A Density-Functional Theory Structural Database for Discovery of Novel Actinide Waste Forms

Abstract

While high-level nuclear waste is effectively incorporated into borosilicate glasses for disposal, issues remain for handling transuranic (TRU) elements. Computational methods can be used to increase the efficiency for novel waste form discovery that can sequester specific species within different waste streams. Density-functional theory databases, such as the Materials Project and the Open Quantum Materials Database, have aided in the discovery of new materials with targeted properties. This paper discusses a structural database to aid in the discovery of hierarchal waste form materials. Formation enthalpies for over 500 oxideframework crystal structures containing TRU elements were calculated and ranked. The results suggest that phosphate frameworks are highly promising for forming stable TRU-containing waste forms. This information led to the synthesis of a novel uranium phosphate crystal that had a crystal structure similar to that proposed by the database, encouraging its use for other TRU materials.

Rb2Ln[Si2O6]F (Ln = Y, Eu–Lu): Flux Synthesis, Structure Determination, and DFT-Calculated Formation Enthalpies of a Series of Mixed-Anion Rare Earth Cyclosilicates

“…Previous work by our group demonstrated that one can use the host structure for density functional theory (DFT) calculations that determine the 0 K heat of formation of hypothetical TRU containing compositions. For example, DFT calculations for A 2 M IV Si 6 O 15 (A = Na, K, Rb, Cs; M = Ce, Th, U, Np, Pu) compositions correctly predicted the stability of Cs 2 PuSi 6 O 15 , leading to the synthesis and structure determination of Cs 2 PuSi 6 O 15 . , To extend this work to a new family of silicate structures, we again employed DFT calculations to predict the 0 K formation enthalpies for the silicate fluoride structures reported herein. We are applying this methodology as an early screening tool to build on our previous work that demonstrated the utility of DFT-computed formation enthalpies for yielding dependable estimations of the relative stability of TRU containing silicates in order to follow up, when warranted, with attempts at synthesizing the TRU containing compositions. , …”

Flux Crystal Growth of the Extended Structure Pu(V) Borate Na2(PuO2)(BO3)

“…Specifically, we employed the rotationally invariant approach of Dudarev et al with the Hubbard correction of 4.0 eV on the plutonium atoms . This choice of correction was found to be consistent with the previously recognized methods used for the development of the structural database of the Center for Hierarchical Waste Form Materials as well as the Open Quantum Materials Database …”

Crystallization of A3Ln(BO3)2 (A = Na, K; Ln = Lanthanide) from a Boric Acid Containing Hydroxide Melt: Synthesis and Investigation of Lanthanide Borates as Potential Nuclear Waste Forms

“…To investigate the phase stability of transuranic element containing borate salts, we selected Na 3 Nd­(BO 3 ) 2 (space group P 2 1 / n ), Na 3 Tm­(BO 3 ) 2 (space group P 2 1 / n ), K 3 Nd­(BO 3 ) 2 (space group Pnma ), and K 3 Tm­(BO 3 ) 2 (space group Pnnm ) as unique parent structures and substituted Nd and Tm with Am and Cm (as well as Np and Pu) to construct the daughter compounds. We have followed the established methods by the Open Quantum Materials Database (OQMD) and Center for Hierarchical Waste Form Materials (CHWM) structural database to examine the energetics of parent and daughter prototypical structures. Electronic structure calculations were performed with density functional theory (DFT) , using the projector augmented-wave (PAW) method as implemented in the Vienna Ab initio Simulation Package (VASP). − Our calculations used the Perdew–Burke–Ernzerhof (PBE) for the exchange–correlation functional.…”