Innovations  

Building a Power-Producing Fusion Reactor

The construction challenges facing this revolutionary form of energy production
 Nuclear reactors are complex, challenging facilities
 
 

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On July 16th, 1945, the detonation of precisely-placed high explosives inside a device dubbed ‘the gadget’ created incredible pressures that, converging on a small piece of plutonium suspended in its center, released unprecedented explosive forces and propelled the world into the atomic age. The ‘Trinity’ test in White Sands, New Mexico was the first occurrence of man-made nuclear fission, which would spawn a class of civilization-ending weapons and one of the most controversial forms of energy production ever devised.

Nuclear fission – the splitting of atoms – not only unleashes incredible destructive power, but also creates radioactive byproducts that remain dangerous for eons of atomic half lives. As a form of power, the operating costs, as well as the toll on the biosphere, drastically reduces the attractiveness of one of humanity’s most important, and monstrous, achievements.

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Nuclear fusion, in contrast, is the joining together of two or more atomic nuclei to create heavier elements, which also releases enormous energies. The byproducts of a fusion reaction, however, are far more stable than their fission counterparts – though the process does create a high number of fast neutrinos that radiate containment materials. Leapfrogging over important but technical specifics, radioactive byproducts from nuclear fusion would remain dangerous for a mere 50-100 years, as opposed to the thousands of years from fission. In addition, the fuel sources for fusion (typically hydrogen) are bountiful and virtually endless, as opposed to the difficult-to-obtain isotopes necessary for fission reactions.

So what’s the holdup? It’s been over 60 years since fusion was used to detonate the world’s first hydrogen bomb, yet fusion has not become a mainstream source of energy production as with fission. The truth is, we’ve been experimenting with power-producing fusion for over a half century, but have yet to create a system where the output exceeds the energy input. The incredible temperatures needed to sustain nuclear fusion, as well as a number of other factors, means that net-positive fusion reactions are still confined to the center of stars – for now.

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Two main methods are being investigated for viable fusion power – magnetic containment and inertial containment. Magnetic containment devices use a unique characteristic of plasmas (fully ionized gases) – their electrical conductivity – to create powerful magnetic fields around the plasma field, which creates a strong inward pressure. This, in turn, increases the density of the plasma, creating denser magnetic fields, which leads to stronger inward pressures – a chain reaction that ideally culminates in a fusion reaction of the gas. A device for this process would have to withstand incredibly high pressures and temperatures – over 150 million degrees Fahrenheit – while also absorbing the stray neutrinos that bounce off the containment walls, cool down, and thereby lower the temperature of the reaction and ruin its efficiency. The most advanced experiments today have only produced 65 percent of the energy required to sustain the reactions.

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The ITER (International Thermonuclear Experimental Reactor) in the south of France is a $15 billion trial of this type of reactor, which broke ground in 2007. Scheduled to be fully operational by 2019, the facility is designed to produce 500 megawatts of output for every 50 megawatts of input – or a ten-fold increase. Three interconnected cooling systems, two water and one liquid nitrogen, will dissipate 450 megawatts of power during peak usage.

Inertial confinement techniques have their own construction challenges. Using a system of high-powered lasers, inertial containment fusion (ICF) compresses and heats a small pellet of hydrogen fuel to reach ‘ignition’ – a state of sustained implosion that produces more energy than is put in. The National Ignition Facility, completed in 2009, is the United States’ experimental facility for ICF, and uses some of the world’s largest lasers in the pursuit of igniting a hydrogen source. As of March 2012, the facility has successfully shot 1.875 million joules, but has yet to achieve sustained fusion.

The incredible temperatures, precise physics, radioactive containment and extreme energies required and produced by fusion reactors present incredible construction challenges to the nations and international organizations pursuing the commercialization of fusion-based power. As ITER continues to rise and the NIF ramps up its experiments, a world wrought with worries of global warming and diminishing fossil fuels waits with growing anticipation for a successful, and less destructive, application of the power of the atom.

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