SPENT FUEL PROCESSING

It is clearly understood that at some time in the future it will be necessary to process the RRSF. Moreover, several factors may anticipate the need for processing the spent fuel and making provisions for the subsequent disposal of its derivatives. One reason is the end of the US Foreign Research Reactor Spent Fuel Acceptance Programme in 2019. Another reason could be the reduction in research reactor utilization due to the replacement by alternative technologies to produce neutron fluxes and radioisotopes. This, consequently, could lead to the closure of many research reactors and their associated operational and interim storage facilities. 

For spent fuel processing, two main approaches can be considered conditioning for disposal, and reprocessing. Both processes produce long lived radioactive wastes that need to be disposed of in deep geological repositories. The main differences between them are the type and the final volume of waste to be disposed. 

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Collins, E.D., Benker, D.E., Felker, L.K. et al. 2005. Development of the UREX + 3 flowsheet - An advanced separations process for spent fuel processing. ANS 2005 Winter Meeting, Washington, DC, November 17. 

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

The characteristics of the refurbishing site and its facilities must also be integrated into the overall design, and will take into account spent fuel processing, waste treatment, and disposition of other materials and components. The extent to which other equipment is refurbished may also influence the character of the site. A barge-mounted system might be entirely refurbished therefore, the site design would need to consider this entire refurbishment activity. 

The indefinite deferral of or lack of decision about the next activity of RRSF management, spent fuel processing, might lead to the extended interim storage option. 

The regional countries share a common strategy for spent fuel processing and join in a partnership to install a conditioning plant in one of the partner countries. The plant will process the whole spent fuel inventory (turnover and backlog). 

Currently, aluminium based spent fuels from research reactors are in operational and interim wet storage. However, for an eventual extended storage as well as for disposal, there are some concerns about the suitability of the aluminium as a matrix resistant to water corrosion. Therefore, the preferred alternatives are extended storage in dry conditions and disposal of the derivatives from spent fuel processing instead of its direct disposal. 

Masson, M., et al., 2006. Block-type HTGR spent fuel processing CEA investigation program and initial results. Nuclear Engineering and Design 236, 516—525. 

An estimated 4 Ci of cbuld have been in the 230 MTU of spent fuel processed at the Nuclear Fuel Services plant at West Valley, NY, depending upon the reactor exposure of the fuels. Most of this probably was sent to the high level waste storage tanks on site. 

If the spent fuel is processed in a nuclear fuel reprocessing plant, the radioactive iodine species (elemental iodine and methyl iodide) trapped in the spent fuel elements ate ultimately released into dissolver off gases. The radioactive iodine may then be captured by chemisorption on molecular sieve 2eohtes containing silver (89). 

In addition, solvent extraction is appHed to the processing of other metals for the nuclear industry and to the reprocessing of spent fuels (see Nuclearreactors). It is commercially used for the cobalt—nickel separation prior to electrowinning in chloride electrolyte. Both extraction columns and mixer-settlers are in use. 

By-Products. The PUREX process is efficient at separating uranium and plutonium from everything else in the spent fuel. Within the high level waste stream are a number of components which have, from time to time, been sufficiendy interesting to warrant their recovery. The decision to recover a particular isotope is usually based on a combination of market incentives and desired waste reduction. 

Off-Gas Treatment. Before the advent of the shear, the gases released from the spent fuel were mixed with the entire dissolver off-gas flow. Newer shear designs contain the fission gases and provide the opportunity for more efficient treatment. The gaseous fission products krypton and xenon are chemically inert and are released into the off-gas system as soon as the fuel cladding is breached. Efficient recovery of these isotopes requires capture at the point of release, before dilution with large quantities of air. Two processes have been developed, a cryogenic distillation and a Freon absorption. 

When reactor-grade plutonium is left in spent fuel, the large size of the fuel assembhes and the lethal radiation fields make it extremely difficult to divert the material covertly. Once the reactor-grade plutonium is separated in the commercial reprocessing option, however, the radiation barrier is almost eliminated, and in certain steps of the process the plutonium is in powder or Hquid form, which is much more easily diverted than large, bulky fuel... 

The licensing process consists of two steps construction and operating license that must be completed before fuel loading. Licensing covers radiological safety, environmental protection, and antitru,st considerations. Activities not defined as production or utilization of special nuclear material (SNM), use simple one-step. Materials Licenses, for the possession of radioactive materials. Examples are uranium mills, solution recovery plants, UO fabrication plants, interim spent fuel storage, and isotopic separation plants. 

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. 

Perhaps there should be centralized areas for storage of spent fuel from present reactor types. These storage areas should be adjacent to reprocessing plants which would be built to process the spent fuel to provide the new fuel for the Fast Reactors going on line. 

See for example Electrometallurgical Techniques for DOE Spent Fuel Treatment Final Report, National Research Council, National Academy Press, Washington, D.C., 2000 Alternatives for High-Level Waste Salt Processing at the Savannah River Site, National Research Council, National Academy Press, Washington, D.C., 2000. 

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