Future of Nuclear Power Worldwide
Mehmet Ergin Secretary General, Islamic World Academy of Sciences Professor in Physical Chemistry
ABSTRACT
Energy production from fossil fuels, mainly natural gas and coal, contribute significantly to the global warming through large-scale greenhouse gas emissions, hundreds of billions of tones of carbon in the form of carbon dioxide. At least for the next few decades, one of the realistic options for reducing carbon dioxide emissions from energy production could be increasing use of nuclear power. Today, nuclear power supplies 16% of world electricity consumption. Experts project worldwide electricity consumption will increase substantially in the coming decades, especially in the developing world, accompanying economic growth and social progress. However, official forecasts call for a mere 5% increase in nuclear electricity generating capacity worldwide by 2020, while electricity use could grow by as much as 75%. These projections entail little new nuclear plant construction and reflect both economic considerations and growing anti-nuclear sentiment in key countries. The limited prospects for nuclear power today are attributable, ultimately, to four unresolved problems: costs, safety, waste, and proliferation. The nuclear power industry has been developing and improving reactor technology since 1950, and is preparing for the next generations of reactors to fill orders in the next two decades. Several generations of reactors are commonly distinguished. Generation I reactors were developed in 1950-60s and outside the UK none are still running today. Generation II reactors are typified by the present US fleet and most in operation elsewhere. Generation III (and 3+) are the Advanced Reactors that will be discussed in this paper. The first is in operation in Japan and others are under construction or ready to be ordered. Generation IV designs are at concept stage and will not be operational before 2020 at the earliest. In this paper, consideration will be given to what would be required to retain nuclear power as a significant option for reducing greenhouse gas emissions and meeting growing needs for electricity supply; then how some of the innovative nuclear-fission technologies being developed today attempt to address the challenges facing nuclear energy. It suggests some areas for collaborative research and development that could reduce the time and cost required to develop new technologies.
1. INTRODUCTION
Energy is an essential part of everyday life. We use it to heat and light our homes, to power our businesses, and to transport people and goods. Without a clean, secure, and sufficient supply of energy we would not be able to function as an economy or a modern society. In delivering this energy we face two major challenges: climate change and energy security.
Climate change represents a significant risk to global ecosystems, the world economy and human populations. The scientific evidence is compelling that human activities, and in particular emissions of greenhouse gases such as carbon dioxide, are changing the world’s climate. In 2005, 40% of global carbon dioxide emissions were created by the generation of electricity.
Temperatures and sea levels are rising. There is no scientific consensus on just how long we have to avoid dangerous and irreversible climate change, but the overwhelming majority of experts believe that climate change is already underway, and without action now to dramatically reduce carbon dioxide emissions, we will have a hugely damaging effect on our country, planet, and way of life.
The generation of electricity from fossil fuels is a major and growing contributor to the emission of carbon dioxide, a greenhouse gas, that contributes significantly to global warming.
We share the scientific consensus that these emissions must be reduced. There are only a few realistic options for reducing carbon dioxide emissions from electricity generation:
• increased efficiency in electricity generation and end- use;
• introduction of carbon capture and sequestration at fossil-fuel power plants on a massive scale;
• expand use of renewable energy sources such as wind, solar, biomass, and geothermal;
• increase use of nuclear power .
It is likely that we shall need all of these options and accordingly it would be a mistake at this time to exclude any of these four options from an overall carbon emissions management strategy.
Research by the Organization for Economic Co-Operation and Development (OECD) Nuclear Energy Agency, the European Atomic Forum and the IAEA identify a range of carbon dioxide emissions from nuclear power between 2 and 6gC/KWh (grams of carbon per kilowatt hour) which is equivalent to between 7 and 22gCO2/KWh. This means that the lifecycle carbon emissions from nuclear power stations is similar to that from wind generation but just a few per cent of the carbon emissions from fossil fuel power stations. (Figure 1).
1. Figure 1: The lifecycle carbon emissions from nuclear power stations are low and comparable to those from wind generation. They are significantly lower than emissions from fossil fuel power stations.
Nuclear power generates 16% of world electricity consumption today. Experts project worldwide electricity consumption will increase substantially in the coming decades, especially in the developing world, accompanying economic growth and social progress. However, official forecasts call for a mere 5% increase in the nuclear electricity generating capacity worldwide by 2020, while electricity use could grow by as much as 75% (Table 1).
These projections entail little new nuclear plant construction and reflect both economic considerations and growing anti-nuclear sentiment in key countries. The limited prospects for nuclear power today are attributable, ultimately, to four unresolved problems: cost, safety, waste, and proliferation.
Table 1: Comparison of predicted and measured amplifier performance
To preserve the nuclear option for the future requires overcoming the four challenges mentioned above – cost, safety, waste, and proliferation.
Today, nuclear power is not an economically competitive choice.
Moreover, unlike other energy technologies, nuclear power requires significant government involvement because of safety, proliferation, and waste concerns. If in the future carbon dioxide emissions carry a significant “price”, however, nuclear energy could be an important option for generating electricity.
According to the report released on 23 October 2007 by the International Atomic Energy Agency (IAEA) Nuclear Power has a bright future globally.
The IAEA makes two annual projections concerning the growth of nuclear power, a low and a high. The low projection assumes that all nuclear capacity that is currently under construction or firmly in the development pipeline gets completed and attached to grid, but no other capacity is added. In this low projection, there would be growth in capacity from 370 GWe at the end of 2006 to 447 GWe in 2030.
In the IAEA’s high projection, which adds in additional reasonable and promising projects and plans, global nuclear capacity is estimated to rise to 679 GWe in 2030. That would be an average growth rate of about 2.5%/yr.(Figure 2).
Figure 2: Percentage of Electricity Supplied by Nuclear Power, Regional Distribution
According to the Figure 2, the largest increase in nuclear capacity (in terms of net power added) will occur in the Far East, while the strongest growth in percentage terms will occur in the Middle East and South Asia. Net capacity also increases in Eastern and Western Europe, but stays essentially flat in North America.
Nuclear power’s share of worldwide electricity production rose from less than 1 percent in 1960 to 16 percent in 1986, and that percentage has held essentially constant in the 21 years since 1986. Nuclear electricity generation has grown steadily at the same pace as overall global electricity generation.
Other findings in the report:
• There were 435 operating nuclear reactors around the world as of the end of 2006, including 103 in the United States, 59 in France, 55 in Japan, and 31 in Russia.
• 29 plants are under construction, including 7 in Russia and 15 in various Asian countries.
• Of the 30 countries with nuclear power, the percentage of electricity supplied by nuclear ranged widely: from a high of 78 percent in France; to 54 percent in Belgium;
39 percent in Republic of Korea; 37 percent in Switzerland; 30 percent in Japan; 19 percent in the
USA; 16 percent in Russia; 4 percent in South Africa;
and 2 percent in China. (Figure 3) .
• India, another country experiencing rapid growth in energy use, gets less than 3 percent of its electricity from nuclear but plans to increase that figure to 10 percent by 2022.
Figure 3: Percentage Nuclear Share of total Electricity Generation in 2006
“Nuclear power’s prominence as a major energy source will continue over the next several decades,” the report concludes.
If nuclear deployment on the scale of the global growth scenario, a MIT (2003) study, (1000 nuclear plants each 1000 MWe by 2050) were to occur, however, it would avoid a significant amount of carbon dioxide emissions, largely by displacing carbon emitting fossil fuel generation. Today, carbon equivalent emission from human activity totals about 6,500 million metric tones per year. This value will probably more than double by 2050, depending on the assumptions made. The 1000 GWe of nuclear power assumed in the global growth scenario would avoid about 800 million tones of carbon equivalent if the electricity generation displaced was gas-fired and 1,800 million tones of carbon equivalent if the generation was coal-fired, (assuming no capture and sequestration of carbon dioxide combustion product). In 2050, deployment of 1000 GWe of nuclear power would generate about 20% of worldwide electricity production, if electricity production grows 2% per year. Evidently, the global growth scenario would have nuclear power generating significant
amounts of electricity that would otherwise likely be generated by fossil fuels.(Table 2).
Table 2: Global Growth Scenario
Projected capacity comes from the global electricity demand scenario which entails growth in global electricity consumption from 13.6 to 38.7 trillion kWe-hrs from 2000 to 2050 (2.1%
annual growth). The market share in 2050 is predicated on 85% capacity factor for nuclear power reactors. Note that China, India, and Pakistan are nuclear weapons capable states.
Other developing countries includes as leading contributors Iran, South Africa, Egypt, Thailand, Philippines, and Vietnam.
2. THE CHALLENGES OF NUCLEAR POWER EXPANTION
2.1 Fuel Cycles
The nuclear fuel cycle refers to all activities that occur in the production of nuclear energy. The process includes ore mining, enrichment, fuel fabrication, waste management and disposal, and finally decontamination and decommissioning of facilities. All steps in the process must be specified, because each involves different technical, economic, safety, and environmental consequences. A vast number of different fuel cycles appear in the literature, and many have been utilized to one degree or another.
Fuel cycles are separated into two classes; open and closed. In the open or once-through fuel cycle, the spent fuel discharged from the reactor is treated as waste (Figure 4). In the closed fuel cycle today, the spent fuel discharged from the reactor is reprocessed, and the products are partitioned into uranium (U) and plutonium (Pu) suitable for fabrication into oxide fuel or mixed oxide fuel (MOX) for recycle back into a reactor.(Figure 5).The rest of the spent fuel is treated as high-level waste (HLW). In the future, closed fuel cycles could include use of a dedicated reactor that would be used to transmute selected isotopes that have been separated from spent fuel (Figure 6). The dedicated reactor also may be used as a breeder to produce new fissile fuel by neutron absorption at a rate that exceeds the consumption of fissile fuel by the neutron chain reaction. In such fuel cycles the waste stream will contain less actinides, which will significantly reduce the long-term radioactivity of the nuclear waste.
Figure 4: Open Fuel Cycle: Once-Through Fuel – Projected to 2050
Figure 5: Closed Fuel Cycle: Plutonium Recycle (MOX option – one recycle) – Projected to 2050
Figure 6: Closed Fuel Cycle: Full Actinide Recycle – Projected to 2050
If we review the operating characteristics of three representative nuclear fuel cycle deployments:
• conventional thermal reactors operating in a “once- through” mode, in which discharged spent fuel is sent directly to disposal.
• Thermal reactors with reprocessing in a “closed” fuel cycle, which means that waste products are separated from unused fissionable material that is recycled as fuel into reactors. This includes the fuel cycle currently used in some countries in which plutonium is separated from spent fuel, fabricated into a mixed plutonium and uranium oxide fuel, and recycled to reactors for one pass. This fuel cycle is known as Plutonium Recycle Mixed Oxide, or PUREX / MOX, as mentioned above.
• Fast reactors1 with reprocessing in a balanced “closed”
fuel cycle, which means thermal reactors operated worldwide “once-through” mode and a balanced number of fast reactors that destroy the actinides separated from thermal reactor spent fuel. The fast reactors, reprocessing, and fuel fabrication facilities would be co-located in secure nuclear energy “parks” in industrial countries.
1 A fast reactor more readily breeds fissionable isotopes potential fuel – because it utilizes higher energy neutrons that in turn create more neutrons when absorbed by fertile elements, e.g., fissile Pu-239 is bred from neutron absorption of U-238 followed by beta emission from the nucleus.
Detailed analysis of the relative merits of these representative fuel cycles with respect to key evaluation criteria can be summarized as follows:
The once-through cycle has advantages in cost, proliferation , and fuel cycle safety, and disadvantageous in respect to long-term waste disposal; the two closed cycles have clear advantages only in long-term aspects of waste disposal, and disadvantages in cost, short-term waste issues, proliferation risk, and fuel cycle safety (Table 3). Cost and waste criteria are likely to be the most crucial for determining nuclear power’s future.
Table 3: Fuel Cycle Types and Criteria Ratings
Both once-through and closed cycles can operate on U and Th fuel and can involve different reactor types, e.g., Light Water Reactors (LWR), Heavy Water Reactors (HWR), Supercritical Water Reactors (SCWR), High Temperature and very High Temperature Gas Cooled Reactors (HTGR), Liquid Metal and Gas Fast Reactors (LMFR and GFR), or Molten Salt Reactors (MSR) of various sizes. Today, almost all deployed reactors are
of the LWR type. The introduction of new reactors or fuel cycles will require considerable development resources and some period of operating experience before initial deployment.
2.2 Safety
Because of the accidents at Three Mile Island in 1979 and Chernobyl in 1986, a great deal of attention has focused on reactor safety. However, the safety record of reprocessing plant is not good, and there has been little safety analysis of fuel cycle facilities using, for example, the probabilistic risk assessment method. Here we address reactor safety, the continuing availability of trained personnel for nuclear operations, the threat of terrorist attack, and nuclear fuel cycle safety, including nuclear fuel reprocessing plants.
Reactor safety – Probabilistic Risk Assessment (PRA) identifies possible failures that can occur in the reactor, e.g., pipe breaks or loss of reactor coolant flow, then traces the sequences of events that flow, and finally determines the likelihood of their leading to core damage.
With regard to implementation of the global growth scenario during the period 2005 – 2055, both the historical and the PRA data show an unacceptable accident frequency. The expected number of core damage accident during the scenario with current technology would be 4. We believe that the number of accidents expected during this period should be 1 or less, which would be comparable with the safety of current world LWR fleet. A larger number poses potential significant public health risks and, would destroy public confidence. We believe a ten-fold reduction in the likelihood of a serious reactor accident, i.e., a core damage frequency of 1 in 100,000 reactor years, (at the moment it is about 1 in 10,000 in US), is a desirable goal and is also possible, based on claims of advanced LWR designers, that we believe plausible.
In fact, advanced LWR designers claim that their plant designs already meet this goal, with even further reduction possible. If these claims and other plant improvements and cost reductions are verified, advanced LWRs will be in a very good position to drive a large share of a global growth scenario market.
Additional gains may come with the introduction of High- Temperature Gas Reactors (HTGRs). In principle the HTGR may be superior to the LWR in its ability to retain fission products in a loss-of-coolant accident, because of fuel form and because core temperatures can be kept sufficiently low due to low power density design and high heat capacity of the core, if RD&D validates this future. Two HTGR plants of small capacity and modular design are under development for eventual commercial application.
Trained Personnel – Realization of the mid-century scenario has important implications for safety, and especially in training and qualification of people competent to manage and operate the plants safely, including the supporting infrastructure necessary for maintenance, repair, refueling, and spent fuel management.
Development of competent managers and identification of effective management processes is a critical element in achieving safe and economic nuclear power plant operations. For developed countries that now operate nuclear plants, these tasks require attention to the rejuvenation of the entire workforce. For developing countries, however, this challenge is much greater, because of the lack of workers in many skills required in nuclear
power plant construction, and maintenance. The workforce must be trained and grow from a small or negligible base.
Terrorist Attack – Terrorists have demonstrated their ability to inflict catastrophic damage. Nuclear facilities as potential targets have not yet escaped notice. On the other hand experts have concluded that civil works and security provisions make nuclear plants hard targets. On the other hand, the hazards are on a scale previously considered to be extremely rare in evaluation of sever reactor accidents. The question is what new security measures, if any, are appropriate? We believe there is no simple, one-size-fits- all answer. It depends on many factors including threat evaluation, plant location, facility design, and government security resources and practices. The strength of containment buildings and structures presents a major obstacle and hardened target for attack for nuclear plant safety.
Nuclear Fuel Cycle Safety – Realization of the global growth scenario entails construction and operation of many fuel cycle facilities around the world, and also the facilities and repositories associated with waste management. There are varying degrees of risk to public safety associated with these facilities, and therefore a need for systematic evaluation of risk on a consistent basis that takes into account evaluations performed heretofore on individual fuel cycle facilities.
The need for such an evaluation is especially important in the case of reprocessing plants. France, the United Kingdom and Japan have reprocessing plants in operation, based on aqueous PUREX separation technology and improvements to it over many years.
Pyro-reprocessing and dry reprocessing R&D has been done with no commercial application as yet. Aqueous separation plants have high inventories of fission products, as well as fissile material of work in process, and many waste streams. Future improvements in separation technology may be capable of reducing radioactive materials inventories, measured as a fraction of annual throughput, but inventories will continue to be large, because of the large annual product required, if and when reprocessing comes into wider commercial use many years in the future.
2.3 Waste Management
Nuclear power stations generate long-lived radioactive waste that needs to be handled and stored carefully and ultimately disposed of in an appropriate long-term management facility. Although the majority of this waste is of a low level of radioactivity, there are also higher level wastes and spent fuel from nuclear power stations that need to be managed.
The management and disposal of radioactive waste from the nuclear fuel cycle is one of the most difficult problems currently facing the nuclear power industry throughout the world. Today, almost fifty years after the first commercial nuclear power plant entered service, no country has yet succeeded in disposing of high-level nuclear waste – the longest-lived, most highly radioactive, and most technologically challenging of the waste streams generated by the nuclear industry.
Independent experts have concluded that geologic repositories, constructed in rock formations hundreds of meters below the earth’s surface, will be capable of safely isolating the waste from the biosphere. Although several experimental pilot facilities have
been built, there are no operating high-level waste repositories, and all countries have encountered difficulties with their programs. Meantime, many of the discussions surrounding alternative reactors and fuel cycles are motivated by a desire to reduce high-level waste management challenges.
2.4 Non-proliferation
Nuclear power should not expand unless the risk of proliferation from operation of the commercial nuclear fuel cycle is made acceptably small. A nuclear power can expand with acceptable incremental proliferation risk, provided that reasonable safeguards are adopted and that deployment of reprocessing and enrichment ore restricted.
Today, the objective is to minimize the proliferation risks of nuclear fuel cycle operation. We must prevent the acquisition of weapon-usable material, either by diversion (in the case of plutonium) or by misuse of fuel cycle facilities (including related facilities, such as research reactors or hot cells) and control, to the extent possible, the know-how about how to produce and process either HEU (enrichment technology) or plutonium.
This proliferation concern has led, over the last half century, to an elaborate set of international institutions and agreements, none of which have proved entirely satisfactory. The Nuclear Nonproliferation Treaty (NPT) is the foundation of the control regime, since it embodies the renunciation of nuclear weapons by all signatories except for the declared nuclear weapon states – the P-5 (the United States, Russia, the United Kingdom, France, China) – and a commitment to collaborate on developing peaceful uses of nuclear energy. However, non-signatories India and Pakistan tested nuclear weapons in 1998, and signatories, such as South Africa and North Korea, have admitted to making nuclear weapons.
The International Atomic Energy Agency (IAEA) has responsibility for verifying NPT compliance with respect to fuel cycle facilities through its negotiated safeguards agreements with NPT signatories. With modest nuclear infrastructure, any nation could carry out the separation at the scale to acquire material for several weapons. Further, the MOX fuel cycle has led to an accumulation of about 200 tones of separated plutonium in several European countries, Russia and Japan. This is equivalent to 25,000 weapons using the IAEA definition of 8kg / weapon.
Separated plutonium is especially attractive for theft or diversion and is fairly easily convertible to weapons use, including by those sub-national groups that have significant technical and financial resources.
We conclude that the current non-proliferation regime must be strengthened by both technical and institutional measures with particular attention to the connection between fuel cycle technology and safeguardability.
3. INNOVATIVE NUCLEAR REACTOR DEVELOPMENTS
About 85% of the world's nuclear electricity is generated by reactors derived from designs originally developed for naval use.
These and other second-generation nuclear power units have been found to be safe and reliable, but they are being superseded by better designs.
Most of the new plants expected to come on line in the next few years incorporate substantial modifications and improvements on existing reactor designs, including safety features that simplify cooling requirements in the event of an accident. These designs are therefore expected to provide more reliable safety performance at lower overall cost. Most of the plants that are now under construction or have recently come on line use Generation III+ reactor designs. The forth generation reactors could, in addition to incorporating passive safety features, achieve further improvements in cost and performance while also reducing waste disposal requirements by minimizing fuel throughput and/or recycling spent fuel.
Reactor suppliers in North America, Japan, Europe, Russia and South Africa have a dozen new nuclear reactor designs at advanced stages of planning, while others are at a research and development stage. Fourth-generation reactors are at concept stage.
Generation III (III+) Reactors Third-generation reactors have:
• a standardized design for each type to expedite licensing, reduce capital cost and reduce construction time,
• a simpler and more rugged design, making them easier to operate and less vulnerable to operational upsets,
• higher availability and longer operating life - typically 60 years,
• reduced possibility of core melt accidents,
• minimal effect on the environment,
• higher burn-up to reduce fuel use and the amount of waste,
• burnable absorbers (“poisons”) to extend fuel life.
The greatest departure from second-generation designs is that many incorporate passive or inherent safety features2 which require no active controls or operational intervention to avoid accidents in the event of malfunction, and may rely on gravity, natural convection or resistance to high temperatures.
Many are larger than their predecessors. Increasingly they involve international collaboration. Certification of designs is on a national basis, and is safety-based. In Europe there are moves towards harmonised requirements for licensing.
2 Traditional reactor safety systems are 'active' in the sense that they involve electrical or mechanical operation on command.
Some engineered systems operate passively, eg pressure relief valves. They function without operator control and despite any loss of auxiliary power. Both require parallel redundant systems. Inherent or full passive safety depends only on physical phenomena such as convection, gravity or resistance to high temperatures, not on functioning of engineered components.
However, in Europe reactors may also be certified according to compliance with European Utilities Requirements (EUR). These are basically a utilities’ wish list of some 5000 items needed for new nuclear plants. Plants certified as complying with EUR include Westinghouse AP1000, Gidropress’ AES-92, Areva’s EPR, GE’s ABWR, Areva’s SWR-1000, and Westinghouse BWR 90.
Generation IV Reactors
Concerns over energy resource availability, climate change, air quality, and energy security suggest an important role for nuclear power in future energy supplies. While the current Generation II and III nuclear power plant designs provide an economically and publicly acceptable electricity supply in many markets, further advances in nuclear energy system design can broaden the opportunities for the use of nuclear energy. To explore these opportunities, the U.S. Department of Energy’s Office of Nuclear Energy has engaged governments, industry, and the research community worldwide in a wide-ranging discussion on the development of next-generation nuclear energy systems known as
“Generation IV.”
Generation IV International Forum (GIF):
The objective of the U.S. Generation IV Nuclear Energy Systems Initiative is to develop and demonstrate advanced nuclear energy systems that meet future needs for safe, sustainable, environmentally responsible, economical, proliferation-resistant and physically secure energy. Under U.S. DOE leadership, this initiative has led a group of ten countries (Argentina, Brazil, Canada, France, Japan, the Republic of Korea, the Republic of South Africa, Switzerland, the United Kingdom, and the United States) and Euratom to jointly plan the fulfillment of this objective. In 2002, the Generation IV International Forum (GIF) was chartered, establishing a Policy Group as the highest policy- making organization, an Experts Group as the technical advisory organ, and a Secretariat to administer and coordinate GIF activities. In 2003, the GIF, together with the Department’s Nuclear Energy Research Advisory Committee, issued A Technology Roadmap for Generation IV Nuclear Energy Systems. Based on the Roadmap, GIF countries are jointly preparing collaborative R&D programs to develop and demonstrate candidate concepts. (Figure 7)
3.1 Innovative Reactor Designs
All of the innovative reactor designs in Table 4 can be used in small and medium-sized reactors3, although some of the designs are also appropriate for large reactors. Several of the designs offer temperatures well above those available from current water- cooled reactors.
3.1.1 Light-Water Reactors
Name, Country, Type, Capacity, Developer, Style, Current Use, The innovative reactor groups are described briefly below: The five light-water reactors (LWRs) in Table 4 have outputs of 300
3 The IAEA classifies reactors according to their electrical output as follows: less than 300 Mwe as small reactors, 300 MWe to 700 MWe as medium-sized reactors and greater than 700 MWe as large reactors
MWe or less. They use traditional pressurized-water reactor (PWR)technologies (Figure 8), such as a pressure vessel housing the reactor core, fuel enriched to approximately 3.5% in 235U, and light-water coolant, but they incorporate innovative configurations and features to achieve their design objectives.
Figure 7: The evolution of nuclear power.
Figure 8: Pressurised Water Reactor.
The KLT-40C, like today’s operating PWRs, is a pressure- vessel/loop (PV/loop) reactor. In this configuration, hydraulic loops that include a circulation pump and a steam generator connect to the pressure vessel and provide coolant circulation through the reactor core. The other four designs are integral reactors, in which all components of the nuclear steam supply system (NSSS) and the reactor system, including the pressurizer, the primary heat exchangers and any reactor coolant pumps, are housed within a single pressure vessel.
The CAREM-25, which produces 100 MWth/27MWe, is a demonstration or prototype reactor.
The designers of all five reactors strive to enhance safety by increasing the amount of water (on a per-MW basis) in the pressure vessel, reducing the core-power density and increasing the use of passive systems, relative to current PWRs. All of these reactors use fuel and have fuel cycles similar to those of current PWRs.
Table 4: Innovative Reactor Designs
3.1.2 Heavy-Water Reactors
The CANDU X is a pressure-tube (PT) reactor. No pressure vessel is used – rather, the reactor coolant boundary within the core consists of a large number of pressure tubes, surrounded by a moderator. The design uses the traditional CANDU equipment configuration for the NSSS; innovative features in the Mark I model include the use of supercritical heavy water for the reactor coolant and of supercritical light water to power the turbine- generator. Supercritical coolant substantially increases the pressure and temperature of the reactor coolant system over those in current CANDU plants (Figure 9). Further innovations proposed for later CANDU X models include the use of supercritical light water as the reactor coolant and the use of a direct cycle.
The CANDU X retains the passive safety features of current CANDU reactors, such as the two passive shutdown systems, and
its design strives to enhance safety by incorporating additional passive decay heat removal capabilities.
The net output of the CANDU X is in the range of 350MWe to 1150MWe, depending on the number of fuel channels used. For heat applications, the temperature capability of the design is greater than that of current pressurized heavy-water reactors (PHWRs), but well below that of high-temperature gas-cooled reactors and liquid-metal fast reactors.
Figure 9: CANDU reactor.
3.1.3 Liquid-Metal Fast Reactors
The two liquid-metal fast reactor designs have outputs of 300 MWe and 675 MWe. They are lead-cooled, pool-style reactors, in which the core is housed in a pool that has near-atmospheric pressure at the coolant surface. The BREST 300 uses a loop configuration for the primary heat removal system, while the steam generators for the Energy Amplifier are housed within the reactor pool.
The BREST 300 uses a mononitride mixed (uranium-plutonium) fuel that is compatible with the lead reactor coolant.
The Energy Amplifier is a hybrid reactor that integrates accelerator and metal-cooled reactor technologies to produce power using a sub-critical reactor core. A beam of high-energy protons from the accelerator is directed at a lead target, which ejects neutrons. The neutrons are only slightly moderated by the lead in the target, are multiplied under subcritical conditions in the reactor core and contribute to the breeding process taking place in the mixed ThUO2 oxide fuel.
These designs offer temperatures substantially above those available from current water-cooled reactors, increasing thermodynamic efficiency. They take advantage of this feature as well as of passive safety features to reduce capital and operating costs, and they have lower fuel-cycle costs than current water- cooled reactors. They can operate as breeders or near-breeders to increase resource utilization and can ease the management of radioactive waste by consuming plutonium and transmuting minor actinides into stable isotopes.
3.1.4 Gas Reactors
The two gas-cooled reactor designs are PV/loop reactors that use helium as the coolant and graphite as the moderator. They build
on developments in high-temperature gas-cooled reactor (HTGR) technology over the last 40 years. They also benefit from the operating experience of the AVR and Peach Bottom prototype/demonstration reactors, the THTR demonstration reactor and the Fort St. Vrain4 demonstration/ commercial reactor, as well as recent advances in gas-turbine technology. The Fort St. Vrain plant experienced major problems with water ingress via the helium circulators. The designs considered here incorporate features to avoid this problem as well as other problems encountered during the operation of prototype and commercial reactors.
These designs use the TRISO5 fuel-particle design that has been developed over the past 40 years, largely in the United States and Germany. Designers believe that traditional containment structures of the type used with water-cooled reactors are not needed with this fuel, which would reduce construction and operating costs.
The GT-MHR core structure consists of stacks of hexagonal graphite blocks that have passages for the helium coolant flow and columns of graphite pellets that contain the TRISO fuel particles. In the PBMR, the active core consists of a large number of “pebbles” about the size of billiard balls surrounded by columns of graphite reflector blocks. Some pebbles are graphite and serve a moderator function; others contain TRISO particles with fissile material; still others may contain TRISO particles with fertile fuel.
Both designs use direct cycles and modern, high-efficiency gas- turbine technology to simplify the energy conversion equipment and to increase thermodynamic efficiency. The compact configuration of the reactors and of the helium-turbine power conversion systems reduces area requirements for plants.
With net electrical outputs in the range of 100 MWe to 300 MWe, the GT-MHR and PBMR are considered small reactors.
Compared with current water-cooled reactors, they offer a substantial increase in temperature for heat applications.
3.1.5 Molten-Salt Reactors
The FUJI is a low-pressure vessel (LPV)/loop-style reactor. It uses a graphite moderator and a molten-salt coolant. The design builds on the molten-salt reactor technology developed at Oak Ridge National Laboratory (ORNL) in the United States and the operating experience of the Molten-Salt Reactor Experiment (MSRE), which was operated by ORNL for over 32 months in the late 1960s.
4 The AVR and THTR reactors operated in Germany, the Peach Bottom reactor operated in Pennsylvania in the United States, and the Fort St. Vrain reactor operated in Colorado in the United States.
5 TRISO particles, with an outside diameter of less than one mm, have a uranium or thorium oxide core with four coatings.
Designers believe that silicon carbide coatings can serve the containment function that is provided by the containment buildings of water-cooled reactors. A porous, pyrolytic-carbon inner coating accommodates fission gases. The pressure- retaining capability of the TRISO particle is maintained up to about 1,600°C, which is above the temperature reached under the most severe accident scenarios.
A unique feature of molten-salt reactors is that the uranium and thorium fuel is dissolved in the molten-salt coolant. The salt mixture can include 232ThF4 (which is fertile), 233UF4 (which is fissile) and 7LiF-BeF2 (the principal solvent salt). These reactors have very strongly negative temperature-reactivity coefficients, stemming from the combination of the strong negative temperature-reactivity coefficient provided by the graphite moderator and the reduction in molten-salt density, and hence in the amount of fuel in the core, that accompanies increasing temperature.
The FUJI, with an electrical output of 100 MWe, is considered a small reactor. Its designers strive to enhance safety by exploiting the inherent and passive safety features made possible by the technology. The design ensures that no materials with moderating capability are located in the vicinity of the reactor vessel, so that the molten-salt/fuel fluid cannot achieve criticality outside the core in the event of an accident involving leakage of molten salt from the vessel. The design offers a substantial increase in temperature capability for heat applications as compared with current water-cooled reactors.
3.1.6 Others
The Radkowsky Thorium Fuel Reactor (RTFR) concept is not a reactor design, but rather a fuel and fuel-cycle concept that can be adapted for use in water-cooled reactors. Although applicable in principle to both light-water-cooled and heavy-water-cooled reactors, the design focus to date has been on LWR applications (PWRs).
The RTFR fuel concept consists of a seed-blanket unit fuel assembly containing enriched uranium (less than 20% 235U) in the central region and thorium in the surrounding blanket. The blanket material also contains a small amount (about 0.1%) of enriched uranium. The principal benefits of the concept include the use of abundant thorium fuel, which preserves uranium resources, and a substantial reduction in the quantities of uranium-derived actinides that are produced during reactor operation.
4. CONCLUSION
Nuclear power could provide significant benefits to future generations, particularly in terms of reducing carbon emissions and contributing to energy security and thereby supporting economic growth. It is likely to be more cost effective than alternative forms of low-carbon generation. However, the creation of nuclear waste is also a potential burden while it requires active management or care and maintenance, and radioactive waste remains potentially hazardous for many years to come. This needs to be balanced against the likelihood that without new nuclear power, a greater proportion of the capacity needed to replace the existing nuclear and fossil fuel stations would come from additional fossil fuel power stations. Increasing the amount of fossil fuel plant would increase the emissions of carbon dioxide into the atmosphere, adding to the growing problem of man-made climate change. Further, a decision not to allow energy companies the option of investing in new nuclear power stations would mean that one less source of electricity generation would be available to future generations, which could have implications for future diversity and security of supply. The ethical issues around radioactive waste are discussed further in the CoRWM report on
“Ethics and Decision Making for Radioactive Waste” (although the discussions reported in that document focus primarily on legacy waste).
Allowing energy companies to build new nuclear power stations would create new radioactive waste that needs to be managed.
Compared to the existing nuclear power stations in the UK, the designs of power stations that might be constructed would create less waste by volume because of the improved, more efficient reactor designs which use fewer components. Because of their longer expected lives, they would generate more electricity.
However this means that there would be a larger increase in the radioactivity compared to the increase in volume of waste – principally from spent fuel – although as with all radioactive substances the activity would decline over time.
Scientific consensus and international experience suggests that waste from new nuclear power stations does not raise such different technical issues compared with nuclear waste from legacy nuclear programs as to require a different technical solution. It could therefore technically be accommodated in the same disposal facilities for intermediate level waste and high level waste/spent fuel as the existing legacy. If waste from new nuclear power stations were accommodated together with legacy waste, it would increase the overall size and cost of a geological disposal facility. However, it is likely that some of the initial infrastructure costs would be common to legacy and new wastes. The additional costs resulting from accommodating new build waste would arise principally from the construction of additional vaults.
A number of OECD countries, as well as others, wish to expand their use of nuclear energy or keep open the option of doing so in the future. Concerns over energy security and the need to reduce emissions of greenhouse gases and other atmospheric pollutants are among the reasons cited by several industrialized countries for wishing to keep this option open. Developing countries, many of which lack indigenous energy resources, are interested in enhancing their standards of living while minimizing energy imports.
The context in which any new nuclear generating capacity will be constructed is one of increasingly privatized and deregulated energy markets coupled with heightened public concern over nuclear power. At a minimum, new nuclear plants must maintain or exceed current levels of safety and must be economically competitive with other means of generating electricity, especially natural-gas combined-cycle plants. Improved ways of dealing with the waste generated by nuclear plants and of addressing nonproliferation concerns will also be important.
Nuclear energy technologies incorporating incremental, evolutionary changes to today’s operating reactors are one option for the future. They will certainly continue to be developed and used. But additional, innovative technologies are likely to be needed if new nuclear power plants are to compete successfully in highly-competitive energy markets and to overcome the other challenges facing nuclear power
5. RECOMMENDATIONS
The governments should, as part of their near-term R&D program, develop more fully the capabilities to analyze life-cycle health and safety impacts of fuel cycle facilities and focus reactor
development on options that can achieve enhanced safety standards and are deployable within a couple of decades.
Research programs should be launched to determine the viability of geologic disposal in deep boreholes within a decade. A network of centralized facilities for storing spent fuel for several decades should be established internationally.
IAEA safeguards should move to an approach based on continuous materials protection, control and accounting using surveillance and containment systems, both in facilities and during transportation, and should implement safeguards in a risk- based framework keyed to fuel cycle activity.
Fuel cycle analysis, research, development, and demonstration efforts must include explicit analysis of proliferation risks and measures defined to minimize proliferation risks.
International spent fuel storage has significant nonproliferation benefits for the growth scenario and should be negotiated promptly and implemented over the next decade.
Many different approaches have been adopted for different reactors to meet the same basic design requirement under similar circumstances. Increased cross-fertilization among reactor designs and design teams would be fruitful.
Many components and technologies that have been commercialized by the aerospace, automotive, petro-chemical and other industries may be useful in the nuclear industry. Increased co-operation with non-nuclear researchers, and increased tracking of non-nuclear industrial developments, could benefit innovative reactor design efforts.
The designs considered, except for the GT-MHR and the PBMR, focus on the nuclear steam-supply system (NSSS). They do not specifically address the balance-of-plant (BOP), where heat from the nuclear reactor is converted to useful energy. Since the BOP represents a major portion of both capital and operating costs, its design must be given careful attention if economic objectives are to be met.
Several of the innovative designs considered in this study were developed on the assumption that in future energy markets, demand may not be driven solely by the need for electricity. New demand will arise for process heat, district heating or seawater desalination for the production of potable water. In general terms, taking advantage of co-production options and improving the flexibility of application can improve the competitiveness of nuclear power plants.
Specific attention is needed to reducing the cost of operation, maintenance and inspection. This is particularly important for small reactors, and can be partially addressed by siting several units together and using common support functions and facilities.
However, placing more than about 2,000 MWth of capacity at a single site reduces the potential for using a large fraction of the output for process-heat applications.
Because of their compact design or the type of coolant they use, several of the innovative reactor designs considered here present new challenges to the provision of efficient, cost-effective and reliable maintenance and inspection of the reactor, the pressure and containment vessels, and other components important to safety. Obstacles to in-service inspection include restricted access
and restricted space resulting from very compact configurations, and the presence of obstacles such as insulation or solidified coolant.
Nuclear R&D expenditures today are aimed primarily at maintaining and enhancing the performance of operating reactors.
Assuming that low investment will continue, commercial availability for most of the designs considered here could require 10 to 15 years or longer.
Further collaboration in developing innovative fission reactor designs is warranted. Collaboration could help designers make the most effective use of limited R&D resources and could reduce the time and cost required to make technologies commercially available. It could also help increase cross-fertilization among development efforts and ensure fuller use of the broad experience base developed to date.
Make better use of experience to date. Design groups should consider directing strong efforts toward ensuring that previous design and operating experience with relevant coolants, moderators, systems, components, configurations and procedures is fully incorporated into current R&D programmes.
Increase cross-fertilization of ideas among those working on various reactor types. Design groups should consider familiarizing themselves thoroughly with the features and technologies that are currently used or proposed by other design groups, and should consider evaluating potential alternative approaches to meeting their own design requirements.
The INPRO, the GIF and other international projects should continue the analysis begun in this study. These findings and recommendations are only indicative. They represent a starting point for planning the collaborative R&D and analysis elements of the INPRO, the GIF and other international programs. These programs may find these recommendations useful in planning the collaborative elements of their work. But this survey should be expanded to cover a broader range of innovative reactor designs and concepts, so as to provide a more comprehensive set of findings and recommendations.
We believe the nuclear option should be retained, precisely because it is an important carbonfree source of power that can potentially make a significant contribution to future electricity supply.
6. REFERENCES
[1] INTERNATIONAL ATOMIC ENERGY AGENCY, (2008), Latest News Related to PRIS and the Status of Nuclear Power Plants
[2] AUSTRALIAN URANIUM ASSOCIATION, (2007), Advanced Nuclear Power Reactors, Nuclear Issues Briefing Paper 16
[3] INTERNATIONAL ENERGY AGENCY, (2002),
Innovative Nuclear Reactor Development, Opportunities for International Co-operation, OECD/IEA
[4] LIVESCIENCE STAFF, (2007), Nuclear Power Has Bright Future, Live Science
[5] AN INTERDISCIPLINARY MIT STUDY, (2003), The Future of Nuclear Power
[6] INTERNATIONAL ENERGY AGENCY, (2006), World Energy outlook
[7] A REPORT FROM THE IAEA, (2007), Nuclear Power Worldwide: Status and Outlook
[8] INTERNATIONAL ATOMIC ENERGY AGENCY, (2007), Report: Nuclear Power Has Bright Future
[9] ENERGY WHITE PAPER, (2007), Meeting the Energy Challenge
[10] IAEA-TECDOC-1210, (2001), Safety Related Design and Economic Aspects of HTGR, Vienna: IAEA
[11] INTERNATIONAL ENERGY AGENCY, 2001, Nuclear Power in the OECD, Paris: OECD/IEA
[12] NUCLEAR ENERGY AGENCY, (2000), Nuclear Energy in a Sustainable Development Perspective, Paris: OECD/NEA
