We are due to revisit the thoriumquestion again. The bottom line has always been that if one were to havenuclear power, and weapons are not a consideration, then thorium is moreproductive and safer for several reasons, not least that it needs a separatesystem to provide neutrons.
Today we are actually at the end of thenuclear age if the emerging Focardi – Rossi reactor proves (see my posts) to bethe heat engine it is billed to be. Yetcontinuance of thorium work is well indicated as a system in place capable ofconsuming the large supply of nuclear materials presently in existence. All of it is best consumed slowly in athorium nuclear reactor to produce usable heat. That includes both plutonium and uranium and all spent fuel rods.
Radiated materials are anothermatter as they are best stuck in a salt mine somewhere and generally forgottenabout.
It is a reasonable engineeringsolution and likely supports additional production of medical isotopes. It may even pay for itself even though itwill have to operate for centuries to dispose of all the fuel produced to date.
Thorium: A safer alternative for nuclear power generation?
By FrankLeonard
20:26 May 26, 2011
Thorium could provide a cleaner and more abundant alternative touranium (Photo: Three Mile Island NuclearPower Plant/ Lyndi & Jason via Flickr)
The world's growing need for energy, the limits of our supply of fossilfuels and concern about the effects of carbon emissions on the environment haveall prompted interest in the increased use of nuclear power. Yet the very word"nuclear" carries with it an association of fear. People areconcerned about the waste produced by reactors, the possibility of catastrophicaccidents as highlighted by recent events in Japan
The answer could be thorium - an element occurring as a silvery metalthat's more abundant, cleaner and can produce more bang-per-buck in energyterms than uranium.
So how does thorium differ from uranium and plutonium, and why isn't itbeing used?
First, a quick run-down on how nuclear energy works.
What is nuclear power?
The word "nuclear" refers to the nucleus, or dense center ofthe atom. In a nuclear power reactor, these nuclei are split into smaller partsthrough a process known as fission. A sub-atomic particle known as a neutronstrikes the nucleus of an atom of suitable fuel (particular isotopes of theheavy elements uranium and plutonium) breaking it into its component parts.Each fission results in the release of energy in the form of electromagneticradiation and kinetic energy in the fragments of the split nucleus. This effectis twofold; the release of energy will produce heat, and the release ofneutrons, which can in turn fission other atoms.
In material that has typically been employed as nuclear fuel, thisreaction occurs in a "chain reaction" and is self-sustaining. Whenthis is occurring, the reactor can be said to be"'critical". In afission weapon, a mass of plutonium or uranium in excess of critical isassembled very quickly, with a flood of neutrons from a device known as an"initiator". The release of energy is extremely rapid and results ina massive explosion.
In a nuclear power reactor, the reaction is far slower and morecontrolled - the heat produced can be harnessed to boil water to spin turbinesfor the generation of electricity and this has been in practice for decades.The use of nuclear reactors for power generation began on 27 June 1954 at theObninsk power plant in the former Soviet Union and has continued in numerous countries to this day.
There are of course, some significant problems with nuclear power.Fission reactions will always result in the production of radioactive wasteproducts which require secure storage and pose a health risk to humans and theenvironment. There is the possibility that the operators may lose control ofthe fission chain reaction resulting in an accidental release of this material(often referred to as a "meltdown"). There's also the concern thatreactors may also be used for the production of material suitable fornuclear weapons.
Modern nuclear reactors
The two main types of reactors used for commercial power generation arethe pressurized water reactor (PBR) and the boiling water reactor (BWR), whichboth typically make use of uranium in the form of uranium oxide fuel rods. Thecriticality of the reactor is managed by control rods, which when insertedabsorb neutrons that would otherwise cause the chain reaction to continue. Thereactor can be shut down, or "scrammed", by the rapid insertion ofthese control rods. However, this is a manual process and there is apossibility of an error occurring.
Criticality, fertility and the potential of thorium
The element thorium, named after the Norse god of thunder, may providea safer alternative as a fuel. The key difference between thorium and othernuclear fuels is that it cannot sustain a chain reaction on its own.Fissile fuels like uranium and plutonium are able to sustain a chain-reaction,yet fission can also be achieved in material like thorium that is not fissilebut fertile - i.e. it can produce fissile material, if neutrons are providedfrom an outside source.
Thorium is estimated to be three to four times more plentiful thanuranium in the Earth's crust and has the advantage of being found in nature inthe one isotope, which makes it suitable as a nuclear fuel as it need not beenriched to separate the right isotope. For convenience, thorium fuel can beused in the form of a liquid molten salt mixture.
Accelerator Driven System
Fission occurs in thorium when atoms absorb a neutron to become aheavier isotope and quickly decay into an isotope of the element protactiniumand then an isotope of uranium, which is fissioned when struck by an additionalneutron. The number of neutrons produced is not sufficient for a self-sustainedchain reaction.
A particle accelerator could be used to provide the necessaryneutrons for fission to occur in thorium and a nuclear reactor making use ofsuch an outside neutron source would be known as an 'accelerator driven system'(ADS).
The notion of the ADS is credited to Carlo Rubbia of the EuropeanOrganisation for Nuclear Research (CERN) joint winner of the 1984 Nobel Prize for Physics. TheADS would likely be far smaller than other reactors and if the accelerator wereto be turned off, the nuclear reaction would cease, although it should be notedthat even in a reactor which is not critical, the heat from the decay ofmaterials can be significant and cooling is required.
In a thorium reactor, quantities of other fuels could be included,without the fuel being capable of sustaining a chain reaction, and thus thereactor could be used to provide energy from disposing of material such asplutonium from disassembled nuclear weapons. It's also possible to ensure thatthe reactors are designed in such a way that it is not possible to extractfissile material, which can be used to manufacture nuclear weapons.
Though all nuclear reactors will produce waste products, a reactorfulled by thorium will produce far less long-lived waste products than onefueled by uranium or plutonium, with waste decaying to the same level ofradioactivity as coal ashes after 500 years.
Thorium also produces more energy from the same amount of materialcompared to uranium.
"Two hundred tonnes of uranium can give you the same amount ofenergy you can get from one tonne of thorium," Rubbia told the BBCNews in a recent interview.
Towards a thorium reactor
Though several reactors have made use of thorium for experimentalpurposes, a thorium power reactor is not as yet a reality. Countries like Russia , India and China
So why has it taken so long for thorium to hit the nuclear poweragenda? The key reason seems to be that because it can't be used to make anuclear bomb, it was largely ignored during the Manhattan
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