Radiation reactors
- 2. Nuclear Reactions Uranium is a fairly common element on Earth and was incorporated into the planet during the planet's formation U-238 makes up 99 percent of the uranium on the planet Uranium-235 makes up about 0.7 percent of the remaining uranium found naturally Uranium-235 has an interesting property
- 3. Nuclear Reactions U-235 decays naturally, just as U-238 does, by alpha radiation U-235 also undergoes spontaneous fission a small percentage of the time Fission is defined as “the splitting of an atom” Also, U-235 is one of the few materials that can undergo induced fission
- 4. Nuclear Reactions If a free neutron runs into a U-235 nucleus, the nucleus will absorb the neutron without hesitation, become unstable and split immediately The probability of a U-235 atom capturing a neutron as it passes by is fairly high In a reaction two or three neutrons are ejected from each fission causing other fissions to occur
- 6. Nuclear Reactions Theprocess of capturing the neutron and splitting happens very quickly (1 x 10-12 seconds) picoseconds An incredible amount of energy is released, in the form of heat and gamma radiation, when a single atom splits The energy is released because the products and the neutrons, together, weigh less than the original U-235 atom
- 7. Nuclear Reactions The difference in weight is converted directly to energy at a rate governed by the equation E = mc2 a pound of highly enriched uranium used to power a nuclear submarine or nuclear aircraft carrier is equal to about a million gallons of gasoline a pound of uranium is smaller than a baseball and a million gallons of gasoline would fill a five-story building
- 8. Nuclear Reactions In order for a reactor to work, a sample of uranium must be enriched , so that it contains two to three percent or more of uranium-235 Weapons-grade uranium is composed of 90 percent
- 9. Nuclear Power uranium is formed into pellets with approximately the same diameter as a dime and an inch long These pellets are then placed in rods that are “super critical” meaning they would over heat and melt if left alone To prevent this, control rods made of a material that absorbs neutrons are inserted
- 10. Nuclear Power The depth the rods are inserted into the uranium, determines the amount of fission taking place All the way in… the reactions stop All the way out….the reactions increase until meltdown occurs The uranium bundle acts as an extremely high-energy source of heat. It heats the water and turns it to steam
- 12. Nuclear Power The steam drives a steam turbine, which spins a generator to produce power In some plants the steam contacts other water and turns it to steam… this way, the radioactive water never touches the turbine there is little difference between a nuclear plant and a coal or oil-fired plant except for the source of the heat used
- 13. Nuclear Power The reactor's pressure vessel is typically housed inside a concrete liner that acts as a radiation shield the containment vessel is protected by an outer concrete building that is strong enough to survive such things as crashing jet airliners
- 15. Nuclear Power Uranium-235 is not the only possible fuel for a power plant. Another fissionable material is plutonium-239
- 16. Nuclear Power Plutonium-239 can be created by U-238 fission, therefore some reactors are used to make weapons grade plutonium If fact, the first reactors every produced were used for this purpose…. Atomic bombs Research reactors work on the same principals as power reactors, however are used for other purposes
- 17. Nuclear Power They can be used to expose materials to high levels of radiation To bombard elements with neutrons to create new isotopes And can be used to work on new energy possibilities How safe are they? Do they hurt the environment?
- 18. Nuclear Safety Compared with a coal-fired power plant, nuclear power plants are a dream come true from an environmental standpoint coal-fired power plant actually releases more radioactivity into the atmosphere than a properly-functioning nuclear power plant Fossils fuel plants (oil/coal) release huge amounts of carbon into the atmosphere, C-14 is radioactive
- 19. Nuclear Safety There are also drawbacks with nuclear power… Mining and purifying uranium has not, historically, been a very clean process Improperly-functioning nuclear power plants can create big problems i.e. The Chernobyl Spent fuel from nuclear power plants is toxic for centuries and there is no safe permanent storage facility for it, yet
- 20. Nuclear Safety Transporting nuclear fuel to and from plants also poses some risk Unfortunately, there are less new nuclear power plants being constructed due to these risks At some point however, there will be no more fossil fuel and we will have no choice but to build more nuclear power plants
- 21. Reactor Types There are a couple different types of reactors, all use the same principle of nuclear fission The four types are … Graphite Moderated Reactor Fast Breeder Reactor (FBR) Liquid Metal (LMFBR) (most common type of breeder)
- 22. Reactor Types LightWater Reactor (LWR) Heavy Water Reactor (HWR) There are two types of light water reactors Boilingwater reactor Pressurized water reactor Boiling water reactor CoolantType - water Moderator Type – water
- 23. Reactor Types Fuel - uranium-dioxide (UO2) Comments - steam generated inside the reactor goes directly to the turbine
- 25. Reactor Types Pressurized water reactor Coolant Type - water Moderator Type – water Fuel - uranium-dioxide (UO2) Comments - steam is generated outside the reactor in a secondary heat transfer loop
- 27. Reactor Types Heavy Water reactors work just like light water reactors, however, instead of using water H2O…. Normal hydrogen is replaced with deuterium H2
- 28. Reactor Types There are two types of Graphite moderated reactors… Gas Cooled Water Cooled Gas Cooled Coolant Type - gas (carbon dioxide or helium) Moderator Type – graphite Fuel -- uranium
- 29. Reactor Types Comments - used in Britain, and France
- 30. Reactor Types Water Cooled Reactors Coolant Type – water Moderator Type – graphite Fuel -- uranium Comments - used in USA & former Soviet Union, e.g. Chernobyl
- 31. Reactor Types Fast Breeder Reactor (FBR) Coolant Type – molten liquid sodium Moderator Type – none required Fuel - plutonium dioxide and uranium dioxide in various arrangements Comments - breeder reactors are designed to produce more fissile material than they consume