Alternative Nuclear Technologies
Most nuclear reactors now in use in the United States are water moderated reactors whose designs are based on the same designs found in our nuclear submarine fleet. This is an historical anomaly, there are now many other nuclear technologies available that promise a new era of safety, efficiency, and best of all, lowered creation of high-level nuclear waste. Moreover, there are a number of technologies on the horizon which would either reprocess nuclear waste or render it significantly less threatening.
If we can survive the current onslaught against nuclear energy and high-technology in general, we can look forward to seeing improved technologies such as High-Temperature-Gas-Reactors, breeder reactors, transmutation by linear accelerators, fuel reprocessing, fusion energy and a host of other nuclear technologies. However, all these advances still require some disposal or storage of high-level nuclear waste, such as at a site like Yucca Mountain. These alternative technologies impinge on the study of Yucca Mountain because they broaden the spectrum of values that can be placed on nuclear waste. The more valuable the waste is for potential reuse, the more likely Yucca Mountain will be utilized as an interim solution to storage of nuclear spent fuel.
Ninety percent of the energy that is available from uranium nuclear fuel is still contained in the waste. In fact, the main reason spent fuel is removed from reactors is not because of a lack of usable energy, but because of the degradation of the cladding that keeps the fuel intact. A number of processes have been advanced with mixed success that attempt to recover the leftover energy available in spent fuel. Other processes seek to recover some of this energy while at the same time decreasing the radiologic hazards of the remaining waste. We'll touch briefly on a number of these technologies.
By tuning nuclear processes within what is called a breeder reactor, much of the energy left in spent fuel can be recovered by transforming portions of the waste into usable radioactive isotopes. Unfortunately, breeder reactors generate plutonium, which besides being a fissionable reactor material that can fuel power plants, is also a bomb making material. Because of president Carter's concern over the proliferation of nuclear weapons, America stopped its development of the Clinch River Breeder Reactor demonstration plant in 1980. Generating a bomb from the fissionable uranium found within reactor spent fuel requires high-tech separators and sophisticated processing. In contrast, plutonium is readily separated from nuclear waste (though not in someone's garage) and is more easily constructed into a crude bomb, hence the fear of weapons proliferation and terrorism. This is likely a moot point at this time because the fall of the former Soviet Union and the existence of other stockpiles of fissionable materials makes it relatively easy for nations which wish to obtain nuclear status to obtain the seed materials from blackmarket warhead stockpiles.
President Reagan overturned Carter's edict against breeder reactors, but escalating costs made restarting the Clinch River program infeasible.
Even without a breeder reactor, reprocessing spent fuel by separating out usable fissionable material was long thought a viable option for recycling at least part of our nuclear waste. Spent fuel rods actually contain almost 4% U235, but are removed from service because of degradation of their mechanical properties rather than because of a decrease in their power generating capability. Separation and reprocessing of usable fuel is already done in France as an integral part of their nuclear energy program at their Phoenix facility. However, the reprocessing process is presently 1.5 to 2 times as expensive as using primary uranium feedstock. Thus the reprocessing option has been killed by economics rather than the viability of the process. Some hope exists, however, that expensive chemical separation may not be necessary and that spent fuel could merely be ground up and reused after minimal repackaging. Such a possibility would make retrievability at Yucca Mountain a key issue.
In a breeder reactor, neutrons from a reactor core irradiate a blanket of uranium and transform it into plutonium through the capture of a neutron by the uranium atom. Advanced research on such a breeder reactor is being conducted at the Argonne National Laboratories Integral Fast Reactor, in which neutrons are used not only for the production of new fuel, but also to generate heat to run power turbines. The Integral Fast Breeder Reactor is designed to irradiate its own waste, allowing the reactor to generate its own fuel as well as reduce the amount of high-level radioactive waste all reactors create at some level. With modifications, the Integral Fast Reactor could also irradiate the waste from other plants as well and depending on the isotope either convert elements into useful radioactive substances or to non-radioactive forms.
An alternative way to transmute nuclear waste is by irradiating it with neutrons from a particle accelerator s(ee Figure ). Protons are accelerated into a lead target which spews neutrons that transmute the waste and also generate enough heat to produce surplus energy. One advantage of accelerator based transmutation technology is that if problems arise, for example the creation of excessive heat, the accelerator can be simply shut down to stop the process. Another advantage is that substantial amounts of energy can also be recovered from the process. Both the Los Alamos and Brookhaven National Laboratories have been studying accelerator based transmutation technology and private industry is also involved. Once again, cost is the driving factor
ALTERNATIVE REACTOR TECHNOLOGIES
Part of the disposal equation is also the availability of cleaner and more efficient reactor designs. Among such options are high-temperatuure gas reactors, modular designs which take advantage of mass production techniques to eliminate production error, fast integral reactors which use fast neutrons to degrade or process waste materials, ad infinitum. Designs already available would create substantially less waste per amount of energy produced. Unfortunately, because of the bottleneck created by Yucca Mountain, it is unlikely any advanced reactors will be built given the possibility that long term storage will not be available at the end of the process. This creates a situation in which not only are safer and more efficient designs kept from production, but older designs are operated towards or past their design lifetimes, further compromising safety.
Fusion energy, the energy source of the future, also requires the disposal of high-level nuclear waste. Where nuclear reactors represent the release of energy from controlled atomic bombs, fusion harnesses the even greater energy availabily from the processes that drive hydrogen bombs and the sun. When two hydrogen atoms are compressed and heated to extreme densities and temperatures, they fuse to form a helium atom that is slightly less massive than the two hydrogens. This small mass differential is converted through Einstein's famous equation, E = MC2, into large amounts of energy. In practice, two isotopes of hydrogen called deuterium and tritium are used because they are easier to fuse than elemental hydrogen.
Both deuterium and tritium are radioactive and because they combine with oxygen to make water, are easily dispersed through the environment. More importantly as the source of an energetic radiation spectrum ranging from gamma rays to x-rays to atomic nuclei, fusion processes generate energetic neutrons which irradiate the containment walls and transform various elements into long lived high-level nuclear waste material. For example, if 316SS (a stainless steel) is used in the walls of a plasma fusion reactor, the following induced radioactive materials would be created:
55Fe Iron-55 2.94 year half life
58Co Cobalt 58 72 year half-life
54Mn Magnesium-54 310 day half-life
60Co Cobalt-60 525 year half-life
[after Nuclear Fusion, Keishiro Niu, Cambridge University, 1989, p221]
Although the half lives of these radioactive substances are relatively shorter than those found in fission reactors, their quantities will still be substantial. In any event, the promise of fusion power still appears to be decades away from being fulfilled because the technology is exotic. Even with the technical problems of fusion power solved, it is not clear that it will be economically competitive in the near future, especially for intermediate sized plants.
FUTURE USES OF NUCLEAR WASTE
Although reprocessing and transmutation are not now cost effective and fusion energy is many years distant, we have taken the time to explain these technologies because of what they imply for the Yucca Mountain project:
1) At some time in the future, perhaps less than 100 years, it may become economical to reprocess or transmute spent fuel. This implies that Yucca Mountain may some day become a valuable energy resource repository. The question this raises is who will have deed over this resource and for what period of time will the repository be designed to remain open for retrieval of spent fuel.
2) The Third World cannot afford to overlook nuclear power as an energy source if it wishes to thrive. Even if the materials stored at Yucca Mountain may never have economic benefit to the United States, they may have benefit to other world nations. In that case, the total risk to the environment from nuclear materials may well be advanced if Yucca Mountain becomes an internationally recognized and competent center for nuclear waste disposal, transmutation and reprocessing technology.
3) If Nevada became the energy capital to the world, compensation for this service would not presently go to Nevada. Nevada's current political incumbents may be in the process of walking away from an energy bonanza and benefits that would dwarf the Alaska pipeline profits paid to that northernmost state. Consequently, forward thinking politicians might be negotiating now for the rights to these potentially invaluable resources, recognizing that Nevada may at some point become the central nuclear technology center in the world..
4) Reprocessing, transmutation, new reactor designs, etc., do not eliminate all high-level nuclear waste and may in certain circumstances actually increase the volume of waste. This means the need for a long term geologic repository, such as Yucca Mountain, is not going to be eliminated with forseeable technologies.
5) Unless we wish to eliminate nuclear power and depend solely on hydrocarbon and solar technologies, which have environmental and technical problems of their own, there will be a continuing need for geologic storage of high-level nuclear waste. The Third World may well remain impoverished and potential enemies if we force them to compete for limited traditional energy resources. Yucca Mountain could conceivably evolve into the energy "bank" of the world.
Shutting down Yucca Mountain may delay the inevitable transformation of our nation to nuclear energy sources, but it does not stop the international movement towards nuclear energy nor the need for our nation to find alternative means for disposing of the waste we have already created. A moratorium on new nuclear technology (imposed defacto by delay of the Yucca Mountain project) thus poses serious risks for both ourselves and the world environment by hobbling America's design of new generations of efficient and safe reactors that would keep us economically competitive. Although these reactors would create less than a quarter as much nuclear waste as present designs, they are unlikely to be pursued if geologic storage is cut off.