The Reduced-Moderation Water Reactor (RMWR), also referred to as the Resource-renewable BWR, is a proposed type of
light water moderated
nuclear power 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 from ...
, featuring some characteristics of a
fast neutron reactor
A fast-neutron reactor (FNR) or fast-spectrum reactor or simply a fast reactor is a category of nuclear reactor in which the fission chain reaction is sustained by fast neutrons (carrying energies above 1 MeV or greater, on average), as opposed ...
, thereby combining the established and proven technology of light water reactors with the desired features of fast neutron reactors. The RMWR concept builds upon the
Advanced Boiling Water Reactor
The advanced boiling water reactor (ABWR) is a Generation III boiling water reactor. The ABWR is currently offered by GE Hitachi Nuclear Energy (GEH) and Toshiba. The ABWR generates electrical power by using steam to power a turbine connected ...
and is under active development in theoretical studies, particularly in
Japan.
Hitachi and the
Japan Atomic Energy Agency
The is an Independent Administrative Institution formed on October 1, 2005 by a merger of two previous semi-governmental organizations. While it inherited the activities of both JNC and JAERI, it also inherited the nickname of JAERI, "Genken" ...
are both involved in research.
Even in
Generation II PWRs, the neutron spectrum is not fully thermalised. The goal of the RMWR is to depart further from the thermal neutron spectrum in order to achieve a
breeder ratio of slightly greater than one, so that after the initial fuel charge no enrichment of the uranium input to the fuel cycle is required. The RMWR concept is dependent on
nuclear fuel reprocessing
Nuclear reprocessing is the chemical separation of fission products and actinides from spent nuclear fuel. Originally, reprocessing was used solely to extract plutonium for producing nuclear weapons. With commercialization of nuclear power, the ...
in order to achieve its objective of a resource renewable fuel cycle. Hitachi has proposed the FLUOREX process as reprocessing technology for this purpose, instead of the more conventional
Purex
PUREX (plutonium uranium reduction extraction) is a chemical method used to purify fuel for nuclear reactors or nuclear weapons. PUREX is the ''de facto'' standard aqueous nuclear reprocessing method for the recovery of uranium and plutonium ...
technology.
In contrast to regular light water reactors and in order to achieve a harder neutron spectrum, which is optimal for breeding purposes, the RMWR uses hexagonal fuel assemblies and Y-shaped control rods. The fuel is
MOX
Mixed oxide fuel, commonly referred to as MOX fuel, is nuclear fuel that contains more than one oxide of fissile material, usually consisting of plutonium blended with natural uranium, reprocessed uranium, or depleted uranium. MOX fuel is an al ...
(Mixed Oxide), consisting of 18%
plutonium
Plutonium is a radioactive chemical element with the symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, and forms a dull coating when oxidized. The element normally exhibi ...
, which is surrounded by
depleted uranium in the blanket region.
Another RMWR breeder design intends on closing the nuclear fuel cycle by mixing
thorium
Thorium is a weakly radioactive metallic chemical element with the symbol Th and atomic number 90. Thorium is silvery and tarnishes black when it is exposed to air, forming thorium dioxide; it is moderately soft and malleable and has a high ...
with reprocessed
transuranics, which include plutonium, in a thorium containing MOX fuel. The neutron speed would be in the
spectrum
A spectrum (plural ''spectra'' or ''spectrums'') is a condition that is not limited to a specific set of values but can vary, without gaps, across a continuum. The word was first used scientifically in optics to describe the rainbow of colors ...
that could purportedly
transmutate the long-lived
fission products like
Tc-99
Technetium-99 (99Tc) is an isotope of technetium which decays with a half-life of 211,000 years to stable ruthenium-99, emitting beta particles, but no gamma rays. It is the most significant long-lived fission product of uranium fission, produ ...
&
I-127 and as the neutron spectrum is hard/fast enough, to also be capable of burning the usually troublesome
minor actinide
The minor actinides are the actinide elements in used nuclear fuel other than uranium and plutonium, which are termed the major actinides. The minor actinides include neptunium (element 93), americium (element 95), curium (element 96), berkeliu ...
s quite efficiently.
Hitachi announced a collaboration with three U.S. universities on the development of the RBWR/RMWR in 2014.
See also
*
Supercritical water reactor, a similar and perhaps even overlapping concept.
*
Clean And Environmentally Safe Advanced Reactor
The Clean and Environmentally Safe Advanced Reactor (CAESAR) is a nuclear reactor concept created by Claudio Filippone, the Director of the Center for Advanced Energy Concepts at the University of Maryland, College Park and head of the ongoing CAE ...
, preliminary work in the 1990s.
References
External links
IAEA Advanced Reactors Information System: Reduced-Moderation Water Reactor
{{Nuclear fission reactors
Light water reactors
Nuclear power reactor types