ML17037C242

Letter Responding to the November 30, 1973 Letter Concerning the Extent and Consequences of Possible Inverted Poison Tubes in the Control Blades and Requiring Further Action Be Implemented within 15 Days After Receipt of Letter

ML17037C242
Person / Time
Site:	Nine Mile Point
Issue date:	04/09/1974
From:	Skovholt D US Atomic Energy Commission (AEC)
To:	Schneider R Niagara Mohawk Power Corp
References
Download: ML17037C242 (4)

Text

Distribution APR g )g74 Docket File AEC PDR.

Local PDR Docket No. 50-220 Branch Reading JRBuchanan, ORNL DJSkovholt, L:OR TJCarter, L:OR ACRS (16)

Hiagaxa Mohawk Power Corporation RO (3)

ATTN: Hr. R. R. Schneider OGC Vice Pxesidont - Electric DLZiemann, L:ORB if/2 Operations CJDeBevec, L:ORB II2 300 Erie Boulevard Pest JLSapir, L:ORB //2 Syracuse, New York 13202 RH)iggs, L:ORB II2 SVarga, L:RP Gentlemen:

In a letter dated November 30, 1973, you submitted information concerning the extent and consequences of possible invertod poison tubes in the control blades of the Nine Mile Point Unit 1 reactor. He have reviewed your submittal along with the associated General Electric generic sub-mittal dated October 8, 1973, and have concluded that without additional supporting evidence the assumption of a homogeneous dofect rate of 5X is not )ustified. In addition, relatively small groupings of defective blades can pxoduce the maximum undesirable effects. Therefore, to maintain the current safety margin requirements until an inspection of the xods is performed, we are requiring that the following action be implemented within 15 days after receipt of this letter.

1. Subtract a value of 0.2X delta k from the current allowable insequence control rod reactivity worth.

2. Add a value of 10 psi to the maximum pressure calculated for the safety valve sizing pressurization transient and confirm that adequate margin exists.

3. Establish a procedure to report any observed reactivity anomaly greater than 0.5X to the AEC within 10 days of the observation.

It is important that uncertainties associated with the possible presence of defective control blades be either significantly reduced ox eliminated as soon as practicable. You should, therefore, inspect a homogeneous sampling of about 50X or more of the control rods during the next refueling outage and complete the inspection of the entire core within the next two refueling outages.

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Niagara Mohawk Power Corporation - 2 APR g 797y If the calculated potential shutdmm margin loss (assuming full settling in all the observed inverted poison tubes) extrapolated to include uninspected rods is less than 0.5X delta k, add the calculated value to 0.25/ delta k to obtain the minimum shutdown margin requirement for the following fuel cycle. You may xeduce the minimum shutdown margin require-ments by the calculated xeactivity uncertainty removed by the replacement.

of defective blades.

If the results of the inspection yield a potenti.al equivalent full-core shutdown margin loss greater than 0.51 delta k, inspection results should be submitted to the AEC for review befoxe the end of the outage and some amount of blade replacement may be required.

Based upon the inspection x'esults and any blade replacements, subsequent restrictions on insequence contxol rod xeactivity worths and pressure margins will be ad)usted to reflect known core conditions.

In the interim, we strongly encourage the performance of-an inservice inspection of control rods during any shutdown of significant duration before your next refueling outage.

Sincerely, Donald J. Skovholt Assistant Director for Operating Reactors Directorate of Licensing cc: J. Bruce HacDonald, Esquire Dr. William Geymoux Deputy Comnd.ssioner and Counsel Staff Coordinator New York State Department of New York State Atomic Fnergy Council Commerce -and Counsel to the New York State Department of Commerce Atomic Energy Council 112 State Street 99 Washington Avenue Albany, New York 12207 Albany, New York 12210 Anthony ?'. Roisman, Esquire Axvtn Z. Upton, Esquire Berlin, Roisnan and Kessler LeBoeuf, Lamb, Leiby 5 HacRae 1712 N Street, N. W.

1757 N Street, N. W. Washington, D. C. 20036 Washington, D. C. 20036 Oswego Ci.ty Library L:ORB // L:ORB I/ L:0 L:0 X740Y SURHAM23v'ATCW JLSapir: sg CJDeB c DLZiemann DJ o holt 4/8/74 IJ gP~ c,lf lw 4/ /7'4 Porm hEC-3ld (Rev. 9.33) hECM 0240 CI'0 CA2 IO 1IA00 I $ 20 204

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