Energy for the Millennium
As we start the new millennium, we are faced with many problems. This is to address just the energy crisis. In doing so, we may find we are confronting other problems as well.
For most of the last century, we have had the promise of unlimited power from nuclear sources. Due to the amount of radioactive waste produced by fission reactors and the necessity for transporting this deadly material to storage sites, this power source has become unpopular, Perhaps justifiably so.
We need a source of nuclear power that does not produce nuclear waste and that does not produce gamma radiation. Such a source is easily shielded and relatively harmless in the unshielded state. There are a number of isotopes that bear these characteristics. These are the pure beta emitters. The most well known of these is Carbon14. A few others are Hydrogen3 (Tritium), Argon39, and Nickle63. These all decay with only beta emission and the decay products are stable. This characteristic of a stable decay product is quite important. The currently used beta emitters such as strontium 90 decay into other isotopes that have quite deadly gamma radiation.
In order for these to form a useful energy source, they need to have a long half life. All the ones I listed have a long half life. They also need to have enough energy output per kilogram. Those listed vary greatly in energy output. Argon39 and Hydrogen3 seem to be the most attractive from an energy per kilogram standpoint.
There is a third consideration, that of loss of containment of the isotope. This could be unintentional, as in an accident, or through military or terrorist actions. Hydrogen3 if burned turns into water. This exchanges readily with water in the human body and could cause some harm. Carbon14 in the form of Carbon dioxide is also readily exchanged in the body and would be damaging. However, there are forms that are stable, which I will discuss later. Argon39 is the best from the standpoint of the biosphere. It is completely non reactive. Unfortunately, it is a gas and therefore more difficult to contain. It is also difficult to produce.
After considering these factors, my recommendation is to use Carbon14. If this is combined with Titanium, it becomes quite stable. Titanium Carbide is a refractory material that does not combine readily with air below 1000 degree Celsius. As this compound decays, the product would be Titanium Nitride which is also refractory with very similar characteristics. The slight density change as the material decays would probably cause cracking. If the material were already a powder, possibly alloyed with a softer metal, such as Cobalt, this problem would be eliminated. No gas is produced, and the volume is only slightly reduced (about 0.5%per 1000 years ), so cracking of the containment should not be a problem. Water could be run directly over the fuel elements to generate steam and neither the water, nor any impurities in the water, would become radioactive. Since no neutrons and no gamma rays are produced, a thermoelectric generator instead of steam might be used. This might be more in line with the 1000 year lifetime since it would have no moving parts.
Now lets look at a few details. Titanium Carbide would produce a self heating of about 0.93 watts/Kg. Having a density of 4930 Kg/cubic Meter it requires approximately 220 cubic meters per megawatt of heat generated. This is comparable to the volume of existing reactors but, allowing for insulation and steam pipes, it might require quite a bit more than that. The form of the fuel elements would probably be plates with a metal coating. The Beta emissions would not penetrate the coating and the plates, if thin enough, would not self heat to the point of being uncomfortably hot. For example a plate with a layer of active material 2.5 CM thick would have about a 20 degree Celsius temperature rise if placed on edge in free air. Since there would be no external radiation, these could be safely held in the hand and would just feel warm. If they were broken open, the radiation would only penetrate the air for a few centimeters, but would burn the skin (similar to a sunburn) if touched. Stacking the plates to increase the volume to surface area ratio and insulating them would increase the temperature for power generation Unlike fissionable material, the heat buildup is linear with volume and there is no "critical mass" reaction. A plate 60 CM (about a two feet) thick would self heat to 500 degrees in air. The good news is that since there is no “critical mass”, this form is scalable to any size. It could power a flashlight, a locomotive, a cruise ship, or a city.
A power plant using this material would produce power at an almost constant rate. The decrease in energy output over the next 1000 years would only be 11.4%. There would be no need to shut down and refuel before that time. There would be no gamma radiation and no radioactive waste produced. There would also be no carbon dioxide emissions, nor any nitrous oxides produced. Careful design could separate the plates to provide air cooling in the event of loss of coolant.
Now for the bad news. Carbon14 must be produced in a nuclear reactor. Yes, that's right, one of those nasty nuclear waste generating radioactive things. The good news is that Carbon14 is very easy to produce in a reactor. Since the Carbon14 fuel elements can be safely transported, the reactors can be anywhere, even on the moon. If the reactors are placed where the nuclear waste would be stored, there would be no need to transport the waste. In fact just exposing nitrogen to the neutron radiation from nuclear waste produces more Carbon 14.
Part of the reason I chose Carbon14 is its' safety. While the Titanium carbide is very stable and unlikely to be decomposed by accident, a dedicated terrorist could intentionally burn it with a cutting torch, but the product would dissipate rapidly in the atmosphere which already contains about 60 tons of Carbon14..
A power source that produces no Carbon Dioxide emissions, no Radioactive Waste, no other waste of any kind and doesn't need to be refueled for a least 1000 years. This seems like a reasonable approach to supplying our power needs for the next millennium.
CRC Handbook of Chemistry and Physics