well, i probably over estimated the end of world if that cunami was 0.8 gigaton however nuclear winter could be real problem.

enrichment is quite trivial to do, all you need is lots of elecricity, i think best is magnetic ion, or gell separation, centrifuges take too much space, and produce poor and unpredictable results.
magnetic separator can easily make almost completely pure isotopes no matter what initial mixture was. this will not work with uranium, ulness you have personal power plant to power that magnetic separator.