Towards a multiscale approach for assessing fission product behaviour in UN

Ab initio modelling of soluble and insoluble fission products (soluble FP's such as Nb, Y, Gd, Nd, Zr, Sm, Eu, and Ce and insoluble FP's like Ba, Mo, Sr, Rh, Pd, and Ru) in uranium nitride is carried out by assessing the incorporation, along with their contributions to local swelling of the fuel matrix. FP in UN have shown to be preferably accommodated at U vacancies in bound [100]-Schottky defects, nevertheless, similar incorporation energies were found at a single U vacancy. From the investigated incorporation and migration mechanism, we found that fission products in UN predominately migrate along U-U vacancies, since the incorporation energies for all FP are lowest at single U vacancy or at the U vacancy in a Schottky defect. The energy required to induce a migration of a volatile FP from an N vacancy to U vacancy is about 4 – 5.5 eV. The local volume changes caused by the fission-product substitution have been assessed by means of DFT and combined with the fission-product concentrations obtained by means of neutron calculations (SCALE) to predict fission product swelling in UN. The linear swelling of nitride fuel resulting from these calculations, and the assumption that fission products do not interact and form secondary phases, leads to a reasonable estimation for the swelling rate as a function of burn-up (or time) when compared with empirical correlations in the open literature.

KLIPFEL Marco;  DI MARCELLO Valentino;  SCHUBERT Arndt;  VAN DE LAAR Jacques;  VAN UFFELEN Paul; 

2013-09-27

ELSEVIER SCIENCE BV

JRC81682

0022-3115,   

http://www.sciencedirect.com/science/article/pii/S002231151301074X,    https://publications.jrc.ec.europa.eu/repository/handle/JRC81682,   

10.1016/j.jnucmat.2013.08.056,