ML20105C701

Discusses Util Plans to Lower CRD Support Structures to Facilitate Maint Work Under Vessel & to Reduce Radiation Exposure to Plant Personnel.Supporting Documentation Encl

ML20105C701
Person / Time
Site:	LaSalle
Issue date:	09/16/1992
From:	Shields J COMMONWEALTH EDISON CO.
To:	Murley T NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM), Office of Nuclear Reactor Regulation
Shared Package
ML20105C704	List: ML20105C701 ML20105C706 ML20105C713 ML20105C720
References
NUDOCS 9209220364
Download: ML20105C701 (4)

Text

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• il . 1403 Opus Place

• Downers Grovo, Illinois 60$15 September 16, 1992 Dr. Thomas E. Murley Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, D.C. 20555 Attn: Document Contrui Clerk

Subject:

LaSalle County Station Units 1 and 2 Lowering of the CRD Support Structure NRC_Doche tJios,_50-313_acL50dM

Dear Dr. Murley,

During the upcoming Unit 1 and Unit 2 refuel outages, (LlR05 and L2R05) Commonwealth Edison (CECO) plans on lowering the Control Rod Drive (CRD) support structures to facilitate maintenance work under the vessel, and thereby reducing radiation exposure to plant personnel The CR0 support structure limits the downward motion of a control rod following a postulated CRD housing failure 50 that any resulting nuclear transient will not cause fuel damage. The clearance betweea the CRD housings and the support plate must be sufficient to prevent vertical contact stresses due to thermal expansion during plant operation.

Hith the current design, the maximum deflection of the support steel due to a drive housing failure is 3 inchus, as discussed in UFSAR sectior 4.6.2.3.1.2.1. As evaluated in UfSAR section 4.6.2,3.3.1, " Sudden withdrawal of_any control rod through a distance of one drive notch at any position in the core.does not produce a transient sufficient to damage any radioactive-material barrier." Therefore, the current 3 inch deflection.due to housing failure-is bounded by the consequences of the 6 inch rod withdrawal. Section 3/4.1.3 of both the Unit I ar- Unit 2 Technical Specification Bases state that the maximum deflection of the support plate is 3 inches, and draws a comparison to the consequences of a normal withdrawal increment. ,

After the lowering of the support plate, the maximum deflection of the support steel due to a drive housing failure has been calculated to be is 3.65 inches, which is still. bounded by the 6 inch criteria for sudden rod withdrawal.

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'Or. Thomas ~E. Murley .

42- September 16, 1992 CECO has performed a Safety Analysis per 10 CFR 50.59, and determined th&t an Unreviewed Safety Question does not exist as a result of this oesign <

change. Copies of these evaluations are included as Attachment A. A marked-up copy of each unit's Technical Specification Bases, showing the requasted revision of the maximum support steel movement due to a CRD housing failure, is included as Attachment B. It is requested that these pages be revised to reflect the modifications. As part of the modiffration process, the UFSAR will be revised to reflect this design change.

If there are any questions, please contact this office.

Respectfully, k j ///

JoAnn Shields L Nuclear Licensing Administrator i

Attachments: Attachment A - Safety Evaluations

/.ttachment B - Marked-up Bases pages cc: A.B. Davis, Regional Administrator - RIII B.L. Siegel, Project Manager - NRR D.L.-Hills, Senior Resident. Inspector - LSCS Office of Nuclear Saf':ty - IUNS l

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ATTACHMENT A-SAFETY EVALUATIONS 9

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l ATTACHMENT B I- MARKED-UP BASES PAGES ZNLD21195

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