Fission products, separating

Flexi-bil ity Contin-uous operation Fission-product separation U/Pu separation Ease of waste handling ... 

Many of the fission products formed in a nuclear reactor are themselves strong neutron absorbers (i.e. poisons ) and so will stop the chain reaction before all the (and Pu which has also been formed) has been consumed. If this wastage is to be avoided the irradiated fuel elements must be removed periodically and the fission products separated from the remaining uranium and the plutonijjm. Such reprocessing is of course inherent in the operation of fast-breeder reactors, but whether or not it is used for thermal reactors depends on economic and political factors. Reprocessing is currently undertaken in the UK, France and Russia but is not considered to be economic in the USA. 

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. 

Heres, X., Nicol, C., Bisel, L., Baron, P, Ramain, L. 1999. PALADIN A one step process for actinide(III)/fission product separation. Proc. GLOBAL 99, Nuclear Technology - Bridging the Millennia, Jackson Hole, WY, August 29 to September 3, pp. 585-591. 

TABLE 9.1 Fission Product Separations in Flow Systems Tc Separation ... 

Dietz, M. L. Horwitz, E. R Combining solvent extraction processes for actinide and fission product separations. In Science and Technology for Disposal of Radioactive Tank Waste, eds. W. W. Schulz and N. J. Lombardo, Plenum Press, New York, 1998, pp. 231-243. 

Now, new information on 97Y has been obtained at the fission product separator JOSEF [LAW76] which indicates that this nucleus has shell model... 

Preliminary investigation has shown that most fission products are not soluable in alkali metal nitrate melts and that they are not dissolved by addition of 100% nitric acid vapor. If these characteristics are verified by further experiments, a fission product separation is easily envisioned. One could react the fuel with the molten nitrate, dissolve the uranate with the addition of 100% nitric acid, and separate the uranium from the remaining solids, which should consist of both plutonium dioxide and fission products. 

Probably the most efficient way of eliminating the fission products is by the solvent extraction method. We are much indebted to Mr. Tepe for discussing this system with us. The solvent extraction method would permit a continuous operation and cause a holdup of only one hour in the column. As a result it would appear that such a purification increases the amount of 23 required by only 4%. However, it is likely that it will be impossible to use the solution of uranium in heavy water directly in the column because the deuterium will exchange with the hydrogen of the solvent. For this reason it will be necessary to separate first the uranium salt from the heavy water which may be a more time consuming operation than the operation of the colmnn itself and consequently increase the holdup more than the fission product separation itself does. 

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. 

Barrachina, M. and Vlllar, M. A. (JEN-160-DQ/I-54). Study of the Short-Lived Fission Products. Separation of Iodine and Xenon Fission Radionuclides. (Junta de Energia Nuclear, Madrid (Spain). Division de Quimica). 1965. 24 p. Dep. rnn. 20 41034... 

D. W. Bareis, a Continuous Fission Product Separation Process. I. Removal of the Rare Earths Lanthanum, Cerium, Praseodymium, and Neodymium) from a Typical Liquid Bismuth—Uranium Reactor Fuel by Contact with Fused LiCl-KCl Mixture, USAEC Report BNL-125, Brookhaven National Laboratory, 1951. 

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