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.)

Although a commercial fusion plant might start to be constructed in 20 years, this green power generation option (ie where CO2 is not generated) will not be in operation sufficiently to limit carbon emissions to the amounts required in the next 40 years; however the timetable could be speeded up with more funding. The process needs considerable power to start up therefore other green methods of electrical power production will always be needed the development of which is likely to proceed well ahead of fusion power.

There are three 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.

The subsequent step is to build several experimental 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) Inertial Confinement Fusion. HIPER - High Power Laser Energy Research -alternative approach using huge lasers.

The Rutherford Appleton Laboratory in Oxfordshire is developing a prototype experimental reactor or Hiper (high petawatt energy reactor.)

A fuel pellet of frozen fuel (deuterium and Tritium) of the order of 2 mm wide is fired across a steel vacuum chamber. Pulsed lasers using 1 petawatt of power are directed to hit the pellet fast enough to compress it, reduce it 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. Neutrons are projected out into a lithium blanket where the heat is collected in a fluid which is piped out to generate steam to drive turbines as in a conventional power station (refs 159.)

More about hiper

The National Ignition Facility (US) is building a multi laser device of very high energy to create fusion.

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

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.

40 years before fusion likely to make an impact

It will probably take ten years before the ITER experiment is operational, ten years before problems are ironed out, another ten years to build several demonstration reactors 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).

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.

MAST was built after JET and at minimal cost.