0
Critical is that point when the population of fission events is neither growing nor decreasing, and that it is sustained by its own means. In this state, on a large scale statistical basis, exactly one neutron produces one fission, which goes one to produce one neutron, which goes on to produce one fission, and so on and so forth. Subcritical is the state where that population is decreasing, and supercritical is where that population is increasing.
Criticality is also related to power output, as the number of fission events is directly tied to energy or power output. When you ramp a nuclear reactor up in power, you go slightly supercritical while you increase the population, and therefore the energy output, but once you achieve your target power, you let your moderator step in and modulate the power in a self-modulating cycle. Similarly, as you trim power down, you go slightly subcritical while you decrease the population, and then you let the moderator kick back in, that is, unless you lose control and you initiate a trip/scram, taking the reactor to shutdown, which is way-way-subcritical.
What else can I help you with?
What happens when the mass of fissile material used in nuclear weapons is subcritical?
Nothing, it has to become supercritical for a nuclear detonation to happen. Most bombs perform this transition from subcritical state to supercritical state by an implosion driven by conventional explosive lenses. Once supercritical a neutron source is fired through the fissile material to start the reaction leading to the nuclear detonation.There is a special type of test detonation called a hydronuclear test where the amount of fissile material remains subcritical throughout the implosion. When the neutron source fires the reaction simply multiplies the number of neutrons by a factor then dies out. No nuclear detonation happens. Measurements of this neutron flux can tell about the quality of the implosion, safety, etc. But as there is no nuclear yield, several of the nuclear test ban treaties allowed these hydronuclear tests while banning tests with nuclear yields.
How heavy water is used to make plutonium from uranium?
Heavy water can be used in a nuclear reactor to moderate the speed of neutrons, making it easier for uranium-238 to absorb a neutron and become plutonium-239. This process is known as breeding plutonium in a reactor and is one method of producing plutonium for nuclear weapons or fuel.
Is plutonium reusable?
Directly, no. Once fissioned the plutonium is gone (it has transformed to other lighter elements). However indirectly using a breeder reactor, yes. A plutonium fueled breeder reactor with a uranium breeding blanket will produce more plutonium (from uranium-238) than it consumes. This breeder reactor can at the same time be generating electricity like any other power reactor.
What is one negtive effect nuclear fusion has?
One potential negative effect of nuclear fusion is the production of radioactive waste. While fusion produces less long-lived radioactive waste compared to fission, the materials used in the reactor can become activated and need to be safely managed and stored.
What does neutron absorption accomplish in a nuclear reactor?
Neutron absorption, or neutron capture, converts fertile materials, which cannot be used directly for fuel in a nuclear reactor, into fissile or fissionable fuels, which can. Current nuclear reactors use fission to provide heat. Fission requires one of three kinds of fuel, fissile, fissionable, or fertile. Fissile fuel undergoes fission spontaneously and provides sufficient neutrons in the process to produce a chain reaction, if there is a enough such fuel around, or a critical mass. Fissionable fuel will undergo fission if it is hit hard by a neutron with the proper energy. Fertile material can be converted into fissile or fissionable fuel through neutron capture. Neutron capture happens when a neutron collides with the nucleus of an atom. becoming part of it. This changes the isotope of the atom, increasing the number by one. Thus n + 232Th -> 233Th. The half life of 232Th is 14 billion years, but he half life of 233Th is a little less than 22 minutes. So the 233Th quickly decays, producing 233Pa. 233Pa has a half life of a little less than 27 days, so it also quickly decays, and it produces 233U. 233U is fissile, so it undergoes fission spontaneously and is a useful fuel for the nuclear reactor. Thus, the neutron capture has converted material that cannot be used directly for fission into something that can. In a conventional reactor, the neutrons needed are produced by the decay of fissile fuel. There are other kinds of reactors, however, such as an accelerator driven system, in which the neutrons are produced from outside the reactor. This means that a critical mass is not really necessary to produce the reaction. The accelerator driven system, also called an energy amplifier or subcritical reactor, is now in the development stage. Please bear in mind that this description of things is quite simplistic. Things usually happen this way in a neutron flux, but there are a lot of other outcomes. An atom of 233U is likely to capture another neutron and become 234U, for example. Also, collisions with neutrons cause atoms to decay or divide, and so the half lives do not represent what is actually going on in the reactor; an atom with a 27 day half life is very unlikely to last that long in a neutron flux.
Is the nuclear reactor useful to made atom bombs?
Yes, the nuclear reactor can be useful when it comes to making nuclear weapons. Uranium can be lowered into the operating reactor and can be bathed in the neutron flux to become (through nuclear transformation) plutonium. Plutonium is ready to be shaped into the subcritical masses used in nuclear weapons.
Why it is impossible for a nuclear power plant to become a nuclear bomb?
In order for fissile material to become a nuclear bomb, a sufficient amount of it must be assembled to exceed critical mass, and must be "held" there for a short period to allow the chain reaction to build sufficiently. By using conventional explosives to drive subcritical masses of nuclear material (like uranium or plutonium) together in an instant to achieve critical mass and cause the material to become supercritical, we can get a nuclear blast. Anything less will create a "dud" with no blast but only a release of some energy and the forcing apart of the nuclear material. If nuclear material is concentrated and critical mass is achieved, nuclear fission will occur and a chain reaction will build. But the energy released will be so great that it will attempt to force the nuclear material apart and stop the reaction. In a nuclear reactor, we achieve criticality and build a chain, but it is not able to go "run away" and behave like a nuclear weapon. Any "accident" or even a "catastrophe" at a reactor plant will only allow the melting of core material and the release of radiation. No blast will occur because there is no "force" to keep a critical mass of material together for a sufficient period to allow the chain to build to a high enough level to get that blast.
How many years of experience do you need to become a nuclear reactor system engineer?
my cousin became a nuclear reactor engineer and he said it was about 12 years
What is a nuclear blast?
I am sorry, I do not understand your question. Please clarify "subatomic".If you actually meant subcritical, it is when they make a test device that is deliberately designed to never become critical. Such a device cannot produce a nuclear yield, but they can still make measurements on it (e.g. neutron flux peak, x-ray flux) helpful in designing functional nuclear weapons.
What is a nuclear subatomic blast?
I am sorry, I do not understand your question. Please clarify "subatomic".If you actually meant subcritical, it is when they make a test device that is deliberately designed to never become critical. Such a device cannot produce a nuclear yield, but they can still make measurements on it (e.g. neutron flux peak, x-ray flux) helpful in designing functional nuclear weapons.
What happens when the mass of fissile material used in nuclear weapons is subcritical?
Nothing, it has to become supercritical for a nuclear detonation to happen. Most bombs perform this transition from subcritical state to supercritical state by an implosion driven by conventional explosive lenses. Once supercritical a neutron source is fired through the fissile material to start the reaction leading to the nuclear detonation.There is a special type of test detonation called a hydronuclear test where the amount of fissile material remains subcritical throughout the implosion. When the neutron source fires the reaction simply multiplies the number of neutrons by a factor then dies out. No nuclear detonation happens. Measurements of this neutron flux can tell about the quality of the implosion, safety, etc. But as there is no nuclear yield, several of the nuclear test ban treaties allowed these hydronuclear tests while banning tests with nuclear yields.
What is meant by supercritical and how does it relate to making a nuclear bomb?
A subcritical mass cannot sustain a nuclear chain reaction, it dies exponentiallyA critical mass can sustain a nuclear chain reaction, but it remains constant neither increasing nor decreasingA supercritical mass not only sustains a nuclear chain reaction but it increases exponentially until the mass explodesA nuclear fission bomb must become supercritical at some time in order to explode.
Does the water used to cool a nuclear reactor get contaminated?
In a properly operating nuclear reactor, water used to cool the reactor is not contaminated. This water, called primary coolant, is quite pure. And after shutdown and cooldown, the water has little radiation in it. But if the reactor has some malfunction that overheats the fuel, fuel elements can rupture or melt (a meltdown) and fission products, which are hightly radioactive, can be released into the coolant (the water). The water is then contaminated.
What could happen when the uranium pellets in the rods ate the core of a nuclear reactor become overheated?
When uranium pellets in a nuclear reactor become overheated, the fuel rods can start to melt, leading to a loss of structural integrity. This can result in a partial or full meltdown of the reactor core, releasing radioactive materials into the environment and potentially causing a nuclear accident like the one that occurred in Chernobyl or Fukushima. Cooling systems must be maintained to prevent overheating.
How heavy water is used to make plutonium from uranium?
Heavy water can be used in a nuclear reactor to moderate the speed of neutrons, making it easier for uranium-238 to absorb a neutron and become plutonium-239. This process is known as breeding plutonium in a reactor and is one method of producing plutonium for nuclear weapons or fuel.
Does uranium need to be changed in order to be used?
Yes, the nuclear fuel from a nuclear reactor must be replaced at some intervals, because the fuel can be poisoned with neutron absorbers and the clad can become fragile and unsure; the "burned" fuel is recycled.
What does a 'reflector' do in the core of a fission atomic bomb?
The reflector in a nuclear weapon core is made of a material which can reflect neutrons from fission in the core back into the core, instead of wasting them. A tamper can permit a smaller mass of nuclear fuel (an unreflected subcritical mass of nuclear material can quickly become critical if a reflector is used). Depending on the material, they can also have a neutron-moderation effect. The tamper in many nuclear weapons is also the reflector.
