Seeking examples of nuclear reactions that generate heat but not radionuclides

[treehouse]

I'm writing about emerging technologies the richest people on Earth would be thrilled to have. In fact, its already hit the noosphere. Now I'm writing another appeal to investing in people (this one focusing more on biopersonal impacts than technosocial development) and wish to publish it with a concise explanation of intraplanetary post-scarcity.

What known nuclear reactions generate heat but not radionuclides?

 

[Norman]

How are you defining heat here?