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Non-nuclear energy

Fusion power plant

Fission and radiation protection
Fusion
   

How can fusion produce electricity in a future power plant? The fusion reaction can be simply written as:

Tritium (3H) + deuterium (2H) >> Helium (4He) + a high-energy neutron (n)

The Fusion Reaction

In a fusion power plant most of the energy produced by the reactions in the plasma is carried by the neutrons. These high energy neutrons (14 MeV) are captured and their energy used to generate electricity. The energy of the neutrons is absorbed in the structures lining the plasma chamber (known as a torus) walls. The remaining energy in the helium (4He) particles maintains the high plasma temperature. An outline design for a fusion power plant is shown below.

In a fusion power plant the plasma would be confined in a large vacuum vessel surrounded by a neutron absorbing breeding blanket. The breeding blanket has a dual function: it converts the energy of the neutrons into thermal energy and it ‘breeds’ new tritium from lithium to provide more reaction elements.

A large scale vacuum systems is required to ensure an ultra high vacuum in the reactor vessel and to maintain the vacuum surrounding the Superconducting coils located outside the reactor vessel that provide the required strong magnetic field to confine the plasma away from the vessel walls.

Cryogenics (circulating very low temperature liquids) are used to remove the waste and impurities from the plasma, cool the super-conducting magnet coils to allow them to operate, separate the waste gasses into their different individual components for disposal or recycling, provide the cooling for the Radio Frequency heating sources and control the gas pressure of neutral beam systems.

A circulating coolant removes the heat from the blanket and, in the heat exchangers, steam is generated to drive turbines for electricity production.

© Image: CEA  Fusion Power Plant Concept

The main challenge in fusion is to maintain the high temperature of the plasma for long periods of time. In a burning plasma the energy of the Helium nuclei are the main contributors to heating the plasma. However, the plasma is constantly being cooled by impurities picked up from the vessel wall. A divertor system in the vacuum vessel extracts waste gases and power from the plasma and new deuterium and tritium is continuously injected into the plasma.

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