by David Bodansky
Talk given at American Physical Society Centennial Meeting, Atlanta, Georgia, March 25, 1999
1. Introduction
The development of nuclear energy has come to a near halt in the United States and in much of the rest of the world. The construction of new U.S. reactors has ended and although there has been a rise in nuclear electricity generation in the past decade, due to better performance of existing reactors, a future decline appears inevitable as individual reactors reach the end of their economically useful lives.
An obstacle to nuclear power is the publicly perceived environmental risk. During this development hiatus, it is useful to step back and take a look at nuclear-related risks in a broad perspective. For this purpose, we categorize these risks as follows:
• Confined risks. These are risks that can be quantitatively analyzed, and for which the likelihood and scale of possible damage can be made relatively small.
• Open-ended risks. These are risks that cannot be well quantified by present analyses, but which involve major dangers on a global scale.
As discussed below, public concern has focussed on risks in the confined category, particularly reactor safety and waste disposal. This has diverted attention from more threatening, open-ended risks of nuclear weapons proliferation, global climate change, and potential scarcity of energy in a world of growing population. The rationale for this categorization and the connection between nuclear power and these open-ended risks are discussed below.
2. Confined risks
a. Nuclear reactor accidents
The belief that reactor accident risks are small is based on detailed analyses of reactor design and performance, and is supported by the past safety record of nuclear reactors, excluding the accident at Chernobyl in 1986. Defects in the design and operation of the Chernobyl reactor were so egregious that the Chernobyl experience has virtually no implications for present reactors outside the former Soviet Union. Chernobyl is a reminder, however, of the need for careful, error-resistant design if there is to be a large expansion of nuclear power in many countries.
At the end of 1998 there had been over 8000 reactor-years of operation outside the former Soviet Union, including about 2350 in the United States. Only one accident, that at Three Mile Island, has marred an otherwise excellent safety record. Even at TMI, although the reactor core was severely damaged, there was very little release of radioactivity to the environment outside the reactor containment. Subsequently, U.S. reactors have been retrofitted to achieve improved safety and, with improved equipment and greater attention to careful procedures, their operation has become steadily more reliable.
A next generation of reactors can be even safer, either through a series of relatively small evolutionary steps that build directly upon past experience or through more radical changes that place greater reliance on passive safety features--such as cooling water systems that are directly triggered by pressure changes (not electrical signals) and that rely on gravity (not pumps). It would in fact be remarkable if the accumulated past experience, both good and bad, would not improve the next generation.
b. Nuclear waste disposal
The second dominant public concern is over nuclear wastes. Current plans are to dispose of spent fuel directly, without reprocessing, keeping it in solid form. Confinement of the spent fuel is predicated on its small volume, the ruggedness of the planned containers, the slowness of water movement to and from a site such as Yucca Mountain, and the continual decrease in the inventory of radionuclides through radioactive decay.
Innumerable studies have been made to determine the degree to which the radionuclides will remain confined. One way to judge the risks is to examine these studies as well as independent reviews. An alternate perspective on the scale of the problem can be gained by considering the protective standards that have been proposed for Yucca Mountain.
Proposed standards were put forth in preliminary form by the EPA in 1985. These set limits on the release of individual radionuclides from the repository, such that the attributable total cancer fatalities over 10,000 years would total less than 1000. This target was thought to be achievable when the only pathways considered for the movement of radionuclides from the repository were by water. However, the development of the site was put in jeopardy when it was later recognized that escaping 14C could reach the "accessible environment" relatively quickly in the form of gaseous carbon dioxide. A release over several centuries of the entire 14C inventory at Yucca Mountain would increase the worldwide atmospheric concentration of 14C by about 0.1%, corresponding to an annual average dose of about 0.001 mrem per year for hundreds of years. The resulting collective dose to 10 billion people could be sufficient to lead to more than 1000 calculated deaths.
It is startling that 14C might have been the show-stopper for Yucca Mountain. It appeared that this could occur, until Congress took the authority to set Yucca Mountain standards away from the EPA pending future recommendations from a panel to be established by the National Academy of Sciences (NAS). The panel issued its Report in 1995. It recommended that the period of concern extend to up to one million years and that the key criterion be the average risk to members of a "critical group" (probably numbering less than 100), representing the individuals at highest risk from potentially contaminated drinking water. It was recommended that the calculated average risk of fatal cancer be limited to 10-6 or 10-5 per person per year. According to the estimates now used by federal agencies to relate dose to risk, this range corresponds to between 2 mrem/year and 20 mrem/year.
Taking the NAS panel recommendations into consideration, but not fully accepting them, the EPA in August 1999 proposed a standard whose essential stipulation is that for the next 10,000 years the dose to the maximally exposed future individual is not to exceed 15 mrem per year. This may be compared to the dose of roughly 300 mrem per year now received by the average person in the United States from natural radiation, including indoor radon.
Attention to future dangers at the levels represented by any of these three standards can be contrasted to our neglect of much more serious future problems, to say nothing of the manner in which we accept larger tolls today from accidents, pollution, and violent natural events. While we have responsibilities to future generations, the focus should be on avoiding potential disasters, not on guarding people thousands of years hence from insults that are small compared to those that are routine today.
c. Fuel cycle risks
Risks from accidents in the remainder of the fuel cycle, which includes mining, fuel production and waste transportation have not attracted as much attention as those for reactor accidents and waste disposal, in part because they manifestly fall into the confined-risk category. Thus, the September 1999 accident at the Tokaimura fuel preparation facility resulted in the exposure of many of the workers, including two cases of possibly fatal exposures. It involved an inexcusable level of ignorance and carelessness and may prove a serious setback to nuclear power in Japan and elsewhere. However, the effects were at a level of harm that is otherwise barely noticed in a world that is accustomed to coal mine accidents, oil rig accidents, and gas explosions. The degree of attention given the accident is a measure of the uniquely strict demands placed on the nuclear industry.
3. Open-ended risks
a. Nuclear weapons proliferation.
The first of the open-ended risks to be considered is that of nuclear weapons proliferation. A commercial nuclear power program might increase this threat in two ways:
To date, the potential case of Iran aside, commercial nuclear power has played little if any role in nuclear weapons proliferation. The long-recognized nuclear weapons states---the United States, the Soviet Union, the United Kingdom, France, and China---each had nuclear weapons before they had electricity from nuclear power. India's weapons program was initially based on plutonium from research reactors and Pakistan's on enriched uranium. The three other countries that currently have nuclear weapons, or are most suspected of recently attempting to gain them, have no civilian nuclear power whatsoever: Israel, Iraq, and North Korea.
On the other side of the coin, the threat of future wars may be diminished if the world is less critically dependent on oil. Competition over oil resources was an important factor in Japan's entry into World War II and in the U.S. military response to Iraq’s invasion of Kuwait. Nuclear energy can contribute to reducing the urgency of such competition, albeit without eliminating it. A more direct hope lies in stringent control and monitoring of nuclear programs, such as attempted by the International Atomic Energy Agency. The United States' voice in the planning of future reactors and fuel cycles and in the shaping of the international nuclear regulatory regime is likely to be stronger if the United States remains a leading player in the development of civilian nuclear power.
In any event, the relinquishment of nuclear power by the United States would not inhibit potential proliferation unless we succeeded in stimulating a broad international taboo against all things nuclear. A comprehensive nuclear taboo is highly unlikely, given the heavy dependence of France, Japan, and others on nuclear power, the importance of radionuclides in medical procedures, and the wide diffusion of nuclear knowledge &emdash;&emdash; to say nothing of the unwillingness of the nuclear weapons states to abandon their own nuclear weapons.
b. Global climate change
The prospect of global climate change arises largely from the increase in the atmospheric concentration of carbon dioxide that is caused by the combustion of fossil fuels. While the extent of the eventual damage is in dispute, there are authoritative predictions of adverse effects impacting many millions of people due to changes in temperature, rainfall, and sea level. Most governments profess to take these dangers seriously, as do most atmospheric scientists. Under the Kyoto agreements, the United States committed itself to bring carbon dioxide emissions in the year 2010 to a level that is 7% lower than the 1990 level. Given the 11% increase from 1990 to 1997, this will be a very difficult target to achieve.
Nuclear power is not the only means for reducing CO2 emissions. Conservation can reduce energy use, and renewable energy or fusion could in principle replace fossil fuels. However, the practicality of the necessary enormous expansion of the most promising forms of renewable energy, namely wind and photovoltaic power, has not been firmly established. Additionally, we cannot anticipate the full range of resulting impacts. Fusion is even more speculative, as is the possibility of large-scale carbon sequestration. If restraining the growth of CO2 in the atmosphere warrants a high priority, it important to take advantage of the contribution that nuclear power can make---a contribution clearly illustrated by French reliance upon nuclear power.
c. Global population growth and energy limits
The third of the open-ended risks to be considered is the problem of providing sufficient energy for a world population that is growing in numbers and in economic aspirations. The world population was 2.5 billion in 1950, has risen to about 6 billion in 1999, and seems headed to some 10 billion in the next century. This growth will progress in the face of eventual shortages of oil, later of gas, and still later of coal.
The broad problem of resource limitations and rising population is sometimes couched in terms of the "carrying capacity" of the Earth or, alternatively, as the question posed by the title of the 1995 book by Joel Cohen, How Many People Can the Earth Support? As summarized in a broad review by Cohen, recent estimates of this number range from under 2 billion to well over 20 billion, centering around a value of 10 billion.
The limits on world population include material constraints as well as constraints based on ecological, aesthetic or philosophical considerations. Perhaps because they are the easiest to put in "objective terms," most of the stated rationales for a given carrying capacity are based on material constraints, especially on food supply which in turn depends upon arable land area, energy, and water.
Carrying capacity estimates made directly in terms of energy, in papers by David Pimentel et al. and by Gretchen Daily et al., are particularly interesting in the present context as illustrations of the possible implications of a restricted energy supply. Each group concludes that an acceptable sustainable long-term limit to global population is under 2 billion, a much lower limit than given in most other estimates. They both envisage a world in which solar energy is the only sustainable energy source. For example, in the Pimentel paper the authors conclude that a maximum of 35 quad of primary solar energy could be captured each year in the United States which, at one-half the present average per capita U.S. energy consumption rate, would suffice for a population of 200 million. For the world as a whole, the total available energy would be about 200 quads, which Pimentel et al. conclude means that "1 to 2 billion people could be supported living in relative prosperity."
One can quarrel with the details of this argument, including the maximum assumed for solar power, but it dramatically illustrates the magnitude of the stakes, and the centrality of energy considerations.
4. Conclusions
If a serious discussion of the role of nuclear power in the nation's and world's energy future is to resume, it should focus on the crucial issues. Of course, it is important to maintain the excellent safety record of nuclear reactors, to avoid further Tokaimuras, and to develop secure nuclear waste repositories. But here --considering probabilities and magnitudes together -- the dangers are of a considerably smaller magnitude than those from nuclear weapons, from climate change, and from a mismatch between world population and energy supply.
The most dramatic of the dangers are those from nuclear weapons. However, as discussed above, the implications for nuclear power are ambiguous. For the other major areas, the picture is much clearer. Nuclear power can help to lessen the severity of predicted climate changes and can help ease the energy pressures that will arise as fossil fuel supplies shrink and world population grows. Given the seriousness of the possible consequences of a failure to address these matters effectively, it is an imprudent gamble to let nuclear power atrophy in the hopes that conservation and renewable energy, supplemented perhaps by fusion, will suffice.
It is therefore important to strengthen the foundations upon which a nuclear expansion can be based, so that the expansion can proceed in an orderly manner &emdash; if and when it is recognized as necessary. Towards this end, the federal government should increase support for academic and industrial research on nuclear reactors and on the nuclear fuel cycle, adopt reasonable standards for waste disposal at Yucca Mountain, and encourage the construction of prototypes of the next generation of reactors for use here and abroad. Little of this can be done without a change in public attitudes towards nuclear power. Such a change might be forcibly stimulated by a crisis in energy supply. It could also occur if a maverick environmental movement were to take hold, driven by the conclusion that the risks of using nuclear power are less than those of trying to get by without it.
Department of Physics, Box 351560
University of Washington
Seattle, WA 98195
1. Joel E. Cohen, How Many People Can the Earth Support?
(W.W. Norton & Co, New York, 1995).
2. David Pimentel et al, "Natural Resources and Optimum Human
Population," Population and the Environment, A Journal of
Interdisciplinary Studies 15, no. 5 (May 1994), 347-69.
3. Gretchen C. Daily, Ann H. Ehrlich and Paul R. Ehrlich, "Optimum
Human Population Size," Population and the Environment, A
Journal of Interdisciplinary Studies 15, no. 6 (July 1994),
469-475.
This paper was originally published by : Physics & Society, Volume 29, Number 1, January 2000, reproduced with the author's and publisher's authorization.
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