[ RadSafe ] Fuel condition at TMI

[James Barnes]

Dear all;

Have a very specific question about the fuel failure at TMI.

The sequence I recall is:

1)    Reactor water levels dropped and tops of fuel bundles were exposed.

2)    The Zircaloy fuel tubes overheated and cracked (with extensive melting of 
the Zircaloy), releasing fission products to the reactor and auxiliary systems.

3)    Fuel pellets were then mechanically dislodged from the fuel bundles and 
fell down into the fuel assembly and reactor structures, and some quantity to 
the bottom of the reactor vessel.

My question is this:

The fuel pellets themselves are generally uranium in a ceramic matrix 
(correct?).  My sense is that ceramic matrices don't melt, they crack into 
pieces ("sinter"; a point that the Wikipedia entry on ceramic fuels seems to 
imply).  Thus, when the pellets were overheated and ejected, they tended to 
crack into pieces and one got tiny pieces of fuel circulating in the system and 
pieces of fuel pellets dropping into the reactor internals.

Was there ever any evidence that that actual fuel pellets themselves had 
undergone melting.  If so, can any of you send me credible references to this 
point?

Thanks,

Jim Barnes, CHP
james.g.barnes at att.net