Let’s go back to the centrifuges for a moment. We had briefly mentioned the several ways of how to destroy a gas centrifuge. The possibility that seems most likely when looking at the Stuxnet 315 attack code is that Stuxnet simply tries to break the rotor (that big black thingy that you saw) by overstress. This can be done by going through a lot of acceleration/deceleration cycles. A centrifuge rotor has an upper limit on the number of cycles it can tolerate before breaking. (Enrichment centrifuge experts can perhaps stick a hard number on this.)
However, our estimate is that trying to break the rotors by simply putting them through a/d cycles with the periods of uninterrupted operation that Stuxnet inserts between would just take too long. The attackers wouldn’t want to wait several years before the rotors break.
If we had to do the job on the centrifuges, we would attempt to give them a good grill during the a/d cycles. Heat increases the stress on the rotors dramatically. And there are those heating elements installed on the enrichment centrifuges; the principal question is if they can be manipulated by the 315’s. Technically this could be done via the frequency converters. Many frequency converters do have some kind of built-in RTU where you would hardwire additional sensors and actuators. So what the frequency converter experts would want to look for is any manipulations of the analog outputs. Gas centrifuge experts could perhaps enlighten us on how the heating elements are controlled.