ML17199F980
| ML17199F980 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 12/19/1986 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML17199F979 | List: |
| References | |
| NUDOCS 8701150011 | |
| Download: ML17199F980 (2) | |
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e ENCLOSURE l UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION
. RELATING TO MARK I CONTAINMENT PROGRAM - VACUUM BREAKER INTEGRITY COMMONWEALTH EDISON COMPANY I.
INTRODUCTION DRESl)EN NIJCLEJl.R POWER STATION UNITS 2 AND 3 DOCKET NOS.: 50-237 AND 249 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 the assurance of the structural inte9..rity 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 struc-tural integrity of vacuum breakers in the Dresden Station Units 2 and 3 (nresden 2 and 3) for the NRC staff. Results of the review are reported in the
- attached document, TER-C5506-324, "Structural Evaluation of the Vacuum Breakers (Mark I Containment Program), Commonwealth Edison Company, Dresden Station Units 2 and 3."
FRC has concluded that vacuum.breakers in Dresden 2 and 3 will provide adequate margins of safety under the revised loadings in the Mark I containment for all operating conditions, and therefore need not be modified.
- NRC staff reviewed the attached document and concurred with the FRC findings.
II.
DISCUSSION In each of the Dresden 2 and 3 Mark I Containments, there are twelve 18 11 external type vacuum breakers made by Atwood - Morrill mounted on six exterior headers connecting the suppression chamber and the vent line exterior of the wetwell.
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 9ravity, seismic, and hydrodynamic loads. The 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 specific 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 OT time. This issue was reviewed and approved by NRC on December ?4, 1984.
Loadings were comhined according to the FSAR commitments.
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- ~. To determine the structural inteqrity of the vacuum hreakers, results from a finite element model and ANSYS program analyses were compared with desiqn limits specified in the ASME Boiler and Pressure Vessel Code,Section III, Diyision 1, Subsection NC, 1977 Edition and addenda up to Summer 1977. It was.
found that the hydrodynamic chugging force in nresden 2 and 3 will not signifi-cantly increase the impact velocity on vacuum breakers to cause any ~dditional loadin9.
Since the original desiqn margin does not n~ed improvement, the licensee rlecided that no modifications w~re needed ~n the construction of its vacuum breakers.
ThP licensee, however, did replace the original aluMinum cast discs with aluminum plate material for better ductility.
ITT.
CONCLUSION The ~nalytical method used by the licensee to evaluate critical stre~ses has*
been reviewed and found to be adequate.
The structural analysis indicates.
that t~e existing vacuum breaker desiqn is acceptable and no additional modifications are required.
Principal contributor:
H. Shaw Dated:
December 19, 1986.