ELV-01949, Forwards Info Re Status of Pen Branch Fault Investigation. Investigations Conducted So Far Still Indicate That Pen Branch Fault Not Capable

Forwards Info Re Status of Pen Branch Fault Investigation. Investigations Conducted So Far Still Indicate That Pen Branch Fault Not Capable

ML20055H878
Person / Time
Site:	Vogtle
Issue date:	07/26/1990
From:	Hairston W GEORGIA POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
ELV-01949, ELV-1949, NUDOCS 9007310080
Download: ML20055H878 (3)

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- Georo4a Power Ccmpany -

.D 333 Picenont Aenuo-Aflanta. Georg<a 30308 4- Telephone 404 52G3195 Ma4tg Ad&ess 40 lnverness Center Pa*way Fwt Office Don 1295

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Dirmingham. Aletsama 35201 Teicphone 205 668 5581 July 26, 1990 trie mrun garrc smem W. G. He6rstan, HI Senor Vu President naciear operatons ELV-01949 0510 4

Docket Nos. 50-424 50-425-l U. S. Nuclear Regulatory Commission l ATTN:' Document Control Desk Washington, D. C. 20555 Gentlemen: i V0 GILE ELECTRIC GENERATING PLANT PEN BRANCH FAULT INVESTIGATION STATUS In a-letter dated January 30, 1989 Georgia Power Company committed to meet ,

periodically with the Department of Energy at the Savannah River Site and keep I the NRC informed of any new information when it becomes available on this subject. The investigations conducted ~so far still-indicate that the Pen Branch Fault is not capable. The attached provides a status report of-the Savannah River Laboratory investigation of this fault.

Should you have any questions please inquire.

Sincerely, g.). /bW W. G. Hairston, III-WGH,III/ JAB /gm Attachment xc-w/ attachment:

Georaia Power Comoany Mr. C. K. McCoy Mr. G. Bockhold, Jr.

Mr. R. M. Odom Mr. P. D. Rushton NORMS U. S. Nuclear Reaulatory Commission Mr. S. D.-Ebneter, Regional Administrator '

, Mr. T. A. Reed, Licensing Project Manager, NRR Mr. B. R. Bonser, Senior Resident inspector, Vogtle 0

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ATTACHMENT e L PEN BRANCH FAULT STATUS OF SAVANNAH RIVER SITE-INVESTIGATIONS The Pen Branch Fault (PBF) was described in a draft technical paper authored-by '

David Snipes, Wallace Fallaw, and Van Price, Jr.:(DP-MS-88-219). As a result of the discovery of this fault, the Department of Energy (DOE) Savannah River Site-  :

and the Westinghouse Savannah River Company, Savannah River Laboratory instituted an investigative program to explore the nature of the fault. 3 reprocessing the Conoco seismic Tne planned reflection investigative surveys, program

2) drilling of PBF consists deep core of 1) holes bracketing the proposed ,

fault. trace, 3) conducting shallow high resolution seismic reflection survey!.

across the proposed fault trace, and 4) excavating trenches across the proposed-fault trace. The following is a status of-the. investigative program:. .

1. Conoco Seismic Reflection Surveys The Conoco surveys consist of.approximately 135 miles of 'vibroseis reflection surveys which were performed during the-period of October -

198) to May-1988. A final report was issued:by Conoco to. Savannah River' Laboratory during January 1989 (Research Report 1809-005-006-1-89). A contract has been awarded to Virginia Polytechnical--Institute to reprocess the Conoco seismic data. This contract began in May, 1990, and is scheduled to be completed by October,- 1991. The reprocessing is

)lanned in two phases;. shallow reprocessing of the data-from the a aasement to grnund surface and very deep reprocessing from the basement to the Moho Discontinuity. The-shallow data will have priority and the 4 lines will most likely be processed in numerical order, i

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2. PBF Series Deep Core Hole Drillina The PBF series of drill holes were completed' in. pairs bracketing the l proposed fault trace as indicated by the Conoco data-(attached figure).

l -. The wells were constructed in pairs in order to assess the change:in l elevation of key stratigraphic marker horizons across.the fault. The l core holes were completed during the fall of 1989 and analysis of the 1 core was conducted during the fall and winter-of 1989.-  !

Analyses of the core hole irformation and Conoco results indicate that  !

the PBF trends' northeast aci iss the. site and closely parallels the Triassic Dunbarton basin noi chern boundary fault. Faulting during Cretaceous into Eocene time resulted in the formation of the :PBF in the Coastal Plain sediments covering the basement rock. In other words,1the:

PBF is most likely a reactivation of the Dunbarton basin border fault that moved during Cretaceous into Eocene time.

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t y ATTACHMENT (CONTINUED)

PEN BRANCH FAULT l' STATUS OF SAVANNAH RIVER SITE INVESTIGATIONS -

The. fault dip is close to vertical and in the crystalline basement slip direction was criginally down to the southeast. Movement during.

Cretaceous into Eocene appears to reverse, that is, up to the southeast.

-The fault appears to be similar to other: faults mapped in the Atlantic Coastal Plain region from Georgia to Virginia as late Mesozoic to Tertiary faults.- ,

Data.obtained from the PBF series and other core holes constrains. fault offset to the Dry Branch-formation, the youngest,~ shallowest strata that' -i is broken by the fault. The formation is considered-to be lower upper-Eocene, about 36 to 40 million years old. Two of'the PBF wells will be.

extended in depth into the crystalline basement in order to penetrate.

deeper portions of the fault. This may provide evidence of separate periods of activation on the ' original basin border fault. Preliminary "

i and ongoing investigations indicate that the fault is not capable,.but-further. study is planned.

3. Shallow Hioh Resolution Seismic Reflection

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Shallow high resolution seismic reflection surveys (18 line-km) are-planned to be conducted during'the last half of this year. .The surveys are planned to determine the-proximity of the fault to.the surface in-the upper 200 feet of Coastal Plain sediments and the geometry. of-the fault. The surveys presently are planned to be conducted in three general areas of the fault traco: 1) southwest end near PBF 6 drill .

hole, 2) northeast end north of Par pond, and 3) near4 the center of'the .

plant area. J

4. Excavated Trenches a

One or.more trenches excavated to an approximate depth of 25 to 35 feet 'l are planned across the trace of the. postulated fault. .The number and-  !

location of the trenches have not been set but will be determined based upon the results of the shallow high resolution seismic reflection ,

surveys. At present, the trenches are planned for excavationLduring the l

.first half of fiscal year 1991.

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