Journal of the Electrochemical Society, Vol.147, No.2, 642-649, 2000
Thermodynamics of neptunium in LiCl-KCl eutectic/liquid bismuth systems
Thermodynamic properties of neptunium in LiCI-KCl eutectic/liquid bismuth systems in the temperature range 400-500 degrees C have been studied using a galvanic cell method for the pyrometallurgical reprocessing of nuclear spent fuels. The standard potential of the Np/Np(III) couple vs. the Ag/AgCl (1 wt % AgCl) reference electrode in LiCl-KCl eutectic was measured and given by the equation E-Np/Np(III)(0) = -2.0667 + 0.0007892 T (sigma = 0.0009), where E is in volts, T is in kelvin, and cr is the standard deviation. The potential of neptunium-bismuth alloy, ENp-Bi, was measured as a function of neptunium concentration, X-Np in Bi. The corves for EBi-Np vs. log X-Np (in Bi) indicated the neptunium solubility in liquid bismuth to be 0.33 +/- 0.02, 0.61 +/- 0.08, and 1.06 +/- 0.09 (+/-sigma) atom % at 400, 450, and 500 sigma degrees C, respectively. The excess partial free energy of neptunium in liquid bismuth was represented by the equation, (Np) (xs) (kcal/g atom) = - 32.5 (+/-0.7) + 0.0072 (+/-0.0010) T. The values of the solubility and excess partial free energy for neptunium were closer to those for plutonium rather than uranium.