Anothe problem is that reactor hull temp is updated per each element, so next element work with changed temperature. As a result, anything after serious heat source (like uranium 4-pack) will heat much more than those before. It was not as apparent when elements were small, but now is glaring.
My suggestion is to accumulate hull heat changes (and may be, all element heat changes) in variable(s) and apply changes only after end of cycle.