Ceramic Mineral Waste-Forms for Nuclear Waste Immobilization

Abstract

Crystalline ceramics are intensively investigated as effective materials in various nuclear energy applications, such as inert matrix and accident tolerant fuels and nuclear waste immobilization. This paper presents an analysis of the current status of work in this field of material sciences. We have considered inorganic materials characterized by different structures, including simple oxides with fluorite structure, complex oxides (pyrochlore, murataite, zirconolite, perovskite, hollandite, garnet, crichtonite, freudenbergite, and P-pollucite), simple silicates (zircon/thorite/coffinite, titanite (sphen), britholite), framework silicates (zeolite, pollucite, nepheline /leucite, sodalite, cancrinite, micas structures), phosphates (monazite, xenotime, apatite, kosnarite (NZP), langbeinite, thorium phosphate diphosphate, struvite, meta-ankoleite), and aluminates with a magnetoplumbite structure. These materials can contain in their composition various cations in different combinations and ratios: Li–Cs, Tl, Ag, Be–Ba, Pb, Mn, Co, Ni, Cu, Cd, B, Al, Fe, Ga, Sc, Cr, V, Sb, Nb, Ta, La, Ce, rare-earth elements (REEs), Si, Ti, Zr, Hf, Sn, Bi, Nb, Th, U, Np, Pu, Am and Cm. They can be prepared in the form of powders, including nano-powders, as well as in form of monolith (bulk) ceramics. To produce ceramics, cold pressing and sintering (frittage), hot pressing, hot isostatic pressing and spark plasma sintering (SPS) can be used. The SPS method is now considered as one of most promising in applications with actual radioactive substances, enabling a densification of up to 98–99.9% to be achieved in a few minutes. Characteristics of the structures obtained (e.g., syngony, unit cell parameters, drawings) are described based upon an analysis of 462 publications.

Partitioning of rare earths in multiphase nuclear waste glass‐ceramics

“…The presence of Ca and/or Zr in a keiviite‐type phase is supported by mineralogy, since similar structures are formed in CaZrSi 2 O 7 gittinsite, 63 CaZrTi 2 O 7 zirconolite‐2M, and K 2 ZrTi 2 O 7 khibinskite 64 . It is well‐known that Ca + Zr is a frequent substitution in crystals for 2 RE atoms 37,49 …”

“…Rare‐earth oxyapatites have been under intensive investigation for decades as crystalline phases for immobilization of nuclear waste. There are two RE sites in this structure which substitute many different large ions, including alkali (Na), alkaline earth (Ca, Sr, Ba), RE, and actinide metals (Th, U, Np, Pu, Am, Cm, trivalent, and tetravalent), making it a very flexible crystal for incorporating multiple elements 48,49 . The formation of an oxyapatite phase is highly desirable, due to the flexibility to accommodate various cations of many sizes, including large fission products, and the high chemical durability due to the high fraction of SiO 2 50 .…”

Pyrochlore glass‐ceramics fabricated via both sintering and hot isostatic pressing for minor actinide immobilization

“…Pyrochlore‐structured materials (with general formula A 2 B 2 X 6 Y, in which A and B are 8‐ and 6‐coordinated cation sites, and X and Y are 4‐coordinated anion sites) have long been recognized as suitable host phases for incorporating a wide range of cations including minor actinides 30‐34 . Among them, titanate pyrochlores (A 2 Ti 2 O 7 ) have been extensively studied 35‐38 . Pyrochlore glass composite materials 39 were first proposed and made by mixing glass powder with crystalline pyrochlore and sintering at <700°C.…”

Study of the Incorporation of Biomass Bottom Ashes in Ceramic Materials for the Manufacture of Bricks and Evaluation of Their Leachates

“…This waste is classified as non-hazardous; however, it has high percentages of some chemical elements that can present environmental problems. Therefore, the use of these biomass bottom ashes has a triple function: firstly, to eliminate the deposition of this waste in a landfill; secondly, to obtain ceramic material, brick, cheaper; and thirdly, to retain the chemical elements that may cause damage to the environment [42].…”