ML19207A743
| ML19207A743 | |
| Person / Time | |
|---|---|
| Site: | Summer  |
| Issue date: | 07/26/1979 |
| From: | Tibbitts D Office of Nuclear Reactor Regulation |
| To: | Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 7908220241 | |
| Download: ML19207A743 (7) | |
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JUL 2 61979 DOCKET N0. 50-395 APPLICANTS: SOUTH CAROLINA ELECTRIC AND GAS COMPANY SOUTH CAROLINA PUBLIC SERVICE AUTHORITY FACILITY:
VIRGIL C. SUMMER NUCLEAR STATION, UNIT NO.1 StBJECT:
SLMMARY OF MEETING HELD ON JUNE 22, IC9 WITH SOUTH CAROLINA ELECTRIC AND GAS COMPANY CONCERNING RESERVOIR INDUCED SEISMICITY AT THE SLMMER SITE On June 22, 1979 we met with representatives of the South Carolina Electric and Gas Company (SCEE), Dames and Moore, and Woodward-Clyde.
Dr. Pradeep Talwani, an independent consultant, also attended the meeting. The principal purpose of the meeting was to discuss the microseisnic activity in the area of the Stomer site. Also, at the conclusion of the meeting a few items. relating to foundation engineering matters were discussed.
The meeting was held in Bethesda, Maryland and the persons attending all or part of the meeting are listed,in the Enclosure.
The slides presented in the meeting are available from the project manager.
In the portion of the meeting dealing with microseismic activity SCE&G covered the following subjects : (1) Monticello Reservoir and operation of the Fairfield Pump Storage Facility, (2) regional and local geology, (3) regional and local seisnicity, (4) seismic studies at Monticello Reservoir, and (5) reservoir induced seismicity. The following discussions summarize the presentations:
Monticello Reservoir and Operation of the Fairfield Pumped Storage Facility The Monticello Reservoir is the upper pool of the Fairfield Pumped Storage Facility.
The reservoir is formed by 4 earthen dams; the main dam is 5000 feet long and 180 feet high. The reservoir has a total volune of 400,000 acre-feet.
The reservoir was filled, between December 3,1977 and February 8,1978, by pumping water from the lonar pool of tho pumped storage facility. During a nor-mal operating cycle, 29,000 acre-feet of water will go through the power house; the dram-dom on the Monticello Reservoir is 4.5 feet. Under emergency condi-tions, SCE&G can lower the level of the reservoir 7.5 feet. A normal generation /
punping cycle would have about eight hours of generation, 9.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> of pumping and 6.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> where the punp/ turbines are idle.
Regional and Local Geology The site is located in the Charlotte Belt metamorphic zone of the Piedmont physio-graphic province.
The Charlotte Belt is complised of metamorphic rocks that are approximately 360 million years old. The metamorphic rocks are interrupted by plutons of granodiorite, an igneous rock approximately 270 million years old.
054 202 7908220M/ i
. RIL 2 4 y Previous field investigations defined five mappable rock units within ten miles o' the plant: Charlotte Belt gneiss (country rock), Carolina Slate Belt rock, mismatite, granodf orite (granitic rock), and "granosfel."
The rock units under the reservoir and immediately surrounding the plant are country rock, migmatite, and granodiorite.
In general, the migmatite separates the country rock and the granodiorite; the migmatite is a gradational assortment of intimately mixed and altered elements from the country rock and the granitic rock.
The fault system closest to the site is the Goat Rock fault system; the site is 14 miles from the closest splay of this fault systen.
No faulting is observed on the surface in the near site area. In the excavation for the reactor building, near-vertical shear zones were found.
Investigations conducted at that time indicated that the shear zones were at least 45 million years old.
Regional and Local Seismicity The most significant earthquakes in the region were the Charleston, South Carolina earthquake ( August 31, 1886), the Union County earthquake (January 1,1913), and the Lake Murry earthquake (July 26, 1945). The epi-central intensities of these events wre X, VII, and VI, respectively; the intensity 0 the site from these earthquakes were VI to VII, IV and V, respectively. The Charleston earthquake was in the Coastal Plain province; and therefore it is not moved to the site area. Homver, repetition of the Charleston earthquake in the Charleston area is the basis for the operating basis earthquake (0BE).
The safe shutdown earth-quake (SSE) is assumed to be an intensity VII earthquake. The g values for structures on rock and structures on soil are.15g and.25g, respectively, for the SSE and.l g and.15 g, respectively, for the CBE.
Seismic Studies at Monticello Reservoir When the reservoir was filled in December 1977, the applicants had in place a microseismic monitoring network.
The network consisted of four statiens surround-ing the reservoir. The microseimic activity began about three weeks after the filling began.
The seisnic activity prior to filling the reservoir was about one event every six days; this is based on a seisometer at Jenkinsville, South Carolina, 3.2 miles from the station.
The activity increased to 85 locatable events per days by February 1979. The activity then decreased to about 8 per day, but bursts of activity (up to 30 events per day) have occurrred.
The mean magnitude for the locatable events is about 0.5; the highest magnitude recorded was 2. 8.
Several of the higher magnitude events were also recorded on a USGS accelerograph located on the abutment of one of the dams. Magnitude 2. 7 and 2. 8 events, recorded in August and October of 1978, mre found to have peak accelera-tion of about.25g at 10-15 Hertz. The peak acoleration in each case, occurred in a single spike. Both events were very short; the durations did not exceed
.6 seconds.
The applicants were asked to cormtent on (1) the comparison of these two events and OBE and (2) the foundation conditions under the accelerometer.
The appli-cants' consultants respondeo to the first item with a discussion of three points.
First the OBE is an event with many relatively high amplitude frequencies; the high amplitudes of local events were associated with a single frequency.
- Second, 04 203
-3 M 2 81979 designing for the OBE results i', combining the stresses of many modes of vibra-tion; the local events would oniy excite a single mode, if any. Third, the locai events were of short duration and produced only a single cycle of the peak accel-eration; resonance would not occur. In summarizing they concluded that the local events would have not an effect on the seisnic design of the plant.
We asked the applicants' consultants if they had done a comparison of the CBE design response spectra and the speura from the 2.7 and 2.8 events.
They had not.
They did not have digitized versions of these records; the USGS still had the original records. We felt that such a comparison was very important; SCE&G stated that they would provide such a comparison.
We briefly discussed the foundation :onditions at the accelerometer. It was not known if the instrunent was located on rock. With the exception of several water storage tanks and the essential water intake structure and pumphouse, the seismic Category I buildings are founded on rock. SCE&G stated they would provide us with information on the instrument's foundation.
Cr Taiwani gave a presentation on his studies of the microseisnic activity at the Monticello Reservoir. The main points of his presentation are as follows:
1.
The delay in the initial seismic activity and change in the level of activity suggest that the cause of the activity is a mechanism other than direct loading by the increased water level.
Dr. Talwani suggested that movement resulted from changed in pore pressure in the rocks. Movement would then be be a function of a change in water level and the time it took for the pare pressure at the epicenter to be affected. Dr. Talwani had correlated seismic activity with reservoir elevation, with some success; he was now attempting to also correlate reservoir elevation with depth of the epicenters.
2.
The microseismic events were located in two general areas; one was a band under the center of the reservoir and the other was under the main dam.
The location of the events started under the center of the reservoir and then moved about 0.5 miles to the west. Later the activity developed in the area of the main dam.
The events were first calculated to be between 1 to 5 kilometers in depth, but additional stations provided a better estimate of the depths.
Dr. Talwani believes most of the earthquakes are located in the upper 500 meters.
3.
The activity appeared to be focused in the transition zones between the county rock and the igneous plutons.
From the records it appeared that the direction of the movement did not correspond to any geological features.
Cr. Talwani suggested that joint patterns may influence focal mechanisas.
Reservoir Induced Seismicity A representative of Woodward-Clyfe stated that reservoir induced seismicity in shallow reservoirs like the Monticello Reservoir is very rare (26 cases out of 10,700 reservoirs). Homver, he also stated that the reservoir could not trigger G4 204
., M t s tgp an earthquake larger than the current OBE at the Sunner site.
This was bned on two points. First, large earthquakes (magnitude 5.0 cr greater) have been triggered only in those cases where active faulting was also present in the hydrologic regime of the reservoir; there are no active faults in the immediate area of the Sunmer station.
Second, large triggered events are generally very deep events ( depths greater than 5.0 km). The earthquakes at the Summer site were at smaller depths.
The reviewer agreed that large earthquakes are not expected; however, the activity, while minor, warranted careful attention.
We requested that SCE&G docunent their assessment in the FSAR.
The applicants stated that the information we requested would be provided by September 1979.
Foundation Engineering In the week prior to the meeting, we had several telephone discuss *c..s with SCE&G regarding the seismic Category I tanks founded on engineered fill and saprolite, the foundation conditions of the by-pass line to the circulating water intake structure, and inspections of the essential service water intake structure.
The applicants provided additional information on these subjects in the meeting.
Regarding the tanks, the condensate storage tank (CST) and the diesel generator fuel oil tanks were not founded on rock. The settlement of the CST was computed by comparing the elevation of the CST's concrete pad taken before construction of the tank (October 1976) with elevation after the tank was completed and filled (June 1979).
The settlement appeared to be about 0.04 or less feet.
The geo-technical revieur stated that this satisfied his concerns and he requested that SCE&G doctment this in the FSAR.
The fuel oil storage tanks were buried under-ground; a layer of saprolite separated the engineered fill of the foundation and rock. We requested that they determine if there had been any significant settle-ment. They stated that they currently had no data on this, but they were con-fident that the fuel oil tanks and fuel oils were sound.
We requested that they provide us with more information on this matter.
The foundation conditions for the by-pass line was presented as docurented in the GC files. The foundation was similar to other seismic Category I lines even though the line was not seisnic Category I.
SCE&G stated that they would include surveillance requirements in the technical specirications for this line.
The last item discussed was the recent underwater inspection of the service water tunnel. Only four new cracks were observed. SCE&G stated that the results of the inspection would be docunented in a final report on the settlement of the intake structure and pumphouse. SCE&G also agreed to bi-yearly survey the puap-house and intake structure after the unit receives and operating license.
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Dean L. Tibbitts Light Water Reactors Branch No. 2 Division of Project Management Enclosure :
Attencance List ccs w/ enclosure:
See next page pg 20,3
Mr. E. H. Crews, Jr., Vice President and Group Executive - Engineering gut, g,",7$
and Construction South Carolina Electric & Gas Company P. O. Box 764 Colunbia, South Carolina 29218 cc:
Mr. H. T. Babb General Manager - Nuclear Operations South Carolina Electric & Gas Company P. O. Box 764 Coluubia, South Carolina 29218 G. H. Fischer, Esq.
Vice President & General Counsel South Carolina Electric & Gas Company P. O. Box 764 Colunbia, South Carolina 29218 Mr. Wi.li an C. Mescher President & Chief Executive Officer South Carolina Public Service Authority 223 North Live Oak Drive Moncks Corner, South Carolina 29461 Mr. Wi ll i am A. Wi lli am s, Jr.
Vice President South Carolina Public Service Authority 223 North Live Oak Drive Moncks Corner, South Carolina 29461 Wallace S. Murphy, Esq.
General Counsel South Carolina Public Service Authority 223 North Live Oak Drive Moncks Corner, South Carolina 29461 Troy B. Conner, Jr., Esq.
Conner, Moore & Corber 1747 Pennsylvania Avenue, N. W.
Washington, D. C.
20006 Mr. Ma rk B. hhi tak er, Jr.
Licensing and Staff Engineer South Carolina Electric & Gas Company P. O. Box 764 Colunbia, South Carolina 29218 Mr. O. W. Di xon Group Manager, Production Engineering South Carolina Electric & Gas Company
_k qg6 P. 0. Box 764 0
L Colunbia, South Carolina 29218
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Nr. E. H. C re ws, Jr.
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W. Brett Allen Bursey Route 1 Box 93C Little Mountain, South Carolina 29076 s
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R 26 m ENCLOSURE ATTENDANCE LIST KETING KITH SCE a3 ON THE SUMKR STATION J t;NE 22, 197 9 NRC - STAFF P. Sobel D. Gillen R. Gonzales S. Davis L. Reiter R. Jackson SOUTH CAROLINA ELECTRIC AND GAS C0 WANY M. Whitaker R. M:Whorter WOOD)ARD-CLYDE J. Lovegreen W. Gardner UNIVERSITY OF SOUTH CAROLINA P. Taiwani i
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