Information Notice 1994-75, Minimum Temperature for Criticality

Minimum Temperature for Criticality

ML031060434
Person / Time
Site:	Beaver Valley, Millstone, Hatch, Monticello, Calvert Cliffs, Dresden, Davis Besse, Peach Bottom, Browns Ferry, Salem, Oconee, Mcguire, Nine Mile Point, Palisades, Palo Verde, Perry, Indian Point, Fermi, Kewaunee, Catawba, Harris, Wolf Creek, Saint Lucie, Point Beach, Oyster Creek, Watts Bar, Hope Creek, Grand Gulf, Cooper, Sequoyah, Byron, Pilgrim, Arkansas Nuclear, Braidwood, Susquehanna, Summer, Prairie Island, Columbia, Seabrook, Brunswick, Surry, Limerick, North Anna, Turkey Point, River Bend, Vermont Yankee, Crystal River, Haddam Neck, Ginna, Diablo Canyon, Callaway, Vogtle, Waterford, Duane Arnold, Farley, Robinson, Clinton, South Texas, San Onofre, Cook, Comanche Peak, Yankee Rowe, Maine Yankee, Quad Cities, Humboldt Bay, La Crosse, Big Rock Point, Rancho Seco, Zion, Midland, Bellefonte, Fort Calhoun, FitzPatrick, McGuire, LaSalle, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant, Crane
Issue date:	10/14/1994
From:	Grimes B Office of Nuclear Reactor Regulation
To:
References
IN-94-075, NUDOCS 9410070143
Download: ML031060434 (9)

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C.

20555-0001

-

October 14, 1994

NRC INFORMATION NOTICE 94-75: MINIMUM TEMPERATURE FOR CRITICALITY

Addressees

All holders of operating licenses or construction permits for pressurized- water reactors (PWRs).

PurwosR

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

notice to alert addressees to potentially non-conservative initial conditions

that were used in the analysis of some design-basis transients. As a result, some plant technical specifications for minimum temperature for criticality

may not be adequately conservative. 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

Commonwealth Edison Company (Zion Nuclear Station Units I and 2) and New York

Power Authority (Indian Point Nuclear Power Plant Unit 3) have informed the

NRC that their technical specifications for minimum temperature for

criticality were not supported by the safety analyses for their plants.

The

licensing analysis performed by Westinghouse for Zion assumed a nominal hot- zero-power (no-load) ^Derating temperature of 286 0C [547 OF], but Zion's

technical specifications allow criticality if the average reactor coolant

system temperature is greater then 260 *C [500 0F1. The safety analysis for

Indian Point 3 was also performed at 286 0 C [547 F], but its technical

specifications allow criticality at 232 C [450 °FJ, a limit which was set by

reactor vessel material considerations. A review of Indian Point records

Indicated that the reactor was brought critical below 286 °C (547 OF] several

times in the early life of plant operations (before 1988).

The lowest

temperature during these instances was 272 'C 1521 OF].

After discovering a potential to operate the plant in a region outside that

analyzed, both licensees instituted administrative controls to ensure that the

minimum temperatures for criticality are bound by the safety analyses

performed for their plants.

In addition, both licensees submitted license

amendments to NRC to revise the minimum temperature for criticality.

Further details concerning these events are in a 10 CFR Part 21 report to NRC

prepared for the Zion plant, dated March 18, 1993, and in Indian Point 3 Licensee Event Report 93-046-00, dated December 1,

1993.

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IN 94-75

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October 14, 1994 Discuss on

For transient analysis performed for hot-zero-power cases, small changes

(e.g., 3 'C [6 OF]) in initial conditions such as allowed by standard

technical specifications would have a negligible impact on analysis results.

However, if PWRs are allowed to achieve criticality significantly below the

temperature that was previously analyzed at hot-zero-power, the following

safety concerns would be raised:

(1) The transient analyses, such as "rod withdrawal from subcritical," "rod

ejection," 'zero power feedwater malfunction," and "boron dilution

event" documented in the Final Safety Analysis Report, might not have

been analyzed at temperatures below hot-zero-power and could be non- conservative. This could cause the analyses results with small margins

to violate specified fuel design limits (i.e., centerline fuel melt or

departure from nucleate boiling) for one or more of these postulated

transients.

(2) The response of the power range ex-core nuclear instrumentation may be

adversely effected by the increased density of the reactor coolant at

lower temperatures.

This could result in a higher power being reached

before a power range reactor trip occurs which might violate specified

fuel design limits for transients that rely on this trip.

(3) The moderator temperature coefficient will become more positive, perhaps

causing a violation of existing technical specifications.

Higher values

of moderator temperature coefficient could exceed those used in some of

the transient safety analyses. A more positive moderator temperature

coefficient at power would result in reactivity insertion that could

increase the consequences of an anticipated-transient-without-scram

event.

New analyses may justify criticality at somewhat lower temperatures. For

example, Commonwealth Edison Company performed the necessary safety analyses

for the Zion station and the staff approved a technical specification

amendment to change the minimum temperature for criticality to 277 *C

[530 OF).

This information notice requires no specific action or written response.

If

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

the technical contact listed below or the appropriate Office of Nuclear

Reactor Regulation (NRR) project manager.

Brian K. Crimes, Director

Division of Project Support

Office of Nuclear ReL.tor Regulation

Technical contact:

George A. Schwenk, NRR

(301) 504-*2814 Attachment:

List of Recently Issued NRC Information Notices

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I

Attachment

IN 94-75

October 14, 1994 LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

Information

Date of

Notice No.

Subject

Issuance

Issued to

94-74

94-73

94-72

94-71

94-70

94-69

94-68

94-67

94-66

Facility Management

Responsibilities for

Purchased or Contracted

Services for Radiation

Therapy Programs

Clarification of Critical- ity Reporting Criteria

Increased Control Rod

Drop Time from Crud

Buildup

Degradation of Scram

Solenoid Pilot Valve

Pressure and Exhaust

Diaphragms

Issues Associated with Use

of Strontium-89 and Other

Beta Emitting Radiopharma- ceuticals

Potential Inadequacies

in the Prediction of Torque

Requirements for and Torque

Output of Motor-Operated

Butterfly Valves

Safety-Related Equip- ment Failures Caused by

Faulted Indicating Lamps

Problem with Henry

Pratt Motor-Operated

Butterfly Valves

Overspeed of Turbine-

Driven Pumps Caused by

Govern'r Valve Stem

Binding

10/13/94

10;12/94

10/05/94

10/04/94

09/29/94

09/28/94

09/27/94

09/26!94

09/19/94

All U.S. Nuclear Regulatory

Commission Medical

Licensees.

All fuel fabrication

facilities.

All holders of OLs or CPs

for pressurized water

reactors.

All holders of OLs or CPs

for boiling water reactors

(BWRs).

All U.S. Nuclear Requlatory

Commission Medical

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.

All holders ot OLs or CPs

for nuclear power reactors.

OL

0

Operating License

CP

• Construction Permit

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IN 94-75

October 14, 1994 Discussion

For transient analysis performed for hot-zero-power cases, small changes

(e.g., 3 °C (6 OF]) in initial conditions such as allowed by standard

technical specifications would have a negligible impact on analysis results.

However, if PWRs are allowed to achieve criticality significantly below the

temperature that was previously analyzed at hot-zero-power, the following

safety concerns would be raised:

(1) The transient analyses, such as "rod withdrawal from subcritical," 'rod

ejection," "zero power feedwater malfunction," and 'boron dilution

event" documented in the Final Safety Analysis Report, might not have

been analyzed at temperatures below hot-zero-power and could be non- conservative. This could cause the analyses results with small margins

to violate specified fuel design limits (i.e., centerline fuel melt or

departure from nucleate boiling) for one or more of these postulated

transients.

(2) The response of the power range ex-core nuclear instrumentation may be

adversely effected by the increased density of the reactor coolant at

lower temperatures. This could result in a higher power being reached

before a power range reactor trip occurs which might violate specified

fuel design limits for transients that rely on this trip.

(3) The moderator temperature coefficient will become more positive, perhaps

causing a violation of existing technical specifications.

Higher values

of moderator temperature coefficient could exceed those used in some of

the transient safety analyses. A more positive moderator temperature

coefficient at power would result in reactivity insertion that could

increase the consequences of an anticipated-transient-without-scram

event.

New analyses may justify criticality at somewhat lower temperatures.

For

example, Commonwealth Edison Company performed the necessary safety analyses

for the Zion station and the staff approved a technical specification

amendment to change the minimum temperature for criticality to 277 OC

[530 OF].

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

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

the technical contact listed below or the appropriate Office of Nuclear

Reactor Regulation (NRR) project manager. - r7n'n! dby rian K.

C-;M3

Brian K. Grimes, Director

Division of Project Support

Office of Nuclear Reactor Regulation

Technical contact: George A. Schwenk, NRR

(301) 504-2814 Attachment:List of Recently Issued NRC Information Notices

• SEE PREVIOUS CONCURRENCE

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09/20/94

'O/ ?/94 DOCUMENT NAME: 94-75.IN

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IN 94-XX

September xx, 1994 This informati'jn notice requires no specific action or written response. If

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

the technical contact listed below or the appropriate Office of Nuclear

Reactor Regulation (NRR) project manager.

Brian K. Grimes, Director

Division of Operating Reactor Support

Office of Nuclear Reactor Regulation

Technical contact:

George A. Schwenk, NRR

(301) 504-2814 Attachment:

List of Recently Issued NRC Information Notices

• SEE PREVIOUS

SRXB/DSSA

GSchwenk*

08/31/94 SC:SRXB/DSSA

LPhillips*

09/12/94 CONCURRENCE

OGCB/DORS

PCWen*

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RCJones*

09/12/94 Tech Ed

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09/14/94 C:OTSB/DORS

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ELDoolittle*

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BKGrimes

09/ /94 DOCUMENT NAME: G:\\PETER\\MINTEMP.IN

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IN 94-XX

September xx, 1994

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

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

the technical contact listed below or the appropriate Office of Nuclear

Reactor Regulation (NRR) project manager.

Brian K. Grimes, Director

Division of Operating Reactor Support

Office of Nuclear Reactor Regulation

Technical contact:

George A. Schwenk, NRR

(301) 504-2814 Attachment:

List of Recently Issued NRC Information Notices

• SEE PREVIOUS

SRXB/DSSA

GSchwenk*

08/31/94 SC:SRXB/DSSA

LPhillips +*

G9//:W94 CONCURRENCE

OGCB/DORS

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ELDoolittle*

09/20/94 D:DORS

BKGrimes

09/ /94 DOCUMENT NAME: G:\\PETER\\MINTEMP.IN

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IN 94-XX

September xx, 1994 This information notice requires no specific action or written response. If

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

the technical contact listed below or the appropriate Office of Nuclear

Reactor Regulation (NRR) project manager.

Brian K. Grimes, Director

Division of Operating Reactor Support

Office of Nuclear Reactor Regulation

Technical contact: George A. Schwenk. NRR

(301) 504-2814 Attachment:

List of Recently Issued NRC Information Notices

• SEE PREVIOUS

SRXB/DSSA

GSchwenk*

08/31/94 A ~/DSSA

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