Why Do We Say Nuclear Power is “Green”?

People use the term “green” when an energy source: (1) does not pollute the air, water or land we live on and (2) is a sustainable source of energy.  As far as environmental pollution, nuclear plants produce zero airborne emissions that can cause health problems for people, flora or fauna.  Nuclear power plants cause the smallest number of deaths each year than any other energy source, including renewable sources.  The table below compares the yearly deaths due to the 7 common sources from data compiled by the World Health Organization and the European study Externe.  Most of the deaths from the 3 fossil fuels are due to heart, lung and blood diseases inflicted upon the general public by burning fossil fuel.  However, all 7 entries also include accidents by workers during construction, generation, and distribution of the energy source.

Nuclear power plants also generate zero green house gases (CO2), Sulfur Dioxide, or Nitrogen Oxides nor do they inject carbon particulates into the air.
Nuclear radiation is confined to within the reactor pressure vessel and the concrete containment dome.  In the US, no radioactivity above the natural background radiation from cosmic rays and in the soil has been found surrounding the containment domes.  The Chernobyl facility was built in a common industrial building, had no containment  dome and had so many other faults that it shouldn’t  even be considered next to the performance and quality of our US facilities.  The Chernobyl facility should never have been built and could never have passed the very strict licensing process of the US Nuclear Regulatory Commission.

Nuclear power plants have been generating electricity for over 60 years during which engineers have developed 3 generations of technology so far where each successive generation was safer than the preceding one.  According to the Nuclear Energy Agency the world has enough Uranium reserves at extraction costs less than $130/kg to fuel  these 3rd generation (Gen 3) facilities for only about 70 to 80 years(1).   Not sustainable, but remember that this is just the first step in the evolution of nuclear power plants.  Gen 4 reactors will be in use in the next 20 to 30 years, long before we run out of Uranium.  

One leading design for Gen 4 reactors, now under development in the U.S., India, and China is called a Molten Salt Reactor (MSR) which uses liquid Thorium Fluoride salt as fuel.  This system uses an ingenious fuel cycle in which one new fuel nucleus is formed for each one that is destroyed to release energy continuously.  Thorium (Th-232) is called “fission fertile” which means that it can breed fissionable isotopes but is not fissionable itself.  The Thorium cycle can achieve an efficiency converting fuel into energy of 95+% compared to Gen3 reactors using Uranium which have an energy efficiency of 0.5%.  In addition Thorium abundance in the earth’s crust is 4 times that of Uranium and natural Thorium is already 100% Th-232 so enrichment is not necessary.  Uranium 235, the fissionable part of natural Uranium, is only 0.72% abundant and must be enriched to at least 3% to work in a reactor.  So it is clear that Gen 3 reactors do not use scarce Uranium fuel very efficiently.

Therefore if the Uranium reserves can supply all of the Gen 3 plants for 70 years, how long can we run future Gen 4 plants on Thorium?  If one computes all the Thorium enhancements over Uranium, you get the following:  70 yrs X Thorium/Uranium supply Factor (4) X Thorium  Efficiency Factor (95/0.5) X Fuel Dilution Factor (100/3) X  Enrichment Penalty (3/0.72) = 70 X 4 X 190 X 33.3 X 4.16 = 7,369,689 years. But this is only true today where nuclear generates only about 6% of the world’s electricity and no consideration is made for massive need for electrification of developing nations and world population growth.  Taking  these growth factors into consideration, Thorium fuel should last approximately  300,000 to 500,000 years.    While this is not strictly sustainable, it should still last us through the next 2 or 3 ice ages (during the last 1 million years there have been 7 ice ages).  Actually the fuel only has to last to the next ice age (about 100,000 years from now) when our entire civilization will be turned upside down anyway.

The MSR type reactor is not just a concept.  An MSR prototype was developed at Oak Ridge Nation Labs (ORNL) in the early 1960s and was successfully operated for 4 years from 1965 to 1969.  However water-cooled Uranium reactors for the US Navy had already created an industrial base for that design, despite long-standing recommendations to broaden reactor designs to use thorium.  Consequently the entire Thorium MSR program was terminated by the US Atomic Energy Commission in the early 1970s.
MSR power plants have many other features besides the very efficient use of any fertile/fissile fuels.

1. Virtually no nuclear bomb proliferation is possible.  The Thorium reaction manufactures almost no Pu-239 and there are almost no long-lived transuranics in the small amount waste produced.
2. The MSR has what industry calls “passive safety” using a “freeze plug“ in the salt loop’s low point, meaning if all electric power is lost, the frozen fuel plug melts and all the liquid fuel drops into an underground holding tank with no human operator action.  This is where the 1962-69 MSR’s salt still resides at ORNL.  It could be re-used.
3. Since there are no long lived transuranics in the waste, it needs safe storage for only a few hundreds of years rather than many thousands of years.  The volume of waste is far less than what is presently produced by Gen 3 reactors.
4. There is no water, and no high pressure reaction vessel, thus no possibility of steam or other explosions.  Salt allows much higher operating temperatures, so an MSR can deliver more power and avoid steam entirely, using  gases like CO2 or Helium to convey energy to the turbine generators.
5. There is no need to site MSR plants near the coast, lakes or rivers because the higher operating temperatures (600oC)  allow the use of air cooling instead of water.
6. The higher operating temperatures permit the use of gas turbines rather than steam turbines which yield a thermal to electric efficiency of 45% rather than the 35% achieved today.
7. There need not be shutdowns for refueling as is done today.  Refueling will be done while the reactor is running at full power, because the liquid salt fuel can be added to the molten salt on the fly.  The reactor can be operating 365 days a year, 24 hours a day, every year.  And it will do this by using 1/100 the land of any other sustainable power source.

These features plus several other more technical ones show that there is no pollution of the air, water and land the human race needs so desperately and that the next generation nuclear reactors burning Thorium can generate electric power well into the next few ice ages. This is why we say nuclear power is green!

(1) Nuclear Energy Agency (NEA). 3 June 2008.  Uranium 2007: Resources, Production and Demand, also known as the Red Book