ML20137D583

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Responds to L Reiter 770926 Request for Addl Info Re Rept Entitled Seismic Monitoring Program at North Anna Site in Central Virginia - 740121-770801. Regional Epicenter Map Encl
ML20137D583
Person / Time
Site: North Anna, 05000000
Issue date: 10/25/1977
From: Brown S
VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To: Case E, Stolz J
Office of Nuclear Reactor Regulation
Shared Package
ML20136A555 List: ... further results
References
FOIA-85-363 NUDOCS 8508220518
Download: ML20137D583 (2)


Text

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ATI70 BENT 2 __

October 25, 1977

  • I Mr. Edson G. Caso, Acting Director Scrlal No. 463 Office of Nuclear Reactor Regulation PSECC/l!UBJ r:bcb Attention: Mr. J. F. Stolz, Chief Dockot Hos: 50-330 Light 11ater Reactors Dranch llo.1 50-339 Division of Project Manageront 50-404 U. S. huclear Regulatory Commission 50-405 Washington, D. C. 20555 . ,

Dear Mr. Case:

This letter is in rcsponse to a telephonc request by Dr. Reiter on Septenber 26, 1977 for additional Information pertaining to a report titled "A SEISMIC P.0:ilTORING FROGRAM AT THE t10RTil Alit:A SITE 111 CENTRAL VIRGilll A - JAilVARY 21,.1974 Tt! ROUGH AUGUST 1,1977," which was forwarded

, to you on September 13, 1977 !,y our letter Scrial No. 393. Dr. Rei ter requested two items of additional Inforo.ation:

1. Hypocentor location error.. estimates, and ,
2. A composite figure showing all events recorded on a map which also showed the geology.

As explained to Dr. Reiter, hypocenter error estimates are pro-vided in chapters 11 and til of the report in Tables 1-11, 2-11, 3-11, 5-11, 6-11, 1, 2, 3, 5, 6, and 7 under the colunns noted "tRH/ERZ." These values of standard error are calculated by the "IlYPD-71" computer program.

Forty (40) copics of a floure titled " REGIONAL EPICEtiTER MAP, PERIOD: JANUARY 21,1974, T;ll'.0VCil AUGUST 1,1977" arc enclosed for your uso. This figure shows the geology and all locatable events recorded within tac prescribed five second S-P Intcryal (-451,m of station no.1) .

!!ont toring of events outsido the 45 len radius has never been a notwork requirencnt. Some locatable events in the 45 to 100 kn rango fron stration number 1 were recorded by our network as well as others. Theso events are shown only to give a comparison of regional activity.

8500220518 FOIA 850722 PDR PDR BELL 85-363

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. Mr. Edson G. Casa 2 i

f As shown on Figure 5 In Chapter 111 of the above referenced ,

report, the outermost network stations are approximately ten (10) miles frora the power station. Locatability of events diminishes beyond these stations. This is rest notable in lower 1cvel activity (it<1.0). Thus

- you will notice the lack of lesser nagnitude events with Increased illstance from the site. This should neither be construed as a lack of f

activity beyond the network boundary, nor a confineraent of activlty with-in the network. The location of these very low icyc1 events where possible has been shown voluntarily by Vepco, and has not been a requirenont of the-NRC.

If we can be of any further assistance In your review of this Infonution, please contact us.

Very truly yours, cc.ui S,:-s v,!

S, C. EROWN JK.

Sam C. Brown, Jr.

Vice President

[ . Power S tation Engineering and Construction e

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