FUSION ENERGY

INTRODUCTION

Nuclear fusion promises to be an important long-term energy source to complement other renewable energy options and could eventually replace nuclear fission power plants. Fusion power plants might start to produce electrical power before 2050 and have been estimated as capable of meeting 20% of global energy requirements by 2100 if the process proves commercially viable. This seems a reasonable forecast; in the modern era, major technological advances generally require about 50 years to achieve wide-scale adoption.

Fusion energy offers a number of very significant potential advantages. In current research programmes a fusion reaction converts hydrogen isotopes (deuterium and tritium) into helium, an inert gas, with large energy output. Deuterium is readily extracted from ordinary water and tritium can be derived by a subsidiary breeder process within a fusion power plant based on lithium, a metal available in the earth’s crust. This fusion process is highly efficient and a single kilogram of fusion fuel could produce as much energy as 10 million kilograms of fossil fuels. The reaction cycle cannot run away or generate hazards to local communities, security issues are much lower than those associated with nuclear fission and irradiated material from fusion power plants would be safely disposable within 100 years. The economics of fusion-generated electric power are expected to be comparable with those of current technology.

To generate power from a fusion reaction, low-density gas is heated to temperatures above 100 million degrees C (10 times the central temperature of the Sun). Neutrons ejected from the resulting plasma reaction are slowed down by an external blanket of lithium, producing thermal power which in turn is utilised to generate electric power. The plasma is confined and protected from contact with solid surfaces by strong magnetic fields created by superconducting magnets. The most promising magnetic confinement arrangement is a doughnut-shaped chamber called a tokomak. The Joint European Torus (JET) located at Culham near Oxford is the largest tokomak in the world.

THE JET RESEARCH PROGRAMME

The JET programme is managed by UKAEA on behalf of partner nations under the European Fusion Development Agreement, and operates as a user facility similar to those for other fields of advanced physics research such as CERN. The JET tokamak itself was designed to study controlled fusion processes on an appropriate scale and based on the deuterium-tritium fuel mixture that would be used in a commercial fusion power plant. The JET programme has created the world’s largest and most powerful fusion research facility and has proved an outstanding example of European collaboration.

Construction of JET began in 1978 and machine operations started in 1983. The first controlled release of fusion power was achieved in 1991. An increasingly important spin-off activity became the staged design programme for the international successor project ITER (see next section). Current research now includes further development of advanced technologies to support ITER in appropriate fields, including system design and materials investigations, manufacture of reactor components, remote handling, magnets and cryogenics, vacuum systems, plasma heating, breeder technology and diagnostics.

ITER

Full approval for the ITER project was achieved in 2006 and plant construction is now in progress. ITER will provide a link between JET and future commercial fusion power plants. It is being financed, built and run by an international scientific partnership involving EU countries, USA, the Russian Federation, China, India and Korea, with considerable industrial involvement. The plant will be located on a site in southern France adjacent to an existing large-scale energy research facility.

A large research programme established the practical feasibility of the design and involved construction of full-scale prototypes of key components. The design objective is to produce 500 MW of fusion power continuously for at least 400 seconds. The plasma volume will be 10 times that of JET, probably close to that of future commercial reactors, and the power multiplication factor (power out over power in) should be about 10, in comparison with that of a commercial reactor, which should attain a factor of 30-40. The intended operational life of the ITER plant is at least 20 years after activation in 2016.

DEMO

DEMO should follow on from ITER as a pilot project for the construction of commercial fusion power plants. Assuming it has broadly the same physical dimensions as ITER, its fusion thermal power level will have to be about 3 times higher if it is to deliver 500 MW of continuous electrical power into the French grid. This will involve significantly higher performance levels, high systems reliability and the capability to refuel and maintain the plant within very limited periods of down-time.

If DEMO fully achieves its design objectives, the final step on the road to fusion power might be its employment as a prototype for a first-of-series commercial 1000 MW power station. While it is difficult to forecast when this milestone might be reached, 2050 seems a reasonable estimate.

David Bright

Latest Progress

Fusion within a year ? 20/01/10