Monday, March 10, 2008

Uranium or thorium?

I have just argued in my last post that the world's supply of Uranium is virtually limitless. There are estimates that the world supply of thorium is three to four times as plentiful as the supply of Uranium. Both U238 and thorium 232 can serves as a basis for a future energy supplies. It is clear that both thorium and uranium can be tapped for far more energy than the current generation ofd light water reactors produce. Currently light water reactors extract 1% of the energy present that could be produced by natural uranium. It then converts a little less than a third of that energy into electricity. Thus the Light Water Reactor has a 0.3% overall efficiency in capturing energy from uranium, and converting it into electricity. A metal Liquid Fluoride Thorium Reactor can capture 100% of the energy of thorium and convert 45% of it into electricity. A carbon-carbon can potentially convert up to 60% of the energy in Thorium into electricity. Thus a LFTR can be 200 times more fuel efficient than a LWR.

There are uranium cycle reactors that are potentially efficient as the LFTR, but only one type of uranium fuel cycle reactor approaches the many other advantages of the LFTR. The LFTR is extremely sage. The LFTR is a molten-salt reactors. The safety features of MSRs is discussed in a paper by Uri Gat, and H.L. Dodds.

They record the following safety features:

* Simple reactor structure

* Continuous removal of fission products

* A high negative reactivity temperature coefficient that slows down chain reaction as reactor temperature rises

* The LFTR can be self-controlling

* No externally operated controls are required

* Safety can be passive

* Safety is inherent and safety features cannot be altered by tampering, and are thus fool proof

* Ultimate shut-down is accomplished by draining the liquid fuel from the reactor core

* A drain plug can be operated automatically by using a material that melts when the reactor reaches an undesirable heat level

* Core dranaged powered by gravity

* The drain container can be in a shape that prevents drained fuel from become critical

The Fluoride salt coolant is safe because:

* It does not react with water or air

* There is no fire or explosion hazards

* It is non-corrosive with respect to very desirable and suitable structural materials like carbon based materials

* They are stable to high temperatures and exert low pressure

* Liquid salts are often used in industry as heat transfer media for their inertness and safety

* In the event of an accidental spill, liquid salt freezes in place without spreading

* A core meltdown is not a problem, because the fuel is already a liquid

* Since the coolant is also the fuel, a loss of coolant accident is does not lead to fuel overheating

Clearly then the LFTR gas numerous safety advantages when compared to uranium cycle reactors.

A second advantage of the LFTR was its superior fuel processing capacity for fuel processing. Xenon, a highly radioactive gas, that poisons nuclear reactions, can be continuously stripped from the LFTR. From a safety viewpoint this means that Xenon will not escape from the reactor in the event of an accident. From an fuel economy viewpoint, this means that the reactor will transform thorium into fissionable U233 more efficiently. Other undesirable gases and fission products can be removed from liquid fluoride salts.

The LFTR produces only one fissionable U233 atom for every atom it burns. Thus if it was decided to remove U233 from the reactor in order to produce atomic bombs, this would immediately lead to reactor shutdown, since the reactor could not opperate without its fuel. In addition along with U233, highly radioactive U232 is produced in the thorium fuel cycle. U232 considered to be so dangerous, that it constitutes a major barrier to nuclear proliferation with U233. Therefor the LFTR is proliferation resistant.

The LFTR does not produce nuclear waste. Most thorium byproducts fyel cycle byproducts have short half lives, and thus are quickly cease to be radioactive. Most stable byproducts are materials that are useful to industry. Fissionable byproducts remain inn the reactor till burned. Virtually no transuranium elements are produced in the thorium fuel cycle. Thus once nuclear byproducts become stable non-radioactive materials the can be seperated and processed for industrial use.

Thus LFTRs are safe, 200 times more efficient than LWRs, proliferation resistant and does not produce nuclear waste. In addition continuous chemical processing of the reactor fuel eliminates the need for expensice secondary fuel reprocessing plants. Thus the Thoriun cycle reactor possess enormous advantages over the light water reactor.

2 comments:

Neurovore said...

Hello, I frequently visit the Depleted Cranium blog by Dr. Buzzo, and saw this blog in his links page. I have heard about the LFTR concept, but I do have a few questions about it.

1. What sorts of technological hurdles would need to be overcome in order to build it? If the technology exists to build one, then what is the main problem from preventing its construction, other than political opposition? Is political opposition to all things "nuclear" the main problem?

2. I know the Japanese are working on this concept with the design of their Fuji II reactor, but is the LFTR concept practically dead and buried in the US with no hope of revival? Who else is working on this?

3. How seriously is the LFTR path being considered for future GenIV development?

Charles Barton said...

1. What sorts of technological hurdles would need to be overcome in order to build it? If the technology exists to build one, then what is the main problem from preventing its construction, other than political opposition? Is political opposition to all things "nuclear" the main problem?
Answer: Two sucessful prototype MSRs were built in Oak Ridge in the 1950's and 60's. Using the plans of the second prototype it would be possible to build a MSR today. In addition, during the 1970s detailed plans were developed for a Molten Salt Power reactor were developed. Most of the technological challenges were had been overcome before the project was ended.

Dr Ralph Moir has given a list of projects that he theinks are priorities for MSR development to procede. http://nucleargreen.blogspot.com/2008/08/msrlftr-development-moir-again.html


2. I know the Japanese are working on this concept with the design of their Fuji II reactor, but is the LFTR concept practically dead and buried in the US with no hope of revival? Who else is working on this?
The French have a serious program of MSR development that began by examining the earlier Oak Ridge program. They have made design decisions and the will conduct research on their design concept. It is always possible for the United States to get into the game. It is just amatter of Picking up where Oak Ridge left off.

3. How seriously is the LFTR path being considered for future GenIV development? The French seem to be very serious about it. In the United States that is no political support at the moment, but that could change greatly over the next few years.

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