ML19225B857
| ML19225B857 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 06/08/1979 |
| From: | Counsil W NORTHEAST UTILITIES |
| To: | Grier B NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| References | |
| NUDOCS 7907260183 | |
| Download: ML19225B857 (2) | |
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June 8, 1979 Docket No. 50-245 Mr. Bcyce H. Grier Director, Region I Office of Inspection and Enforcement U. S. Nuclear Regulatory Commission King of Prussia, PA 19406
Reference:
(1) Boyce Grier letter to W. G. Counsil dated March 8,1979, forwarding I&E Bulletin 79-02.
(2)
Reportable Occurrences - R0-78-7/8L, R0-78-8/1T.
Gentlemen:
Millstone Nuclear Power Station, Unit No. 1 Pipe Succort Base Plate Desion: 'Jsino Concrete Exoansion Anchor Bolts In Reference (1), Northeast Nuclear Energy Company (NNECO) was requested to verify and aescribe, through existing documentation, various design require-ments involving pipe support base plates that use concrete expansion anchor bolts in Seismic Category I systems.
This lettar is not intended to provide our final response to Reference (1),
ra+her, it serves to provide information relative to *!NEC0's current st tus, plans and schedules.
NNECO started a testing program on May 1,1979, to verify that the design requirements had been met for the field installation of pipe support base plate 3 and the associated concrete expansion anchor bolts.
The majority of the concrete expansion bolts on Seismic Category I piping systens are the self drilling shell type ancho, s.
Due to several problems associated with trying to verify that the shell was not in contact with the support plate, it became quite obvious that testing the existing anchors to obtain reliable test results would be very time consuming and in some cases almost impossible to accomplish.
Therefore, it was decided t;o repla e all load carrying shell type anchors with wedge type anchors during this refueling outage on the safety related portion of the safe shutdown systems and on those on other Seismic Category I systems that are normally inaccessible during power operation.
This replacement approach was undertaken because it was deemed to be more expedient than a testing program.
The minimin safe shutdown systems are the isolation condenser, shutdown cooling, condensate storage and transfer system, service water, reactor building closed cooling water system, emergency diese.1 generator, control rod drive systen, and emergency gas turbine generator systen.
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. The new type anchor bolts are designed for a minimum safety factor of four (4), as required by Reference (1), item 2.
Bolt load analy;.s was performed to account for the effects of shear tension interaction, minimum edge distance, and proper bolt spacing.
The base plate flexibility was also accounted for in the calculation of the anchor bolts loads.
In a majority of cases, thicker base plates were used to assure rigid plated design.
The design bolt loads were calculated by Bechtel Power Corporation using standard type calculational methods and/or empirical formulas based on their finite element analysis results. Additionally, Nor.heast Utilities will verify and check the design bolt loads using the finite element model developed by Teledyne Engineering Services (TES).
This model was developed as part of the generic program in response to Reference (1).
The generic program by TES is being sponsored by a utilities owners group of which Northeast Utilities is a member. This generic program was presented to the NRC on April 26, 1979, and was well received by the staff.
Cyclic load design requirements (Reference (1), items 3 and 4a) were also discussed.
As part of the generic program, cyclic load tests will be conducted to define preload requirements.
Supplemental to the cyclic load tests, the generic program will include test verificatica of the finite element model and shear / tension interaction tests.
The scheduled completion of the generic testing program is projected for July 15, 1979.
As stated previously, the replacement of the load carrying self drilling anchor bolts and the necessary base plates on the specified minimum safe shutdown systems will be completed prior to returning the unit to coeration.
In addition, all shell type bolts located in areas which are normally inaccessible during operation on the main steam system, the core spray system, the low pressure coolant injection (LPCI) system and the feedwater system will alsr be replaced prior to startup from refueling.
The remaining anchor bolts on these four systems will be replaced as expeditiously as possible within the constraints of technical specifications, manpower and material requirements.
During the 1978 refueling outage, a number of anchor bolts and support plates were replaced as indicated in Reference (2).
No design changes to these previously improved areas are anticipated.
- However, they are included within the scope of our efforts on Reference (1) for the purposes of inspection and testing.
The remaining Seismic Category I pipino systems will be evaluated for anchor bolt loads and base plate flexibility and any necessary modifications and/or changes a these systems will be pursued. The final report, to be submitted in July 1979, in addition to being responsive to the numerated items in Reference (1), will provide the completed status of all Category I Seismic systems.
Very truly yours, NORTHEAST NUCLEAR ENERGY COMPANY
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WMt W
G. Counsil Vice President 398 330