Experience on mixed carbide fuels with high ‘Pu’ content for Indian fast breeder reactor – An overview

Hyperstoichiometric Plutonium rich (70%) mixed Uranium Plutonium carbide fuel was proposed as the driver fuel for Indian Fast Breeder Test Reactor (FBTR) after some deliberations. The issues of mixed carbide fuel and of plutonium rich (70%) carbide fuel, in particular, are: presence of ‘O’ impurity, clad carburization, lower solidus temperature, lower thermal conductivity and pyrophorocity. The paper highlights the extensive research and development carried out to address the above issues. The modification incorporated in the different process steps of fabrication flow sheet is also presented. The performance of the fuel has been assessed by periodic Post Irradiation Examination (PIE) of the fuel sub-assemblies for extension of life. Till date the fuel has seen a burn up of 155 Gwd/t without any pin failure.