Development of a performance analysis code for vibro-packed MOX fuels

The compression characteristics and effective elastic moduli of granular UO2 compacts were measured to evaluate the mechanical properties of vibro-packed MOX fuels. These properties were incorporated into a pellet-type fuel performance analysis code CEDAR with evaluation models for the thermochemical behaviors of the vibro-packed MOX fuels to develop a vibro-packed MOX fuel performance analysis code CEDAR-VIPAC, ver. 1.0. Calculations were made by the developed code on a vibro-packed MOX fuel pin irradiated at BN-600 in Russia. The calculated stress-strain state showed that the contact pressure on the inner cladding surface was small enough not to cause local deformations due to excess FCMI. Additionally, the code results showed that the compression characteristics of the vibro-packed fuels contributed considerably to the central void formation or growth. Because they agreed well with the behaviors obtained from the experimental data, it is concluded that the code provided a reasonable explanation of the thermochemical and mechanical behaviors of vibro-packed MOX fuels under irradiation.