The $UO_2$ fuel pellet is composed of grains which are different in shape and size. The grain size and distribution of the pellet change as the fuel burns up. This change would greatly affect fission gas release from $UO_2$ fuel.
This study was undertaken to investigate the influence of the power history on the grain size distribution in equiaxed grain growth region and so on the fission gas release, and to develop a mechanistic model, so-called GDIS (Grain size DIStribution) program, for the calculation of grain size distribution in the fuel pellet. The GDIS program contains the standard distribution of which average grain size is 8㎛. The grain size distribution of an $UO_2$ pellet can be calculated by providing the average grain size of the pellet to the program.
This program was adapted to KAFEPA (KAERI / AECL Fuel Element Performance Analysis) code as a subroutine to calculate both the grain size distribution and the fission gas release, where KAFEPA code has been used for CANDU fuel performance calculation.
In the present verification, only the fission gas release prediction was compared with experimental data, because of the lack of the in-reactor data of the grain size distribution.
As a conclusion, the present model agreed well with the experimental data, compared with the prediction of the original KAFEPA code in which an empirical correlation of grain growth is incorporated as a function of the average grain size.
