Nuclear Fusion Power Source of the Future?

Nuclear fusion – power source of the future?

For the past 4.6billion years the Earth has received a free source of energy that now powers the majority of biological processes. This source of energy, the Sun, has a diameter of 1,392,000km, ca. 109 times that of Earth, and a mass (ca. 2 × 1030 kilograms) 330,000 times that of Earth. The volume of the Sun could hold over 1.3million Earths. It accounts for about 99.86 % of the total mass of the Solar System. The source of this energy is nuclear fusion (the Sun is effectively a giant fusion reactor). All atoms in the universe heavier than hydrogen and helium were created by fusion processes in stars like the Sun. Scientists are looking at whether this form of energy could be used to solve the Earth’s energy problems. Not only will this energy supply continue to power life processes on Earth for billions of years to come, but this form of energy also holds the potential to provide all the Earth’s energy needs for perpetuity. Nuclear fusion power offers:

· Plentiful fuel

At an appropriate scale that can meet mankind’s long-term needs.

· Energy security

The main fuel source is found in seawater.

· Clean energy

Fossil fuels are not involved and so there are no greenhouse gas emissions. The technique does not result in long-lived radioactivity.

· Safe operation

Energy is not stored and so there is no chance of ‘meltdown’ or catastrophic failure.

On a planet that is increasingly facing serious issues regarding climate change and pollution, rising demands on natural resources, and where energy security is an increasing problem for many countries, nuclear fusion offers a long-term sustainable solution. Investigation into the technology that will make energy supply through nuclear fusion a possibility is still at an early stage, and concentrated research and development effort will be needed to make it a reality.

What is nuclear fusion?

The fuel for nuclear fusion reactors are lithium and two isotopes of hydrogen: deuterium (which is very common – found in seawater) and tritium (very rare – for every 1017 of hydrogen there is only one tritium. It is not found naturally and must be created, although fortunately it is created in a closed cycle as part of the fusion process).

Nuclear fission involves the splitting of atoms, whereas fusion involves combining them. In the fusion process, deuterium and tritium fuse to produce helium and a neutron. In this process, mass is lost which releases lots of energy (from Einstein’s equation e = mc2). For fusion to work repulsion between atoms needs to be overcome – once close enough, nuclear strong forces (strong attractive forces responsible for holding atoms together) take over which allow fusion to take place. For these repulsion forces to be overcome, atoms need to be heated to 100million degrees centigrade. In this process, a plasma is formed (the 4th state of matter after solid, liquids, and gases), of which 99.999% of all material in the universe is made of (in daily life, strip light is an example of a plasma).

How would a nuclear fusion power plant work?

A power plant would be made of two components – a powerful laser that causes the fusion to occur and a turbine that generates electricity. This form of energy generation is nuclear inertial fusion using a laser.

The laser

· Lasers would be fired concentrically around a small core containing deuterium and tritium – the core would be cryogenically cold so that atoms are more likely to move together and fuse (if hot they are more likely to move apart). This compresses the fuel.

· An ignition laser would be fired through a cone – this causes plasma to form and intense heat is generated (100million degrees Celsius).

A mini star is created – the neutrons release energy that passes into a heat exchanger.

The turbine

· The heat exchanger heats water that drives a turbine – the turbine generates electricity (in the same way as energy is generated by fossil fuel plants and nuclear fission – see textbook page 113).

For energy generation to be financially viable, there needs to be net energy gain (more energy produced than used).

Interesting facts
Using nuclear fusion, 1km2 of seawater would generate the same amount of energy as the whole of the world’s oil reserves.
Nuclear fusion is 1million times as effective as burning oil, gas or coal.
70g of water could generate the same amount of energy as a super-tanker of oil.

Where we are at the moment

A fusion generator will work, as outlined above, by firing a seed or ‘core’ (which is very small) into a chamber. Lasers would focus on it from all sides to compress fuel and an ignition laser fired in, in order to heat and cause plasma to form, which then allows fusion to take place. Currently this could be done at a rate of twice a day given current laser technology (current lasers can only fire twice a day). Plans are being developed for a trial nuclear fusion plant called HiPER (High Power laser Energy Research facility): this will be a new laser (which is scheduled to be built by 2025, assuming funding can be found) which will aim to seed the generator four times a second. A fusion generator would need this rate of ‘mini star formation’ to be viable, in order to create a power station that can generate levels of power at a Giga Watt (GW) scale.