ML20210K249

Safety Evaluation Supporting Analytical Method Used by Licensee to Evaluate Critical Stresses

ML20210K249
Person / Time
Site:	Cooper
Issue date:	09/25/1986
From:	Office of Nuclear Reactor Regulation
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Shared Package
ML20210K247	List: ML20210K242 ML20210K249 ML20212A824
References
NUDOCS 8610010347
Download: ML20210K249 (2)

Text

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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATING TO MARK I CONTAINMENT PROGRAM - VACUUM BREAKER INTEGRITY COOPER NUCLEAR STATION DOCKET NO.: 50-298 I. INTRODUCTION In addition to the evaluation of the suppression chamber, torus attached piping, pressure relieving lines, etc, under defined loadings, the Mark I containment program required assurance of the strucural integrity of vacuum breakers during operation in all Mark I plants. This additional requirement was categorized as a separate effort, as the adequacy of other components was already discussed in a separate Safety Evaluation.

The Franklin Research Center (FRC) has performed an evaluation of the structural integrity of vacuum breakers in the Cooper Nuclear Station (Cooper) for the NRC staff. Results of the review are reported in the attached document, TER-C5506-418, " Structural Evaluation of the Vacuum Breakers (Mark I Containment Program), Nebraska Public Power District, Cooper Nuclear Station." FRC has concluded that actions taken by the licensee are adequate to restore the original design margin of safety for its vacuum breakers under the revised loadings in the Mark I containment. NRC staff reviewed the attached document and concurred with g the FRC findings.

p II. DISCUSSION j In the Cooper Mark I Containment, there are twelve 18" internal type  :

vacuum breakers made by General Precision Engineering. Vacuum breakers I are located at six of the eight intersections of the ring header and vent i lines in the suppression chamber. There are two vacuum breakers at each location. Loadings on Mark I structures and vacuum breakers are based on the General Electric Company Report, NED0-21888, " Mark I Containment Program Load Definition Report," Revision 2, dated November, 1981. For vacuum breakers, the loadings included are gravity, seismic, and hydrodynamic loads. The hydrodynamic forcing functions were developed by Coninuum Dynamics, Inc. , by using a dynamic model of a Mark I pressure suppression system and the full scale test facility data. The system model was capable of predicting pressure transients at specified locations in the vent system. Loading across the vacuum breaker disc causedbypressuredifferentialsbasedontestdatawasthusq(antified as a function of time. The methodology was reviewed and approved by NRC on December 24, 1984 with certain specified conditions on its use. The licensee's use of the model was consistent with the NRC conditions.

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4 To determine the structural integrity of the vacucm breakers, results from a finite element model and ANSYS program analyses were compared with design limits specified in the ASME Boiler and Pressure Vessel Code,Section III, Division 1, Subsection NC, 1977 Edition and addenda up to Summer 1977. It was found that critical stresses in all parts of the Cooper vacuum breakers are below the Code allowables for every service level. They vary from 46% to a maximum of 85% of the Code allowable values. The licensee therefore concluded that Cooper vacuum breakers require no modifications.

III. CONCLUSION The analytical method used by the licensee to evaluate critical stresses has been reviewed and found to be adequate. The maximum stress in the Cooper vacuum breakers is 85% of the Code allowable. The existing design is structurally adequate and requires no modification.

Principal Contributor: H. Shaw Dated:

September 25, 1986 V

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