Time to take stock of the fuel cycle3 April 2002
The OECD's Nuclear Energy Agency revisited the nuclear fuel cycle. It found an industry reacting to cope with a slow-growth market, where the need to replace ageing technology is coming up against reduced investment in R&D.
The nuclear fuel cycles in use today are the result of four decades of technological development, but the basic elements of these fuel cycles were established a long time ago, when the ground rules and development objectives were different. Developments in the fuel cycle were initially driven by the needs of the defence industry, and later by the type of nuclear power plant chosen in each country. Decisions taken then still affect the industry.
In the 1970s nuclear power was perceived as the solution to dwindling fossil fuel reserves and uranium was also considered a scarce commodity. To meet the needs of a large military programme and an anticipated growth in nuclear power, large facilities were constructed for all the stages of the fuel cycle and in some countries reprocessing facilities were developed. But after the slowdown in civilian nuclear power development and agreements to reduce nuclear weapons programmes, production capacities at fuel cycle facilities, with the exception of uranium mining, exceed demand.
Current demand for natural uranium is 60,000t per year. Known reserves of uranium represent at least 70 years of consumption by existing reactors, while estimated reserves are sufficient for 250 years.
Social and political changes have also affected the nuclear power industry. The areas most under discussion have been the role of nuclear power and concerns over the back end of the fuel cycle. The result has been increased regulatory constraints - and costs. At the same time energy markets have been deregulated and utilities have been under pressure to reduce their prices. Since many components of the nuclear cost base are 'sunk' costs (capital or taxes) the target for cost reductions has frequently been operation and maintenance or the fuel cycle - which are typically 23% and 20%, respectively, of the generating cost.
The response to a low-growth fuel cycle market has been consolidation: by mergers and acquisitions companies are hoping to increase market share and economies of scale, or find synergies. In parallel, there has been a marked reduction in R&D funding in all parts of the nuclear industry, a side effect of which will be to reduce nuclear skills and infrastructure.
As the power industry focuses on short-term economics and reduces funding for nuclear industry and R&D infrastructure, it will become more difficult to develop new options for any part of the fuel cycle. It is important to revisit the stages of the fuel cycle while cooperative research can still be used to develop alternatives if necessary.
The fuel cycle can be viewed as a chain of value-adding steps, which have been improved by constant competitive pressure and which have responded to increasing regulatory pressure by reducing their environmental impact.
Uranium resources are estimated at around 4Mt, recoverable at below $130/kgU. However, market conditions now make it uneconomic to mine uranium at prices above $40/kgU. In the next 20 years low-cost uranium production from new projects will be mainly from high-grade unconformity-type deposits, mineral deposits and sandstone-type deposits amenable to in-situ leaching (ISL), although conventional mining will retain its market.
Primary production fills around 60% of world uranium demand. The remainder is from uranium stockpiles, re-enrichment of depleted uranium, recycling of uranium and plutonium and the use of former weapons-grade material. These four supplies of uranium will continue to be available; this will keep prices low and delay expansion of primary production.
The environmental impact of the extraction and processing of uranium is mainly caused by mining and mill tailings. Radon release during mining has the greatest radiological impact. ISL does not produce tailings, and uranium extraction during gold mining in South Africa has effectively reduced the environmental burden of the tailings and improved efficiency.
Conversion of U3O8 to 'yellowcake' - UF6 - provides a readily vapourisable compound ready for enrichment in gas diffusion or centrifuge plants. The process is chemically hazardous because of the aggressive chemicals required, but it produces relatively little radioactive effluent - mainly alpha-activity from natural uranium. In France depleted UF6 is reconverted to U3O8, because the latter is much more stable and therefore suitable for long-term storage. Similar reconversion is planned in the USA.
The enrichment market is oversupplied and utility enrichment bid requests meet with aggressive competition from primary enrichers who want to build market share. In the coming decade all suppliers will face the problem of replacing obsolete equipment - by 2005, 90% of enrichment equipment will be more than 15 years old and 70% will be more than 25 years old. The facilities that house the equipment are often substantially older. Companies will have to decide soon whether to replace capacity with high-performance gas centrifuges or laser isotope separation technology, but since work on laser separation has almost come to a standstill, centrifuge technology is the most likely choice. Laser separation may make a comeback if reprocessing does, as it is the only method that will allow sustainable recycling of reprocessed uranium.
For each ton of fresh fuel, 6-8 tons of depleted uranium is produced as a by-product. This may eventually be used as a source of more U-235 or as fuel for fast breeder reactors, but its eventual disposal must still be managed. In the USA the NRC says that deep disposal of some kind will be required, but no decisions have been made on long term management.
Fuel fabrication represents 3% of the total cost of nuclear electricity, but the influence of fuel design on the overall economy of nuclear power production is considerable. Improving fuel utilisation not only reduces fuel costs, but also improves the flexibility and reliability of the fuel assembly, improving the plant capacity factor. Reducing the cost of fuel fabrication will not always improve the overall economics of generation.
Fabrication capacity is well in excess of requirements - about 50% above, in the case of LWR fuel. This is driving suppliers to consolidate and reduce costs. Fuel development is focused on improving flexibility, as simple baseload operation becomes less attractive in deregulated markets and plants need to time outages to market conditions. Over the past 30 years developments in burnup, fuel utilisation and reliability have improved fuel use, decreasing costs and reducing uranium requirements by around 25%. This also reduces waste. Work on improving burnup continues but is limited by regulatory limits of 50-55GWd/tHM. Burnup might be increased to 65-70GWd/tHM but this would require investment of time and resources as well as regulatory changes.
When fuel is removed from a reactor it has to be stored in the reactor's spent fuel storage pool for several years to allow decay of short-lived fission products and to reduce the rate of heat production from the spent fuel. Afterwards, it can be reprocessed or moved to long-term or interim storage.
Interim storage is most often in dry storage casks, considered to be a mature, licensed technology with low operating costs. Dry storage casks have restrictions dictated by the integrity of the fuel rod cladding and how and when the fuel is loaded into the cask. The shielding requirements of the cask must be designed to meet the conflicting requirements of gamma and neutron source terms. Higher burnup fuel places tighter restrictions on the cask. Casks are typically licensed for around 50 years but there are no technological reasons that would limit the use of dry storage up to at least 100 years.
There are radiological and life-cycle arguments in favour of reprocessing. Separating plutonium from the fuel can reduce radiotoxicity by a factor of ten, and the plutonium becomes available, along with recovered uranium, for use in MOX fuel for LWRs or directly in FBRs. This was an attractive option when it seemed that the nuclear industry would continue to grow and uranium would be scarce, and it is still being pursued as such by Japan, which has very few natural resources. In general reprocessing has fallen out of favour and is regarded by nuclear companies operating in increasingly aggressive markets as an unnecessary cost. In a 1994 study the NEA found that direct disposal had a slight cost advantage, although in fact the costs of the two options overlapped, but since then the market has changed and competition and consolidation have reduced fuel cycle costs.
The once-through fuel cycle is the norm in most countries and the UK's British Energy, for example, is lobbying hard to switch from reprocessing to the once-through cycle. This would see spent fuel transported to a conditioning and encapsulation plant before final disposal in a deep repository.
While final storage sites for intermediate and low level waste have gone into operation in most countries, high level waste sites - to house spent fuel or vitrified waste from reprocessing, and other long-lived or high heat-emitting waste - have been more problematic. In recent years the concept has moved forward, but there is support for postponement and for review of alternative solutions. International groups of experts have repeatedly confirmed that disposal is ethical, environmentally sound and safe, and that other options are, at best, complementary. Debates on this subject are not entirely neutral, as the lack of established disposal facilities is often cited by people opposing nuclear development. The lack is also used to justify ever-improved conditioning and disposal options, possibly to beyond societal significance, with the risk of siphoning R&D efforts off from more fruitful projects.
In many HLW site programmes, emphasis is on engineered barriers, but the natural or geological barriers in a deep repository play a crucial role in determining long-term safety.
In a market-driven environment the industry is less able to fund the long-term R&D needed to develop and deploy advanced fuel cycles. Political pressures and competing budget priorities have also reduced government funding for nuclear R&D.
Nuclear must also overcome other challenges. Deploying new reactor concepts and fuel cycles will always be lengthy and expensive. Multilateral or international programmes will be increasingly important in developing new products and in minimising the period from concept to reality.
The public must see that the industry is responsible in managing waste and that the effect of disposal on the environment will be very small. To do this, facilities for disposing of high level waste and spent fuel must go into operation. Work must continue on new technology or processes that will reduce the amount of waste to be disposed of, or reduce its harmful lifetime.
Systems that conserve uranium resources or use plutonium should be developed. That should include novel cycles to dispose of military plutonium, among other developments that minimise the potential to divert nuclear material for weapons purposes.
TablesToday’s commercial enrichment facilities Conversion plants and processes Commercial fuel fabrication plants HLW repository sites and laboratories