Radwaste Immobilisation Using Microspheres
Immobilisation of Long-lived Radionuclides Using Ultraporous Blocks Based on Thermostable Microspheres
Tech Area / Field
- ENV-APC/Air Pollution and Control/Environment
8 Project completed
Senior Project Manager
Ryabeva E V
Khlopin Radium Institute, Russia, St Petersburg
- Mining and Chemical Complex, Russia, Krasnoyarsk reg., Zheleznogorsk\nSiberian Branch of RAS / Krasnoyarsk Scientific Center, Russia, Krasnoyarsk reg., Krasnoyarsk-26
- Idaho National Engineering and Environmental Laboratory, USA, ID, Idaho Falls
Project summaryAt a number of scientific centers porous inorganic materials were studied as a primary matrix for immobilization of long-lived radionuclides with their following disposal.
For these purposes the following materials were used: porous glasses (P.Macedo, Catholic University, US); foam corundum (V.Zakharov, Institute of Physical Chemistry, RF); silica gel (A.Nardova, Institute of Chemical Technology, RF).
Scientists of the V. G. Khlopin Radium Institute over many years (1975-1985) had studied porous fireclay (chamotte) and diatomite as matrices for RW immobilization. However, the saturation of these matrices with waste components occurs only at temperatures of solution boiling, and for drying in pores additional heating is necessary.
Within the framework of the Project a new approach for porous matrices using based on thermostable glasscrystalline microspheres the size 10-400 mm is planned to realise.
Microspheres are called glass-crystalline as they consist of crystalline phases and an X-ray amorphous phase (glass). Ceramic blocks for radionuclide immobilization will be formed from glass-crystalline microspheres of two types. The first type includes aluminosilicate hollow microspheres. The size of microspheres is 0.10–0.16 mm, the wall thickness is 5-10 mm. The microspheres are characterized by a high content of the X-ray-amorphous phase of composition CaOЧAl2O3Ч3SiO2 – 80 %. The main crystalline phase is SiO2 with minor inclusions of magnetite and hematite.
The second type includes magnetic vitroceramic mictospheres. The active component includes spinel phase (80 mass %) of solid solution of magnetite and Mg (Mn)-ferrite and a-Fe2O3 phase (~ 5-7 mass %). The high temperature calcium silicate eutectic of composition CaOЧ3SiO2 and/or CaOЧSiO2 is used as a binder.
The formation of ultraporous blocks from these microspheres gives birth to unique surface-active properties that are responsible for rapid and complete impregnation of blocks with waste solution at room temperature. Then, when blocks are removed from solution, due to the difference in partial pressure of water inside blocks and on their surface, a fast drying of matrix occurs.
Preliminary studies have shown the feasibility of using the ultraporous matrices formed from hollow or filled microspheres the size of 10-400 mm with different chemical composition for immobilization of such long-lived radionuclides as 99Tc, 95Zr, Np and Pu.
The combination of ultraporous blocks properties with possibility of precipitation in pores matrices of long-lived radionuclide oxides provides a means for reliable immobilization of long-lived radionuclides with a sharp volume reduction, which can approve ratio 1:40, depending on the salt concentration in liquid waste.
Collaborators from USA will serve to information distribution among scientists and organizations interesting in plutonium waste immobilization problems and will help to use these results in practice.
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