  Massive runaway positrons are generated by runaway electrons in tokamaks. The
fate of these positrons encodes valuable information about the runaway
dynamics. The phase space dynamics of a runaway position is investigated using
a Lagrangian that incorporates the tokamak geometry, loop voltage, radiation
and collisional effects. It is found numerically that runaway positrons will
drift out of the plasma to annihilate on the first wall, with an in-plasma
annihilation possibility less than 0.1\%. The dynamics of runaway positrons
provides signatures that can be observed as diagnostic tools.
