The Natural Philosopher wrote:

every reactor problem has actually resulted in a serious FIRE as well
with the graphite moderators catching alight, and the general mess
that results more or less stops fissioning as well. Its nasty, its
dirty, but it wont melt its way to the center of the earth, although
if it did, it would be pretty safe, cos the evidence is that that is
where all the fissile uranium sits, helping keep your world warm,
anyway.

Are you saying now that the earth has a nuclear reaction going on at its
centre, and that's the reason it's pretty warm down there?