Chemistry 25.3

Fission and Fusion of Atomic Nuclei 25.3 Fission and Fusion of Atomic Nuclei The sun is not actually burning. If the energy given off by the sun were the product of a combustion reaction, the sun would have burned out approximately 2000 years after it was formed, long before today. You will learn how energy is produced in the sun.

Nuclear Fission What happens in a nuclear chain reaction? 25.3

25.3 Nuclear Fission When the nuclei of certain isotopes are bombarded with neutrons, they undergo fission, the splitting of a nucleus into smaller fragments.

25.3 Nuclear Fission In a chain reaction, some of the neutrons produced react with other fissionable atoms, producing more neutrons which react with still more fissionable atoms.

Nuclear Fission 25.3 Nuclear Fission In nuclear fission, a uranium-235 nucleus breaks into two smaller nuclei and releases neutrons. Predicting What happens when the released neutrons strike other uranium-235 nuclei?

25.3 A Nuclear Power Plant Nuclear Fission A nuclear reactor uses controlled fission to produce useful energy. The illustration shows the basic components of a nuclear reactor. Energy from the fission process heats the circulating coolant. The heated coolant is used to produce steam that turns a steam-driven turbine. The turbine drives a generator to produce electrical energy.

25.3 Nuclear Fission Neutron Moderation Neutron moderation is a process that slows down neutrons so the reactor fuel (uranium-235 or plutonium-239) captures them to continue the chain reaction.

25.3 Nuclear Fission Neutron Absorption Neutron absorption is a process that decreases the number of slow-moving neutrons. Control rods, made of a material such a cadmium, are used to absorb neutrons.

Take a close look at a nuclear fission chain reaction. Animation 30 Take a close look at a nuclear fission chain reaction.

25.3 Nuclear Waste Nuclear Waste Why are spent fuel rods from a nuclear reaction stored in water?

25.3 Nuclear Waste Water cools the spent rods, and also acts as a radiation shield to reduce the radiation levels. Racks at the bottom of this pool contain spent fuel rods. The blue glow is from beta particles that the rods emit into the water.

Nuclear Fusion How do fission reactions and fusion reactions differ? 25.3 Nuclear Fusion Nuclear Fusion How do fission reactions and fusion reactions differ?

25.3 Nuclear Fusion Fusion occurs when nuclei combine to produce a nucleus of greater mass. In solar fusion, hydrogen nuclei (protons) fuse to make helium nuclei and two positrons.

25.3 Nuclear Fusion Fusion reactions, in which small nuclei combine, release much more energy than fission reactions, in which large nuclei split.

The potential fuels are inexpensive and readily available. 25.3 Nuclear Fusion The use of controlled fusion as an energy source on Earth is appealing. The potential fuels are inexpensive and readily available. The problems with fusion lie in achieving the high temperatures necessary to start the reaction and in containing the reaction once it has started.

25.3 Section Quiz. 25.3.

25.3 Section Quiz. 1. One of the control mechanisms for a sustainable nuclear chain reactor involves slowing down the released neutrons so they may be captured by other nuclei. This is done using moderators. shielding. absorbers. control rods.

25.3 Section Quiz. 2. Spent fuel rods are stored in lead-lined containers. deep pools of water. thick concrete bunkers. cadmium or graphite containers.

25.3 Section Quiz. 3. Choose the correct words for the spaces. In solar fusion, _______ nuclei fuse to form _______ nuclei. helium, hydrogen hydrogen-1, hydrogen-2 hydrogen, helium hydrogen-1, hydrogen-3

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