Development of Transuranium Element Recovery from High-Level Radioactive Liquid Waste. Conversion TRU Oxalates to Chlorides.

Abstract

The separation methods of transuranium elements (TRUs) from high-level radioactive liquid waste (HLW) are classified into two categories, such as the wet processes and dry processes. A new partitioning process which combines the wet process and dry process has been developed by Toshiba Corporation. Figure 1 shows this process which combines oxalate precipitation and electrorefining. The oxalate precipitation yields good TRU recovery and electrorefining gives good TRU separation from HLW. There are three steps in the process. First, TRUs, lanthanides and alkaline earth elements whose oxalates are lower in solubility are recovered from HLW by the addition of oxalic acid. The previous paper(1) shows the experimental study which satisfies the requirement of 99.9% recovery of simulated TRUs from simulated HLW by the oxalate precipitation. In the second step, theseoxalates are converted to chlorides. In the final step, the TRUs are recovered on a cathode by electrorefining after dissolving the chlorides in eutectic KC1-LiC1 salt.The TRU oxalates were converted to chlorides by inducing reactions with CoCl2, HCl or CCl4 at 500 °C(2)-(4). The materials of apparatus must be using corrosion resistance at high temperature. Further, it is necessary for tetravalent TRU chlorides such as NpCl4, whose vapor pressures are high(5), to be recovered. Therefore, the conversion from oxalates to chlorides satisfies the requirements of no use of corrosive gas and lower reaction temperature.This note describes an experimental study to confirm the new partitioning process, which is found to satisfy the requirement for conversion of simulated TRU oxalates to chlorides without corrosive gas and at lower temperature.