Quote from IHFBI happen to find Jed's explanation more persuasive. Thomas suggests a "heating element loosely coupled to both the hot core and the primary system." The simple problem with this hypothesis is that, to my knowledge, nobody saw or reported such a "loosely coupled" heating element. And the unit was opened for inspection for all witnesses to see.
I don't think you've read Jed's critique. Any old heating element will do for that.
But, in any case, all I meant was one that is thermally coupled to both core and primary circuit which, if you think about it, is bound to be the case. Hoe good is the coupling is not clear from a casual inspection.
Are you saying there was no heating element because no-one saw it?