ML19257A173

Responds to 791114 Ltr Re Review of Design & Location for Intake Structure,Embayment & Barge Slip.Advises That Intake Structure Not safety-related & Low Level Intake Structure Preferable to High Level Design

ML19257A173
Person / Time
Site:	River Bend
Issue date:	12/21/1979
From:	Weigand J GULF STATES UTILITIES CO.
To:	Sells D Office of Nuclear Reactor Regulation
References
RBG-7056, RBG-7057, NUDOCS 8001020403
Download: ML19257A173 (3)

Text

s GULF STATES UTILITIES COMPANY o ,s:,r.: ee:,22- . ses .ves- ras 4 2 : 4 AeEA c ; C. E - 3 338 65?

December 21, 1979 RBG - 7056 File G9.5 Donald E. Sells, Acting Chief Environmental Projects Branch 2 Division of Site Safety and Environmental Analysis U. S. Nuclear Regulatory Commission Washington, D.C. 20555

Dear Mr. Sells:

River Bend Station Units 1 & 2 Docket Nos. 50-458, 50-459 In response to your letter dated November 14, 1979, this letter documents the results of Gulf States Utilities' technical review of the design and location for our intake structure, embayment, and barge slip. As noted in Section 2.4.2 of the SER the intake structure is not safety related.

Intake structure design alternatives are discussed in Section 10.2 of the Environmental Report (ER), while alternate River Access Road locations are presented in Section 10.10.2 of the ER. The NRC Staff evaluated and concurred with our choice in Section 9.2.2 and Section 9.2.9 of the Final Environmental Statement. This design was also evaluated from a flood potential standpoint in Section 2.4 of the PSAR and Section 2.4.2 of the SER. The NRC Staff concluded that "the design basis water level for the platform intake structure is conservative."

In finalizing and optimizing the design of the embayment area, it became evident that a low-level intake structure would be preferable to the one of a high-level (platform) design. The final design was evaluated and found to be better on an overall basis when considering such factors as protection from barge impact, susceptibility to river migration, hydraulic performance, cost and environmental impact.

The proposed intake pump structure is a dry pit, siphon-type, reinforced concrete structure, flood protected to El + 60 feet MSL (Probable Maximum Flood water level is El + 56.5 feet MSL), the same as for the original 1663254b[t .

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' Donald E. Sells Page 2 December 21, 1979 platform intake structure. The structure is surrounded by an earthen embankment to El + 50 feet MSL protecting it from impact by heavy debris.

The structure itself can withstand the effects of any debris which can be expected to pass over the embankment.

The design provides for an embayment, a man-made recession excavated into the east bank of the river with an orientation normal to the flow of the river. The intake piping and screens and the barge slip for barge unloading are located within this embayment. The intake structure itself is located approximately 250 feet inland of the top of the riverbank.

Locations of the embayment area and River Access Road remain the same.

The shape of the embayment provides favorable hydraulic behavior at the intake screen location and significant protection against impact by floating debris. Because the top of the intake pipes is at El + 3 feet MSL, most debris will simply pass over the pipes and screens. During the infrequent periods of very low water, the probability of heavy debeis entering the embayment through the narrow river front opening is very small, particularly since any such debris must enter in a direction normal to the flow of the river.

The embankment and River Access Road are sufficiently high (El + 50 feet MSL) to permit access to the pump structure during floods up to the maximum recorded event. Other means of access may be used when extreme conditions warrant.

The barge slip is a drive-off arrangement where the barge is grounded at a location along the slip determined by the water elevation at the time of delive ry. An earthen ramp is constructed up to the grounded barge and deliveries are unloaded onto the ramp and then up the River Access Road to the plant. The slip will only be used periodically during construction of the plant and deliveries can be scheduled for normal water levels.

The embayment shape will be protected against bank erosion by stone rip-rap. Although higher than normal floods in the last 6-8 years have caused riverbank erosion to be greater than normal, we feel that the rate of erosion averaged over a number of years is not great enough to warrant more extensive erosion control measures at this time. The erosion will be monitored and additional control measures instituted if necessary.

Construction of the River Access Road is complete and the attendant environmental impacts have already taken place. Installation of intake piping along the road has begun. Clearing and excavation operations have already begun for the embayment and barge slip so that the majority of the terrestrial impacts have been felt there as well. The environmental costs for relocating the embayment area at this time would be great.

Although the potential problems identified by your staf f hydrologist represent design considerations commonly associated with the construction 1663 255 -

. Donald E. Sells Page 3 December 21, 1979 of river front facilities, these considerations have been adequately incorporated into our design. We re-emphasize that these structures are not safety-related and that original considerations for location and design are still valid.

If you have any further questions contact the undersigned.

Sincerely,

. k &'

G. Weigand General Manager-Nuclear Projects 1663 256 i

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