ML19337A615
| ML19337A615 | |
| Person / Time | |
|---|---|
| Site: | Summer  |
| Issue date: | 09/23/1980 |
| From: | Nichols T SOUTH CAROLINA ELECTRIC & GAS CO. |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8009290337 | |
| Download: ML19337A615 (4) | |
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SOUTH CAROLINA ELECTRIC a GAS COMPANY POST OFFsCE SON,64 CotuMs A. SOUTH CAROUNA 29288 e,ce p.e,fe $ $ fcIre,,v.
September 23, 1980 (Nuclear Operations)
Mr. Harold R. Denton, Director Office of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission Washington, D. C.
20555
Subject:
Virgil C. Summer Nuclear Station Docket No. 50-395 Request for Additional Information Floodplain Management
Dear Mr. Denton:
South Carolina Electric and Gas Company, acting for itself and as agent for South Carolina Public Service Authority, herewith submits re-sponses to the generic requests for additional information relating to Executive Order 11988 on Floodplain Management, as requested by Mr.
Robert L. Tedesco's letter of August 28, 1980.
1.
Provide descriptions of the floodplains of all water bodies, including intermittent water courses; within i
or adjacent to the site.
On a suitable scale map pro-vide delineations of those areas that will be flooded during t'e one-percent flood in the absence of plant effects (i.e., pre-construction floodplain).
RESPONSE
The Virgil C. Summer Nuclear Station is located adjacent to Monticello Reservoir, approximately 1 mile east of the Broad River and 2.5 miles northeast of Parr Dam.
The site is situated on a hilltop at an average elevation of 435.0', about 180 feet above the Broad River floodplain.
The elevations of the one-percent flood in the absence of plant e ffects, have been conservatively estimated to be 426.0' for Monticello Reservoir and 274.4' for the Broad River.
Figure 2.4-3 of the FSAR provides approxi-mate delineations of the pre-construction floodplains for both water bodies.
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2.
Provide details of the methods used to determine the floodplains in response to 1. above.
Include your assumptions of and bases for the pertinent parameters used in the computation of the one-percent flood flow and water elevation.' If studies approved by the Flood Insur-ance Administration (FIA), Housing and Urban Development (HUD) or the Corps of Engineers are available for the site or adjoining area, the details of analyses need not be supplied. You can instead provide the reports from which you obtained the floodplain information.
RESPONSE
The one-percent flood elevation for Monticello Reservoir was computed assuming an initial normal maximum pool elevation of 425.0' and cor-responding surface area of 10.6 square miles.
Based on Technical Paper No. 40, the 100-year point rainfall would be 7.6 inches in 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.
This point rainfall was conservatively assumed to occur over the entire 17.4 square mile drainage area contributing to Monticello Reservoir.
To be further conservative, no precipitation losses were assumed to take place during the rainfall event.
The resultant rise in water level of Lake Monticello would be 1.0 foot, corresponding to a 100-year flood clevation of 426.0'.
The one-percent flood elevation for the Broad River was computed assum-ing an initial normal maximum pool elevation of 266.0', corresponding to the spillway crest gates at Parr Dam in the raised position.
From Table 2.4-2 of the OLER, the 100-year peak discharge for the Broad River at Richtex would be approximately 207,000 cfs.
Based on the methods and assumptions ide-tified in Section 2.4.2.1 of the FSAR, the corresponding peak flood discharge for the Broad River at Parr Dam would be 194,200 cfs.
From the weir equation, the resulting surcharge ever Parr Dam would be 8.4 feet, corresponding to a 100-year flood elevation of 274.4'.
1 REFERENCE i
Technical Paper No. 40, Rainfall Frequency Atlas of the United States, U. S. Department of Commerce, Weather Bureau, 1961..
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3.
Identify, locate on a map, and describe all structures and' topographic alterations in the floodplains.
I
RESPONSE
Figure 2.4-1 of the FSAR illustrates all structures and topographic ~
alterations within the floodplain of Monticello Reservrir.
The principal structures are the embankments which form the service water pond.
The north, cast, and south dams have a crest elevation of 438.0' and crest lengths of about 1,500 feet, 1,150 feet, and 765 feet, respectively. The crest of the west embankment is at elevation 435.0',
coinciding with the adjoining plant yard grade, and is about 1,900 feet long. Other structures within the Monticello Reservoir floodplain include the circulating water intake and discharge structures, the discharge canal which has a length of approximately 1,600 feet with Invert elevation at 404', and an earthfill jetty about 2,600 feet long with a top elevation of 435.0'.
There are no structures er topographic alterations within the Broad
.Rtver floodplain associated with the Virgil C. Summer Nuclear Station.
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4.
D'iscuss the hydrologic effects of all items identified in the response to 3. above.
Discuss the potential for altered flood flows and levels, both upstream and down-stream.
Include the potential effect of debris accumu-lating on the plant structures.
Additionally, discuss the effects of debris generated from the site on down-stream facilities.
nr..00NSE
'ibn structures and topographic alterations within the floodplain of Monticello Reservoir would produce no perceivable effects on its flood hydrology.
There exists little or no potential for altered flood IcVels, because the volume of flood water inflow is dependent upon pre-cipitation, and the. resultant flood level upon the initini reservoir level and surface area.
Little or no potential exists for debris to accumulate on the plant structures or to be generated from the site, because no significant flow velocities would occur in Monticello Reser-voir.
There are no structures or topographic alterations within the Broad River floodplain associated with the Virgil C. Summer Nuclear Station and therefore no potential hydrologic effects.
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'5.
Provide the details of your analysis used in response to
- 4. above, to the icvel of detail similar to that identified in 2 above.
RESPONSE
No analysis was required in response to Questions 4.
Very truly yours T. C. Nichols, Jr.
RBW:TCN:jw cc:
W. F. Kane B. A. Bursey V. C. Summer C. H. Fischer W. A. Williams, Jr.
T. C. Nichols, Jr.
E. H. Cr,ews, Jr.
H. T. Babb D. A. Nauman O. S. Bradham
'e O. W. Dixon, Jr.
J. B. Knotts, Jr.
R. B. Clary J. L. Skolds
' NPCF/Whitaker
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