Fusion vs fission: clean, green nuclear energy technologies explained
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Clean, cheap nuclear energy is often touted as a
means to battle climate change. But how close are we to having nuclear
plants that fit the clean, green bill? What are the different
technologies and what do they offer?
More than 10 per cent of the
world's electricity currently comes from nuclear power plants. These
existing plants all rely on nuclear fission — a chain reaction where
uranium atoms are split to release extraordinary amounts of energy and,
unfortunately, high levels of radioactive waste.
But a different
type of nuclear reaction — nuclear fusion — has been the focus of
research to develop nuclear power without the radioactive waste problem.
Nuclear fusion is the reaction that powers the Sun. It involves
smashing hydrogen atoms together under extraordinary temperature and
pressure, fusing them together to form helium atoms and releasing a
large amount of energy and radioactive waste. But unlike fission, this
radioactive waste is short-lived, quickly decaying to undetectable
levels.
Nuclear fusion happens readily in stars like the Sun,
because their cores reach extreme temperatures of over 15 million
degrees Celsius, and pressures billions of times greater than our
atmospheric pressure on Earth.
Fusion reactors would need to
recreate these extreme conditions on Earth, and researchers are using
two different approaches to achieve this: tokamak reactors and laser
fusion.
Tokamak reactors
Separate groups of scientists in
Germany and China have recently announced they have made breakthroughs
in nuclear fusion using tokamak reactors.
Tokamak reactors use a doughnut-shaped ring to house heavy and super-heavy isotopes of hydrogen, known as deuterium and tritium.
Normal
hydrogen — which is also known as protium — consists of a single proton
in its nucleus orbited by an electron. Deuterium differs in that the
nucleus also contains a neutron, and tritium has a proton and two
neutrons in its nucleus.
These isotopes are heated to 100 million degrees Celsius by powerful electric currents within the ring.
At these extreme temperatures electrons are ripped off their atoms, forming a charged plasma of hydrogen ions.
Magnets confine the charged plasma to an
extremely small area within the ring, maximising the chance that the
superheated ions will fuse together and give off energy. The heat
generated can be used to turn water into steam that spins turbines,
producing electricity.
Over 200 experimental tokamaks have been built worldwide, but to date they have all consumed more energy than they produce.
A
massive international tokamak project — the International Thermonuclear
Experimental Reactor (ITER) — aims to turn that situation around.
The
ITER is designed to produce 10 times as much energy as it takes to run,
becoming the first ever net energy producing fusion reactor. It is
currently being built in the south of France, but with the first fusion
experiments scheduled for 2027 it will be some time before we know if
that goal has been reached.
In the meantime, physicists in
Germany are using a variant of the tokamak, known as the Wendelstein 7-X
stellarator. This uses a twisting ring design with changes in geometry
and differing magnetic fields to control the plasma for longer periods
of time compared to the short bursts tokamaks achieve.
Last week,
physicists at the stellarator announced they had created a hydrogen
plasma using two megawatts of microwave radiation to heat hydrogen gas
to 80 million degrees Celsius for a quarter of a second.
At the same time, scientists in China said
they had achieved temperatures of 50 million degrees Celsius (three
times hotter than the core of the Sun) for 102 seconds at their
experimental tokamak fusion reactor called the Experimental Advanced
Superconducting Tokamak (EAST).
Laser fusion
While tokamaks and
stellarators use magnets to confine plasmas, another body of research is
focusing on a different strategy to trigger fusion reactions, using
high-powered lasers.
Laser fusion uses ultra-short bursts of very
powerful lasers to generate the extreme temperatures and pressures
needed to trigger a fusion reaction.
These laser pulses can heat and compress hydrogen isotopes to a fraction of their size, forcing them to fuse into helium and release high-energy neutrons.
The
Lawrence Livermore National Laboratory's National Ignition Facility in
California achieves deuterium–tritium nuclear ignition using a laser
producing over two million joules of energy in a sudden pulse lasting
just one nanosecond (one thousand millionth of a second).
The
downside to laser fusion systems using deuterium and tritium is that
they still produce high-energy neutrons (neutron radiation) which can
cause other materials to become radioactive.
Nuclear fusion power could be a reality in 10 to 15 yearsEmeritus Professor Heinrich Hora
An alternative laser fusion method being developed by
scientists including Emeritus Professor Heinrich Hora of the Department
of Theoretical Physics at the University of New South Wales, uses normal
hydrogen protons and the commonly found element boron 11.
Instead
of high-energy neutrons, hydrogen–boron 11 (HB11) fusion produces an
avalanche of helium nuclei, resulting in extremely low levels of
radioactivity — less even than produced by burning coal.
"Every
HB11 reaction produces three helium particles, each of which collide
with more boron to produce another three reactions and so on," said
Professor Hora.
The HB11 process requires two lasers, the first to
generate a powerful magnetic confinement field in a coil to trap the
fusion reaction in a small area for a nanosecond, while a second more
powerful laser triggers the nuclear fusion process.
"The
triggering laser provides an extremely short duration pulse of just a
picosecond, which is a millionth of a millionth of a second, and a
thousand times shorter than the [nanosecond pulse] lasers at Lawrence
Livermore," said Professor Hora.
Picosecond pulses achieve fusion
through electrodynamic forces — directly converting optical laser energy
into mechanical motion — smashing the target material together to
trigger fusion.
Professor Hora says early HB11 fusion trials at
the Prague Asterix Laser System, using high-energy iodine lasers, have
generated more energy than needed to trigger the fusion process.
"For
every joule of energy put into the fusion process by the lasers, the
HB11 reaction generates 10,000 joules," says Professor Hora.
"Nuclear fusion power could be a reality in 10 to 15 years."
The thorium wildcard
With
the goal of clean energy in mind, the focus isn't only on nuclear
fusion. A cleaner form of nuclear fission is the subject of research
around the globe.
Existing nuclear power stations rely on fission,
using uranium 235, which is unstable and readily loses neutrons. These
neutrons collide with other uranium atoms, splitting them and causing
further collisions with even more uranium atoms in a chain reaction.
But all these high-energy neutrons result in large amounts of radioactivity.
Thorium fission reactors — first developed in the 1950s — could be a cleaner alternative.
Thorium
is lighter than uranium, it doesn't undergo fission, and can't create
runaway meltdown like uranium. Instead a seed of uranium or plutonium is
injected into the thorium fuel, or a particle beam is fired at it to
kick things off.
The process involves thorium 232 atoms being
bombarded with neutrons to produce thorium 233 atoms, which quickly
decay into protactinium 233, and then uranium 233, which undergoes
fission similar to current nuclear power plants.
Unlike uranium
235, which creates self-sustaining chain reactions, thorium reactors
only work as long as you keep firing neutrons, giving them an automatic
failsafe to prevent meltdown.
Thorium reactors also produce just a
fraction of the radioactive waste of conventional nuclear power
stations, they aren't suitable for making weapons grade material, and
can even be used to consume existing nuclear waste as a fuel source.
Thorium is three times as abundant as uranium, with Australia having the world's largest known reserves.
The
United States, India, Israel, the United Kingdom, China, Norway, Chile
and Indonesia are all examining thorium nuclear reactor projects.
Topics:
nuclear-energy,
research,
science-and-technology
ASX: Australian shares fall by $36 billion in global slump
Australian shares have lost $36 billion, following steep falls on Wall Street and across Europe.
Key points
- ASX 200 index down 2.4 per cent in morning trade
- Banks and most resources stocks lower, gold miners surge
- Australian dollar holds steady at 70.7 US cents
The benchmark ASX 200 index was down 2.4 per cent at 4,857
points by 11:18am (AEDT), while the All Ordinaries was 115 points lower
at 4,907.
That followed declines of 1.4 per cent on Wall Street and between 2.7 to 4.7 per cent on the major European markets.
The market heavyweight banks and miners again led the major indices lower.
NAB
has been hammered, falling 4.3 per cent in early market action, while
ANZ was down 3.5 per cent, Westpac off 3.3 per cent and the Commonwealth
Bank losing 2.6 per cent to $74.43.
Regional institution Bank of Queensland slumped 6.6 per cent after warning of funding pressures and a corporate restructure, while Bendigo and Adelaide Bank was down 4.4 per cent to $9.83 and investment bank Macquarie was off 3.9 per cent to $60.73.
Until [a sharp sell-off and strong rebound] comes there will be no clarity, absolutely no confidence and a bucket load of concern.Chris Weston, IG Markets
The major miners were again a drag on the market: BHP Billiton
was down 3.4 per cent to $15.84, Rio Tinto was 0.7 per cent lower,
Fortescue down 2.1 per cent and South32 had fallen 4.6 per cent to
$1.12.
The energy sector was also being sold off after West Texas crude plunged back below $US30 a barrel overnight.
Woodside
was 2.7 per cent lower at $26.67, Santos down 5.3 per cent, Origin off
3.9 per cent and Oil Search had fallen 2.2 per cent to $6.75.
The
rare winners on today's market were mainly gold miners - Newcrest was up
8.25 per cent to $16.80 after spot prices rose again to $US1,191 an
ounce, the highest prices since June.
JB Hi-Fi also bucked the downward trend, rising 1.3 per cent, following its report yesterday of a 7.5 per cent rise in first-half profits.
IG's
chief market strategist Chris Weston said markets are being pummelled
on serious doubts about the outlook for the global economy and strength
of major financial institutions, such as Deutsche Bank.
We saw pretty steep declines for leading financial names. Goldman Sachs shares had their biggest fall in six years.Tom Piotrowski, CommSec
"For those who have traded the overnight move it almost feels
like something big is brewing, similar to August 24 and the quasi-flash
crash capitulation move we saw," he cautioned.
"These markets need
a strong shake up and sharp downside move, followed by a wave of buying
to settle things down, but until that comes there will be no clarity,
absolutely no confidence and a bucket load of concern."
Deutsche
Bank shares fell around 8 per cent overnight, and CommSec market analyst
Tom Piotrowski said that sell-off spread to other banks.
"Similarly
on Wall Street, we saw pretty steep declines for leading financial
names. Goldman Sachs shares had their biggest fall in six years," he
told ABC News 24.
"There is something of a unifying theme
throughout the markets around the world. That is why the domestic banks
are under such pressure."
The Australian Stock Report's head of research, Chris Conway, agreed that something nasty is brewing.
Media player: "Space" to play, "M" to mute, "left" and "right" to seek.
"Without being dramatic, this feels a little
different. The S&P 500 closed below key support at 1,870 in the US
overnight - an extremely important technical level," he wrote in a note
after the local market opened.
While much of Asia is closed for
the Lunar New Year holiday, Japan's Nikkei had slumped 4.5 per cent
shortly after midday (AEDT), with US dollar weakness pushing the yen to
its highest level against the greenback in more than a year, a big blow
to Japanese exporters.
The Australian dollar had managed to
resist the equity market and commodity sell-off overnight, but started
falling close to midday, reaching 70.4 US cents despite US dollar
weakness.
The local currency had slumped to 62.8 euro cents, 81 Japanese yen and 48.7 British pence.
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