An Accelerator-Driven System (ADS), is a nuclear reactor that is very different from the conventional reactors currently in use. There are several different kinds of ADSs, including the Energy Amplifier and others. Regardless of type, the properties of an ADS include the following:
- It cannot have a run-away reaction and melt down.
- It cannot be used to produce nuclear bombs or nuclear terrorist devices.
- It can use thorium as fuel, and we have enough of this to supply us for several thousand years.
- Alternatively, it can be used to consume our high-level radioactive waste.
- It produces very little waste and nearly no long-term waste.
- Regardless of the fuel it uses, the waste it produces is about as radioactive as coal ash after 500 years or less.
A simplified explanation of the ADS is easy enough to understand. A particle accelerator provides a continuous supply of neutrons to a sub-critical mass of radioactive material. Since neutrons cannot be easily accelerated, they are typically created by accelerating protons, which are used in a process called “spallation” to produce cascades of neutrons. The neutrons cause certain radioactive material to undergo fission, producing heat.
The heat of an ADS is sufficient to produce steam, driving a turbine, to produce electricity. The electricity is drives the particle accelerator, with plenty of power to spare for electric power production. The designs I have seen would take about 10% of the power to drive the accelerator, with 90% available for other uses. Alternately, the heat from the ADS can be used for other purpose, if they are needed, using only a portion, or even none, of the heat for electric power generation.
There has been some opposition to ADSs because some people believe that because they could provide a way to get rid of nuclear waste, they would provide an excuse to continue the use of conventional nuclear power plants operating at critical mass. The amount of fuel used in a conventional nuclear reactor is typically about 0.7%. By contrast, the ADS can use nearly 100% because it is not necessary to maintain a critical mass, new fuel can be added as needed, and the waste can be removed continually in ongoing evaporation of lead, which is captured. This means the waste a conventional nuclear plant produces in one year would power an ADS of equal output for over 50 years. Conventional nuclear plants are too inefficient to continue being used as supply, and it is unnecessary to do so, if the much more efficient ADSs are used to replace them. The waste we have already generated would keep a fleet of ADSs going for centuries.
Another way to look at this is that the ADSs can provide a safe way to render nuclear waste safe. Long-term radionuclides in nuclear waste can be nearly 100% consumed by using them for fuel in an ADS. The output of the ADS in energy is very significant, and would alone provide sufficient reason to build them, but the waste powering the ADS cannot be reduced to relatively safe material by another known practical means. The other solution currently under discussion is to bury it and guard it for a period of time many times longer than human history.
ADS systems were first designed nearly thirty years ago. The first design was probably produced at Los Alamos. The next I know of was the Energy Amplifier, which was invented at CERN, under the leadership of Carlo Rubbia. His instructions to the staff of the project were to design a nuclear reactor that could not melt down, produced as close to no waste as possible, and could not be used to make bombs or terrorist devices.
There have been many people who tried to get them built and put into service, both to produce power and as a means of dealing with the dangers of nuclear waste. The designs put forward have been similar in many respects. An Italian design of an Energy Amplifier was completed to the point that a price could be estimated: €500 million (roughly $650 million) for a plant producing 650 MWe. A similarly sized conventional nuclear plant at that time would probably have cost four to ten times as much.
So far, none of the designs tried has been attempted. The basic science behind the reactors has been tested, and found to work. An initially holdup was that no one had ever built a powerful enough particle accelerator. More recently, several have been built for other purposes. I should mention that they need not be very big, they only need to produce very powerful particles.
Currently, there is a design underway in China. I have not been able to get much in the way of details about this, but the Chinese media has announced that 170 scientists have been hired, and a budget of $350 million has been given to the project. A link to the news article is [HazardEx].
Another design being promoted is from Muons, Inc. and ADNA Corp. The people in these organizations are trying to interest the US military in using their ADS design as a system for transmuting plutonium from obsolete nuclear bombs into much less dangerous substances. The military has 34 tons of plutonium they want to get rid of, and the Muons/ADNA people have a very interesting way to get rid of it.
The Fischer-Tropsch reaction converts carbon monoxide and hydrogen into alkanes, which include such substances as diesel oil and gasoline. The carbon monoxide can come from a variety of fuel sources, among which are coal and biomass, and the hydrogen is usually produced by electrolysis of water. The people at Muons/ADNA calculate that the 34 tons of plutonium would produce enough diesel oil to power the US military for about 30 years, leaving a small pile of radioactive material. The waste can be dealt with rather easily and will not be dangerous for more than a couple of centuries. A link on this is at [Green Car Congress]. The military seemed to be uninterested because it was an untried design.
I think this beats digging a hole in the ground someplace and hoping nobody disturbs it for a million years.