Nuclear weapons without 90%-enriched uranium

A correction. Some days ago I said that one needs to enrich uranium to at least 90% to build a bomb. However, the nuclear engeneer Sérgio Guerreiro Ribeiro remembered in "O Globo" (in Portuguese) that it is not necessarily so. It is also possible to make it with plutonium-239 (Pu-239), that is produced as “waste” in common nuclear power plants. And a bomb needs about 8 kg of Pu-239, against 25 kg of uranium-235. Plutonium produced normally in power plants have 60% of Pu-239 and a weapon needs 93%, but there are techniques to reach this proportion. Useful numbers to assess scenarios...