Information Notice 1992-39, Unplanned Return to Criticality During Reactor Shutdown: Difference between revisions
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| issue date = 05/13/1992 | | issue date = 05/13/1992 | ||
| title = Unplanned Return to Criticality During Reactor Shutdown | | title = Unplanned Return to Criticality During Reactor Shutdown | ||
| author name = Rossi C | | author name = Rossi C | ||
| author affiliation = NRC/NRR | | author affiliation = NRC/NRR | ||
| addressee name = | | addressee name = | ||
Line 13: | Line 13: | ||
| document type = NRC Information Notice | | document type = NRC Information Notice | ||
| page count = 12 | | page count = 12 | ||
}} | }} | ||
{{#Wiki_filter:UNITED | {{#Wiki_filter:UNITED STATES | ||
NUCLEAR REGULATORY COMMISSION | |||
OFFICE OF NUCLEAR REACTOR REGULATION | |||
WASHINGTON, D.C. 20555 May 13, 1992 NRC INFORMATION NOTICE 92-39: UNPLANNED RETURN TO CRITICALITY DURING | |||
REACTOR SHUTDOWN | |||
==Addressees== | ==Addressees== | ||
All holders of operating licenses or construction permits for nuclear | All holders of operating licenses or construction permits for nuclear power | ||
reactors. | |||
==Purpose== | ==Purpose== | ||
The U.S. Nuclear Regulatory Commission (NRC) is issuing this | The U.S. Nuclear Regulatory Commission (NRC) is issuing this information | ||
notice to alert addressees to recent events involving unplanned returns to | |||
criticality caused by the cooldown of the reactor coolant system during reactor | |||
shutdowns. 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== | ==Description of Circumstances== | ||
The licensees for the following plants recently experienced | The licensees for the following plants recently experienced unplanned | ||
criticalities during reactor shutdowns: the Monticello Nuclear Generating | |||
Plant, the Big Rock Point Nuclear Plant, and the Grand Gulf Nuclear Station. | |||
Monticello | |||
On June 6, 1991, an unplanned criticality occurred at the Monticello Nuclear | |||
Generating Plant during a reactor shutdown when an unanticipated cooldown | |||
occurred in conjunction with rod insertion. The licensee initiated this | |||
shutdown to repair a leaking safety-relief valve shortly after the plant was | |||
returning to power following a refueling outage. | |||
Since this shutdown occurred shortly after the cycle startup, the reactor did | |||
not generate sufficient decay heat to produce the steam needed to supply the | |||
normal steam system loads and still maintain pressure in the reactor. As | |||
control rods were being inserted using notch insertion, the reactor coolant | |||
system pressure and temperature began to decrease. As long as the operator | |||
continued to insert control rods, the reactor remained subcritical. | |||
However, when the operator stopped inserting control rods to review and | |||
evaluate plant conditions, the cooldown continued, adding sufficient | |||
reactivity to overcome the negative reactivity from the insertion of control | |||
rods and causing the reactor power to increase. The reactor power continued to | |||
92050_* | |||
,, j'A C | |||
i / 1 ( / /CDQc | |||
K) | |||
IN 92-39 May 13, 1992 increase until an intermediate-range monitor (IRM) tripped on a high-high flux | |||
setpoint, causing a reactor scram. | |||
Further details of the event may be found in Licensee Event Report | |||
50-263/91-15 or NRC Inspection Report 50-263/91-13. | |||
===Big Rock Point=== | |||
On November 30, 1991, an unplanned criticality occurred at the Big Rock Point | |||
Nuclear Plant during a reactor shutdown when a cooldown occurred in conjunction | |||
with a rod insertion. The event occurred during a scheduled shutdown for a | |||
refueling outage. | |||
After taking the main turbine off line and bringing the reactor to a | |||
subcritical condition, the licensee delayed actions to continue inserting | |||
control rods while changing shifts. However, the reactor coolant system | |||
continued to cool down because the normal steam system loads were removing | |||
heat. The cooldown added sufficient reactivity to eventually overcome the | |||
effects of the control rods, and the reactor returned critical. The operators | |||
noticed the condition in approximately 2 minutes and took the appropriate | |||
actions to return the reactor subcritical. | |||
Further details of the event may be found in Licensee Event Report | |||
50-155/91-OO9-orJNRC-Inspection-Report 50-155/91-25. _ _ _ | |||
Grand Gulf | |||
On December 30, 1991, an unplanned criticality occurred at the Grand Gulf | |||
Nuclear Station during a reactor shutdown when a cooldown occurred in | |||
conjunction with a rod insertion. The event occurred during a scheduled | |||
shutdown for a maintenance outage to replace a recirculation pump shaft. To | |||
minimize the release of plated-out radioactive material from the fuel cladding | |||
and channels to the reactor coolant system, a slow power reduction and a slow | |||
cooldown were prescribed for this shutdown. | |||
The slow power reduction and the effects of an earlier outage minimized reactor | |||
decay heat and xenon peaking. The operators were driving rods into the core | |||
individually because gang drive for the control rods was unavailable. This | |||
made the reactivity insertion slower than normal. The operators inserted | |||
rods to reduce flux to range 3 on the IRMs and stopped rod insertion in order | |||
to perform a source range monitor surveillance. Indicated power reached IRM | |||
range 1. However, the reactor coolant system continued to cool down because | |||
the normal steam system loads were removing heat. In order not to affect the | |||
source range monitor surveillance, the shift supervisor elected to not insert | |||
control rods and alerted the operators to the possibility of a return to | |||
criticality as the cooldown continued. The reactivity added by the cooldown | |||
eventually overcame the effects of the control rods. The reactor returned to a | |||
critical condition, and reactor power increased on a reactor period between 300 | |||
to 800 seconds. The operators, having been trained on a similar event at | |||
another BWR, were monitoring the condition and expected the power to increase | |||
to the point of adding heat, where the fuel and moderator temperature coeffi- cients would halt the reactor power increase. As the power increased, the | |||
IN 92-39 May 13, 1992 reactor operator ranged the IRMs to prevent a reactor scram. Power level | |||
remained on scale. The power increase was terminated with the IRMs reading on | |||
range 7 and 8. The operators completed the source range monitor surveillance, then resumed inserting rods and successfully completed the shutdown. | |||
Further details of the event may be found in NRC Inspection Report | |||
50-416/92-04 and Licensee Event Report 50-416/91-16. | |||
Discussion | |||
The underlying principle of reactivity management is to maintain the reactor | |||
in the desired condition by properly anticipating, controlling, and responding | |||
to the plant's changing parameters. The experience at Monticello, Big Rock | |||
Point, and Grand Gulf indicates that shutdowns in situations with low decay | |||
heat present a unique challenge to reactivity control if inadvertent recritica- lity is to be prevented. These events emphasize the importance of the operator | |||
giving continuous attention to plant parameters during a shutdown. Further, accepting recriticality without prior management approval and procedures, i.e., | |||
an ad-hoc approach, raises concerns due to the lack of opportunity for contin- gency planning. | |||
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 contacts listed below or the appropriate Office of | |||
Nuclear Reactor Regulation (NRR) project manager. | |||
Va&res'E.Rossi, Director | |||
Division of Operational Events Assessment | |||
Office of Nuclear Reactor Regulation | |||
Technical contacts: Melvyn Leach, RIII | |||
(708) 790-5559 Geoffrey Wright, RIII | |||
(708) 790-5695 Paul O'Connor, NRR | |||
(301) 504-1307 Attachment: List of Recently Issued NRC Information Notices | |||
z | |||
z | |||
Attachment 1 I-0 | |||
IN 92-39 | |||
.< Z G2 May 13, 1992 OD n Page I of 1 | |||
; co | |||
* a | |||
om | |||
LIST OF RECENTLY ISSUED | |||
>0 o) Z NRC INFORMATION NOTICES | |||
Enenz q | |||
m Z -n M Information | |||
m 0n a | |||
.4- information Date of | |||
rn - 0 cn | |||
n Notice No. Subject Issuance Issued to | |||
o a - | |||
0 h <- | |||
0 92-38 Implementation Date for 05/12/92 All holders of OLs or CPs | |||
the Revision to the EPA for nuclear power reactors, Manual of Protective non-power reactors and | |||
Action Guides and Pro- materials licensees auth- tective Actions for orized to possess large | |||
Nuclear Incidents quantities of radioactive | |||
material. | |||
1 92-37 Implementation of the 05/08/92 All Nuclear Regulatory | |||
Deliberate Nisconduct Rule Commission Licensees. | |||
92-16, Loss of Flow from the Re- 05/07/92 All holders of OLs or CPs | |||
Supp. 1 sidual Heat Removal Pump for nuclear power reactors. | |||
during Refueling Cavity | |||
Draindown | |||
I 92-36 Intersystem LOCA Outside 05/07/92 All holders of OLs or CPs | |||
Containment for nuclear power reactors. | |||
' 92-35 Higher Than Predicted Ero- 05/06/92 All holders of OLs or CPs | |||
sion/Corrosion in Unisol- for nuclear power reactors. | |||
able Reactor Coolant Pres- sure Boundary Piping Inside | |||
Containment at A Boiling | |||
Water Reactor | |||
92-34 New Exposure Limits for | |||
Airborne Uranium and | |||
Thorium | |||
05/06/92 All licensees whose opera- tions can cause airborne | |||
concentrations of uranium | |||
( | |||
and thorium. | |||
92-33 Increased Instrument 04/30/92 All holders of OLs or CPs | |||
-u Response Time When for nuclear power reactors. | |||
0 Pressure Dampening | |||
rn> Devices are Installed | |||
mD | |||
- C > 0 | |||
D2 zzz> Operating License | |||
u) D- I CP - 'Construction Permit | |||
0 | |||
IN 92-39 May 13, 1992 reactor operator ranged the IRMs to prevent a reactor scram. Power level | |||
remained on scale. The power increase was terminated with the IRMs reading on | |||
range 7 and 8. The operators completed the source range monitor surveillance, then resumed inserting rods and successfully completed the shutdown. | |||
Further details of the event may be found in NRC Inspection Report | |||
50-416/92-04 and Licensee Event Report 50-416/91-16. | |||
Discussion | |||
The underlying principle of reactivity management is to maintain the reactor | |||
in the desired condition by properly anticipating, controlling, and responding | |||
to the plant's changing parameters. The experience at Monticello, Big Rock | |||
Point, and Grand Gulf indicates that shutdowns in situations with low decay | |||
heat present a unique challenge to reactivity control if inadvertent recritica- lity is to be prevented. These events emphasize the importance of the operator | |||
giving continuous attention to plant parameters during a shutdown. Further, accepting recriticality without prior management approval and procedures, i.e., | |||
an ad-hoc approach, raises concerns due to the lack of opportunity for contin- gency planning. | |||
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 contacts listed below or the appropriate Office of | |||
Nuclear Reactor Regulation (NRR) project manager. Original Signed by | |||
Nhedes E, Rossi | |||
Charles E. Rossi, Director | |||
Division of Operational Events Assessment | |||
Office of Nuclear Reactor Regulation | |||
Technical contacts: Melvyn Leach, RIII | |||
(708) 790-5559 Geoffrey Wright, RIII | |||
(708) 790-5695 Paul O'Connor, NRR | |||
(301) 504-1307 Attachment: List of Recently Issued NRC Information Notices | |||
*SEE PREVIOUS CONCURRENCE | |||
OFC RIII ADR4-5:PD4-1 SC:DOEA:OEAB ADM:RPB C:DST:SRXB C:DOEA:OEAB | |||
NAME GWright* PO'Connor* RDennig* JMain* RJones* AChaffee* | |||
DATE 03/11/92 03/17/92 03/11/92 03/11/92 03/13/92 04/13/92 OFC C:DOEA:OGCB D X, | |||
NAME CBerlinger* | |||
DATE 04/21/92 05/ 7/92 DOCUMENT NAME: IN 92-39 | |||
IN 92-XX | |||
April xx, 1992 Further details of the event may be found in NRC Inspection Report | |||
50-416/92-04 and Licensee Event Report 50-416/91-16. | |||
Discussion | |||
The underlying principle of reactivity management is to maintain the reactor | |||
in the desired condition by properly anticipating, controlling, and responding | |||
to the plant's changing parameters. The experience at Big Rock Point, Grand | |||
Gulf, and Monticello indicates that shutdowns in situations with low decay heat | |||
present a unique challenge to reactivity control if inadvertent recriticality | |||
is to be prevented. These events emphasize the importance of the operator | |||
giving continuous attention to plant parameters during a shutdown. Further, accepting recriticality without prior management approval and procedures, i.e., | |||
an ad-hoc approach, raises concerns due to the lack of opportunity for contin- gency planning. | |||
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 contacts listed below or the appropriate Office of | |||
Nuclear Reactor Regulation (NRR) project manager. | |||
Charles E. Rossi, Director | |||
Division of Operational Events Assessment | |||
Office of Nuclear Reactor Regulation | |||
Technical contacts: Melvyn Leach, RIII | |||
(708) 790-5559 Geoffrey Wright, RIII | |||
(708) 790-5695 Paul O'Connor, NRR | |||
(301) 504-1307 Attachment: List of Recently Issued NRC Information Notices | |||
*SEE PREVIOUS CONCURRENCE | |||
OFC RIII ADR4-5:PD4-1 SC:DOEA:OEAB ADM:RPB C:DST:SRXB C:DOEA:OEAB | |||
NAME GWright* PO'Connor* RDennig* JMain* RJones* AChaffee* | |||
DATE 03/11/92 03/17/92 03/11/92 03/11/92 03/13/92 04/13/92 OFC C:DOEA:OGCB D:DOEA | |||
NAME CBerlinger* CRoss tD | |||
DATE 04/21/92 /9 OFFICIAL RECORD COPY DOCUMENT NAME: IN DENKIG | |||
IN 92-XX | |||
April xx, 1992 Further details of the event may be found in NRC Inspection Report | |||
50-416/92-04 and Licensee Event Report 50-416/91-16. | |||
Discussion | |||
The underlying principle of reactivity management is to maintain the reactor | |||
in the desired condition by properly anticipating, controlling, and responding | |||
to the plant's changing parameters. Once a reactor has been placed in a | |||
subcritical condition during a plant shutdown, it is of primary importance | |||
that the reactor be maintained in that subcritical condition. Raising the | |||
range of the IRMs in the event of recriticality can be inappropriate if the | |||
licensed operators do not have management's oversight, training, and specific | |||
procedures for this. | |||
The experience at Grand Gulf and Monticello indicate that slow shutdowns in | |||
situations with low decay heat present a unique challenge to reactivity | |||
control and require the operator and management to give careful attention to | |||
avoid recriticality. The events at Monticello and Big Rock Point also highlight | |||
the importance of the operator giving continuous attention to plant parameters | |||
during a shutdown. | |||
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 contacts listed below or the appropriate Office of | |||
Nuclear Reactor Regulation (NRR) project manager. | |||
Charles E. Rossi, Director | |||
Division of Operational Events Assessment | |||
Office of Nuclear Reactor Regulation | |||
Technical contacts: Melvyn Leach, RIII | |||
(708) 790-5559 Geoffrey Wright, RIII | |||
(708) 790-5695 Paul O'Connor, NRR | |||
(301) 504-1307 Attachment: List of Recently Issued NRC Information Notices | |||
*SEE PREVIOUS CONCURRENCE | |||
OFC RIII ADR4-5:PD4-1 SC:DOEA:OEAB ADM:RPB C:DST:SRXB C:DOEA:OEAB | |||
NAME GWright* PO'Connor* RDennig* JMain* RJones* AChaffee* | |||
DATE 03/11/92 03/17/92 03/11/92 03/11/92 03/13/92 04/13/92 OFC C:DO J | |||
f D:DOEA | |||
NAME CBerlinger CRosswa'y | |||
DATE f/;11/ 92 / 92 OFFICIAL RECORD COPY DOCUMENT NAME: IN DENNIG | |||
IN 92-XX | |||
March xx, 1992 Further details of the event may be found in NRC Inspection Report | |||
50-416/92-04 and Licensee Event Report 50-416/91-16. | |||
Discussion | |||
The underlying principle of reactivity management is to maintain the reactor | |||
in the desired condition by properly anticipating, controlling, and responding | |||
to the plant's changing parameters. Once a reactor has been placed in a | |||
subcritical condition during a plant shutdown, it is of primary importance | |||
that the reactor be maintained in that subcritical condition. In the event of | |||
recriticality, promptly inserting control rods and terminating the cooldown are | |||
more conservative actions than raising the range of the IRMs to prevent scram | |||
while waiting on the changing temperature to reverse the direction of the | |||
power. Raising the range of the IRMs in the event of recriticality can be | |||
inappropriate if the licensed operators do not have management's oversight, training, and specific procedures. | |||
The experience at Grand Gulf and Monticello indicate that slow shutdowns in | |||
situations with low decay heat present a unique challenge to reactivity | |||
control and require the operator and management to give careful attention to | |||
avoid recriticality. The events at Monticello and Big Rock Point also highlight | |||
the importance of the operator giving continuous attention to plant parameters | |||
during a shutdown. | |||
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 contacts listed below or the appropriate Office of | |||
Nuclear Reactor Regulation (NRR) project manager. | |||
Charles E. Rossi, Director | |||
Division of Operational Events Assessment | |||
Office of Nuclear Reactor Regulation | |||
Technical contacts: Melvyn Leach, RIII | |||
(708) 790-5559 Geoffrey Wright, RIII | |||
(708) 790-5695 Paul O'Connor, NRR | |||
(301) 504-1307 t'/ ' f' 4.f, IV | |||
Attachment: List of Recently Issued NRC Information Notices | |||
*SEE PREVIOUS CONCURRENCEC | |||
OFC RIII ADR4-5:PD4-1 SC:DOEA:OEAB ADM:RPB C:DST:SRXB C:D0EA:OEAB | |||
NAME GWright* PO'Connor* RDennig* JMain* RJones* AChaffee | |||
DATE 03/11/92 03/17/92 03/11/92 03/11/92 03/13/92 q1/t3/92 OFC C:DOEA:OGCB D:DOEA | |||
===NAME CBerlinger CRossi=== | |||
DATE / /92 / /92 OFFICIAL RECORD COPY DOCUMENT NAME: IN DENNIG | |||
IN 92-XX | |||
March xx, 1992 Further details of the event may be found in NRC Inspection Report | |||
50-416/92-04 and Licensee Event Report 50-416/91-16. | |||
Discussion | |||
The underlying principle of reactivity management is to maintain the reactor | |||
in the desired condition by properly anticipating, controlling, and responding | |||
to the plant's changing parameters. Once a reactor has been placed in a | |||
subcritical condition during a plant shutdown, it is of primary importance | |||
that the reactor be maintained in that subcritical condition. In the event of | |||
recriticality, promptly inserting control rods and terminating the cooldown are | |||
more conservative actions than raising the range of the IRMs to prevent scram | |||
while waiting on the changing temperature to reverse the direction of the | |||
power. Raising the range of the IRMs in the event of recriticality can be | |||
inappropriate if the licensed operators do not have management's oversight, training, and specific procedures. | |||
The experience at Grand Gulf and Monticello indicate that slow shutdowns in | |||
situations with low decay heat present a unique challenge to reactivity | |||
control and require the operator and management to give careful attention to | |||
avoid recriticality. The events at Monticello and Big Rock Point also highlight | |||
the importance of the operator giving continuous attention to plant parameters | |||
during a shutdown. | |||
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 contacts listed below or the appropriate Office of | |||
Nuclear Reactor Regulation (NRR) project manager. | |||
Charles E. Rossi, Director | |||
Division of Operational Events Assessment | |||
Office of Nuclear Reactor Regulation | |||
Technical contacts: Melvyn Leach, RIII | |||
(708) 790-5559 Geoffrey Wright, 'RIII | |||
(708) 790-5695 Paul O'Connor, NRR | |||
(301) 504-1307 Attachment: List of Recently Issued NRC Information Notices | |||
*SEE PREVIOUS CONCURRENCE | |||
OFC RIII ADR4-5:PD4-1 SC:DOEA:OEAB ADM:RPB C:DST:SRXB C:DOEA:OEAB | |||
NAME GWright* PO'Connor (OK RDennig* JMain* RJones* AChaffee | |||
DATE 03/11/92 3 /17/92 Xis 192 03/11/92 03/13/92 / /92 OFC C:DOEA:OGCB D:DOEA | |||
===NAME CBerlinger CRossi=== | |||
DATE / /92 / /92 | |||
IN 92-XX | |||
March xx, 1992 Further details of the event may be found in NRC Inspection Report | |||
50-416/92-04 and Licensee Event Report 50-416/91-16. | |||
Discussion | |||
The underlying principle of reactivity management is to maintain the reactor | |||
in the desired condition by properly anticipating, controlling, and responding | |||
to the plant's changing parameters. Once a reactor has been placed in a | |||
subcritical condition during a plant shutdown, it is of primary importance | |||
that the reactor be maintained in that subcritical condition. Since recriti- cality has not been avoided, promptly inserting control rods and terminating | |||
the cooldown are more conservative actions than raising the range of the IRMs | |||
to prevent scram while waiting on the changing temperature to reverse the | |||
direction of the power. Raising the range of the IRMs in the event of recriti- cality can be inappropriate if the licensed operators do not have management's | |||
oversight, training, and specific procedures. | |||
The experience at Grand Gulf and Monticello indicate that slow shutdowns in | |||
situations with low decay heat present a unique challenge to reactivity | |||
control and require the operator and management to give careful attention to | |||
avoid recriticality. The events at Monticello and Big Rock Point also highlight | |||
the importance of the operator giving continuous attention to plant parameters | |||
during a shutdown. | |||
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 contacts listed below or the appropriate Office of | |||
Nuclear Reactor Regulation (NRR) project manager. | |||
Charles E. Rossi, Director | |||
Division of Operational Events Assessment | |||
Office of Nuclear Reactor Regulation | |||
Technical contacts: Melvyn Leach, RIII | |||
(708) 790-5559 Geoffrey Wright, RII | |||
(708) 790-5695 Paul O'Connor, NRR | |||
(301) 504-1307 Attachment: List of Recently Issued NRC Information Notices | |||
*SEE PREVIOUS CONCURRENCE | |||
OFC :RIII :S Oq;:EfAB:ADM:RPB :C:D B :C:DOEA:OEAB :C:DOEA:OGCB :D:DOEA | |||
____ | |||
_ _________----_ -- ____________ ---- _ -:--------------- | |||
NAME :GWright* :Rbennig :JMain* j Jones :AChaffee :CBerlinger :CRossi | |||
DATE :03/11/92 :3 /11/92 :03/11/92 : /13/92 : / /92 : / /92 : / /92 OFFICIAL RECORD COPY | |||
Document Name: IN DENNIG | |||
Further details of the event may be found in NRC Inspection Report 50-416/92-04 and Licensee Event Report 50-416/91-16. | |||
Discussion | |||
The underlying principle of reactivity management is to maintain the reactor in | |||
the desired condition by properly anticipating, controlling, and responding to | |||
the plant's changing parameters. Once a reactor has been placed in a | |||
subcritical condition, as part of a plant shutdown, it is of primary importance | |||
that the reactor be maintained in that subcritical condition. Given that | |||
recriticality has not been avoided, prompt insertion of control rods and | |||
termination of the cooldown are more conservative actions than upranging IRMs | |||
to prevent scram while waiting on temperature coefficients to turn power. | |||
Upranging IRMs in the event of recriticality can be inappropriate if management | |||
oversight, prior training, and specific procedures are absent. | |||
The experience at Grand Gulf and Monticello indicate that slow shutdowns in | |||
situations with low decay heat present a particular challenge to reactivity | |||
control, and require heightened operator and management awareness to avoid | |||
recriticality. In addition, the events at Monticello and Big Rock Point | |||
highlight the importance of continuous operator attention to plant parameters | |||
in the course of a shutdown. | |||
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 contacts listed below or the appropriate Office of Nuclear | |||
Reactor Regulation (NRR) project manager. | |||
Charles E. Rossi, Director | |||
Division of Operational Events Assessment | |||
Office of Nuclear Reactor Regulation | |||
Technical contacts: Melvyn Leach, RIII | |||
(708) 790-5559 Geoffrey Wright, RIII | |||
(708) 790-5695 Paul O'Connor, NRR | |||
(301) 504-1307 Attachment: List of Recently Issued NRC Information Notices | |||
OFC :RIII :SC:DOEA:OEAB:ADM:RPB :C:DST:SRXB :C:DOEA:OEAB :C:DOEA:OGCB :D:DOEA | |||
NAME :GWright :RDennig :JMain_ w :RJones :AChaffee :CBerlinger :CRossi | |||
DATE ://92 :1/92 :3/11 /92 :1/92 ://92 :1 /92 :/ /92 OFFICIAL RECORD COPY | |||
Document Name: IN DENNIG/DUP | |||
IN 92-XX | |||
March xx, 1992 Further details of the event may be found in NRC Inspection Report | |||
50-416/92-04 and Licensee Event Report 50-416/91-16. | |||
Discussion | |||
The underlying principle of reactivity management is to maintain the reactor | |||
in the desired condition by properly anticipating, controlling, and responding | |||
to the plant's changing parameters. Once a reactor has been placed in a | |||
subcritical condition, as part of a plant shutdown, it is of primary importance | |||
that the reactor be maintained in that subcritical condition. Given that | |||
recriticality has not been avoided, prompt insertion of control rods and | |||
termination of the cooldown are more conservative actions than upranging | |||
IRMs to prevent scram while waiting on temperature coefficients to turn power. | |||
Upranging IRMs in the event of recriticality can be inappropriate if management | |||
oversight, prior training, and specific procedures are absent. | |||
The experience at Grand Gulf and Monticello indicate that slow shutdowns in | |||
situations with low decay heat present a particular challenge to reactivity | |||
control, and require heightened operator and management awareness to avoid | |||
recriticality. In addition, the events at Monticello and Big Rock Point | |||
highlight the importance of continuous operator attention to plant parameters | |||
in the course of a shutdown. | |||
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 contacts listed below or the appropriate Office of | |||
Nuclear Reactor Regulation (NRR) project manager. | |||
Charles E. Rossi, Director | |||
Division of Operational Events Assessment | |||
Office of Nuclear Reactor Regulation | |||
Technical contacts: Melvyn Leach, RIII | |||
(708) 790-5559 Geoffrey Wright, RIII | |||
(708) 790-5695 Paul O'Connor, NRR | |||
(301) 504-1307 Attachment: List of Recently Issued NRC Information Notices | |||
List of Recently Issued NRC Information Notices | |||
OFC :R111 bC:DOEA:OEAB:ADM:RPB :C:DST:SRXB :C:DOEA:OEAB :C:DOEA:OGCB :D:DOEA | |||
NAME :GWrightV' :RDennig :JMain :RJones :AChaffee :CBerlinger :CRossi | |||
DATE :3 /II/92 ://92 :/ /92 :/ /92 :/ /92 :/ /92 :/ /92 OFFICIAL RECORD COPY | |||
Document Name: IN DENNIG}} | |||
{{Information notice-Nav}} | {{Information notice-Nav}} |
Latest revision as of 03:22, 24 November 2019
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555 May 13, 1992 NRC INFORMATION NOTICE 92-39: UNPLANNED RETURN TO CRITICALITY DURING
REACTOR SHUTDOWN
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 recent events involving unplanned returns to
criticality caused by the cooldown of the reactor coolant system during reactor
shutdowns. 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
The licensees for the following plants recently experienced unplanned
criticalities during reactor shutdowns: the Monticello Nuclear Generating
Plant, the Big Rock Point Nuclear Plant, and the Grand Gulf Nuclear Station.
Monticello
On June 6, 1991, an unplanned criticality occurred at the Monticello Nuclear
Generating Plant during a reactor shutdown when an unanticipated cooldown
occurred in conjunction with rod insertion. The licensee initiated this
shutdown to repair a leaking safety-relief valve shortly after the plant was
returning to power following a refueling outage.
Since this shutdown occurred shortly after the cycle startup, the reactor did
not generate sufficient decay heat to produce the steam needed to supply the
normal steam system loads and still maintain pressure in the reactor. As
control rods were being inserted using notch insertion, the reactor coolant
system pressure and temperature began to decrease. As long as the operator
continued to insert control rods, the reactor remained subcritical.
However, when the operator stopped inserting control rods to review and
evaluate plant conditions, the cooldown continued, adding sufficient
reactivity to overcome the negative reactivity from the insertion of control
rods and causing the reactor power to increase. The reactor power continued to
92050_*
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IN 92-39 May 13, 1992 increase until an intermediate-range monitor (IRM) tripped on a high-high flux
setpoint, causing a reactor scram.
Further details of the event may be found in Licensee Event Report
50-263/91-15 or NRC Inspection Report 50-263/91-13.
Big Rock Point
On November 30, 1991, an unplanned criticality occurred at the Big Rock Point
Nuclear Plant during a reactor shutdown when a cooldown occurred in conjunction
with a rod insertion. The event occurred during a scheduled shutdown for a
refueling outage.
After taking the main turbine off line and bringing the reactor to a
subcritical condition, the licensee delayed actions to continue inserting
control rods while changing shifts. However, the reactor coolant system
continued to cool down because the normal steam system loads were removing
heat. The cooldown added sufficient reactivity to eventually overcome the
effects of the control rods, and the reactor returned critical. The operators
noticed the condition in approximately 2 minutes and took the appropriate
actions to return the reactor subcritical.
Further details of the event may be found in Licensee Event Report
50-155/91-OO9-orJNRC-Inspection-Report 50-155/91-25. _ _ _
Grand Gulf
On December 30, 1991, an unplanned criticality occurred at the Grand Gulf
Nuclear Station during a reactor shutdown when a cooldown occurred in
conjunction with a rod insertion. The event occurred during a scheduled
shutdown for a maintenance outage to replace a recirculation pump shaft. To
minimize the release of plated-out radioactive material from the fuel cladding
and channels to the reactor coolant system, a slow power reduction and a slow
cooldown were prescribed for this shutdown.
The slow power reduction and the effects of an earlier outage minimized reactor
decay heat and xenon peaking. The operators were driving rods into the core
individually because gang drive for the control rods was unavailable. This
made the reactivity insertion slower than normal. The operators inserted
rods to reduce flux to range 3 on the IRMs and stopped rod insertion in order
to perform a source range monitor surveillance. Indicated power reached IRM
range 1. However, the reactor coolant system continued to cool down because
the normal steam system loads were removing heat. In order not to affect the
source range monitor surveillance, the shift supervisor elected to not insert
control rods and alerted the operators to the possibility of a return to
criticality as the cooldown continued. The reactivity added by the cooldown
eventually overcame the effects of the control rods. The reactor returned to a
critical condition, and reactor power increased on a reactor period between 300
to 800 seconds. The operators, having been trained on a similar event at
another BWR, were monitoring the condition and expected the power to increase
to the point of adding heat, where the fuel and moderator temperature coeffi- cients would halt the reactor power increase. As the power increased, the
IN 92-39 May 13, 1992 reactor operator ranged the IRMs to prevent a reactor scram. Power level
remained on scale. The power increase was terminated with the IRMs reading on
range 7 and 8. The operators completed the source range monitor surveillance, then resumed inserting rods and successfully completed the shutdown.
Further details of the event may be found in NRC Inspection Report
50-416/92-04 and Licensee Event Report 50-416/91-16.
Discussion
The underlying principle of reactivity management is to maintain the reactor
in the desired condition by properly anticipating, controlling, and responding
to the plant's changing parameters. The experience at Monticello, Big Rock
Point, and Grand Gulf indicates that shutdowns in situations with low decay
heat present a unique challenge to reactivity control if inadvertent recritica- lity is to be prevented. These events emphasize the importance of the operator
giving continuous attention to plant parameters during a shutdown. Further, accepting recriticality without prior management approval and procedures, i.e.,
an ad-hoc approach, raises concerns due to the lack of opportunity for contin- gency planning.
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 contacts listed below or the appropriate Office of
Nuclear Reactor Regulation (NRR) project manager.
Va&res'E.Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical contacts: Melvyn Leach, RIII
(708) 790-5559 Geoffrey Wright, RIII
(708) 790-5695 Paul O'Connor, NRR
(301) 504-1307 Attachment: List of Recently Issued NRC Information Notices
z
z
Attachment 1 I-0
.< Z G2 May 13, 1992 OD n Page I of 1
- co
- a
om
LIST OF RECENTLY ISSUED
>0 o) Z NRC INFORMATION NOTICES
Enenz q
m Z -n M Information
m 0n a
.4- information Date of
rn - 0 cn
n Notice No. Subject Issuance Issued to
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0 h <-
0 92-38 Implementation Date for 05/12/92 All holders of OLs or CPs
the Revision to the EPA for nuclear power reactors, Manual of Protective non-power reactors and
Action Guides and Pro- materials licensees auth- tective Actions for orized to possess large
Nuclear Incidents quantities of radioactive
material.
1 92-37 Implementation of the 05/08/92 All Nuclear Regulatory
Deliberate Nisconduct Rule Commission Licensees.
92-16, Loss of Flow from the Re- 05/07/92 All holders of OLs or CPs
Supp. 1 sidual Heat Removal Pump for nuclear power reactors.
during Refueling Cavity
Draindown
I 92-36 Intersystem LOCA Outside 05/07/92 All holders of OLs or CPs
Containment for nuclear power reactors.
' 92-35 Higher Than Predicted Ero- 05/06/92 All holders of OLs or CPs
sion/Corrosion in Unisol- for nuclear power reactors.
able Reactor Coolant Pres- sure Boundary Piping Inside
Containment at A Boiling
Water Reactor
92-34 New Exposure Limits for
Airborne Uranium and
05/06/92 All licensees whose opera- tions can cause airborne
concentrations of uranium
(
and thorium.
92-33 Increased Instrument 04/30/92 All holders of OLs or CPs
-u Response Time When for nuclear power reactors.
0 Pressure Dampening
rn> Devices are Installed
mD
- C > 0
D2 zzz> Operating License
u) D- I CP - 'Construction Permit
0
IN 92-39 May 13, 1992 reactor operator ranged the IRMs to prevent a reactor scram. Power level
remained on scale. The power increase was terminated with the IRMs reading on
range 7 and 8. The operators completed the source range monitor surveillance, then resumed inserting rods and successfully completed the shutdown.
Further details of the event may be found in NRC Inspection Report
50-416/92-04 and Licensee Event Report 50-416/91-16.
Discussion
The underlying principle of reactivity management is to maintain the reactor
in the desired condition by properly anticipating, controlling, and responding
to the plant's changing parameters. The experience at Monticello, Big Rock
Point, and Grand Gulf indicates that shutdowns in situations with low decay
heat present a unique challenge to reactivity control if inadvertent recritica- lity is to be prevented. These events emphasize the importance of the operator
giving continuous attention to plant parameters during a shutdown. Further, accepting recriticality without prior management approval and procedures, i.e.,
an ad-hoc approach, raises concerns due to the lack of opportunity for contin- gency planning.
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 contacts listed below or the appropriate Office of
Nuclear Reactor Regulation (NRR) project manager. Original Signed by
Nhedes E, Rossi
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical contacts: Melvyn Leach, RIII
(708) 790-5559 Geoffrey Wright, RIII
(708) 790-5695 Paul O'Connor, NRR
(301) 504-1307 Attachment: List of Recently Issued NRC Information Notices
- SEE PREVIOUS CONCURRENCE
OFC RIII ADR4-5:PD4-1 SC:DOEA:OEAB ADM:RPB C:DST:SRXB C:DOEA:OEAB
NAME GWright* PO'Connor* RDennig* JMain* RJones* AChaffee*
DATE 03/11/92 03/17/92 03/11/92 03/11/92 03/13/92 04/13/92 OFC C:DOEA:OGCB D X,
NAME CBerlinger*
DATE 04/21/92 05/ 7/92 DOCUMENT NAME: IN 92-39
IN 92-XX
April xx, 1992 Further details of the event may be found in NRC Inspection Report
50-416/92-04 and Licensee Event Report 50-416/91-16.
Discussion
The underlying principle of reactivity management is to maintain the reactor
in the desired condition by properly anticipating, controlling, and responding
to the plant's changing parameters. The experience at Big Rock Point, Grand
Gulf, and Monticello indicates that shutdowns in situations with low decay heat
present a unique challenge to reactivity control if inadvertent recriticality
is to be prevented. These events emphasize the importance of the operator
giving continuous attention to plant parameters during a shutdown. Further, accepting recriticality without prior management approval and procedures, i.e.,
an ad-hoc approach, raises concerns due to the lack of opportunity for contin- gency planning.
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 contacts listed below or the appropriate Office of
Nuclear Reactor Regulation (NRR) project manager.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical contacts: Melvyn Leach, RIII
(708) 790-5559 Geoffrey Wright, RIII
(708) 790-5695 Paul O'Connor, NRR
(301) 504-1307 Attachment: List of Recently Issued NRC Information Notices
- SEE PREVIOUS CONCURRENCE
OFC RIII ADR4-5:PD4-1 SC:DOEA:OEAB ADM:RPB C:DST:SRXB C:DOEA:OEAB
NAME GWright* PO'Connor* RDennig* JMain* RJones* AChaffee*
DATE 03/11/92 03/17/92 03/11/92 03/11/92 03/13/92 04/13/92 OFC C:DOEA:OGCB D:DOEA
NAME CBerlinger* CRoss tD
DATE 04/21/92 /9 OFFICIAL RECORD COPY DOCUMENT NAME: IN DENKIG
IN 92-XX
April xx, 1992 Further details of the event may be found in NRC Inspection Report
50-416/92-04 and Licensee Event Report 50-416/91-16.
Discussion
The underlying principle of reactivity management is to maintain the reactor
in the desired condition by properly anticipating, controlling, and responding
to the plant's changing parameters. Once a reactor has been placed in a
subcritical condition during a plant shutdown, it is of primary importance
that the reactor be maintained in that subcritical condition. Raising the
range of the IRMs in the event of recriticality can be inappropriate if the
licensed operators do not have management's oversight, training, and specific
procedures for this.
The experience at Grand Gulf and Monticello indicate that slow shutdowns in
situations with low decay heat present a unique challenge to reactivity
control and require the operator and management to give careful attention to
avoid recriticality. The events at Monticello and Big Rock Point also highlight
the importance of the operator giving continuous attention to plant parameters
during a shutdown.
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 contacts listed below or the appropriate Office of
Nuclear Reactor Regulation (NRR) project manager.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical contacts: Melvyn Leach, RIII
(708) 790-5559 Geoffrey Wright, RIII
(708) 790-5695 Paul O'Connor, NRR
(301) 504-1307 Attachment: List of Recently Issued NRC Information Notices
- SEE PREVIOUS CONCURRENCE
OFC RIII ADR4-5:PD4-1 SC:DOEA:OEAB ADM:RPB C:DST:SRXB C:DOEA:OEAB
NAME GWright* PO'Connor* RDennig* JMain* RJones* AChaffee*
DATE 03/11/92 03/17/92 03/11/92 03/11/92 03/13/92 04/13/92 OFC C:DO J
f D:DOEA
NAME CBerlinger CRosswa'y
DATE f/;11/ 92 / 92 OFFICIAL RECORD COPY DOCUMENT NAME: IN DENNIG
IN 92-XX
March xx, 1992 Further details of the event may be found in NRC Inspection Report
50-416/92-04 and Licensee Event Report 50-416/91-16.
Discussion
The underlying principle of reactivity management is to maintain the reactor
in the desired condition by properly anticipating, controlling, and responding
to the plant's changing parameters. Once a reactor has been placed in a
subcritical condition during a plant shutdown, it is of primary importance
that the reactor be maintained in that subcritical condition. In the event of
recriticality, promptly inserting control rods and terminating the cooldown are
more conservative actions than raising the range of the IRMs to prevent scram
while waiting on the changing temperature to reverse the direction of the
power. Raising the range of the IRMs in the event of recriticality can be
inappropriate if the licensed operators do not have management's oversight, training, and specific procedures.
The experience at Grand Gulf and Monticello indicate that slow shutdowns in
situations with low decay heat present a unique challenge to reactivity
control and require the operator and management to give careful attention to
avoid recriticality. The events at Monticello and Big Rock Point also highlight
the importance of the operator giving continuous attention to plant parameters
during a shutdown.
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 contacts listed below or the appropriate Office of
Nuclear Reactor Regulation (NRR) project manager.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical contacts: Melvyn Leach, RIII
(708) 790-5559 Geoffrey Wright, RIII
(708) 790-5695 Paul O'Connor, NRR
(301) 504-1307 t'/ ' f' 4.f, IV
Attachment: List of Recently Issued NRC Information Notices
- SEE PREVIOUS CONCURRENCEC
OFC RIII ADR4-5:PD4-1 SC:DOEA:OEAB ADM:RPB C:DST:SRXB C:D0EA:OEAB
NAME GWright* PO'Connor* RDennig* JMain* RJones* AChaffee
DATE 03/11/92 03/17/92 03/11/92 03/11/92 03/13/92 q1/t3/92 OFC C:DOEA:OGCB D:DOEA
NAME CBerlinger CRossi
DATE / /92 / /92 OFFICIAL RECORD COPY DOCUMENT NAME: IN DENNIG
IN 92-XX
March xx, 1992 Further details of the event may be found in NRC Inspection Report
50-416/92-04 and Licensee Event Report 50-416/91-16.
Discussion
The underlying principle of reactivity management is to maintain the reactor
in the desired condition by properly anticipating, controlling, and responding
to the plant's changing parameters. Once a reactor has been placed in a
subcritical condition during a plant shutdown, it is of primary importance
that the reactor be maintained in that subcritical condition. In the event of
recriticality, promptly inserting control rods and terminating the cooldown are
more conservative actions than raising the range of the IRMs to prevent scram
while waiting on the changing temperature to reverse the direction of the
power. Raising the range of the IRMs in the event of recriticality can be
inappropriate if the licensed operators do not have management's oversight, training, and specific procedures.
The experience at Grand Gulf and Monticello indicate that slow shutdowns in
situations with low decay heat present a unique challenge to reactivity
control and require the operator and management to give careful attention to
avoid recriticality. The events at Monticello and Big Rock Point also highlight
the importance of the operator giving continuous attention to plant parameters
during a shutdown.
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 contacts listed below or the appropriate Office of
Nuclear Reactor Regulation (NRR) project manager.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical contacts: Melvyn Leach, RIII
(708) 790-5559 Geoffrey Wright, 'RIII
(708) 790-5695 Paul O'Connor, NRR
(301) 504-1307 Attachment: List of Recently Issued NRC Information Notices
- SEE PREVIOUS CONCURRENCE
OFC RIII ADR4-5:PD4-1 SC:DOEA:OEAB ADM:RPB C:DST:SRXB C:DOEA:OEAB
NAME GWright* PO'Connor (OK RDennig* JMain* RJones* AChaffee
DATE 03/11/92 3 /17/92 Xis 192 03/11/92 03/13/92 / /92 OFC C:DOEA:OGCB D:DOEA
NAME CBerlinger CRossi
DATE / /92 / /92
IN 92-XX
March xx, 1992 Further details of the event may be found in NRC Inspection Report
50-416/92-04 and Licensee Event Report 50-416/91-16.
Discussion
The underlying principle of reactivity management is to maintain the reactor
in the desired condition by properly anticipating, controlling, and responding
to the plant's changing parameters. Once a reactor has been placed in a
subcritical condition during a plant shutdown, it is of primary importance
that the reactor be maintained in that subcritical condition. Since recriti- cality has not been avoided, promptly inserting control rods and terminating
the cooldown are more conservative actions than raising the range of the IRMs
to prevent scram while waiting on the changing temperature to reverse the
direction of the power. Raising the range of the IRMs in the event of recriti- cality can be inappropriate if the licensed operators do not have management's
oversight, training, and specific procedures.
The experience at Grand Gulf and Monticello indicate that slow shutdowns in
situations with low decay heat present a unique challenge to reactivity
control and require the operator and management to give careful attention to
avoid recriticality. The events at Monticello and Big Rock Point also highlight
the importance of the operator giving continuous attention to plant parameters
during a shutdown.
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 contacts listed below or the appropriate Office of
Nuclear Reactor Regulation (NRR) project manager.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical contacts: Melvyn Leach, RIII
(708) 790-5559 Geoffrey Wright, RII
(708) 790-5695 Paul O'Connor, NRR
(301) 504-1307 Attachment: List of Recently Issued NRC Information Notices
- SEE PREVIOUS CONCURRENCE
OFC :RIII :S Oq;:EfAB:ADM:RPB :C:D B :C:DOEA:OEAB :C:DOEA:OGCB :D:DOEA
____
_ _________----_ -- ____________ ---- _ -:---------------
NAME :GWright* :Rbennig :JMain* j Jones :AChaffee :CBerlinger :CRossi
DATE :03/11/92 :3 /11/92 :03/11/92 : /13/92 : / /92 : / /92 : / /92 OFFICIAL RECORD COPY
Document Name: IN DENNIG
Further details of the event may be found in NRC Inspection Report 50-416/92-04 and Licensee Event Report 50-416/91-16.
Discussion
The underlying principle of reactivity management is to maintain the reactor in
the desired condition by properly anticipating, controlling, and responding to
the plant's changing parameters. Once a reactor has been placed in a
subcritical condition, as part of a plant shutdown, it is of primary importance
that the reactor be maintained in that subcritical condition. Given that
recriticality has not been avoided, prompt insertion of control rods and
termination of the cooldown are more conservative actions than upranging IRMs
to prevent scram while waiting on temperature coefficients to turn power.
Upranging IRMs in the event of recriticality can be inappropriate if management
oversight, prior training, and specific procedures are absent.
The experience at Grand Gulf and Monticello indicate that slow shutdowns in
situations with low decay heat present a particular challenge to reactivity
control, and require heightened operator and management awareness to avoid
recriticality. In addition, the events at Monticello and Big Rock Point
highlight the importance of continuous operator attention to plant parameters
in the course of a shutdown.
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 contacts listed below or the appropriate Office of Nuclear
Reactor Regulation (NRR) project manager.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical contacts: Melvyn Leach, RIII
(708) 790-5559 Geoffrey Wright, RIII
(708) 790-5695 Paul O'Connor, NRR
(301) 504-1307 Attachment: List of Recently Issued NRC Information Notices
OFC :RIII :SC:DOEA:OEAB:ADM:RPB :C:DST:SRXB :C:DOEA:OEAB :C:DOEA:OGCB :D:DOEA
NAME :GWright :RDennig :JMain_ w :RJones :AChaffee :CBerlinger :CRossi
DATE ://92 :1/92 :3/11 /92 :1/92 ://92 :1 /92 :/ /92 OFFICIAL RECORD COPY
Document Name: IN DENNIG/DUP
IN 92-XX
March xx, 1992 Further details of the event may be found in NRC Inspection Report
50-416/92-04 and Licensee Event Report 50-416/91-16.
Discussion
The underlying principle of reactivity management is to maintain the reactor
in the desired condition by properly anticipating, controlling, and responding
to the plant's changing parameters. Once a reactor has been placed in a
subcritical condition, as part of a plant shutdown, it is of primary importance
that the reactor be maintained in that subcritical condition. Given that
recriticality has not been avoided, prompt insertion of control rods and
termination of the cooldown are more conservative actions than upranging
IRMs to prevent scram while waiting on temperature coefficients to turn power.
Upranging IRMs in the event of recriticality can be inappropriate if management
oversight, prior training, and specific procedures are absent.
The experience at Grand Gulf and Monticello indicate that slow shutdowns in
situations with low decay heat present a particular challenge to reactivity
control, and require heightened operator and management awareness to avoid
recriticality. In addition, the events at Monticello and Big Rock Point
highlight the importance of continuous operator attention to plant parameters
in the course of a shutdown.
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 contacts listed below or the appropriate Office of
Nuclear Reactor Regulation (NRR) project manager.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical contacts: Melvyn Leach, RIII
(708) 790-5559 Geoffrey Wright, RIII
(708) 790-5695 Paul O'Connor, NRR
(301) 504-1307 Attachment: List of Recently Issued NRC Information Notices
OFC :R111 bC:DOEA:OEAB:ADM:RPB :C:DST:SRXB :C:DOEA:OEAB :C:DOEA:OGCB :D:DOEA
NAME :GWrightV' :RDennig :JMain :RJones :AChaffee :CBerlinger :CRossi
DATE :3 /II/92 ://92 :/ /92 :/ /92 :/ /92 :/ /92 :/ /92 OFFICIAL RECORD COPY
Document Name: IN DENNIG