Density Functional Theory (DFT) studies on extraction of Europium and Americium from Spent Nuclear Waste

Abstract

Spent nuclear waste produced by nuclear reactors containing several long-lived radioactive nuclei, including uranium, plutonium, Fission products, and minor actinides (Np, Am, Cm), is hazardous. Extraction of highly radioactive nuclides with longer half-lives, in particular minor actinides, is required for safe and long-term waste disposal. However, it is a very difficult and challenging step in the spent nuclear fuel reprocessing to separate trivalent actinides, particularly Am+3 from trivalent lanthanides i.e., Eu+3

, due to their similar physiochemical properties such as chemical nature, oxidation state, and ionic radii. In this work, Density Functional Theory (DFT) calculations at the energy level of B3LYP/SDD hybrid density functional were conducted to evaluate the extraction behavior of Am+3 and Eu+3 metal with the organo phosphinodithioic acid ligand and its derivatives in the ratios of 1:1, 1:2, and 1:3 in n-dodecane solvent. The obtained computational findings confirmed that a 1:2 metal-ligand ratio is the ideal ratio for extracting the Am/Eu metals in n-dodecane solvent using organo phosphinodithioic acid ligands. Moreover, it has been found that Am is best extracted with an organo phosphinodithioic acid ligand derivative, benzyl(phenyl) phosphinodithioic acid (BphPT2), whereas Eu is best extracted with pyridazin-3- yl(pyridazin-3-ylmethyl) phosphinodithioic acid (PPPT2).