Nuclear Fission Plant Efficiency

Nuclear fission plants are currently enormously inefficient. At present, they extract only about .7% of natural uraniums thermal energy potential, and of that .7%, they convert less than 40% into electrical power.

In other words, their overall efficiency is only about .28%, less than 3 parts in 1000 of natural uraniums energy potential is utilized. This is actually a major reason that nuclear fission power plants produce so much long lived radioactive waste, because so much of that energy potential is not utilized.

Of that .28% that is successfully extracted, about 17% will be lost in transmission line loss, and about 50% will go unused because it will at a time when there is less demand than there is electricity produced and nuclear fission reactors can not be rapidly throttled.

So by the time all of these losses are concerned, perhaps .1% or 1/1000th of natural uraniums energy potential is actually utilized and a much greater quantity of waste is produced than need be produced.

Almost all of these losses can be eliminated, many of them with economic benefits.

One of the places that I can see a fairly economical improvement in efficiency is the heat dissipated in the cooling towers. Although the water entering these towers is not hot enough to recover additional mechanical energy via the Carnot cycle, it still can be used for things like space heating or driving some low temperature industrial processes. In countries like Sweden this is already done, waste heat from nuclear plants is piped to cities to provide residential and commercial space heating. Another potential use is for agriculture as a source of heat to prevent freezing or to grow in colder climates than otherwise be possible. The heat is going to end up in the atmosphere anyway so why not use it to displace some other heat source that would be heating the atmosphere in addition?

Approximately 17% of the energy put into the electricity transmission system never makes it to the consumer. The bulk of that energy is radiative losses. That is, the energy is radiated away from the long distance AC power transmission lines. Not only is this energy wasted, but there are also negative health effects, most notably leukemia, associated with AC electromagnetic fields.

For lines longer than 300km, converting those lines from AC transmission to DC transmission is economical. It frees up some of the right away because clearance is no longer required because of radiation concerns. DC lines do not radiate energy. DC lines can cut that average 17% loss into the low single digit area. DC lines also substantially upgrade the power line’s capacity because of two factors. First, the line can be run at the highest voltage the insulators are rated for as opposed to AC transmission where on average the voltage is only .707 that of the peak voltage. Second, on long AC transmission lines, heat causes mechanical sagging of the lines. This lengthens the lines and causes a phase shift over the length of the line which causes losses and additional heating. DC lines eliminate the phase issue allowing higher currents to be transmitted through the conductors. The combination of both higher average voltage and higher currents leads to substantially improved capacity over the same conductors with the same insulators. Lastly DC transmission eliminates susceptibility to either cascading power failures or space weather induced damage. Upgrading our transmission capacity this way would be the equivalent of adding about 15% more generating capacity to the nations electrical grids with no increases in pollution, thermal emissions, and improvements in reliability and health. It would also make it possible for intermittent renewable resources to provide a larger share of our energy needs.

A substantial portion of the energy produced by nuclear reactors at night and during low load times goes up the cooling towers because nuclear power plants, at least those of todays designs, can not readily be throttled up and down in power levels. There is enough surplus power at night to totally provide for all our daily commuting needs if that energy could be efficiently captured and used for that purpose. Doing that would eliminate our dependence upon foreign oil almost entirely because the percentage of oil used for our daily commute almost equals the two thirds that we import.

There are technologies available that would allow this. One technology is the plug-in hybrid and also all electric vehicles. The plug-in hybrid is a more practical alternative for many people because they’re not restricted to the short range provided by a relatively low capacity battery pack. For long trips, they can fill up and slurp gas the traditional way. But the majority of commutes are less than 20 miles and so can be completed entirely on electricity.

There are some people out there trying to suggest that this may result in an increase in air pollution because 50% of the electricity we generate comes from coal, but this is misinformation, and the reason for it is, that coal fired plants, like nuclear plants, can not be rapidly throttled and thus they burn coal at night but the energy is just wasted. Plug-in hybrids will simply be using energy that otherwise would have been dissipated in a cooling tower and will generate no more heat at the power plant but eliminate pollution from burning gasoline within the electric range of the vehicle. The one exception to this would be the evening or night shift commuter that recharges during the day.

There are other ways this energy could be harnessed, some of which are being used with solar and wind farms today. There is a battery technology that uses liquid electrodes and relies on changes to the oxidation state of vanadium often called a vanadium redox battery, that can be used to store electricity on an industrial or utility scale. The vanadium redox batterys’ capacity is limited only by the size of tanks used to hold the liquid electrode material. Vanadium redox batteries can be left in discharged states for long periods of time and don’t degrade with charge cycles to any appreciable degree. The downside of these batteries is that their energy / volume ratio is too low to make them practical for anything but fixed installations.

Another technology where geology makes it practical is hydro-storage where during times of surplus electrical generation, water is pumped up hill to a higher reservoir, and then during times of surplus it is allowed to run downhill through a turbine to generate electricity.

Then there are a few emerging technologies that could be used to turn surplus electricity into fuel. There are two technologies that can convert electricity, carbon dioxide, and water, into butynol, a 4-carbon alcohol that can be used as a replacement for gasoline in gasoline powered vehicles but provides better fuel mileage, power, and about 97% reduction in emissions. Although it’s energy content is slightly lower than gasoline, other factors make it burn more efficiently resulting in better mileage and power.

One technology uses a reverse fuel-cell device that uses a catalyst to convert electricity, water, and carbon dioxide directly into butynol. Butynol can also be used as a jet engine fuel and is being considered as a renewable replacement by Virgin Airlines and this reverse fuel cell technology was developed to that end. An alternate method involves electrolyzing carbon dioxide into carbon monoxide and oxygen. The carbon monoxide is then combined with steam to create a gas that can then be catalytically converted into any number of hydrocarbon products, including butynol.

These plants could be built close to coal plants and then the carbon dioxide from the coal plant turned into automotive fuel rather than being released into the atmosphere or geologically sequestered. If we actually got to the point where we were using all of the CO2 produced by coal and gas fired plants, we could sequester carbon dioxide directly from the atmosphere.

Greater improvements require more substantial economic investments, but making those investments would both improve globally our standard of living and reduce the burden of managing radioactive wastes that we will otherwise be leaving to future generations.

Most promising is a type of nuclear reactor that uses fast neutrons to fission not only U-235, but also U-238, thorium, and the transuranic elements produced in conventional fission reactors as well as those produced in these reactors. They would be combined with an integral pyrolytic fuel reprocessing facility to reprocess spent fuel on-site. The pyrolytic process does not separate plutonium from other transuranics and therefore does not at any point produce bomb-grade material. In addition, since the material would never leave the reactor site, there would be no opportunity for terrorists to intercept it during transit.

This type of plant uses a liquid metal such as sodium or lead, a liquid salt, or helium as a coolant. Helium has some significant advantages. It’s already a gas so an over-power situation isn’t going to turn the coolant into something not effective as such. These types of reactors automatically limit their reaction rate based on something known as Doppler spectrum broadening. Basically, to be absorbed efficiently and initiate another fission, a neutron must possess a certain energy level. As objects heat up, an atom may be moving either towards an approaching neutron, increasing the energy, or away from it, decreasing the energy, and in both cases the likelihood of an induced fission is reduced. So these reactors carry a negative thermal coefficient.

Helium allows operation at a high temperature which results in high thermal conversion efficiencies. Metal and salt cooled reactors operate at temperatures exceeding those of boiling water or pressurized water reactors, but less than those of helium gas cooled reactors. Other coolants are somewhat reactive, lead in particular is very reactive, and thus corrode plumbing, but helium is chemically inert. Sodium spontaneously combusts in the presence of air; so there are certain safety issues associated with it’s use as a coolant.

These reactors, through their high efficiency, can reduce waste volumes to about 1% of that produced by a conventional once-through boiling or pressurized water reactor. In addition, by burning the actinides, the waste they produce consists only of fission products which only require storage for about 300 years (assuming no further treatment) rather than 50,000 required for the waste produced by existing reactors. Further, these generation IV burning reactors can use the waste from conventional reactors as fuel eliminating the need for long term storage.

There are additional technologies which can turn the longest lived fission produces into products that decay very rapidly reducing the storage requirements to around 20 years, however these technologies do require energy and thus reduce slightly the overall energy efficiency.

France and Japan are both pouring money into research and implementing these types of reactors, we should be as well. Properly implemented nuclear fission can provide for our energy needs for millions of years.

Because so much more energy is recovered from uranium this way; uranium from sources such as extraction from seawater become economical. This is what extends the fuel supply for so long. Because thorium can also be used as a fuel and it is 3x more plentiful in the Earth’s crust than is uranium, this also extends the fuel supply considerably.

We do not have to have an energy crisis, nor do we need to have ever increasing levels of carbon dioxide in our atmosphere, and neither do we have to live in poverty and fight wars over oil. There is plenty of energy to go around if we produce, distribute, and utilize it wisely.