[emilfihlman]

This depends only on system input energy statistics.

At low temperatures (the lower you go) and low radiation (the lower you go) there is not enough energy in the system to exceed activation energy and break down DNA (meaning statistically it's extremely unlikely (arbitrarily) for enough energy to enter the system in a short enough period of time to break down the structure) (there's always the minuscule chance that some wavefunction posits enough energy into the system of course).