High temperature investigation of the solid/liquid transition in the PuO2-UO2-ZrO2 system

The solid/liquid transitions in the quaternary U-Pu-Zr-O system are of great interest for the analysis of core meltdown accidents in Pressurised Water Reactors (PWR) fuelled with uranium-dioxide and MOX fuels. During a severe accident the Zr-based cladding can become completely oxidised due to the interaction with the oxide fuel and the water coolant. In this framework, the present analysis is focused on the pseudo-ternary system UO2-PuO2-ZrO2. The melting/solidification behaviour of five pseudo-ternary and one pseudo-binary ((PuO2)50(ZrO2)50) compositions have been investigated experimentally by a laser heating method under pre-set atmospheres. The effects of an oxidising or reducing atmosphere on the observed melting/freezing temperatures, as well as the amount of UO2 in the sample, have been clearly identified for the different compositions. The oxygen-to-metal ratio is a key parameter affecting the melting/freezing temperature because of incongruent vaporisation effects. In addition, a detailed thermodynamic model for the UO2-PuO2-ZrO2 system has been developed using the CALPHAD method. Finally, thermodynamic calculations have been performed to interpret the present laser heating results, as well as the high temperature behaviour of the cubic (Pu,U,Zr)O2±x-c mixed oxide phase. A good agreement was obtained between the calculated and experimental data points. This work enables an improved understanding of the major factors relevant to severe accident in nuclear reactors.

QUAINI Andrea;  GUENEAU Christine;  GOSSÉ Stéphane;  SUNDMAN B.;  MANARA Dario;  SMITH Anna;  BOTTOMLEY Paul;  LAJARGE Patrick;  ERNSTBERGER Markus;  HODAJ F; 

2016-01-05

ELSEVIER SCIENCE BV

JRC96685

0022-3115,   

https://publications.jrc.ec.europa.eu/repository/handle/JRC96685,   

10.1016/j.jnucmat.2015.10.007,