Funny how everyone is immediately concerned with a few thousands of cubic meters of solid waste that literally loses its harm exponentially quickly and we can store underground while all the billions of tons of toxic liquid and gaseous waste coming from a sleuth of industrial applications (including renewables production) constantly being pumped in the biosphere never get a mention
Rate of decay for a specific isotope is constant, so its abundance decays exponentially. Of course a species can transmute in a new radionuclide so the process in total will not be exactly exponential, but pretty close. Seen on a log scale it’s awfully close to a straight line