Development of a mixed oxide fuel pin performance analysis code “CEDAR”: Models and analyses of fuel pin irradiation behavior

• A computer code CEDAR was developed to analyze irradiation behaviors of mixed-oxide fuel pins.
• The code features mechanistic analyses of fuel pin irradiation behaviors.
• Fuel pin irradiation behaviors were interpreted from code analyses for the actual irradiation tests.

A deterministic computer code, CEDAR, has been developed to analyze the irradiation behaviors of mixed-oxide fuel pellet pins in sodium cooled fast breeder reactors. The finite element method was incorporated into the mechanical calculation segment of the code to enable the proper analysis of stress–strain status in the fuel pellet and cladding, and mechanical interaction between the fuel pellet and cladding (PCMI). The code features mechanistic analyses of the irradiation behaviors of fuel pins by integrating a number of models to analyze major irradiation phenomena, thus expressing actual fuel pin irradiation behaviors as accurately as possible. The analysis capabilities of the code were validated by calculations of fuel pellet temperatures, fractional fission gas releases of fuel pins and fuel pin cladding diametral strain profiles. Mechanisms of fuel pin irradiation behaviors such as redistribution of Americium, PCMI and joint oxide gain (JOG) formation were interpreted from code analyses for the actual irradiation test fuel pins.