Environmental Impact Statement - radioactive monticello

Description of Site and Environment
the shoreline. At the intake structure,-the approach channel reduces to approximately 63 ft
wide. Water enters the intake structure over a 63-ft wide concrete sill that serves as a sediment
barrier. At the center of the sill is a 12.5-ft wide stop log section that can be removed during
low river levels to allow water to flow unobstructed. On the plant side of the sill is a concrete
apron extending the width of the approach channel and 16 ft upstream of the bar rack. The bar
rack includes a motor-operated bar rack rake that prevents large debris from entering the intake
structure. The bar rack rake lifts debris into a trash hopper to prevent the debris from
re-entering the river. After the bar rack, the water is divided into two separate streams that
pass through two parallel traveling screens located 10 ft behind the bar racks. The traveling
screens have 3/8-in. mesh that removes fine debris. The traveling screens are normally rotated
and rinsed every 12 hours and are run'continuously When the river temperature is above 50 0 F.
The debris, as well as any impinged organisms, are rinsed from the traveling screens into a
common sluiceway that extends back to the river downstream of the intake structures. From
the traveling screens, water passes through the service water pump bay and two parallel
motor-operated sluice gates before reaching the circulating water pumps.
The circulating water system consists of two circulating water pumps, each rated 140,000 gpm,
mounted over each end of the intake structure. These pumps are designed to circulate
292,000 gpm of cooling water through the main condenser. The plant service water system
consists of three service water pumps each with 6000 gpm capacity. These pumps supply over
10,000 gpm to meet all nonreactor requirements during normal operating conditions.
Effluent from the condenser and service water system is piped approximately 600 ft through two
108-in. steel pipes to the discharge structure at the head of the discharge canal. The discharge
structure is constructed of reinforced concrete and measures 50 ft by 54 ft by 38 ft high, with
the roof approximately 5 ft above grade. The discharge structure includes two isolation and two
sluice gates. The motor-operated sluice gates can isolate the discharge flow from the
discharge canal. During once-through or open-cycle operation, the sluice gates are open and
the circulating water is returned to the Mississippi River through the discharge canal. The
bottom of the discharge canal was constructed on a 0.25 percent slope in an easterly direction
approximately 1000 ft to where it enters the river. An overflow weir was added in 1980 to allow
normal outflow of cooling water from the discharge canal, re-establishing the previously existing
shoreline of the river. The weir inhibits fish from entering the canal. The discharge weir
consists of an earth filled dike and a vertical sheet-pile overflow section.
Monticello also has the capability of utilizing two mechanical draft cooling towers to meet
surface water appropriations limits and thermal discharge limits as needed (see Section 2.2.2.).
Two cooling tower pumps are located at the discharge structure and are designed to deliver
151,000 gpm to each cooling tower. In this mode of operation, control gates can isolate the
Mississippi River from the main intake structure and the discharge structure. Cooled water
from the cooling tower basins is then allowed to flow by gravity to the circulating water pumps in
the intake structure. Cooling tower blowdown is piped by gravity to the discharge canal.
Makeup water to replace water lost from cooling tower evaporation, drift, and blowdown is
August 2006 2-7 NUREG-1437, Supplement 26 1