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Nuclear power is the only energy-producing technology which takes full responsibility for all its wastes and fully costs this into the product. The amount of radioactive wastes is very small relative to wastes produced by fossil fuel electricity generation. Used nuclear fuel may be treated as a resource or simply as a waste.
The radioactivity of used fuel and all nuclear wastes diminishes with time. Safe methods for the final disposal of high-level wastes are technically proven; the international consensus is that this should be deep geological disposal.
Wastes
All parts of the nuclear fuel cycle produce some radioactive waste (radwaste) and the cost of managing and disposing of this is part of the electricity cost, i.e. it is internalized. At each stage of the fuel cycle there are proven technologies to dispose of the radioactive wastes safely.
Wastes from the nuclear fuel cycle are categorized as high-, medium- or low-level wastes by the amount of radiation that they emit. These wastes come from a number of sources and include:
Management of operational waste: Low level wastes
Low-level Wastes (LLW) are generated from hospitals, laboratories and industry, as well as the nuclear fuel cycle. It comprises paper, rags, tools, clothing, filters etc. which contain small amounts of mostly short-lived radioactivity. It is not dangerous to handle, but must be disposed of more carefully than normal garbage.
The low-level wastes arising from the whole nuclear fuel cycle represent some 90% of the total volume of radioactive waste generated during the lifetime of a nuclear power plant but contain only about 1% of the total radioactivity. To reduce its volume, it is often compacted or incinerated (in a closed container) before disposal. A 1000 MWe nuclear power reactor can be expected to produce around 100 m3 of low level waste every year.
Disposal sites for such wastes are in operation in many countries. Typically, these are shallow landfill sites, which contain the wastes safely.
Intermediate level waste
Internmediate-level wastes (ILW) contain higher radioactivity levels then LLW, and require shielding when they are handled. Only a small proportion of the intermediate-level waste remains significantly radioactive for years, so short -lived intermediate - level waste can often be disposed of with LLW.
Typically, these wastes arise from dismantled internal structures of the reactor core, which become radioactive after prolonged operation. They also include: the control rods, which regulate the nuclear reaction, the source assemblies, which are used to initiate a nuclear reaction after new fuel has been loaded, and other rods that limit the reactivity of fresh fuel.
The maintenance of a 1000 MWe nuclear power reactor produces less than 0. 5 m3 of long-lived ILW each year. If the spent fuel goes for reprocessing, then the cladding from the spent fuel adds an additional 3 m3 of ILW. Including decommissioning, each 1000 MWe reactor is reckoned to account for 70 m3 of ILW per year.
ILW from reactor operation and from reprocessing used fuel is treated and conditioned by incorporating it into cement or an organic solid (bitumen or resin) and then placing it in containers for shielding. Special packages are used for transporting long-lived intermediate level waste. These packages meet internationally approved standards that ensure that the waste is safely contained.
Disposal of ILW is underground, in specially constructed repositories not necessarioy very deep. Several countries are already doing this but in many, long-lived ILW is being safely stored and contained at interim storage facilities. Ultimately some long-lived ILW will go to deep geological disposal as with high-level waste.
High Level Wastes
There are two types of high level waste (HLW), fission products and transuranics separated from the spent fuel and the spent fuel elements themselves from the reactor core when they are not reprocessed. Both types of HLW must be treated prior to disposal. HLW from reprocessing is incorporated into solid blocks of borosilicate glass. This process is known as vitrification. For direct disposal, used fuel assemblies require encapsulation in containers made, for example, of stainless steel or copper.
In reprocessing , when the fission products are first extracted from the spent fuel they are in liquid form, having been dissolved in acid (usually nitric acid). This liquid can be safely retained in stainless steel tanks that are equipped with cooling systems until it is converted into a solid, which is a more convenient material for management, storage, transport and disposal. After drying it is incorporated into molten borosilicate glass which is allowed to solidify inside a stainless steel canister.
Vitrification produces a stable solid that has the high-level waste incorporated its structure. A year's waste from a 1000 MWe reactor is contained in 5 tonnes of such glass, or about 12 canisters 1.3 metres high and 0.4 metres in diameter. These can be readily transported and stored, with appropriate shielding
In either case however there is a cooling period of about 50 years between removal from the reactor and disposal, with the conditioned spent fuel or conditioned HLW being retained in interim storage. This is because the level of radioactivity and heat from the used fuel fall rapidly in the first few years and is down to about one thousandth of the level at discharge by 40 years. Such long term storage facilities may be at one central place as in Sweden or at the reactor site, as in the US A . They may again be underwater or dry storage, where circulating air removes the heat generated by the spent fuel. The structure and design of both the building and containers protects the outside world from radiation exposure and the fuel from potential outside hazards.
Deep Geological Disposal
At the present time, there are no disposal facilities (as opposed to storage facilities) in operation in which used fuel, not destined for reprocessing, and the waste from reprocessing can be placed. Although technical issues related to disposal have been addressed, there is currently no pressing technical need to establish such facilities, as the total volume of such wastes is relatively small. Further, the longer it is stored the easier it is to handle, due to the progressive diminution of radioactivity.
There is also an increasing reluctance to dispose of used fuel because it represents a significant energy resource which could be reprocessed at a later date to allow recycling of the uranium and plutonium.
Many countries are developing plans for disposal of HLW in geological repositories buried in stable rock formations hundreds of metres beneath the surface.
The process of selecting appropriate sits for deep geological repositories is now under way in several countries with the first expected to be commissioned some time after 2010. Finland and Sweden are well advanced with plans and site selection for direct disposal of used fuel, since their p arliaments decided to proceed on the basis that it was safe, using existing technology. The USA has opted for a final repository in Nevada . There have also been proposals for international HLW repositories in optimum geology.
Further Reading:Waste Management in the Nuclear Fuel CycleRadioactive WastesTransport of Radioactive MaterialsRadioactive Wastes - Myths and RealitiesInternational Nuclear Waste Disposal ConceptsSynrocAccelerator-driven Nuclear EnergyJapanese Waste and MOX Shipments From EuropeRadioactive waste repository & store for AustraliaThe "back end" of the nuclear fuel cycle