Nuclear reactor physics An induced nuclear fission event.
Nuclear reactor physics An example of an induced nuclear fission event.
A neutron is absorbed by the nucleus of a uranium atom, which in turn splits into fast-moving lighter elements fission products and free neutrons.
Though both reactors and nuclear weapons rely on nuclear chain-reactions, the rate of reactions in a reactor occurs much more slowly than in a bomb. Just as conventional power-stations generate electricity by harnessing the thermal energy released from burning fossil fuelsnuclear reactors convert the energy released by controlled nuclear fission into thermal energy for further conversion to mechanical or electrical forms.
Nuclear fission When a large fissile atomic nucleus such as uranium or plutonium absorbs a neutron, it may undergo nuclear fission. The heavy nucleus splits into two or more lighter nuclei, the fission productsreleasing kinetic energygamma radiationand free neutrons.
A portion of these neutrons may later be absorbed by other fissile atoms and trigger further fission events, which release more neutrons, and so on. This is known as a nuclear chain reaction. To control such a nuclear chain reaction, neutron poisons and neutron moderators can change the portion of neutrons that will go on to cause more fission.
Some experimental types of reactor have used berylliumand hydrocarbons have been suggested as another possibility. The kinetic energy of fission products is converted to thermal energy when these nuclei collide with nearby atoms. The reactor absorbs some of the gamma rays produced during fission and converts their energy into heat.
Heat is produced by An explanation of nuclear reactor radioactive decay of fission products and materials that have been activated by neutron absorption. This decay heat-source will remain for some time even after the reactor is shut down.
A kilogram of uranium U converted via nuclear processes releases approximately three million times more energy than a kilogram of coal burned conventionally 7.
The heat is carried away from the reactor and is then used to generate steam. Most reactor systems employ a cooling system that is physically separated from the water that will be boiled to produce pressurized steam for the turbineslike the pressurized water reactor.
However, in some reactors the water for the steam turbines is boiled directly by the reactor core ; for example the boiling water reactor. Nuclear reactor controlNuclear reactor physicsPassive nuclear safetyDelayed neutronIodine pitSCRAMand Decay heat The rate of fission reactions within a reactor core can be adjusted by controlling the quantity of neutrons that are able to induce further fission events.
Nuclear reactors typically employ several methods of neutron control to adjust the reactor's power output. Some of these methods arising naturally from the physics of radioactive decay and are simply accounted for during the reactor's operation, while others are mechanisms engineered into the reactor design for a distinct purpose.
The fastest method for adjusting levels of fission-inducing neutrons in a reactor is via movement of the control rods. Control rods are made of neutron poisons and therefore tend to absorb neutrons. When a control rod is inserted deeper into the reactor, it absorbs more neutrons than the material it displaces—often the moderator.
This action results in fewer neutrons available to cause fission and reduces the reactor's power output. Conversely, extracting the control rod will result in an increase in the rate of fission events and an increase in power.
The physics of radioactive decay also affects neutron populations in a reactor. One such process is delayed neutron emission by a number of neutron-rich fission isotopes. These delayed neutrons account for about 0.
The fission products which produce delayed neutrons have half lives for their decay by neutron emission that range from milliseconds to as long as several minutes, and so considerable time is required to determine exactly when a reactor reaches the critical point. Keeping the reactor in the zone of chain-reactivity where delayed neutrons are necessary to achieve a critical mass state allows mechanical devices or human operators to control a chain reaction in "real time"; otherwise the time between achievement of criticality and nuclear meltdown as a result of an exponential power surge from the normal nuclear chain reaction, would be too short to allow for intervention.
This last stage, where delayed neutrons are no longer required to maintain criticality, is known as the prompt critical point. There is a scale for describing criticality in numerical form, in which bare criticality is known as zero dollars and the prompt critical point is one dollar, and other points in the process interpolated in cents.
In some reactors, the coolant also acts as a neutron moderator. A moderator increases the power of the reactor by causing the fast neutrons that are released from fission to lose energy and become thermal neutrons.
Thermal neutrons are more likely than fast neutrons to cause fission. A higher temperature coolant would be less dense, and therefore a less effective moderator. In other reactors the coolant acts as a poison by absorbing neutrons in the same way that the control rods do.
In these reactors power output can be increased by heating the coolant, which makes it a less dense poison. Nuclear reactors generally have automatic and manual systems to scram the reactor in an emergency shut down. These systems insert large amounts of poison often boron in the form of boric acid into the reactor to shut the fission reaction down if unsafe conditions are detected or anticipated.
The common fission product Xenon produced in the fission process acts as a neutron poison that absorbs neutrons and therefore tends to shut the reactor down. Xenon accumulation can be controlled by keeping power levels high enough to destroy it by neutron absorption as fast as it is produced.
Fission also produces iodinewhich in turn decays with a half-life of 6. When the reactor is shut down, iodine continues to decay to xenon, making restarting the reactor more difficult for a day or two, as the xenon decays into cesium, which is not nearly as poisonous as xenon, with a half-life of 9.Learn more about how nuclear energy works from Duke Energy a leading nuclear plant operator for more than 40 years.
All nuclear reactors are devices designed to maintain a chain reaction producing a steady flow of neutrons generated by the fission of heavy nuclei. They are, however, differentiated either by their purpose or by their design features. Free online Nuclear Power Plant Simulator game.
Tips & Strategies: The best way to play the game is to increase the 3 slider controls a little at a time and give the reactor a chance to level off. 1. A device in which nuclear fission initiates a controlled chain reaction, producing heat energy typically used for power generation, and neutrons and fission products often used for military, experimental, and medical purposes.
Also called atomic reactor. 2. A device, such as a tokamak, in which. After recruit training, NF candidates report to the NF “A” School in Charleston, SC for technical training in their specific ratings.
They then attend Nuclear Power School (NPS) in Charleston, SC, where they learn theory and practical application of nuclear physics and reactor engineering. How to Cool a Nuclear Reactor.
Japan's devastating earthquake caused cooling problems at one of the nation's nuclear reactors, and authorities scrambled to prevent a meltdown.