ML20096D049

Discusses Independent Assessment Program,Phase 3 Open Item Re Force Distribution in Axial Restraints.Util Must Evaluate Effects of Double Trunnions on Basis of Support Ductility

ML20096D049
Person / Time
Site:	Comanche Peak
Issue date:	08/10/1984
From:	Williams N CYGNA ENERGY SERVICES
To:	George J TEXAS UTILITIES ELECTRIC CO. (TU ELECTRIC)
References
84042.014, NUDOCS 8409050523
Download: ML20096D049 (2)

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taevstas 101 Cahtornia Street. 5ete 1000. S 3n Francisco CA 941115894 4'5 3M %M

- August 10,1984 84042.014 e

Mr. J. George Project Manager Texas Utilities Generating Company g Highway FM 201 Glen Rose, Texas 76043

Subject:

Force Distribution in Axial Restraints - Phase 3 Open item Comanche Peak Steam Elec tric Station Independents Assessment Program - Phose 3 Texas Utilities Generating Company Job No. 84042

Reference:

Motion for Sumniary Disposition Regarding Allegations Concerning Considera-tion of Force Distribution in Axial Restraints, July 9,1984

Dear Mr. George:

N During the Phase 3 pipe support review Cygna raised a question concerning the appropriate loading to be used in sizing standard cornponents (struts and snubbers) which are used in pairs to form oxial restraints. The concern was not with the pipe stress analysis modeling techniques for this type of support, but rather with the oppropriateness of sizing the struts or snubbers assuming a 50% - 50% load split. TUGCO responded by referring Cygno to the above referenced Motion for Summary Disposition, i

Based on a review of that document, Cygno does not agree with the interpretation that the 4 rotational constroint provided by ' the double trunnion trapeze supports constitutes a l2 condition of restraint of free end displacement. And, therefore, on increase in the

('lowable stress fors these supports is not appropriate. Justification for the 50% load split must be provided on on oppropriate basis. Orr such basis would be to demonstrate that the support system provided sufficient ductility (deformation) to insure that the proper redistribution of forces occurs prior to achieving ultimate load.

Cygna understands that Dr. lotti has performed some studies on a pipe stress problem to determine unether the pipe axial and rotational displacements are coincident in time.

• Although we have not reviewed the results, Dr. lotti believes the correlation will be low.

However, it may be difficult to justify the uncoupled nature of these displacements on a generic basis.

While Cygna hos noted that TUGCO has chosen a 50% - 50% load split for the design of the supports, the same is not true of the welded ottochment local stress evoluotion, in all but one of the 16 double trunnion axiot restraints reveiwed during all four phases of the Independent Assessment Program, the full load (100%) was assumed for each trunnion 8409050523 840810 . I PDR ADOCK 05000 .

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Mr. J. George August 10,1984 Page 2 design. Although we think a check of all double trunnions should be made to ensure on appropriate load split, it appears this will not be a problem. Given this disagreement on the support design, however, Cygno believes that TUGCO must either evaluate the effects on the basis of support ductility or review the supports on a more specific basis without the increased allowable before Cygno con close this item for the purposes of the Phase 3 reviews.

If you prefer to have further technical discussions on this matter please notify me of this fact.

Very truly yours, o

N. H. Williams Project Manager cc: Mr. S. Burwell (USNRC)

Mr. S. Treby (USNRC)

Mrs. J. Ellis (CASE)

Mr. D. Wade (TUGCO)

Mr. G. Grace (TUGCO/EBASCO)

Mr. D. Pigott (OHS)

Mr. R. Ballard (G&H)