ML19249B561

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Responds to IE Bulletin 79-02,Revision 1.Base Plates W/Some Degree of Flexibility re-evaluated & Modified to Ensure Max Loads Do Not Exceed Allowable Loads & Stress
ML19249B561
Person / Time
Site: North Anna Dominion icon.png
Issue date: 07/06/1979
From: Brown S
VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To: James O'Reilly
NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
References
402B, NUDOCS 7909040560
Download: ML19249B561 (2)


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.3 JUL 9 A10 : 18 July 6, 1970 Serial No. 4023 Mr. James P. O'Reilly, Director PSE&C/RHW ,Ill: b aT.

Office of Inspection & Enforcement U. S. Nuclear Regulatory Comissicn Docket No. 50-339 Region II 101 Marietta Street, Suite 3100 Atlanta, Georgia 30303

Dear Mr. O'Reilly:

Our letter of May 24, 1979, Serial No. 402, in response to IE Bulletin 79-02 was our report on pipe This support base platethe letter provides designs using additional concrete expansion anchor bolts. 21, 1979.

information requested by IE Bulletin 79-02 Revision No. I dated June Item 1 of the revised bulletin requires that justification be determining flexibility is different from that submitted when the criterie" '9e...the case plates should be considered flexible if stated in the bulletin:

the unstiffened distance between the member welded to the plate and Thethe edge of the base plate is greater than twice the thickness of the plate."

description of the analytical model revised bulletin also requires that "...a used to verify that pipe support base plate flexibility is accounted for in the calculation of anchor bolt loads..." be submitted with our response to the bulletin.

The criteria used to determine base plate flexibility in the design of the pipe supports for No*th Anna Unit 2 was de.' eloped as the result of compa-ing finite element computer results with manual calculation m which assumed base plate rigidity.

"ANSYS" as developed by Swanson Analysis System, Inc.Base of Houston, plates were PA was used to model typical base plates in establishing this criteria.

modeled as finite element beams on elastic foundations Theusing results various of thisplate sizes, thicknesses, loads, and anchor bolt patterns.

finite element analysis were compared with the Asresults a resultofofmanual these calculations which anaylzed the base plates as being rigid.

comparisons, it was found that where the ratio of the unstiffened distance between the member welded to the plate and the outermost anchor bolts, as compared to the base plate thickness, was less than or equal to five to one, loads could be conservatively calculated by using a rigid then anchor bolt Base plates which met this criteria were analyzed as base plate analysis.

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Base elates where this ratio was greater than five to one were considered to t.we some degree of flexibility as a finite element analysis could result in higher anchor bolt loads than would be calculated using a rigid analysis. Base plates falling in this category were re-evaluated and modified as necessary to ensure that maximum anchor bolt loads would not exceed the allowable bolt loads and that base plate stresses would not exceed the allowable design stress.

The response to items 2, 3, and 4 of the revised bulletin as addressed for North Anna Unit 2 is as stated in our previous letter of May 24, 1979.

If you require any further information on this subject, please contact us.

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