Developing Waste Forms for Transuranic Elements: Quaternary Neptunium Fluorides of the Type NaxMNp6F30 (M = Ti, V, Cr, Mn, Fe, Co, Ni, Al, Ga).

A series of quaternary Np(IV) fluorides was synthesized using a mild hydrothermal synthesis approach. The compositions are all of the type NaxMNp6F30, where M = Ti(III), V(III), Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Al(III), and Ga(III) and x = 4 for divalent metals, x = 3 for trivalent metals. The compounds all crystallize in the P-3c1 space group and are isotypic with actinide analogues NaxMAn6F30 (An = Ce, U, Th, Pu). Structure data from the neptunium crystals were combined with data from the other actinide analogues to establish the tetravalent, nine-coordinated ionic radii of neptunium (1.030(2) Å), plutonium (1.014(1) Å), and cerium (1.012(2) Å). Radiation damage studies were also carried out on a surrogate material, the cerium analogue Na3AlCe6F30, which indicates that the structure type has low resistance to amorphization. Density functional theory calculations were carried out to compute the band gaps and enthalpies of formation variations among the isotypic cerium and actinide structures to compare the stability of the structures.

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.

A series of alkali metal rare-earth borates were prepared via high-temperature flux crystal growth, and their structures were characterized by single crystal X-ray diffraction (SXRD). Na3Ln(BO3)2 (Ln = La-Lu) crystallize in the monoclinic space group P21/n, the potassium series K3Ln(BO3)2 (Ln = La-Tb) crystallize in the orthorhombic space group Pnma, while the Ln = Dy, Ho, Tm, Yb analogues crystallize in the orthorhombic space group Pnnm. To demonstrate the generality of this synthetic technique, high-entropy oxide (HEO) compositions K3Nd0.15(1)Eu0.20(1)Gd0.20(1)Dy0.22(1)Ho0.23(1)(BO3)2 and K3Nd0.26(1)Eu0.29(1)Ho0.22(1)Tm0.14(1)Yb0.10(1)(BO3)2 were obtained in single crystal form. Radiation damage investigations determined that these borates have a high radiation damage tolerance. To assess whether trivalent actinide analogues of Na3Ln(BO3)2 and K3Ln(BO3)2 would be stable, density functional theory was used to calculate their enthalpies of formation, which are favorable.

Data on Cu- and Ni-Si-Mn-rich solute clustering in a neutron irradiated austenitic stainless steel.

The data presented in this article is supplementary to the research article "Phase instabilities in austenitic steels during particle bombardment at high and low dose rates" (Levine et al.) [5]. Needle-shaped samples were prepared with focused ion beam milling from a 304L stainless steel that was irradiated with fast neutrons (E > 0.1 MeV) in the BOR-60 reactor at 318 °C to 47.5 dpa. Atom probe tomography (APT) experiments in voltage mode were then conducted on a Cameca LEAP 5000X HR. Atom position, range, and mass spectrum files after reconstruction with Cameca's IVAS software are included. Cu- and Ni-Si-Mn-rich solute nanoclusters were identified and analyzed using the Open Source Characterization of APT Reconstructions (OSCAR) program. Python code for OSCAR [4], information on the program's underlying algorithm, and sample output files are provided. A proximity histogram of a Ni-Si-Mn-rich cluster and a 1D density/solute concentration profile of a Cu-rich cluster are given to demonstrate OSCAR's analytical functionalities. The provided APT dataset is valuable for benchmarking phase instabilities in neutron-irradiated austenitic stainless steels that occur at high doses. The OSCAR program can be reused to process other APT data sets where solute nanoclustering is of interest.

Predicting structural material degradation in advanced nuclear reactors with ion irradiation.

Swelling associated with the formation and growth of cavities is among the most damaging of radiation-induced degradation modes for structural materials in advanced nuclear reactor concepts. Ion irradiation has emerged as the only practical option to rapidly assess swelling in candidate materials. For decades, researchers have tried to simulate the harsh environment in a nuclear reactor in the laboratory at an accelerated rate. Here we present the first case in which swelling in a candidate alloy irradiated ~ 2 years in a nuclear reactor was replicated using dual ion irradiation in ~ 1 day with precise control over damage rate, helium injection rate, and temperature and utilize physical models to predict the effects of radiation in reactors. The capability to predict and replicate the complex processes surrounding cavity nucleation and growth across many decades of radiation dose rate highlights the potential of accelerated radiation damage experiments. More importantly, it demonstrates the capability to predict the swelling evolution and the possibility to predict other features of the irradiated microstructure evolution that control material property degradation required to accelerate the development of new, radiation-tolerant materials.