In a period of 40 years, nuclear power has taken its place alongside the traditional primary sources of electric energy. In 1994, the fossil fuels (coal, oil, and natural gas) generated 64% of the world' s electricity, hydroelectric installations generated 18%, and nuclear power plants almost 18%. The nuclear production was achieved by 425 reactors operating in 30 countries with a combined installed capacity of 356 GWe. For the future, 66 reactors (total installed capacity 57 GWe) are already being built, and 59 reactors (installed capacity 51 GWe) are on order.
Four nuclear reactor types have been developed for commercial electricity generation:
Continuing development and the experience of construction and operation for 40 years have naturally led to improvements in technology, performance, and economy. The trend is for these improvements to continue, confirming nuclear power as an important primary electricity generator.
It is equally natural that the rapid development of a new technology should encounter difficult issues - of a social as well as a technical nature.
An energy technology that contributes nearly 20% to world electricity generation must be reliable and cost-effective to have achieved such a market share. Competition among nuclear suppliers and with other energy technologies appears to be an adequate mechanism for ensuring continued technical and economic effectiveness. However, major cost reductions will be necessary for nuclear power to compete with cheap pipeline gas in most of the Western Hemisphere for the next few decades.
While these technical and economic aspects are internal matters for the industry, there are other facets of nuclear power generation that have become issues of wider concern. In the past 40 years, the industry has made substantial progress in technical and institutional arrangements for plant and operational safety, waste management, effects on the environment, and nuclear weapons proliferation. However, if nuclear power is to fulfill its potential role in the future, more work must be done on these issues to gain public acceptance.
The safety requirements of nuclear installations are defined and implemented by technical, legal, and administrative measures. In all countries, the siting, design, construction, and operation of power plants and other nuclear facilities are subject to regulation and licensing. No plant can be operated without exhaustive and detailed examination of its safety and its impact on the environment. Guidelines published by the IAEA cover all aspects of the process.
In countries using designs of the Western Hemisphere, these measures have been adopted and have proved adequate to ensure the safety of the public. There has been no significant release of radioactivity beyond the confines of a plant, even in the accident at Three Mile Island where half the reactor core was damaged. The measures are not only adequate but necessary. As an example, the reactors developed by the former Soviet Union do not conform fully to the safety standards adopted by other countries. The accident at Chernobyl released considerable quantities of radioactive material to the atmosphere, and radioactive contamination crossed national boundaries. Thus, there is no cause for complacency, and while the record is good, it is always subject to improvement. Technical developments and rising safety targets require continuing effort and vigilance.
The requirement accepted by the nuclear industry worldwide is that wastes shall not be released to the environment at levels of radioactivity that can harm people. Generally, storage with human supervision precedes ultimate disposal. Low-level wastes are normally disposed of by burial in a suitable location. The radiation from high-level wastes has too long a life for simple burial. It is placed in engineered storage on a nuclear site, i.e., a structure designed to provide shielding from the radiation and to remove the heat. The engineered stores require continuous supervision.
Clearly, continuous supervision cannot be relied upon for the time needed for the radioactivity to decay to safe levels. Times of the order of geologic epochs rather than human dynasties are necessary. Techniques for immobilizing the waste have been developed, and stable geologic structures have been identified for deep burial. However, neither the technologies for immobilizing waste nor sites for deep burial have yet been approved by governments, and currently, all high-level waste remains under human control.
Some see the lack of a policy for the disposal of high-level waste as a failure of the nuclear industry. Similar criticism is applied to low-level wastes resulting, in some cases, in the denial of approval for the construction of technically adequate low-level depositories.
Measures to prevent the diversion of nuclear technology and nuclear materials to military applications began around 1945. Regional schemes and bilateral agreements were established, and in 1970 the international Treaty on the Non-Proliferation of Nuclear Weapons (NPT) came into effect. The treaty promotes the peaceful use of nuclear energy and requires multilateral cooperation in preventing the diversion of nuclear technology to military applications.
A safeguards system to identify any diversion of nuclear materials is operated by the IAEA under the NPT. The system requires that accounts (material balances) of fissile materials be audited by international teams drawn from countries other than the one being audited.
The NPT was extended indefinitely at the 1995 Reevaluation Conference and remains the heart of the nonproliferation regulatory regime.
Nuclear power is almost unique in that the public perceives its risks as being much higher than calculated by experts in the field. The concern has led the public to exercise its rights of intervention in the licensing of nuclear facilities, and the effect has been to delay and even inhibit the construction of nuclear power plants. If nuclear power is to continue to develop as an important technology, it will need to improve its public acceptance.
The future world energy demand was estimated by the World Energy Council (WEC) in its report " Energy for Tomorrow' s World" (Ref.1). Its estimates of world energy demand up to the year 2020 are based on the median value of the UN population projections and WEC predictions of the rates of economic growth and the efficiency of energy use.
The WEC report also projects the demand for the years 2050 and 2100, extrapolated from the year 2020, to evaluate global environmental impact. The demand is estimated for three cases (Fig.1); A (high growth), B (reference case), and C (ecologically driven). In Table 1 the WEC estimates of world energy demand for the years 2050 and 2100 are shown as a multiple of the energy demand for 1990.
Our study analyzed and projected world energy demands (Table 2 and Fig.2) in a way similar to the WEC study, but assuming
Our projections of energy demand for both 2050 and 2100 are similar to the WEC results. Both the high-growth and the ecologically driven WEC cases are considered unrealistic. Therefore, the median prediction represented by the WEC reference case is used as our estimate for the future.
These studies indicate that the increase in world energy demand will be dominated by the low-income countries; their needs in 2050 are predicted to be about seven times the 1990 reference value.
The WEC (Ref.1) and other investigators (Ref.2) have examined the supply capability of major energy options in the twenty-first century:
They conclude that the extractable quantities of the fossil fuels are limited and that there will be a transition from the use of petroleum and natural gas to coal. They predict that this trend, combined with possible restrictions on the emission of carbon dioxide gas to the atmosphere, will cause the use of fossil fuels to peak around the middle of the twenty-first century at roughly 1.5 times the current consumption. Meanwhile, assuming further technical advances, the renewable energies should increase to a level between 15 and 25% of the total energy demand between 2050 and 2100. Nuclear energy is expected to supply the remainder of energy.
Based on the WEC prediction for the reference case, the share of nuclear power in the total primary energy supply would be 15% in 2050 and 28% in 2100.a Compared to 1994, nuclear power supply would increase by 8 times by 2050 and 21 times by 2100. The WEC predicts that nuclear power will be used wholly for the generation of electricity.
Based on the WEC estimates of the world demand for nuclear power, let us look at the availability of nuclear fuel resources (Ref.3). The relevant nuclear fuel resources are both the amount of natural uranium as a source of fissile uranium (uranium-235) and the amount of fissile plutonium, which are the fuels for the global, long-term use of nuclear power. Two cases are investigated: without fuel recycling and with recycling. The best use of available plutonium would be for recycling; i.e., as much plutonium as required would be recycled from all the spent fuel in the world.
The installed capacity of nuclear power for the WEC reference case (Fig.3) is shown in Table 3.
|Total Capacity, GWe||321||570||2519||6745|
The construction rate to achieve these capacities is shown in Table 4, corresponding to an average of 65 new plants of 1000 MWe annually until the year 2050, and 85 new plants annually between 2050 and 2100.
|1990 to 2020||2020 to 2050||2050 to 2100|
The construction rate rises to an average of about 100 plants per year in the middle of the century when we add in the replacement of plants that are more than 40 years old. These plans are feasible, given the technology and industrial capacity available, even today. The types of conventional nuclear reactor to be constructed are assumed to be PWR, BWR, and CANDU in the proportions found in 1985.
For the program with fuel recycling, the FBR is assumed to have a breeding ratio of 1.2 and a system doubling time of 40 years; i.e., the amount of plutonium available will double in 40 years. This is considered a feasible target. Based on the Red Book (Ref.4), of the Organization for Economic Cooperation and Development/Nuclear Energy Agency, the world' s "known" resources of uranium at a cost up to $130 per kilogram of uranium are 3.7 million tonnes, and "undiscovered" resources are 13 million tonnes; thus, the "total" or "speculative" resources are 17 million tonnes.
If plutonium is not recycled, the cumulative demand for natural uranium will exceed the world' s current known resources around the year 2030. Uranium demand will exceed the world' s speculative resources around 2070, reaching 45 million tonnes in 2100 (Fig.4).
When plutonium is recycled, the demand for uranium depends heavily on the date of introduction of the fast reactor. Two typical scenarios envisage the introduction of the FBR in 2030 and 2050, each with a transition period of 30 years. In this transition period, both conventional nuclear reactors and FBRs are constructed in parallel, but construction gradually shifts entirely to the fast breeder. The transition period is necessary to ensure adequate supplies of plutonium for the initial inventory and thus guarantee uninterrupted construction.
The cumulative uranium demand levels out at appproximately 12 million tonnes when the FBR is introduced beginning in 2030 and at 23 million tonnes when the FBR is introduced in 2050. The 20-year delay in the introduction of the FBR makes a great difference in uranium demand. The supply of the expected amount of nuclear power at reasonable cost and with reliability depends on the availability of resources that are recoverable with reasonable energy and cost. This in turn requires a suitable timing of the shift from conventional thermal reactors to FBRs.
For interest, the results for the WEC cases of high and low growth are also given. High growth causes a shortage of plutonium, the transition period to FBRs takes 45 years instead of the 30 years in the reference case, and cumulative uranium demand levels out at 18 million tonnes around 2080. When growth is low, there is enough plutonium to supply the initial inventory of FBRs and it is not necessary to have a transition period.
The reference growth rate requires a substantial proportion of the world' s known uranium resources, and high growth rates would require larger resources. In fact, abundant uranium exists in the Earth' s crust and ocean. There are geologic indications that more uranium remains to be discovered, but it is not certain that we could recover, at reasonable cost, far greater quantities than the speculative amount. Data so far obtained from experiments suggest that the extraction of uranium from seawater at reasonable cost is doubtful. Indeed, it is questionable whether very dilute uranium can be termed a resource.
Thorium is another nuclear material that may be used in nuclear reactions. Thorium-232 is a fertile material that converts to fissile uranium-233 in the same way that uranium-238 produces fissile plutonium. At present, the stock of uranium-238 in the world (i.e., depleted uranium from about 1 million tonnes of natural uranium excavated so far) would, if converted to fissile plutonium, be sufficient to supply world energy for hundreds of years. What is important in evaluating the ability to supply nuclear power are the fissile materials uranium-235 and plutonium; the amount of fertile material is not critical. As the technology of plutonium utilization is being developed for commercialization in the future, thorium utilization will likely be considered an option only if there is difficulty with the FBR or plutonium technology.
It is difficult to project the use of nuclear fusion reactions from the current level of research to commercial energy supply in less than 50 to 100 years. We expect continuing research aimed at a future energy resource.
When nuclear power contributes a considerable percentage to the total energy supply, there are positive effects on the world economy and on the global environment. The gross domestic product (GDP) of the world is increased, the health risk from power generation is reduced, and the environmental effects are small. The radiation effects associated with nuclear energy are described in the next section.
When nuclear power is replaced by fossil fuels, the temperature of the atmosphere rises causing a decrease in GDP. These effects have been simulated by quantitative analyses, such as the DICE optimization model developed by Nordhaus (Ref.5), expanded to incorporate restrictions of energy resources.
Turning now to the risk of different energy systems, we find that surveys of past data indicate that the risk of nuclear power is the lowest of all the power generating systems, including renewable energies (Ref.6). The risk is represented by fatality rates, immediate and delayed, for both occupational workers and the public, per gigawatt-year of operation of a total fuel cycle. The maximum immediate risk to the public from nuclear power is about 10% of the risk from oil-fired power systems, while the maximum delayed risk is about 3%.
The external costs or environmental costs exemplify the benefits of nuclear power. The external cost of nuclear power is low compared with the external cost for fossil fuel of about 2 cents/kWh and is calculated by Centre d' Etude sur l' Evaluation de la Protection dans le Domaine Nucleaire (CEPN) of France at 0.31 cents/kWh and by Oak Ridge National Laboratory (ORNL) of the United States at 0.022 cents/kWh (Ref.7). The difference between the two depends on the discounting of the effect for 100 000 years of carbon-14 produced by fuel reprocessing-a discount rate 0% by CEPN and 3% by ORNL.
The radiation effects associated with using nuclear power in the future are very small compared to those from exposure to natural and medical radiation. The world' s average individual effective radiation dose is 2.4 millisieverts (mSv) from natural radiation and 0.6 mSv from medical procedures. Nuclear energy utilization in 1989 contributed 0.01 mSv or less than 1% of the average individual dose. These figures are taken from a report on the biologi