Now If I might way in on this reactor descusion... Warning incomeing technobabble:
(from zeonic corps)Gundam_X12:
A nuclear reactor is designed in such a way that its energy is used to power its systems - there's no overflow, no excess energy stored. At max performance, 100% energy output is used. Example: in an intense combat situation, where all of the mobile suit's weapons systems are active, or when it is running at full speed.
Other example: when a warship is running full speed, 100% of its power is used to propel the ship.
But if additional strain is put on the reactor - meaning if it is asked to supply more energy than it is designed to, the reactor core will begin to overheat. the reactor will overload, and the result is a core meltdown.
It's a common misconception in the CE-fandom that nuclear reactors=infinite power.
That's not really it. a nuclear reactor in a mobile suit can power that MS's systems infinitely, but that's basically all it can handle. It's specifically designed that way.
And my explenation:
While it was stated that Destiny Gundam did posses a nuclear engine, never officially was it mentioned that the suit possesed an NJammer Cancler(i.e. still with-in the junius treaty) This means that when in a combat zone the suit would operate like a battery powered suit with the exception of the hyper capacitor being a great deal more advanced than previous "batteries". However once leaveing a battlefield (or just leaveing the presence of an NJammer) the suits Nuclear engine would be able to replenish the suits capacitor without needing to land in a mothership. This may seem odd but also note that there is no "Unsubdude" line in Destiny's operating system, While Strike Freedom's OS does.
Thats my theory at least...