Nasal developed a reactor, orion iirc, that was basically nuclear pulse propulsion: a directed nuclear explosion would propel a jet of plasma on a shield on the back of the ship to propel it, and the ship would use regular explosion for propulsion.

I don’t know the exact dynamic of the nuclear explosion. The temperature turns a lot of things into plasma indeed. But I suspect some construction of the bomb (specific layers with specific materials) could make some kind of frag work.

At the very least you can have an efficient plasma bomb anyway. Your frag is simply plasma in this case. Plasma is still matter that can have high kinetic energy, but it’s very hot too and with specific electromagnetic properties.

In this case, the atomic explosion replaces your powder, and what matters is everything around it.