ML19339A593
| ML19339A593 | |
| Person / Time | |
|---|---|
| Site: | LaSalle  |
| Issue date: | 10/28/1980 |
| From: | Delgeorge L COMMONWEALTH EDISON CO. |
| To: | Tedesco R Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8011040380 | |
| Download: ML19339A593 (8) | |
Text
{{#Wiki_filter:* Commonwealth Edison One First National Plaza Chicago, Illinois O Chicago,lilinois60690 Address Reply to: Post Office Box 767 October 28, 1980 Mr. Robert L. Tedesco Assistant Director for Licensing Division of Licensing U.S. Nuclear Regulatory Commission Washington, DC 20555
Subject:
LaSalle County Station Units 1 and 2 Revision 1 to Response Concerning Executive Order 11988 (Flood Plain Management) NRC Docket Nos. 50-373/-374 References (a): R. L. Tedesco letter to D. L. Peoples dated August 5, 1980. (b): L. O. DelGeorge letter to R. L. Tedesco dated October 16, 1980.
Dear Mr. Tedesco:
The LaSalle County assessment on Flood Plain Management requested in Reference (a) was submitted in Reference (b). The enclosed errata are submitted as Revision 1 of that assessment. It should be noted that the changes embodied therein are insignificant, but are provided for accuracy. The sections of the response that have changed are noted in the margin. Also included is one copy of the figures which are again provided unchanged from those originally submitted in Reference (b). If there are any further questions in this regard, please direct them to this office. Very truly yours,
/i (H}
L. O. DelGeorge Nuclear Licensing Administrator Enclosure cc: RIII Resident Inspector - LSCS 'Bool y
// .8013040 2 i 7749A
LSCS-FSAR NRC QUESTION RELATING TO FLOOD PLAIN MANAGEMENT ,
- - N'... ; ', ly < Provide ld$sc'ript'i$ns"of" the Efidodpl$iS$ hf iflS'a#te$bodids, including intermittant water courses; within or adjacent to the site. On a suitable scale map provide delineations of those areas that will be flooded during the one-percent chance flood in the absence of plant effects (i.e., pre-construction floodplain).
- 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 com-putation of the one-percent flood flow and water elevation.
If studies approved by Flood Insurance 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.
- 3. Identify, locate on a map, and describe all structures and topographic alterations in the floodplains.
- 4. Discuss the hydrologic effects of all items identified in 3 above. Discuss the potential for altered flood flows and levels, both upstream and downstream. Include the potential effect of debris accumulating on the plant structures. Additionally, discuss the effects of debris generated from the site on downstream facilities.
- 5. Provide the details of your analysis used in response to 4 above. The level of detail is similar to that identified I
in item 2 above. .
RESPONSE
The La Salle County Station (LCCS) is regionally located in the Illinois River basin. A detailed description of the drain-age basin of the Illinois River and its tributaries is given in LSCS, ER(OLS) Section 2.4.1.2. Locally South Kickapoo Creek discharges into the Illinois River from the south 0.5 miles downstream of the river screenhouse. Other streams in the vicinity are shown in Figure 1 and also in Figure 2.4.3 of LSCS , ER(OLS) .
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. LSCS-FSAR RGv.1 The plant buildings, the cooling lake are sited over 210 ft.
- above the 100-year flood level with the Illinois River. The
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. riv.er..screenhouse and . the .outfall structure which are.. located: .6*,1, ' ^ .*:;* 'd.*( " *
'in'.or ' near 'the flood plain of 'the' Illinois River' 'a'nd its tri
butaries are shown in Figures 1 and 2. Figures 1 and 2 also
- show the extent of flood prone areas due to one percent chance flood prior to the construction of LSCS. These flood prone
- areas were delineated by the Federal Emergency Management Agency, Department of Housing and Urban Development and U.S. Geological Survey (U.S. Department of Housing and Urban Development, 1978; l U.S. Geological Survey, 1975) .
j It is evident from the Figures 1 and 2 that the plant buildings and the cooling lake do not alter the flood plain of any of the rivers or streams in the vicinity so as to affect flood- ]< prone areas. The river screenhouse, located at river-mile 294.5 approximately 2.5 miles upstream of Marseilles Dam, encroaches on the Illinois
- River flood plain as shown in Figures 2 and 3. The river l screenhouse structure has a plain area of 60 x 80 ft. with the
' I 60 ft. dimension parallel to the river. The effect of this encroachment on 100-year flood level in the Illinois River i is as follows. i The 100-year flood elevation in the Illinois River at the location of the river screenhouse was computed by backwater
- analysis starting from Marseilles Dam. The river cross-t sections were obtained from the U.S. Army Corps of Engineers, i Chicago District. The 100-year flood flows at Peoria-Marshall l County Line (river mile 185) and at Dresden Island (river mile 2*J1) are 91,500 cfs and 89,000 cfs, respectively. (Illinois State Water Survey 1980) . The flood flow at Marseilles Dam during July 1957 flood was 93,900 cfs and the corresponding
; stage upstream of the dam was 484.6 feet. (U.S. Army Corps of Engineers, 1980). This flood discharge is greater than the i 100-year flood discharge at Peoria-Marshall County line which is downstream of Marseilles Dam. Therefore, a flow of 93,900 cfs was conservatively used in the present analysis to estimate the effect of LSCS facilities on the flood prone areas of the Illinois River. The starting elevation of 484.6 feet was ~
used at Marseilles Dam for the backwater analysis. The water surface elevation in the Illinois River at the location of the screenhouse was 491.3 feet for preconstruction condition. At this elevation, the area of cross-section of the Illinois River is 15,230 square feet and the encroachment area due to river screenhouse is 290 square feet, which is less than 2% of the ori-ginal cross-section. Backwater computations with river screan- , house in place indicated that this minor encroachment caused negligible difference in the flood levels wither upstream or downstream of the screenhouse. Hence, it is concluded that the emplacement of the river screenhouse does not cause any measur-able change in the river flood levels for the 100-year flood.
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LSCS-FSAR R EW. I The outfall structure consists of a free discharge valve with a stilling basin and discharge channel constructed below i
.. ., m ; _' n,axisting grade.- ' It. has encorachment . inco. the.. flow . cross . ._ _. ,s?,,.' . , ei.'J.?e
'section, corresponding to a 100-year flood.
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Therefore, the structure does not affect the preconstruction flood levels.
~
From the above factor, it is concluded that the LSCS structures in the flood plains of the Illinois River (and its tributaries) can not cause alteraticns in the flood levels due to a one per-cent chance flood. No pumping station debris is generated and disposed of into l these waterways from the LSCS facilities. Debris accumulation at the plant structures is not expected and, hence, there is no potential effect on the flood-prone areas. s s *% , G. E e a D
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References:
..l.. U.S. Department of. Housing'and. Urban Development,. Federald * :Dy*,b.
Emergency ~ Management Agency, Flood Hazard Boundary Map, La Salle County, Illinois, May 26, 1978.
- 2. U.S. Geological Survey, Map of Flood Prone Areas, Marseilles 15' Quadrangle Sheet, 1971, reprinted 1975.
- 3. Illinois State Water Survey, certified Q. 100 List, f Computer Printout, March 13, 1980. -
- 4. .U.S. Army Corps of Engineers, unpublished list of flood levels in Illinois P.iver from M. Jakofsky, Chicago District, Chicago, Illinois, September 15, 1980.
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- -t - -_ M - pggy MANAGEMEN T AGENCY, DEPART- FIGURE I MENT OF HOL.EJNG AND URSAN NENT, MAP Nos. 00@ ILLINOIS RIVER AND ITS T TRIBUTARIES IN lhE VICINITY 000 A, OOE2 A AND OOSA ., fg73 OF LSCS STATON
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. REFEREME: USGS MAPOF p.DOD PRONE AREAS, FLOOD PLAIN OF ILLINOIS RIVER MARSklLLES IS , QUADRANGLE,1975. (VICIN6TY OF RIVER SCREENHOUSE)
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~ HORIZONTAL 0 10 - 20 VERTICAL FGRD3 ILLINOIS RIVER CROSS SECTION
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