ClimateandFuel

Nuclear Fusion Power Development and Experimentation

Unlimited fuel, unlimited power, no waste, safe, no CO2.

There is the intent that the FUSION process will provide unlimited electrical power and it has the following advantages over other forms of power generation:-

• There is unlimited fuel available.
• The process does not produce CO2 or other greenhouse gases.
• It is inherently safe. If fuel supply ceases the reactor shuts down.
• There is no medium term shutdown heat (unlike fission reactors.)
• There are no byproducts that could be adapted for military purposes.
• There are negligible waste products (ref 149.)

After along period of building experimental reactors (JET & ITER), a demonstation fusion power station (which generates electricity) might start to be constructed as early as 2030 and commercial reactors could follow. The process needs considerable power to start up.

There are several lines of research and development :-

1. Magnetic Confinement Fusion. Tokamac (Torus). JET and ITER

In the Fusion process 'light' atoms are fused together to release heat in a 'plasma' state at very high temperatures or temperatures and pressure. Deuterium and Tritium, the best of 13 possible fusion fuel combinations, are fused to create Helium 4 plus neutrons and energy (heat.)

Tritium (half life 12.5 years) is bred from lithium in the torus:-

More details of the Fusion Process

An initial development in the UK is the JET (Joint European Tokamac) fusion reactor (ref 107) which has resulted in an output of 16 MW for 1 to 2 seconds from an input power of 24MW. There are other experimental tokomacs in Russia, USA, Japan and other countries.

The International Thermonuclear Experimental Reactor (ITER)(ref 149) is being built in France with participation of the EU, Japan, China, Russia, US, South Korea, India. This aims to generate 500 MW from an input of 50MW (ref 121). The site however will consume 200MW. The first "burn" is expected around 2022. JET cannot operate continuously as it gets too hot so ITER is a supperconducting machine and should operate continuously. While external power is required to start the machine it may be for the operation to become self sustaining. JET will now be used to develop new materials for ITER.

The subsequent step is to build several demo. reactors around the world, which should each generate 1300 MW with a net output this time at 1000 MW each.

V strong magnetic forces, v high temperatures, vacuum enclosure, near zero absolute temperature for superconductivity (ITER), in a torus.

At 150 million deg K the "fuel" exists as 'plasma' where the electrons (-) and ions (+) are separate. Heating to plasma temperature is carried out by a neutral beam (D2 neutralized) injected at very high speed, radio frequency and microwave energy, ohmic reaction to the induced current up to 15 million amps, using superconducting coils and helium nuclei produced - the latter which maintains the reaction.

The magnetic confinement is created by a toroidal field, produced by coils (18 for ITER), surrounding the vacuum vessel, 6 poloidal coils and a field produced by current in the plasma. These form a helical field around the torus to confine the plasma. Other coils shape and position the plasma.

The energy generated by fusion is transferred via alpha particles and neutrons to the lithium breeding blanket, heat will be extracted from heat exchangers, steam generated eventually to power turbo generators.

No impurities must be present so a very low vacuum is required within a vacuum vessel (see sketch below)

A lithium blanket is placed in the vessel to make ('breed') tritium (half life of 12.5 years).

The main cryogenic load is liquid helium cooling of the magnets to achieve superconductivity at 4 deg K (absolute.)

"Ash" in the form mainly of Helium is extracted and reprocessed. The ports for introducing Deuterium and Lithium are not shown in the sketch.

The central solenoid is in 6 sections (from the top CS3U, CS2U, CS1U, CS1L,CS2L,CS3L) so the currents (up to 46 thousand amps) are separately controlled in each to help control the plasma pulse which could look rather like this:-

See detail about the central solenoid and operation.

see more on ITER and fusion

2) Laser Inertial Fusion. (NIF - LIFE - HIPER)

The National Ignition Facility (USA)and the Rutherford Appleton Laboratory in Oxfordshire are developing a prototype experimental reactor for fusion energy generation.

Fuel pellets of frozen fuel (deuterium and Tritium) of the order of 2 mm wide are fired in sequence across a steel vacuum chamber. A laser is magnified and split into 192 lasers 40 cm X 40 cm, focussed down and directed to hit the pellets fast enough to compress them to 100 million atmospheres (pascals), reduce them to a size of a few microns in a billionth of a second and to a temperature of 100 million deg C, where fusion can take place (3 million C at edge). Neutrons are projected out into a lithium blanket where the heat (at 600C)is collected in a fluid which is piped out to generate steam to drive turbines as in a conventional power station (refs 159.) Tritium is generated from the lithium blanket.

more detail of multi laser device See National Ignition Facility.

3 Magnetised Target Fusion

'General Fusion' , Canada is developing a process where lithium is heated and magnetically compressed to create fusion. The company believes that they could be the first to produce operating reactors which would initially be 100 MW each.

More details of Magnetised Target Fusion

4 Aneutronic Fusion (neutron emission carries less than 1% of energy released).

One device consists of six electromagnetic rings arranged as a cube.  Electrons are accelerated into the device due to the electric field. In the device, magnetic fields confine most of the electrons and those that escape are retained by the electric field. This configuration traps the electrons in the middle of the device focusing them near the center  and fusion takes place.

Most of the energy produced by Aneutronic fusion is  in the form of charged particles instead of neutrons  which could thus be converted directly into electricity by various methods;  inductive, based on changes in magnetic fields, or electrostatic, based on making charged particles work against an electric field.

Boron 11 is being considered as the fuel but this requires a much higher operational temperature than in the case of deuterium and lithium.

EMC2 Device Corporation, a charitable organisation, is designing with a view to building and testing a 100 MW demonstation model; based on previous experimental models. For more detail and photos goto : EMC2 Fusion Device Corporation

This could be more compact and cheaper than the  thermal production of electricity if the more extream conditions can be accomodated.

Fuel options plentiful.

100 kg of Deuterium (obtained from 2800 tons of sea water) and 150 kg of tritium (obtained from 10 tons of lithium ore) could in the future produce 1000 MW of electrical power for 1 year (ref 138). There is sufficient Lithium to provide all the worlds energy for 1000 years plus and of course unlimited water. Tritium can also be produced in a heavy water moderated reactor. (Fusion fuel could provide 4 million times the energy obtained from coal.)

A Deuterium - Deuterium fusion reactor/device would provide limitless energy from only water. However even higher temperatures would be required so it is unlikely to be considered in the near future.

It could be 40 years before fusion likely to make an impact on clean power supply.

In the case of ITER it will may take eight years before the experiment is operational, ten years before problems are ironed out, another ten years to build several demonstration fusion power stations around the world and another ten before these are proved (ref 149).

Considerable development must follow and new materials found and tested. The digital mock up of JET has a million parts and of ITER 10 million parts to design and construct (ref 157).

Cold Fusion - Low Energy Nuclear Reaction - Chemically assisted Nuclear Reaction

An alternative where fusion might be possible without immense heat has been investigated but generally rejected by most scientists. More detail.

Model of the JET fusion reactor.

Orange - Laminated magnet iron structure. Gray vertical cylinder on left - injection of ions at very high speed, neutralized, to raise temperature of plasma in Torus. Royal blue piping - RF energy to raise temperature. The copper coils around the iron structure are cooled internally by gas/liquid to remove electrical heat whereas for ITER the coils are superconducting and thus produce no heat.

JET fusion Tokamac, Culham. Showing Torus where plasma is heated to 100 million deg K

Tiles (square) bolted to centre core. These are now being replaced for a new design to be tested for ITER. RF heating panels shown on right and back left.

JET torus mock up for engineers to practice detailed work in protective clothing Culham UK

Control room for JET fusion Tokamac, Culham (showing half of the room and JET shut down).

JET plasma current was increased to 4.3 million amps in April 2009 (to H mode) whilst applying the full magnetic field of 3.45 Tesla. This took a power of 27 MW injected into the plasma (deuterium), 23 MW from increased neutral beam power, 4 MW from radio frequency (RF) power. Later in 2010 new materials for ITER will be tested.

Mega Amp Spherical Tokamac (MAST) Culham UK used for diagnostics, development and testing materials etc in Plasma. This more compact reactor could be developed as an advanced fission reactor in the future.