DOE OSTI2013
During the early stages of spent fuel reprocessing, the fuel rods are cut and dissolved to separate the solid metallic parts of the rods (cladding and end pieces) from the radioactive nitric acid solution containing uranium, plutonium, minor actinides and fission products (FP). This solution contains small, solid particles produced during the shearing process. These small particles, known as 'fines', are then separated from the liquid by centrifugation. At the La Hague plant in France, the fines solution is transferred to the vitrification facilities to be incorporated into borosilicate glass along with the highly radioactive FP solution. These fines are also composed of Zr, Mo and other noble metals (i.e. Ru, Pd, Rh, etc.) that are added before vitrification to the the FP solution that already contained noble metals. As noble metals has the potential to modify the glass properties (including viscosity, electrical conductivity, etc.) and to be affected by sedimentation inside the melter, their behavior in borosilicate glass has been studied in depth over the years by the AREVA and CEA teams which are now working together in the Joint Vitrification Laboratory (LCV). At La Hague, the R7 vitrification facility started operation in 1989 using induction-heated metallic melter technology and was quickly followed by the T7 vitrification facility in 1992. Incorporating the fines into glass has been a challenge since operation began, and has given rise to several R and D studies resulting in a number of technological enhancements to improve the mixing capability of the melters (multiple bubbling technology and mechanical stirring in the mid-90's). Nowadays, the incorporation of fines into R7T7 glass is well understood and process adaptations are deployed in the La Hague facilities to increase the operating flexibility of the melters. The paper will briefly describe the fines production mechanisms, give details of the resulting fines characteristics, explain how the metallic particles can influence the glass properties and challenge vitrification technologies and finally, give a rundown of the R and D efforts which have produced innovative solutions contributing to the operational excellence of AREVA's vitrification facilities in the La Hague reprocessing plant. (authors)
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗