ML20214T492

Safety Evaluation Accepting Licensee 830511 & 860117 Responses to Generic Ltr 83-08 Re Mod of Vaccum Breakers on Mark I Containments

ML20214T492
Person / Time
Site:	Vermont Yankee
Issue date:	11/24/1986
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20214H099	List: ML20214H094 ML20214T463 ML20214T492
References
GL-83-08, GL-83-8, NUDOCS 8612080607
Download: ML20214T492 (2)

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\...../ SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATING TO MARK I CONTAIN'4ENT PROGRAM - VACUUM BREAKER INTEGRITY j VERMONT YANK 5E NUCLEAR POWER CORPORATION l VERMONT YANKEE NUCLEAR STATION DOCKET NO.: 50-271 i

1 1 l I. INTRODUCTION l In addition to the evaluation of the suppression chamber, torus attached i

piping, pressure relieving lines, etc, under the newly defined loadings, the l Mark I containment program required the assurance of the structural integrity i of vacuum breakers during operation in all Mark I plants. This additional

. requirement was categorized as a separate effort, as the adequacy of other '

j components was already discussed in a separate Safety Evaluation.

4 The Franklin Research Center (FRC) has performed an evaluation of the struc-

tural integrity of vacuum breakers in the Vermont Yankee Nuclear Station l (Vermont Yankee) for the NRC staff. Results of the review are reported in the

! attached document, TER-C5506-320, " Structural Evaluation of the Vacuum Breakers (Mark I Containment Program), Vermont Yankee Nuclear Power Corporation, Vermont Yankee Nuclear Station." FRC has concluded that Vacuum breakers in Vermont ,

j Yankee will provide adequate margins of safety under the revised loadings in the Mark I Containment for all operating conditions, and therefore need not be l modified. NRC' staff reviewed the attached document and concurred with the FRC findings.

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j l II. DISCUSSION l In the Vemont Yankee Mark I Containment, there are two 18" external type vacuum

, breakers made by Atwood - Morrill mounted on two 18" external lines connecting j the drywell and the wetwell. Loadings on Mark I structures and vacuum breakers i are based on the General Electric Company Report, NEDO-21888, " Mark I Contain-j ment Program Load Definition Report," Revision 2, dated November, 1981. For vacuum breakers, the loadings included are gravity, seismic, and hydrodynamic j loads. The hydrodynamic forcing functions were developed by Continuum Dynamics, j Inc. by using a dynamic model of a Mark I pressure suppression system and the i full scale test facility data. The system model was capable of predicting j pressure transients at specific locations in the vent system. Loading across

the vacuum breaker disc caused by pressure differentials based on test data was j thus quantified as a function of time. This issue was reviewed and approved j by NRC on December 24, 1984. Loadings were combined according to the FSAR j commitments.

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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 hydrodynamic chugging force in Vermont Yankee will not signi-ficantly increase the impact velocity en vacuum breakers to cause any additional loading. Since the original design margin does not need improvement, the licensee decided that no modifications are needed on the construction of its vacuum breakers. The licensee, however, did replace the original aluminum cast discs with aluminum plate material for better ductility. This is desir-able and acceptable.

• III. CONCLUSION The licensee has found that safety margins of the Vermont Yankee vacuum breakers vere not effected by the hydrodynamic chugging force. The' methodology of the

- analysis and the conclusions are acceptable.

Principal Contributor: H. Shaw Dated: November 24, 1986

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