Page 108 - How It Works - Book of Amazing Answers To Curious Questions, 12

� AMAZIG ANSWERS TO CURIOUS QUESTIONS

What is nuclear

�ower? Is it an ecological saviour

or a looming catastrophe?

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ter the Three Mile Island meltdown in enriched uranium oxide, comprising 96-97 per are 150-200 bundles of 12-foot-long fuel rods.
979 and the Chernobyl disaster in 1986, cent uranium-238 and three to four per cent Each bundle includes 200-300 individual rods,
uclear power shot to the top of the uranium-235. Uranium is the heaviest of all which are made from small uranium oxide
environmental villains list. But in the face of natural elements and one of the easiest to break pellets. The rods are immersed in a coolant and
mounting global warming concerns, it might be apart. When a relatively slow-moving free housed in a steel pressure vessel.
poised for a comeback. Since nuclear power neutron runs into a uranium-235 atom, the atom The fission reaction continues indefinitely
produces no greenhouse gasses, proponents will absorb the neutron, and the extra energy when, on average, more than one neutron from
are touting it as a greener alternative to fossil will make the atom unstable. The atom each fission reaction encounters another
fuels. They argue that one pound of enriched immediately splits apart into two smaller uranium atom. This state is called
uranium !the chief nuclear fuel) can provide the atoms and two to three free neutrons. A fraction supercriticality. In order to safely heat the
same energy as 3 million pounds of coal or 1 of the atom's original mass becomes energy, in water, the reactor must keep the fuel slightly
million gallons of gasoline. the form of heat and high-energy photons supercritical, without allowing a runaway
But there's quite a catch. Nuclear fuel called gamma rays. fission reaction.
produces radioactive waste, which can cause With the right mix of uranium-235, you get a The key mechanism for controlling the
cancer, trigger birth defects, and spawn chain reaction. Some of the free neutrons reaction rate are a series of control rods, made
mutants. The technology is both fascinating generated in the fission reaction encounter from neutron-absorbing material such as
and ominous and we'll be explaining just how other uranium-235 atoms, causing those atoms cadmium. Operators can move the control rods
it works over the next few pages. to split apart, producing more free neutrons. in and out of the bundles of uranium rods. To
Nuclear power plants are complexes that Collectively, the splitting atoms generate a slow down the fission reaction, operators lower
span many square miles, but the real action substantial heat. All the equipment in a nuclear the rods into the bundles. The rods absorb
happens on a subatomic level. The sole purpose plant has one core function: safely harnessing neutrons from the fission reactions, preventing
of a plan tis to harness the energy of nuclear this heat to generate electricity. them from splitting additional nuclei.
fission - a reaction where an atom's nucleus The heart of a nuclear power plant is the Operators can stop the fission reaction by
splits into two smaller nuclei. reactor, which contains the uranium fuel and lowering the control rods all the way into the
Specifically, nuclear plants typically derive the equipment that controls the nuclear fission uranium rod bundle. To accelerate the fission
power from inducing nuclear fission in reaction. The central elements in the reactor reactions, operators partially raise the rods out

How does a pressuri wate reac tum subac ''Proponents are
part actity into usable power? touting it as a

1. Fuel rods 5. Pressuriser 9. Turbine
Hundreds of U-foot The pressuriser contains Rushing steam spins greener alternative
uranium rods undergo a water, air, and steam. By the turbine.
fission reaction, releasing adding 01' releasing air in
substantial heat. the pressuriser, operators 10. Generator to fossil fuels ''
can control the pressure of The turbine spins a rotor
2. Reactor the coolant water around that sits in a magnetic field
A steel pressure vessel the reactor. in a generator, inducing an
contains the uranium rods, electric current.
surrounding water and 6, Heat exchanger
other reactor components. A pipe carries hot water 11. Transfonner
from the reactor to a The generatOf transmits
3. Control rods separate reservoir of water. electricity to a
Operators can speed up or transformer coonected to
slow down the fission 7. Steam the power grid.
reaction by raising and generator
lowering neutron- The hot pipe leading from U. Condenser
absorbing rods between the reactor heats a A pipe carrying a steady
the fuel rods. separate reservoir of water supply of cold water,
to the boiling point, typically from a cooling
4. Pump generating steam. tower, cools the steam,
A water pump keeps causing it to change back
water circulating, which 8. Steam line to liquid water.
transfers heat away from Steam travels from
the reactor core. the steam generator to
the turbine.
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