If food irradiation is a hazard, where do you sit if you have an x-ray control for metal? Just thought I'd throw that in there to mix things up!
I would suspect, but I don't know, that they would be most interested in foods which could naturally contain radioactive material. Now this may be more common than you think. I'm from the UK and so the two obvious places I would think of are the Cornwall where there are high radon levels; can that affect any foodstuffs produced there? Also Welsh lamb had restrictions imposed after Chernobyl due to the fact that low levels of contamination went over the UK and then (unsurprisingly) it rained in Wales. These have been lifted now but I would imagine this is the kind of thing they are thinking of? Rare though.
Food irradiation is not a radiological hazard as irradiation does not make food radioactive, decades of research worldwide has determined so. Radioactivity in foods can occur by two routes: contamination of foods with radioactive substances or by penetration of energy into the nuclei of the atoms that make up the food.
The irradiation process involves passing food through an irradiation field; however, the food itself never contacts a radioactive substance. Also, the ionizing radiation used by irradiators is not strong enough to disintegrate the nucleus of even one atom of a food molecule.
One would not consider x-ray machine for metal control as a radiological hazard because the radiation dose typically received by objects scanned by a cabinet x-ray system is 1 millirad or less. The average dose rate from background radiation is 360 millirad per year. The minimum dose used in food irradiation for food preservation or destruction of parasites or pathogens is 30,000 rad.
The radiological hazards that do need to be taken into consideration are the examples that you provided: crops grown in regions where high levels of radionuclides are known or have been detected such as Chernobyl, Fukushima and other areas that may have been affected by these disasters.
With FSMA the FDA wants to make sure we are taking these hazards into consideration when conducting our hazard analysis regardless of how rare they may seem because a product can be contaminated.