Erich Zimmer

SGMP — an advanced method for fabrication of UO2 and mox fuel pellets

Abstract The External Gelation of Uranium (EGU) process, though originally developed for preparation of fuel particles for High-Temperature Reactors (HTR), was also found to be attractive for Sol-Gel Microsphere Pelletization (SGMP) of UO2 and mixed oxide (MOX) fuel. No major changes of the process were necessary. However, for producing “porous microsphere” carbon black was added to the broth and later burnt out from the gel micropheres. Both “porous” and “non-porous” microspheres have been easily pelletized and sintered to high densities (≥ 95% TD) at relatively low temperatures (≤ 1500 ° C) in CO2 atmosphere. The “porous” microspheres led to sintered pellets having closed pores in the diameter range of 2–5 μm. Such pellets are good for retention of fission gases and are hence recommended for water-cooled reactor fuel pins. The pellets prepared from “non-porous” microspheres had “open pores” and are suitable for LMFBR fuel pins. UO2—5% CeO2 and UO2-30% CeO2 were chosen to simulate MOX fuels for thermal and fast reactors, respectively.

Dissolution of thorium-uranium mixed oxides in concentrated nitric acid

Abstract Thorium-uranium mixed oxides, (Th, U)O 2 , of different ratios of the heavy metals were prepared by sol-gel techniques. The oxides, well characterized by physical and chemical methods, were subjected to dissolution with an excess of boiling nitric acid for 140 h. Mixed oxides with thorium concentrations up to 60% have been dissolved almost completely. At higher thorium concentrations, the fraction of the dissolved oxides decreases sharply and pure ThO 2 is not dissoluble at all. By extrapolation from the dissolution behavior of pure ThO 2 with small crystallite size, speculations about the possible dissolution mechanism have been made.

A Study of Pulse Columns for Thorium Fuel Reprocessing (I)

Two 5-m pulse columns with the same cartridge geometries have been installed for Thorex process studies. First, the differences of the aqueous and the organic continuous modes of operation have been investigated. Flow characteristics and extraction efficiencies of acetic acid and thorium nitrate have been obtained. Then, the uranium and thorium coextraction and partitioning have been carried out. The concentration profiles of thorium, uranium, and nitric acid along columns have been determined for the coextraction and the partitioning process and the Height Equivalent Theoretical Stage values have been calculated from these data.

Droplet Diameters and Axial Mixing in Pulse Columns in the Comparison of the Aqueous to Organic Continuous Mode of Operation

Two 38-mm-diam, 5-m-high pulse columns are investigated to evaluate the droplet diameters and axial mixing in the comparison of the aqueous to organic continuous mode of operation. It is observed that the average droplet diameters are dominated by pulse intensity and are independent of throughputs. Through the evaluation of axial eddy diffusivities, it is concluded that the axial diffusivity coefficient depends mainly on pulse intensity, and the value for the dispersed phase is similar to that for the continuous phase at the same pulse intensity.