ML19329A390
| ML19329A390 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 01/30/1978 |
| From: | Stepp J Office of Nuclear Reactor Regulation |
| To: | Schwencer A Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML19329A386 | List: |
| References | |
| NUDOCS 8001030963 | |
| Download: ML19329A390 (5) | |
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11EEOR.V3CM 702: Albert Sch*.:encer, Chief, Operating Reactors tranch 61, 003 FROM:
'J. Carl-Stepp, Chief, Ccoscience: Eranch,'DSE SULJECT:
SZIS !ICITY XE.iR OCOMEE NUCLE *.R GESEMTING STATION UNITS 1, 2 5 3 Enclosed is our recor. ended actions with respect to the ongoing er.irth-c.unke szarr. naar tha Ceonee Nuclear Str. tion.
These reco=nendations ucre prepared by Drs'. Jackson and J. Eclicher of ny staff af ter con-versations with your staff and the 1.icensec. The data upon which these recontendariens ara based are very limited. Thus our reco==en-
-dations reflect an approprinta level of caution.
To date the activity has the characteristics of an carthquake swarm.
Typically earthquaka svar:is have many events of near equal magnitude.
- The' largest earthqcake in this swarn to dace hr.s been magnitude 2.2.
,0ur experience ::ich earthcuake swar= activity indicates that the largest event uhich should be expected :-in exceed by no more than about one-nagnitud2 enit the magnitude c.
the frequent activity.
Since tne Iraquent activity in this suarm to date is about magnitude 2.0, va can state conservn:ivaly that a ocnimum event larger than about 3.5_ should not be e:pected unless there is an upwcrd chif t in the na3-nitude of-the-frequent events.
Therefore, tha activity to date does not'indicata an i=aediate safety concern for the Oconee units, but continued monitoring and daily reporting is needed.
. We anticipate that : the investigations va have reco ended will enable us to. evaluate the tectonic cause of these earthquakes and the hacard that is implied.
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l Carl' Re~pp,. '1 O l J,
- . Chief Geoscience's Branch
./ Division'of Site Safety and Environmental.\\nalysis
Enclosure:
As stated-.
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'l!. Denton D. Muller K. Coller
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t.'.: E ii k'e consider the recent microcar thquake activity in the vicinit.y oC Str.mp Crack Church, South Carolina to be a r.:atter of. concern because 'of the pro:-:i:.iity of Oco:iee necir:ar pEant. The Setivity, at
. present, exhibita' the character of an carthqunha swarm in that many
.ceents occurred :hich verc of about equal magnitude (nect 2) without the occurre:.ce of a single dominant carthquaka. Should the activity persisc without signific-..c increase in earth lunke magnitude, this 1
- activity uill not pose a safety hazard to the Oconee units.
However, even the f similar cicroearthquake sequences have occurred 'cisewhere without accompaniment by larger shocks, it is our judgment that this activity be tr= eed with caution until the tectonic
. causes and implications are understood.. Duke Power should aggres ively s
' develop the infornation required to assess the nature of this micro-earthquake activity and its relationship to tectonic structure.
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We reco::t:iend that a program include as a minimum the following objectives:
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_A network of microearthquake instruments should be maintained in the area to determine hypocentral locations and when feasible,,
magnitudes and composite focal plane solutions. This network should be continued in operation for at least some weeks af ter the apparent cessation of activity.
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A ca, lor ;;oal is to-reveal any potential relationships between the microcarthquake -activity and significant geologic structures.
For this purposa there must be developed both an adcquate base of regional geologic data and.a hypocen;ral catalog of reasonable i
quality.
c). ' Apart frc= 3eolo31c conditions the hypocentral catalog itself r
- should be enardnad for indications of internal consistency.
That is, ge::e:rically planar groups of hypocenters or coherent focal plane sa'_utions may provide evidence of a larger fault.
i S.ich tectonic stress may have accumulated.
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- Tne spati:1 c: tent of hypocenters should be carefully monitored.
Duke Po.ter C pany should carefully look for indications of
'significant increase in this spatial entent.
L'e -regard the above as a minimum program to be followed by Duke The ERC should be informed daily by telephone of the Power Company.
number of microaarthquakes, the maximum magnitudc. and any significant changes in hypocentral locations. In addition Duke Power Company l
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should provide as soon as reasonably possible a written report detailing:
-(1) whatever evidence exists for' the presence or absence of geologic structures that may be associated with the microcarthquake activity, (2) a' discussion of the trends, dip and extent of any structures with which the earthquakes can be associated, and (3) a discussion and i
presentation' of' any data defining the tectonic structure at the site.
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We also recorr.ead that the Division of Innpectici nad Enforce =cnt be infort::ed of this activity and that they certify the strong rot ton instru: tents at the plant site are functionine,.
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Lvta.ePecov *eow 273.a,*2 Mr. E. G. Case, Acting Director j 'g.' i [.~ [
g Of fice of ?:uclear l'.cactor Regulation U. S. Nuclear Re;;ulatory Commission l'OR INFOri :' ATION Washington, D. C.
20555 AND,/OR REyl' yi ONL'r i
RE: Oconee nuclear Station Docket So. 50-269, -270, -287
Dear Mr. Case:
In r.ecent weeks there has been a general increase of seismic activity.
in the Jocassee/K m ee area, centered near Stamp Creek Church, three miles northwest of 0:onee Nuclear Station. The number of micro earth-quake events and the maxi:r.um local magnitude have been reported to you. daily by telephone since their initial detection on December 29,
.1977.
Dul
)wer Company is currently assessing the nature of this recent activity.
Seismic monitoring of this area will continuu in order'to support this analysis.
An attempt will be made to relate the activity to known geologic structures. Additionally, the tectonic structure 1
.in this area will be examined.
It is anticipated that a written report will be submittedin llarch 1978, which will include an analysis of these evsnts.
Very truly yours, bec:
llCT, ESC, DCll, LJ B, 1*RU, LCD, 5011, RSS William'O. Parker, Jr.
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