Take a look at the article in Jane’s Intelligence Review (subscription only) by Geoff Forden and John Thomsen expanding on a proposal to develop a multinational consortium to operate a five million SWU-kg a year enrichment facility at Natanz.
I wondered about the self-destruct mechanism, the longer article has an explanation.
As I suspected, the self-destruct mechanism is a centrifuge-specific approach:
For instance, the bottom of the T-21’s bearing, which circulates oil between it and its support cup, is extremely complex and difficult to manufacture. It might be possible to arrange so that the bearing would be destroyed if the rotor was stopped to modify the plant to produce highly enriched uranium (the rotors are usually left running permanently because of the difficulty in bringing them back to speed, so this should not be a major problem in normal operation). If this happened, Iran would find it impossible to use the centrifuges without a major development programme lasting many years. It could also be arranged that, instead of simply destroying the bearing, the whole rotor would be destroyed by smashing it into the casing cylinder because of conservation of angular momentum.
Interestingly, one of the most controversial elements of the proposal—to supply advanced Urenco T-21 centrifuges that are 50 times as powerful as Iran’s P1 design—works as a safeguard, since Iran would have rather more difficulty repairing the more technologically complex centrifuges.