RECYCLING FUEL
Any spent fuel still contains some of the original U-235 as well as much of the plutonium which has been formed in the reactor; in total some 96 percent of the original uranium and over half of the original energy content (ignoring U-238).
Reprocessing, such as undertaken in Europe, separates this uranium and plutonium from the actual wastes so that they can be recycled for use in a nuclear reactor as a mixed oxide fuel. This is the "closed fuel cycle".
(This is very much what is to happen with the tiny quantities of spent fuel from the Australian research reactor at Lucas Heights near Sydney. Some of this spent fuel has been returned to Europe for reprocessing, and the small amount of separated waste will eventually be returned to Australia for disposal as intermediate-level waste.)
The plutonium arising from reprocessing commercial fuel, though only about one percent of the spent fuel, is recycled through a mixed oxide (MOX) fuel fabrication plant where it is mixed with depleted uranium oxide in fresh fuel.
European reactors currently use over five tonnes of plutonium per year in fresh MOX fuel, though all nuclear power reactors routinely burn much of the plutonium which is continually formed within them by neutron capture.
The use of MOX simply means that some plutonium is incorporated as part of the fresh fuel. (Plutonium arising from the civil nuclear fuel cycle is not suitable for bombs because it contains far too much of the Pu-240 isotope, due to the length of time the fuel has been in the reactor.)
Major commercial reprocessing plants are operating in France and UK, with capacity of some 4700 tonnes per year and cumulative civilian experience of 60,000 tonnes over 40 years. These also undertake reprocessing for utilities in other countries, notably Japan, which has made over 140 shipments of spent fuel to Europe since 1979. At present most Japanese spent fuel is reprocessed in Europe, with the vitrified waste and the recovered U and Pu (as MOX) being returned to Japan to be recycled.
COST OF RADIOACTIVE WASTE MANAGEMENT:
Financial provisions are made for the management of civilian radioactive waste of all kinds. The costs of managing and disposing of wastes from nuclear power plants represent about 5 percent of the total costs of electricity generated.
Many nuclear utilities are required by governments to put aside a levy (eg 0.1 cents per kilowatt hour in USA) to provide for management and disposal of wastes. At the end of 1998 some US$ 15 billion had been committed to the US waste fund by electricity consumers.
DISPOSING OF HIGH-LEVEL WASTES:
In 1997, considering 20 countries which account for most of the world's nuclear power generation: storage capacity at the reactors was 148,000 tonnes of spent fuel, with 59 percent of this utilised. Away from reactor storage capacity was 78,000 t, with 44 percent utilised. Annual arisings are about 12,000 tonnes. Final disposal is thus not urgent.
France is furthest ahead with preparation for disposal of high-level waste. In 1989 and 1992 it commissioned commercial plants to vitrify high-level waste following reprocessing of oxide fuel, though facilities exist elsewhere, notably UK and Belgium. Capacity of these western European plants is 2500 canisters (1000 t) per year and some have been operating for 18 years.
The Australian Synroc (synthetic rock) is a more sophisticated way to
immobilize such waste, and this process may eventually come into commercial use for civil wastes (it is curently being developed for US military wastes).
The process of selecting appropriate deep final repositories is now underway in several countries with the first expected to be commissioned some time after 2010. Sweden is well advanced with plans for direct disposal of spent fuel, its Parliament having decided that this, using existing technology, is acceptably safe.
The USA has opted for a final repository in Nevada. There is also a proposal for an international high-level waste repository in optimum geology, - Australia is a possible location.
To date there has been no practical need for final repositories for high-level waste, as surface storage for 30-50 yrs is first required for heat and radioactivity to dissipate to facilitate final disposal.
NATURE'S OWN NUCLEAR WASTE REPOSITORY:
Geological disposal of radioactive materials is congruent with natural processes. Nature has already proven that geological isolation is possible through several natural examples (or "analogues").
The most significant case occurred almost 2 billion years ago at Oklo in what is now Gabon in West Africa, where six spontaneous nuclear reactions occurred within a rich vein of uranium ore. (At that time the concentration of U-235 in all natural uranium was about 3 percent.)
These natural nuclear reactors continued for about 500,000 years before dying away. They produced all the radio-nuclides found in high-level waste, including over 5 tones of fission products and 1.5 tones of plutonium.
The radio-nuclides remained at the site and eventually decayed into non-radioactive elements. The study of such natural phenomena is an important component in the assessment of geologic repositories and is the subject of several international research projects.
However, it must be noted that the Oklo reactions proceeded because groundwater was present as a moderator in the "enriched" and permeable uranium ore. An important criterion for artificial repositories is that they are likely to stay dry.
Source: www.uic.com.au
© 2000 Mena Report (www.menareport.com)
