Lockheed claims that they can have a working prototype of a fusion reactor in five years, and commercially available fusion power plants in ten years.
More incredibly, Lockheed claims that the reactor could be as small as seven by 10 feet -- small enough to fit on the back of a truck. A fusion-powered submarine could stay submerged indefinitely, getting its fuel (hydrogen) and air (oxygen) from seawater. A fusion-powered airplane could stay aloft for months.
Fission-powered subs can already stay submerged for months at a time. And practically speaking, aircraft require routine ground maintenance to avoid falling out of the sky. Where fusion is the real game-changer, though, is in generating electricity and spaceflight.
Generating Electricity
Lockheed says its fusion reactor could be plopped into existing 100 MW gas turbine power plant, replacing the methane-burning equipment with a fusion reactor and a heat exchanger.
Current nuclear reactors use fission, in which atoms of heavy elements like uranium are split to produce heat, which generates steam, which spins turbines to make electricity. The atomic bombs dropped on Japan used fission. The hydrogen bombs first detonated in the 1950s were fusion bombs: the intense heat and pressure required to fuse hydrogen atoms were produced by detonating fission devices.
Fission produces a lot of highly radioactive elements, such as plutonium, which need to be sequestered for thousands of years. Fission also produces high-speed neutrons (which is what causes fission reactions to proceed). If there are too many neutrons, the nuclear reaction can run away and detonate like an atomic bomb.
There are two major approaches to fusion for power generation: inertial confinement and magnetic confinement. The National Ignition Facility at Lawrence Livermore National Laboratory uses inertial confinement: giant lasers blast a pellet of hydrogen isotopes from all directions to produce high pressure and temperature.
The concept of magnetic confinement gained popular currency with Star Trek's "magnetic bottle," which they said contained antimatter. With fusion, magnetic fields are used to compress hydrogen plasma to very high pressures and temperatures, causing the atoms to fuse.
The sun does this using gravity instead of magnetic fields.
Both inertial and magnetic confinement fusion have been demonstrated in labs, but they have not achieved a sustained reaction, where they generate more energy than they consume.
Depending on exactly which reaction is used, fusion may use isotopes of hydrogen (deuterium and tritium) and produce harmless helium, or it may produce short-lived radioactive isotopes such as tritium (hydrogen 3). It typically produces neutrons, which have to be trapped to convert their energy to heat.
Magnetic confinement has been on the cusp of a breakthrough for fifty years. This time, Lockheed thinks that by reducing the size of the hardware and increasing the strength of the magnetic field with superconductors they will finally be able to make magnetic confinement work.
Revolutionizing Spaceflight
Rockets work on Newton's Third Law of equal and opposite reaction. They burn fuel, which is ejected out the nozzle, propelling the payload forward. The acceleration you achieve depends on the mass ejected and its velocity: the faster the propellant is ejected (specific impulse), the faster you go.
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| Hohmann Transfer Orbit |
Because our spacecraft require this "Hohmann transfer orbit," we only launch when the planets are properly aligned. That imposes a launch window that lasts a short time and doesn't recur for months or years.
"Ion" engines with higher specific impulse have been in design for decades. These use electrical fields to accelerate charged particles to speeds much higher than can be obtained by chemical rockets. The high specific impulse allows the ion engine to fire constantly, producing a constant thrust with a modest amount of propellant.
A fusion engine could produce an even higher specific impulse, with the speed of light being the only limit. With such a high specific impulse, it becomes possible to accelerate constantly at high thrust without running out of propellant.
It's within the realm of possibility that a fusion-powered spacecraft could get to the moon in a day by accelerating constantly at 1 g (the acceleration of earth's gravity) to the halfway point, flipping around and decelerating the rest of the way. Getting to Mars would take two to four days, depending on where earth and Mars are in their orbits.
Will It Melt Down or Blow Up Like a Hydrogen Bomb?
Fission reactors can melt down, like Chernobyl in Russia or Fukushima in Japan. They depend on control rods, cooling or other mechanical means to prevent the fission reaction from occurring too quickly. A fission reactor contains tons of uranium. If too many neutrons are being shot through the nuclear fuel, there's a chance of a runaway reaction and an atomic detonation, or more likely, that the fuel will get too hot and melt through the containment vessel.
With fusion, the difficulty is not slowing down the reaction, the problem is sustaining it. The amount of hydrogen in a fusion reactor is quite small. That's because fusion produces so much energy: e = mc2, after all. One gram of hydrogen produces 339 gigajoules of energy, or 94 megawatt-hours. That means a 100 MW fusion reactor would use a couple of grams of hydrogen per hour: that's a couple of ounces a day. (It's also probably a hydrogen isotope -- deuterium and tritium, from heavy water.)
If something goes wrong in a fusion reactor, the magnetic field collapses, and the reaction stops. All that's left is a few ounces of hot hydrogen.
To stop a fusion reaction, you turn of the power. It's like blowing out a candle. The containment vessel does, however, need to be strong enough to contain the hydrogen plasma when the magnetic field drops.
A fusion reactor is probably a lot less dangerous than a fission reactor, but more dangerous than wind and solar because reactor cores become radioactive over time.
Drawbacks
Most magnetic confinement fusion reactions under consideration produce neutrons. Something needs to absorb those neutrons, heat up and turn turbines. Over time neutrons will affect the components of the reactor and its shielding, making them brittle and slightly radioactive, just as for existing fission reactors.
Some fusion reactions under consideration produce a radioactive isotope of hydrogen (tritium, or hydrogen 3), which has a half-life of 12.3 years. Tritium and old shielding have to be disposed of, but they're far less dangerous than fission byproducts like plutonium that are radioactive for millennia.
For spaceflight, these fast neutrons are reaction mass: the faster the better.
Is It for Real?
This is hard to say. Scientists have been on the brink of a fusion breakthrough for fifty years. They've used superconducting magnets in the past. Is Lockheed's approach that different? Have they miniaturized the reactor enough to remove the instabilities in the magnetic field that have plagued traditional tokamak designs for decades?
I can't say for sure. But this has the potential to totally change everything about energy production. With cheap, portable fusion reactors coal and natural gas plants will be totally obsolete: fuel for fusion is extracted from seawater. There's no need for miners to die miles beneath the surface of the earth, or for frackers to inject toxic chemicals into the earth.
Fusion plants will probably not be cheap initially, especially compared to wind and solar which are already becoming cheaper than coal and gas. Extracting deuterium and tritium from seawater will probably start out to be expensive and get cheaper over time, but will probably always be more expensive than free energy from the wind and sun.
Fusion is not a panacea because there is still the problem of disposing of radioactive reactor cores. But these are minor problems compared to radioactive waste from fission plants, and the CO2 emitted by burning fossil fuels.
That does make fusion plants good candidates to pick up the slack when wind and solar generation are slack.
And having the technology in our back pockets that allows us to go to the stars is probably the best insurance plan the human race can get.
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