PROCESSED SPENT FUEL DISPOSAL

LILW from conditioning and HLW from reprocessing have different impacts on deep geological repositories. The most important one relates to thermal effects and radiolysis shortly after disposal. However, the low amount produced in comparison with the co-disposed nuclear power plant spent fuel makes this effect negligible. 

It is well known that repositories studied so far have been for power reactor fuel with initial enrichment of 4% or less, being about 1% the remnant enrichment in the spent fuel inventory. Repeating these studies for research reactor fuel, including the environmental impact assessment, would be enormously expensive. Besides, criticality considerations and the susceptibility of the materials to degradation lead to the conclusion that direct disposal of RRSF cannot be considered a viable option. 

Therefore, unless the selected option considers the possibility to retrieve the remaining uranium composite existing in the spent fuel from research reactors, the trend is to effectively dilute the concentration of U to below 2% to match the remnant enrichment level of nuclear power plant spent fuel. 

Regardless of the solution adopted for the RRSF, international consensus suggests that, due to the long lived nuclides that it contains, the disposal of the processed RRSF shall be planned for a deep geological repository. 

For countries with spent fuel arising from nuclear power plants, the same deep geological repository is highly likely to be used for the relatively small amount of processed RRSF to be disposed. However, it must be underlined that the IAEA increasingly sees the need for multinational solutions for countries with small nuclear power programmes or one or more research reactors and no nuclear power programme, since individual geological repositories for these countries seems prohibitively expensive. 

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PROCESSED SPENT FUEL DISPOSAL NATIONAL CONTEXT... 

Nuclear energy, which is obtained when nucleons (protons and neutrons) are allowed to adopt lower energy arrangements and to release the excess energy as heat, does not contribute to the carbon dioxide load of the atmosphere, but it does present pollution problems of a different land radioactive waste. Optimists presume that this waste can be contained, in contrast to the burden of carbon dioxide, which spreads globally. Pessimists doubt that the waste can be contained—for thousands of years. Nuclear power depends directly on the discipline of chemistry in so far as chemical processes are used to extract and prepare the uranium fuel, to process spent fuel, and to encapsulate waste material in stable glass blocks prior to burial. Nuclear fusion, in contrast to nuclear fission, does not present such serious disposal-related problems, but it has not yet been carried out in an economic, controlled manner. 

Riel Processing, Spent-Fuel Transportation, Storage and Waste Disposal... 

The main drawback to nuclear power is the production of radioactive waste. Spent fuel from a nuclear reactor is considered a high-level radioactive waste, and remains radioactive for a veiy long time. Spent fuel consists of fission products from the U-235 and Pu-239 fission process, and also from unspent U-238, Pu-240, and other heavy metals produced during the fuel cycle. That is why special programs exist for the handling and disposal of nuclear waste. 

Nuclear power plants use fuel rods with a life span of about three years. Each year, roughly one-third of spent fuel rods are removed and stored in cooling basins, either at the reactor site or elsewhere. Typical modern nuclear power plants discharge about 30 tons of the spent fuel per reactor per year. Comparatively little of Lite radioactive wastes, as is currently reliably known worldwide, has been processed for return to the fuel cycle. Actually, fuel reprocessing causes a net increase in the volume of radioactive wastes, but, as in the ease of military wastes, they are less hazardous in the long term. Nevertheless, the wastes from reprocessing also must be disposed of with great care. 

Energy F oductlon Spent Fuel ( processing— Waste Disposal... 

The classical Purex process was designed to produce nearly pure uranium and plutonium. The Chemical Engineering Division of Argonne National Laboratory has demonstrated UREX+, an advanced aqueous process with five extraction trains that split commercial reactor spent fuel into five streams 1) a nearly pure uranium stream (95.5% of the heavy metal in the spent fuel) 2) technetium sent to transmutation (0.08 /o) 3) Pu/Np converted to MOX fuel for LWR fuel and Am/Cm for transmutation or fast-flux reactor fuel (0.962 /o) 4) Cs/Sb decay heat producers sent to interim decay storage (0.017 /o) and 5) a mixed fission product stream (3.44 /o) composed of gases and solids incorporated into a waste form for geological repository disposal.f The percentages shown are computed from Table 1. 

Development of a one-step electrochemical process to reduce LWR spent fuel (UO2) to metallic form is under development at Argonne National Laboratory The transuranic metals are separated by pyroproces-sing technology. This reduces waste that requires repository disposal. The transuranic metals could be cast into fuel suitable for the Generation IV reactors or transmuted reducing them to fission products. 

Magnox cladding, which has been removed mechanically from spent fuel rods at the start of reprocessing operations, is contaminated with small pieces of fuel and will require treatment before disposal to the environment. At present, this waste is stored under water (to eliminate any fire risk) in large concrete silos and processes are now under development for the conditioning of this waste to make it suitable for disposal. The favored processing route comprises the following operations ... 

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