The Clean and Environmentally Safe Advanced Reactor (CAESAR) is a

nuclear reactor A nuclear reactor is a device used to initiate and control a fission nuclear chain reaction or nuclear fusion reactions. Nuclear reactors are used at nuclear power plants for electricity generation and in nuclear marine propulsion. Heat fr ...

concept created by Claudio Filippone, the Director of the Center for Advanced Energy Concepts at the

University of Maryland, College Park The University of Maryland, College Park (University of Maryland, UMD, or simply Maryland) is a public land-grant research university in College Park, Maryland. Founded in 1856, UMD is the flagship institution of the University System of ...

and head of the ongoing CAESAR Project. The concept's key element is the use of

steam Steam is a substance containing water in the gas phase, and sometimes also an aerosol of liquid water droplets, or air. This may occur due to evaporation or due to boiling, where heat is applied until water reaches the enthalpy of vaporizatio ...

as a moderator, making it a type of

reduced moderation water reactor The Reduced-Moderation Water Reactor (RMWR), also referred to as the Resource-renewable BWR, is a proposed type of light water reactor, light water moderated nuclear power reactor, featuring some characteristics of a fast neutron reactor, thereby c ...

. Because the

density Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' can also be used. Mathematicall ...

of steam may be controlled very precisely, Filippone claims it can be used to fine-tune

neutron flux The neutron flux, φ, is a scalar quantity used in nuclear physics and nuclear reactor physics. It is the total length travelled by all free neutrons per unit time and volume. Equivalently, it can be defined as the number of neutrons travellin ...

es to ensure that

neutron The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the atomic nucleus, nuclei of atoms. Since protons and ...

s are moving with an optimal energy profile to split nuclei – in other words, cause fission. The CAESAR reactor design exploits the fact that the

fission product Nuclear fission products are the atomic fragments left after a large atomic nucleus undergoes nuclear fission. Typically, a large nucleus like that of uranium fissions by splitting into two smaller nuclei, along with a few neutrons, the release ...

s and

daughter isotope In nuclear physics, a decay product (also known as a daughter product, daughter isotope, radio-daughter, or daughter nuclide) is the remaining nuclide left over from radioactive decay. Radioactive decay often proceeds via a sequence of steps (de ...

s produced via nuclear reactions also decay to produce additional

delayed neutron In nuclear engineering, a delayed neutron is a neutron emitted after a nuclear fission event, by one of the fission products (or actually, a fission product daughter after beta decay), any time from a few milliseconds to a few minutes after the ...

s. Filippone claims that unlike light water-cooled fission reactors, where fission occurring in enriched

fuel rod Nuclear fuel is material used in nuclear power stations to produce heat to power turbines. Heat is created when nuclear fuel undergoes nuclear fission. Most nuclear fuels contain heavy fissile actinide elements that are capable of undergoing ...

s moderated by liquid-water

coolant A coolant is a substance, typically liquid, that is used to reduce or regulate the temperature of a system. An ideal coolant has high thermal capacity, low viscosity, is low-cost, non-toxic, chemically inert and neither causes nor promotes corrosi ...

ultimately creates a Maxwellian

thermal neutron The neutron detection temperature, also called the neutron energy, indicates a free neutron's kinetic energy, usually given in electron volts. The term ''temperature'' is used, since hot, thermal and cold neutrons are moderated in a medium wi ...

flux profile, the neutron energy profile from delayed neutrons varies widely. In a conventional reactor, he theorizes, the moderator slows these neutrons down so that they cannot contribute to the reaction; has a comparatively large cross-section for neutrons at high energies. Filippone maintains that when steam is used as the moderator, the average neutron energy is increased from that of a liquid water-moderated reactor such that the delayed neutrons persist until they hit another nucleus. The resulting extremely high

neutron economy Neutron economy is defined as the ratio of an adjoint weighted average of the excess neutron production divided by an adjoint weighted average of the fission production. The distribution of neutron energies in a nuclear reactor differs from the f ...

, he claims, will make it possible to maintain a self-sustaining reaction in fuel rods of pure , once the reactor has been started by enriched fuel. Skeptics , however point out that it is generally believed that a controlled, sustained chain reaction is not possible with . Starting in the 1930s Physicists have used the Six factor formula and its derivative Four factor formula to calculate the behavior of nuclear chain reactions inside a mass of fissile material. Based on these calculations even an infinitely large mass of pure U-238 is incapable of sustaining a chain reaction with only its own neutron production, some level of fissile enrichment is always required. It can undergo fission when impacted by an energetic neutron with over 1 MeV of

kinetic energy In physics, the kinetic energy of an object is the energy that it possesses due to its motion. It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acce ...

. But the high-energy neutrons produced by fission (after quickly losing energy by inelastic scattering), are not, themselves, sufficient to induce enough successive fissions in to create a critical system (one in which the number of neutrons created by fission is equal to the number absorbed). Instead, bombarding with neutrons below the 1 MeV fission threshold causes it to absorb them without fissioning (becoming ) and decay by

beta emission In nuclear physics, beta decay (β-decay) is a type of radioactive decay in which a beta particle (fast energetic electron or positron) is emitted from an atomic nucleus, transforming the original nuclide to an isobar of that nuclide. For exam ...

to (which is itself

fissile In nuclear engineering, fissile material is material capable of sustaining a nuclear fission chain reaction. By definition, fissile material can sustain a chain reaction with neutrons of thermal energy. The predominant neutron energy may be t ...

). The energy of

s is so low that contribution to fission is almost 0.0000, requiring some fissile material to keep the reactor safely under prompt criticality: (e.g. in natural

uranium Uranium is a chemical element with the symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weak ...

and preferably also some moderator, possibly outside the extra-fast core).

References

External links

The Clean And Environmentally Safe Advanced Reactor (CAESAR) ProjectHail, Caesar
Economist article

Popular Mechanics article from 1998 describing a related reactor design (NPTRE) proposed by Dr. Filippone.

Article from University of Maryland newsletter. {{Nuclear fission reactors Nuclear power reactor types Pseudoscience

See also

References

External links