Cooper Nuclear Station

Cooling Water Intake Struct

Presentation to EPA

March 2, 2009
What We re’ Going to Discu

Discu

• Where we are located located• Intake structure design & features• Ch ll a enges we face

– Sedimentation– Debris

• What we’ve done to meet the challenge
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Cooper Nuclear Station
Intake Description

• The Intake Structure provides a sou

Missouri River water to:

– Circulating Water System, which cools t

Condenser, and

– Service Water System, which cools both safet

and non‐safety related components.

• Cooling Cooling water is drawn from the river 

sloping weir wall.

– Wall was installed installed in the early 1970s to 

sediment inflow into the intake.

– Wall was designed based on river flows typic

1960s and early 70s.
Intake Description

• Traveling Water Screens (TWS) are 

downstream of the Intake Structure Trash Rack

– The purpose of the TWS is to remove debris from 

water prior to its supply to the suction of Circulating Water (CW) pumps and the four Serv(SW) pumps.

– There are nine TWS; two for each of the four C

and one for the SW pumps.

• Circulating Water (CW) systems for plant conden

during normal operations:

– Four pumps provide cooling water at 159 000 , gpm ea

cfs total) and

– Three other pumps provide 30,000 gpm (67 cfs total) 

and fire water.
Intake Structure
Sediment

• The Cooper intake was designed in acc

with recognized recognized criteria criteria for intakes intakes on rivers.

– Majority of the suspended solids was expecte

through the circulating water system,

– Some material was also expected to settle o

intake and reach an acceptable acceptable equilibrium equilibrium wpumps were placed in operation.

– This, however, did not hold true in the case o

and attempts to operate the pumps on a cobasis were hampered by the jamming of the screens due to high deposition of sediment iand behind them.
Sediment

• There are apparently several reasons for this s

deposit:

– The river has high velocities and sediment 

capacity at this location and the sudden redvelocities within the intake passages tends to rel ti l a ve y heavy b tt o om sedi t men l d oa qui kl cy.

– The upstream portion of the protective sheet pi

in place after construction (to serve as a rem

possible possible barge impact problem) problem) creates creates eddies r

r

increase of sediment deposition in the vicinitwithin the intake area.

– The rapidly rapidly shifting shifting normal river bottom im

im

adjacent to the front face of the intake tends thigher level that the bottom of the intake. Matt eh river bottom te ds n to be ca ed rri into t eh inta 
Sediment

• Sediment load increases with increased 

from the Platte and Nishnabotna Nishnabotna rivers

rivers

• Lower water levels increases the sedim

carrying capacity.

• Sunken trash and debris accumulations 

base of the t h ras racks can act like weir

further slowing the water velocity and c

more sedi t men to drop out.
Sediment

• The increased siltation has forced:

– Pump shutdowns after clogging up the tr

and reducing the head available for pump

– Mechanical removal methods such as ex

and divers have offered CNS only sh

sol ti u ons.

– Significantly increased traveling water 

maintenance and operational problems, instrainer backwashes, and restricted flow with the Intake Structure Structure Circulating Circulating Wate
Sedimentation

• The major preventive measure already 

place to address the seasonal sediment

concern to have divers manually clean d

from the trash racks and de‐sand the In

Structure bays.

• This cleaning is performed every 6 mon

the spring and in the fall.

– The spring cleaning addresses the increa

sand build up rate from the low river leve

spring runoff.

– The fall cleaning removes the sunken

t as /deb s rash/debris which a sol inc eases creases t eh sed 

sed

build up rate.
Cloud of Suspended Suspended 0.5 MM 
Debris

• Debris lodges in the condenser tubes

– Reduces condenser efficiency and requires the frequent b

of the Main Condenser in an attempt to dislodge the a

debris.

– Creates clogging and high differential pressures within th

requiring increased cleaning to maintain system operability

• During power operation, condenser backwashing prov

term improvement to condenser performance, but 

repeated repeated on approximately approximately a weekly basis.

– There were 45 backwashes during 2002– Each backwash evolution requires a plant power reductio

the net CNS generation loss associated with condenser b

was approxi tl ma e y 3,220 MWhrs

– In addition, the backwash process is not fully effective in 

debris. The debris that cannot be dislodged must be remoduring each refueling outage.
Debris lodged in Main Conde
Typical River Trash
What We ve ’ Done

• Cut weir wall and added turning vanes

– Reduced sediment sediment into the bays– Approx $2.2M

• Changed screen design

– Flow through to dual flow– Keep trash off condenser condenser– Approx $6M

• Operational Challenges remain

– Continue to backwash condenser– Continue Continue to dredge intake structure structure to

mechanically remove sediment
Dual vs. Thru Flow Scree