Spent nuclear fuel reprocessing purex process

RADIATION EFFECTS IN SPENT NUCLEAR FUEL REPROCESSING 2.1. Purex Process... 

In fact, the first description of such a scheme, involving the application of SFE to spent nuclear fuel reprocessing, appeared shortly after publication of these results. Specifically, Smart et al.43 outlined two possible approaches to SC-C02-based reprocessing. In the first, dubbed the wet SF-PUREX process, SC-C02 merely serves as a replacement for the organic solvent (i.e., a normal paraffinic hydrocarbon) used in... 

FIGURE 2.11 Generic description of the PUREX process. (Based on NBA, Spent nuclear fuel reprocessing flowsheet, OECD Nuclear Energy Agency, Paris, France, NEA/NSC/ WPEC/DOC(2012)15, 2012.)... 

The centrifugal contactor was first used to reprocess spent nuclear fuel at the SRS in 1966 (Webster et al., 1969). For almost 40 years, this 18-stage 25-cm SRL contactor was used for the extraction and scrub sections (the A-bank) of the PUREX (plutonium-uranium extraction) process at the SRS. Contactor operation stopped when the facility in which they were housed was shut down in 2003. This 18-stage contactor replaced a 24-stage mixer-settler. Mixer-settlers continued to be used for the rest of the processing, as most of the radiation was removed in the A-bank. The ability to... 

The CTH actinide separation process was developed as a possible means to reduce the expected long term dose to man from a geologic repository containing solidified radioactive waste from the reprocessing of spent nuclear fuel The distribution data for the elements present in significant amounts in the high level liquid waste (HLLW) from a Purex plant, the general principles and the flowsheet have been described in detail elsewhere A... 

The Purex process is the only one with commercial-scale operating history. This military technology has been modified to treat domestic spent nuclear fuel. The focus of international commercial efforts to reprocess domestic spent fuel is to recover uranium and plutonium in the spent fuel. 

Some countries, e.g., France, Japan, Russia, and the United Kingdom have chosen to reprocess their spent nuclear fuel to recycle uranium and plutonium as nuclear fuel and to obtain a high active waste (HAW) firaction that is less radiotoxic than the spent fuel itself. In this process, very high separation factors are necessary. The fission product activity has to be reduced by a factor of > 10 and the separation factor between uranium and plutonium must be at least 2 x lO. All full-scale reprocessing processes are based on solvent extraction, and today the plutonium uranium redox extraction (PUREX) process dominates the market completely. 

The simplified PUREX method, in which purification processes for Pu and U are eliminated, could be considered. Centralized reprocessing is assumed. The spent nuclear fuel (SNF) will be reprocessed and only HLW will be discarded minor actinides (MAs) could be recycled, if MA recovery and MA fuel fabrication processes are established. 

Organophosphoras compounds have since become the most-used neutral extractants. The ester tributyl phosphate (TBP) especially has become very important as the extractant of the Purex process, used almost exclusively in all modem reprocessing of spent nuclear fuels. Also, with these extractants, the actinides are generally extracted as nitrates [161,162]. 

The solvent extraction process that uses TBP solutions to recover plutonium and uranium from irradiated nuclear fuels is called Purex (plutonium uranium extraction). The Purex process provides recovery of more than 99% of both uranium and plutonium with excellent decontamination of both elements from fission products. The Purex process is used worldwide to reprocess spent reactor fuel. During the last several decades, many variations of the Purex process have been developed and demonstrated on a plant scale. 

Reprocessing is based on liquid-liquid extraction for the recovery of uranium and plutonium from used nuclear fuel (PUREX process). The spent fuel is first dissolved in nitric acid. After the dissolution step and the removal of fine insoluble solids, an organic solvent composed of 30% TriButyl Phosphate (TBP) in TetraPropylene Hydrogenated (TPH) or Isopar L is used to recover both uranium and plutonium the great majority of fission products remain in the aqueous nitric acid phase. Once separated from the fission products, back-extraction combined with a reduction of Pu(I V) to Pu(III) allows plutonium to be separated from uranium these two compounds can be recycled.2... 

The extended radiation time for the domestic fuel increases the quantity of fission products and the higher actinides. Pure plutonium product poses nuclear weapons proliferation risk and is the primary reason reprocessing is not practiced in the United States. The modified PUREX process has been practiced on an industrial scale in Europe and supports the production of mixed uranium-plutonium fuel. Blended UO2 and PUO2 powder is compacted and sinter to form the mixed oxide (MOX) fuel pellets much like the enriched UO2 fuel. Natural and depleted uranium can be used to prepare MOX fuel and is the demonstrated option to recover fuel values from spent fuel. 

The PUREX process for reprocessing spent nuclear reactor fuels was developed in the United States and first used at the US Atomic Energy Commission (AEC) Savannah River Site in 1954. It was used next at the US AEC Hanford site in 1956, and soon thereafter achieved worldwide acceptance as the premier fuel-reprocessing scheme. 

The dry process for reprocessing of nuclear spent fuel should in principle greatly reduce generation of liquid wastes such as those in the current Purex process. Reaction (9) occurs efficiently for UO3 in supercritical CO2 but not for UO2. According to our experiments, in the case of UO2, an oxidizing agent such as H2O2 has been shown to promote the dissolution of the oxide in supercritical CO2 (35). 

The main methods used for reprocessing of SNF flowsheet were reviewed in a 120 pages report by the Nuclear Energy Agency (NEA 2012). The three main processes are the so-called hydrometallurgy processes (PUREX and UREX), pyromet-allurgy processes and its variations, and the fluoride volatility process (quite like the method used at the uranium conversion facilities discussed in Chapter 1). The report reviewed in detail several of these processes that are deployed in different facilities for various types of spent fuel (NEA 2012). In this section, we shall try to briefly present an overview of the main points and the analytical aspects. 

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