There are reactor designs that use highly enriched uranium but these are not used for commercial power. They are used when very compact reactors are needed (or when getting heavy water to replenish water supply is impossible to get).

Also, due to reactor design it is not possible for a nuclear explosion to occur. Very specific geometries and designs must be met for a nuclear explosion. Yet, this seems to be what you meant by “Yes, even unenriched Uranium will explode, if you pile up more than the critical mass at which an uncontrollable chain fission reaction will start.” An “uncontrollable chain fission reaction” is not necessarily a nuclear explosion. It takes much more than exceeding critical mass to result in a nuclear explosion. It may result in a steam explosion as the water is heated up to a pressure greater than the system can handle if heat is added too fast. This is called “prompt critical”. There have been a number of prompt criticality accidents, but none have ended up in a nuclear explosion as the heat from the reaction tends to disrupt the geometry and stopping the reaction naturally.