ML20024G587
| ML20024G587 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 04/01/1974 |
| From: | Skovholt D Office of Nuclear Reactor Regulation |
| To: | Mayer L NORTHERN STATES POWER CO. |
| References | |
| NUDOCS 9102130400 | |
| Download: ML20024G587 (3) | |
Text
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piptribution M cket File AEC PDR APR 1 1974 tocai poR i
Docket No. 50-263 Branch Reading RJBuchanan, ORNL DJSkovholt, L 0R j
TJCarter, L 0R ACRS (16)
R0 (3)
Northern States Fover Company OGC ATTH: Mr. L. O. Hayer, Director of DLZiemann, LIORB #2 j
Uuclear Steport Services JJShea, L:0RB #2 414 Nico11st Mall JLSapir, L 0RB #2 j
Minneapolis, Minnesota 55401 RMDiggs, L:0RB $2 SVarga, L RP GentIcmen In a letter dated October 17, 1973, the extent and consequences of possible inverted poison tubes in theyou sub control blades of the Monticello reactor. We have reviewed your sub-adttal along with the associated General Electric g,anerf c submittal dated Octobar 8,1973. and have concluded that without Sdditional supporting evidence the assumption of a homogeneous Urser rate of 5%
is not justified.
In addition, rah'.ively small groupings of dafective blades can produce the mar *wtna undesirable effects.
i Therefore, to inaintain the current safety margin requirements until au inspection of the rods is performed, we are requiring that the following action j
be in:plemented within 15 days afte.r receipt of this letter.
1.
Subtract a value of 0.2% delta k from the current allowable insequence control rod reactivity worth.
I 1.
Add a value of 10 poi to the maximum pressure calculnted for the safety valve sird.ng pressurization transient and confirm that adequate margin exists.
3.
Establish a procedure to report any observed reactivity anomaly greater than 0.5% to the AEC within 10 days of the obeetwation.
It is important that uncertainties associated with the possible presence i
of defective control blades be either significantly reduced or eliminated j
as soon as practicable.
You should, therefore, inspect a homogeneous l
sampling of about 50% or core of the control rods durina the next i
refuelint outage and complete the inspection of the entire core within the u=at two rafualfag cutages.
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9102130400 740401 ADOCK 050g3 PDR P
o Forthern States power cowany Apg
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If the calculated potential shutdown margin losa (assuming full settling i
in all the observed inverted poison tubeu) extrapolated to include uniumpected rods is lose than 0.5% delta k, add the calculated value to 0.25% delta k to obtain the minimum shutdown margin requirament for the following fuel cycle. You may reduce the ministe shutdown margin i
requirements by the calculated reactivity uncertainty removed by the replacement of defedtive blades.
If the results of the inspection yield a potential equivalent full core shutdown margin loss greater than 0.5% delta k. inspection resulta should be submitted to the AEC for review before the end of the outage and some amotant of blade replacesent may be required.
t Based upon the, inspection results and any blade replacements, subsequent restrictions on insequence control rod reactivity worths and pressure margins will be adjusted to reflect known core conditions.
in the interia, we strongly encourage the performance of an innervics inspection of control roda during any shutdmn of significant duration I
I before your next refueling outage.
i i
I Sincerely, i
l w n:.i s,.a ty D,, D.ovholt Donald J. Skovholt Assistant Director for Operating Reactors Directorate of Licensing ces See next page l
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- iorthern States Power Company 3-i APR 11974 i
j cci Arthur Ranquiet, Esquire Vice President - Law j
Northern States Power Company 414 Nicollet Mall Minneapolis, Mimosota 55401 Geraid Omrnoff Shaw, Pittm, Potte, Trowbridge & Madden 910 - 17th Street, N. W.
Washington, D. C.
20006 Howard J. Yosel, Esquire Knittle & Voge) 1154 East crain Exchange Building 412 South 4th Street Minneapolis, Minnesota 55415 l
Steve Cadler, P. E.
l 2120 Cirter Avenue St. Paul, Minnesota 55108 Mr. Daniel L. Picker Assistant City Attorney 647 City Hall st. Paul, Minnesota 55102 6
Warren R. Lawson, M. D.
Secretary & Emscutive Officer State Department of Health 717 Delaware Street, S. E.
Minneapolis, Minnesota 55440 Sandra S. Cardebring, Esquire llinnesota Follution Control Agency 1935 W. Comty Road 32 1:oseville, Minnesota 55113 j
Environmental Library of Minnesota c
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Fotos AEC.)l, (Rev. 9 95) AFCM 0240 4-
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