Frequently asked questions
I've heard a lot about Generation IV reactors. What are they and what are Generation II and III reactors?
Civil nuclear power technology has developed over a number of decades and has been characterised, until now, by three stages of development. The first generation of prototypes were constructed in the 1950s and 60s and culminated in the construction of the first series of civil nuclear power reactors. The construction of the second generation of reactors started at the beginning of the 1970s and marked the widespread appearance of Light Water Reactors (LWR), either Pressurized Water Reactors (PWR) or Boiling Water Reactors (BWR), both using normal water as coolant and moderator. These designs required the uranium fuel to be slightly enriched in the fissile isotope (U-235) and, therefore, relied on parallel advances in mass uranium enrichment technology. Though more refined designs of these reactors have evolved since the 70s, in particular as a result of operational feedback, the LWRs constructed in the 80s and early 90s are essentially of the same "Gen-II" stock, and these now constitute the vast majority of reactors currently in operation worldwide. More significant evolutionary developments have been integrated into the latest LWR designs available today, with regard to design lifetime (typically 60 years compared with 40 years in the past) and safety issues, in particular the behaviour under severe accident scenarios. These new designs are classified as Gen-III or III+, and the first commercially available reactors of this generation are now under construction. Most, if not all, reactor vendors worldwide have an approved Gen-III model to propose to potential customers and any nuclear new-build over the next two or three decades will largely involve these designs.
In the year 2000, experts from around the world (in the context of the Generation IV International Forum - GIF) began formulating the requirements for a fourth generation of nuclear systems that could respond to the world's future energy needs, in particular in a scenario of increased demand, especially for electricity, and reduced CO2 emissions leading to more widespread recourse to nuclear energy. Saving uranium natural resources and minimising waste production become major concerns in such a scenario, in addition to satisfying economic competitiveness and maintaining stringent standards of safety and proliferation resistance. The emergence of new applications, such as hydrogen production or water desalination, are expected to offer other uses for Gen-IV technology. These new markets and boundary conditions are resulting in a veritable revolution in nuclear technology, leading to the industrial deployment of fast neutron reactors and high temperature reactors and associated fuel cycle facilities. The possible designs that are currently under investigation, and for which the GIF is organising an extensive R&D international collaboration, have collectively been labelled Gen-IV. It will take at least two or three decades before the deployment of commercial Gen-IV systems, though in the meantime a number of prototypes will need to be built and operated. The Gen-IV concepts currently under investigation are not all on the same timeline and some might not even reach the stage of commercial exploitation.
So, in what ways will Generation IV reactors be different from today's reactors? Does this mean that present day reactors are unsafe, unsustainable and dirty?
(Has Gen-IV got anything to do with nuclear fusion? B ut why should we back both generation IV and fusion ... if fusion is successful, won't this make Gen-IV obsolete?)
Scientists are currently investigating a number of promising Gen-IV reactor designs spanning a range of operating conditions and using a variety of components and techniques (e.g. type of coolant, fuel composition, operating temperatures, neutron spectra, etc.). Technological breakthroughs are required in a number of fields.
Since they have been designed to operate in a thermal (less energetic) neutron spectrum, current Gen-II and Gen-III Light-Water Reactors (LWR) can extract fission energy from only a small fraction of the uranium in the fuel (effectively only the "fissile" U-235 component, which makes up <1% of natural uranium). Under such conditions, known and easily accessible uranium reserves are capable of sustaining only a few more decades of operation of the world's fleet of LWRs. Four of the six Gen-IV designs currently under investigation are so-called "fast-breeder" reactors, which have the capability of exploiting the full energetic potential of the uranium, thus greatly extending resource sustainability by factors of 50 to 100. A fast reactor operates in a more energetic neutron spectrum, and is able, via nuclear transformations within the fuel, to "breed" fissile plutonium (Pu-239) from fertile uranium (U-238), which can then be recycled in fresh fuel. In this way, the energetic potential of U-238, representing more than 99% of the original natural uranium, can also be exploited.
Fast reactors are not new; several have operated in the past as research or demonstration facilities and one or two are still in operation today. However, Gen-IV fast reactor designs will represent a radical rethink of current technology. In particular, the objective is to extract and recycle not only the bred Pu-239 but also the other (so-called minor) actinides that are produced in the fuel by nuclear transformation. This "full actinide" recycling will be a key attribute of Gen-IV fast reactor systems and associated fuel cycles, as it will reduce the radiotoxicity and heat generation of the ultimate waste for disposal and increase overall proliferation resistance of the fuel cycle.
Another revolutionary aspect of Gen-IV technology will be the ability of certain reactor types - the high-temperature reactors - to co-generate both electricity and process heat for industrial purposes (hydrogen production, seawater desalination…)
The operational safety of past and current reactors needs to be viewed in the context of the trend towards the optimisation offered by Gen-IV concepts. Present reactors are operated to a high level of safety and under the strict regulatory control of national nuclear safety authorities. The latest Gen-III reactors have been designed to exhibit more favourable characteristics particularly in the event of severe accidents. Gen-IV plants aim at reaching safety levels at least as high as those of Gen III reactors
Nuclear reactors liberate energy "trapped" within the nucleus, essentially by converting mass into energy according to the famous Einstein equation E=mc2. However, the nuclear processes involved in fission are entirely different from those that would be involved in a future fusion reactor. Fission splits heavy nuclei (essentially fissile isotopes such as U-235 or Pu-239) into lighter elements (so-called fission products), whereas fusion combines light nuclei such as H-2 or H-3 (the hydrogen isotopes deuterium and tritium) into heavier nuclei. Therefore the technology and the challenges in the two cases are very different, and whereas nuclear fission is a proven technology with the equivalent of thousands of years of reactor operating experience, commercial fusion has yet to be realised and the process has only been demonstrated fleetingly in test facilities. However, the potential of fusion power is enormous, promising essentially limitless energy and producing much less radioactive waste than fission systems, and for this reason many countries in the world are prepared to invest heavily in the necessary research. Nonetheless, considerable scientific challenges remain, and the earliest possible exploitation of a commercial fusion reactor is not foreseen before the second half of this century. Because of the very high stakes (increasing energy demand, environmental concerns, etc.), is it clearly important to maintain a broad-based approach to support for R&D on all innovative and future energy systems; many technical issues are still to be resolved in all areas and no one technology is likely to be able to address all the world's future energy requirements.
Will Generation IV reactors help us to achieve our ambitious CO2 reduction targets, improve security of energy supply/competitiveness?
Nuclear energy is already helping us to achieve ambitious CO2 reduction targets and to improve security of energy supply at a stabilised and affordable cost. Continued operation of existing plants, including through plant-life extension programmes backed by necessary R&D activities, and new-build of Gen-III plants will contribute to these important objectives before Gen-IV systems come on stream. Indeed, commercial deployment of Gen-IV reactors is not foreseen before 2030 at the earliest, and all current activities involving Gen-IV designs are at the level of R&D. However, the increased sustainability of Gen-IV systems, employing fast reactors and a closed fuel cycle, will enable these systems to make a much more significant and prolonged contribution to the generation of competitive, secure and CO2-free energy as part of a portfolio of future low carbon energy sources and carriers. Though the principal role of nuclear energy will probably remain the base load generation of electricity, very high temperature reactors will also have positive impacts in the area of cogeneration of electricity and process heat for industrial applications, for example the mass production of hydrogen by water splitting as part of a petroleum-free economy.
So, Generation IV means widespread use of fast breeder reactors and therefore reprocessing ... but won't this mean we need mo re large reprocessing plants like at La Hague and Sellafield, leading to more low-level radioactive waste and increased radioactive effluent discharges to the environment?
These new reprocessing plants will enable all the minor actinides produced in the reactor to be recycled back into fresh fuel ... this might be good to reduce the proliferation risk, but won't this lead to increased radiation exposure of workers in both the reprocessing and fuel fabrication plants?
But surely we cannot recycle everything ... exactly how much highly toxic radioactive waste will be produced each year by a typical Generation IV reactor, and how does this compare with current reactors? Won't this mean we'll still need to find a solution to long-term management of such waste, e.g. construction and operation of geological disposal facilities?
The ambitious targets for increased sustainability of civil nuclear power, and optimal exploitation of the world's uranium reserves, can only be achieved through the future deployment of fast breeder reactors and associated fuel cycles. This will enable fissile isotopes (essentially Pu-239) that have been "bred" within the reactor to be extracted from spent fuel, mixed with com mo nly available "fertile" uranium feedstock (essentially U-238) whose energetic potential cannot be exploited in the reactors operating today, and recycled back into the reactor as fresh fuel. This will greatly increase the sustainability of known uranium reserves. However, this strategy relies on the availability of recycling - or reprocessing - plants, and as with all industrial facilities there will be an environmental impact. Nonetheless, these plants will have to comply with the very strict regulations governing radioactive effluent discharges, and operate at a high level of safety with regard to protection of the work force, just as in today's operating reprocessing facilities. Is it true that the recycling of all minor actinides, along with the Pu-239, will result in much higher levels of radioactivity in many of the processes in the reprocessing and subsequent fuel fabrication plants, and the workforce will therefore need to be adequately protected with appropriate shielding and re mo te handling apparatus. This technology is already proven in current day facilities dealing with MOX (mixed-oxide fuel) production. In addition, all low-level operational radioactive waste produced in these facilities will need to be managed according to approved and controlled practices.
The recycling of all the minor actinides back into the reactor as part of the fresh fuel enables them to be "burnt" in the reactor and transformed into so-called fission products. These fission products are separated out from the fuel in the reprocessing plant and constitute the "ultimate" waste from the process. This waste must be managed and ultimately disposed of in line with accepted and approved practice. Though the radioactivity of the waste will decay much more rapidly, and the radiotoxicity is much lower, once the minor actinides have been removed, it will still be necessary to dispose of the waste in geological repositories in order to ensure optimal protection of people and the environment over the timescales during which the waste remains a potential hazard. Nonetheless, the quantities of this ultimate waste will be much less than from current fuel cycles for the same energy production. In addition, with the removal of the minor actinides, heat generation is also greatly reduced, enabling a much more efficient use of space in geological disposal facilities.
The availability and extent of uranium reserves and the associated cost is a controversial issue; is there any impact on the deployment strategy of Generation-IV systems?
Clearly the availability of uranium reserves is one of the drivers for the development of fast reactors, which constitute an important element of Generation-IV systems. However, this is not the only driver for Generation-IV technology as a whole. Other aspects such as waste management, safety, competitiveness, proliferation resistance and co-generation of heat and electricity also play an important part. In the end, the promise of Generation-IV technology is that it will offer many advantages in a number of areas, irrespective of the extent of uranium reserves. The most complete picture of the world's uranium resources is provided by the NEA's "Red Book". The key messages from the new edition, published in June 2008, are the following:
Watch an Introduction to Generation IV Nuclear Energy Systems and the International Forum (requires Adobe Flash Player, or download in pdf format, 1.2 mb)
Download an Overview of the GIF (pdf, 161 kb)