When testing the UNEX process for recovery of the Cs+Sr and An+REE fractions, the following results for recovery of radionuclides were attained: Cs — 99.7%, Sr > 99.98%, Eu > 99.92%. These data permit the bulk HLW being treated to be transferred into the low-level waste (LLW) category, suitable for cementing and subsequent near-surface storage. Barium and lead were almost completely co-extracted with long-lived radionuclides in this process; zirconium and molybdenum were also partly co-extracted. Sodium, potassium iron and mercury remained in the low-level raffinate. In this UNEX process variant, the recovery of HLW components is shown in Table 9.14.

Results of UNEX process tests with the combined recovery of Cs, Sr, An and REE (flowsheet in Fig. 9.6)

When testing the UNEX process, prime attention was given to the work flow which included the combined recovery of Cs, Sr, An and REE into one high-level product to be solidified. It was necessary to reach a degree of

radionuclide recovery such that the UNEX-process raffinate conforms to standards established for LLW. The distribution of radionuclides obtained from tests on real HLW in the Idaho National Laboratory is presented in Table 9.15. The distribution of HLW macrocomponents over the workflow products is shown in Table 9.16.

The results of testing show that the recovery rates for Cs, Sr and An are equal to 99.4%, 99.995% and 99.96%, respectively. These recovery rates are sufficient to move the raffinate (the bulk of the wastes being treated) into the LLW category.

The combined stripping of radionuclides was carried out effectively by a solution containing 1 M guanidine carbonate and 20 g/l DTPA. The HLW macrocomponents Ba and Pb were extracted almost completely, whilst Zr, Mo, K, Ca and Fe were only partly extracted (by 87%, 32%, 28%, 10% and 8%, respectively).