Information Notice 1992-39, Unplanned Return to Criticality During Reactor Shutdown

Unplanned Return to Criticality During Reactor Shutdown

ML031200314
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, Three Mile Island, 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
Issue date:	05/13/1992
From:	Rossi C E Office of Nuclear Reactor Regulation
To:
References
IN-92-039, NUDOCS 9205060036
Download: ML031200314 (12)

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_*,, C j'A 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 I-0.<OD n; co> 0 m Z.4-m rn o 0 0 z Z G2-cn a En z* om o) Z en q-n M 0n a 0 n a -h <-Attachment

1 IN 92-39 May 13, 1992 Page I of 1 LIST OF RECENTLY ISSUED NRC INFORMATION

NOTICES Date of Information

information

Notice No.92-38 1 92-37 92-16, Supp. 1 I 92-36' 92-35 Subject Implementation

Date for the Revision to the EPA Manual of Protective

Action Guides and Pro-tective Actions for Nuclear Incidents Implementation

of the Deliberate

Nisconduct

Rule Loss of Flow from the Re-sidual Heat Removal Pump during Refueling

Cavity Draindown Intersystem

LOCA Outside Containment

Higher Than Predicted

Ero-sion/Corrosion

in Unisol-able Reactor Coolant Pres-sure Boundary Piping Inside Containment

at A Boiling Water Reactor New Exposure Limits for Airborne Uranium and Thorium Increased

Instrument

Response Time When Pressure Dampening Devices are Installed Issuance 05/12/92 05/08/92 05/07/92 05/07/92 05/06/92 Issued to All holders of OLs or CPs for nuclear power reactors, non-power

reactors and materials

licensees

auth-orized to possess large quantities

of radioactive

material.All Nuclear Regulatory

Commission

Licensees.

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.-u 0 rn>mD-C > 0 u) D-D2 zzz>0 92-34 92-33 I CP -'05/06/92 All licensees

whose opera-tions can cause airborne concentrations

of uranium and thorium.04/30/92 All holders of OLs or CPs for nuclear power reactors.(Operating

License Construction

Permit

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/;11/9 2/ 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 IV t'/ ' f'(301) 504-1307 4.f, 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