Old assemblies must be replaced with new. The used fuel is moved to the plant's spent fuel pool. The fuel is removed from the reactor and moved to the pool entirely under water. The water provides cooling for the fuel and helps shield workers from radiation exposure. The pool walls are stainless steel backed by steel-reinforced concrete several feet thick.
Heat exchangers help cool the water in the pool.
The spent-fuel pool was originally designed to hold used fuel only for a short time, in limited quantities, until it could be shipped away for reprocessing into new fuel. For a variety of reasons, reprocessing has not become a reality in the United States. Without reprocessing or a final disposal site from the federal government, used-fuel pools have been filling up. Cooling Towers Monticello uses river water in its condenser to condense steam back to water after it has been used to run the turbine generator. The river water passes through thousands of tubes inside the condenser.