Management of long lived actinides

In an attempt to reduce the burden for future generations, the nuclear community is looking for solutions to reduce the amount of long-lived radioactive waste and its radiotoxicity. One promising solution consists in recovering the long-lived isotopes (neptunium Np, americium Am, curium Cm) from the spent fuel and re-irradiate them in a Generation IV (fast) reactor to transmute them into radioactive elements with shorter half-lives. A thorough knowledge of the inherent characteristics and behaviour under normal and accidental conditions of this advanced nuclear fuel, to which minor actinides have been incorporated, i.e. with (U,Pu,Np,Am,Cm)O2 composition, is essential for the safe use of future Generation IV nuclear reactors.  This requires to develop thermodynamic models for the (U-Pu-Np-Am-Cm-O) system and each sub-system. The binary U-O, Pu-O and ternary U-Pu-O systems are well described in the literature, since (U,Pu)O2 fuel is also used in current Light Water Reactors. However, very little is known on the other systems. We are therefore working on the development of thermodynamic models for these systems. One example is the development of a model for the neptunium-oxygen system using the CALPHAD method. This model can serve as input for computer simulation codes modelling the behaviour of next generation fuel.

Reference

A.L. Smith, J.-Y. Colle, O. Beneš, R.J.M. Konings, B. Sundman, C. Guéneau, Thermodynamic assessment of the neptunium-oxygen system: Mass spectrometric studies and thermodynamic modelling, Journal of Chemical Thermodynamics, 103 (2016) 257-275, doi.org/10.1016/j.jct.2016.07.040