Porous alumina-silica (Gubka) as a matrix for REE-TUE strip solution immobilization

The immobilisation of strip product (TUE + REE), collected at Russian research centers and laboratories during R and D on partitioning technology for liquid high-level radioactive waste (HLW), was studied using simulated solutions. Ultraporous glass crystalline material 'Gubka' (G) and multiple processing stages were used to immobilize the simulated strip product. The processing consisted of the following stages: Gubka saturation by solution - drying into Gubka pores - compaction by cold uniaxial pressing followed by sintering (CUPS) or hot uniaxial pressing (HUP). The following compositions were compacted by CUPS method: Two-phase composition: 1) G-Nd2O3 (Nd - simulator of AmIII, CmIII; REE). Three-phase compositions: 1) G-Nd2O3-M2IIIO3 (MIII=Al or Cr or Fe, Nd2O3/M2IIIO3=1) -- with the expectation of synthesising NdMIIIO3 with perovskite structure; 2) G-Nd2O3-MIVO2 (MIV=Zr or Ce; Nd2O3/MIVO2=0.3/0.7) -- with the expectation of synthesising a cubic solid solution of 0.2Nd2O3 0.7MIVO2 with fluorite structure; 3) G-Nd2O3-P2O5 (Nd2O3/P2O5 = 1) -- with the expectation of synthesising monazite (NdPO4). XRD, EMPA and SEM methods showed that G-monazite matrix was the most promising matrix for the solidification of the strip product (TUE+REE). After CUPS synthesis the samples were polyphase materials, with a crystalline phase dispersed into a aluminium silicate glassy matrix. Dense low-porosity G-monazite matrix was fabricated using HUP at 1000 deg. C and 300 kg/cm2 (29.4 MPa). (author)