To clarify, this is an implosion type bomb, it uses chemical explosive lenses to compress the plutonium core with pressure to make it supercritical, where it then explodes outwards. Its classified as "Pure Fission" as it doesn't use any fusion reactions to boost the explosion or the neutron production.
this isnt pure fission it has tnt which is a chemical reaction to explode rather than a nuclear reaction that fission is