ML20128B205

Forwards Rept Summarizing Conditions & Bases Acceptable to Licensing for Return to Power for Monticello Re Control Rod Problem

ML20128B205
Person / Time
Site:	Monticello
Issue date:	08/03/1973
From:	Stello V US ATOMIC ENERGY COMMISSION (AEC)
To:	Skovholt D US ATOMIC ENERGY COMMISSION (AEC)
References
NUDOCS 9212030593
Download: ML20128B205 (2)

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D. J. Skovbolt, Assistant Director for Operating Reacters, L N00fTICEL1h OPERATICII The enclosed report summarises the conditions and bases acceptable to Licensing for the recurs to power for Monticello with respect to the i

control rod problem.

Originai sined by

. Victor Str IM Victor Stallo, Jr. , Assistaat Director for Reactor Safety Directorate of Licenslag Enclosure Revised Shutdown Margia for Monticello Operation ect S. Emmauer J. Hendria D. F. Ross A. Giambasse E. Bailey Distribution:

J. G. Ka$plar Docket file CPB Reading J. Shea L Reading (M. Groff) i l

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RE_ VISED SilUTDOWN MARCIN F(u MONTICELLO OPERATION There is ir.dicatiot that some Monticello control assemblics may have manufacturing shutdown margin.defects that could have a significant effect on the reactor j (A discussion of this problem with respect to the Millstone Unit 1 Plant is presented in a special report issued by the Millstone Power Company on July The manufacturing defects could result " Reactor Control Blade in settling of BEvaluation")

C powder in th control blades during reactor operation. 4 Such settling would result in a decrease in the shutdown margin.

The current Technical Specification requirement is that the shutdown margin be at least 0.25% throughout the cycle. The Regulatory staff has reviewed the Monticello control rod problem and bas concluded that an additional margin possible of settling 0.55 be ofadded B C.to this shutdown margin requirement to allow for 4 This means that with the most reactive control-

, rod out of the reactor, at any time during the cycle. a minimum shutdown margin of 0.75% must be present allow for transient Sm and Xe, These det erminations of shutdown margin should if present.

requirement on shutdown margin is sufficientWe believe this additional 0.5%

in margin due to settling of E G gin the control rods.to allow for short-term changes Because of the B 4 C during operation, further measurements of the shu required periodically. e shortly by the Licensing staff.The frequency of these measurements will be established Prior to startup of Monticello, shutdown margin demonstrations should be made with each control rod withdrawn, in turn.

that definitely limits the possibility of defective control assembliWe those manufactured at Wilmington, N. C.

are not aware es to In addition, we believe it is desirable to make several measurements of the shutdown margin up to a critical reactor state prior to power operation (these measurements should not violate Technical Specification limits).

will verify the actual shutdown margin. These critical measurements  ;

This value can be compared with '

resultsthe during ofcycle.

later measurements to determine changes in the shutdown margin i

The problem associated with insufficient t return to criticality following a coolucan, with the mostshutdown margin is a possibl out.

If, for example, an extreme amount reactive rod. stuck ceivable that k cf settling occurred, it is con-supercritical sbe could be negated in whole or in part . . This bin the c the operator of boric acid from the Standby Liquid C y the addition by ontrol System.  !

!!owever, from equilibrium operation, due toe the phenomenon woulti rapid l35 owing This a cooldownbuildup  !

l to add more boron, if necessary.be dominant for over 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, time providing s i

not operative, temperature the reactor coefficient. In that would seek a stable level based on thin ca e negative removc the generated heat. case, we believe, the RHR systems could I

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