ML20212L894
| ML20212L894 | |
| Person / Time | |
|---|---|
| Site: | Pilgrim |
| Issue date: | 01/15/1987 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20212A711 | List: |
| References | |
| NUDOCS 8701290424 | |
| Download: ML20212L894 (2) | |
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%[1 UNITED STATES jM ' fl NUCLEAR REGULATORY COMMISSION g
WASHINGTON, D. C. 20555
, :,l SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATING TO MARK I CONTAINMENT PROGRAM - VACUUM BREAKER INTEGRITY BOSTON EDISON COMPANY - PILGRIM NUCLEAR POWER STATION DOCKET NO.:
50-293
1.0 INTRODUCTION
In addition to the evaluation of the suppression chamber, torus attached piping, pressure relieving lines, etc, under the newly defined loadings, 4
the Mark I containment 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 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 Pilgrim Nuclear Power Station (Pilgrimi for the NRC staff. Results of the review are reported in the attached document, TER-C5506-328, " Structural Evaluation of the Vacuum Breakers (Mark I Containment Programi, Pilgrim Nuclear Power 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 the FRC findings.
?.0 DISCUSSION l
In the Pilgrim Mark I Containment there are ten 18" internal type vacuum
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hreakers made by General Precision Engineering. One vacuum breaker is mounted on the vent line end caps at the intersection of each vent line and l
the ring header in the suppression chamber. Loadings on Mark I structures t
and vacuum breakers are based on the General Electric Company Report, NEDO-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 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 of time. This issue was reviewed and approved by NRC on December 24, 1984. Loadings were combined according to the Final Safety Analysis Report 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 P!C,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 ellowable stress limits. By. changing SA-516 Gr 70 (pallet and hinge arn) and SA-320 B8 (hinge shaft and hinge arm stud) to SA-705 Gr630 (pallet) and SA-564 Gr 630 (hinge arm, hing'e shaft and hince arm stud), both adequately heat treated (age hardened at 1,100 FI, the allowable stress limits changed from 35 and 30 ksi. to 70 ksi. Proper safety margins were thus restored.
3.0 CONCLUSION
The licensee has restored the safety margins of the Pilgrim vacuum breakers by replacing critical parts with adequate materials. The corrective action is acceptable and the staff therefore concludes that this issue is closed.
Principal Contributor:
P. Shaw Dated:
January 15, 1987 i
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