ML20207R854

Safety Evaluation Re Facility Mark I Containment Vacuum Breaker Structural Integrity.Licensee Restored Safety Margins of Breakers by Replacing Critical Parts W/Adequate Matl.Corrective Action Acceptable

ML20207R854
Person / Time
Site:	Fermi
Issue date:	03/12/1987
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20207R850	List: ML20207R854
References
NUDOCS 8703180210
Download: ML20207R854 (2)

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UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 n\...../a SAFETY EVALUATION BY THE OFFICE OF NHCLEAR REACTOR REGULATION RELATING TO MARK I CONTAINMENT pROGPAM - VACUUM BREAKER INTEGRITY DETROIT FplSON COMPANY (Deco)

FERMI-2 DOCKET P!0. 50-341 I. INTRODUCTION in addition to the evaluation of the suppression chanter, torus attended piping, pressure relieving lines, etc, under the newly defined loadinas, the Mark I containnent program required the 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 ade-quacy of other components was already discussed in a separate Safety Eval-uation.

Py letter dated August 18, 1982, the Detroit Edison Company submitted an evaluation of the drywell-to-wetwell vacuum breakers for Fermi-2. The evaluatter supplied information for the Fenni 2 vacuum breakers and their ability to withstand chugging and condersation oscillation loads. This document was reviewed, and the results of the staff's findings and deter-minations are summarized below.

II. DISCUSSION AND FVALUATION In the Femi-2 Mark I containment design, there are twelve IP-inch inter-nal type vacuum breakers manufactured by General Precision Engineering.

Two vacuum breakers each are located at six of the eight intersections of the ring header and vent lines in the suporession chamber. Loadiras on Mark I structures and the vacuum breakers are based on the General Electric Company Report, NE00-21888, " Mark I Containment Program Load Definition Report," Revision 7, dated November 1981. For the vacuum breakers, the loadings included are gravity, seismic, and hydrodynamic loads. The hydro-dynamic forcing functions were developed by Continuum Dynamics, Inc. by using dynamic medes of a Mark I pressure suppression system and the full scale test facility data. The system model was capable of predicting pres-sure transients at specific locations in the vent system. Loading across a the vacuum breaker disc caused by pressure differentials based on test data r$$ was thus quantified as a function of time. This issue was reviewed and ap-58S proved by NRC on December 24, 1984 Loadings were combined according to the oo FSAR commitments. The new loading combinations increased the maximum design So impact velocity for the vacuum breakers from 4.0 rad /sec to 7.6 rad /sec.

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-u To determine the structural integrity of the vacuum breakers, results

$0 from a finite element model analyses using the ANSYS program were com-m, < pared with the design limits specified in the ASME Roiler and Pressure r1 Vessel Code,Section III, Division 1. Subsection NC, 1977 Edition, and NE addenda up to Sumer 1977. It was found that the pallet, the hinge arm.

"'t the hinge shaft, and the hinge arm stud could become overstressed. The licensee decided to remedy the situation by using material with a higher

7. .. . a allowable stress limit for these components. By replacing SA-516 GR 70 material with SA-564 GR 630 material, the allowable stress limit was changed from 17.5 ksi to 32.8 ksi and the alloweble impact velocity was changed from 5.2 rad /see to 9.3 rad /sec. Proper safety margins were thus restored.

III. CONCLtlSION The licensee has restored the safety margins of the Fermi-2 vacuum break-ers by replacine critical parts with adequate material. The corrective action is acceptable.

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