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A subcritical reactor —regardless of neutron spectrum— can also "breed" fissile nuclides from fertile material, allowing in principle the consumption of very low grade actinides (e.g. Spent MOX fuel whose plutonium-240 content is too high for use in current critical thermal reactors) without the need for highly enriched material as used in ...
In the arms control context, particularly in proposals for a Fissile Material Cutoff Treaty, the term fissile is often used to describe materials that can be used in the fission primary of a nuclear weapon. [6] These are materials that sustain an explosive fast neutron nuclear fission chain reaction. Under all definitions above, uranium-238 (238 U
, as the fertile material. In the reactor, 232 Th is transmuted into the fissile artificial uranium isotope 233 U which is the nuclear fuel. Unlike natural uranium, natural thorium contains only trace amounts of fissile material (such as 231 Th), which are insufficient to initiate a nuclear chain reaction. Additional fissile material or another ...
These materials are called fertile materials since they can be bred into fuel by these breeder reactors. Breeder reactors achieve this because their neutron economy is high enough to create more fissile fuel than they use. These extra neutrons are absorbed by the fertile material that is loaded into the reactor along with fissile fuel.
Thorium-232 is a fertile material; it can capture a neutron to form thorium-233, which subsequently undergoes two successive beta decays to uranium-233, which is fissile. As such, it has been used in the thorium fuel cycle in nuclear reactors; various prototype thorium-fueled reactors have been designed. However, as of 2024, thorium fuel has ...
Far more abundant are fertile isotopes, which, after absorbing a neutron, eventually become fissile isotopes. So let us imagine our reactor fuel that contains 5% fissile isotopes (U-235, in this case), and 95% fertile isotopes (U-238, for example). While the fissile isotopes burn up, a large number of neutrons are generated.
238 U can be used as a source material for creating plutonium-239, which can in turn be used as nuclear fuel. Breeder reactors carry out such a process of transmutation to convert the fertile isotope 238 U into fissile 239 Pu. It has been estimated that there is anywhere from 10,000 to five billion years worth of 238 U for use in these power ...
This effort culminated in the Molten-Salt Reactor Experiment that used 232 Th as the fertile material and 233 U as the fissile fuel. Due to a lack of funding, the MSR program was discontinued in 1976. Thorium was first used commercially in the Indian Point Unit 1 reactor which began operation in 1962. The cost of recovering U-233 from the spent ...