ML19329A268
| ML19329A268 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 05/02/1977 |
| From: | Stepp J Office of Nuclear Reactor Regulation |
| To: | Schwencer A Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8001020842 | |
| Download: ML19329A268 (7) | |
Text
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'l J CKET FILE (50-269/270/287)
MAY 0 2 1977 NRR RDG f
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MEMDRANDON FOR:
Albert Schwencer, Chief, Operating Isactors Branch #1
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FRON:
J. Carl Stepp, Chief, Geosciences Braneb. DSE 3
SUBJECT:
OCONEE/J0CASSEE DAM SEISMICITT
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4 i PLANT NAME: Oconee
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LICENSING STAGE: Operating Reactor i
DOCKET NUMBERS: 50-269/270/287 i
RESPONSIBLE BRANCE: OR-1; Don Neighbors, PM I
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Attached is'our recomumended action for resolution of the issue which
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has been raised by seismicity at the Jocassee Dem. Since my memorandum i
to you on this subject dated March 7, we have met with Duka Power j
Company and consultants and visited the Dam site. As a result of those discussions, we have formed the attached informational requirements.
t We believe that this information will permit us to make a complete i
evaluation of the (1) hasard to the das posed by earthquake activity in the region and (2) the stability of the dan under any potential j
aarthquaka loading.
i We recommend that action be taken to assura compliance with the recomunended actions. This request for information was prepared by
- l Drs. L. Heller, R. Jackson, J. Kelleher and D. Simpson.
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i Original Signed by J. C. StePp J l l;
J. Carl Stepp, Chief Geosciences Branch
}I Division of Site Safety and h;
Environmental Analysis i
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4 This meno refers to the recent meeting concerning induced seismicity I
at Jocassee Dam among Duke Power Company (DPC), the NRC staff and various We herein describe appropriate steps to evaluate the potential consultants.
seismic hazard. The program we recommend is threefold: A short-term report due July 1,1977, a monitoring program to be implemented by August 1, 1977, and a longer-term report that will describe the findings of the monitoring program.
SHORT TERM REPORT This report should address formally the questions raised during the recent meeting at Jo'cassee dam, a) Seismicity: All seismic observations gathered to date should be provided in an organized manner, including numbers of events r6 corded, hypocentral data, focal mechanisms where
- determined, epicenter maps and depth cross-sections, locations and changes in operating stations and descriptions of network capacity. Also included should be a log of water-level fluctua-tion.
The report on seismic studies prepared by Law Engineering provides adequate seismic information for the time interval mid-October 1975 'until late-June 1976. This report should.tua resubmitted as part of the total report.
For the interval from late June 1976 until the present, no seismic data have been presented to us other than informal oral descriptions.
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Censviuently, the nisaic infor ation fer this 1cttar interval should be presented in a formal written report treated in all the detail described in the first paragraph of this section.
N b)
Geologic Reconnaissance of the Site Area:
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The reports submitted to date do not appear 't'o be current arid should
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be modified to depict clearly the current understanding of the-location of faulting in the vicinity of Lake Jocassee and the Lake Jocassee Dam. The report of Dr. Conn.(Engineering Geology of the Keowee-Toxaway Project, of December 1966, and June ]974) discusses faulting in the vicinity of the dam;
- clarification of his findings should be provided.
-The relevant geologic maps of the site and region and an' assessment of the age of last movement on faults in the vicinity of the Lake Jocassee Dam should be provided. Typical construction photographs of the dam rock foundation and abutments should also be provided.
c)
In order to evaluate the seismic adequacy of the dam the following information should be provided:
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The embankment design and specification should be described,
along with the foundation treatments used; 2.
Seepage rates and changes in seepage rates should be described and plotted; 9
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Groundwater profiles (phreatic surface) through the
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abutments and foundation of the dam should be plotted; 4.
The ability of the foundation of the dam to resist the effects of potential fault movements should be assessed and reported.
Past measurements of the settling, displacement and cracking of the dam should be interpreted to estimate the existing state of strain, particularly in the core of the dam. The additional strain which can safely be tolerated st auld be estimated and related to the magnitude of potential fault movement; 5.
The tolerance of the abutment material to strain and cracking resulting from fault movement should be estimated
' based on the properties of the saprolites and the magnitude of potential fault movement.
If abutment cracking i
cannot be ruled out than the piping and erosional resistance of the weathered rock should be assessed.
6.
A detailed description of the Federal Power Commission monitoring program for seismic safety should be provided. The dam operating plans in the event of significant seismic excitation should be pro-vided together with plans for immediate inspections and readings of critical instruments.
Ir. add,ition, a plan for the prompt ai.d formal involvement of.Ddke Power Co. geotechnical consultants should be developed to assure that evidence detrimental to the safety of Jocassee dam is not overlooked.
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P.CtHTO?.P!G P:kOG?aM At present it_ canoot be stated that the relatively high levels of activity of late 1975-1976 will not resu:re.
Consequently, it is essential to. maintain a monitoring network which will provide accurate and timely information concerning size, frequency and hypocentral data for possible futuxa seismic activity.of the future.
a) Seismic Stations:
Until November 1978, three permanent stations should be, operated by Duke Power and recorded l
et the damsite.
Two to four microearthquake recorders should i
be used to augment these stations until December,1977. At that time a decision will be made, based on the level of activity during 1977, as to whether to continue operation of
. i theImicroearthquakerecorders. The two stations in addition to SMT should be installed as soon as possible. Suggested locations for these statioris are shown in the attached figure.
If possible, arrangements should be made with the USGS and USC to incorporate one or all of the Jocassee stations in the South Carolina network. 'This.would allow recording of these stations on the develocorder at USC.
If arrangements are made to include the stations in the network, it mhy be possible to use USGS radio frequencies for radio telemetry.
1 To improve the timing resolution for the permanent stations 3t recording speeds of 120 m/ min should be used on the helicorders.
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9 Quarterij reports should be provided b)
Reporting P.ocedures:
to the NRC within one month of the end of each reporting period.
These reports should include the following:
Short report of the general level 'of seismicity 'and 1.
Text:
and any changes in seismicity.
2.
Tables:
Catalog of all earthquakes recorded; a.
List of all hypocenters located (HYP071 Format);
b.
Operational report:
c.
i) location of stations; Times of operation of each station, number of days li) recording for each station, total number of station-days reporting; iii)
Report of reasons for any statien failures;
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3.
Figures:
Station locations; a.
Epicenter locations (with magnitude shown by symbol size b.
i)
For reporting period-Cumulative, from October,1975; ii)
Graphs of daily water le' vel (and daily range), change 3
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in water level / day, number of earthquakes / day, energy release / day, all plotted on the same time scale, for the-
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the reporting period; t
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Graphs of the parameters in item 3, chove, for ten d '.
day intervals from October,1975; Cross-sections of earthquake depths 'with error bars) e.
along profiles oriented U-S, E-W, HE-SW, NW-SE and any other profiles suggested by the data.
If sufficient data are available, 4.
Other Information:
"b-values" and focal mechanisms should aise be determin Interpretation of the significance of these parameters is -
not required from Duke Power. Company station data (HYP071 form and direction of motion at each station should be included f
in~ the report for all earthquakes used in focal mechanism determinations.
A copy of at least one " typical" seismogram should be in-cluded with each report to show data quality and type of activity.
If felt earthquakes occur, intensity surveys should be carried out and summaries of intensity reports and contoured intensity maps should be included in the report.
The HRC should be informed by telephone 4
5.
Abnormal Activity:
Any~of the of any unusual activity as soon as possible.
followi,ng unusual should be considered activity:
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s Any earthquake larger than magnitude 2; a.
b.
More than 100 events per week; Any plans to make unusual changes in water level c.
in the reservoir.
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