  The mechanism leading to the formation of the observed products of the
collinear cluster tripartition is carried out within the framework of the model
based on the dinuclear system concept. The yield of fission products is
calculated using the statistical model based on the driving potentials for the
fissionable system. The minima of potential energy of the decaying system
correspond to the charge numbers of the products which are produced with large
probabilities in the sequential fission (partial case of the collinear cluster
tripartition) of the compound nucleus. The realization of this mechanism
supposes the asymmetric fission channel as the first stage of sequential
mechanism. It is shown that only the use of the driving potential calculated by
the binding energies with the shell correction allows us to explain the yield
of the true ternary fission products. The theoretical model is applied to
research collinear cluster tripartition in the reaction $^{235}$U(n$_{\rm
th}$,f). Calculations showed that in the first stage of this fission reaction,
the isotopes $^{82}$Ge and $^{154}$Nd are formed with relatively large
probabilities and in the second stage of sequential fission of the isotope Nd
mainly Ni and Ge are formed. This is in agreement with the yield of the isotope
$^{68}$Ni which is observed as the product of the collinear cluster
tripartition in the experiment.
