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, featuring some characteristics of a
fast neutron reactor, 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 and is under active development in theoretical studies, particularly in
Japan
Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...
.
Hitachi
() is a Japanese multinational corporation, multinational Conglomerate (company), conglomerate corporation headquartered in Chiyoda, Tokyo, Japan. It is the parent company of the Hitachi Group (''Hitachi Gurūpu'') and had formed part of the Ni ...
and the
Japan Atomic Energy Agency 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
A breeder reactor is a nuclear reactor that generates more fissile material than it consumes. Breeder reactors achieve this because their neutron economy is high enough to create more fissile fuel than they use, by irradiation of a fertile mate ...
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 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 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), consisting of 18%
plutonium, which is surrounded by
depleted uranium
Depleted uranium (DU; also referred to in the past as Q-metal, depletalloy or D-38) is uranium with a lower content of the fissile isotope than natural uranium.: "Depleted uranium possesses only 60% of the radioactivity of natural uranium, hav ...
in the blanket region.
Another RMWR breeder design intends on closing the nuclear fuel cycle by mixing
thorium with reprocessed
transuranics, which include plutonium, in a thorium containing MOX fuel. The neutron speed would be in the
spectrum that could purportedly
transmutate the long-lived
fission products
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 ...
like
Tc-99 &
I-127 and as the neutron spectrum is hard/fast enough, to also be capable of burning the usually troublesome
minor actinides 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
The supercritical water reactor (SCWR) is a concept Generation IV reactor, designed as a light water reactor (LWR) that operates at supercritical pressure (i.e. greater than 22.1 MPa). The term ''critical'' in this context refers to the c ...
, a similar and perhaps even overlapping concept.
*
Clean And Environmentally Safe Advanced Reactor, 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