87 Sentences With "fission reaction" | Random Sentence Generator

Fusion reactions release many times the energy of a fission reaction.

One fission reaction leads to another, and this explosive energy is what fuels nuclear bombs.

Before flight, the boron carbide would be fully inserted into the reactor to prevent a fission reaction.

That's where the nuclear fission reaction takes place, powered by fuel composed of uranium dioxide baked into ceramic pellets.

Antineutrinos make up a substantial fraction (around 4.5 percent) of the total energy released in a nuclear fission reaction.

Nuclear "boosting" is a process by which the energy created by a weapon is more powerful than a fission reaction.

Thermonuclear weapons typically use a fission explosion to create a fusion reaction, which is far more powerful than a fission reaction.

Only uranium-235 can sustain the fission reaction that makes a nuclear weapon do its thing, but the infinitesimal amounts found in nature won't quite cut it.

Only uranium-23.6 can sustain the fission reaction that makes nuclear reactors tick, so turning the ore into usable fuel requires separating the uranium-22024 out in a process called enrichment.

Instead of triggering a fission reaction, they use large amounts of electricity—enough to meet the power needs of several hundred average American homes—to heat the fuel cell several thousand degrees.

This process of fusion releases even more energy per unit of mass than fission does, and the energy released from the fusion reaction also feeds back into the fission reaction, increasing its output.

But when Leo Szilard invented the nuclear chain reaction, he didn't know which atoms could be induced to go through a fission reaction and produce neutrons that would then produce more fission reactions.

The heat from the fission reaction is used to heat liquid sodium, which transfers this heat to eight Stirling engines that convert the heat into mechanical motion to drive electric generators and produce electricity.

Once it is extracted, however, the fission reaction will begin and cannot be stopped completely, although the rate of fission—and hence heat output—can be controlled by the depth of the boron rod in the reactor.

TEPCO retracts Wednesday's statement about a possible self-sustained fission reaction, and now claims that the xenon was a result of the normal decay of radioisotopes in the fuel.

Boric acid is injected into reactor number 2 after the discovery of xenon in its containment vessel. The presence of xenon may be an indication that a self-sustained fission reaction has been occurring.

A fizzle can spread radioactive material throughout the surrounding area, involve a partial fission reaction of the fissile material, or both.Theodore E. Liolios." The Effects of Nuclear Terrorism: Fizzles." (PDF) European Program on Science and International Security.

The fission reaction releases energy and neutrons. The released neutrons can hit other uranium or plutonium nuclei, causing new fission reactions, which release more energy and more neutrons. This is called a chain reaction. The reaction rate is controlled by control rods that absorb excess neutrons.

To control such a nuclear chain reaction, Control rods containing neutron poisons and neutron moderators can change the portion of neutrons that will go on to cause more fission. Nuclear reactors generally have automatic and manual systems to shut the fission reaction down if monitoring detects unsafe conditions.

There are several advantages relative to conventional NTR designs. As the peak neutron flux and fission reaction rates would occur outside the vehicle, these activities could be much more vigorous than they could be if it was necessary to house them in a vessel (which would have temperature limits due to materials constraints). Additionally, a contained reactor can only allow a small percentage of its fuel to undergo fission at any given time, otherwise it would overheat and melt down (or explode in a runaway fission chain reaction). The fission reaction in an NSWR is dynamic and because the reaction products are exhausted into space it doesn't have a limit on the proportion of fission fuel that reacts.

In the early 2000s, research was undertaken by Sandia National Laboratories, Los Alamos National Laboratory, The University of Florida, Texas A&M; University and General Atomics to use direct conversion to extract energy from fission reactions, essentially, attempting to extract energy from the linear motion of charged particles coming off a fission reaction.

Stability at low pressure permits less robust reactor vessels and increases reliability. The high reactivity of fluorine traps most fission reaction byproducts. It appeared that the fluid salt would permit on-site chemical separation of the fuel and wastes. The fuel system was located in sealed cells, laid out for maintenance with long-handled tools through openings in the top shielding.

In 1942, he was invited to participate in the Manhattan Project. As part of the Manhattan Project, Slotin performed experiments with uranium and plutonium cores to determine their critical mass values. After World War II, Slotin continued his research at Los Alamos National Laboratory. On 21 May 1946, Slotin accidentally began a fission reaction, which released a burst of hard radiation.

In order to start up a controllable fission reaction, the assembly must be delayed-critical. In other words, k must be greater than 1 (supercritical) without crossing the prompt-critical threshold. In nuclear reactors this is possible due to delayed neutrons. Because it takes some time before these neutrons are emitted following a fission event, it is possible to control the nuclear reaction using control rods.

They conducted experiments with a spherical geometry (hollow spheres) of uranium surrounded by heavy water. Trial L-I was done in August 1940, and L-II was conducted six months later. Results from trial L-IV, in the summer of 1942, indicated that the spherical geometry, with five metric tons of heavy water and 10 metric tons of metallic uranium, could sustain a fission reaction.

William Rudolph Kanne, also known as W. Rudolph Kanne (7 July 1913 – 24 October 1985), was a physicist, inventor and pioneer in the field of gas flow through ionization detectors, a member of the group responsible for the first self-sustained nuclear chain fission reaction at Staggs Field in Chicago, and participated in the Manhattan Project at the Chicago, Oak Ridge and Hanford sites.

Mini-Mag Orion (MMO), or Miniature Magnetic Orion, is a proposed type of spacecraft propulsion based on the Project Orion nuclear propulsion system. The Mini-Mag Orion system achieves propulsion by compressing fissile material in a magnetic field, a Z-pinch, until fission occurs. This fission reaction propels the craft. MMO should be able to propel 100 tons to Mars within 3 months or to Jupiter in about one year.

Decay heat, while dangerous and strong enough to melt the core, is not nearly as intense as an active fission reaction. During the post shutdown period the reactor requires cooling water to be pumped or the reactor will overheat. If the temperature exceeds 2200 °C, cooling water will break down into hydrogen and oxygen, which can form a (chemically) explosive mixture. Decay heat is a major risk factor in LWR safety record.

At 11 p.m. on 16 June 1958 a criticality accident occurred in the C-1 Wing of Building 9212 at the facility, then operating under the management of Union Carbide. In the incident, a solution of highly enriched uranium was mistakenly diverted into a steel drum, causing a fission reaction of 15–20 minutes duration. Eight workers were hospitalized for moderate to severe radiation sickness or exposure, but all eventually returned to work.

The first procedure is to properly shut down the site and stow any spent fuel or waste. The waste and reactors are often at extremely high temperatures due to the fission reaction that occurs. The waste is often placed in cooling pools filled with treated water where they await to cool to handling temperatures. Once the waste is cool enough it will often be stored in radioactive-resistant containers to await being disposed of.

One benefit of such reactors is the relatively short half-lives of their waste products. For proton accelerators, the high-energy proton beam impacts a molten lead target inside the core, chipping or "spalling" neutrons from the lead nuclei. These spallation neutrons convert fertile thorium to protactinium-233 and after 27 days into fissile uranium-233 and drive the fission reaction in the uranium. Thorium reactors can generate power from the plutonium residue left by uranium reactors.

This property, known as the negative temperature coefficient of reactivity, makes PWRs very stable. In event of a loss-of-coolant accident, the moderator is also lost and the active fission reaction will stop. Heat is still produced after the chain reaction stops from the radioactive byproducts of fission, at about 5% of rated power. This "decay heat" will continue for 1 to 3 years after shut down, whereupon the reactor finally reaches "full cold shutdown".

Reflectors were arranged around the outside of the reactor to provide the means to control the reactor. The reflectors were composed of a layer of beryllium, which would reflect neutrons, thus allowing the reactor to begin and maintain the fission process. The reflectors were held in place by a retaining band anchored by an explosive bolt. When the reflector was ejected from the unit, the reactor could not sustain the nuclear fission reaction and the reactor permanently shut down.

Many artificial radionuclides of technological importance are produced as fission products within nuclear reactors. A fission product is a nucleus with approximately half the mass of a uranium or plutonium nucleus which is left over after such a nucleus has been "split" in a nuclear fission reaction. Caesium-137 is one such radionuclide. It has a half-life of 30 years, and decays by beta decay without gamma ray emission to a metastable state of barium-137 ().

The neutron flux at the imaging focal plane is measured by a CCD imaging array with a neutron scintillation screen in front of it. The scintillation screen is made of zinc sulfide, a fluorescent compound, laced with lithium. When a thermal neutron is absorbed by a lithium-6 nucleus, it causes a fission reaction that produces helium, tritium and energy. These fission products cause the ZnS phosphor to light up, producing an optical image for capture by the CCD array.

It dominates in stars with masses less than or equal to that of the Sun, whereas the CNO cycle, the other known reaction, is suggested by theoretical models to dominate in stars with masses greater than about 1.3 times that of the Sun. In general, proton–proton fusion can occur only if the kinetic energy (i.e. temperature) of the protons is high enough to overcome their mutual electrostatic repulsion.Ishfaq Ahmad, The Nucleus, 1: 42, 59, (1971), The Proton type-nuclear fission reaction.

Controlled, viable fusion power has proven elusive, despite the occasional hoax. Technical and theoretical difficulties have hindered the development of working civilian fusion technology, though research continues to this day around the world. Nuclear fusion was initially pursued only in theoretical stages during World War II, when scientists on the Manhattan Project (led by Edward Teller) investigated it as a method to build a bomb. The project abandoned fusion after concluding that it would require a fission reaction to detonate.

The fission reaction was sustained for hundreds of thousands of years, cycling on the order of hours to a few days. These natural reactors are extensively studied by scientists interested in geologic radioactive waste disposal. They offer a case study of how radioactive isotopes migrate through the Earth's crust. This is a significant area of controversy as opponents of geologic waste disposal fear that isotopes from stored waste could end up in water supplies or be carried into the environment.

However, in this engine the propellant can be anything with suitable properties as there will be no reaction on the part of the propellant. In a NSWR the nuclear salt-water would be made to flow through a reaction chamber and out of an exhaust nozzle in such a way and at such speeds that critical mass will begin once the chamber is filled to a certain point; however, the peak neutron flux of the fission reaction would occur outside the vehicle.

Most neutrons in a reactor are prompt neutrons; that is, neutrons produced directly by a fission reaction. These neutrons move at a high velocity, so they are likely to escape into the moderator before being captured. On average, it takes about 13 μs for the neutrons to be slowed by the moderator enough to facilitate a sustained reaction, which allows the insertion of neutron absorbers to affect the reactor quickly. As a result, once the reactor has been SCRAMed, the reactor power will drop significantly almost instantaneously.

In this instance, the "gun" is part of a nuclear weapon and contains an explosively propelled sub-critical slug of fissile material within a barrel to be fired into a second sub-critical mass in order to initiate the fission reaction. Potentially confused with this usage are small nuclear devices capable of being fired by artillery or recoilless rifle. In civilian use, the captive bolt pistol is used in agriculture to humanely stun farm animals for slaughter. Shotguns are normally civilian weapons used primarily for hunting.

He saw an analogy between the plutonium fission reaction and the newly discovered supernovae, and he was able to show that exploding super novae produced all of the elements in the same proportion as existed on Earth. He felt that he had accidentally fallen into a subject that would make his career. Autobiography William A. Fowler His work explained the production of all heavier elements, starting from hydrogen. Hoyle proposed that hydrogen is continuously created in the universe from vacuum and energy, without need for universal beginning.

A simplified summary of the above explanation is: # An implosion assembly type of fission bomb explodes. This is the primary stage. If a small amount of deuterium/tritium gas is placed inside the primary's core, it will be compressed during the explosion and a nuclear fusion reaction will occur; the released neutrons from this fusion reaction will induce further fission in the 239Pu or 235U used in the primary stage. The use of fusion fuel to enhance the efficiency of a fission reaction is called boosting.

Decay heat as fraction of full power for a reactor SCRAMed from full power at time 0, using two different correlations In a typical nuclear fission reaction, 187 MeV of energy are released instantaneously in the form of kinetic energy from the fission products, kinetic energy from the fission neutrons, instantaneous gamma rays, or gamma rays from the capture of neutrons.DOE fundamentals handbook - Nuclear physics and reactor theory - volume 1 of 2, module 1, page 61 An additional 23 MeV of energy are released at some time after fission from the beta decay of fission products. About 10 MeV of the energy released from the beta decay of fission products is in the form of neutrinos, and since neutrinos are very weakly interacting, this 10 MeV of energy will not be deposited in the reactor core. This results in 13 MeV (6.5% of the total fission energy) being deposited in the reactor core from delayed beta decay of fission products, at some time after any given fission reaction has occurred. In a steady state, this heat from delayed fission product beta decay contributes 6.5% of the normal reactor heat output.

In nuclear engineering, prompt criticality describes a nuclear fission event in which criticality (the threshold for an exponentially growing nuclear fission chain reaction) is achieved with prompt neutrons alone (neutrons that are released immediately in a fission reaction) and does not rely on delayed neutrons (neutrons released in the subsequent decay of fission fragments). As a result, prompt criticality causes a much more rapid growth in the rate of energy release than other forms of criticality. Nuclear weapons are based on prompt criticality, while most nuclear reactors rely on delayed neutrons to achieve criticality.

Experimental Breeder Reactor I in Idaho, USA. Sometimes the switch will have a flip cover to prevent inadvertent operation A scram or SCRAM, also known as AZ-5 (), is an emergency shutdown of a nuclear reactor effected by immediately terminating the fission reaction. It is also the name that is given to the manually operated kill switch that initiates the shutdown. In commercial reactor operations, this type of shutdown is often referred to as a "SCRAM" at boiling water reactors (BWR), a "reactor trip" at pressurized water reactors (PWR) and EPIS at a CANDU reactor.

This means that with rising temperature the neutron moderation drops and the nuclear fission reaction in the core is dampened, leading to a lower core temperature. This means as more energy is taken out of the core the moderation rises and the fission process is stoked to produce more heat. The concept for this type of nuclear reactor was developed by the scientists Otis Peterson and Robert Kimpland of the Los Alamos National Laboratory (LANL) in New Mexico.Peterson, O.G., Kimpland, R.H., Coates, D.M.: Compact, Self-Regulating Nuclear Reactor.

In the event of a reactor overheating thermal expansion of the salt stops the fission reaction and if necessary triggers freeze valves to drain the reactor and separating the fuel from the moderator. Hazardous fission products iodine-131, cesium-137 and strontium-90 are chemically bound in the reactor salt preventing their release. The steam/electrical section features the same design and cost ($700/kw) of a 500 MWe coal plant. A 1 GWe nuclear component requires less than 400 tons of supercritical alloys and other exotic materials.

The natural nuclear reactor formed when a uranium-rich mineral deposit became inundated with groundwater that acted as a neutron moderator, and a nuclear chain reaction took place. The heat generated from the nuclear fission caused the groundwater to boil away, which slowed or stopped the reaction. After cooling of the mineral deposit, the water returned, and the reaction restarted, completing a full cycle every 3 hours. The fission reaction cycles continued for hundreds of thousands of years and ended when the ever-decreasing fissile materials no longer could sustain a chain reaction.

One group, studying distant quasars, has claimed to detect a variation of the fine structure constant at the level in one part in 105. Other authors dispute these results. Other groups studying quasars claim no detectable variation at much higher sensitivities. For over three decades since the discovery of the Oklo natural nuclear fission reactor in 1972, even more stringent constraints, placed by the study of certain isotopic abundances determined to be the products of a (estimated) 2 billion year-old fission reaction, seemed to indicate no variation was present.

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.

Conducted on May 25, 1951, Item was the first test of an actual boosted fission weapon, nearly doubling the normal yield of a similar non-boosted weapon. In this test, deuterium-tritium (D-T) gas was injected into the enriched uranium core of a nuclear fission bomb. The extreme heat of the fissioning bomb produced thermonuclear fusion reactions within the D-T gas. While not enough to be considered a full nuclear fusion bomb, the large number of high-energy neutrons released nearly doubled the efficiency of the nuclear fission reaction.

This causes the immediate cessation of steam flow and an immediate rise in BWR pressure. This rise in pressure effectively subcools the reactor coolant instantaneously; the voids (vapor) collapse into solid water. When the voids collapse in the reactor, the fission reaction is encouraged (more thermal neutrons); power increases drastically (120%) until it is terminated by the automatic insertion of the control rods. So, when the reactor is isolated from the turbine rapidly, pressure in the vessel rises rapidly, which collapses the water vapor, which causes a power excursion which is terminated by the Reactor Protection System.

The hafnium controversy is a debate over the possibility of 'triggering' rapid energy releases, via gamma ray emission, from a nuclear isomer of hafnium, 178m2Hf. The energy release is potentially 5 orders of magnitude (100,000 times) more energetic than a chemical reaction, but 2 orders of magnitude less than a nuclear fission reaction. In 1998, a group led by Carl Collins of the University of Texas at Dallas reported having successfully initiated such a trigger. Signal-to-noise ratios were small in those first experiments, and to date no other group has been able to duplicate these results.

A boosted fission weapon usually refers to a type of nuclear bomb that uses a small amount of fusion fuel to increase the rate, and thus yield, of a fission reaction. The neutrons released by the fusion reactions add to the neutrons released due to fission, allowing for more neutron-induced fission reactions to take place. The rate of fission is thereby greatly increased such that much more of the fissile material is able to undergo fission before the core explosively disassembles. The fusion process itself adds only a small amount of energy to the process, perhaps 1%.

On 1 November 2011 TEPCO said that xenon-133 and xenon-135 were detected in gas-samples taken from the containment vessel of reactor 2, in a concentration of 6 to 10 (or more) parts per million becquerels per cubic centimeter. Xenon-135 was also detected in gas samples collected on 2 November. These isotopes are the result of nuclear fission-reaction of uranium. Because the short half-lifes of these gases: (Xe-133: 5 days Xe-135: 9 hours), the presence could only mean that nuclear fissions were occurring at some places in the reactor.

In this reaction, a neutron plus a fissionable atom causes a fission resulting in a larger number of neutrons than the single one that was consumed in the initial reaction. Thus was born the practical nuclear chain reaction by the mechanism of neutron-induced nuclear fission. Specifically, if one or more of the produced neutrons themselves interact with other fissionable nuclei, and these also undergo fission, then there is a possibility that the macroscopic overall fission reaction will not stop, but continue throughout the reaction material. This is then a self-propagating and thus self-sustaining chain reaction.

Conversely, when the control rods are lifted out of the way, more neutrons strike the fissile uranium-235 (U-235) or plutonium-239 (Pu-239) nuclei in nearby fuel rods, and the chain reaction intensifies. The core shroud, also located inside of the reactor, directs the water flow to cool the nuclear reactions inside of the core. The heat of the fission reaction is removed by the water, which also acts to moderate the neutron reactions. An alternative form of nuclear fuel would be fissile uranium-233 (U-233) made by the neutron-bombardment of the common thorium-232.

It is also electrically conductive, and so needs to be applied more carefully than regular non-conductive compounds. Two thermal interfaces have already been developed: Thermal Grizzly Conductonaut and Coolaboratory Liquid Ultra, with thermal conductivities of 73 and 38.4 W/mK respectively. However, they must be carefully applied with a Q-tip (unlike ordinary thermal compounds, where no manual spreading is needed), and cannot be used on aluminum heatsinks as aforementioned. Galinstan is difficult to use for cooling fission-based nuclear reactors, because indium has a high absorption cross section for thermal neutrons, efficiently absorbing them and inhibiting the fission reaction.

99mTc is conveniently available in high radionuclidic purity from molybdenum-99, which decays with 87% probability to 99mTc. The subsequent decay of 99mTc leads to either 99Tc or 99Ru. 99Mo can be produced in a nuclear reactor via irradiation of either molybdenum-98 or naturally occurring molybdenum with thermal neutrons, but this is not the method currently in use today. Currently, 99Mo is recovered as a product of the nuclear fission reaction of 235U, separated from other fission products via a multistep process and loaded onto a column of alumina that forms the core of a 99Mo/99mTc radioisotope "generator".

Since 1 neutron is required to sustain the fission reaction, this leaves a budget of less than 1 neutron per fission to breed new fuel. In addition, the materials in the core such as metals, moderators and fission products absorb some neutrons, leaving too few neutrons to breed enough fuel to continue operating the reactor. As a consequence they must add new fissile fuel periodically and swap out some of the old fuel to make room for the new fuel. In a reactor that breeds at least as much new fuel as it consumes, it is not necessary to add new fissile fuel.

The "Thin Man" design was an early nuclear weapon design proposed before plutonium had been successfully bred in a nuclear reactor from the irradiation of uranium-238. It was assumed that plutonium, like uranium-235, could be assembled into a critical mass by a gun-type method, which simply involved shooting one sub-critical piece into another. To avoid pre-detonation or "fizzle", the plutonium "bullet" would need to be accelerated to a speed of at least —or else the fission reaction would begin before the assembly was complete, blowing the device apart prematurely. Thin Man was long, with wide tail and nose assemblies, and a midsection.

Under normal circumstances, a critical or supercritical fission reaction (one that is self- sustaining in power or increasing in power) should only occur inside a safely shielded location, such as a reactor core or a suitable test environment. A criticality accident occurs if the same reaction is achieved unintentionally, for example in an unsafe environment or during reactor maintenance. Though dangerous and frequently lethal to humans within the immediate area, the critical mass formed would not be capable of producing a massive nuclear explosion of the type that fission bombs are designed to produce. This is because all the design features needed to make a nuclear warhead cannot arise by chance.

The reactors are shut down using special control rods to deter the fission reaction and allow for the cooling of the reactor and fuel inside. Once cool, the fuel is taken out and dealt with like the waste, while the reactor is sealed in order to allow no escape of radioactive particles or gases. Lastly the heating water is then pumped out and put in containers to await proper decontamination; the coolant is also removed and stored for proper disposal. This procedure is often performed by the company that owned the plant, and if the company is unable to then properly qualified contractors are brought in.

Some downsides to the design include the radiation hazards inherent to nuclear pulse propulsion as well as the limited availability of the antiprotons used to initialize the nuclear fission reaction. Even the small amount required by the ACMF engine is equal to the total antimatter production at the facilities CERN and Fermilab over many years, although these create antimatter only as a byproduct of physics experiments, not as a goal. ICAN-II is similar to the Project Orion design put forth by Stanislaw Ulam in the late 1950s. The Orion was intended to be used to send humans to Mars and Venus by 1968.

Keff < 1, a subcritical multiplication is achieved which increases the neutron background and produces energy from fission reactions. Although the number of fissions produced in the RTG is very small (making their gamma radiation negligible), because each fission reaction releases almost 30 times more energy than each alpha decay (200 MeV compared to 6 MeV), up to a 10% energy gain is attainable, which translates into a reduction of the 238Pu needed per mission. The idea was proposed to NASA in 2012 for the yearly NASA NSPIRE competition, which translated to Idaho National Laboratory at the Center for Space Nuclear Research (CSNR) in 2013 for studies of feasibility.Design of a high power (1 kWe), subcritical, power source .

Columbia was established as King's College by royal charter of George II of Great Britain in reaction to the founding of Princeton College. It was renamed Columbia College in 1784 following the American Revolution, and in 1787 was placed under a private board of trustees headed by former students Alexander Hamilton and John Jay. In 1896, the campus was moved to its current location in Morningside Heights and renamed Columbia University. Columbia scientists and scholars have played an important role in scientific breakthroughs including: brain-computer interface; the laser and maser; nuclear magnetic resonance; the first nuclear pile; the first nuclear fission reaction in the Americas; the first evidence for plate tectonics and continental drift;N.

In any reactor, a SCRAM is achieved by inserting large amounts of negative reactivity mass into the midst of the fissile material, to immediately terminate the fission reaction. In light-water reactors, this is achieved by inserting neutron-absorbing control rods into the core, although the mechanism by which rods are inserted depends on the type of reactor. In PWRs, the control rods are held above a reactor's core by electric motors against both their own weight and a powerful spring. A SCRAM is designed to release the control rods from those motors and allows their weight and the spring to drive them into the reactor core, rapidly halting the nuclear reaction by absorbing liberated neutrons.

At the same time, the rocket effect on the surface of the hohlraum would force the radiation case to speed outwards. The ballistic case would confine the exploding radiation case for as long as necessary. The fact that the tamper material was uranium enriched in U is primarily based on the final fission reaction fragments detected in the radiochemical analysis, which conclusively showed the presence of U, found by the Japanese in the shot debris. The first-generation thermonuclear weapons (MK-14, 16, 17, 21, 22 and 24) all used uranium tampers enriched to 37.5% U. The exception to this was the MK-15 ZOMBIE that used a 93.5% enriched fission jacket.

Values of k larger than 1 mean that the fission reaction is releasing more neutrons than it absorbs, and therefore is referred to as a self-sustaining chain reaction. A mass of fissile material large enough (and in a suitable configuration) to induce a self-sustaining chain reaction is called a critical mass. When a neutron is captured by a suitable nucleus, fission may occur immediately, or the nucleus may persist in an unstable state for a short time. If there are enough immediate decays to carry on the chain reaction, the mass is said to be prompt critical, and the energy release will grow rapidly and uncontrollably, usually leading to an explosion.

Ernest Rutherford commented in the article that inefficiencies in the process precluded use of it for power generation. However, the neutron had been discovered in 1932, shortly before, as the product of a nuclear reaction. Szilárd, who had been trained as an engineer and physicist, put the two nuclear experimental results together in his mind and realized that if a nuclear reaction produced neutrons, which then caused further similar nuclear reactions, the process might be a self- perpetuating nuclear chain-reaction, spontaneously producing new isotopes and power without the need for protons or an accelerator. Szilárd, however, did not propose fission as the mechanism for his chain reaction, since the fission reaction was not yet discovered, or even suspected.

It was immediately apparent to many scientists that, in theory at least, an extremely powerful explosive could be created, although most still considered an atomic bomb was an impossibility. Perrin defined a critical mass of uranium to be the smallest amount that could sustain a chain reaction. The neutrons used to cause fission in uranium are considered slow neutrons, but when neutrons are released during a fission reaction they are released as fast neutrons which have much more speed and energy. Thus, in order to create a sustained chain reaction, there existed a need for a neutron moderator to contain and slow the fast neutrons until they reached a usable energy level.

Lise Meitner and her nephew, the physicist Otto Robert Frisch, published the physical explanation in February 1939 and named the process "nuclear fission". Soon after, Fermi hypothesized that the fission of uranium might release enough neutrons to sustain a fission reaction. Confirmation of this hypothesis came in 1939, and later work found that on average about 2.5 neutrons are released by each fission of the rare uranium isotope uranium-235. Fermi urged Alfred O. C. Nier to separate uranium isotopes for determination of the fissile component, and on February 29, 1940, Nier used an instrument he built at the University of Minnesota to separate the world's first uranium-235 sample in the Tate Laboratory.

These are devices incorporated in nuclear weapons which produce a pulse of neutrons when the bomb is detonated to initiate the fission reaction in the fissionable core (pit) of the bomb, after it is compressed to a critical mass by explosives. Actuated by an ultrafast switch like a krytron, a small particle accelerator drives ions of tritium and deuterium to energies above the 15 keV or so needed for deuterium-tritium fusion and directs them into a metal target where the tritium and deuterium are adsorbed as hydrides. High-energy fusion neutrons from the resulting fusion radiate in all directions. Some of these strike plutonium or uranium nuclei in the primary's pit, initiating nuclear chain reaction.

The fusion process alone currently does not achieve sufficient gain (power output over power input) to be viable as a power source. By using the excess neutrons from the fusion reaction to in turn cause a high-yield fission reaction (close to 100%) in the surrounding subcritical fissionable blanket, the net yield from the hybrid fusion–fission process can provide a targeted gain of 100 to 300 times the input energy (an increase by a factor of three or four over fusion alone). Even allowing for high inefficiencies on the input side (i.e. low laser efficiency in ICF and Bremsstrahlung losses in Tokamak designs), this can still yield sufficient heat output for economical electric power generation.

In a fission bomb, at sea level, the total radiation pulse energy which is composed of both gamma rays and neutrons is approximately 5% of the entire energy released; in neutron bombs it would be closer to 40%, with the percentage increase coming from the higher production of neutrons. Furthermore, the neutrons emitted by a neutron bomb have a much higher average energy level (close to 14 MeV) than those released during a fission reaction (1–2 MeV). Technically speaking, every low yield nuclear weapon is a radiation weapon, including non-enhanced variants. All nuclear weapons up to about 10 kilotons in yield have prompt neutron radiation as their furthest-reaching lethal component.

Immediately after the earthquake, the electricity-producing Reactors 1, 2, and 3 automatically shut down their sustained fission reactions by inserting control rods in a safety procedure referred to as a SCRAM, which ends the reactors' normal running conditions, by closing down the fission reaction in a controlled manner. As the reactors were now unable to generate power to run their own coolant pumps, emergency diesel generators came online, as designed, to power electronics and coolant systems. These operated normally until the tsunami destroyed the generators for Reactors 1–5. The two generators cooling Reactor 6 were undamaged and were sufficient to be pressed into service to cool the neighboring Reactor 5 along with their own reactor, averting the overheating issues the other reactors suffered.

On 21 May 1946, with seven colleagues watching, Slotin performed an experiment that involved the creation of one of the first steps of a fission reaction by placing two half-spheres of beryllium (a neutron reflector) around a plutonium core. The experiment used the same plutonium core that had irradiated Harry Daghlian, later called the "demon core" for its role in the two accidents. Slotin grasped the upper 228.6 mm (9-inch) beryllium hemisphere with his left hand through a thumb hole at the top while he maintained the separation of the half-spheres using the blade of a screwdriver with his right hand, having removed the shims normally used. Using a screwdriver was not a normal part of the experimental protocol.

If the temperature of the fuel bundles increases to the point where they are mechanically unstable, their horizontal layout means that they will bend under gravity, shifting the layout of the bundles and reducing the efficiency of the reactions. Because the original fuel arrangement is optimal for a chain reaction, and the natural uranium fuel has little excess reactivity, any significant deformation will stop the inter-fuel pellet fission reaction. This will not stop heat production from fission product decay, which would continue to supply a considerable heat output. If this process further weakens the fuel bundles, the pressure tube they are in will eventually bend far enough to touch the calandria tube, allowing heat to be efficiently transferred into the moderator tank.

Her non-citizen status did not preclude her from working for the Office of Scientific Research and Development (OSRD), to which she gave her methods without compensation. Before the Manhattan Project, polonium had been used only in small samples, but the project proposed to use both polonium and beryllium to create a reaction forcing neutrons to be ejected and ignite the fission reaction required for the atom bomb. Plutonium plants, based on her specifications for what was needed to process element, were built in the New Mexico desert at Los Alamos National Laboratory, but Rona was given no details. Rona's methods were also used as part of the experiments conducted by the Office of Human Radiation Experiments to determine the effects of human exposure to radiation.

The U.S. Navy awarded Columbia University $6,000 in funding, most of which Enrico Fermi and Szilard spent on purchasing graphite. A team of Columbia professors including Fermi, Szilard, Eugene T. Booth and John Dunning created the first nuclear fission reaction in the Americas, verifying the work of Hahn and Strassmann. The same team subsequently built a series of prototype nuclear reactors (or "piles" as Fermi called them) in Pupin Hall at Columbia, but were not yet able to achieve a chain reaction. The Advisory Committee on Uranium became the National Defense Research Committee (NDRC) on Uranium when that organization was formed on 27 June 1940.. Briggs proposed spending $167,000 on research into uranium, particularly the uranium-235 isotope, and plutonium, which was discovered in 1940 at the University of California.

In 1919, Ernest Rutherford was able to accomplish transmutation of nitrogen into oxygen at the University of Manchester, using alpha particles directed at nitrogen 14N + α → 17O + p. This was the first observation of an induced nuclear reaction, that is, a reaction in which particles from one decay are used to transform another atomic nucleus. Eventually, in 1932 at Cambridge University, a fully artificial nuclear reaction and nuclear transmutation was achieved by Rutherford's colleagues John Cockcroft and Ernest Walton, who used artificially accelerated protons against lithium-7, to split the nucleus into two alpha particles. The feat was popularly known as "splitting the atom", although it was not the modern nuclear fission reaction later discovered in heavy elements, in 1938 by the German scientists Otto Hahn, Lise Meitner, and Fritz Strassmann.

At RMI's headquarters the south- facing building complex is so energy-efficient that, even with local -40 °F (-40 °C) winter temperatures, the building interiors can maintain a comfortable temperature solely from the sunlight admitted plus the body heat of the people who work there. The environment can actually nurture semi- tropical and tropical indoor plants. The Lovinses described the "hard energy path" as involving inefficient liquid-fuel automotive transport, as well as giant centralized electricity-generating facilities, often burning fossil fuels such as coal or petroleum, or harnessing a fission reaction, greatly complicated by electricity wastage and loss. The "soft energy path" which they wholly preferred involves efficient use of energy, diversity of energy production methods (and matched in scale and quality to end uses), and special reliance on "soft technologies" (alternative technology) such as solar, wind, biofuels, and geothermal.

Experiments along a similar line to Fermi's, by Irène Joliot-Curie, Frédéric Joliot-Curie and Pavle Savić in 1938 raised what they called "interpretational difficulties" when the supposed transuranics exhibited the properties of rare earths rather than those of adjacent elements. Ultimately on December 17, 1938, Otto Hahn and Fritz Strassmann provided chemical proof that the previously presumed transuranic elements were isotopes of barium, and Hahn wrote these exciting results to his exiled colleague Lise Meitner, explaining the process as a 'bursting' of the uranium nucleus into lighter elements. Meitner and Otto Frisch utilized Fritz Kalckar and Niels Bohr's liquid drop hypothesis (first proposed by George Gamow in 1935) to provide a first theoretical model and mathematical proof of what Frisch coined nuclear fission. Frisch also experimentally verified the fission reaction by means of a cloud chamber, confirming the energy release.

Air-burst fuzing also increases the range that people's skin will have a line-of-sight with the nuclear fireball. However, as a result of the high altitude of the explosion, most of the radioactive bomb debris is dispersed into the stratosphere, with a great column of air therefore placed between the vast majority of the bomb debris/fission reaction products and people on the ground for a number of crucial days before it falls out of the atmosphere in a comparatively dilute fashion. This "delayed fallout" is henceforth not an immediate concern to those near the blast. On the other hand, the only time that fallout is rapidly concentrated in a potentially lethal fashion in the local/regional area around the explosion is when the nuclear fireball makes contact with the ground surface, with an explosion that does so, being aptly termed a surface burst.

In fact, Taylor indirectly referenced a concept for a nuclear reactor which is inherently similar to a reactor that he patented in 1964. Taylor spent much of his time studying the risk potential of the nuclear power fuel cycle after learning about the detrimental effects that his nuclear weapons had on the environment, so he sought to explore new opportunities for safer use of nuclear power. In his writing, Taylor argued that the most dangerous and devastating events that could possibly occur during nuclear research would most likely happen at reactors that are incapable of running efficiently and maintaining a safe temperature. Taylor went on to state that the prioritization of safety in nuclear reactors is relatively low compared to how it should be, and that if one were to create a nuclear reactor with the capability of cooling down—without the initiation of a fission reaction—then efforts at harvesting nuclear energy would be more incentivized and exponentially safer.

Isolated and stored anti-matter could be used as a fuel for interplanetary or interstellar travel as part of an antimatter catalyzed nuclear pulse propulsion or other antimatter rocketry, such as the redshift rocket. Since the energy density of antimatter is higher than that of conventional fuels, an antimatter-fueled spacecraft would have a higher thrust-to-weight ratio than a conventional spacecraft. If matter–antimatter collisions resulted only in photon emission, the entire rest mass of the particles would be converted to kinetic energy. The energy per unit mass () is about 10 orders of magnitude greater than chemical energies,(compared to the formation of water at , for example) and about 3 orders of magnitude greater than the nuclear potential energy that can be liberated, today, using nuclear fission (about per fission reaction or ), and about 2 orders of magnitude greater than the best possible results expected from fusion (about for the proton–proton chain).