ML20212H567

Safety Evaluation Supporting Util Response to Generic Ltr 83-08 Re Restoring Safety Margins of Vacuum Breakers by Replacing Critical Parts W/Adequate Matls

ML20212H567
Person / Time
Site:	Brunswick
Issue date:	01/16/1987
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20211P084	List: ML20211P078 ML20212H551 ML20212H567
References
GL-83-08, GL-83-8, NUDOCS 8701210500
Download: ML20212H567 (3)

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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION i l

RELATING TO MARK I CONTAINMENT PROGRAM - VACUUM BREAKER INTEGRITY BRUNSWICK STEAtt ELECTRIC PLANT UNITS 1 AND 2 DOCKET NOS.: 50-325 AND 50-324 I. INTRODUCTION In addition to the evaluation of the suppression chamber, torus attached piping, pressure relieving lines, etc, under the newly defined loadings, the Mark I containment program required assurance of the structural 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. To address the concerns related to structural integrity of vacuum breakers the NRC issued Generic Letter 83-08, dated February 2,1983, requesting the licensees either to submit plant unique calculations which formed the bases for modifications to the vacuum breakers or to provide justification for acceptability of as-built vacuum breakers.

By letter dated June 23, 1983, the licensee provided its response to the -

Generic Letter 83-08, committing to modifications of vacuum breakers pallets, vacuum breakers hinge shafts, vacuum breakers arms, and vacuum breakers hinge arm studs. By a subsequent letter dated December 13, 1985, as supplemented March 28, 1986, the licensee confirmed that its analysis of the vacuum breaker structural integrity was based on NRC approved methodology.

The Franklin Research Center (FRC) has performed an evaluation of the structural integrity of vacuum breakers in the Brunswick facility for the .NRC staff. Results of the review are reported in the attached document, TER-C5506-3.21, " Structural Evaluation of the Vacuum Breakers (Mark I Containment Program), Carolina Power and Light Company, Brunswick Steam Electric Plant Units 1 and 2." 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 the FRC findings.

II. DISCUSSION In the Brunswick Mark I Containment, there are eight 18" internal type vacuum breakers made by General Precision Engineering. One vacuum breaker is located at the intersection of each vent line and the ring header in the suppression chamber. 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 8701210500 870116 PDR ADOCK 05000324 P PDR

hydrodynamic forcing functions were developed by Continuum 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 caused by pressure differentials based on test data was thus quantified as a function of time. This issue was reviewed and approved by NRC on December 24, 1984. Loadings were combined according to FSAR commitments.

To determine the structural integrity of the vacuum 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 the pallet, the hinge arm, the hinge shaft and the hinge arm stud could become overstressed. The licensee, decided to remedy the situation by using different materials for these parts to increase their allowable stress limits. By changing SA-516 Gr 70 (pallet and hinge arm) and SA-320 B8 (hinge shaft and hinge arm stud) to SA-705 Gr630 (pallet) and SA-564 Gr 630 (hinge arm, hinge shaft and hinge arm stud), both adequately heat treated (age hardened at 1,100 F), the allowable liinits stress change from 35 and 30 ksi.

to 70 ksi. Proper safety margins were thus restored.

III. CONCLUSION

. The licensee has restored the safety margins of the Brunswick vacuum breakers by replacing critical parts with adequate materials. The corrective action is acceptable. The staff therefore recommends that this issue be closed.

Principal Contributor: H. Shaw Dated: January 16, 1987 i

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