Reprocessing of nuclear fuels by fluoride volatilization with sulfur hexafluoride

A new procedure was developed for the reprocessing of nuclear fuels by fluoride volatilization, based on the fact that uranium or other uranium containing fuels can be fluorinated in a single step to uranium hexafluoride with sulfur hexafluoride at temperatures above 800° C. The essential reactions taking place can be represented by the following equations : U0 $_{2}$ + SF $_{6}$ - -> UF $_{6}$ + S0 $_{2}$ / UC $_{2}$ + SF $_{6}$ + 3O $_{2}$ - -> UF $_{6}$ + 2CO $_{2}$ + SO $_{2}$ / U + SF $_{6}$ + O $_{2}$ - -> UF $_{6}$ + SO $_{2}$ / Advantageous for the use of sulfur hexafluoride is its property to be noncorrosive up to temperatures of about 500° C. In order to perform the process, the fuels are first pulverized in a known manner and then fluorinated either with pure sulfur hexafluoride alone or together with oxidation agents like oxygen, air, manganese dioxide or others. The fluorination can be done in two steps. At first the starting material is fluorinated at temperatures between 700° C and 800° C, separating the non volatile uranyl fluoride from the easily volatile fission product fluorides. Afterwards, in the second step the U02 F is transformed to the easily volatile UF6 at about 900° C. For the reprocessing of coated particle containing fuels it has proved appropriate, either to crack and pulverize these particles prior to fluorination or to treat them at temperatures of about 900° C up to 1100° C with oxygen or a mixture of oxygen and sulfur hexafluoride, eventually in the presence of combustion catalysts. The fluorination can be achieved using either the fluidized bed or the conventional rotating oven technique. As contructing material for the ovens, besides others; especially pure alumina has stood the test. The advantages of the new procedure are not only its simplicity and economy, another important fact is the absolute untoxicity of sulfur hexafluoride. lt does not act corrosive on any part of the gas inlet system. Small amounts of fluorine contained in the off-gas stream may be reconverted into sulfur hexafluoride by reaction with sulfur. This adds another advantage of re-using the so formed sulfur rexafluoride. A required high factor of recontamination of the formed uranium hexafluoride may be achieved applying the known absorption-desorption technique on sodium fluoride columns