Development and validation of ALFUS: An irradiation behavior analysis code for metallic fast reactor fuels

An irradiation behavior analysis code for metallic fast reactor fuel, ALFUS, has been revised so that it can be applied to stress-strain analysis of U-Pu-Zr ternary fuel pins. The stress-strain calculation in ALFUS is closely coupled with models for slug deformation mechanisms, such as swelling due to accumulation of fission gas bubbles and nongaseous fission products. These models include the key parameters: threshold gas swelling for open pore formation, compressibility of the open pores, and accumulation rate of nongaseous fission products. The parameter values have been determined based on theoretical or experimental considerations. An empirical model has also been introduced into ALFUS to treat the effect of the large radial cracking that is a characteristic phenomenon in the ternary,fuel slug. The irradiation behaviors of the ternary, fuel pins of various design specifications have been analyzed using ALFUS. The analytical results are in fair agreement with the measured data for fission gas release, slug axial elongation, and cladding deformation. The calculated histories of swelling components can reasonably explain the dependency of measured cladding strain data on burnup and initial fuel smear density. One may conclude that ALFUS is valid for irradiation behavior analysis of the metallic fuel pin and is applicable to a wide range of fuel pin specifications. The methodology developed for ALFUS can be a basis for the design procedure for the metallic fuel pin.