Pollution from Coal vs. Nuclear

Updated December 13, 2015

Pollution from coal, per gigawatt-year

According to ORNL, Coal provides about 6150 kilowatt-hours(kWh)/ton thermal energy.

Existing coal-fired plants of 1000 megawatts capacity burn about 4 million tons of coal* each year.
4 million tons of carbon produce 4x44/12 million tons of CO2. That's about 14.7 million tons. For the carbon in coal, perhaps 85%, probably more like
12.5 million tons of CO2, and several thousand tons of sulphur and nitrogen oxides, which are actually pathogenic and carcinogenic.
Plus the ash and microscopic flying glassy particulates, some of them even radioactive!
Note that even without the threat of Global Oceanic Warming, health considerations alone justify replacing coal burning with nuclear.
Gas might be cleaner per MWh than coal, but even if you do not count the unexamined consequences of fracturing shale to get it, gas turbines emit poisonous, acid nitrogen oxides. It also comes out of the ground with significant amounts of nasty sulphur compounds. Methane apparently produces twice as much electric power per ton of CO2 as coal, but any methane, CH4, that leaks from the fractured shale without being captured has tens of times the greenhouse effect of a similar quantity of CO2.

*That should provide 20,910 million kWh/yr, of thermal energy at 85% carbon. A non-leap year is 8,760 hours, so one year at 1000 MWe is 8,760 million kWh. So the heat engine efficiency is somewhat less than 40%, because the capacity factor is more like 75% to 90%.

Nuclear Waste from an Efficient Modern Design

Nuclear Energy provides about 10 million kWh electrical energy per kg of fuel consumed, in present reactors.
so 10,000 million kWh per tonne of real waste products. But even if we count the associated unconsumed uranium and plutonium as "waste", we have about 25 to 30 tons of "spent nuclear fuel" to compare with the ten million tons of carbon dioxide, and thousands of tons of poisonous gases.

Nuclear Breeder Fission Reactors

There are two types of breeder reactor, both of which have a negative thermal coefficient of reactivity, meaning that as the fuel gets hotter, the reaction slows down. The atomic nuclei get further apart as the fuel gets hotter, the apparent target for the neutrons is smaller, and besides, slightly hotter neutrons are going faster and are slightly harder for the nuclei to capture.

Fast Neutron Reactors

The ARC-100 reactor,derived from the IFR's EBR II, abandoned by Clinton, will run at 90% capacity factor for 20 years, requiring disposal of just less than 1.7 tons of short-lived fission products at the very end of that time. The fuel is refurbished with that same mass of un-enriched, even depleted, uranium. So 1000 MW per year from ten ARC100 reactors will produce
about 17 tons of nuclear waste in 20 years.
That is thousands of times less toxic than even just the annual sulfur and nitrogen oxides from the coal, or even from an equivalent amount of pure methane in gas turbines. It would save 250 million tons of carbon dioxide in those 20 years — just by replacing one base load coal burner.

GE/Hitachi's PRISM design has similar qualities, and the same ancestry.

Liquid Fuel Thermal Breeder Reactors

These renewable, sustainable designs are descendants of the MSRE (Molten Salt Reactor Experiment) that was abandoned by Nixon
They differ from the fast neutron reactors in that the fuel itself being liquid, the non-fissile but 'fertile' isotope can be continously replaced. They also make use of neutrons "moderated" to speeds that can sustain a chain reaction with low-enrichment fuel.

The MSR's principle is that fluorides of actinides, such as uranium, thorium, and plutonium, and the intermediates neptunium and protactinium, can be dissolved in a solvent of liquid lithium fluoride, perhaps also with beryllium fluoride. This liquid is both the fuel and the primary coolant. Unlike water, it needs no high pressure to keep it from boiling. It carries the energy to a heat exchanger, to a similar fluid also at near atmospheric pressure. With a fissionable starter, the reactor generates replacement fissile fuel from the fertile, common U-238 or Th-232, by neutron bombardment at the same time as the fission chain reaction is providing heat energy. Once again, the fact of an unpressurized liquid fuel system means that there is no worry about solid fuel melting down. The possibility of runaway heat is securely prevented by a plug that is like the fuse that protects an electric circuit. It is kept solid by a refrigerating circuit driven by the power from the reactor that also circulates the fuel, which carries off the heat energy. The plug melts at any temperature higher than that of the desired activity, and dumps the fuel into a container of reaction-killing neutron capturing material if the refrigerating power that keeps it solid fails.

For some time, this proposed technology has included the Liquid Fluoride Thorium Reactor, LFTR, which is being explored by FLiBe Energy. Their website says that:

Fission of one atom of nuclear fuel releases over one-million-times more energy than burning of any hydrocarbon or other fuel molecule. With LFTR technology, 6,600 tons of thorium could provide the energy equivalent of the annual global consumption of 5 billion tons of coal, 31 billion barrels of oil, 3 trillion cubic meters of natural gas, and 65,000 tons of uranium.
Note that uranium is indeed being used with monstrous inefficiency at present
But note that the reference to uranium refers only to LWR use of uranium, which is certainly wasteful by a factor of about twenty.

There is an even newer design, from about 2011, called Transatomic Power or TAP, using just lithium fluoride as the solvent, and designed to consume either uranium or thorium, and of course the not exactly spent fuel that is erroneously feared and condemned as nuclear "waste". Its huge improvement is the use of hydrogen rather than carbon for the moderator, using solid zirconium hydride instead of liquid oxygen dihydride, H2O, which is also called water. It is calculated that this design can use and breed from fuel with fissile content of 1.8%, as contrasted with 3.6% for the present PWR designs, or even 15% for the best IFR breeder design.

The fast neutron reactor (FNR) designs would require about the same tonnage of fuel as the LFTR.

In the long run, the LFTR consumes thorium as fissile uranium. The FNR and TAP consume non-fissile uranium U-238 as fissile plutonium.
We should also note that any technology that is to supply every demand of the electrical grid, whether at the national, state, or local level, needs peaking reserve. At present, that provides a very profitable market for gas turbines. That's because at times of expected sharp increases in the demand, the gas turbines are scheduled to run at full speed at less than full load, and when the load jumps, so does the rate of supplying gas to the turbine.
The California electric energy crisis of 2000-2001 came when the hydroelectric capacity had been reduced by unusually small rainfall and winter snowfall. The owners of gas turbine capacity were able to charge premium rates for simply running their turbines at very little load, as reserve. The value of standby "spinning reserve" was enormous. By contrast, the value of capricious weather dependent supply is much lower than that of base load.
Ontario's drastic shutdown of coal coincided with a larger increase in the installed capacity of gas turbines, than nuclear. But the gas turbines provide 13% of the energy, whereas nuclear provides 58%, and hydro 26%.
If the resource being used to reduce CO2 emissions, free from fracking and oil tankers and coal emissions, is as unremittingly beyond our control as wind is, we need more such reserve. The load-following characteristics of the IFR and SMR technologies may be as good as gas turbines. If not, then when electrical demand is low they can provide battery electricity, or hydrogen from electrolysis of water. Sorensen asserts that the LFTR is highly appropriate for desalination of water. That would deal with another dwindling quasi-fossil reserve, the water in the aquifers that are being reduced faster than rainfall can refill them.


A Paradox

Clinton The IFR program was canceled by the Clinton administration, in the belief that its plutonium would make bombs more readily available, which is false.

Nixon The LFTR program was canceled by the Nixon administration, on the grounds that it was unsuitable for bomb making, which is true.

What About Biomass?

Let's look at how we might substitute whole growth renewable photosynthesis, low fertilizer input, Short Rotation Coppice.
That's fast growing trees, willow, that can be cut every three years, and regrow from the stump. The roots persist. You harvest one third of the plantation every year.
From : energy saving community, UK

If it all goes well, you should be able to get something between 6.5 and 16 dry tonnes per year out of your 2 acres once your SRC is established.

Assume the high value, and a similar plantation of 640 acres (a square mile). A good figure for wood is just about 4000 kWh thermal energy per tonne. That would be 320 x 16 x 4000 kWh, which is just over 20 million kWh, per annum. Divide by the number of hours (8760) in a year, to get an average power rating. It comes to 2,338. Now use a wildly optimistic efficiency, 40%, for thermal->electric conversion, we get 935 kW. To get the equivalent of a 90% capacity factor 100MW breeder reactor, 90,000 kW, you'd need over 90 square miles, and very good luck. At the low figure, you'd need more than twice as much. To put a 1000 MW base load coal burner out of business, you'll need ten times as much, 900 square miles. Alternatively, you might find some bio-engineered way to convert wood (mostly complex polysaccharides and lignins) to ethanol. You won't get as much as 2/3 of the energy there either, before you burn the ethanol, because you have to feed the yeasts and bacteria, or whoever. Best rate per square mile, 1,543 kWh of energy. That's about enough for a thousand automobiles driving 15,000 miles a year and getting 30 mpg.

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