Term
| What do uranium compounds spontaneously emit? |
|
Definition
| various rays that were capable of exposing photographic plates previously wrapped in light proof paper |
|
|
Term
| When is energy released in nuclear? |
|
Definition
| when some sort of rearrangement of nuclear particles or other energy transformations occur in high-energy nuclei and energy is released, commonly in the form of alpha (α), beta(β) or gamma(Υ) radiation |
|
|
Term
| What does each alpha particle contain? |
|
Definition
| contains 2 protons (p) and 2 neutrons(n) and carries a charge of +2 |
|
|
Term
| What are beta rays composed of? |
|
Definition
|
|
Term
|
Definition
| electromagnetic radiation similar to visible light but have much higher frequencies and energies |
|
|
Term
| Does the nuclei of all atoms (not just the radioactive ones) contain large quantities of energy? |
|
Definition
|
|
Term
|
Definition
| Large nuclei break into smaller fragments during nuclear fission and have a total mass that is less than that of the original nuclei. The lost mass appears in the form of energy |
|
|
Term
| When does nuclear fission take place continuously? |
|
Definition
| in all nuclei containing a total number of protons and neutrons greater than 230 |
|
|
Term
| Is fission a practical energy source? |
|
Definition
| Fission takes place much too slowly to constitute a practical energy source but the nuclei of a few heavy elements can be induced to undergo nuclear fission by bombarding them with other small particles |
|
|
Term
| What happens when a uranium-235 is hit by a relatively slow-moving, low energy neutron? |
|
Definition
| the neutron is absorbed into the nucleus which becomes very unstable |
|
|
Term
| What happens with the unstable nucleus during nuclear fission? |
|
Definition
| breaks up into a combination of fragments |
|
|
Term
| What is the mass difference between the particles on the left side and the right side of the nuclear reaction equivalent to? |
|
Definition
| 3.22x10-4 ergs or 3.06 x 10-14 Btu |
|
|
Term
| The energy that is liberated in this and other fission reactions appears as kinetic energy of the fission fragments and neutrons (89%). What happens to the remaining 11%? |
|
Definition
| carried off as radioactive emissions |
|
|
Term
| The energy that is available from a uranium fission process is as follows |
|
Definition
| A 235-gram sample of uranium-235 contains 6 x 1023 fissionable nuclei |
|
|
Term
| How is the total energy released in nuclear fission calculated? |
|
Definition
| (6 x 1023 nuclei) (3.06 x 10-14 Btu/nucleus) = 1.8 x 1010 Btu |
|
|
Term
|
Definition
The nuclei of lightweight elements will combine or fuse when heated to very high temperatures and produce heavier nuclei. The nuclear fusion process is somewhat analogous to the reverse of nuclear fission
• The products have less total mass than the reactants and the differences appears as energy |
|
|
Term
| Overall fusion reaction of the sun takes place in steps: |
|
Definition
Two hydrogen nuclei fuse to produce a deuteron, a positron and a
neutrino
A deuteron is a particle consisting of one proton and one neutron, a positron is a positively charged electron and a neutrino is a very small uncharged particle2. The deuterons of the reaction fuse with other hydrogen nuclei to form helium-3 and gamma rays
• 3. Pairs of helium-3 nuclei fuse to form ordinary helium-4 nuclei plus more hydrogen nuclei |
|
|
Term
|
Definition
The mass difference between the right and left sides of reaction accounts for the release of about 4 x 10-15 Btu of energy or about
1 x 10 -15 Btu per hydrogen nucleus reacted • One gram of fissionable uranium produces 76.6 million Btu • One gram of hydrogen undergoing fusion produces 600 million Btu |
|
|
Term
| The fusion reactions of the sun take place in a central core where the temperature is estimated to be what? |
|
Definition
| 15 million degrees Kelvin |
|
|
Term
| A fission bomb must be detonated to achieve what? |
|
Definition
| the high temperatures necessary to start fusion |
|
|
Term
| What are chain reactions? |
|
Definition
• In certain reactions neutrons are produced by the fission of a uranium-235 nucleus. This creates the possibility for chain reactions and if only one of the neutrons produced each time reacts with another uranium-235 nucleus, a chain reaction results and the fission process proceeds at a constant rate
• The process is said to be self propagating or critical when such conditions prevail and if more than one of the generated neutrons causes another reaction, a superficial condition is created which
leads to an explosion |
|
|
Term
| What is a nuclear reactor used for? |
|
Definition
| used to control the release of nuclear energy from fission reactions. |
|
|
Term
| What are 5 essentials for reactors? |
|
Definition
1. A quantity of fissionable material sufficient to create a self- sustaining or critical nuclear reaction must be present
• 2. A moderator is needed to slow the high-energy neutrons produced during fission and the slower neutrons have a higher probability of colliding with other fissionable nuclei
• 3. A means for controlling the rate of the resulting reaction is required
• 4. The reactor must be surrounded by shielding • 5. A cooling system is necessary |
|
|
Term
| what are the two nuclear reactor control rods? |
|
Definition
One is used to control the rate of the fission reactions and the energy
output of the system
• A second set is used only in the event of an emergency and can be employed to shut the reactor down very rapidly |
|
|
Term
| Reactors that were chosen for continued development were in which ordinary water is used as a moderator and coolant |
|
Definition
the light water
reactor (LWR) and the high temperature gas-cooled reactors (HTGR) |
|
|
Term
| Light water reactors are classified into what two categories? |
|
Definition
| • Boiling water reactors (BWR) and • Pressurized water reactors |
|
|
Term
| Boiling water reactors acts as both a moderator and coolant. What happens with the water? |
|
Definition
| The water is heated to a temperature about 135°C and steam is generated at a pressure of approximately 1000 pounds |
|
|
Term
| What happens in a pressurized water reactor? |
|
Definition
• Here again water serves as both a coolant and moderator. Water is maintained at a pressure of about 2000 pounds per square inch which allows it to be heated to 300°C without boiling
• Hot water is pumped to a heat exchanger where much of the heat is transferred to a secondary water filled loop maintained at a lower pressure
• The steam that is generated in the secondary loop is used to drive an electrical generator |
|
|
Term
| High Temperature Gas-Cooled Reactors (HTGR) |
|
Definition
HTGR efficiency is about 40%. The system has been under development in the United States since 1958
• Graphite is used as a moderator and helium is the preferred coolant for HTGRs. Helium gas is used because it has good thermal transport properties and is chemically inert
• Helium can escape through extremely small openings and so reactor vessels must be leak proof
• During its operation the HTGR helium gas at a pressure of 300-400 pounds per square inch is forced through the reactor core where it is heated to 750°C |
|
|
Term
| What is a breeder reactor? |
|
Definition
• It gets its name from the fact that it will produce more nuclear fuel material than it consumes
• They have the capability of converting non-fissionable substances into fissionable nuclear fuels
• The fissionable material used is uranium-235. This isotope constitutes only 0.72% of naturally occurring uranium and the other 99.27% is made up of non fissionable uranium-238
• The actual fuel elements of light water reactors contain uranium oxide which has been enriched so that 2.5 – 3.5 % of the uranium present is uranium -235 |
|
|
Term
| More info on breeder reactors: |
|
Definition
• Here the rate of fission process decreases until the process becomes very inefficient and could cease
• Fuel elements are periodically removed from the reactor and sent to chemical reprocessing plants where any remaining fissionable material is recovered and the fuel poisons are removed
• A synthetic element called plutonium is the fissionable material that is recovered from used fuel elements during reprocessing and is found to consist of unreacted uranium-235
• A reaction between uranium-238 and neutrons generated by the fission of uranium-235 produces plutonium |
|
|
Term
| Fuels for Fission Reactors |
|
Definition
• Fission reaction ultimately depends on uranium-235 as a fuel although plutonium-239 and uranium-233 are fissionable but they must be produced in breeding reactions that originally began with uranium-235
• Uranium must be put through a complicated process before it can be used as a nuclear fuel. The process is known as a fuel cycle which consist of eight steps
• 1. Uranium-bearing ore is mined and milled • 2. Uranium oxide is extracted from the ore and is then refined and
chemically converted into gaseous uranium hexafluoride • 3. The uranium hexafluoride is enriched in uranium-2354. The enriched uranium hexafluoride is converted into appropriate fuel material
• 5. Fuel elements are fabricated from fuel material • 6. The fuel elements are used in a reactor • 7. Spent fuel elements are reprocessed • 8. The radioactive wastes must be transported and disposed of safely |
|
|
