Advanced Nuclear Fission Technology
Please read the physics of fission
before reading this section.
Uranium Fast Breeder Reactors
Natural Uranium consists of 0.7% 235U and 99.3% 238U. All commercial Power reactors used in the world today utilize the 235U component in natural Uranium as the primary means of maintaining a chain reaction. The most troublesome component of nuclear waste are the tran-Uranic elements that occur when 238U captures a neutron and transmutes to 239Pu. Further neutron captures on this element lead to a buildup of long-lived transuranic nuclei. However 239Pu is also fertile and undergoes fission like 235U. Advanced reactor designs exploit this to convert the 238U to 239Pu. If the reactor avoids the slowing down, "thermalization" of neutrons, there are sufficient excess neutrons that it is possible to convert more 238U to 239Pu than 235U is consumed. These reactors use the unmoderated "fast" neutrons directly produced via the fission process.
Thus these reactors "breed"
239Pu from 238U and so produce more fuel than they consume. The use of fast-breeder technology makes it possible to increase the efficiency of Uranium use by over a factor of 50. It is then possible to exploit the vast quantities of depleted Uranium stockpiled around the world to generate electricity. In addition the excess neutrons can be used to transmute the long-lived transuranic waste from current Nuclear Power reactors to ever-heavier isotopes until they eventually fission. Thus these reactors can be used to "burn" the most troublesome component of nuclear waste.
There have been a number
of reactors that demonstrated
that the Fast-Breeder concept works in principle at large scale. The superphenix
reactors in France and Japan have had serious technical issues and superphenix has been shut down. This type of reactor is more costly to construct and more difficult to operate than a conventional second-generation Power Reactor. Never-the-less these experiments have provided valuable data that will be used as input for the "Fourth Generation" nuclear reactors presently under research and development.
Thorium Breeder Reactors
Thorium is an element that is 3 times more abundant than Uranium on earth. It has a single stable isotope 232Th. In a nuclear reactor this isotope can capture a neutron and be converted to 233U. 233U undergoes fission like 235U and 239Pu. However when 233U fissions it releases more neutrons than either 235U or 239Pu. Consequently it is possible to to construct a breeder reactor that utilizes thermal neutrons to both generate energy and to breed 233U from Thorium given sufficient initial quantities of 233U mixed with 232Th.
A further advantage of Thorium breeders is that the amount of transuranic waste is vastly decreased compared to a Uranium or Plutonium based reactor.
The Indian Nuclear Power program
has a long term goal of utilizing the Thorium cycle to obtain energy independence.
Accelerator Driven Fission.
Over the last 10 years the idea of using a high current, high energy accelerator to drive Nuclear Fission has emerged. These are the Accelerator Driven Systems or ADS. Unlike a Nuclear Reactor, an ADS drives Nuclear reactions that will stop if the proton beam from the accelerator stops. Thus there is no prospect of nuclear chain reactions proceeding out of control. ADS can be used to either generate energy or to transmute transuranic long-lived waste into much shorter lived radio-nuclei, or they can be used to do both. In addition these systems hold prospect of efficiently burning 238U and naturally occurring Thorium, which is 3 times more abundant than Uranium. Over the last 10 years the ADS has progressed from proof of principle experiments to one tenth scale
More details of Accelerator driven Fission systems are found here
The Fourth Generation Reactors
In 2002 the Gen iV Internation Forum (GIF) nations (Argentina, Brazil, Canada, France, Japan, Korea, South Africa, Switzerland, Russia, United Kingdom and the United States of America) proposed a long term research and developement program
to investigate 6 promising new reactor designs.
The six design concepts are:
These reactor concepts are designed to address the energy needs of the World into the far future (post 21st century).
- They efficiently utilize Uranium (many can employ depleted Uranium or "spent" fuel from current reactors).
- Destroy a large fraction of nuclear waste from current reactors via transmutation.
- Generate Hydrogen for transportation and other non-electric energy needs.
- Be inherently safe and easy to operate.
- Provide inherent resistance to Nuclear Weapons proliferation.
- Provide a clear cost advantage over other forms of energy generation.
- Carry a financial risk no greater than other forms of energy generation.
These reactor concepts are at various levels of development. The first deployments of Generation IV reactors are not expected until 2015. Most will not be ready before 2025. However the long term potential of these projects is enormous. For example one Molten-Salt Reactor designed to consume one tonne of Uranium per year, could supply sufficient Hydrogen to supply 3 million
passenger vehicles. The waste from the plant's year's operation would occupy half the volume of a typical domestic refrigerator. The radioactivity of the waste would diminish to background levels in about 500 years.