Friday, September 19, 2008

The Ultimately Efficient Reactor

I have been challenged to apply Rocky Mountain Institute principles to Liquid Fluoride Thorium Reactor technology. I am happy to do so, because the LFTR is the not only the Ultimately Efficient Reactor, but I believe that it may well be the ultimately efficient human system for providing energy to society. This might be seen as an astonishing claim, but consider these facts. The average wind Energy Returned on Energy Invested (EROEI) from 114 studies is 25.2, and this is considered a very good EROEI. Photo voltaic EROEI runs from 10 to 30. According to Chris Vernon of the Oil Drum, the EROEI of concentrated solar power runs from 27 with energy storage, to 44 without storage. An accurate account of nuclear EROEI is difficult to obtain because of dramatically different technologies. For example the EROEI of CANDU reactors using natural or slightly enriched Uranium is dramatically higher than Light Water Reactors, using more enriched Uranium. Gaseous diffusion enrichment takes 50 times as much energy as centrifuges. Extracting reactor fuel from mine tailings takes less energy than direct mining.

Finally thorium does not need energy sapping enrichment, and fuel fabrication. Thorium reprocessing inside the LFTR relies on internal reactor heat, and reactor derived energy. The once through LWR has been estimated to have an EROEI of from 5 to 10. The LFTR uses nuclear fuel about 160 times more efficiently. Using that efficiency alone, we would have an EROEI of between 800 and 1600 all other things being equal between the LFTR and the LWR. All other things are not equal, however. LWR fuel receives energy sapping enrichment and fabrication, while LFTR fuel does not. LWR "spent fuel" requires considerable energy to keep cool. But even our rough underestimate, it is clear that LFTR EROEI will run at least 20 times greater than the most efficient renewable and perhaps much more.

According to the Rocky Mountain Institute:
 
At the heart of all our work is a simple but powerful notion: using natural resources much more productively — efficiently — is both profitable and better for the environment. Indeed, integrative design often makes large resource savings work better and cost less than small ones.

Let's see how LFTR efficiency works in RMI terms.  The LFTR will derive its fuel from a previously unwanted heavy metal, that has until now gone to waste. The fuel source is thorium, a heavy metal that is found in abundance in uranium mine tailings, phosphate mining tailings, and coal fly ash from power power plants. Currently thorium leaches into the environment from these sources, creating a pollution problem. In addition thorium is found in a rare earth's deposit at Lemhi Pass in Idaho. When that deposit is mined, hundreds of thousands of tons of up ill now useless thorium will be made available for human use. The United States produces 3000 tons of coal thorium in ash from coal-fired power plants every year, enough to provide all of the energy the United States will consume during the year. This is a resource that is not only going to waste at present, but by wasting it we are actually creating an environmental pollution problem.

Thus at the heart of the LFTR is the idea that thorium, a largely wasted resource can and should be used in the most productive fashion possible.

In addition to containing thorium, the 50 million tons of phosphate mining tailing produced by the United States contains significant amounts of fluoride. Fluorides leaching from mining tailings pose a significant environmental pollution problem. Even in low concentrations, fluorides are toxic to many organisms. Thus recovery of wasted fluorides from phosphate mining tailings, would not only be useful, but would decrease fluoride related environmental pollution.

Thus both fluoride and thorium, which are abundantly available in nature, are mined in large amounts, but are almost entirely wasted, By utalizing fluoride and thorium, the LFTR would be using these natural resources much more efficiently, in fact enormously more efficiently than current usage.

The LFTR makes modest demands on all resources, but none of the resources used in LFTRs would find a higher use in terms of energy productivity.

Not only does the LFTR make use of thorium, a now largely wasted heavy metal found in mining tailings and coal fly-ash, but it uses the thorium with incredible efficiency. Typically less 0.6% of mined uranium is used in light water reactors. In contrast, 98% of thorium used in LFTRs will be used in the nuclear process, the other 2% is transformed into isotopes that can be used as fuel in modified liquid salt reactors. Thus potentially every gram of thorium that is now the waisted byproduct of mining can be used to provide society with energy. Because the LFTR" can extract energy from thorium so efficiently, that the human use of the thorium fuel cycle will be sustainable for millions of years.

Other materials used in the construction of LFTRs would find no higher use in terms of energy output.

Not only does the LFTR make efficient use of natural resources, but it has great potential to make efficient use of human resources as well.  First,  LFTRs can and should be used in factories.  Factories almost always make more efficient use of labor, than on site construction processes.  The efficient use of labor in factory production of LFTRs would be a significant way to lower production costs.  

The operations of LFTRs also make efficient use of labor as well.  Because many control functions are performed automatically by the LFTR, the need for operator active control is largely eliminated.  The passive safety features of the LFTR mean that operator action is not required if a problem is encountered.  Safety features are passive, and shutdown and emergency cooling can be initiated automatically.  Operator error has almost always been the cause of major reactor problems.   By removing decisions from operators' hands and turning them over to the laws of nature,  reactor safety will actually be enhanced.  

Given the use of computers and sophisticated monitoring, a single operation room, can serve dozens of LFTRs.  Manpower will largely be devoted to security and maintenance.   Reactors will be maintained remotely, with specially designed machines, that maintenance workers will monitor and control.   Maintenance workers will rotate between reactors as the preform scheduled maintenance tasks.  Refueling can be accomplished continuously and automatically without operator intervention, and without reactor shut down. Because LFTRs have reduced staffing requirements, finding well qualified staff should not be a problem.

3 comments:

donb said...

Continuing on in the Rocky Institute mode: LFTR can be fabricated efficiently and cheaply using factory methods, producing relatively small reactors, which due to enhanced safety and zero emissions, can be placed closer to point of load, and also open up the possibility of combined heat and power to a greater degree.

Some of the ideas from the Rocky Mountain Institute are quite good. But they often go off track in the implementation.

DV8 2XL said...

Oh! Well done Charles

Charles Barton said...

I plan several more posts in this mode.

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