the final core configuration.
8905240229
.
.
-
IN 89-51 May 31, 1989 Discussion:
As a result of longer fuel operating cycles, utilities have been increasing
the enrichment of reload fuel.
Some of these fresh reload assemblies may be
highly reactive under refueling conditions. Although analyses are performed
to confirm that the refueling boron concentration is sufficient to maintain
the required shutdown margin (subcriticality) for the final core configuration, these analyses may not be sufficient to assure that the shutdown margin will be
maintained for all intermediate fuel assembly positions.
In addition, explicit
procedural controls may not exist to control the location and movement of highly
reactive fuel assemblies during refueling.
Because a significant amount of
reactivity can be added to subcritical configurations by the addition of a
single highly reactive assembly, it is possible that an inadvertent criticality
could occur if a number of such assemblies are grouped together.
With this
highly reactive fuel, subcritical multiplication-(inverse count rate) may not
provide adequate warning of an approach to criticality.
Combustion Engineering, Inc. (CE), the nuclear fuel design consultant for
Calvert Cliffs, recognized this potential problem and recently issued an
information bulletin regarding shutdown margin during refueling to all utili- ties with CE-designed plants.
These utilities have been advised to review
their fuel shuffle procedures that control the location of highly reactive
fuel and to be aware that the refueling boron concentration' necessary to
maintain the required shutdown margin, which is based on the final core
conf -gu a--I
maT nut bersufftwa-to-ass re'that-the-r-requtred shutduwui
-
margin will be maintained for all intermediate -fuel assembly positions.
In
circumstances in which explicit analyses areinot available for each inter- mediate fuel assembly position, CE recommends positioning fuel only in
intermediate core locations that will contain fuel of equal or greater
reactivity in the final core configuration.
No specific action or written response is required by this information notice.
If you have any questions regarding this matter, please contact the technical
contact listed below or the Regional Administrator of the appropriate regional
office.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contact:
Laurence I. Kopp, NRR
(301) 492-0879 Attachment:
List of Recently Issued NRC Information Notices
I
.
-
,
'Attachment
May 31, 1989 LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
Information
Date of
Notice No.
Subject
Issuance
Issued to
88-88, Supp. 1
89-50
89-49
Degradation of Westinghouse
ARD Relays
Inadequate Emergency
Diesel Generator Fuel
Supply
Failure to Close Service
Water Cross-Connect
Isolation Valves
5/31/89
5/30/89
5/22/89
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 nuclear
power reactors.
89-48
_ 89-47
Design Deficiency in the
Turbine-Driven Auxiliary
Feedwater Pump Cooling
Water System
tntll_
.roblc-mEl
Worn or Dlstorted Hose;
Clamps'on. Self-Contained
Breathing Apparatus
5/22/89
All holders of OLs
or CPs for nuclear
power reactors.
~+-5l8/aS
-lA.1,,
bol depr if s,,,
or CPs for nuclear
power reactors and
fuel facilities.
89-46
89-45
89-44
88-82, Supp. 1
Confidentiality of
Exercise Scenarios
Metalclad, Low-Voltage.
Power Circuit Breakers
Refurbished with Sub- standard Parts
Hydrogen Storage on the
Roof of the Control Room
Torus Shells with Corrosion
and Degraded Coatings in
BWR Containments
5/11/89
5/8/89
4/27/89
5/2/89
All holders of licenses
for fuel cycle facilities
and byproduct material
licensees having an
approved emergency
response plan.
All holders of OLs
or CPs for nuclear
power reactors.
All holders of OLs
or CPs for nuclear
power reactors.
All holders of OLs
OL = Operating License
CP = Construction Permit
IN 89-51 May 31, 1989 Discussion:
As a result of longer fuel operating cycles, utilities have been increasing
the enrichment of reload fuel.
Some of these fresh reload assemblies may be
highly reactive under refueling conditions.
Although analyses are performed
to confirm that the refueling boron concentration is sufficient to maintain
the required shutdown margin (subcriticality) for the final core configuration, these analyses may not be sufficient to assure that the shutdown margin will be
maintained for all Intermediate fuel assembly positions.
In addition, explicit
procedural controls may not exist to control the location and movement of highly
reactive fuel assemblies during refueling. Because a significant amount of
reactivity can be added to subcritical configurations by the addition of a
single highly reactive assembly, it is possible that an inadvertent criticality
could occur if a number of such assemblies are grouped together. With this
highly reactive fuel, subcritical multiplication (inverse count rate) may not
provide adequate warning of an approach to criticality.
Combustion Engineering, Inc. (CE), the nuclear fuel design consultant for
Calvert Cliffs, recognized this potential problem and recently issued an
information bulletin regarding shutdown margin during refueling to all utili- ties with CE-designed plants.
These utilities have been advised to review
their fuel shuffle procedures that control the location of highly reactive
fuel and to be aware that the refueling boron concentration necessary to
maintain the required shutdown margin, which is based on the final core
configuration, may not be sufficient to assure that their required shutdown
margin will be maintained for all intermediate fuel assembly positions.
In
circumstances in which explicit analyses are not available for each inter- mediate fuel assembly position, CE recommends positioning fuel only in
intermediate core locations that will contain fuel of equal or greater
reactivity in the final core configuration.
No specific action or written response is required by this information notice.
If you have any questions regarding this matter, please contact the technical
contact listed below or the Regional Administrator of the appropriate regional
office.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contact:
Laurence I. Kopp, NRR
(301) 492-0879 C
4
2 Attachment: List of Recently Issued NRC Informat
on
5
- SEE PREVIOUS PAGE FOR CONCURRENCE
D/ A
- C/OGCB:DOEA:NRR*RPB:ARM
C
CHBerlinger
TechEd
05/ i9H
05/23/89
05/17/89
- OGCB:DOEA:NRR
- SRXB:DEST:NRR *C/S
XB:DEST:NRR
- SAD/DEST:NRR
- D/DEST:NRR
JGuillen
LKopp
WHodges
AThadani
LCShao
05/17/89
05/18/89
05/19/89
05/17/89
05/22/89
I
.
-~ ~
IN 89-XX
May xx, 1989 Discussion:
As a result of longer fuel operating cycles, utilities have been increasing the
enrichment of reload fuel.
Some of these fresh reload assemblies may be highly
reactive under refueling conditions. Although analyses are performed to
confirm that the refueling boron concentration is sufficient to maintain the
required shutdown margin (subcriticality) for the final core configuration, these analyses may not be sufficient to assure that the shutdown margin will be
maintained for all intermediate fuel assembly positions.
In addition, explicit
procedural controls may not exist to control the location and movement of
highly reactive fuel assemblies during refueling. Because a significant amount
of reactivity can be added to subcritical configurations by the addition of a
single highly reactive assembly, it is possible that an inadvertent criticality
could occur if a number of such assemblies are grouped together. With this
highly reactive fuel, subcritical multiplication (inverse count rate) may not
provide adequate warning of an approach to criticality.
Combustion Engineering, Inc. (CE), the nuclear fuel design consultant for
Calvert Cliffs, recognized this potential problem and recently issued an
information bulletin regarding shutdown margin during refueling to all utili- ties with CE-designed plants.
These utilities have been advised to review
their fuel shuffle procedures that control the location of highly reactive fuel
and to be aware that the refueling boron concentration necessary to maintain
the required shutdown margin, which is based on the final core configuration, may not be sufficient to assure that their required shutdown margin will be
maintained for all intermediate fuel assembly positions.
In circumstances in
which explicit analyses are not available for each intermediate fuel assembly
position, CE recommends positioning fuel only in intermediate core locations
that will contain fuel of equal or greater reactivity in the final core
configuration.
No specific action or written response is required by this information notice.
If you have any questions regarding this matter, please contact the technical
contact listed below or the Regional Administrator of the appropriate regional
office.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contact:
Laurence I. Kopp, NRR
(301) 492-0879 Attachment:
List of Recently Issued NRC Informationoti
D/DOEA:NRR
C/OG X 'EA:NRR
CERossi
CHBerlinger
05/ /89
05/ /89 OG
SRXB:D J NRR C/SRXB:D T
R
SAD DEST
JGu
en
LKopp
WHodges
AThajani
05
89
05/fa/89
05/( /8
05/
89 RPB:ARM
TechEd
05/ FV8 D/DEST: NRR,0 .
LCShao
05J / 8;9t