b'ElectrochemicalTin doped indium oxide electrodes maintained their electrochemical manipulation and radiolyticperformance, exhibited increased photocurrent densities, and facilitated electrochemical manipulation of neptunium oxidation states in evaluation of organicnonpolar media when exposed to intense gamma radiation under phase neptunium a variety of used nuclear fuel reprocessing solvent conditions.T his research evaluated an innovative approach to precisely control the oxidation state distribution of neptunium (Np) under used nuclear fuel reprocessing conditions using electrochemical methods. The electrochemical behavior of nanoporous indium tin doped oxide (nITO) and planar fluorine-doped tin oxide (pFTO) electrodes were assessed before and after exposure to gamma radiation PROJECT NUMBER: by probing the ferrocenium/ferrocene couple. The electrochemical behavior of nITO 22P1065-033FP electrodes remained relatively unchanged when gamma irradiated ( 100 kGy) in the presence and absence of n-dodecane. However, the electrochemical behavior of pFTO TOTAL APPROVED AMOUNT:electrodes drastically changed upon absorption of gamma radiation under similar $125k over 1 year conditions, affording ferrocenium/ferrocene peak separations (Ep) of 200 and 76 mV PRINCIPAL INVESTIGATOR:in air and in contact with dodecane, respectively. This observation suggests that the Gregory Holmbeck radiolytic damage imparted in pFTO electrodes in contact with n-dodecane improves their electron transfer kinetics. CO-INVESTIGATORS:Jacy Conrad, INL Cyclic voltammetry and bulk electrolysis of aqueous 1.0 M nitric acid solutions Christopher Dares,containing Np(IV), Np(V), and Np(VI) ions at glassy carbon electrode, nITO, and Florida International Universitypolyphosphate modified nITO working electrodes were performed using the Jeffrey McLachlan,standard Calomel electrode (SCE) as a reference electrode. The Np(VI/V) couple at Florida International Universityglassy carbon electrode was found to be chemically reversible and electrochemically irreversible, exhibiting a Ep = 500 mV at 5 mV s 1 . This behavior was attributed to COLLABORATORS: an unfavorable interaction between the Np(VI/V) ions and the nominally nonpolar Brookhaven National Laboratory glassy carbon electrode surface. At the bare nITO electrode, the Np(VI/V) couple was California State University Long Beach quasi-reversible, with a Ep = 150 mV at 5 mV s 1 , attributed to a more favorable Colorado School of Mines interaction with the relatively increased polarity of the nITO surface. Florida State UniversityDiethylhexyl butyramide (DEHBA) and di-2-ethylhexyl isobutyramide are the two butyramide ligand candidates to replace tributyl phosphate in industrial scale used nuclear fuel reprocessing technologies. We evaluated the feasibility of performing electrochemical manipulations of Np in neat DEHBA. The high resistivity of neat DEHBA prohibits electrochemical measurements; however, upon pre-equilibration with aqueous 4.0 M nitric acidas would be the case in real-world used nuclear fuel reprocessing flowsheetsdissociated protons and nitrate ions partition into the DEHBA phase, sufficiently lowering its resistivity and facilitating electrochemical measurements. All electrochemical measurements performed in this matrix were referenced to the SCE. The liquid junction potentials between the electrode and solution and the solutions high resistivity likely shift this reference from standard values reported in aqueous media, so we report these data as referenced to the SCE*. The cyclic voltammogram of this solution at glassy carbon electrode is characterized by a single electrochemically irreversible redox couple centered at 0.4 V vs. SCE*, a cathodic current takeoff at-0.15 V vs. SCE*, and a gradual anodic current takeoff at1.0 V vs. SCE*. 70 These redox events likely correspond to ligand- or electrode-based reactions.'