  Collisions of actinide nuclei form, during very short times of few $10^{-21}$
s, the heaviest ensembles of interacting nucleons available on Earth. Such very
heavy ions collisions have been proposed as an alternative way to produce heavy
and superheavy elements. These collisions are also used to produce super-strong
electric fields by the huge number of interacting protons to test spontaneous
positron-electron ($e^+e^-$) pair emission predicted by the quantum
electrodynamics theory. The time-dependent Hartree-Fock theory which is a fully
microscopic quantum approach is used to study collision dynamics of two
$^{238}$U atomic nuclei. In particular, the role of nuclear deformation on
collision time and on reaction mechanisms such as nucleon transfer is
emphasized. These calculations are pessimistic in terms of transfermium
elements ($Z>100$) production. However, the highest collision times
($\sim4\times10^{-21}$ s at 1200 MeV) should allow experimental signature of
spontaneous $e^+e^-$ emission. Surprisingly, we also observe ternary fission
due to purely dynamical effects.
