How nuclear fusion reactor How nuclear fusion reactor worksworks

Why should we use nuclear Why should we use nuclear

fusion ?fusion ? • Abundant fuel supplyAbundant fuel supply• SafeSafe• CleanClean• Less nuclear waste Less nuclear waste

 Abundant fuel supply - Deuterium can be readily extracted from seawater, and excess tritium can be made in the fusion reactor itself from lithium, which is readily available in the Earth's crust. Uranium for fission is rare, and it must be mined and then enriched for use in reactors.

Safe - The amounts of fuel used for fusion are small compared to fission reactors. This is so that uncontrolled releases of energy do not occur. Most fusion reactors make less radiation than the natural background radiation we live with in our daily lives.

 

Clean - No combustion occurs in nuclear power (fission or fusion), so there is no air pollution.

 

Less nuclear waste - Fusion reactors will not produce high-level nuclear wastes like their fission counterparts, so disposal will be less of a problem. In addition, the wastes will not be of weapons-grade nuclear materials as is the case in fission reactors.

Physics of Nuclear Fusion: ReactionsPhysics of Nuclear Fusion: Reactions

• Proton-proton chain - This sequence Proton-proton chain - This sequence is the predominant fusion reaction is the predominant fusion reaction scheme used by stars such as the scheme used by stars such as the sun. Two pairs of protons form to sun. Two pairs of protons form to make two deuterium atoms. make two deuterium atoms.

• Two helium-3 atoms combine to Two helium-3 atoms combine to form beryllium-6, which is unstable. form beryllium-6, which is unstable.

• Beryllium-6 decays into two helium-Beryllium-6 decays into two helium-4 atoms. 4 atoms.

A consortium from the United States, Russia, Europe and Japan has proposed to build a fusion reactor called the International Thermonuclear Experimental Reactor (ITER) in France, to demonstrate the feasibility of using sustained fusion reactions for making

To achieve fusion, you need to create To achieve fusion, you need to create special conditions to overcome this special conditions to overcome this

tendency. Here are the conditions that tendency. Here are the conditions that make fusion possible:make fusion possible:

• High temperature - The high temperature High temperature - The high temperature gives the hydrogen atoms enough energy to gives the hydrogen atoms enough energy to overcome the electrical repulsion between overcome the electrical repulsion between the protons. Fusion requires temperatures the protons. Fusion requires temperatures about 100 million Kelvin.At these about 100 million Kelvin.At these temperatures, hydrogen is a plasma, not a temperatures, hydrogen is a plasma, not a gas. Plasma is a high-energy state of matter gas. Plasma is a high-energy state of matter in which all the electrons are stripped from in which all the electrons are stripped from atoms and move freely about. The sun atoms and move freely about. The sun achieves these temperatures by its large achieves these temperatures by its large mass and the force of gravity compressing mass and the force of gravity compressing this mass in the core. this mass in the core.

•We must use energy from microwaves, lasers and ion particles to achieve these temperatures.

•High pressure - Pressure squeezes the hydrogen atoms together. They must be within 1x10-15 meters of each other to fuse. The sun uses its mass and the force of gravity to squeeze hydrogen atoms together in its core.

We must squeeze hydrogen atoms together by using intense magnetic fields, powerful lasers or ion beams. With current technology, we can only achieve the temperatures and pressures necessary to make deuterium-tritium fusion possible. It is easier to extract deuterium from seawater than to make tritium from lithium. Also, deuterium is not radioactive, and deuterium-deuterium reactions will yield more energy.

Fusion Reactors: Magnetic Fusion Reactors: Magnetic ConfinementConfinement

• "Tokamak" is a Russian acronym for "Tokamak" is a Russian acronym for "toroidal chamber with axial "toroidal chamber with axial magnetic field."magnetic field."

• Magnetic confinement uses Magnetic confinement uses magnetic and electric fields to heat magnetic and electric fields to heat and squeeze the hydrogen plasma. and squeeze the hydrogen plasma. The ITER project in France is using The ITER project in France is using this method. this method.

Plasma toroidPlasma toroid

• A reactor of this A reactor of this shape is called a shape is called a tokamak. The ITER tokamak. The ITER tokamak will be a tokamak will be a self-contained reactor self-contained reactor whose parts are in whose parts are in various cassettes. various cassettes. These cassettes can These cassettes can be easily inserted and be easily inserted and removed without removed without having to tear down having to tear down the entire reactor for the entire reactor for maintenance. maintenance.

The ITER fusion reactor has following The ITER fusion reactor has following

partsparts • Vacuum vessel - holds the plasma and Vacuum vessel - holds the plasma and

keeps the reaction chamber in a keeps the reaction chamber in a vacuum .vacuum .

• Neutral beam injector (ion cyclotron Neutral beam injector (ion cyclotron system) - injects particle beams from system) - injects particle beams from the accelerator into the plasma to help the accelerator into the plasma to help heat the plasma to critical temperature heat the plasma to critical temperature

• Cooling equipment (cryostat, Cooling equipment (cryostat, cryopump) - cool the magnets cryopump) - cool the magnets

• Magnetic field coils (poloidal, toroidal) - Magnetic field coils (poloidal, toroidal) - super-conducting magnets that confine, super-conducting magnets that confine, shape and contain the plasma using shape and contain the plasma using magnetic fields .magnetic fields .

• Transformers/Central solenoid - supply Transformers/Central solenoid - supply electricity to the magnetic field coils .electricity to the magnetic field coils .

• Blanket modules - made of Blanket modules - made of lithium,absorb heat and high-energy lithium,absorb heat and high-energy neutrons from the fusion reactionneutrons from the fusion reaction

• Diverters - exhaust the helium Diverters - exhaust the helium products of the fusion reaction products of the fusion reaction

Magnetic-confinement fusion process:

The power needed to start the fusion reaction will be about 70 megawatts, but the power yield from the reaction will be about 500 megawatts. The fusion reaction will last from 300 to 500 seconds. (Eventually, there will be a sustained fusion reaction).

The lithium blankets outside the plasma reaction chamber will absorb high-energy neutrons from the fusion reaction to make more tritium fuel. The blankets will also get heated by the neutrons.

The fusion reactor The fusion reactor will heat a stream of will heat a stream of

deuterium and deuterium and tritium fuel to form tritium fuel to form high-temperature high-temperature

plasma. It will plasma. It will squeeze the plasma squeeze the plasma so that fusion can so that fusion can

take placetake place

• The heat will be The heat will be transferred by a transferred by a water-cooling loop water-cooling loop to a heat exchanger to a heat exchanger to make steam. to make steam.

• The steam will The steam will drive electrical drive electrical turbines to produce turbines to produce electricity. electricity.

• The steam will be The steam will be condensed back condensed back into water to into water to absorb more heat absorb more heat from the reactor in from the reactor in the heat the heat exchanger. exchanger.

•

• Fusion reactors will Fusion reactors will use abundant use abundant sources of fuel, will sources of fuel, will not leak radiation not leak radiation above normal above normal background levels, background levels, and will produce and will produce less radioactive less radioactive waste than current waste than current fission reactors. fission reactors.

THE ENDTHE END