New mechanisms of accelerated fission gas release from uranium fuel under the accidents

Theoretical study of accelerated gas release from nuclear fuel under accidents is carried out. It is shown that the above acceleration is conditioned by specific physical mechanisms acting only under increased temperature conditions. The first mechanism causing formation of intergranular gas channel system is of percolation character, and in a certain degree it is similar to channel system formation at grain boundaries. The second mechanism being the high-temperature phase transformation in uranium fuel provides for radical activation of all diffusion processes. 17 refs., 2 figs., 2 tabs