Uranium reprocessing irradiated nuclear fuel

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. 

RepU that is defined as uranium recovered from reprocessed irradiated nuclear fuel (also known as spent fuel) and thus will contain artificial uranium isotopes like U and (and also traces of other actinides and fission products) or SEU for slightly enriched uranium that contains 0.9%-2.0% of... 

Applicability of SFE to nuclear fuel reprocessing has been proposed by Smart and Wai et al. (17, 18). We have developed a new process which employs a high pressure mixture of TBP-HNO3-H2O-CO2 as is described in this chapter and this approach has indicated a very efEcient extraction of uranium from UO2. Now, the nuclear industries have paid attention to the applications of SFE to future processes. In Japan, we have started a four-year project with nuclear plant construction companies to demonstrate uranium and plutonium extraction from a mixed oxide fuel using the high pressure mixture. On the other hand, uranium and plutonium will be extracted from the irradiated nuclear fuel with TBP(HN03)i.s(H20)o.6 in the same project. 

In production of fuel for a fast reactor, uranium — natural or depleted — is only needed to make up for the fission products separated during reprocessing of irradiated nuclear fuel (INF), which accounts for about 10% of the fresh fuel mass. For a thermal reactor, natural uranium is enriched to a required level, with roughly 10% of the mined uranium going into fuel, while its remaining 90% ends up in the tails of enrichment processes and is not involved in energy generation. 

Nuclear fuel reprocessing was first undertaken with the sole purpose of recovering plutonium, for weapons use, from uranium irradiated in nuclear reactors. These reactors, called the production reactors, were dedicated to transmuting as much of the uranium as possible to plutonium. From its original scope of recovering exclusively plutonium, with no attempts to either recover or recycle uranium, nuclear fuel reprocessing has since grown into a much more sophisticated and complex operation with expanded scope. It is now called upon to separate uranium and plutonium from the fission products, and to purify these elements to levels at which these fissile materials can be conveniently recycled for reuse. The present scope also extends to fission products separation and concentration. 

Viewed in the context of the actinide lifespan, the nuclear fuel cycle involves the diversion of actinides from their natural decay sequence into an accelerated fission decay sequence. The radioactive by-products of this energy producing process will themselves ultimately decay but along quite different pathways. Coordination chemistry plays a role at various stages in this diversionary process, the most prominent being in the extraction of actinides from ore concentrate and the reprocessing of irradiated fuel. However, before considering these topics in detail it is appropriate to consider briefly the vital role played by coordination chemistry in the formation of uranium ore deposits. 

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