voronoi occupation

Dear all,
I am using LAMMPS 2014.07.14 for radiation damage simulation. when I use “voronoi occupation” command for simulation of radiation damages produced in a Fe bcc single crystal, I have found some following points and have some questions about them:
1- some zeros for the first column of compute output and some more than 1 numbers for the second column are displayed even before radiation occurred (before given more kinetic energy to a single atom in the crystal). It seems that thermal fluctuation itself can produce some vacancy and interstitials. If it is correct how can I distinct between vacancy and interstitials produced by radiation or thermal fluctuation?
2- number of vacancies (zeros in first column) is not equal to the total number of interstitials in any timestep, but I expect to have equal number of vacancies and interstitials in single pure crystal.
3- If a number in column 2 is more than 1 (as an example 3) it means that the number of interstitials in the voronoi cell is equal to the number minus 1 (equal to 2 for the example)? Should I sum over any number of second column x minus one (sum over (x-1)) to calculate the total number of the interstitials?
Sincerely yours,