Reply #7: Actually it was a chart recorder.

[Throckmorton]

And the older pneumatic/electric ones do indeed stick, but are for the most part no longer used.

The lesson from TMI is that the reactor core will be far more damaged than expected. The "studies" concluded that 15 to 20% of the core at TMI had melted, when they finally pulled the reactor head, about 5 years after the melt down, it was "discovered" that 50 to 60% of the fuel had melted.

While I don't usually like to guess about these things, my personal experience with this generation of reactor cores leads me to believe that the melted fuel, now given the idiotic name "Corium" has pool in the bottom of the vessel. From there, it has undoubtedly overheated and failed the Grafoil seals on at least some number of CEDM (control rod) penetrations, allowing melted fuel to exit the reactor pressure vessel into the primary containment.

These failed penetrations will of course also allow coolant to leak by as well, along with the entrained/dissolved fuel fragments.