Operation
The material used for the reactor
is uranium-238 and uranium-235 in the form of ceramic pellets
packaged into a tube about 6mm in diameter and a few meters
long. According to Dr. David Brenner, Director of the Center
for Radiological Research, “A nuclear reactor can’t operate
with natural uranium. It has to have a bigger proportion of
uranium-235 to operate.” Uranium-235 is naturally found in
concentrations of about 0.7%. Through a process called
enrichment, Uranium-235 is boosted to a concentration of 3%.
These rods are inserted into the reactor to maintain the
required mass. In order to control the reaction, control rods
are inserted and removed to slow or accelerate the chain
reaction. The rods full of uranium are separated by water.
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Pressurized Water Reactors
In a pressurized Water Reactor,
there are three separate, interacting water systems. The first
system is the water surrounding the uranium rods. This water
absorbed the immense amount of heat energy that is generated
from the fission. The water in this system is kept under such
high pressure that it is able to absorb all that heat while
remaining in liquid form. Instead, it circulates through a
pipe system that passes through a steam generator which
contains the second closed water system. Heat is then
transferred from the initial water system to the second which
causes the water to turn into the vapor used to turn the
turbine. The vapor then cools down in the heat exchange
chamber (which contains the third water system) condenses, and
repeats the process. The water in the third system take the
heat from the second system and removes it via the cooling
tower.
Image
from World Nuclear Asscociation
Boiling Water Reactors
A boiling water reactor uses only
two water systems. The first water system surrounds the core
of the reactor and absorbs the heat. The water then vaporizes
and turns the turbine on the generator, thus producing
electricity. The steam then flows into the cooling system
where its heat is absorbed by cool water and the cycle
repeats.
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