ML20206H778

SER Accepting Rev 4 to Core Stratification Sample Acquisition Program,Dtd 860611

ML20206H778
Person / Time
Site:	Three Mile Island
Issue date:	06/19/1986
From:	NRC
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ML20206H776	List: ML20206H770 ML20206H778
References
NUDOCS 8606260294
Download: ML20206H778 (4)

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CORE STRATIFICATION SAMPLE ACQUISITION SAFETY EVALUATION REPORT 1

INTRODUCTION The Core Stratification Sample Acquisition Safety Evaluation Reports (SER) revision 1, (reference 1) and revision 3 (reference 2) have been reviewed and approved by the NRC staff (references 3 and 4). GPUN submitted revision 4 (reference 5) on June 11, 1986. This revision clarifies the drilling limits and flush water sources, allows the option to use other water cleanup systems other than the Defueling Water Cleanup System, and addresses the option of leaving casing in a bore hole.

EVALUATION i The changes addressed by this revision are evaluated as follows:

1. The drilling depth has been clarified to indicate that core bore will be limited to the top of the flow distributor unless TV camera viewing of the lower head region immediately below the drill bit shows a clear path.

This clarification provides better assurance that the load produced by drilling operations 'till not be imparted to incore nozzle penetrations.

) 2. Sources of borated water to be used for drill bit cooling, casing and drill string rinse, and camera purge have been clari.fied. The clarification indicates that bit cooling and flush will be normally from the Internals Indexing Fixture region of the reactor vessel; camera purge water will be from two 55-gallon supply tanks; and casing and drill string rinse will be from the Borated Water Storage Tank. In all these cases, the water source is required by procedure to have sufficient boration; i.e., greater than 4950 ppm boron to prevent dilution of the boron concentration being maintained in the reactor vessel. This clarification better identified water sources to be used.

3. In order to provide increased flexibility, other methods of reactor water cleanup are proposed for use if the Defueling Water Cleanup System (DWCS) is not operational. These other systems include the Submerged Demineralizer System and the Temporary Reactor Vessel Filtration System.

While DWCS is preferable in terms of effectiveness in monitoring water clarity, the other systems are con:;idered to be able to maintain

sufficient water clarity should their use be required.

These clarifications do not depart from or alter the staff conclusions in references 3 and 4.

4. In order to provide for long term camera access to the lower core region after a successful core bore, the option to leave a portion of the casing extending approximately one foot above the surface of the fuel debris was proposed. In this event, the casing will be cut so that rejoining to other sections of casing is not possible. Creation of a string of casing long enough to reach the vessel wall is effectively prevented. In this

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case the staff finds that an equivalent level of protection of reactor vessel integrity to that previously evaluated, is maintained.

Retrieval of the casing is possible and has been planned if this option is exercised. Sufficient tooling to extract the casing is available and has been demonstrated as effective.

CONCLUSIONS The staff has reviewed the changes to the Core Stratification Sampic Acquisition Program presented in revision 4. The majority of the changes do not affect the staffs previous conclusions. The staff has determined that the licensee's proposed methodology for leaving drill casing in the core has an adequate level of safety incorporated. We therefore conclude that Core Stratification Sample Acquisition activities (revision 4) can be implemented without significant risk to the health and safety of the public.

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References

1. GPUN let.ter with attached SER from F. R. Standerfer, 4410-85-L-0147, to B. J. Snyder dated August 30, 1985.

2., GPUN letter with attached SER from F. R. Standerfer, 4410-85-L-0248, to W. D. Travers dated December 31, 1985.

3. NRC letter with attached Safety Evaluation NRC/TMI 86-041, W. D. Travers to F. R. Standerfer dated May 5 1986.

4. NRC letter with attached Safety Evaluation _liRC/TMI 86-052, W. D. Travers to F. R. Standerfer dated May 28, 1986.

5. GPUN letter with attached SER from F. R. Standerfer, 4410-86-L-0101, to W. D. Travers dated June 11, 1986.

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