Fast reactor future â the vision of an atomic energy pioneer
Nuclear energy can contribute to the solution of global energy problems
Leonard J. Koch, winner of the 2004 Global Energy International Prize. Originally presented at the Programme of International Symposium âScience and Societyâ, March 13, 2005, St. Petersburg, Russia.
Energy has become a dominant, if not the dominant, field of science impacting society. In the last century, manâs use of energy increased more than it did in the entire previous history of civilization. It has resulted in the highest standard of living in history, but it has also created a global dependence on energy that may become very difficult to meet. That is the primary global energy problem. More specifically, it is the growing recognition that the increasing global demand for petroleum will exceed the supply.
Science has produced many uses for petroleum, but by far the most demanding of the unique capabilities of petroleum is its use for transportation of people and goods. Science has created a very mobile global society. Petroleum has made this possible because of its unique capability to serve as an energy source and as an energy âcarrierâ. Excluding natural gas, which I include in a very broad definition of âpetroleumâ, there is no alternative to petroleum that can serve both functions. There are energy sources and there are energy carriers, but no single alternative that can satisfactorily combine both capabilities.
It is generally agreed that the Earth was endowed with about two trillion barrels of oil and that about one trillion barrels have been extracted and used. Also, it is rather generally agreed that the present extraction rate of about 82 million barrels a day is at, or near, the peak rate that is achievable. Demand has been increasing and is expected to continue to increase. Although these figures would suggest that there is only a 35 year supply of petroleum remaining, of course, this is not what will happen, or what should be used for planning purposes. A long, gradual transition period will occur during which a variety of alternatives to petroleum in its various applications must be found and used. The challenge for science and technology is to endure that sufficient alternatives are acceptable, available and ready when needed.
Many people and organizations are addressing this matter. They have produced a variety of predictions and conclusions. They are readily and extensively available on the internet. At best, these predictions are disturbing and describe a difficult and, perhaps, an unpleasant transition period. At worst, they predict a catastrophe and the end of life and we now know it.
They generally agree that no single substitute for petroleum will be found and there is a wide disparity in the predicted acceptability of combinations of energy sources and energy carriers. Electricity and hydrogen are recognized as potential energy carriers. Electricity is well established. Hydrogen possesses superb âcombustionâ characteristics, but will require much more development and, will require an immense infrastructure. Its distribution will be difficult and expensive. If it is to be the eventual substitute for petroleum, a huge energy source with very long term availability will be required to produce the hydrogen.
There is little agreement on energy sources that can fulfill this potential demand. Coal is environmentally unacceptable, wind and solar are unreliable, because they require âthe wind to blow or the sun to shineââ while hydro and nuclear are considered inadequate because of available resources.
Nuclear energy is included in this latter category because the estimated reserves of uranium are found to be inadequate. this conclusion is scientifically incorrect! It is based on an immature technology which does not incorporate established scientific knowledge.
The âscienceâ of nuclear energy is very simple and very specific. a pound of uranium contains the energy equivalent to about 5,000 barrels of oil or about 200,000 gallons of gasoline. in scientific terms, one kilogram of uranium contains the energy equivalent of almost two million liters of gasoline.
The United States has an inventory of more than one million tons of uranium in storage in the form of âspent fuelâ from reactors, and âdepleted uraniumâ from uranium enrichment plants. This inventory contains the energy equivalent of about ten trillion barrels of oil! The total global inventory of this material must be at least 3 or 4 times as large. These nuclear energy reserves are already mined and refined, the uranium (and thorium) still remaining in the Earth combined with the existing stockpile make this a virtually inexhaustible energy supply.
Clearly, the problem is not that the global uranium reserves are inadequate; it is that the contained energy is not being extractable using todayâs immature technology, only about one percent of the energy is extracted from natural uranium! The balance remains in the inventories described earlier. The scientific requirements for extracting this energy have been understood for more than 50 years. The technology for doing so has not yet been developed.
Nuclear energy is produced by the fission of uranium atoms in a nuclear reactor. Natural uranium, as it occurs in the earth, is composed of two isotopes, uranium-235 which is fissionable, and uranium-238 which is not fissionable, but is âfertileâ and when it absorbs a neutron it is transformed into plutonium-239 which is fissionable.
Natural uranium consists of about 0.7% U-235 and about 99.3% U-238. Rhe U-238 can only be fissioned if it is first âtransmutedâ to Pu-239. Therefore, natural uranium can only produce energy effectively by transmuting U-238 to Pu-239. The combination of fission and transmutation occurs in any nuclear reactor in which the fuel contains U-235 and U-238 or Pu-239 and U-238.
It occurs in all of the power reactors operating in the world today. In most of them, an adjustment is made in the U-235 concentration to enhance operation. The 0.7% U-235 content is âenrichedâ to about 3.0%. This process produces âdepleted uraniumâ which contains about 99.8% U-238. None of the energy contained in this enormous global inventory of depleted uranium has been extracted.
The current generation of nuclear power reactors convert about 1 atom of U-238 into Pu-239 for each 2 atoms of U-235 fissioned. Some of the Pu-239 atoms are fissioned in situ. Therefore, a very small amount of the energy contained in the U-238 is extracted in todayâs nuclear power plants. Virtually all of it remains in the spent fuel. The net result of these operations is that about one percent of the energy contained in the original natural uranium energy source has been extracted. The remaining 99% is contained in the spent fuel and depleted uranium. Virtually all of this energy is contained in U-238 which must be converted to Pu-239 to extract it.
This can be accomplished most efficiently in fast reactors fueled with Pu-239 and U-238. In this system, about 3 atoms of U-238 are converted to Pu-239 for each 2 atoms of Pu-239 fissioned. Because these machines can produce more plutonium than they consume, they are called âbreedersâ. The current conventional reactors which are about one third as efficient are called âconvertersâ.
From the very early days of the nuclear age, it was predicted that the energy contained in uranium could be extracted by recycling nuclear fuel in fast reactors. It was recognized also that this could only be accomplished if the following questions were answered favorably. Would the neutronics produce a âbreederâ type performance? Could energy be extracted usefully and acceptably from large fast neutron power reactors? Could nuclear fuel be recycled through such reactors in the manner required to extract the energy?
The first two questions have been answered. The plutonium â uranium fuel system in fast reactors will permit energy to be extracted from U-238. It has been shown that large fast power reactors can indeed produce useable energy. This has been done, probably most convincingly, in Russia at the BN-600 power station. In addition, work in other countries corroborate that fast power reactors can be used to produce electricity and for other uses.
The third question has not been answered adequately. Nuclear fuel has not been recycled to the extent necessary to demonstrate the capability to extract a significant fraction of the energy contained in uranium! This is the remaining challenge for science and technology.
I was deeply involved in a very early attempt to advance this technology. It evolved into the EBR-ll project; the Experimental Breeder Reactor No. 2., developed by Argonne National Laboratory in the United States. It was developed to demonstrate, on a small scale, the feasibility of power generation, but much more importantly, to advance fuel recycle technology. It was a relatively small plant, generating only 20,000 kilowatts of electricity, but it incorporated a complete âfuel cycle facilityâ interconnected to the nuclear reactor plant. Although fast reactor power plant projects were proceeding in the United States and other countries, none of them incorporated provisions for direct on-site fuel recycle. Therefore, the EBR-II experience is unique and important.
The fuel selected for the first phase of operation was an enriched uranium metal alloy which was actually established by the fuel refining process which had been selected. Neither plutonium, nor plutonium-uranium technology, were available at the time (the 1950?s). A relatively simple and imperfect fuel processing system was selected to provide a âstarting pointâ for the development of this technology, with recognition that much additional technology development would be required. The uranium metal fuel was to be processed by melt refining which removed fission products from molten uranium by volatilization and oxidation. This process provided adequate purification for fast reactor fuel recycle, even though all of the fission products were not removed.
It was estimated that at nominal equilibrium conditions, after several fuel cycles, this process would produce an alloy consisting of about 95% uranium and 5% fission products (about 2.5% molybdenum and 2% ruthenium plus a small amount of âothersâ). This alloy was named âfissiumâ and it was decided to create this alloy for the initial fuel loading to avoid a constantly changing fuel composition with each fuel recycle. It was not expected that this first phase of operation would demonstrate a true breeder fuel recycle. That was planned for the next phase.
Simultaneously, some very preliminary laboratory-scale experiments indicated that electrorefining of plutonium-uranium metallic alloys might prove to be suitable for recycle of this fuel in fast power reactors. As a result, the EBR-II program plan was to operate initially on an enriched uranium fuel cycle and shift to a plutonium-uranium fuel cycle later when the technology for that fuel cycle was developed. It was thought that valuable power reactor fuel recycle experience could be obtained during the first phase even though it was not a true breeder fuel cycle.
Only the first phase was accomplished, and only on a limited scale. Five total reactor core loadings were recycled through the reactor. About 35,000 individual fuel elements were reprocessed, fabricated and assembled into almost 400 fuel subassemblies. An administrative decision was made that the United States nuclear power program would concentrate on oxide nuclear fuel for all power reactors, including fast reactors. The EBR-II fuel recycle program, based on metal fuel, was terminated. Reactor operation was continued for more than 20 years, but the fuel was not recycled. The reactor continued operation as a âfissium-fueledâ, base load, electrical generating station and a fast neutron irradiation facility. The fuel cycle facility was used for examination of irradiated fuel and other materials.
Even though this program was interrupted, it produced and demonstrated some very useful technology that will be applicable to future recycle systems and provides an overall perspective of nuclear fuel recycle requirements. It includes the performance of highly complex operations in a very strong radiation field and the removal of fission product decay heat during fuel fabrication and assembly operations. Even though future systems may be less demanding, this technology and experience will be invaluable.
Each future recycle system will create unique requirements related specifically to the fuel, the fuel form and the design of the individual fuel elements. They will include removing the spent fuel from its container; (most probably a cylindrical tube), reprocessing the fuel and installing it in a new container.
It is this part of the total fuel recycle process that requires much development and demonstration. There are a variety of potential fuels and fuel forms and a variety of potential purification and fabrication processes which will produce a variety of fuel recycle characteristics and requirements . The composition of the fuel will change during recycle and an equilibrium, or near equilibrium, composition will eventually result. This scenario has not been produced for any of the potential fuel systems, nor will it be, until the required operational experience has been obtained. Global attention is needed because this will be a very slow, long-term undertaking. There are no quick fixes! A fuel cycle will probably take about three years, and several cycles will be required to establish a reasonable demonstration of the total performance of a specific recycle process. There will be, almost certainly, more than one total fuel recycle system to pursue; possibly several. Each will be unique and produce its own results and create its own requirements.
I have proposed that the United States initiate a program to begin the process by constructing a âfuel recycle reactorâ (FRR) designed specifically to provide a facility in which these fuels can be recycled. I do not believe that a single facility of this kind can begin to do the job that is necessary to establish this badly needed technology. I know that it is presumptuous of me to suggest what other countries should do; but, I propose that a vigorous international effort be undertaken to develop and establish the technology required to recycle nuclear fuel in fast power reactors and thus make it possible for the world to use the tremendous capability which exists in the global resources of nuclear fuel.
This is a timely international challenge. I note that Japan is considering the restart of their Monju fast reactor and are exploring international participation ÂĄn fuel cycle technology. I note also that India is proceeding with their first fast power reactor with a capacity of 500 megawatts and plans to build three more by 2020. I find this to be a very interesting development; India has maintained a continuing technical interest in fast reactors since the very early days of nuclear power. I expect this program will bring a new perspective to nuclear power and fuel recycle. India has a strong interest in the U-233 thorium cycle because of their large indigenous supply of thorium.
Th-232, which is not fissionable, is similar to U-238; when it absorbs a neutron, it is transformed into fissionable U-233. This process also can be best accomplished in fast reactors and requires fuel recycle. Therefore, fuel recycle technology also must be developed to extract this source of energy. The vast global thorium reserves should be included in estimates of total global nuclear energy capability.
On a longer range basis, the magnitude of the demand for energy sources will eventually become dominant. In addition to providing an alternative to dwindling petroleum resources, there will be the need to provide for the continuing growth in demand for energy to satisfy the needs of increasing global population and their standard of living.
For nuclear energy to contribute significantly to satisfying this enormous potential demand, it will be necessary to not only develop the technology, but to make it acceptable!
History has established a relationship between nuclear energy and nuclear weapons that is not clearly defined or well understood. Nuclear weapons are produced from fissionable materials, but recycled power reactor fuel is not a suitable source for that material. Even the spent fuel after only one fuel cycle in current generation power reactors is unsuitable for weapons use. After multiple recycles, the fuel is essentially useless for weapons.
It will be necessary to demonstrate that nuclear energy on the vast scale I have suggested will not result in unacceptable nuclear waste. Efficient fuel recycle has the potential capability of virtually eliminating this requirement. The primary problem presented by the long term storage of spent fuel is the long half-life of the actinides produced in the spent fuel. They can be destroyed by fission.
A complete nuclear fuel recycle process will destroy these actinides and produce energy from those that fission. At equilibrium, all of the necessary processes will be operating simultaneously. Pu-239 will be fissioning, the higher isotopes of plutonium will be fissioning, or absorbing neutrons and transmuting into isotopes that fission and are destroyed.
The ideal fuel cycle will recycle all of the uranium, the plutonium isotopes and the other actinides and remove only fission products during each fuel cycle. The nuclear waste will consist primarily of fission products which will be far easier to store and virtually all of the energy will have been extracted from the original energy source, natural uranium. A similar scenario can be developed for thorium. The science is firmly established. The technology is needed. The incentive to do so is enormous. It is to provide an inexhaustible supply of energy for the foreseeable future and beyond.
Thanks to Barry Brooks at bravenewclimate.com for sharing this.