Another twist (or should that be 'spin'?) to the original tale at the time of the sudden closure last year was that the Iranian military (read 'a couple of top generals') were upset that the commercial contract for the running of the new airport went to a Turkish/Canadian consortium and not to the people they thought should have got it - ie, they/them/themselves.
Now that rings even more true than the radioactive spill story. (Still, it might be interesting to see what happens to your trusty dosiemeter [if you have one] when and after a visit to Imam Khomeini International.)