It is possible to create a kind of continuous recycling program where the plutonium from the spent MOX fuel is used to start the fast-spectrum system; the spent fuel from the fast-spectrum system is reprocessed; all the plutonium and minor actinides go back into new fuel, and so forth. In principle, nothing but fission fragments goes to a repository and these only need to be stored for a few hundred years. This sounds good in principle, but there’s much work to do before putting it into practice.
Proliferation Prevention: Preventing the proliferation of nuclear weapons is an important goal of the international community. Achieving this goal becomes more complex in a world with a much expanded nuclear-energy program involving more countries. Opportunities for diversion of weapons- usable material exists at both the front end of the nuclear fuel cycle, the U-235 enrichment stage; and at the back end of the nuclear fuel cycle, the reprocessing and treatment of spent fuel stage. The more places this work is done, the harder it will be to monitor.
Clandestine weapons development programs have come from both ends of the fuel cycle. Pakistan and South Africa, which voluntarily gave up its weapons in an IAEA supervised program, made their weapons from the front end of the fuel cycle. Libya was headed that way until it recently abandoned the attempt.
There is uncertainty about the intentions of Iran. India, Israel, and North Korea obtained their weapons material from the back end of the fuel cycle using heavy-water-moderated reactors to produce the necessary plutonium.
The level of technical sophistication of these countries ranges from very
low to very high, yet all managed to succeed. The science behind nuclear
weapons is well known and the technology seems not that hard to master through
internal development or illicit acquisition.
It should be clear to all that the only way to limit proliferation by nation States is through binding international agreements that include effective inspection as a deterrent, and effective sanctions when the deterrent fails.
We in the science and technology (S&T) community can give the diplomats improved tools that may make the monitoring that goes with agreements simpler and less overtly intrusive. These technical safeguards are the heart of the systems used to identify proliferation efforts at the earliest possible stage. They must search out theft and diversion of weapons-usable material as well as identifying clandestine facilities that could be used to make weapons-usable materials.
The development of advanced technical safeguards has not received much funding recently. An internationally coordinated program for their development needs to be implemented. Proliferation resistance and monitoring technology should be an essential part of the design of all new reactors, enrichment plants, reprocessing facility, and fuel fabrication sites.
There are technologies not yet deployed that can give real-time results in critical areas. One does not have too wait long to see if uranium-235 is within declared limits in an enrichment plant. One issue that is being revisited is the relative proliferation resistance of the once-through fuel cycle compared to those of various reprocessing strategies.
An analysis has been done by an international group of experts for the US Department of Energy and documented in their November 2004 report, “An Evaluation of Proliferation Resistant Characteristics of Light Water Reactor Fuels.” The methodology created in this analysis gives a risk score for every phase of the nuclear fuel cycle and then sums the risks over time.
All of the variants of once-through and reprocessing have about the same score. The increased risk during the phase where plutonium is available in reprocessing scenarios is balanced by the decreased risk of diversion during enrichment, where less enrichment is required, and the increased radiation barrier after the second burn and the increased difficulty of fashioning the weapon from ever-more degraded materials.
These scores should not be read as precision measurements. All they really say is that to sensible people once through is not that different from reprocessing.
IAEA Director General ElBaradei and US President George Bush have proposed that internationalization of the nuclear fuel cycle begin to be seriously studied. In an internationalization scenario there are countries where enrichment and reprocessing occur. These are the supplier countries. The rest are user countries. Supplier countries make the nuclear fuel and take back spent fuel for reprocessing, separating the components into those that are to be disposed of and those that go back into new fuel.
If such a scheme were to be satisfactorily implemented, there would be enormous benefits to the user countries, particularly the smaller ones. They would not have to build enrichment facilities nor would they have to treat or dispose of spent fuel.
Neither is economic on small scales and repository sites may not be available with the proper geology in small countries. In return for these benefits, user countries would give up potential access to weapons- usable material from both the front end and the back ends of the fuel cycle.
If this is to work, an international regime has to be created that will give the user nations guaranteed access to the fuel that they require. This is not going to be easy and needs a geographically and politically diverse set of supplier countries.
Reducing the proliferation risk from the back end of the fuel cycle will be even more complex. It is essential to do so because we have seen from the example of North Korea how quickly a country can “break out” from an international agreement and develop weapons if the material is available. North Korea withdrew from the Nuclear Non-Proliferation Treaty at short notice, expelled the IAEA inspectors, and reprocessed the spent fuel from their Yongbyon reactor, thus acquiring the plutonium needed for bomb fabrication in a very short time.
Supplier countries that should take back the spent fuel for treatment are not likely to do so without a solution to the waste-disposal problem. In a world with a greatly expanded nuclear power program there will be a huge amount of spent fuel generated worldwide. The projections mentioned earlier predict more than a terawatt (electric) of nuclear capacity producing more than 20,000 tons of spent fuel per year.
This spent fuel contains about 200 tons of plutonium and minor actinides and 800 tons of fission fragments. The once-through fuel cycle cannot handle it without requiring a new Yucca Mountain scale repository every two or three years. Reprocessing with continuous recycle in fast reactors can handle this scenario. Only the fission fragments have to go to a repository and that repository need only contain them for a few hundred years rather than a few hundreds of thousands of years.
In summary, nuclear energy is an important component of a strategy to give the world the energy resources it needs for economic development while reducing consumption of fossil fuels with their greenhouse-gas emissions. If this is to happen on a large scale, advances in both physical S&T and political S&T will be required.
We on the physical side can produce better and safer reactors, better ways to dispose of spent fuel, and better safeguards technology. This can best be done in an international context to spread the cost and to create an international technical consensus on what should be done. Countries will be more comfortable with what comes out of such developments if they are part of them.
While the physical development can best be done in an international context, the political S&T can only be done internationally. The IAEA seems to be the best place to start and the first baby steps have already been taken. I look forward to larger steps of both kinds in the future.
Burton Richter is on the faculty of the Stanford Linear
Accelerator Center (SLAC), Stanford University, and served as SLAC Director
from 1984-99. He was awarded the 1976 Nobel Prize in physics with Samuel
C. Ting “for their pioneering work in the discovery of heavy elementary
particle of a new kind.”
This article is adapted from the author’s keynote address to the IAEA’s Scientific Forum, September 2005. Click here for graphs and tables which accompanied his keynote address.