ML19329A277
| ML19329A277 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 01/12/1978 |
| From: | Stepp J Office of Nuclear Reactor Regulation |
| To: | Schwencer A Office of Nuclear Reactor Regulation |
| References | |
| FOIA-79-86 NUDOCS 8001020850 | |
| Download: ML19329A277 (4) | |
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BM JAN 12 i
Albert Schwencer, Chief, Operating Reactors Branch fl DOR MEMDRANDUM POR:
J. Carl St.epp, Chief Geosciences Branch, DSE FROM:
SEISMICITY NEAR OCONEE NUCLEAR GENERATING STATION
SUBJECT:
UNITS 1, 2 & 3
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Enclosed is our recomunended acchns with respect to the ongoins earth-These recommendations j
quake swara near the Oconee Nuclear Station.
I were prepared by Drs. Jackson and J. Kelleher of my staff af ter con-4 versations with your staff and the Licensee. The data upon which dations are based are very limited. Thus our recom:nen-these ree j
dations reflect an appropriate icvel of caution.
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To date the activityshas the characteristics of ^an earthquake swarm.
I Typically earthquake swarms have many events of near equal magnitude.
The largest earthquake in this swarm to date has been magnitude 2.2.
Our experience with earthquake swarm activity indicates that the largest event which should be expected vill exceed by no more than about one magnitude unit the magnitude.! the frequent activity.
j Since the frequent activity in this swarm to date is about magnitude 2.0, we can state conservatively that a maximum event larger than about l
3.5 should not be expected unless there is an upward s.hif t in the mag-Therefore, the activity to date does nitude of the frequent events.
not indicate an innediate safety concern for the Oconeo units, but continued monitoring and daily reporting is needed.
We anticipate that the investigations we have recornnended will enable l
us to evaluate the tectonic cause of these earthquakes and the hazard i
that is implied.
DIS UTION:
[Driginal Signed by J. C. Stepp KET FILE (50-287)
J. Carl Stepp, Chief
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OCONEE NUCLEAR CEi4ERATING STATION UNITS 1-3 RECOM1 ENDED ACTIONS WITil RESPECT TO AN EARTilQUAKE SUARM NEAR STAMP CREEK CilURCll We consider the recent microenrthquake activity in the vicinity of Stamp Creek Church, South Carolina to be a matter of concern L cause of the proximity of Oconce nuclear plant. The activity, at present, exhibits the character of an earthquake swarm in that many events occurred which were of about equal magni' 'de (near 2) without the occurrence of a single dominant carthquake.
Should the activity persist without significant increase in earthquake magnitude, this i
activity will not pose a safety hazard to the Oconce units.
However, even though similar microcarthquake sequences have occurred elsewhere without accompaniment by larger shocks, it is our judgment that this activity be treated with caution until the tectonic causes and implications are understood. Duke Power should aggressively develop the information required to assess the nature of this micro-carthquake activity and its relationship to tectonic structure.
We reconmend that a p ogram include as a minimum the following objectives:
a)
A network of microcarthquake instruments should be maintcinec 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 majof goal is to reveal any potential relationships between the microcarthquake activity and significant geologic structures For this purpose there must be developed both an adequate base of regional geologic' data and a hypocentral catalog of reasonable quality.
c)
Apart from geologic conditions the hypocentral catalsg itself should be examined for indications of internal consistency.
That is, geometrically planar groups of hypocenters or coherent
-4 focal plane solutions may provide evidence of a larger fault surface over which tectonic stress may have accumulated.
d)
The spatial extent of hypocenters should be carefully monitored.
Duke Power Company should carefully look for indications of significant increase in this spatial extent.
We regard the above as a minimum program to be followed by Duke Power Company.
The NRC should be informed daily by telephone of the number of microcarthquakes, the maximum magnitude and any significant changes in hypocentral locations.
In addition Duke Power Company 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, 4
(2) a discussion of the trends, dip and extent of any structures with which the_ earthquakes can be associated, and (3) a discussion and presentation of any data defining the tectonic structuce at the site.
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. We also recommend that the Division of Inspection and Enforcement be informed of this activity and that they certify the strong motion instruments at the plant site are functioning.
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