Nuclear fusion offers a completely clean method of producing vast amounts of energy. So far the major stumbling block for scientists has been creating a controllable fusion reaction that achieves “net gain”, meaning it gives off more energy than is needed to trigger it. But Canadian startup, General Fusion, is claiming it can build a relatively low-tech prototype nuclear fusion power plant within the next decade for less than a billion dollars.
Fission and fusion
For decades now billions of dollars have been funneled into research looking at a way to build a practical fusion reactor for electricity production. Unlike nuclear fission, the process used in current nuclear power stations where atoms are torn apart to release energy and highly radioactive by-products, nuclear fusion instead involves squeezing two "heavy" hydrogen atoms, called deuterium and tritium, together so they fuse, producing harmless helium and vast amounts of energy.
Scientists around the world are approaching the problem of practical fusion energy from a number of different fronts. Some focus on powerful lasers, while others are looking at expensive superconducting magnets called tokamaks in what is known as Magnetized Target Fusion (MTF). The team at General Fusion are using the MTF approach, but with a new system that they claim is more cost effective.
MTF is a relatively new approach that combines features of the more widely studied magnetic (MCF) and inertial (ICF) approaches. It confines the fusion fuel at low density by magnetic fields while it is heated into plasma, like the MCF approach, and initiates fusion by rapidly squeezing the target in order to dramatically increase the density of the fuel, and thus its temperature, like the inertial approach.
The MTF approach in detail
General Fusion’s variation on the MTF approach involves building a metal sphere about three meters in diameter that will be filled with liquid metal consisting of a lead-lithium mixture. This liquid is spun to open up a vertical cylindrical cavity or vortex in the center of the sphere. Two self-contained magnetized plasma rings composed of deuterium-tritium fuel called spheromaks are then injected into each end of the cavity and merge in the center to form a single magnetized target.
The outside of the sphere is covered with pneumatic rams, which use compressed gas to accelerate pistons to around 50 m/s. These pistons simultaneously impact a set of stationary anvil pistons at the surface of the sphere, which collectively launch a high-pressure spherical compression wave into the liquid metal.
As the wave travels and focuses towards the center, it becomes stronger and evolves into a strong shock wave. When the shock arrives in the center, it rapidly collapses the cavity with the plasma in it. At maximum compression the conditions for fusion are briefly met and a fusion burst occurs releasing its energy in fast neutrons.
The neutrons are slowed down by the liquid metal causing it to heat up. A heat exchanger transfers that heat to a standard steam cycle turbo-alternator to produce electricity for the grid. Some of the steam is used to run the rams. The lithium in the liquid metal finally absorbs the neutrons and produces tritium that is extracted and used as fuel for subsequent shots. This cycle is repeated about one time per second.
Global Fusion say their mechanical brute force approach using low-tech pneumatic rams in place of intrinsically expensive high power pulsed electrical systems reduces the cost of the energy delivered to the plasma by a factor of 10 making such a power plant commercially competitive against the cheapest fossil fuel.
The pumping system that creates the vortex flow also provides a natural means to extract the fusion-heated liquid metal and run it through a heat exchanger to drive a turbine and produce electricity. Unlike other pulsed fusion concepts, with the General Fusion design no structural elements are destroyed during the fusion pulse. This enables rapid pulse repetition rates and low cost of operation since the direct cost of each pulse is only the cost of the fuel that is burned.
General Fusion is in the process of patenting this technology and believes that a reactor working on this principle could be built at a much lower cost than using the conventional magnetic and laser fusion approaches. Such a power plant would make fusion a commercially viable clean power source.
The road ahead
General Fusion intends to create a nuclear fusion reactor in three phases. They have just completed phase one, which saw the construction of a small machine to demonstrate the feasibility of their approach. Phase two, which is expected to take four years, will see the construction of an experimental reactor that will produce enough fusion reaction to achieve break-even. Finally, in phase three, General Fusion will concentrate on turning the prototype into a real, cost-effective and reliable generator.
General Fusion has already raised USD$13.5 million from public and private investors, but is hoping to raise an additional $37 million to kick start phase two of their plan. If their test reactor is successful it hopes to attract enough attention to easily raise the USD$500 million it will need to construct a grid-capable demonstration plant rated at 100 megawatts.
If General Fusion’s approach can deliver on its promise, then USD$500 million would indeed be a bargain price tag for a source of virtually limitless, environmentally friendly power.
Check out the vid below for the General Fusion technique explained by General Fusion's Dr. Michel Laberge.