It is not fusion that is explosive nor is it big particles disintegrating into basic particles that is necessarily explosive, it is chain reaction, where an action triggers one or more other actions that a cascade of energy is released.
So, let the sonic boom be. \(^{235}U\) as a vapor with a specific density can be driven to an disintegration speed. It is the chain reaction that occurs as emissions from the elements' disintegration triggers more disintegrations that is explosive.
Enough said.
