ML20062F027
| ML20062F027 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 11/13/1978 |
| From: | Gilleland J TENNESSEE VALLEY AUTHORITY |
| To: | James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| References | |
| NUDOCS 7812130372 | |
| Download: ML20062F027 (2) | |
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TENNESSEE VALLEY AUTHORITY
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830 Power Building
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NOV 131978 t
i Mr. James P. O'Reilly, Director Office of Inspection and Enforcement U.S. Nuclear Regulatory Commission Region II - Suite 3100 101 Marietta Street Atlanta, Georgia 30303
Dear Mr. O'Reilly:
OFFICE OF INSPECTION AND ENFORCEMENT BULLETIN 78 RII:JPO 50-259, -260, -296 - BROWNS FERRY NUCLEAR PLANT UNITS 1, 2, AND 3 By my letter of July 31, 1978, TVA responded to your June 14, 1978, letter which transmitted IE Bulletin 78-09.
Enclosed is an amended response to IE Bulletin 78-09 for Browns Ferry Nuclear Plant which includes a discussion of other bolted containment closures that would tend to unseat on positive internal pressure.
Very truly yours, 1 ~)iM \\.b l.(
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d4,J.E.Gilleland F
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Assistant Manager of Power Enclosure cc: Office of Inspection and Enforcement (Enclosure)
Division of Reactor Operations Inspection U.S. Nuclear Regulatory Commission Washington, DC 20555 a
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. AMENDED-RESPONSE TO NRC IE BULLETIN NO. 78-09 The technique of bolting down the drywell head at Browns Ferry Nuc1 car Plant is based on achieving the amount of bolt stretch recommended by the drywell head manufacturer.
The drywell head bolts are tightened by either air-operatq impact wrenches or hydraulic torque wrenches.
Ecfore installation of the drywell head, the tools are qualified on a test stand to show that their use in accordance with the procedural guidelines will produce the recommended amount of bolt stretch. The tool is checked on three bolts to verify repeatability of the process.
In addition, before the drywell head installation, the following steps are taken to ensure a good seal between the drywell head and the containment flange.
1.
The upper and lower flange seating surfaces are cleaned with acetone and checked free of any foreign material.
2.
The 0-rings are inspected and replaced if any damaged areas exist. Continuous 0-rings are normally used. Ilowever, when field splicing is required. 0-rings are cut on a 45 angle.for splicing the ring.
3.
The drywell head bolts and nuts are thoroughly cicaned with acetone and a non-metallic brush to prevent thread' galling.
4 All belts are snugged up giving metal-to-metal contact prior to starting the tightening sequence.
5.
A local Icak rate test is run after tightening the drywell head.
Any additional tightening that is required to pass the test is done in incremental amounts and is documented for further evaluation.
The Browns Ferry unit 2 drywell head was installed using the above-described procedure and was followed by a successful local-leak rate test and integrated leak rate test.
In addition to the drywell head, the control rod drive access hatch, the drywell head manway hatch, and the two torus access hatches are bolted containment closures that would tend to unseat on positive internal pressure.
Each of the closures has two 0-ring seating surfaces forming a seal. When one of these closures is opened, the same steps described above for surface cicaning, gasket inspection and replacem*nt, and bolt and nut cleaning are e
followed betore closing the closure.
Airo, a local AcaK rate test is run at the calculated peak accident pressure after tightening the closure. In addition, these clus,ures are checked for leakage during each integrated leak rate test. To date, no leakage has been found at these closures during an integrated leak rate test.
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