- 4470 - NUCLEAR ENERGY - will it work? In December 2022, after more than a decade of effort and frustration, scientists at the US National Ignition Facility (NIF) announced that they had set a world record by producing a fusion reaction that released more energy than it consumed — a phenomenon known as “ignition”.
--------------------------------- 4470 - NUCLEAR ENERGY - will it work?
- The stadium-sized laser facility, housed at
the Lawrence Livermore National Laboratory (LLNL) in California, has achieved
its goal of ignition in four out of its last six attempts, creating a reaction
that generates pressures and temperatures greater than those that occur inside
the Sun.
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- The NIF was designed not as a power plant,
but as a facility to recreate and study the reactions that occur during
thermonuclear detonations after the United States halted underground weapons
testing in 1992. The higher fusion yields are already being used to advance
nuclear-weapons research, and have also fueled enthusiasm about fusion as a
limitless source of clean energy.
-
- The NIF works by firing 192 laser beams at
a frozen pellet of the hydrogen isotopes deuterium and tritium that is housed
in a diamond capsule suspended inside a gold cylinder. The resulting implosion
causes the isotopes to fuse, creating helium and copious quantities of
energy. December, 2022, those fusion
reactions for the first time generated more energy , roughly 54% more, than the
laser beams delivered to the target.
-
- The facility set a new record when its beams
delivered the same amount of energy to the target, 2.05 megajoules, but, this
time, the implosion generated 3.88 megajoules of fusion energy, an 89% increase
over the input energy.
-
- Tiny variations in the laser pulses or
minor defects in the diamond capsule can still allow energy to escape, making
for an imperfect implosion, but the scientists now better understand the main
variables at play and how to manipulate them.
We can still get more than a megajoule of fusion energy.
-
- It’s a long way from there to providing
fusion energy to the power grid, however, and the NIF, although currently home
to the world’s largest laser, is not well-suited for that task. The facility’s
laser system is enormously inefficient, and more than 99% of the energy that
goes into a single ignition attempt is lost before it can reach the target.
-
- Developing more efficient laser systems is
one goal of the DOE’s new inertial-fusion-energy research program. So far, most government investments in
fusion-energy research have gone towards devices known as “tokamaks”, which use
magnetic fields inside a doughnut-shaped ‘torus’ to confine fusion reactions.
-
- NIF latest series of experiments features a
7% boost in laser energy, which should, in theory, lead to even larger yields.
The first experiment in this series was one of the successful ignitions although it didn’t break the record, an input
of 2.2 megajoules of laser energy yielded an output of 3.4 megajoules of fusion
energy.
-
- Costing US$3.5 billion and housed at
Lawrence Livermore National Laboratory in California, the NIF was designed to
bolster nuclear-weapons science. Advances there could also help to develop
nuclear fusion as a safe, clean and almost limitless source of energy.
-
- The NIF’s ignition had been a decade behind
schedule, and some feared that it was beyond reach. The facility’s 192 laser beams delivered
2.05 megajoules of energy to a frozen pellet of the hydrogen isotopes deuterium
and tritium, suspended in a gold cylinder. The resulting implosion caused the
isotopes to release energy as they fused into helium, generating temperatures
six times hotter than the core of the Sun. The reactions produced a record 3.88
megajoules of fusion energy.
-
- Other facilities have generated more fusion
energy over longer periods of time, most notably in tokamak reactors, which use
powerful magnetic fields to confine fusion reactions. This is the technology
under development by the $22-billion ITER project, an international
collaboration near Saint-Paul-lez-Durance, France. Before the NIF’s
achievement, however, no lab had produced a fusion reaction that generated more
energy than it had consumed.
-
- January 2024, pioneering nuclear-fusion
reactor shuts down: what scientists will learn
The decommissioning of the
Joint European Torus near Oxford, UK.
Scientists have begun to decommission one of the world’s foremost
nuclear-fusion reactors, 40 years after it began operations. Researchers will
study the 17-year process of dismantling the Joint European Torus (JET) near
Oxford, UK, in unprecedented detail and use the knowledge to make sure future
fusion power plants are safe and financially viable.
-
- Harnessing the fusion of atoms, the process
that powers the Sun, could provide humans with a near-limitless source of clean
energy. Creating the conditions for fusion in power plants and exploiting the
resulting energy will require complex engineering that hasn’t yet been proved,
meaning that commercial fusion power is still many decades away.
-
- But researchers are pushing ahead with
designs for the first commercial reactors as excitement about fusion grows. In
2022, JET smashed the record for the amount of energy created through fusion.
And the US National Ignition Facility (NIF) in Livermore, California, the
flagship US fusion facility, now routinely generates more energy from a fusion
reaction than was put in.
-
- The NIF calculations do not include the
entire energy requirements of running the facility, which fusion plants would
need to exceed to truly ‘break even’, but physicists have celebrated the
milestones.
-
- JET is important because the facility is a
test bed for ITER, a US$22-billion fusion reactor being built near
Saint-Paul-lez-Durance, France, which aims to prove the feasibility of fusion
as an energy source in the 2030s. Jet has informed decisions on what materials
to build ITER with and the fuel it will use, and it has been crucial to
predicting how the bigger experiment will behave.
-
- The thorniest part of decommissioning the
JET site will be dealing with its radioactive components. The process of fusion
does not leave waste that is radioactive for millennia, unlike nuclear fission,
which powers today’s nuclear reactors. But JET is among the tiny number of
experiments worldwide that have used significant amounts of tritium, a
radioactive isotope of hydrogen.
-
- Tritium, which will be used as a fuel in
future fusion plants including ITER, has a half-life of 12.3 years, and its
radiation, alongside the high-energy particles released during fusion, can
leave components radioactive for decades.
-
- Decommissioning a fusion experiment doesn’t
have to mean “bulldozing everything within sight into rubble and not letting
anyone near the site for ages. Instead,
engineers’ priorities will be to reuse and recycle parts. This will include
removing tritium where possible. This
reduces radioactivity and allows tritium to be reused as fuel.
-
- JET and ITER are both ‘tokamak’ reactors,
which confine gas in their doughnut-shaped cavities. JET uses magnets to
squeeze a plasma of hydrogen isotopes, ten times hotter than the Sun, until the
nuclei fuse.
-
- The last time the fusion community
decommissioned a comparable device was in 1997, when the Tokamak Fusion Test
Reactor at Princeton Plasma Physics Laboratory in New Jersey shut down. Many
parts, such as the equipment for injecting hot beams of gas into the reactor,
were reused, as was the site itself. But the tokamak had to be filled with
concrete, cut up and buried.
-
- JET engineers will use a newly refurbished
robotic system to remove sample tiles for analysis. And they will use remotely
operated lasers to measure how much tritium is in samples that remain inside
the experiment. Like hydrogen, tritium is a gas that “penetrates all materials,
and we need to know exactly how deep the tritium has penetrated.
-
- To extract the tritium from metals,
engineers will heat the components in a furnace before capturing the released
isotope in water. Tritium can be removed from water and turned back into fuel;
leftover materials become low-level waste, the same classification given to
radioactive waste made by universities and hospitals.
-
- Some unaffected parts of JET, such as
diagnostic and test equipment, have already been repurposed in fusion
experiments in France, Italy and Canada.
In its final experiments last Decembers scientists explored inverting
the shape of the plasma in a way that might more readily confine heat.
-
- They also deliberately damaged the facility
by sending a high-energy beam of ‘runaway’ electrons — produced when plasma is
disrupted — careering into the reactor’s inner wall. Analysis of the damage, after the machine is
opened up, will provide useful data to test the detailed predictions.
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May 17, 2024 NUCLEAR
ENERGY - will it work? 4470
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