How does fission release energy

Fusion can involve many different elements in the periodic table. However, researchers working on fusion energy applications are especially interested in the deuterium-tritium DT fusion reaction.

DT fusion produces a neutron and a helium nucleus. In the process, it also releases much more energy than most fusion reactions. In a potential future fusion power plant such as a tokamak or stellarator , neutrons from DT reactions would generate power for our use.

Figure 3. A chain reaction can produce self-sustained fission if each fission produces enough neutrons to induce at least one more fission. This depends on several factors, including how many neutrons are produced in an average fission and how easy it is to make a particular type of nuclide fission.

Not every neutron produced by fission induces fission. Some neutrons escape the fissionable material, while others interact with a nucleus without making it fission. We can enhance the number of fissions produced by neutrons by having a large amount of fissionable material. The minimum amount necessary for self-sustained fission of a given nuclide is called its critical mass.

Some nuclides, such as Pu , produce more neutrons per fission than others, such as U. Additionally, some nuclides are easier to make fission than others. In particular, U and Pu , are easier to fission than the much more abundant U.

Both factors affect critical mass, which is smallest for Pu. The reason U and Pu are easier to fission than U is that the nuclear force is more attractive for an even number of neutrons in a nucleus than for an odd number. When a neutron encounters a nucleus with an odd number of neutrons, the nuclear force is more attractive, because the additional neutron will make the number even.

About 2-MeV more energy is deposited in the resulting nucleus than would be the case if the number of neutrons was already even. This extra energy produces greater deformation, making fission more likely. Thus, U and Pu are superior fission fuels. The isotope U is only 0. This is followed by Kazakhstan and Canada. Most fission reactors utilize U , which is separated from U at some expense. This is called enrichment.

The most common separation method is gaseous diffusion of uranium hexafluoride UF 6 through membranes. Since U has less mass than U , its UF 6 molecules have higher average velocity at the same temperature and diffuse faster.

Another interesting characteristic of U is that it preferentially absorbs very slow moving neutrons with energies a fraction of an eV , whereas fission reactions produce fast neutrons with energies in the order of an MeV. Water is very effective, since neutrons collide with protons in water molecules and lose energy. Figure 4 shows a schematic of a reactor design, called the pressurized water reactor. Figure 4.

A pressurized water reactor is cleverly designed to control the fission of large amounts of U , while using the heat produced in the fission reaction to create steam for generating electrical energy. Control rods adjust neutron flux so that criticality is obtained, but not exceeded.

In case the reactor overheats and boils the water away, the chain reaction terminates, because water is needed to thermalize the neutrons. This inherent safety feature can be overwhelmed in extreme circumstances. Control rods containing nuclides that very strongly absorb neutrons are used to adjust neutron flux. To produce large power, reactors contain hundreds to thousands of critical masses, and the chain reaction easily becomes self-sustaining, a condition called criticality.

Neutron flux should be carefully regulated to avoid an exponential increase in fissions, a condition called supercriticality. Control rods help prevent overheating, perhaps even a meltdown or explosive disassembly. The water that is used to thermalize neutrons, necessary to get them to induce fission in U, and achieve criticality, provides a negative feedback for temperature increases.

In case the reactor overheats and boils the water to steam or is breached, the absence of water kills the chain reaction. Other safety features, thus, need to be incorporated in the event of a loss of coolant accident, including auxiliary cooling water and pumps. Calculate the amount of energy produced by the fission of 1. The total energy produced is the number of U atoms times the given energy per U fission.

We should therefore find the number of U atoms in 1. The number of U atoms in 1. One mole of U has a mass of The number of U atoms is therefore,. This is another impressively large amount of energy, equivalent to about 14, barrels of crude oil or , gallons of gasoline.

But, it is only one-fourth the energy produced by the fusion of a kilogram mixture of deuterium and tritium as seen in Example 1. Calculating Energy and Power from Fusion. Even though each fission reaction yields about ten times the energy of a fusion reaction, the energy per kilogram of fission fuel is less, because there are far fewer moles per kilogram of the heavy nuclides.

The energy released by fission in these reactors heats water into steam. The steam is used to spin a turbine to produce carbon-free electricity. Click above to view our full fission vs fusion infographic. Fusion occurs when two atoms slam together to form a heavier atom, like when two hydrogen atoms fuse to form one helium atom.

This is the same process that powers the sun and creates huge amounts of energy—several times greater than fission.