Two examples are provided below. Neutrinos These weakly interacting, possibly even massless particles may have their origin in nuclear reactions, but they certainly pose no threat to humans or other living things on earth. Trillions or more pass though us every second with absolutely no effect. Yes, microwaves are a form of radiation, but then so are infrared and light. Not all forms of radiation are nuclear in origin.
Radiation is energy in the form of waves and particles that are emitted from a source.
It comes in many forms. It is not necessarily a dangerous thing. Any form of electromagnetic radiation is dangerous at large intensities. One shouldn't operate a broken microwave oven, or place one's hand in boiling water, or stare at the sun. Too much energy is being delivered too quickly over too small an area for these exposures to be safe.