No abstract

A study was made of the effect of moisture on the emanation coefficient and radon flux from uranium mill tailings. A sharp rise in emanation coefficient occurred as the moisture content was increased from the absolutely dry state to 2% water by weight. The emanation coefficients from water-saturated tailings were about four times those from absolutely dry materials. Radon flux was measured from columns of dry, moist and water-saturated tailings. The highest flux came from the column filled with moist tailings. This can be explained by the effect of moisture content on the emanation coefficient. Water-saturated tailings gave the lowest flux because of the much lower diffusion coefficient of radon through water.

A study has been undertaken on the interactions of leachates from actinide-doped Synroc and three Australian granites. Leach testing was carried out on Synroc containing 237 Np, 239 Pu and 244 Cm under MCC-1 conditions in close proximity to granite specimens at 70 °C for 28 days.The presence of the granites increased the pH and reduced the total activity released from the Synroc. Preferential uptake of actinides occurred onto specific secondary minerals, especially hematite, other Fe-oxides/hydroxides, leucoxene, sericite, chlorite and clays. The controlling mechanisms for fixation of actinides on the granties appeared to be adsorption, ionic exchange and reduction by Fe(II). The high sorptive capacity of the alteration minerals significantly reduced the concentration of actinides in solution indicating that hydrothermally-altered granites, with a significant proportion of secondary minerals present, are capable of removing actinides from groundwaters.

The phase chemistries and microstructures of titanate-based ceramics containing simulated high-level nuclear waste with varying sodium contents were compared. Incorporation of relatively low sodium levels (=0.9 wt% NazO) resulted in more complex phase assemblages. The principal hosts for sodium were hibonite and freudenbergite, and, when iron and sodium were present in combination, loveringite was also stabilized. During fabrication, oxygen potential was controlled by Ti-TiOz or TiHz-TiJOS solid-state buffers. These metal and hydride oxygen getters behaved similarly, neither disturbing the phase assemblages nor significantly altering the partitioning of waste elements between radiophases. It is believed that the hydrothermal stability of the sodiumbearing ceramics (containing up to 2.7 wt% NazO) will be comparable to sodium-free material, since less durable sodium-rich phases are encapsulated in a resistant matrix. Extensive formation of glassy phases may cause embrittlement at higher sodium loadings.