Replacing Fossil Fuels by a Different Kind of Nuclear Reactor

by Robert Wolf
 
We use uranium in our electricity producing nuclear plants because it is connected to our need for atomic bombs. We could be building other types of nuclear plants that are greatly safer and less costly than the reactors we use now. In the hunt for an alternative to fossil fuels we are failing to pursue, as other countries are, a very different kind of reactor.
 
Weapons, submarines and nuclear power plants all use uranium as fuel.
That nuclear power plants came to use uranium for their fuel was in large measure because it was the fuel best suited for military weapons and for submarine engines. Enriched uranium (in the fissionable, but <1%, 235 isotope) was critical to both of those military uses even though it is both enormously expensive and difficult to produce.
 
What the public needs to know is that there is, and all along has been, an alternative to the uranium based reactors now in use.
 
Nuclear reactors using a different fuel and a different cooling system were developed nearly as long ago as uranium water cooled reactors: The Molten-Salt Reactor Experiment (1965–1969) was a prototype at Oak Ridge National Laboratory for a thorium breeder reactor power plant. Today we could have liquid fluoride thorium reactors – which use liquid fluoride for cooling and thorium for fuel - rather than the uranium fueled water cooled reactors we use.
 
The public needs to know that that that alternative is presently getting considerable scientific interest - although there is as yet slight corporate and political support for employing them as a non-fossil fuel means of producing energy.
 
Conventional U.S. nuclear reactors are light water reactors (LWRs). They place highly enriched uranium pellets in long rods, which are assembled vertically in a grid pattern and can be withdrawn separately. They are surrounded by 570 degree F water under 70 atm. pressure, which is circulated in order to carry the heat from the fission of uranium atoms away. That heated water is conducted into a separate water system that spins a high-pressure turbine which generates electric power, the desired outcome.
 
The required high pressure systems and containers are massive and expensive both to build and to operate. They are also vulnerable to leaks and ruptures. Should the cooling system fail, these systems are in danger of melting the fuel, which then can burn through the containment vessel into the earth and ground water while releasing radioactive gases. (This possibility is the background to the movie The China Syndrome.)
 
What has caused such great opposition to current nuclear power, an opposition so great that no new plants are being started despite their advantages in this era of seeking alternatives to fossil-fuels?
 
That opposition is not caused by the number of accidental deaths due to reactor failure. With the exception of Chernobyl, there have been only a handful of such deaths world-wide. Two have occurred in the US (that low death rate from its nuclear plants is not commonly known) and two in Japan, one in Argentina, and none in Canada, France, Germany, or Israel. Japan’s tsunami-caused Fukushima accident had no immediate deaths, but is expected to cause 130–640 deaths in the future. Chernobyl had 56 direct deaths - 47 accident workers and 9 children who acquired thyroid cancer - and it is estimated that there will be 4000 additional deaths from cancers caused by radioactive emissions. The Chernobyl melt down was due to both bad design of the reactor and totally incompetent operation.
 
For comparison, yearly direct deaths from coal mining in the US from 1990 thru 2011 have ranged from a low of 18 to a high of 66 (those numbers are greatly reduced from a century ago.) Deaths in the U.S. from particulate matter due to power plant pollution are estimated at 13,000 per year. In contrast, direct deaths from coal mining in China for each year from 2000 thru 2010 have ranged from a low of 2400 to a high of 7200.
 
So if not deaths, what has caused our current opposition to nuclear power to generate electricity? There are 5 factors that have produced that concern: danger of fuel diversion by terrorists or rogue states, explosions, radioactive emission, waste storage, and excessive cost.
 
Fuel diversion is feared because it might result in weapons or dirty bombs to spread long-lived radiation. Both explosions and radioactive emissions are probable and dangerous due to high pressure cooling systems used. Reactor waste is radioactive and must be safely transported and stored for many thousands of years. High cost stems from lack of standardization and interchangeability: new plants are very large and require new designs and elaborate safety reviews, delaying building schedules.
 
To mitigate these worries, an acceptable nuclear plant should use fuel unsuitable for bombs. It should operate at low pressure to reduce the risk of explosions and radiation. It should be very efficient, so as to produce small amounts of waste that can be mostly reprocessed and burned in the reactor, with final waste being stored at a central safe site, such as a salt mine. The reactor should be modular and of small size with a single tested and approved standard design. And finally, it should be fail safe and not susceptible to melt down.
 
These very qualities for an acceptable nuclear reactor describe the 4th generation of reactors currently being proposed: the liquid-fluoride thorium reactor (LFTR) and the Integral Fast Reactor (IFR).
 
 Unlike today’s LWRs, both types operate at low pressure for less risk and lower cost, and also operate at higher temperature for 40% better fuel efficiency, lower cost, and waste burning. Higher temperatures enable more of the reactor heat to be converted to electricity (an efficiency of 40% in an IFR and 50% in a LFTR vs only 35% in a LWR). Both types can reprocess fuel and burn radioactive wastes on site. This minimizes waste processing, transport and storage problems.
 
Both IFR and LFTR have the potential to be air-cooled and to use waste heat for desalinating water. Both the IFR and LFTR are 100-300 times more fuel efficient than LWRs. In addition to solving the nuclear waste problem, they can operate for many centuries using only uranium and thorium that has already been mined. Thorium is 4 times as abundant as uranium, produces 1/100th of the radioactive waste of uranium. Moreover thorium is not suitable for making atomic bombs, nor are its waste products. Thorium does not need enrichment, making it a far more economical fuel.
 
A Fast IFR uses liquid sodium as a coolant, which results in fast neutrons initiating fission. The LFTR is a thorium reactor that uses a chemically-stable fluoride salt for the medium in which nuclear reactions take place. This liquid fuel yields simplicity of operation and eliminates the need to fabricate fuel elements. The fluid fuel in a LFTR is also easy to process and to separate useful fission products, both stable and radioactive. The LFTR has less efficiency than a fast neutron IFR in destroying existing nuclear waste. One sometimes hears the aphorism: The solution to pollution is dilution. This has some useful applications, but definitely not in radioactive waste storage. Burning nuclear waste in the reactor is a definite advantage in simplifying reprocessing and reducing the volume of waste storage. Thorium fission wastes decay in about 300 years due to short half lives. They are 1/10,000 as radioactive as uranium /plutonium wastes after just 300 years.
 
A major advantage of 4th generation liquid fuel systems is that they can shut down automatically upon loss of coolant or failure of the cooling system. As the fuel starts to overheat, a thermal plug in the bottom of the reactor will melt to allow the liquid fuel to drain down into several separated storage containers below the reactor. This separates the fuel enough to quench the nuclear reaction. The reactor is inherently fail-safe from loss of coolant and overheating.
 
China has taken the lead from the U.S. in solar panel production, and also in high speed rail deployment. LFTR reactors are now being developed and constructed in China, and may soon be developed in India, Japan, Israel, Australia & the UK, although not now in the U.S. The U.S. and Australia have the greatest thorium reserves. It is a great pity that timidity and lack of vision in the U.S. have reduced us to second-rate status in energy innovation.
 
Decisions on choosing new energy projects are made on the basis of short term costs and entrenched corporate interests without regard for long term consequences. The U.S. is a major source of CO2 emissions, but China is a much larger source, due to its triple population and greater reliance on coal.
 
The US has the resources, if not the will, to move away from fossil fuels. If we are successful, other countries will be inclined to follow. Success requires the cooperation of all major economies. I worry that the pace of climate change is just slow enough that we will never feel compelled to act, but just fast enough that it will be impossible to avoid disastrous effects after we begin to act.
 
We cannot afford to neglect any alternative to fossil fuels, in order to drastically reduce CO2 emissions in the next decade. The nuclear reactors described here are one such important alternative that we must consider.