Out-of-Pile Properties of Hyperstoichiometric (U0.45Pu0.55)C Fuel for the Fast Breeder Test Reactor

Hyperstoichiometric uranium-plutonium mixed carbide fuel (U0.3Pu0.7)C1+x has been the driver fuel for the sodium-cooled Fast Breeder Test Reactor (FBTR) at Kalpakkam, India. The existing core is being slowly expanded by substituting the earlier fuel with hyperstoichiometric (U0.45Pu0.55)C1+x fuel for operation of the reactor at full power [40 MW(thermal)] and at higher linear heat rating of the fuel. To evaluate the fuel in terms of its in-reactor performance, some of the important out-of-pile thermophysical and thermomechanical property data like the coefficient of thermal expansion, thermal diffusivity, thermal conductivity, and hot hardness have been generated as a function of temperature. The out-of-pile chemical compatibility of the fuel with Type 316 stainless steel (20% cold-worked) cladding material has also been established experimentally. From the data generated in these measurements, it has been concluded that with this fuel the reactor could be operated at full power with a fuel linear heat rating of 400 W/cm. Out-of-pile compatibility experiments indicate that carburization of the clad by carbon transfer from the fuel would not be severe to cause any breach of clad during the residence time of the fuel in the reactor