Nuclear Fusion, the Ultimate Power Source

What’s Good about Nuclear Fusion?

The ultimate energy source, safe, clean and virtually limitless:

1 kilogram of hydrogen fusion fuel = 10,000 tonnes of coal, a ratio of 1: 10 Million

It is available 24/7, so way better than solar, wind, hydrogen, etc. However, producing it is difficult and it may be a long way off. But numerous commercial companies and research organisations are experimenting in hundreds of trials, as the potential rewards are enormous.

What is Nuclear Fusion?

It Powers the Sun & Stars

Our sun’s size and power are extremely large. It consumes 620 million tonnes of hydrogen each second to provide light and heat, yet is about 4.6 billion years old. It is stable, apart from some occasional flares or spots and sustains itself. But don’t worry, it will probably be around another 10 billion years!

What does it do with all that hydrogen every second? Convection currents carry fresh supplies of the sun’s hydrogen into its core, a reaction zone where it it is broken into protons (the nuclei) and  electrons. The protons fuse together to form heavier helium. In addition, already fused material fuses again, creating multiple heavier elements from hydrogen up to iron. This provides the heat and light to keep us alive. Without the sun, there would be no us.

Back to Earth

We will refer to the human equivalent simply as ‘fusion’. It creates power, as like the sun, hydrogen atoms fuse together to form helium, producing huge energy. While the Hydrogen bomb is a fusion reaction, the material in a fusion power plant cannot be weaponised. The cost of the experimental plants is understandably high, but commercial plants are expected to be reasonable for the huge benefits gained. Operational cost is very low.

But fusion is not nuclear fission which powers our existing nuclear power stations. Alas, fission has problems, such as radioactive waste disposal and possible runaway meltdown, e.g., Chernobyl, Fukushima and 3 Mile Island. The material is a target for terrorists to make an atomic bomb.

The Problems

Fusion fuel, isotopes of hydrogen, deuterium (D) and tritium (T), must be heated to around 50 million degrees C, hotter than the sun’s core. It keeps stable only under intense pressure, confined for long enough so the nuclei fuse. These nuclei are positively charged and repel each other. So to create fusion, large forces are needed to overcome this repulsion.

‘Ignition’ occurs once enough fusion reactions become self sustaining. Small amounts of fresh fuel (unlike the sun, adding its own in situ hydrogen) are added so the process continues. Once ignition occurs, the energy is about 4 x that of nuclear fission. The power is proportional to pressure squared, so 4 x the pressure produces 16 x the energy.

How is the Heat Generated?

By external heating. Neutral beam injection and high frequency electromagnetic waves create rapid nuclear collision, transferring their heat energy to the hydrogen nuclei.

How is the Heat Contained?

Intense magnetic fields keep hot hydrogen particles in the centre of a vacuum vessel, the shape of a bottle with no ends. This keeps them from contact with the walls of the machine, which would otherwise melt.

What Generates High Pressure?

Magnetic fields provide it. MIT in the US has achieved record high pressure and temperature in their fusion experiments.

Is it Safe?

If anything major goes wrong, fusion just stops and the only waste is a small amount of helium, an inert, useful gas. There are some known operating problems to be addressed, but are surmountable.

Input Fuels

1 unit input of hydrogen fuel produces around 10 times the output in energy. This means 1kW of fuel outputs to 10kW of power. A fusion reactor uses this heat energy to drive conventional electric generators.

Of the 2 hydrogen isotopes, deuterium is abundant in sea water and readily available. However tritium is rare, less than 20Kg in the world, but can be ‘bred’ and long term availability is not a concern. If it does become unavailable, other isotopes can be used.

This Video is Quirky but Enlightening

 

Present Status of Fusion Development

Because of practical difficulties, a functional model has been repeatedly predicted as ’30 years away’. But the hope is a working model by 2025. This model, known as Tokamak type (Russian: Токамáк, a toroidal apparatus for producing controlled fusion reactions), is being built in southern France, by ITER (International Thermonuclear Experimental Reactor). It is funded by the EU, China, India, Japan, Russia, South Korea and the US.

Older fusion experiments used more input power than output! The Tokamak will use 50 MW input for 500 MW (500,000 kW) output.  It will demonstrate feasibility, but will not be continuous, lasting only in pulses of 400 to 600 seconds. Other large scale trials are being built, the main one being Inertial Confinement Fusion (ICF). It creates fusion by firing multiple lasers concurrently at the hydrogen fuel pellet

Predicting when large working fusion plants will be a reality? One or several decades? Probably sooner than we think.

ITER experimental Tokamak fusion plant in Provence, France