Fission fragment reactor
Encyclopedia
Similar to how the fission-fragment rocket
Fission-fragment rocket
The fission-fragment rocket is a rocket engine design that directly harnesses hot nuclear fission products for thrust, as opposed to using a separate fluid as working mass...

 produces thrust, a fission fragment reactor is a nuclear reactor
Nuclear reactor
A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction. Most commonly they are used for generating electricity and for the propulsion of ships. Usually heat from nuclear fission is passed to a working fluid , which runs through turbines that power either ship's...

 that generates electricity
Electricity
Electricity is a general term encompassing a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning, static electricity, and the flow of electrical current in an electrical wire...

 by decelerating an ion beam
Ion beam
An ion beam is a type of charged particle beam consisting of ions. Ion beams have many uses in electronics manufacturing and other industries. A variety of ion beam sources exist, some derived from the mercury vapor thrusters developed by NASA in the 1960s.-Ion beam etching or sputtering:One type...

 of fission
Nuclear fission
In nuclear physics and nuclear chemistry, nuclear fission is a nuclear reaction in which the nucleus of an atom splits into smaller parts , often producing free neutrons and photons , and releasing a tremendous amount of energy...

 byproducts instead of using nuclear reactions to generate heat
Heat
In physics and thermodynamics, heat is energy transferred from one body, region, or thermodynamic system to another due to thermal contact or thermal radiation when the systems are at different temperatures. It is often described as one of the fundamental processes of energy transfer between...

. By doing so, it bypasses the Carnot cycle
Carnot cycle
The Carnot cycle is a theoretical thermodynamic cycle proposed by Nicolas Léonard Sadi Carnot in 1824 and expanded by Benoit Paul Émile Clapeyron in the 1830s and 40s. It can be shown that it is the most efficient cycle for converting a given amount of thermal energy into work, or conversely,...

 and can achieve efficiencies of up to 90% instead of 40-45% attainable by efficient turbine
Turbine
A turbine is a rotary engine that extracts energy from a fluid flow and converts it into useful work.The simplest turbines have one moving part, a rotor assembly, which is a shaft or drum with blades attached. Moving fluid acts on the blades, or the blades react to the flow, so that they move and...

-driven thermal reactors.

Fission fragment reactor designs generally have several common components. The reactor chamber contains a high surface area nuclear fuel
Nuclear fuel
Nuclear fuel is a material that can be 'consumed' by fission or fusion to derive nuclear energy. Nuclear fuels are the most dense sources of energy available...

 to both facilitate direct emission of fission fragments and assist in cooling the fuel. Generally, if fuels subject to criticality
Criticality
Criticality may refer to:* Critical thinking in education* Critical reflection in adult education* Critical mass in nuclear reactions* Criticality accident* Criticality matrix* Nuclear Criticality Safety...

 are used instead of those that naturally decay
Radioactive decay
Radioactive decay is the process by which an atomic nucleus of an unstable atom loses energy by emitting ionizing particles . The emission is spontaneous, in that the atom decays without any physical interaction with another particle from outside the atom...

 (as in a nuclear battery), a moderator
Neutron moderator
In nuclear engineering, a neutron moderator is a medium that reduces the speed of fast neutrons, thereby turning them into thermal neutrons capable of sustaining a nuclear chain reaction involving uranium-235....

 is typically involved as well. A magnetic mirror
Magnetic mirror
A magnetic mirror is a magnetic field configuration where the field strength changes when moving along a field line. The mirror effect results in a tendency for charged particles to bounce back from the high field region....

 induced by an axial
Axial
Axial may mean:* Along the same line as an axis of rotation in geometry* A type of modal frame in music* One of several anatomical directions in an animal body* Axial age, the period from 800 to 200 BC in China, India and the western world...

 magnetic field
Magnetic field
A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...

 typically collates the fragments into a beam that can then be decelerated to generate power
Electricity generation
Electricity generation is the process of generating electric energy from other forms of energy.The fundamental principles of electricity generation were discovered during the 1820s and early 1830s by the British scientist Michael Faraday...

. The rate the particles decelerate at depends on their energy; as a consequence, the deceleration process also can help provide isotopic separation as an automatic reprocessing
Nuclear reprocessing
Nuclear reprocessing technology was developed to chemically separate and recover fissionable plutonium from irradiated nuclear fuel. Reprocessing serves multiple purposes, whose relative importance has changed over time. Originally reprocessing was used solely to extract plutonium for producing...

 stage.

An earlier design by scientists at Idaho National Engineering Laboratory and Lawrence Livermore National Laboratory
Lawrence Livermore National Laboratory
The Lawrence Livermore National Laboratory , just outside Livermore, California, is a Federally Funded Research and Development Center founded by the University of California in 1952...

 involved the concept of coating fine carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

 wires with fissionable fuel. While this had a high surface area, it proved not enough to radiate the heat absorbed during the reactions, so their design was modified to rotate long wires through the core, giving them time to cool.

A later design by Rodney A. Clark and Robert B. Sheldon involves the use of a dusty plasma
Dusty plasma
A dusty plasma is a plasma containing nanometer or micrometer-sized particles suspended in it. Dust particles may be charged and the plasma and particles behave as a plasma, following electromagnetic laws for particles up to about 10 nm...

 of electrostatically suspended fuel nanoparticle
Nanoparticle
In nanotechnology, a particle is defined as a small object that behaves as a whole unit in terms of its transport and properties. Particles are further classified according to size : in terms of diameter, coarse particles cover a range between 10,000 and 2,500 nanometers. Fine particles are sized...

s in the core. This increases the surface area enough to allow for effective radiative cooling. As the particles naturally ionize as fission occurs, electrostatic suspension is a simple process.
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