Nobel Laureate Burton Richter discusses the promise and the problems of nuclear energy
Nuclear energy is undergoing a renaissance, driven by two very loosely-coupled needs: the first for much more energy to support economic growth worldwide; the second to mitigate global warming driven by the emission of greenhouse gases from fossil fuel.
With the current mix of fuels, growing the economy increases emissions; increased emissions lead to climate change; climate change will eventually harm the economy. Nuclear energy offers one way out of this cycle.
Many forecasts of energy demand in the 21st century all give roughly the
same answer. The International Institute of Applied Systems Analysis (IIASA),
for example, shows in their mid-growth scenario primary energy demand increasing
by a factor of two by mid-century and by nearly another factor of two by
the end of this century. By the year 2030 the developing countries are projected
to pass the industrialized ones in primary energy use. China alone will
pass the United States as the world’s largest energy consumer and
economic growth in China and India is already higher than assumed in the
Supply constraints on two out of the three fossil fuels are already evident. Oil prices have surged. Demand is rising at an average rate of about 1.5 million barrels per day per year requiring the output of another Saudi Arabia every ten years to keep up with increased demand.
There is a lot of natural gas, but there are transport constraints. Natural gas prices also have risen and now are at the unprecedented level of $9-$10 per million BTU.
The only fossil fuel in abundant supply is coal. However, it has serious pollution problems and expensive technological fixes are required to control environmental problems that have large- scale economic consequences.
Concern about global warming is increasing and even the United States government has finally said that there is a problem. The Intergovernmental Panel on Climate Change (IPCC) forecasts, in the business-as-usual case, an increase in atmospheric carbon dioxide to 750 parts per million by the end of the century with a consequent global temperature rise of 2° to 5° C, less at the equator and more at the poles.
We can surely adapt to this increase if it is at the low end and occurs smoothly. If it is at the high end and accompanied by instabilities in climatae, economic and societal disruptions will be very severe.
It is too late to prevent some global warming, but limiting the effect requires a move away from carbon-based fuels. The global-warming issue has caused prominent environmentalists to rethink their opposition to nuclear power. One question to be confronted is which devil would they rather live with, global warming or nuclear energy?
James Lovelock (environmentalist and author of the popular Gaia hypothesis), among others, has come down on the side of nuclear energy. When economic self-interest and environmental self-interest both point in the same direction, things can begin to move in that direction. They now both point to the need for large- scale carbon-free energy. Nuclear energy is one such solution.
While nuclear cannot be the entire solution, it can be an important part if the public can be assured that it is safe, that nuclear waste can be disposed of safely, and that the risk of weapons proliferation is not significantly increased by a major expansion.
About 440 reactors worldwide supply 16% of world electricity. About 350 of these are in the OECD (Organisation for Economic Co-operation and Development) supplying 24% of their electricity. The country with the largest share of nuclear electricity is France at 78%. To an environmentalist, France should be looked at as a model for the world. Its carbon-dioxide intensity (CO2 per unit GDP) is the lowest in the world. If the entire world’s CO2 intensity were as low as France’s, C02 emissions would be reduced by a half, and global warming would be much slowed.
Projections for growth in nuclear power are uncertain because of uncertain costs along with the three potential problems mentioned earlier, safety, waste disposal, and proliferation risk.
Safety: The new generation of light-water reactors has been designed to be simpler to operate and maintain than the old generation, and has been designed with more passive safety systems.
With a strong regulation and inspection system, the safety of nuclear systems can be assured. Without one, the risks grow. No industry can be trusted to regulate itself when the consequences of a failure extend beyond the bounds of damage to that industry alone.
Spent Fuel Treatment: Looking separately at the three main elements of spent fuel there should be little problem.
There is no difficulty with the uranium alone, which makes up the bulk
of the spent fuel. It is not radioactive enough to be of concern; it contains
more U-235 than natural ore and so could be input for enrichment, or could
even be put back in the mines from which it came.
There is no scientific or engineering difficulty with fission fragments, the next most abundant component. The vast majority of them have to be stored for only a few hundred years.
Robust containment is simple to build to last the requisite time. (If the Egyptians could build pyramids that have lasted 6,000 years, we should be able to do at least as well.)
The spent fuel problem comes mainly from the last 1%, which is composed of plutonium and the minor actinides, neptunium, americium and curium. For some of the components of this mix, the toxicities are high and the lifetimes are long.
There are two general ways to protect the public from this material: isolation
from the biosphere for hundreds of thousands of years, or destruction by
Isolation is the principle behind the “once through” system for nuclear fuel as advocated by the United States for weapons-proliferation-prevention reasons. In a world with a greatly expanded nuclear power program, I do not believe the once-through system is workable.
Its problem is a combination of public perception, which I leave to the politicians, and technical limitations. The first technical problem comes from the heat generated in the first 1,500 or so years of storage which limits the density of material that can be placed in a repository. The early heat generated from fission fragments is not difficult to deal with. The decay of plutonium-241 to americium- 241 which then decays to neptunium-237 is the main source of heat during the first 1,000 or so years. Limitations on the allowed temperature rise of the rock of a repository from this source determine its capacity.
The second technical problem is the very long-term radiation. Here the same plutonium to americium to neptunium decay chain maximizes the long-lived component, requiring isolation from the biosphere for hundreds of thousands of years.
To use a US example, if nuclear energy were to remain at the projected 20% fraction of US electricity needs through the end of the century, the spent fuel in a once-through scenario would need nine repositories of the capacity of Yucca Mountain. If the number of reactors in the US increases by mid-century to the 300 Gwe projected in the Massachusetts Institute of Technology (MIT) study, the US would have to open a new Yucca Mountain every six or seven years. This would be quite a challenge since we have not been able to open the first one. In the world of expanded use of nuclear power, the once-through cycle does not seem workable.
The alternative to once-through is a reprocessing system that separates the major components, treating each appropriately and doing something specific to treat the component that produces the long-term risks. The most developed reprocessing system is that of France. The French make mixed oxide fuel, or MOX, by separating plutonium (Pu) from spent fuel and mixing it with an appropriate amount of uranium (U). The left over extra uranium will go to an enrichment facility.
The fission fragments and minor actinides are vitrified for eventual emplacement in a repository. The glass used in vitrification appears to have a lifetime of many hundreds of thousands of years in the clay of the proposed French repository.
MOX fuel plus vitrification solves part of the problem but not all of it. The next question is what to do with the spent MOX fuel. The plan is to keep it unreprocessed until fast-spectrum reactors are deployed commercially. These fast-spectrum reactors burn a mix of plutonium and uranium-238 and can, in principle, burn all of the minor actinides as well.
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