ARTICLES (1)
Advanced Nuclear Reactors – Their Use in Future Energy Supply
John F. Ahearne
Introduction
The term “advanced reactor” is understood to mean reactor design beyond what is now deployed:
“Advanced designs consist of evolutionary designs and designs requiring substantial development efforts. The latter can range from moderate modifications of existing designs to entirely new design concepts. They differ from evolutionary designs in that a prototype or a demonstration plant is required, or that not sufficient work has been done to establish whether such a plant is required.”
Terminology that has become in wide international use is that of generations:
Generation I reactors were the first to be developed and many were small. Perhaps the only Generation I reactors still in operation are six small (under 250 Mwe) gas cooled plants in the UK. All others have been shut down.
Generation II reactors are what constitute most reactors operating today.
Generation III reactors are what have been built in the last few years in France and Japan. Some are called Generation III+, such as the ABWR in Japan, the new Korean PWR, the AP-1000, the EPR, and the ESBWR.
Generation IV reactors are usually referred to as advanced reactors. None have been built and none are close to being under construction.
As of 31 December 2004, there were 440 nuclear plants in operation with a net rating of 365,759 Mwe. The three countries with the largest number of reactors in operation were the United States (104), France (59), and Japan (53). There were 26 reactors under construction at the end of 2004 with the leading countries being India (9), Russia (4), and Japan (3). These numbers indicate the shift of nuclear growth to Asia and away from the US and Western Europe. Accelerating this shift has been the Swedish decision to close down the 12 Swedish nuclear plants (two have now been shutdown) and the German government’s decision to phase out nuclear power in that country.
Two issues whose concern is not uniform across the globe have stimulated the resurgence of interest in nuclear power:
1. global warming and
2. the rising cost of natural gas.
The Asian growth is driven by need for electricity. US interest is due primarily to the rising price of natural gas assisted by a positive attitude by the federal government.
New designs, i.e. “advanced reactors.”
Reactors with the term “advanced” are and have been built. All these are classed as GEN III+. They include the ABWR (advanced boiling water reactor) built in Japan and the Korean APR-1400, modeled after the CE System 80+. The latest with a commitment to be built is the French EPR selected to be built as the fifth reactor in Finland and announced by France to be built in Brittany. Japan also is building two large (1540 Mwe) advanced pressurized water reactors (APWR) of Japanese design. The Korean reactor exemplifies a clear trend in Asia, where countries are designing and building their own reactors. This is seen in Japan, South Korea, China, and India. For example, in June of 2005, the 540 Mwe PHWR Tarapur-4, a reactor designed and built by the Nuclear Power Corporation of India, was connected to the grid.
Using a term of the 1990’s, these are evolutionary reactors, improved (often significantly) modifications of existing reactors. The gas-cooled pebble bed modular reactor (PBMR) also is related to previous reactors but with operational experience limited to one German research reactor and a small pebble bed reactor in operation in China, the 10 MWe HTR-10. China has announced plans to build a 160 Mwe commercial demonstration pebble bed reactor. The early proponent of commercialization has been Eskom, the large South African utility. In South Africa licensing progress has been halted on an EIS objection but the program seems likely to build a 165 Mwe demonstration reactor to be operating within the next ten years. The PBMR offers small size, gas cycle efficiency, and accident-resistant fuel.
Characteristics of newer reactors
Design Supplier Features
ABWR GE 1350 Mwe BWR operating in Japan; being
built in Taiwan.
SWR 1000 Framatome 1013 Mwe BWR. Under development.
ESBWR GE 1380 Mwe passive safety features BWR.
Submitted to the US Nuclear Regulatory
Commission for design certification.
AP1000 Westinghouse 1090 Mwe passive safety features PWR. Not
yet ordered but some US utilities have indicated preference
for this reactor.
EPR Framatome 1545 – 1750 Mwe PWR. Ordered by Finland
and France.
IRIS Westinghouse 100 – 300 Mwe PWR. Under development.
PBMR Eskom 165 Mwe modular reactor. Under
development.
ACR-700 AECL 700 Mwe CANDU heavy water reactor. No
sales yet.
GT-MHR General Atomics 288 Mwe modular gas-cooled reactor for
Russia.
HTR-PM Chinergy 160 Mwe steam cycle pebble bed. Ordered.
4S CRIEPI /Toshiba 10-50 Mwe Na cooled fast reactor;30 year core;
10 Mwe proposed for a remote village in Alaska.
Each of these reactors was designed to be simpler, safer, and have lower cost than currently operating reactors. The passive safety feature reactors rely on gravity, natural circulation, and compressed air to provide cooling of both the core and the containment in the case of a severe accident. This permits a reduction in systems that were designed to force coolant into the system. For example, compared with a typical similar size reactor, passive safety systems in the AP1000 led to 50 % fewer valves, 35 % fewer pumps, 80 % less pipe, 48 % less seismic building volume, and 70 % less cable. Similar passive emergency cooling features are provided in the ESBWR design.
GEN IV
In 2002, the US led the formation of a 10 nation (plus the European Union) organization, the Generation IV International Forum (GIF), to lay out a path for development of the next generation of nuclear plants. GEN IV plants are aimed for deployment before 2030. Six types were selected for further examination by participating countries:
VHTR: the Very High Temperature Reactor, selected by the US. This is planned to use helium cooling, a Brayton cycle for power conversion, and either a prismatic graphite core or a pebble bed core with ceramic and graphite coated fuel particles. The DOE reference design is for a plant of 400-600 Mw of thermal power, passive safety features, and with core outlet temperature approaching 1000 oC, with a design goal of producing hydrogen as well as electricity.
SCWR: the SuperCritical Water-cooled Reactor. By using very high pressure, similar to that in widely-used fossil-fired boilers, water remains a single phase fluid, improving reactor thermal efficiency (about 45 % compared with typical LWRs having 33 %). The reference design is 1700 Mwe with a core outlet temperature of 550 oC. Selected by Canada.
LFR: the Lead-cooled Fast Reactor. Selected by the US but of lower priority than the VHTR.
SFR: the Sodium-cooled Fast Reactor. Japan is taking the lead on the SFR, which also is planned to use a closed fuel cycle.
GFR: the Gas-cooled Fast Reactor would use helium or CO2 as the working fluid.. France is taking the lead on the GFR.
MSR: the molten salt reactor, where the fuel is in the circulating molten salt mixture of fluorides of sodium, zirconium, and uranium. France is leading a GIF steering committee with the US and the European Community and limited programs are underway in France and the European Community to evaluate this concept.
Other reactors
Many other reactors are being studied or developed. These include the following, which do not include all that have been announced or described in the literature.
-- The Indian ATBR (A Thorium Breeder Reactor) designed to run on thorium and produce 600 Mwe.
-- The SSTAR (small, sealed, transportable, autonomous reactor), a lead-cooled fast reactor for 10 to 100 Mwe and contained completely in a sealed container with fuel to last 30 years.
-- Westinghouse BWR 90+, a 1500 Mwe design to meet European Utility Requirements.
-- The Russian Gidopress 1000 Mwe V-392, an improved version of the VVER-1000, is being built in India and China.
-- In July 2005 Russia announced plans to build reactors on boats to supply hard-to-reach locations in the remote northern coast. The reactor probably will be the KLT-40, used in icebreakers, that can provide 30-35 Mwe and up to 20 Mw in heat.
-- The Argentinean CAREM (advanced small nuclear power plant) is an integrated modular 100 Mwt/27 Mwe PWR.
-- The South Korean SMART (System-integrated Modular Advanced Reactor) is a 330 Mwe PWR.
-- The French NP-300 is based on a submarine PWR and can be used for electricity generation (100-300 Mw) or desalination.
The main role of nuclear plants is to generate electricity, usually as a base load generator. However, plants also are used to provide heat (e,g., the four Bilibino 11 Mwe plants in Chukotka, Russia), to power both naval vessels and icebreakers, and for water desalination. A new interest is in using nuclear power to generate hydrogen. This is seen in the US NGNP (Next Generation Nuclear Plant) program which is planned for hydrogen production.
In addition to some of the GEN IV reactors listed above, a design that resulted from earlier work in the GEN IV program is the Advanced High Temperature Reactor (AHTR) which combines the coated-particle graphite-matrix fuel that has high safety value and low-pressure molten salt coolant. The outlet temperature can be 1000o C for use in production of hydrogen. The growing interest in hydrogen is as an energy-carrier to replace oil-based transportation fuels. In addition to production challenges, storage and transportation obstacles remain to be overcome. Industrial heat processes, e.g., metallurgical processing are another application for high temperature reactors.
Until the recent possibility of the use of nuclear power to produce hydrogen, the three factors leading to renewed interest have been population growth (particularly in China and India), continued rise in the price of natural gas (the US), and climate change. Several recent studies have concluded that nuclear power could be one of the options to address the climate change problem.
Challenges
It appears that nuclear power will continue to grow, the larger numbers driven by increases in per capita use of electricity. The largest forecast growth is in China. Nuclear capacity is forecast to grow to 40 Gwe by 2020 and possibly to 300 Gwe by 2040. In India, the current 2.7 Gwe capacity is planned to grow to 20 Gwe by 2020. Much of this growth will use existing designs. If the insatiable demand for electricity continues as the large populations in the developing countries are to improve their living standards, and if nuclear power remains one of the means of supplying that electricity, the new, advanced designs should be available and will offer advantages over those already built. However, getting to the point where some of the most advanced designs will have been tested in a demonstration or prototype system will take time and money.
There are two principal fuel cycles, once-through and closed. In the once-through fuel cycle, spent fuel is removed from the reactor and stored for later permanent disposal. In the closed fuel cycle, the spent fuel is processed to remove fission products and the uranium and plutonium separated for re-use. The requirements for the once-through fuel cycle are for fuel that can withstand much higher burnup than fuel now in use. Currently a “high burn up fuel” will be used for up to 60 Mwd/MTHM (Megawatt days per metric ton of heavy metal). A goal is to reach 100, which would prolong each operating cycle and reduce the total amount of spent fuel that must be stored or disposed of. Developing new fuel recycling processes and bringing them to the point they can be funded and licensed will take at least 10-20 years.
Other research needs relate to materials issues as much higher operating temperatures are planned along with use of coolants not well studied. The reactor design concepts that have not been built will face engineering issues once a prototype operates. Issues will arise for all the novel designs in the GEN IV list and for many of the other new concepts. For example, use of a direct helium cycle (Brayton) will be both a technical and a licensing challenge. Many R&D issues must be successfully addressed before these GEN IV advanced reactors can be expected to make significant contributions to meeting energy needs.
Although not apparently a major factor affecting plans for nuclear power in most areas of the world, in the US, which has the largest nuclear program and the electricity growth demand to support substantial growth in nuclear power, the cost of electricity has been the dominant factor in what type of generation gets built. Whereas two other countries with large nuclear power programs, France and Japan, have extremely limited domestic sources of energy, the US is one of the world’s leaders in coal reserves. As the US has moved to reduce the economic regulation of generation, cost has become a competitive key and “[c]apital cost is the single most important factor determining the economic competitiveness of nuclear energy.”
Most new reactor concepts are described as having construction costs much below those of currently operating reactors. Outside of the US, newer reactors have had construction costs that appear to be around $2000 (US)/kWe. The goal of new designs is to have overnight costs be no more than $1000 (US)/kWe. One approach to achieving substantial cost reduction is the elimination of active safety systems. Another is to reduce the size of the structure, to reduce the total concrete and rebar, which can be a significant cost saving.
“There is a concern, particularly in the United States, that the further expansion of nuclear power will increase significantly the risk of proliferation of nuclear weapons.” With the exception of India and apparently North Korea, nuclear power programs have not been used to develop nuclear weapons. However, the knowledge gained by working in nuclear power programs, such as handling the radioactive material and access to sensitive technologies (A. Khan) can assist in developing nuclear weapons. Nevertheless, the main difficulty in building a nuclear weapon is to obtain the HEU or plutonium needed to make a nuclear weapon. A recent review by the US American Physical Society concluded:
Fuel extracted from a reactor after use, spent fuel, is highly radioactive as well as hot. How to use the uranium and plutonium in that fuel or how to safely dispose of that fuel has been a controversy for decades. For once-through fuel cycles, the generally accepted technical solution has been to dispose of the spent fuel in a geological repository. However, after decades of that being the desired approach, no country has managed to construct a repository. The main obstacle has been public opposition to locating such a facility. Finland is currently the country most likely to first build a geological repository for spent fuel. The United States has been working on developing a repository in Yucca Mountain, Nevada for nearly 20 years. Although substantial tunneling and construction have been done, continued opposition by the State of Nevada has slowed progress substantially, as have problems with the Department of Energy’s program. A license application has not been submitted to the Nuclear Regulatory Commission and, even if all objections were resolved in favor of the site, the repository could not open until well past 2010.
Some countries reprocess the fuel to extract and reuse the uranium and plutonium. This substantially reduces the waste mass (most of that in the spent fuel is uranium) and can separate out the short-lived isotopes that are the primary heat source. France and England operate reprocessing facilities to handle their own fuel and that from other countries. Japan is about to open a reprocessing facility and Russia has operated a facility.
Even after reprocessing, high activity long-lived waste must be stored. If not reprocessed, the problem is larger. The GEN IV systems are planned to be associated with reprocessing (or, in the new euphemism, reuse).
The challenges for expansion of nuclear power differ by country. In Sweden and Germany, well run nuclear power plants are being shut down because of the policy of the elected governments. In Russia, an ambitious plan for nuclear power expansion is held back because of lack of funds. Prime Minister Blair recently said that the new energy plan being developed for the UK will consider new nuclear plants. In the US, the obstacles have been cost and public opinion. The recent Energy Bill in the US offers loan guarantees and production tax credits for new nuclear power plants and may encourage new construction. Expansion in these countries would not have the impact on energy supply as will the large expansion occurring in India and China.
Controversies
In addition to the cost and proliferation, the main controversies regarding nuclear power are whether the publics will accept new nuclear plants, whether sites can be found where the public will accept a geological repository, and whether future development should be based on the once-through or the closed fuel cycle. The first two are public attitude issues, the last is a technical and proliferation policy issue. Regarding public attitudes, bringing the public into decision processes early, although at least in the US the laws require the federal agencies to make the final decisions, will substantially improve the climate for nuclear power to go forward. This has been seen in repository siting in Finland and Sweden.
The issue of sustainability of nuclear power concerns the question as to the adequacy of long-term uranium supply. The amount of uranium available has been argued about for decades. Supporters of moving to breeder reactors (which transform the more prevalent isotope of uranium, U238, which will not fission and therefore cannot be used as a reactor fuel, into plutonium for use as fuel) have claimed the world will run out of uranium to fuel the reactors. It should be noted that the nuclear fuel makes up a very small part of nuclear power operating costs, usually only about one-tenth, and that the price of the uranium is only about one-third of that tenth, with most of the cost being in actually making the fuel from the uranium.
An MIT study examined a growth scenario of going from less than 400,000 Mwe today, worldwide, to at least 1,000,000 Mwe by 2050. The authors wrote (emphasis in original): “We believe that the world-wide supply of uranium ore is sufficient to fuel the deployment of 1000 reactors over the next half century and to maintain this level of deployment over a 40 year lifetime of this fleet.” This study provided a detailed analysis to support this position.
There is enough uranium.
Conclusions
Regarding the main challenges for expansion of nuclear power, safety has been greatly improved, there is increasing effort to address non-proliferation concerns, but little progress has been made in developing a permanent solution to the problem of nuclear waste and resolving public attitude issues. There are a plethora of new designs, promising improved safety and lower cost. These promises must be shown to be met by actual construction and operation. However, GEN III+ plants are being constructed and will be the units on which expansion will be based in the next decade.
As for use in future energy supply, the main role of nuclear power currently is to supply electricity. Since the past decade has demonstrated the linkage between electricity use and GDP, across all economies, the real growth in nuclear power will be in countries that are growing in per capita use of electricity. These are in the developing world of Asia, not in the developed world of the West. Asia is buying and building, Europe is dormant, and the US may restart. In the US there are an increasing number of press releases, but no orders. Vendors and utilities may be waiting to see how new government money will be administered.
If uranium is plentiful, the argument for the closed cycle that it is needed to prevent running out of fuel is not persuasive. The remaining issue is whether the closed cycle is necessary to resolve the inability to site a repository.
Finally, in all new initiatives, the concerned publics should be involved early, not after a decision has been reached. Not doing so is the fundamental reason for Nevada’s vehement opposition to Yucca Mountain.
Acknowledgements: This paper is extracted from a long paper produced for the InterAcademy Council. For that paper, quite helpful reviews were provided by M. Corradini, C. Forsberg, A. Kadak, P. Peterson, J. Taylor, and N. Todreas.
