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Example
of Natural Circulation Cooling - Fluid Flow
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Fluid
Flow Table of Contents
Natural circulation is frequently the primary
means of cooling for pool-type reactors and for irradiated
fuel assemblies stored in pools of water after removal from
the reactor. The heat source
is the fuel assembly. The heat sink is the bulk of the water
in the pool.
Water at the bottom of a fuel assembly
absorbs energy generated by the assembly. The water increases
in temperature and decreases in density. Gravity pulls cooler
(more dense) water into the
bottom of the assembly displacing the warmer water. The
warmer (lighter) water is forced to
give up its position to the cooler (heavier) water. The
warmer (lighter) water rises higher in the
assembly. As water travels up the length of the assembly, it
absorbs more energy. The water becomes
lighter and lighter being continuously forced upward by more
dense water moving in below
it. In turn, the cooler water absorbs energy from the
assembly and is also forced to rise as
natural circulation flow continues. Water exiting the top of
the fuel assembly gives up its energy
as it mixes with the bulk of the water in the pool. The bulk
of the water in the pool is commonly
cooled by circulation through heat exchangers in a separate
process.
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