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THE NUCLEAR FISSION REACTOR

The reactor is a way of getting energy from the uranium fission in a controlled way. The first nuclear fission reactor was made by Enrico Fermi in a squash court in Chicago in 1942.
One form of fission reactor is shown in the diagram.


The CORE of the reactor contains the uranium fuel (an alpha emitter and not very dangerous if handled with care) that is held in thousands of metal tubes in a large block of graphite. The graphite, called the MODERATOR slows down the neutrons emitted at each fission so that they can react better.

Carbon dioxide gas is blown through the reactor core under pressure to take away the heat energy produced by the fission reactor. This gas is then passed over tubes containing water, giving out its heat and turning the water into high temperature steam which is then used to drive turbines and generators.

To increase or decrease the output power of the reactor a large number of CONTROL RODS are used. These are made of boron or boron-steel that gobble up neutrons. They can be lowered into the reactor to reduce the number of neutrons and so lower the power or they can be raised to increase the power.



When the nucleus splits we get two smaller nuclei, two or three neutrons and some energy. This energy appears as heat due to the kinetic energy of the smaller nuclei and the neutrons. The energy is produced because the mass of the uranium nucleus plus the mass of the incoming neutron is slightly greater than the masses of the particles formed after fission. You don't get very much energy from splitting one uranium nucleus but in one kilogram of uranium there are around a million million million million million nuclei and if you could split all of them the energy produced would be very large. In fact if all the nuclei in 1 kg of uranium 235 could be split the energy produced would be about the same as that obtained from burning three thousand tons of coal!

The whole reactor core is contained in a steel pressure vessel and then surrounded by a thick layer of concrete to protect the workers from radiation.


Location, benefits and drawbacks of nuclear power stations

Location
The reactor is a very heavy structure and so it is important that nuclear power stations are built on very stable solid rock.
They need large amounts of water to turn to steam to drive the turbines and also as coolant in the condensing units and so they should be built near the sea, a river estuary or a large lake.
People are not usually too happy about living near a nuclear reactor and so nuclear power stations are usually built in areas of low population.




Benefits and drawbacks of nuclear power

(a) benefits
(i) low or zero carbon dioxide emission
(ii) relatively large uranium fuel reserves

(b) drawbacks
(i) expensive to build
(ii) radiation danger during operation
(iii) danger of terrorist attack
(iv) disposal of radioactive nuclear waste

Nuclear waste
Low level waste
This is gloves, cast off clothing, over shoes etc.

Intermediate level waste
This is fuel containers

High level waste
This is mainly irradiated fuel taken from reactors.
 
 
 
© Keith Gibbs 2013