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TUESDAY APRIL 26 2016 DAILYTELEGRAPH.COM.AU
How does nuclear
energy work?
T
he world’s worst nuclear accident happened on April 26, 1986 — 30 years ago today —
when a reactor exploded at the Chernobyl Nuclear Power Plant. The explosion released
large quantities of radioactive material into the air over much of eastern Europe and
western USSR, damaging the reputation of nuclear energy. Since then other incidents,
accidents and disasters involving nuclear power plants have cast further doubt. Once
seen as the great hope for humanity, producing a cheaper, cleaner power than fossil
fuels, nuclear energy is now seen by many as a threat to the environment.
WHAT IS NUCLEAR ENERGY?
NUCLEAR energy — either in a bomb, a more controlled reaction in a
laboratory or a nuclear power station — is released when atoms are
split or fused together, affecting the nucleus of the atoms and forcing
them to release energy.
The energy released by relatively small amounts of radioactive
material, such as uranium, can be used to heat water, which drives
steam turbines to create electricity, with greater efficiency and fewer
pollutants than fossil fuels. However, it is the waste from the
production of power that is the problem. There are also concerns, that
despite safety measures in nuclear power stations around the world,
accidents have occurred.
WASTE DISPOSAL
THE waste from the production of nuclear energy is highly radioactive
and dangerous to humans and most forms of life, and remains
dangerous for thousands, or in the case of Neptunium-237, millions of
years. Disposing of that waste has become a major global issue. Some
methods have been tried and have failed, including concrete
containers that break down long before the waste becomes safe.
However, in 1978 the Australian Nuclear Science and Technology
Organisation created a “synthetic rock” called Synroc to stabilise and
immobilise the waste.
ATOMIC THEORY
BASED on logic rather than observation, Ancient Greek and Indian
philosophers speculated on all matter being made up of indivisible
particles. The Greeks called these atomom, meaning indivisible.
However, modern atomic theory can trace its origins to the work of
English chemist John Dalton who realised that atomic theory would
help explain some of the laws of chemistry that had been proposed in
the 18th century. After careful experimentation in 1803, Dalton
presented some of his findings. Although some conclusions were
wrong, it spurred others to investigate atoms.
In 1897 English physicist Joseph John Thomson discovered that
atoms were not indivisible but were made up of smaller particles. After
a series of experiments from 1910-11, one of Thomson’s former
students, New Zealand-born, Nobel prize-winning physicist Ernest
Rutherford, proposed a theory that atoms were made up of a large
dense nucleus orbited by smaller electrons.
His model of the atom would later be refined as more was
understood about the structure of atoms and the potential energy
they contained, including the work of German-born physicist Albert
Einstein who, in 1905, proposed his Special Theory of Relativity that
mass was a form of energy (later expressed as E=mc2.)
NUCLEAR REACTION
200 million electron
volts is released by the
decay of one atom. Less
than ½ kg (500g) of highly
enriched uranium (that’s
smaller than a tennis ball) is used
to power a nuclear submarine —
equivalent to the energy of about
4.5m litres of petrol.
A
B
C
D
A neutron hits the nucleus of a uranium atom.
The nucleus splits (fission) into smaller atoms,
releasing heat and several more neutrons.
Each nuclear fission produces gamma
radiation and two or three new neutrons.
Some of these neutrons are absorbed by the
graphite control rods.
While others go on to split further uranium
atoms. The chain reaction has begun.
CONTROL RODS
In order for the reactor to work, the
bundle, submerged in water, must
be slightly supercritical. That means
that, left to its own devices, the
uranium would eventually overheat
and melt.
To prevent this, graphite control
rods that absorb neutrons are
inserted into the bundle. Raising
and lowering the control rods
controls the nuclear reaction.
To produce more heat, the rods are
raised out of the uranium bundle.
To create less heat, they are
lowered into the bundle.
The rods can also be lowered
completely into the uranium bundle
to shut the reactor down in the case
of an accident.
AUSTRALIAN HISTORY
AUSTRALIA entered the nuclear age in 1950 when Australian-born
physicist Mark Oliphant returned from overseas to head up the new
research school of physical sciences and engineering at the Australian
National University in Canberra. Having worked on the Manhattan
Project to develop a nuclear bomb, Oliphant wanted to research
peaceful uses for atomic energy. In 1953, the Atomic Energy Act
established the Australian Atomic Energy Commission (AAEC) to
investigate ways to exploit Australia’s uranium deposits and to set up a
research reactor in Sydney.
The High Flux Australia Reactor (HIFAR) at Lucas Heights, was
officially opened in 1958. Originally, part of its function was to
investigate the establishment of nuclear power stations in Australia,
but that was eventually abandoned. For nearly 50 years the HIFAR
reactor was used for important research, including the environmental
impact of nuclear energy and nuclear waste disposal. In 1987, the
AAEC became the Australian Nuclear Science and Technology
Organisation (ANSTO). In 2007 the HIFAR reactor was shut down and
the OPAL (Open Pool Australian Lightwater) reactor was opened, also
at Lucas Heights.
REACTOR VESSEL
The reactor vessel contains
bundles of fuel and control rods.
Water is pumped into the vessel
and around the rods, acting as
moderator and coolant.
FISSION & FUSION REACTORS
ALL existing nuclear reactors use a process called fission, which
involves splitting the nucleus of an atom. Although possible, the
fusing of atoms to create energy has only been used in bombs.
However, harnessing the fusion reaction for a viable reactor, so far,
is not technically possible. In 1989 scientists claimed to have made a
breakthrough with a process known as cold fusion, where the fusion
reaction takes place at room temperature but they were not able to
reproduce their experiment.
CHERNOBYL
THE world’s worst nuclear accident happened in April 1986 during a
routine test of a cooling system at the Chernobyl power plant in the
Ukraine. When the emergency shutdown failed, the operators lost
control of the reactor in unit No. 4, which resulted in an explosion.
Most of the radiation was released in the first 10 days, but wind and
rain spread it locally and regionally. More than 130,000 people were
evacuated from a 30km zone around the reactor.
By November 1986, a concrete “sarcophagus” had been
constructed to enclose the destroyed reactor.
During the disaster and the immediate aftermath, 31 power station
employees and fire fighters are said to have died. About 100,000
more deaths since have been attributed to radiation. The nearby city of
Pripyat, which was evacuated, remains deserted, a haunting reminder
of the accident 30 years ago.
FUEL ROD
Enriched uranium is
formed into pellets and
arranged into these
long rods.
TIMELINE OF NUCLEAR SCIENCE
New Zealand-born Ernest
Rutherford shows that
radioactivity is a
spontaneous event.
1789
German chemist Martin
Klaproth discovers uranium,
names it after Uranus.
1902
1895
Wilhelm Rontgen produces
X-rays, adding to our
understanding of radiation.
1905
Albert Einstein publishes his
theory on the equivalence
between mass and energy
E=MC2.
1934
1911
Rutherford proposes his
theory that atoms have a
nucleus orbited by electrons.
1935
1896
Henri Becquerel discovers that
pitchblende (an ore containing
radium and uranium) emits beta
radiation. Marie Curie calls the
emissions radioactivity.
1932
James Chadwick discovers
the neutron.
Marie Curie’s daughter, Irene and
her husband Frederic Joliot,
bombard atoms with accelerated
protons and create artificial
radionuclides.
Italian physicist, Enrico Fermi
finds that artificial radionuclides
are formed when using
neutrons, rather than protons.
1939
1939
1941
Otto Hahn and Fritz Strassman
demonstrate atomic fission.
Lise Meitner theorises that severe
vibration leads to the nucleus
splitting into two unequal parts.
They calculate the amount of
energy released from this fission as
200 million electron volts.
US President Roosevelt authorises
research into the development of
atomic weapons.
1942
1945
1945
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