237Np is generated by (n, y) reactions of 235U and by (n, 2n) reactions of 238U, followed by β- decay of 237U. It is produced in nuclear fuel with a rate of ~0.75 and ~0.25 kg/tHM, respectively in thermal and fast reactors, and is present in far larger quantities than the combination of all other isotopes. Being the longest-lived member of the 4n + 1 radioactive decay series, 237Np is thus an important and problematic long-term constituent of high level liquid waste (HLLW). Np used to be treated as a waste through HLLW vitrification but it has become worthier of recovery, to solve radiotoxicity issues but also because of its application in the production of 238Pu, a heat source for thermoelectric devices. Np3+ is a strong reducing agent and Np4+/NpO2+/NpO22+ are the existing forms in acid-dissolved used nuclear fuel. Np4+ and NpO22+ are greatly extractable, in contrast to Np(V) since the low charge of the neptunyl ion NpO2+ forms much weaker complexes. Operating conditions of the conventional PUREX process create an environment where most Np exists as NpO2+ and NpO22+. In the first cycle of the PUREX process, where Np is co-extracted with Pu and U, the more extractable NpO22+ is the major species thanks to oxidation by indigenous HNO3 and HNO2. Remaining Np stays with trivalent fission-produced lanthanides (Ln). In the second cycle, where Pu is separated from U, reductants must be added to reduce Pu4+ to Pu3+ and NpO22+ to NpO2+, if Np is chosen to follow Pu instead of U. The main issues in this step are sensitivity to HNO3/HNO2 concentration and incomplete separation caused by remaining Np4+ with U. Previous studies have shown that an aqueous complexant called 3,4,3-LI(1,2-HOPO) has high affinity to Np4+ and can assist the separation of Np both from U and from Ln. Extraction profiles of Np were determined as a function of several parameters, including complexant concentration, pH, and phase volume ratio. Valence profiles of Np were concluded by UV-vis.

Hydropyridinone-based stabilization and complexation of Np(IV) for separation from PUREX products

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.