In some ways they are interchangeable, though they have slightly different connotations. In my mind I think of an award, or being awarded something, as winning it (sometimes for good act or other virtue, or sometimes just as a matter of chance)- whereas when one is rewarded it seems to have more of a meaning of they recieved positive reinforcement for something they did well. The difference is subtle, and both have multiple contexts in which they mean slightly different things.
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