Nuclear Fusion Reactors

me engineers SEPTEMBER 4, 2015 PATRICK LANDY

The rewards of creating a functional nuclear fusion reactor will be enormous. Such a device will generate safe, emission-free energy using fuel derived from water and lithium. This opportunity has intrigued and stumped scientists worldwide for nearly a century, and for good reason.

The conditions needed to sustain the fusion reaction are extreme and complex. The reaction requires the containment of plasma at hundreds of millions of degrees Celsius. During the reaction, isotopes of hydrogen are “fused,” releasing large quantities of heat energy. Building on many decades of work, scientists and engineers around the world are developing experimental fusion reactors, which briefly replicate the same reactions powering the stars in the night sky.

The method of containing the plasma differentiates the many approaches to fusion. Inertial confinement facilities such as the National Ignition Facility attempt to fuse small spheres of hydrogen fuel using high-powered lasers. Magnetic confinement reactors use conductive coils to create a “bottle” of magnetic fields that retain the burning plasma. Popular designs of confinement reactors include signature donut-shaped tokamaks (NSTX, JET and ITER) and twisting, irregular stellarators (HSX and LHD). ITER, the international thermonuclear experiment reactor, aims to be the first tokamak to produce more energy than what is required to run the machine. Construction on ITER began in 2013.

Magnetic confinement reactors are engineering marvels. A reactor usually consists of a metal vacuum-sealed chamber surrounded by racks upon racks of conductive coils, measurement equipment, pipes, cables, power supplies, and cooling system components. In order for an experiment to operate safely, countless systems need to provide heating, cooling, vast quantities of electrical power, vacuum pressure maintenance, and diagnostics. Operational safety concerns include high voltages, heat, and radiation (the fusion reaction can irradiate components on the inside of the chamber).

Despite numerous developing safety requirements, fusion reactors still offer huge safety advantages over nuclear fission reactors. They do not generate radioactive waste, apart from the recyclable components inside the devices themselves. Fusion reactions also have no chance of burning uncontrollably, due to the tiny amount of hydrogen burned at a time. A power failure or fuel interruption would simply stop the reaction. Fusion fuel also cannot be weaponized.

On large scales, fusion energy is an ideal power source. Unlike fossil fuel power plants, a confinement fusion reactor does not generate carbon dioxide or other greenhouse gases. Additionally, the fuel needed to sustain the reaction can be derived from seawater, which is much more abundant than fossil fuels.

Fusion also distinguishes itself from renewable sources of energy such as solar and wind by offering consistency. An industrial scale fusion reactor will reliably and predictably add thousands of MW to an electricity grid, helping to meet demands not satisfied by the intermittent contributions of solar and wind.

So, when can the world expect to add emission-free, safe, renewable fusion energy to its mix? Due to the significant short-term risks of climate change, the answer to this question matters. The brief answer is that scientists and engineers are still decades away from practically producing electricity from fusion. Full scale experiments on ITER are planned for the late 2020’s, and an industrial scale plant called DEMO is expected to follow.

When ITER finally begins to fuse hydrogen, it will make history as one of the largest, most expensive, and most significant scientific undertakings of all time. Fusion, when it becomes practical, may propel mankind into a new abundant energy era, marking the end of the current “oil age.” But in the meantime, scientists, engineers, politicians, and concerned citizens need to make do with existing energy technologies in the fight against the next few decades of global warming.

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