Controlled Nuclear Fusion The JET Project JET Joint

Controlled Nuclear Fusion The JET Project

JET (Joint European Torus) Click on the underlined parts of the JET to find out more information about them and use it to fill in the concept map in your handouts. Plasma Steam to turbines Torus Pump Container Blanket Water from turbines

Plasma It is a particular state of matter where the atoms are stripped of their electrons. In this state the matter is made only of nuclei, so plasma is positively charged. Therefore, it is capable of carrying an electric current. In D-T reactors a massive current (106 A) is passed through the plasma to give the initial energy to start the fusion reaction by heating the plasma to 108 K. Such high temperatures occur naturally in the Sun and other stars, where the energy provided to the electrons in the atoms is too high for the electrostatic forces from the protons in the nucleus to keep hold of them.

Lithium blanket The Lithium in the blanket is continually bombarded by the neutrons produced in the fusion reaction. This gives rise to another nuclear reaction where the nuclei of Lithium rearrange into He nuclei and Tritium, which is then collected in the core to form part of the plasma. The He nuclei (alpha-particles) are soon after stopped by the concrete container and later gain electrons, becoming Helium atoms. So, the only waste product in a D-T reactor is Helium. The constant bombardment and the closeness to the hot plasma increases the temperature of the blanket to the order of 103 K.

Container The container is a thick layer of concrete surrounding the blanket and the core of the reactor. This layer stops the neutrons produced in the fusion reaction from escaping from inside the reactor and harm the staff operating the machinery.

Torus The torus is a doughnut shape designed to contain the plasma in a confined space, so that the deuterium and tritium nuclei would not escape the core and the intense heat would not affect other parts of the reactor. This is achieved through strong and complicated magnetic field lines around the torus that force the plasma to follow a closed loop. The plasma particles spiral around the field lines and collide with one another. The plasma must be kept from touching the steel container or it would fizzle out losing its energy.

JET (Joint European Torus) Plasma Doughnut shape ng o y str ed b d n ou ds Surr etic fiel n mag t en fin em to E K ns om h r ig ro f H lect pe s e ca eu es ucl n Nuclei of D and T stripped of their electrons Forces plasma to follow a complicated path Plasma particles stay in the core and reaction is sustained Co n rry ca n nt Ca rre cu Achieved by massive current (106 A) Temperature 108 K Steam to turbines Torus Co th llec e c ts or in e Pump Container Stops neutrons from reaching staff Tritium Neutrons released in the fusion reaction rns Tu o int Concrete Water from turbines Blanket Lithium Temperature 103 K

Use the grid below to compare a fission and a fusion reactor Type of reactor Nuclear fission Nuclear fusion Energy output per nucleon 0. 8 Me. V 3 Me. V Advantages Disadvantages Waste remains Relatively low radioactive for thousands of years start-up energies Non-renewable fuel Technology already developed resources Lower energy output Renewable fuel resources Harmless waste products Higher energy output Very high power required for start-up Technology not yet developed