Ceramic Waste Forms for Actinides

Structural Transformations and Disordering in Zirconolite (CaZrTi2O7) at High Pressure

“…8,9 Synthetic analogues of natural zirconolite, based on the formula CaZrTi 2 O 7 , target substitution of trivalent and tetravalent actinides and lanthanide fission products on the Ca and Zr sites based on the comparable ionic radii of these species, with charge compensation introduced on the Ti site as necessary. [10][11][12][13][14][15] Actinide species incorporated within host crystalline lattices undergo alpha decay processes resulting in substantial structural damage that may eventually result in a radiation amorphized or "metamict" material as reviewed by Weber et al 16 For example, α-decay of Pu-239 affords an energetic (5.2 MeV) α-particle and a U--particle deposits its energy in ionisation processes causing relatively few atomic displacements, but recoil of the daughter atom produces 10 3 atomic displacements through ballistic collisions, within a 10 2 nm cascade. 16 Defect accumulation and cascade overlap eventually result in amorphization of the initially crystalline host material.…”

Interstitial Incorporation of Plutonium into a Low-Dimensional Potassium Borate

“…During the last two decades, significant efforts have been made to better understand the incorporation of early actinide elements (namely Th, U, Np, and Pu) into a variety of mineral phases, such as calcite (7)(8)(9)(10)(11)(12)(13)(14)(15), zircon (4,(16)(17), monazite (4,(17)(18), zirconolite (4,(18)(19)(20)(21)(22), perovskite (4,22), garnet (4), pyrochlore (4,(23)(24)(25), brucite (26), and several other systems (27)(28)(29)(30). Particularly for transuranium elements (Np and Pu), it was determined that these can also be incorporated into a series of uranium-or thorium-based minerals such as brannerite (4), ianthinite (31), schoephite, becquerelite, compreignacite, and boltwoodite (32) or even synthetic phases such as Th 2-x/2 An IV x/2 (PO 4 ) 2 (HPO 4 )·H 2 O (An = U, Np, Pu) (33), ThSiO 4 (34), and Ba 3 (UO 2 ) 2 (HPO 4 ) 2 (PO 4 ) 2 (35).…”

“…Particularly for transuranium elements (Np and Pu), it was determined that these can also be incorporated into a series of uranium-or thorium-based minerals such as brannerite (4), ianthinite (31), schoephite, becquerelite, compreignacite, and boltwoodite (32) or even synthetic phases such as Th 2-x/2 An IV x/2 (PO 4 ) 2 (HPO 4 )·H 2 O (An = U, Np, Pu) (33), ThSiO 4 (34), and Ba 3 (UO 2 ) 2 (HPO 4 ) 2 (PO 4 ) 2 (35). The majority of studies focused on examining incorporation mechanisms indicate the presence of a suitable crystallographic site in the lattice for actinide units to reside in the incorporated materials; i.e.…”

Challenges in Modeling the Degradation of Ceramic Waste Forms

“…However, glass has the disadvantages that the waste loading has to be small; devitrification is possible; glass tends to crack easily; and glass is not chemically durable in that it tends to degrade and release radionuclides over the long term [3]. As an alternative to borosilicate glass, radiation-tolerant ceramics tailored for specific waste streams and high waste loading have been the subjects of active research for nearly six decades [2][3][4][5][6][7][8][9][10][11].…”

“…Synroc-C consists of hollandite to immobilize Cs, zirconolite to immobilize actinides, perovskite to incorporate Sr, and rutile. It can accommodate up to 20% loading of high-level waste [11]. Synroc shows good radiation tolerance, and its resistance to leaching has been shown to be far superior to that of glass in laboratory experiments [6].…”