  The first solids that form as a white dwarf (WD) starts to crystallize are
expected to be greatly enriched in actinides. Previously [PRL 126, 1311010] we
found that these solids might support a nuclear fission chain reaction that
could ignite carbon burning and provide a new Type Ia supernova (SN Ia)
mechanism involving an {\it isolated} WD. Here we explore this fission
mechanism in more detail and calculate the final temperature and density after
the chain reaction and discuss a number of open physics questions.
