Information Notice 1989-09, Credit for Control Rods Without Scram Capability in the Calculation of Shutdown Margin

Credit for Control Rods Without Scram Capability in the Calculation of Shutdown Margin

ML031180508
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, 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, 05000000, Zimmer, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant
Issue date:	01/26/1989
From:	Rossi C Office of Nuclear Reactor Regulation
To:
References
IN-89-009, NUDOCS 8901190445
Download: ML031180508 (5)

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON D.C. 20555 January 26, 1989 NRC INFORMATION NOTICE NO. 89-09: CREDIT FOR CONTROL RODS WITHOUT SCRAM

CAPABILITY IN THE CALCULATION OF THE

SHUTDOWN MARGIN

Addressees

All holders of operating licenses or construction permits for test and

research reactors.

Purpose

This information notice is being provided to alert addressees to potential

problems from allowing credit to be taken for the reactivity worth of control

rod(s) that do not have scram capability in the calculation of the shutdown

margin. It is expected that recipients will review the information for ap- plicability to their facilities and consider actions, as appropriate, to

avoid similar problems. However, suggestions contained in this information

notice do not constitute NRC requirements; therefore, no specific action or

written response is required.

Background:

An NRC inspection at a non-power reactor facility identified a situation in

which a shutdown margin less than that required by the licensee's technical

specification was possible. The reactor involved has two types of control

rods: shim rods, which are magnetically coupled to their drive motors and

which are decoupled and rapidly Inserted into the reactor core upon receipt

of a scram signal, and a regulating rod, which is fixed to its drive motor

and drives into the core upon receipt of a scram signal. The regulating

rod was used by the licensee, in addition to the shim rods, to demonstrate

compliance with the technical specification for the shutdown margin.

Discussion:

The shutdown margin is a measure of the reactivity necessary to provide confi- dence that a reactor can be made subcritical by a predetermined amount by means

of the control and safety systems, starting from any permissible operating con- dition. In the calculation of the shutdown margin, it is assumed that the most

reactive control device (i.e., the highest worth rod) is in Its most reactive

condition and that the reactor will remain subcritical without further operator

action. The shutdown margin should also be essentially instantaneously avail- able (within the technical specification limit on rod drop time) upon receipt

of a reactor scram signal. If the shutdown-initiating event is a loss of

facility electrical power, the non-scramiing control rod(s) which are fixed

to their drive motors would not drive into the reactor core.

91190445 7 )

IN 89-09 January 26, 1989 Therefore, if the reactivity worth of the non-scramming control rods(s)

is required to be instantaneously available to meet the shutdown margin

technical specification requirement, it may not be possible to make the

reactor subcritical in a controlled, safe manner.

Subsequent calculations have shown that the licensee did not need to include

the regulating rod in the calculations to meet the technical specification

requirement for shutdown margin. However, to ensure that the non-scrammable

control rod is not used in the calculation of the shutdown margin (the technical

specification would have allowed this), an amendment to the facility operating

license was requested by the licensee and approved by the NRC. The technical

specification states that the shutdown margin is based on scrammable control

rods only.

No specific action or written response is required by this information notice.

If you have any questions about this matter, please contact one of the technical

contacts listed below or the Regional Administrator of the appropriate regional

office.

Ctes

4E. Ross , Drector

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Technical Contacts: John Thompson, NRR

(301) 492-1175 Al Adams, NRR

(301) 492-1121 Attachment: List of Recently Issued NRC Information Notices

IN 89-09 January 26, 1989 Therefore, if the reactivity worth of the non-scramming control rods(s)

is required to be instantaneously available to meet the shutdown margin

technical specification requirement, it may not be possible to make the

reactor subcritical in a controlled, safe manner.

Subsequent calculations have shown that the licensee did not need to include

the regulating rod in the calculations to meet the technical specification

requirement for shutdown margin. However, to ensure that the non-scrammable

control rod is not used in the calculation of the shutdown margin (the technical

specification would have allowed this), an amendment to the facility operating

license was requested by the licensee and approved by the NRC. The technical

specification states that the shutdown margin is based on scrammable control

rods only.

No specific action or written response is required by this information notice.

If you have any questions about this matter, please contact one of the technical

contacts listed below or the Regional Administrator of the appropriate regional

office.

Charles E. Rossi, Director

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Technical Contacts: John Thompson, NRR

(301) 492-1175 Al Adams, NRR

(301) 492-1121 Attachment: List of Recently Issued NRC Information Notices

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12/19/88 12/19/88 12/19/88 1/13/89 1/18/89 1/19/89

IN 88- January , 1989 Therefore, if the core is designed such that the reactivity worth of the

non-scramming control rod(s) is required to be instantaneously available

to meet the shutdown margin technical specification requirement, it may not

be possible to make the reactor subcritical in a controlled, safe manner.

Subsequent calculations have shown that the licensee did not need to include

the regulating rod in the calculations to meet the technical specification

requirement for shutdown margin. However, to ensure that the non-scrammable

control rod is not used in the calculation of the shutdown margin (the

technical specification would have allowed this), an amendment to the facility

operating license was requested by the licensee and approved by the NRC that

states the shutdown margin is based on scrammable control rods only.

No specific action or written response is required by this information

notice. If you have any questions about this matter, please contact one of

the technical contacts listed below or the Regional Administrator of the

appropriate regional office.

Charles E. Rossi. Director

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Technical Contacts: John Thompson, NRR

(301) 492-1175 Al Adams, NRR

(301) 492-1121 Attachment: List of Recently Issued NRC Information Notices

v NRR:PDSNP*NRR:PDSNP EAB:NRR C:OGCB:NRR

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IN 88- December , 1988 is required to be instantaneously available to meet the shutdown margin T/S

requirement, a possible violation of the T/S may result in addition to the

possible inability to bring the reactor subcritical in a controlled, safe

manner.

Subsequent calculations have shown that the licensee did not need to include

the regulating rod in their calculations to meet the T/S requirement for

shutdown margin. However, to insure that the non-scrammable control rod

is not used in the calculation of the shutdown margin (the T/S would have

allowed this), an amendment to the Facility Operating License was requested by

the licensee and approved by the NRC that states the shutdown margin is based

on scrammable control rods only.

No specific action or written response is required by this information

notice. If you have any questions about this matter, please contact the

technical contact listed below or the Regional Administrator of the

appropriate regional office.

Charles E. Rossi, Director

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

John Thompson, NRR

(301) 492-1175 Al Adams, NRR

(301) 492-1121 Attachment: List of Recently Issued NRC Information Notices

• EAB:NfBL NRR:PDSNP EAB:NRR C:EAB:NRR C:OGCB:NRR

JT on:db AA a CMiller RLobel WLanning CHBerlinger

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