French and United Kingdom Experience of High-Burnup Mixed-Oxide Fuel in Sodium-Cooled Fast Breeder Reactors

From the 1960s to the end of the 20th century, considerable studies were performed in Europe on fast breeder reactor fuels for reaching an industrial maturity. In the European plan, the European fast reactor project reached in 1998 the phase of validation of the concept, satisfying the requirements of economy and safety of the countries that contributed to the project.

In this paper, we intend to give an idea about the main obstacles met on the way toward the high burnups: inner corrosion cladding interface, swelling and mechanical behavior of the constitutive materials (clad and wrapper), pin/pin interactions and pin/wrapper mechanical interactions, wrapper interactions within the reactor core, etc.

For this, the paper is divided in three parts:

1. fuels, with an emphasis on the oxide of U and Pu that constitutes the reference in Europe for reaching high burnups

2. cladding and wrapper materials: austenitic stabilized steels and ferritic-martensitic steels, but also the Nimonic alloy favored in the United Kingdom

3. behavior of the subassembly not only in a normal operating situation but during its complete life cycle: transport, in-pile handling, and earthquake resistance.

In conclusion, we define the points of optimization to reach the Generation IV reactors objectives: cladding material (multistabilized austenitic steel grades and oxide dispersion strengthened developments) solutions allowing one to limit the inner clad corrosion, check the potential of alternative fuels such as carbide and nitride, and study the possibilities of including minor actinides for their transmutation.